Highly sensitive and selective detection of dopamine using one-pot synthesized highly photoluminescent silicon nanoparticles.

PubMed

Zhang, Xiaodong; Chen, Xiaokai; Kai, Siqi; Wang, Hong-Yin; Yang, Jingjing; Wu, Fu-Gen; Chen, Zhan

2015-03-17

A simple and highly efficient method for dopamine (DA) detection using water-soluble silicon nanoparticles (SiNPs) was reported. The SiNPs with a high quantum yield of 23.6% were synthesized by using a one-pot microwave-assisted method. The fluorescence quenching capability of a variety of molecules on the synthesized SiNPs has been tested; only DA molecules were found to be able to quench the fluorescence of these SiNPs effectively. Therefore, such a quenching effect can be used to selectively detect DA. All other molecules tested have little interference with the dopamine detection, including ascorbic acid, which commonly exists in cells and can possibly affect the dopamine detection. The ratio of the fluorescence intensity difference between the quenched and unquenched cases versus the fluorescence intensity without quenching (ΔI/I) was observed to be linearly proportional to the DA analyte concentration in the range from 0.005 to 10.0 μM, with a detection limit of 0.3 nM (S/N = 3). To the best of our knowledge, this is the lowest limit for DA detection reported so far. The mechanism of fluorescence quenching is attributed to the energy transfer from the SiNPs to the oxidized dopamine molecules through Förster resonance energy transfer. The reported method of SiNP synthesis is very simple and cheap, making the above sensitive and selective DA detection approach using SiNPs practical for many applications.

"ICT-not-quenching" near infrared ratiometric fluorescent detection of picric acid in aqueous media.

PubMed

Xu, Yongqian; Li, Benhao; Li, Weiwei; Zhao, Jie; Sun, Shiguo; Pang, Yi

2013-05-25

The first "off-on" and ratiometric fluorescent method based on ICT mechanism for picric acid (PA) recognition in the near infrared region was constructed. Key advantages of the unique molecular architecture can fulfil the ratiometric response to electron-deficient featured PA which inclines to quench fluorescence of all reported sensors for PA.

Fluorescence quenching as an indirect detection method for nitrated explosives.

PubMed

Goodpaster, J V; McGuffin, V L

2001-05-01

A novel approach based on fluorescence quenching is presented for the analysis of nitrated explosives. Seventeen common explosives and their degradation products are shown to be potent quenchers of pyrene, having Stern-Volmer constants that generally increase with the degree of nitration. Aromatic explosives such as 2,4,6-trinitrotoluene (2,4,6-TNT) are more effective quenchers than aliphatic or nitramine explosives. In addition, nitroaromatic explosives are found to have unique interactions with pyrene that lead to a wavelength dependence of their Stern-Volmer constants. This phenomenon allows for their differentiation from other nitrated explosives. The fluorescence quenching method is then applied to the determination of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine(HMX), 2,4,6-TNT, nitromethane, and ammonium nitrate in various commercial explosive samples. The samples are separated by capillary liquid chromatography with post-column addition of the pyrene solution and detection by laser-induced fluorescence. The indirect fluorescence quenching method shows increased sensitivity and selectivity over traditional UV-visible absorbance as well as the ability to detect a wider range of organic and inorganic nitrated compounds.

Interaction of Human Hemoglobin with Methotrexate

NASA Astrophysics Data System (ADS)

Zaharia, M.; Gradinaru, R.

2015-05-01

This study focuses on the interaction between methotrexate and human hemoglobin using steady-state ultraviolet-visible and fluorescence quenching methods. Fluorescence quenching was found to be valuable in assessing drug binding to hemoglobin. The quenching of methotrexate is slightly smaller than the quenching observed with related analogs (dihydrofolate and tetrahydrofolate). The quenching studies were performed at four different temperatures and various pH values. The number of binding sites for tryptophan is ~1. Parameter-dependent assays revealed that electrostatic forces play an essential role in the methotrexate-hemoglobin interaction. Furthermore, the complex was easily eluted using gel filtration chromatography.

Ultrasensitive fluorescence immunoassay for detection of ochratoxin A using catalase-mediated fluorescence quenching of CdTe QDs

NASA Astrophysics Data System (ADS)

Huang, Xiaolin; Zhan, Shengnan; Xu, Hengyi; Meng, Xianwei; Xiong, Yonghua; Chen, Xiaoyuan

2016-04-01

Herein, for the first time we report an improved competitive fluorescent enzyme linked immunosorbent assay (ELISA) for the ultrasensitive detection of ochratoxin A (OTA) by using hydrogen peroxide (H2O2)-induced fluorescence quenching of mercaptopropionic acid-modified CdTe quantum dots (QDs). In this immunoassay, catalase (CAT) was labeled with OTA as a competitive antigen to connect the fluorescence signals of the QDs with the concentration of the target. Through the combinatorial use of H2O2-induced fluorescence quenching of CdTe QDs as a fluorescence signal output and the ultrahigh catalytic activity of CAT to H2O2, our proposed method could be used to perform a dynamic linear detection of OTA ranging from 0.05 pg mL-1 to 10 pg mL-1. The half maximal inhibitory concentration was 0.53 pg mL-1 and the limit of detection was 0.05 pg mL-1. These values were approximately 283- and 300-folds lower than those of horseradish peroxidase (HRP)-based conventional ELISA, respectively. The reported method is accurate, highly reproducible, and specific against other mycotoxins in agricultural products as well. In summary, the developed fluorescence immunoassay based on H2O2-induced fluorescence quenching of CdTe QDs can be used for the rapid and highly sensitive detection of mycotoxins or haptens in food safety monitoring.Herein, for the first time we report an improved competitive fluorescent enzyme linked immunosorbent assay (ELISA) for the ultrasensitive detection of ochratoxin A (OTA) by using hydrogen peroxide (H2O2)-induced fluorescence quenching of mercaptopropionic acid-modified CdTe quantum dots (QDs). In this immunoassay, catalase (CAT) was labeled with OTA as a competitive antigen to connect the fluorescence signals of the QDs with the concentration of the target. Through the combinatorial use of H2O2-induced fluorescence quenching of CdTe QDs as a fluorescence signal output and the ultrahigh catalytic activity of CAT to H2O2, our proposed method could be used to perform a dynamic linear detection of OTA ranging from 0.05 pg mL-1 to 10 pg mL-1. The half maximal inhibitory concentration was 0.53 pg mL-1 and the limit of detection was 0.05 pg mL-1. These values were approximately 283- and 300-folds lower than those of horseradish peroxidase (HRP)-based conventional ELISA, respectively. The reported method is accurate, highly reproducible, and specific against other mycotoxins in agricultural products as well. In summary, the developed fluorescence immunoassay based on H2O2-induced fluorescence quenching of CdTe QDs can be used for the rapid and highly sensitive detection of mycotoxins or haptens in food safety monitoring. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01136e

Micro-scale temperature measurement method using fluorescence polarization

NASA Astrophysics Data System (ADS)

Tatsumi, K.; Hsu, C.-H.; Suzuki, A.; Nakabe, K.

2016-09-01

A novel method that can measure the fluid temperature in microscopic scale by measuring the fluorescence polarization is described in this paper. The measurement technique is not influenced by the quenching effects which appears in conventional LIF methods and is believed to show a higher reliability in temperature measurements. Experiment was performed using a microchannel flow and fluorescent molecule probes, and the effects of the fluid temperature, fluid viscosity, measurement time, and pH of the solution on the measured fluorescence polarization degree are discussed to understand the basic characteristics of the present method. The results showed that fluorescence polarization is considerably less sensible to these quenching factors. A good correlation with the fluid temperature, on the other hand, was obtained and agreed well with the theoretical values confirming the feasibility of the method.

Development of a homogeneous assay format for p53 antibodies using fluorescence correlation spectroscopy

NASA Astrophysics Data System (ADS)

Neuweiler, Hannes; Scheffler, Silvia; Sauer, Markus

2005-08-01

The development of reliable methods for the detection of minute amounts of antibodies directly in homogeneous solution represents one of the major tasks in the current research field of molecular diagnostics. We demonstrate the potential of fluorescence correlation spectroscopy (FCS) in combination with quenched peptide-based fluorescence probes for sensitive detection of p53 antibodies directly in homogeneous solution. Single tryptophan (Trp) residues in the sequences of short, synthetic peptide epitopes of the human p53 protein efficiently quench the fluorescence of an oxazine fluorophore attached to the amino terminal ends of the peptides. The fluorescence quenching mechanism is thought to be a photoinduced electron transfer reaction from Trp to the dye enabled by the formation of intramolecular complexes between dye and Trp. Specific recognition of the epitope by the antibody confines the conformational flexibility of the peptide. Consequently, complex formation between dye and Trp is abolished and fluorescence is recovered. Using fluorescence correlation spectroscopy (FCS), antibody binding can be monitored observing two parameters simultaneously: the diffusional mobility of the peptide as well as the quenching amplitude induced by the conformational flexibility of the peptide change significantly upon antibody binding. Our data demonstrate that FCS in combination with fluorescence-quenched peptide epitopes opens new possibilities for the reliable detection of antibody binding events in homogeneous solution.

A Fluorescence Quenching Assay Based on Molecular Beacon Formation through a Ligase Detection Reaction for Facile and Rapid Detection of Point Mutations.

PubMed

Sawamura, Kensuke; Hashimoto, Masahiko

2017-01-01

A fluorescence quenching assay based on a ligase detection reaction was developed for facile and rapid detection of point mutations present in a mixed population of non-variant DNA. If the test DNA carried a targeted mutation, then the two allele-specific primers were ligated to form a molecular beacon resulting in the expected fluorescence quenching signatures. Using this method, we successfully detected as low as 5% mutant DNA in a mixture of wild-type DNA (t test at 99% confidence level).

Fluorescent quenching-based quantitative detection of specific DNA/RNA using a BODIPY® FL-labeled probe or primer

PubMed Central

Kurata, Shinya; Kanagawa, Takahiro; Yamada, Kazutaka; Torimura, Masaki; Yokomaku, Toyokazu; Kamagata, Yoichi; Kurane, Ryuichiro

2001-01-01

We have developed a simple method for the quantitative detection of specific DNA or RNA molecules based on the finding that BODIPY® FL fluorescence was quenched by its interaction with a uniquely positioned guanine. This approach makes use of an oligonucleotide probe or primer containing a BODIPY® FL-modified cytosine at its 5′-end. When such a probe was hybridized with a target DNA, its fluorescence was quenched by the guanine in the target, complementary to the modified cytosine, and the quench rate was proportional to the amount of target DNA. This widely applicable technique will be used directly with larger samples or in conjunction with the polymerase chain reaction to quantify small DNA samples. PMID:11239011

Glutathione-capped CdTe nanocrystals as probe for the determination of fenbendazole

NASA Astrophysics Data System (ADS)

Li, Qin; Tan, Xuanping; Li, Jin; Pan, Li; Liu, Xiaorong

2015-04-01

Water-soluble glutathione (GSH)-capped CdTe quantum dots (QDs) were synthesized. In pH 7.1 PBS buffer solution, the interaction between GSH-capped CdTe QDs and fenbendazole (FBZ) was investigated by spectroscopic methods, including fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, and resonance Rayleigh scattering (RRS) spectroscopy. In GSH-capped CdTe QDs solution, the addition of FBZ results in the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs. And the quenching intensity (enhanced RRS intensity) was proportional to the concentration of FBZ in a certain range. Investigation of the interaction mechanism, proved that the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs by FBZ is the result of electrostatic attraction. Based on the quenching of fluorescence (enhancement of RRS) of GSH-capped CdTe QDs by FBZ, a novel, simple, rapid and specific method for FBZ determination was proposed. The detection limit for FBZ was 42 ng mL-1 (3.4 ng mL-1) and the quantitative determination range was 0-2.8 μg mL-1 with a correlation of 0.9985 (0.9979). The method has been applied to detect FBZ in real simples and with satisfactory results.

Determination of adenine based on the fluorescence recovery of the L-Tryptophan-Cu(2+) complex.

PubMed

Duan, Ruilin; Li, Chunyan; Liu, Shaopu; Liu, Zhongfang; Li, Yuanfang; Yuan, Yusheng; Hu, Xiaoli

2016-01-05

A simple and sensitive method for determination of adenine was developed based on fluorescence quenching and recovery of L-Tryptophan (L-Trp). The fluorescence of L-Trp could efficiently quenched by copper ion compared with other common metal ions. Upon addition of adenine (Ade) in L-Trp-Cu(II) system, the fluorescence was reoccurred. Under the optimum conditions, the recovery fluorescence intensity was linearly correlated with the concentration of adenine in the range from 0.34 to 25.0μmolL(-1), with a correlation coefficient (R(2)) of 0.9994. The detection limit (3σ/k) was 0.046μmolL(-1), indicating that this method could applied to detect trace adenine. In this study, amino acids including L-Trp, D-Trp, L-Tyr, D-Tyr, L-Phe, D-Phe were investigated and only L-Trp could well chelated copper ion. Additionally, the mechanism of quench and recovery also were discussed and the method was successfully applied to detect the adenine in DNA with satisfactory results. Copyright © 2015 Elsevier B.V. All rights reserved.

Hydroxypropyl-beta-cyclodextrin enhanced determination for the Vitamin B12 by fluorescence quenching method.

PubMed

Sun, Jing; Zhu, Xiashi; Wu, Ming

2007-05-01

A novel fluorescence quenching method for the determination of Vitamin B12(VB12) had been developed. It was based on that the fluorescence intensity of erythrosine sodium(ES) could be enhanced by Hydroxypropyl-beta-cyclodextrin(HP-beta-CD) due to the formation of inclusion complex (HP-beta-CD-ES), while the fluorescence intensity of HP-beta-CD-ES was diminished after adding VB12 into the system, and there was a linear relationship between the fluorescence quenching value of the system (DeltaF) and the concentration of VB12 (c). The mechanism of the determination of VB12 was discussed. The results showed that under the optimal conditions, the linear range of calibration curve for the determination of VB12 was 0.0 approximately 2.1 x 10(-5) mol/L, and the detection limit was 1.8 x 10(-7) mol/ L. It could be satisfactorily applied to the determination of VB12 in injections.

Changes in fluorescent emission of cationic fluorophores in the presence of n-alkanes and alcohols in different polarity solvents

NASA Astrophysics Data System (ADS)

Delgado-Camón, Arantzazu; Garriga, Rosa; Mateos, Elena; Cebolla, Vicente L.; Galbán, Javier; Membrado, Luis; Marcos, Susana de; Gálvez, Eva M.

2011-01-01

Berberine and coralyne experience either fluorescence enhancement or quenching when long hydrocarbon chain compounds (e.g., n-alkanes or alcohols) are added to their solutions, depending on solvent polarity. In polar solvents, as methanol or acetonitrile, the added compounds provide an apolar microenvironment that hinders alternative relaxation mechanisms, favouring fluorescence emission. However, alkane additions produce quenching in dichloromethane, which has been explained taking into account ion pairing between cationic fluorophore and counterion. The strong quenching measured after alcohol additions in dichloromethane suggests reversed micelle formation. Procedures and results described here may find practical applications in the development of analytical methods.

Selective detection of Fe2+ by combination of CePO4:Tb3+ nanocrystal-H2O2 hybrid system with synchronous fluorescence scan technique.

PubMed

Chen, Hongqi; Ren, Jicun

2012-04-21

A new method for quenching kinetic discrimination of Fe(2+) and Fe(3+), and sensitive detection of trace amount of Fe(2+) was developed by using synchronous fluorescence scan technique. The principle of this assay is based on the quenching kinetic discrimination of Fe(2+) and Fe(3+) in CePO(4):Tb(3+) nanocrytals-H(2)O(2) hybrid system and the Fenton reaction between Fe(2+) and H(2)O(2). Stable, water-soluble and well-dispersible CePO(4):Tb(3+) nanocrystals were synthesized in aqueous solutions, and characterized by transmission electron microscopy (TEM) and electron diffraction spectroscopy (EDS). We found that both Fe(2+) and Fe(3+) could quench the synchronous fluorescence of CePO(4):Tb(3+) nanocrytals-H(2)O(2) system, but their quenching kinetics velocities were quite different. In the presence of Fe(3+), the synchronous fluorescent intensity was unchanged after only one minute, but in the presence of Fe(2+), the synchronous fluorescent intensity decreased slowly until 28 min later. The Fenton reaction between Fe(2+) and H(2)O(2) resulted in hydroxyl radicals which effectively quenched the synchronous fluorescence of the CePO(4):Tb(3+) nanocrystals due to the oxidation of Ce(3+) into Ce(4+) by hydroxyl radicals. Under optimum conditions, the linear range for Fe(2+) is 3 nM-2 μM, and the limit of detection is 2.0 nM. The method was used to analyze water samples.

[Sensitive Determination of Chondroitin Sulfate by Fluorescence Recovery of an Anionic Aluminum Phthalocyanine-Cationic Surfactant Ion-Association Complex Used as a Fluorescent Probe Emitting at Red Region].

PubMed

Chen, Lin; Huang, Ping; Yang, Hui-qing; Deng, Ya-bin; Guo, Meng-lin; Li, Dong-hui

2015-08-01

Determination of chondroitin sulfate in the biomedical field has an important value. The conventional methods for the assay of chondroitin sulfate are still unsatisfactory in sensitivity, selectivity or simplicity. This work aimed at developing a novel method for sensitive and selective determination of chondroitin sulfate by fluorimetry. We found that some kinds of cationic surfactants have the ability to quench the fluorescence of tetrasulfonated aluminum phthalocyanine (AlS4Pc), a strongly fluorescent compound which emits at red region, with high efficiency. But, the fluorescence of the above-mentioned fluorescence quenching system recovered significantly when chondroitin sulfate (CS) exits. Tetradecyl dimethyl benzyl ammonium chloride(TDBAC) which was screened from all of the candidates of cationic surfactants was chosen as the quencher because it shows the most efficient quenching effect. It was found that the fluorescence of AlS4Pc was extremely quenched by TDBAC because of the formation of association complex between AlS4Pc and TDBAC. Fluorescence of the association complex recovered dramatically after the addition of chondroitin sulfate (CS) due to the ability of chondroitin sulfate to shift the association equilibrium of the association, leading to the release of AlS4Pc, thus resulting in an increase in the fluorescence of the reaction system. Based on this phenomenon, a novel method with simplicity, accuracy and sensitivity was developed for quantitative determination of CS. Factors including the reaction time, influencing factors and the effect of coexisting substances were investigated and discussed. Under optimum conditions the linear range of the calibration curve was 0.20~10.0 μg · mL(-1). The detection limit for CS was 0.070 μg · mL(-1). The method has been applied to the analysis of practical samples with satisfied results. This work expands the applications of AlS4Pc in biomedical area.

A fluorescence-based method for direct measurement of submicrosecond intramolecular contact formation in biopolymers: an exploratory study with polypeptides.

PubMed

Hudgins, Robert R; Huang, Fang; Gramlich, Gabriela; Nau, Werner M

2002-01-30

A fluorescent amino acid derivative (Fmoc-DBO) has been synthesized, which contains 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as a small, hydrophilic fluorophore with an extremely long fluorescence lifetime (325 ns in H2O and 505 ns in D2O under air). Polypeptides containing both the DBO residue and an efficient fluorescence quencher allow the measurement of rate constants for intramolecular end-to-end contact formation. Bimolecular quenching experiments indicated that Trp, Cys, Met, and Tyr are efficient quenchers of DBO (k(q) = 20, 5.1, 4.5, and 3.6 x 10(8) M(-1) x s(-1) in D2O), while the other amino acids are inefficient. The quenching by Trp, which was selected as an intrinsic quencher, is presumed to involve exciplex-induced deactivation. Flexible, structureless polypeptides, Trp-(Gly-Ser)n-DBO-NH2, were prepared by standard solid-phase synthesis, and the rates of contact formation were measured through the intramolecular fluorescence quenching of DBO by Trp with time-correlated single-photon counting, laser flash photolysis, and steady-state fluorometry. Rate constants of 4.1, 6.8, 4.9, 3.1, 2.0, and 1.1 x 10(7) s(-1) for n = 0, 1, 2, 4, 6, and 10 were obtained. Noteworthy was the relatively slow quenching for the shortest peptide (n = 0). The kinetic data are in agreement with recent transient absorption studies of triplet probes for related peptides, but the rate constants are significantly larger. In contrast to the flexible structureless Gly-Ser polypeptides, the polyproline Trp-Pro4-DBO-NH2 showed insignificant fluorescence quenching, suggesting that a high polypeptide flexibility and the possibility of probe-quencher contact is essential to induce quenching. Advantages of the new fluorescence-based method for measuring contact formation rates in biopolymers include high accuracy, fast time range (100 ps-1 micros), and the possibility to perform measurements in water under air.

Anomalous fluorescence enhancement and fluorescence quenching of graphene quantum dots by single walled carbon nanotubes.

PubMed

Das, Ruma; Rajender, Gone; Giri, P K

2018-02-07

We explore the mechanism of the fluorescence enhancement and fluorescence quenching effect of single walled carbon nanotubes (SWCNTs) on highly fluorescent graphene quantum dots (GQDs) over a wide range of concentrations of SWCNTs. At very low concentrations of SWCNTs, the fluorescence intensity of the GQDs is enhanced, while at higher concentrations, systematic quenching of fluorescence is observed. The nature of the Stern-Volmer plot for the latter case was found to be non-linear indicating a combined effect of dynamic and static quenching. The contribution of the dynamic quenching component was assessed through the fluorescence lifetime measurements. The contribution of static quenching is confirmed from the red shift of the fluorescence spectra of the GQDs after addition of SWCNTs. The fluorescence intensity is first enhanced at very low concentration due to improved dispersion and higher absorption by GQDs, while at higher concentration, the fluorescence of GQDs is quenched due to the complex formation and associated reduction of the radiative sites of the GQDs, which is confirmed from time-resolved fluorescence measurements. Laser confocal microscopy imaging provides direct evidence of the enhancement and quenching of fluorescence at low and high concentrations of SWCNTs, respectively. This study provides an important insight into tuning the fluorescence of GQDs and understanding the interaction between GQDs and different CNTs, which is important for bio-imaging and drug delivery applications.

Glutathione-capped CdTe nanocrystals as probe for the determination of fenbendazole.

PubMed

Li, Qin; Tan, Xuanping; Li, Jin; Pan, Li; Liu, Xiaorong

2015-04-15

Water-soluble glutathione (GSH)-capped CdTe quantum dots (QDs) were synthesized. In pH 7.1 PBS buffer solution, the interaction between GSH-capped CdTe QDs and fenbendazole (FBZ) was investigated by spectroscopic methods, including fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, and resonance Rayleigh scattering (RRS) spectroscopy. In GSH-capped CdTe QDs solution, the addition of FBZ results in the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs. And the quenching intensity (enhanced RRS intensity) was proportional to the concentration of FBZ in a certain range. Investigation of the interaction mechanism, proved that the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs by FBZ is the result of electrostatic attraction. Based on the quenching of fluorescence (enhancement of RRS) of GSH-capped CdTe QDs by FBZ, a novel, simple, rapid and specific method for FBZ determination was proposed. The detection limit for FBZ was 42 ng mL(-1) (3.4 ng mL(-1)) and the quantitative determination range was 0-2.8 μg mL(-1) with a correlation of 0.9985 (0.9979). The method has been applied to detect FBZ in real simples and with satisfactory results. Copyright © 2015 Elsevier B.V. All rights reserved.

Determination of catecholamine in human serum by a fluorescent quenching method based on a water-soluble fluorescent conjugated polymer-enzyme hybrid system.

PubMed

Huang, Hui; Gao, Yuan; Shi, Fanping; Wang, Guannan; Shah, Syed Mazhar; Su, Xingguang

2012-03-21

In this paper, a sensitive water-soluble fluorescent conjugated polymer biosensor for catecholamine (dopamine DA, adrenaline AD and norepinephrine NE) was developed. In the presence of horse radish peroxidase (HRP) and H(2)O(2), catecholamine could be oxidized and the oxidation product of catecholamine could quench the photoluminescence (PL) intensity of poly(2,5-bis(3-sulfonatopropoxy)-1,4-phenylethynylenealt-1,4-poly(phenylene ethynylene)) (PPESO(3)). The quenching PL intensity of PPESO(3) (I(0)/I) was proportional to the concentration of DA, AD and NE in the concentration ranges of 5.0 × 10(-7) to 1.4 × 10(-4), 5.0 × 10(-6) to 5.0 × 10(-4), and 5.0 × 10(-6) to 5.0 × 10(-4) mol L(-1), respectively. The detection limit for DA, AD and NE was 1.4 × 10(-7) mol L(-1), 1.0 × 10(-6) and 1.0 × 10(-6) mol L(-1), respectively. The PPESO(3)-enzyme hybrid system based on the fluorescence quenching method was successfully applied for the determination of catecholamine in human serum samples with good accuracy and satisfactory recovery. The results were in good agreement with those provided by the HPLC-MS method.

Micellar-mediated binding interaction between proflavine hemisulfate and salicylic acid: spectroscopic insights and its analytical application.

PubMed

Patil, Dhanshri T; Mokashi, Vidya V; Kolekar, Govind B; Patil, Shivajirao R

2013-01-01

The molecular interactions between salicylic acid (SA) and proflavin hemisulfate (PF) were investigated using fluorescence and UV-VIS absorption spectroscopy in an aqueous micellar environment. Changes in the absorption spectra of SA in the presence of PF indicate a ground state interaction between salicylate and proflavine hemisulfate ions to form a complex. The excitation bands of SA monitored at its emission wavelength reveal a red spectral shift of 8390.54 and 2037.75 cm(-1) when compared with absorption bands. The intensity of both excitation bands decreased in the presence of increasing amounts of PF. The absence of excitation bands of PF rules out the possibility of its direct excitation and suggests energy transfer from excited SA to PF, resulting in quenching of the SA fluorescence. The fluorescence quenching results were found to fit the well-known Stern-Volmer (S-V) relation. S-V plots at different temperatures were used to further evaluate thermodynamic parameters such as ∆G, ∆H and ΔS. The thermodynamic and kinetic data obtained from the quenching results were used to investigate the possible mechanism of binding, the nature of the binding force and the distance between SA and PF molecules. The linear relation between SA fluorescence quenching and PF concentration used to develop an analytical method for the determination of PF from Lorexane (a veterinary cream) using a fluorescence quenching method. Copyright © 2012 John Wiley & Sons, Ltd.

CdTe quantum dot as a fluorescence probe for vitamin B12 in dosage form

NASA Astrophysics Data System (ADS)

Vaishnavi, E.; Renganathan, R.

2013-11-01

We here report the CdTe quantum dot (CdTe QDs)-based sensor for probing vitamin B12 derivatives in aqueous solution. In this paper, simple and sensitive fluorescence quenching measurements has been employed. The Stern-Volmer constant (KSV), quenching rate constant (kq) and binding constant (K) were rationalized from fluorescence quenching measurement. Furthermore, the fluorescence resonance energy transfer (FRET) mechanism was discussed. This method was applicable over the concentration ranging from 1 to 14 μg/mL (VB12) with correlation coefficient of 0.993. The limit of detection (LOD) of VB12 was found to be 0.15 μg/mL. Moreover, the present approach opens a simple pathway for developing cost-effective, sensitive and selective QD-based fluorescence sensors/probes for biologically significant VB12 in pharmaceutical sample with mean recoveries in the range of 100-102.1%.

A new dual-channel optical signal probe for Cu2+ detection based on morin and boric acid.

PubMed

Wang, Peng; Yuan, Bin Fang; Li, Nian Bing; Luo, Hong Qun

2014-01-01

In this work we utilized the common analytical reagent morin to develop a new a dual-channel, cost-effective, and sensitive method for determination of Cu(2+). It is found that morin is only weakly fluorescent by itself, but forms highly fluorescent complexes with boric acid. Moreover, the fluorescence of complexes of morin with boric acid is quenched linearly by Cu(2+) in a certain concentration range. Under optimum conditions, the fluorescence quenching efficiency was linearly proportional to the concentration of cupric ions in the range of 0.5-25 μM with high sensitivity, and the detection limit for Cu(2+) was 0.38 μM. The linear range was 1-25 μM determined by spectrophotometry, and the detection limit for cupric ions was 0.8 μM. Furthermore, the mechanism of sensitive fluorescence quenching response of morin to Cu(2+) is discussed.

CdTe quantum dot as a fluorescence probe for vitamin B(12) in dosage form.

PubMed

Vaishnavi, E; Renganathan, R

2013-11-01

We here report the CdTe quantum dot (CdTe QDs)-based sensor for probing vitamin B12 derivatives in aqueous solution. In this paper, simple and sensitive fluorescence quenching measurements has been employed. The Stern-Volmer constant (KSV), quenching rate constant (kq) and binding constant (K) were rationalized from fluorescence quenching measurement. Furthermore, the fluorescence resonance energy transfer (FRET) mechanism was discussed. This method was applicable over the concentration ranging from 1 to 14μg/mL (VB12) with correlation coefficient of 0.993. The limit of detection (LOD) of VB12 was found to be 0.15μg/mL. Moreover, the present approach opens a simple pathway for developing cost-effective, sensitive and selective QD-based fluorescence sensors/probes for biologically significant VB12 in pharmaceutical sample with mean recoveries in the range of 100-102.1%. Copyright © 2013 Elsevier B.V. All rights reserved.

Method-Unifying View of Loop-Formation Kinetics in Peptide and Protein Folding.

PubMed

Jacob, Maik H; D'Souza, Roy N; Schwarzlose, Thomas; Wang, Xiaojuan; Huang, Fang; Haas, Elisha; Nau, Werner M

2018-04-26

Protein folding can be described as a probabilistic succession of events in which the peptide chain forms loops closed by specific amino acid residue contacts, herein referred to as loop nodes. To measure loop rates, several photophysical methods have been introduced where a pair of optically active probes is incorporated at selected chain positions and the excited probe undergoes contact quenching (CQ) upon collision with the second probe. The quenching mechanisms involved triplet-triplet energy transfer, photoinduced electron transfer, and collision-induced fluorescence quenching, where the fluorescence of Dbo, an asparagine residue conjugated to 2,3-diazabicyclo[2.2.2]octane, is quenched by tryptophan. The discrepancy between the loop rates afforded from these three CQ techniques has, however, remained unresolved. In analyzing this discrepancy, we now report two short-distance FRET methods where Dbo acts as an energy acceptor in combination with tryptophan and naphtylalanine, two donors with largely different fluorescence lifetimes of 1.3 and 33 ns, respectively. Despite the different quenching mechanisms, the rates from FRET and CQ methods were, surprisingly, of comparable magnitude. This combination of FRET and CQ data led to a unifying physical model and to the conclusion that the rate of loop formation in folding reactions varies not only with the kind and number of residues that constitute the chain but also in particular with the size and properties of the residues that constitute the loop node.

A real-time fluorescence assay for protease activity and inhibitor screening based on the aggregation-caused quenching of a perylene probe.

PubMed

Wang, Yan; Zhang, Zhifang; Zhang, Ya; Yu, Cong

2018-06-01

We have established a real-time and label-free fluorescence turn-on strategy for protease activity detection and inhibitor screening via peptide-induced aggregation-caused quenching of a perylene probe. Because of electrostatic interactions and high hydrophilicity, poly-l-glutamic acid sodium salt (PGA; a negatively charged peptide) could induce aggregation of a positively charged perylene probe (probe 1) and the monomer fluorescence of probe 1 was effectively quenched. After a protease was added, PGA was enzymatically hydrolyzed into small fragments and probe 1 disaggregated. The fluorescence recovery of probe 1 was found to be proportional to the concentration of protease in the range from 0 to 1 mU/ml. The detection limit was down to 0.1 mU/ml. In the presence of a protease inhibitor, protease activity was inhibited and fluorescence recovery reduced. Moreover, we demonstrated the potential application of our method in a complex mixture sample including 1% human serum. Our method is simple, fast and cost effective. Copyright © 2018 John Wiley & Sons, Ltd.

Etching-dependent fluorescence quenching of Ag-dielectric-Au three-layered nanoshells: The effect of inner Ag nanosphere

NASA Astrophysics Data System (ADS)

Zhu, Jian; Xu, Zai-jie; Weng, Guo-jun; Zhao, Jing; Li, Jian-jun; Zhao, Jun-wu

2018-07-01

In this report, Ag-dielectric-Au three-layered nanoshells with controlled inner core size were synthesized. The fluorescence emission of the rhodamine 6G (R6G) could be quenched by the three-layered nanoshells distinctly. What's more, the fluorescence quenching efficiency could be further improved by tuning the etching of inner Ag nanosphere. The maximum fluorescence quenching efficiency is obtained when the separate layer just appears between the inner Ag core and the outer Au shell. Whereas the fluorescence quenching efficiency is weakened when no gaps take place around the inner Ag core or the separate layer is too thick and greater than 13 nm. The fluorescence quenching properties of the Ag-dielectric-Au three-layered nanoshells with different initial sizes of the Ag nanoparticles are also studied. The maximum fluorescence quenching efficiency is obtained when the three-layered nanoshells are synthesized based on the Ag nanoparticles with 60 nm, which is better than others two sizes (42 and 79 nm). Thus we believe that the size of initial Ag nanospheres also greatly affects the optimized fluorescence quenching efficiency. These results about fluorescence quenching properties of Ag-dielectric-Au three-layered nanoshells present a potential for design and fabrication of fluorescence nanosensors based on tuning the geometry of the inner core and the separate layer.

Distance Mapping in Proteins Using Fluorescence Spectroscopy: The Tryptophan-Induced Quenching (TrIQ) Method

PubMed Central

Mansoor, Steven E.; DeWitt, Mark A.; Farrens, David L.

2014-01-01

Studying the interplay between protein structure and function remains a daunting task. Especially lacking are methods for measuring structural changes in real time. Here we report our most recent improvements to a method that can be used to address such questions. This method, which we now call Tryptophan induced quenching (TrIQ), provides a straightforward, sensitive and inexpensive way to address questions of conformational dynamics and short-range protein interactions. Importantly, TrIQ only occurs over relatively short distances (~5 to 15 Å), making it complementary to traditional fluorescence resonance energy transfer (FRET) methods that occur over distances too large for precise studies of protein structure. As implied in the name, TrIQ measures the efficient quenching induced in some fluorophores by tryptophan (Trp). We present here our analysis of the TrIQ effect for five different fluorophores that span a range of sizes and spectral properties. Each probe was attached to four different cysteine residues on T4 lysozyme and the extent of TrIQ caused by a nearby Trp was measured. Our results show that for smaller probes, TrIQ is distance dependent. Moreover, we also demonstrate how TrIQ data can be analyzed to determine the fraction of fluorophores involved in a static, non-fluorescent complex with Trp. Based on this analysis, our study shows that each fluorophore has a different TrIQ profile, or "sphere of quenching", which correlates with its size, rotational flexibility, and the length of attachment linker. This TrIQ-based "sphere of quenching" is unique to every Trp-probe pair and reflects the distance within which one can expect to see the TrIQ effect. It provides a straightforward, readily accessible approach for mapping distances within proteins and monitoring conformational changes using fluorescence spectroscopy. PMID:20886836

Correlation of cholinergic drug induced quenching of acetylcholinesterase bound thioflavin-T fluorescence with their inhibition activity

NASA Astrophysics Data System (ADS)

Islam, Mullah Muhaiminul; Rohman, Mostofa Ataur; Gurung, Arun Bahadur; Bhattacharjee, Atanu; Aguan, Kripamoy; Mitra, Sivaprasad

2018-01-01

The development of new acetylcholinesterase inhibitors (AChEIs) and subsequent assay of their inhibition efficiency is considered to be a key step for AD treatment. The fluorescence intensity of thioflavin-T (ThT) bound in the active site of acetylcholinesterase (AChE) quenches substantially in presence of standard AChEI drugs due to the dynamic replacement of the fluorophore from the AChE active site as confirmed from steady state emission as well as time-resolved fluorescence anisotropy measurement and molecular dynamics simulation in conjunction with docking calculation. The parametrized % quenching data for individual system shows excellent correlation with enzyme inhibition activity measured independently by standard Ellman AChE assay method in a high throughput plate reader system. The results are encouraging towards design of a fluorescence intensity based AChE inhibition assay method and may provide a better toolset to rapidly evaluate as well as develop newer AChE-inhibitors for AD treatment.

Quenching of p-Cyanophenylalanine Fluorescence by Various Anions.

PubMed

Pazos, Ileana M; Roesch, Rachel M; Gai, Feng

2013-03-20

To expand the spectroscopic utility of the non-natural amino acid p -cyanophenylalanine (Phe CN ), we examine the quenching efficiencies of a series of commonly encountered anions toward its fluorescence. We find that iodide exhibits an unusually large Stern-Volmer quenching constant, making it a convenient choice in Phe CN fluorescence quenching studies. Indeed, using the villin headpiece subdomain as a testbed we demonstrate that iodide quenching of Phe CN fluorescence offers a convenient means to reveal protein conformational heterogeneity. Furthermore, we show that the amino group of Phe CN strongly quenches its fluorescence, suggesting that Phe CN could be used as a local pH sensor.

A simple fluorescence quenching method for berberine determination using water-soluble CdTe quantum dots as probes

NASA Astrophysics Data System (ADS)

Cao, Ming; Liu, Meigui; Cao, Chun; Xia, Yunsheng; Bao, Linjun; Jin, Yingqiong; Yang, Song; Zhu, Changqing

2010-03-01

A novel method for the determination of berberine has been developed based on quenching of the fluorescence of thioglycolic acid-capped CdTe quantum dots (TGA-CdTe QDs) by berberine in aqueous solutions. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of berberine between 2.5 × 10 -8 and 8.0 × 10 -6 mol L -1 with a detection limit of 6.0 × 10 -9 mol L -1. The method has been applied to the determination of berberine in real samples, and satisfactory results were obtained. The mechanism of the proposed reaction was also discussed.

The mechanism and regularity of quenching the effect of bases on fluorophores: the base-quenched probe method.

PubMed

Mao, Huihui; Luo, Guanghua; Zhan, Yuxia; Zhang, Jun; Yao, Shuang; Yu, Yang

2018-04-30

The base-quenched probe method for detecting single nucleotide polymorphisms (SNPs) relies on real-time PCR and melting-curve analysis, which might require only one pair of primers and one probe. At present, it has been successfully applied to detect SNPs of multiple genes. However, the mechanism of the base-quenched probe method remains unclear. Therefore, we investigated the possible mechanism of fluorescence quenching by DNA bases in aqueous solution using spectroscopic techniques. It showed that the possible mechanism might be photo-induced electron transfer. We next analyzed electron transfer or transmission between DNA bases and fluorophores. The data suggested that in single-stranded DNA, the electrons of the fluorophore are transferred to the orbital of pyrimidine bases (thymine (T) and cytosine (C)), or that the electron orbitals of the fluorophore are occupied by electrons from purine bases (guanine (G) and adenine (A)), which lead to fluorescence quenching. In addition, the electrons of a fluorophore excited by light can be transmitted along double-stranded DNA, which gives rise to stronger fluorescence quenching. Furthermore, we demonstrated that the quenching efficiency of bases is in the order of G > C ≥ A ≥ T and the capability of electron transmission of base-pairs in double-stranded DNA is in the order of CG[combining low line] ≥ GC[combining low line] > TA[combining low line] ≥ AT[combining low line] (letters representing bases on the complementary strand of the probe are bold and underlined), and the most common commercial fluorophores including FAM, HEX, TET, JOE, and TAMRA could be influenced by bases and are in line with this mechanism and regularity.

Spectroscopic studies on the interaction of fluorescein and safranine T in PC liposomes

NASA Astrophysics Data System (ADS)

Bozkurt, Ebru; Bayraktutan, Tuğba; Acar, Murat; Toprak, Mahmut

2013-01-01

In this study, the fluorescence quenching of fluorescein by safranine T in liposome media had been investigated systematically by fluorescence spectroscopy, UV-vis absorption spectroscopy and fluorescence decay lifetime measurements. The spectroscopic data were analyzed using a Stern-Volmer equation to determine the quenching process. The experimental results showed that the intrinsic fluorescence of fluorescein was strongly quenched by safranine T, and that the quenching mechanism was considered as static quenching by forming a ground-complex. The Stern-Volmer quenching constant Ksv, and the bimolecular quenching constant Kq were estimated. The distances between the donor (fluorescein) and the acceptor (safranine T) were calculated according to the Förster non-radiation energy transfer theory. In addition, the partition coefficient of the safranine T (Kp) in the L-egg lecithin phosphatidylcholine liposomes was also calculated by utilizing the fluorescence quenching.

A study of the interaction between malachite green and lysozyme by steady-state fluorescence.

PubMed

Ding, Fei; Liu, Wei; Liu, Feng; Li, Zhi-Yuan; Sun, Ying

2009-09-01

The interaction of a N-methylated diaminotriphenylmethane dye, malachite green, with lysozyme was investigated by fluorescence spectroscopic techniques under physiological conditions. The binding parameters have been evaluated by fluorescence quenching methods. The results revealed that malachite green caused the fluorescence quenching of lysozyme through a static quenching procedure. The thermodynamic parameters like DeltaH and DeltaS were calculated to be -15.33 kJ mol(-1) and 19.47 J mol(-1) K(-1) according to van't Hoff equation, respectively, which proves main interaction between malachite green and lysozyme is hydrophobic forces and hydrogen bond contact. The distance r between donor (lysozyme) and acceptor (malachite green) was obtained to be 3.82 nm according to Frster's theory. The results of synchronous fluorescence, UV/vis and three-dimensional fluorescence spectra showed that binding of malachite green with lysozyme can induce conformational changes in lysozyme. In addition, the effects of common ions on the constants of lysozyme-malachite green complex were also discussed.

Distance-dependent Fluorescence Quenching and Binding of CdSe Quantum Dots by Functionalized Nitroxide Radicals

PubMed Central

Tansakul, Chittreeya; Lilie, Erin; Walter, Eric D.; Rivera, Frank; Wolcott, Abraham; Zhang, Jin Z.; Millhauser, Glenn L.

2010-01-01

Quantum dot (QD) fluorescence is effectively quenched at low concentration by nitroxides bearing amine or carboxylic acid ligands. The association constants and fluorescence quenching of CdSe QDs with these derivatized nitroxides have been examined using electron paramagnetic resonance (EPR) and fluorescence spectroscopy. The EPR spectra in the non-protic solvent toluene are extremely sensitive to intermolecular and intramolecular hydrogen bonding of the functionalized nitroxides. Fluorescence measurements show that quenching of QD luminescence is nonlinear, with a strong dependence on the distance between the radical and the QD. The quenched fluorescence is restored when the surface-bound nitroxides are converted to hydroxylamines by mild reducing agents, or trapped by carbon radicals to form alkoxyamines. EPR studies indicate that photoreduction of the nitroxide occurs in toluene solution upon photoexcitation at 365 nm. However, photolysis in benzene solution gives no photoreduction, suggesting that photoreduction in toluene is independent of the quenching mechanism. The fluorescence quenching of QDs by nitroxide binding is a reversible process. PMID:20473339

High-speed fluorescent thermal imaging of quench propagation in high temperature superconductor tapes

NASA Astrophysics Data System (ADS)

Gyuráki, Roland; Sirois, Frédéric; Grilli, Francesco

2018-07-01

Fluorescent microthermographic imaging, a method using rare-earth fluorescent coatings with temperature dependent light emission, was used for quench investigation in high temperature superconductors (HTS). A fluorophore was embedded in a polymer matrix and used as a coating on top of an HTS tape, while being excited with UV light and recorded with a high-speed camera. Simultaneously, the tape was pulsed with high amplitude, short duration DC current, and brought to quench with the help of a localised defect. The Joule heating during a quench influences the fluorescent light intensity emitted from the coating, and by recording the local variations in this intensity over time, the heating of the tape can be visualised and the developed temperatures can be calculated. In this paper, the fluorophore europium tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorate] (EuTFC) provided sufficient temperature sensitivity and a usable temperature range from 77-260 K. With the help of 2500 image captures per second, the normal zone development was imaged in a 20 μm copper stabilised HTS tape held in a liquid nitrogen bath, and using a calibration curve, the temperatures reached during the quench have been calculated.

Simultaneous one-dimensional fluorescence lifetime measurements of OH and CO in premixed flames

NASA Astrophysics Data System (ADS)

Jonsson, Malin; Ehn, Andreas; Christensen, Moah; Aldén, Marcus; Bood, Joakim

2014-04-01

A method for simultaneous measurements of fluorescence lifetimes of two species along a line is described. The experimental setup is based on picosecond laser pulses from two tunable optical parametric generator/optical parametric amplifier systems together with a streak camera. With an appropriate optical time delay between the two laser pulses, whose wavelengths are tuned to excite two different species, laser-induced fluorescence can be both detected temporally and spatially resolved by the streak camera. Hence, our method enables one-dimensional imaging of fluorescence lifetimes of two species in the same streak camera recording. The concept is demonstrated for fluorescence lifetime measurements of CO and OH in a laminar methane/air flame on a Bunsen-type burner. Measurements were taken in flames with four different equivalence ratios, namely ϕ = 0.9, 1.0, 1.15, and 1.25. The measured one-dimensional lifetime profiles generally agree well with lifetimes calculated from quenching cross sections found in the literature and quencher concentrations predicted by the GRI 3.0 mechanism. For OH, there is a systematic deviation of approximately 30 % between calculated and measured lifetimes. It is found that this is mainly due to the adiabatic assumption regarding the flame and uncertainty in H2O quenching cross section. This emphasizes the strength of measuring the quenching rates rather than relying on models. The measurement concept might be useful for single-shot measurements of fluorescence lifetimes of several species pairs of vital importance in combustion processes, hence allowing fluorescence signals to be corrected for quenching and ultimately yield quantitative concentration profiles.

Intra- and intermolecular fluorescence quenching of N-activated 4,5-dimethoxyphthalimides by sulfides, amines, and alkyl carboxylates.

PubMed

Griesbeck, Axel G; Schieffer, Stefan

2003-02-01

The fluorescent 4,5-dimethoxyphthalimides 1-10 were applied as sensors for intra- and intermolecular photoinduced electron transfer processes. Strong intramolecular fluorescence quenching was detected for the thioether 2 and the tertiary amine 3. The fluorescence of the carboxylic acids 4-7 is pH-dependent accounting for PET-quenching of the singlet excited phthalimide at pH > pKs. At low pH, chromophore protonation might contribute to moderate fluorescence quenching. The arylated phthalimides 9 and 10 show remarkable low fluorescence independent of pH and substituent pattern. Intermolecular fluorescence quenching was detected for the combinations of 1 with dimethyl sulfide, and 1 with triethylamine but not with metal carboxylates.

Application of CdSe quantum dots for the direct detection of TNT.

PubMed

Yi, Kui-Yu

2016-02-01

CdSe quantum dots were synthesized through a simple, green organic-phase method. Paraffin was used as the reaction solvent and a reducing agent, oleic acid was the reaction ligand, and oleyl amine was the stabilizer. Based on the phenomenon of TNT quenched oil-soluble CdSe quantum dot fluorescence, a simple, fast, and direct method of TNT detection was established. Under optimum conditions, the degree of fluorescence quenching of oil-soluble CdSe quantum dots had a good linear correlation with TNT concentration in the 1.0×10(-7)-5.0×10(-5) mol/L range, and the correlation coefficient was 0.9990. TNT detection limit was 2.1×10(-8)mol/L. The method was successfully used to determine TNT-explosion dust samples, results were satisfactory. The fluorescence quenching mechanism of oil-soluble CdSe quantum dots by TNT was also discussed. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

FRET Sensor for Erythrosine Dye Based on Organic Nanoparticles: Application to Analysis of Food Stuff.

PubMed

Mahajan, Prasad G; Bhopate, Dhanaji P; Kolekar, Govind B; Patil, Shivajirao R

2016-07-01

An aqueous suspension of fluorescent nanoparticles (PHNNPs) of naphthol based fluorescent organic compound 1-[(Z)-(2-phenylhydrazinylidene) methyl] naphthalene -2-ol (PHN) were prepared using reprecipitation method shows bathochromically shifted aggregation induced enhanced emission (AIEE) in the spectral region where erythrosine (ETS) food dye absorbs strongly. The average size of 72.6 nm of aqueous suspension of PHNNPs obtained by Dynamic light scattering results shows a narrow particle size distribution. The negative zeta potential of nano probe (-22.6 mV) responsible to adsorb oppositely charged analyte on its surface and further permit to bind nano probe and analyte within the close distance proximity required for efficient fluorescence resonance energy transfer (FRET) to take place from donor (PHNNPs) to acceptor (ETS). Systematic FRET experiments performed by measuring fluorescence quenching of PHNNPs with successive addition of ETS solution exploited the use of the PHNNPs as a novel nano probe for the detection of ETS in aqueous solution with extremely lower limit of detection equal to 3.6 nM (3.1 ng/mL). The estimation of photo kinetic and thermodynamic parameters such as quenching rate constant, enthalpy change (∆H), Gibbs free energy change (∆G) and entropy change (∆S) was obtained by the quenching results obtained at different constant temperatures which were found to fit the well-known Stern-Volmer relation. The mechanism of binding and fluorescence quenching of PHNNPs by ETS food dye is proposed on the basis of results obtained in photophysical studies, thermodynamic parameter, energy transfer efficiency, critical energy transfer distance (R0) and distance of approach between donor-acceptor molecules (r). The proposed FRET method based on fluorescence quenching of PHNNPs was successfully applied to develop an analytical method for estimation of ETS from food stuffs without interference of other complex ingredients. Graphical Abstract A fluorescent organic nanoprobe developed for the detection of erythrosine (ETS) food dye in aqueous medium based on fluorescence resonance energy transfer (FRET). The FRET process between donor (nanoparticles) and acceptor (ETS dye) arises due to oppositely charge attraction through hydrophobic interactions. The proposed method was successfully applied to quantitative determination of ETS dye in food stuff sample collected from local market.

APTS and rGO co-functionalized pyrenated fluorescent nanonets for representative vapor phase nitroaromatic explosive detection

NASA Astrophysics Data System (ADS)

Guo, Linjuan; Zu, Baiyi; Yang, Zheng; Cao, Hongyu; Zheng, Xuefang; Dou, Xincun

2014-01-01

For the first time, flexible PVP/pyrene/APTS/rGO fluorescent nanonets were designed and synthesized via a one-step electrospinning method to detect representative subsaturated nitroaromatic explosive vapor. The functional fluorescent nanonets, which were highly stable in air, showed an 81% quenching efficiency towards TNT vapor (~10 ppb) with an exposure time of 540 s at room temperature. The nice performance of the nanonets was ascribed to the synergistic effects induced by the specific adsorption properties of APTS, the fast charge transfer properties and the effective π-π interaction with pyrene and TNT of rGO. Compared to the analogues of TNT, the PVP/pyrene/APTS/rGO nanonets showed notable selectivity towards TNT and DNT vapors. The explored functionalization method opens up brand new insight into sensitive and selective detection of vapor phase nitroaromatic explosives.For the first time, flexible PVP/pyrene/APTS/rGO fluorescent nanonets were designed and synthesized via a one-step electrospinning method to detect representative subsaturated nitroaromatic explosive vapor. The functional fluorescent nanonets, which were highly stable in air, showed an 81% quenching efficiency towards TNT vapor (~10 ppb) with an exposure time of 540 s at room temperature. The nice performance of the nanonets was ascribed to the synergistic effects induced by the specific adsorption properties of APTS, the fast charge transfer properties and the effective π-π interaction with pyrene and TNT of rGO. Compared to the analogues of TNT, the PVP/pyrene/APTS/rGO nanonets showed notable selectivity towards TNT and DNT vapors. The explored functionalization method opens up brand new insight into sensitive and selective detection of vapor phase nitroaromatic explosives. Electronic supplementary information (ESI) available: Vapor pressure of TNT and its analogues, fluorescence quenching kinetics, fluorescence quenching efficiencies and additional SEM images. See DOI: 10.1039/c3nr04960d

Fluorescence turn-on detection of target sequence DNA based on silicon nanodot-mediated quenching.

PubMed

Zhang, Yanan; Ning, Xinping; Mao, Guobin; Ji, Xinghu; He, Zhike

2018-05-01

We have developed a new enzyme-free method for target sequence DNA detection based on the dynamic quenching of fluorescent silicon nanodots (SiNDs) toward Cy5-tagged DNA probe. Fascinatingly, the water-soluble SiNDs can quench the fluorescence of cyanine (Cy5) in Cy5-tagged DNA probe in homogeneous solution, and the fluorescence of Cy5-tagged DNA probe can be restored in the presence of target sequence DNA (the synthetic target miRNA-27a). Based on this phenomenon, a SiND-featured fluorescent sensor has been constructed for "turn-on" detection of the synthetic target miRNA-27a for the first time. This newly developed approach possesses the merits of low cost, simple design, and convenient operation since no enzymatic reaction, toxic reagents, or separation procedures are involved. The established method achieves a detection limit of 0.16 nM, and the relative standard deviation of this method is 9% (1 nM, n = 5). The linear range is 0.5-20 nM, and the recoveries in spiked human fluids are in the range of 90-122%. This protocol provides a new tactic in the development of the nonenzymic miRNA biosensors and opens a promising avenue for early diagnosis of miRNA-associated disease. Graphical abstract The SiND-based fluorescent sensor for detection of S-miR-27a.

Fluorescence properties of 3-amino phenylboronic acid and its interaction with glucose and ZnS:Cu quantum dots.

PubMed

Kur-Kowalska, Karolina; Przybyt, Małgorzata; Ziółczyk, Paulina; Sowiński, Przemysław; Miller, Ewa

2014-08-14

Preliminary results of a study of the interaction between 3-amino phenylboronic acid and glucose or ZnS:Cu quantum dots are presented in this paper. ZnS:Cu quantum dots with mercaptopropionic acid as a capping agent were obtained and characterized. Quenching of 3-amino phenylboronic acid fluorescence was studied by steady-state and timeresolved measurements. For fluorescence quenching with glucose the results of steady-state measurements fulfill Stern-Volmer equation. The quenching constants are increasing with growing pH. The decay of fluorescence is monoexponential with lifetime about 8.4 ns, which does not depend on pH and glucose concentration indicating static quenching. The quenching constant can be interpreted as apparent equilibrium constant of estrification of boronic group with diol. Quantum dots are also quenching 3-amino phenylboronic acid fluorescence. Fluorescence lifetime, in this case, is slightly decreasing with increasing concentration of quantum dots. The quenching constants are increasing slightly with pH's growth. Quenching mechanism of 3-amino phenylboronic acid fluorescence by quantum dots needs further experiments to be fully explained. Copyright © 2014 Elsevier B.V. All rights reserved.

Synthesis of a novel fluorescent probe based on 7-nitrobenzo-2-oxa-1,3-diazole skeleton for the rapid determination of vitamin B12 in pharmaceuticals.

PubMed

Shang, Zhuo Bin; Wen, Ya Juan; Yan, Xiao Qing; Sun, Huan He; Wang, Yu; Jin, Wei Jun

2014-09-01

A new fluorescent probe, 4-N,N-di(2-hydroxyethyl)imino-7-nitrobenzo-2-oxa-1,3-diazole (HINBD) was synthesized in a single step with reasonably good yield. The water-soluble HINBD emits strongly in the visible region (λex  = 479 nm, λem  = 545 nm) and is stable over a wide range of pH values. It was found that vitamin B12 (VB12 ) had the ability to quench the fluorescence of HINBD, and the quenched fluorescence intensity was proportional to the concentration of VB12 . A method for VB12 determination based on the quenching fluorescence of HINBD was thus established. Interference effects of various substances, including sugars, vitamins, amino acids, inorganic cations and some organic substances have been studied. Under optimal conditions, the linear range is 0.0-2.4 × 10(-5)  mol/L. The determination limit is 8.3 × 10(-8)  mol/L. The method was applied to measure VB12 in pharmaceutical preparations with satisfactory results. Copyright © 2013 John Wiley & Sons, Ltd.

Measuring the Quenching of no Fluorescence Produced from the Excitation of Photo-Fragmented Nitrobenzene Using a Picosecond Laser.

NASA Astrophysics Data System (ADS)

Lue, Christopher J.; Tanjaroon, Chakree; Johnson, J. Bruce; Reeve, Scott W.; Allen, Susan D.

2013-06-01

The military is interested in using spectroscopic methods to detect nitroaromatic compounds related to explosives. Upon absorption of a UV photon, nitrobenzene can dissociate into C_6H_5O and NO. Wynn, et al. have shown that looking at NO fluorescence from the photodissociated nitrobenzene could be a possible detection method. However, the fluorescence can easily be quenched by molecular oxygen and other constituents in air. We have measured fluorescence lifetimes of the nascent NO resulting from photo-fragmented nitrobenzene using a pulsed picosecond tunable laser (pulse width ≈15 ps) by means of a two-color process. In the two-color process, photons of a particular energy dissociated the nitrobenzene while photons of a different energy probed the A^2Σ^+← X^2Π_{(1/2,3/2)} NO band system between 225-260 nm. We have performed the measurements with different background pressures of He, N_2, and air. We present the results of these measurements which indicate considerable quenching of the NO fluorescence due to oxygen. Wynn, C. M.; Palmacci, S.; Kunz, R. R.; and Rothschild, M.Opt. Express, OSA, 2010, 18, 5399-5406

Studies of the interaction between FNC and human hemoglobin: a spectroscopic analysis and molecular docking.

PubMed

Li, Huiyi; Dou, Huanjing; Zhang, Yuhai; Li, Zhigang; Wang, Ruiyong; Chang, Junbiao

2015-02-05

FNC (2'-deoxy-2'-bfluoro-4'-azidocytidine) is a novel nucleoside analogue with pharmacologic effects on several human diseases. In this work, the binding of FNC to human hemoglobin (HHb) have been investigated by absorption spectroscopy, fluorescence quenching technique, synchronous fluorescence, three-dimensional fluorescence and molecular modeling methods. Analysis of fluorescence data showed that the binding of FNC to HHb occurred via a static quenching mechanism. Thermodynamic analysis and molecular modeling suggest that hydrogen bond and van der Waals force are the mainly binding force in the binding of FNC to HHb. Copyright © 2014 Elsevier B.V. All rights reserved.

Fluorescence Quenching of Alpha-Fetoprotein by Gold Nanoparticles: Effect of Dielectric Shell on Non-Radiative Decay

NASA Astrophysics Data System (ADS)

Zhu, Jian; Li, Jian-Jun; Wang, A.-Qing; Chen, Yu; Zhao, Jun-Wu

2010-09-01

Fluorescence quenching spectrometry was applied to study the interactions between gold colloidal nanoparticles and alpha-fetoprotein (AFP). Experimental results show that the gold nanoparticles can quench the fluorescence emission of adsorbed AFP effectively. Furthermore, the intensity of fluorescence emission peak decreases monotonously with the increasing gold nanoparticles content. A mechanism based on surface plasmon resonance-induced non-radiative decay was investigated to illuminate the effect of a dielectric shell on the fluorescence quenching ability of gold nanoparticles. The calculation results show that the increasing dielectric shell thickness may improve the monochromaticity of fluorescence quenching. However, high energy transfer efficiency can be obtained within a wide wavelength band by coating a thinner dielectric shell.

A fluorescence quenching test for the detection of flavonoid transformation.

PubMed

Schoefer, L; Braune, A; Blaut, M

2001-11-13

A novel fluorescence quenching test for the detection of flavonoid degradation by microorganisms was developed. The test is based on the ability of the flavonoids to quench the fluorescence of 1,6-diphenyl-1,3,5-hexatriene (DPH). Several members of the anthocyanidins, flavones, isoflavones, flavonols, flavanones, dihydroflavanones, chalcones, dihydrochalcones and catechins were tested with regard to their quenching properties. The anthocyanidins were the most potent quenchers of DPH fluorescence, while the flavanones, dihydroflavanones and dihydrochalcones, quenched the fluorescence only weakly. The catechins had no visible impact on DPH fluorescence. The developed test allows a quick and easy differentiation between flavonoid-degrading and flavonoid-non-degrading bacteria. The investigation of individual reactions of flavonoid transformation with the developed test system is also possible.

A fluorescent aptasensor for sensitive analysis oxytetracycline based on silver nanoclusters.

PubMed

Hosseini, Morteza; Mehrabi, Fatemeh; Ganjali, Mohammad Reza; Norouzi, Parviz

2016-11-01

A fluorescent aptasensor for detection of oxytetracycline (OTC) was presented based on fluorescence quenching of DNA aptamer-templated silver nanoclusters (AgNCs). The specific DNA scaffolds with two different nucleotides fragments were used: one was enriched with a cytosine sequence fragment (C12) that could produce DNA-AgNCs via a chemical reduction method, and another was the OTC aptamer fragment that could selectively bind to the OTC antibiotic. Thus, the as-prepared AgNCs could exhibit quenched fluorescence after binding to the target OTC. The fluorescence ratio of the DNA-AgNCs was quenched in a linearly proportional manner to the concentration of the target in the range of 0.5 nM to 100 nM with a detection limit of 0.1 nM. This proposed nanobiosensor was demonstrated to be sensitive, selective, and simple, introducing a viable alternative for rapid determination of toxin OTC in honey and water samples. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Green Synthesis of Red-Emitting Carbon Nanodots as a Novel "Turn-on" Nanothermometer in Living Cells.

PubMed

Wang, Chuanxi; Jiang, Kaili; Wu, Qian; Wu, Jiapeng; Zhang, Chi

2016-10-04

Temperature measurements in biology and medical diagnostics, along with sensitive temperature probing of living cells, is of great importance; however, it still faces significant challenges. Herein, a novel "turn-on" carbon-dot-based fluorescent nanothermometry device for spatially resolved temperature measurements in living cells is presented. The carbon nanodots (CNDs) are prepared by a green microwave-assisted method and exhibit red fluorescence (λem =615 nm) with high quantum yields (15 %). Then, an on-off fluorescent probe is prepared for detecting glutathione (GSH) based on aggregation-induced fluorescence quenching. Interestingly, the quenched fluorescence could be recovered by increasing temperature and the CNDs-GSH mixture could behave as an off-on fluorescent probe for temperature. Thus, red-emitting CNDs can be utilized for "turn-on" fluorescent nanothermometry through the fluorescence quenching and recovery processes, respectively. We employ MC3T3-E1 cells as an example model to demonstrate the red-emitting CNDs can function as "non-contact" tools for the accurate measurement of temperature and its gradient inside a living cell. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Position-specific incorporation of fluorescent non-natural amino acids into maltose-binding protein for detection of ligand binding by FRET and fluorescence quenching.

PubMed

Iijima, Issei; Hohsaka, Takahiro

2009-04-17

Position-specific incorporation of fluorescent groups is a useful method for analysis of the functions and structures of proteins. We have developed a method for the incorporation of visible-wavelength-fluorescent non-natural amino acids into proteins in a cell-free translation system. Using this technique, we introduced one or two BODIPY-linked amino acids into maltose-binding protein (MBP) to obtain MBP derivatives showing ligand-dependent changes in fluorescence intensity or intensity ratio. BODIPY-FL-aminophenylalanine was incorporated in place of 15 tyrosines, as well as the N-terminal Lys1, and the C-terminal Lys370 of MBP. Fluorescence measurements revealed that MBP containing a BODIPY-FL moiety in place of Tyr210 showed a 13-fold increase in fluorescence upon binding of maltose. Tryptophan-to-phenylalanine substitutions suggest that the increase in fluorescence was the result of a decrease in the quenching of BODIPY-FL by tryptophan located around the binding site. MBP containing a BODIPY-558 moiety also showed a maltose-dependent increase in fluorescence. BODIPY-FL was then additionally incorporated in place of Lys1 of the BODIPY-558-containing MBP as a response to the amber codon. Fluorescence measurements with excitation of BODIPY-FL showed a large change in fluorescence intensity ratio (0.13 to 1.25) upon binding of maltose; this change can be attributed to fluorescence resonance energy transfer (FRET) and maltose-dependent quenching of BODIPY-558. These results demonstrate the usefulness of the position-specific incorporation of fluorescent amino acids in the fluorescence-based detection of protein functions.

A ratiometric nanoprobe based on silver nanoclusters and carbon dots for the fluorescent detection of biothiols

NASA Astrophysics Data System (ADS)

Zhang, Shuming; Lin, Bixia; Yu, Ying; Cao, Yujuan; Guo, Manli; Shui, Lingling

2018-04-01

Ratiometric fluorescent probes could eliminate the influence from experimental factors and improve the detection accuracy. In this article, a ratiometric nanoprobe was constructed based on silver nanoclusters (AgNCs) with nitrogen-doped carbon dots (NCDs) and used for the detection of biothiols. The fluorescence peak of AgNCs was observed at 650 nm with excitation wavelength at 370 nm. In order to construct the ratiometric fluorescent probe, NCDs with the excitation and emission wavelengths at 370 nm and 450 nm were selected. After adding AgNCs, the fluorescence of NCDs was quenched. The mechanism of the fluorescence quenching was studied by fluorescence, UV-Vis absorption and the fluorescence lifetime spectra. The results indicated that the quenching could be ascribed to the inner filter effect (IFE). With the addition of biothiols, the fluorescence of AgNCs at 650 nm decreased due to the breakdown of AgNCs, and the fluorescence of NCDs at 450 nm recovered accordingly. Thus, the relationship between the ratio of the fluorescence intensities (I450/I650) and biothiol concentration was used to establish the determination method for biothiols. Cysteine (Cys) was taken as the model of biothiols, and the working curve for Cys was I450/I650 = 0.60CCys - 1.86 (CCys: μmol/L) with the detection limit of 0.14 μmol/L (S/N = 3). Then, the method was used for the detection of Cys in human urine and serum samples with satisfactory accuracy and recovery ratios. Furthermore, the probe could be applied for the visual semi-quantitative determination of Cys by naked eyes.

Determination of sunset yellow in soft drinks based on fluorescence quenching of carbon dots

NASA Astrophysics Data System (ADS)

Yuan, Yusheng; Zhao, Xin; Qiao, Man; Zhu, Jinghui; Liu, Shaopu; Yang, Jidong; Hu, Xiaoli

2016-10-01

Fluorescent carbon dots was prepared by heating N-(2-hydroxyethyl)ethylene diaminetriacetic acid in air. The carbon dots were not only highly soluble in water but also uniform in size, and possessed strong blue fluorescence and excitation wavelength-dependent emission properties with the maximum excitation and emission wavelength at 366 nm and 423 nm, respectively. Food colorant sunset yellow whose excitation and emission wavelength at 303 nm and 430 nm could selectively quench the fluorescence of carbon dots, efficient fluorescent resonance energy transfer between the carbon dots and sunset yellow is achieved. This was exploited to design a method for the determination of sunset yellow in the concentration range from 0.3 to 8.0 μmol L- 1, with a limit of detection (3 σ/k) of 79.6 nmol L- 1. Furthermore the fluorimetric detection method was established and validated for sunset yellow in soft drinks samples with satisfactory results.

Fluorescent porous film modified polymer optical fiber via "click" chemistry: stable dye dispersion and trace explosive detection.

PubMed

Ma, Jiajun; Lv, Ling; Zou, Gang; Zhang, Qijin

2015-01-14

In this paper, we report a facile strategy to fabricate fluorescent porous thin film on the surface of U-bent poly(methyl methacrylate) optical fiber (U-bent POF) in situ via "click" polymerization for vapor phase sensing of explosives. Upon irradiation of evanescent UV light transmitting within the fiber under ambient condition, a porous film (POSS-thiol cross-linking film, PTCF) is synthesized on the side surface of the fiber by a thiol-ene "click" reaction of vinyl-functionalized polyhedral oligomeric silsesquioxanes (POSS-V8) and alkane dithiols. When vinyl-functionalized porphyrin, containing four allyl substituents at the periphery, is added into precursors for the polymerization, fluorescence porphyrin can be covalently bonded into the cross-linked network of PTCF. This "fastened" way reduces the aggregation-induced fluorescence self-quenching of porphyrin and enhances the physicochemical stability of the porous film on the surface of U-bent POF. Fluorescent signals of the PTCF/U-bent POF probe made by this method exhibit high fluorescence quenching toward trace TNT and DNT vapor and the highest fluorescence quenching efficiency is observed for 1, 6-hexanedimercaptan-based film. In addition, because of the presence of POSS-V8 with multi cross-linkable groups, PTCF exhibits well-organized pore network and stable dye dispersion, which not only causes fast and sensitive fluorescence quenching against vapors of nitroaromatic compounds, but also provides a repeatability of the probing performance.

Real-time monitoring of hairpin ribozyme kinetics through base-specific quenching of fluorescein-labeled substrates.

PubMed Central

Walter, N G; Burke, J M

1997-01-01

Current methods for evaluating the kinetics of ribozyme-catalyzed reactions rely primarily on the use of radiolabeled RNA substrates, and so require tedious electrophoretic separation and quantitation of reaction products for each data point in any experiment. Here, we report the use of fluorescent substrates for real-time analysis of the time course of reactions of the hairpin ribozyme. Fluorescence of 3' fluorescein-labeled substrates was quenched upon binding to the hairpin ribozyme or its isolated substrate-binding strand (SBS), under conditions of ribozyme or SBS excess. This decrease was accompanied by an increase in anisotropy, and resulted from a base-specific quenching by a guanosine residue added to the 5' end of the SBS, close to fluorescein in the complex. Fluorescence quenching was used to determine rate constants for substrate binding (1.4 x 10(8) M(-1) min(-1)), cleavage (0.15 min(-1)), and substrate dissociation (0.010 min(-1)) by a structurally well-defined ribozyme at 25 degrees C in 50 mM Tris-HCI, pH 7.5, 12 mM MgCl2. These rates are in excellent agreement with those obtained using traditional radioisotopic methods. Measurements of dissociation rates provided physical support for interdomain interactions within the substrate-ribozyme complex. We estimate that 2.1 kcal/mol of additional substrate binding energy is provided by the B domain of the ribozyme. Part of this free energy apparently stems from coaxial stacking of helices in the hinge region between domains, and it is plausible that the remainder might be contributed by direct interactions with loop B. The fluorescence quenching and dequenching methods described here should be readily adaptable to studying a wide variety of RNA interactions and reactions using ribozymes and other model systems. PMID:9085846

Detection of nitrite based on fluorescent carbon dots by the hydrothermal method with folic acid

NASA Astrophysics Data System (ADS)

Lin, Haitao; Ding, Liyun; Zhang, Bingyu; Huang, Jun

2018-05-01

A fluorescent carbon dots probe for the detection of aqueous nitrite was fabricated by a one-pot hydrothermal method, and the transmission electron microscope, X-ray diffractometer, UV-Vis absorption spectrometer and fluorescence spectrophotometer were used to study the property of carbon dots. The fluorescent property of carbon dots influenced by the concentration of aqueous nitrite was studied. The interaction between the electron-donating functional groups and the electron-accepting nitrous acid could account for the quenching effect on carbon dots by adding aqueous nitrite. The products of the hydrolysis of aqueous nitrite performed a stronger quenching effect at lower pH. The relationship between the relative fluorescence intensity of carbon dots and the concentration of nitrite was described by the Stern-Volmer equation (I0/I - 1 = 0.046[Q]) with a fine linearity (R2 = 0.99). The carbon dots-based probe provides a convenient method for the detection of nitrite concentration.

Validated stability-indicating spectrofluorimetric methods for the determination of ebastine in pharmaceutical preparations

PubMed Central

2011-01-01

Two sensitive, selective, economic, and validated spectrofluorimetric methods were developed for the determination of ebastine (EBS) in pharmaceutical preparations depending on reaction with its tertiary amino group. Method I involves condensation of the drug with mixed anhydrides (citric and acetic anhydrides) producing a product with intense fluorescence, which was measured at 496 nm after excitation at 388 nm. Method (IIA) describes quantitative fluorescence quenching of eosin upon addition of the studied drug where the decrease in the fluorescence intensity was directly proportional to the concentration of ebastine; the fluorescence quenching was measured at 553 nm after excitation at 457 nm. This method was extended to (Method IIB) to apply first and second derivative synchronous spectrofluorimetric method (FDSFS & SDSFS) for the simultaneous analysis of EBS in presence of its alkaline, acidic, and UV degradation products. The proposed methods were successfully applied for the determination of the studied compound in its dosage forms. The results obtained were in good agreement with those obtained by a comparison method. Both methods were utilized to investigate the kinetics of the degradation of the drug. PMID:21385439

Synergistic Combination of Unquenching and Plasmonic Fluorescence Enhancement in Fluorogenic Nucleic Acid Hybridization Probes.

PubMed

Vietz, Carolin; Lalkens, Birka; Acuna, Guillermo P; Tinnefeld, Philip

2017-10-11

Fluorogenic nucleic acid hybridization probes are widely used for detecting and quantifying nucleic acids. The achieved sensitivity strongly depends on the contrast between a quenched closed form and an unquenched opened form with liberated fluorescence. So far, this contrast was improved by improving the quenching efficiency of the closed form. In this study, we modularly combine these probes with optical antennas used for plasmonic fluorescence enhancement and study the effect of the nanophotonic structure on the fluorescence of the quenched and the opened form. As quenched fluorescent dyes are usually enhanced more by fluorescence enhancement, a detrimental reduction of the contrast between closed and opened form was anticipated. In contrast, we could achieve a surprising increase of the contrast with full additivity of quenching of the dark form and fluorescence enhancement of the bright form. Using single-molecule experiments, we demonstrate that the additivity of the two mechanisms depends on the perfect quenching in the quenched form, and we delineate the rules for new nucleic acid probes for enhanced contrast and absolute brightness. Fluorogenic hybridization probes optimized not only for quenching but also for the brightness of the open form might find application in nucleic acid assays with PCR avoiding detection schemes.

Designing an anion-functionalized fluorescent ionic liquid as an efficient and reversible turn-off sensor for detecting SO2.

PubMed

Che, Siying; Dao, Rina; Zhang, Weidong; Lv, Xiaoyu; Li, Haoran; Wang, Congmin

2017-03-30

A novel anion-functionalized fluorescent ionic liquid was designed and prepared, which was capable of capturing sulphur dioxide with high capacity and could also be used as a good colorimetric and fluorescent SO 2 sensor. Compared to conventional fluorescent sensors, this fluorescent ionic liquid did not undergo aggregation-caused quenching or aggregation-induced emission, and the fluorescence was quenched when exposed to SO 2 , and the fluorescence would quench when exposed to SO 2 . The experimental absorption, spectroscopic investigation, and quantum chemical calculations indicated that the quenching of the fluorescence originated from SO 2 physical absorption, not chemical absorption. Furthermore, this fluorescent ionic liquid exhibited high selectivity, good quantification, and excellent reversibility for SO 2 detection, and showed potential for an excellent liquid sensor.

Binding of caffeine with caffeic acid and chlorogenic acid using fluorescence quenching, UV/vis and FTIR spectroscopic techniques.

PubMed

Belay, Abebe; Kim, Hyung Kook; Hwang, Yoon-Hwae

2016-03-01

The interactions of caffeine (CF) with chlorogenic acid (CGA) and caffeic acid (CFA) were investigated by fluorescence quenching, UV/vis and Fourier transform infrared (FTIR) spectroscopic techniques. The results of the study indicated that the fluorescence quenching between caffeine and hydroxycinnamic acids could be rationalized in terms of static quenching or the formation of non-fluorescent CF-CFA and CF-CGA complexes. From fluorescence quenching spectral analysis, the quenching constant (KSV), quenching rate constant (kq), number of binding sites (n), thermodynamic properties and conformational changes of the interaction were determined. The quenching constants (KSV) between CF and CGA, CFA are 1.84 × 10(4) and 1.04 × 10(4) L/mol at 298 K and their binding site n is ~ 1. Thermodynamic parameters determined using the Van't Hoff equation indicated that hydrogen bonds and van der Waal's forces have a major role in the reaction of caffeine with caffeic acid and chlorogenic acid. The 3D fluorescence, UV/vis and FTIR spectra also showed that the binding of CF with CFA and CGA induces conformational changes in CFA and CGA. Copyright © 2015 John Wiley & Sons, Ltd.

Sensing and imaging of oxygen with parts per billion limits of detection and based on the quenching of the delayed fluorescence of (13)C70 fullerene in polymer hosts.

PubMed

Kochmann, Sven; Baleizão, Carlos; Berberan-Santos, Mário N; Wolfbeis, Otto S

2013-02-05

We report on a new method for sensing trace oxygen in the gas phase. It is based on the extreme efficiency of the quenching of the thermally activated delayed fluorescence of isotopically enriched carbon-13 fullerene C(70) ((13)C(70)). This fullerene was dissolved in polymer matrixes of varying oxygen permeability, viz., polystyrene (PS), ethyl cellulose (EC) and an organically modified silica gel ("ormosil"; OS). The sensor films (5-10 μm thick), on photoexcitation at 470 nm, display a strong delayed photoluminescence with peaks between 670 and 700 nm. Its quenching by molecular oxygen was studied at 25 and 60 °C and at concentrations from zero up to 150 ppmv of oxygen in nitrogen. The rapid lifetime determination (RLD) method was applied to determine oxygen-dependent lifetimes and for fluorescence lifetime imaging of oxygen. The lower limits of detection (at 1% quenching) vary with the polymer used (EC ∼250 ppbv, OS ∼320 ppbv, PS ∼530 ppbv at 25 °C) and with temperature. The oxygen sensors reported here are the most sensitive ones described so far.

Using a Specific RNA-Protein Interaction To Quench the Fluorescent RNA Spinach.

PubMed

Roszyk, Laura; Kollenda, Sebastian; Hennig, Sven

2017-12-15

RNAs are involved in interaction networks with other biomolecules and are crucial for proper cell function. Yet their biochemical analysis remains challenging. For Förster Resonance Energy Transfer (FRET), a common tool to study such interaction networks, two interacting molecules have to be fluorescently labeled. "Spinach" is a genetically encodable RNA aptamer that starts to fluoresce upon binding of an organic molecule. Therefore, it is a biological fluorophore tag for RNAs. However, spinach has never been used in a FRET assembly before. Here, we describe how spinach is quenched when close to acceptors. We used RNA-DNA hybridization to bring quenchers or red organic dyes in close proximity to spinach. Furthermore, we investigate RNA-protein interactions quantitatively on the example of Pseudomonas aeruginosa phage coat protein 7 (PP7) and its interacting pp7-RNA. We utilize spinach quenching as a fully genetically encodable system even under lysate conditions. Therefore, this work represents a direct method to analyze RNA-protein interactions by quenching the spinach aptamer.

Using resonance light scattering and UV/vis absorption spectroscopy to study the interaction between gliclazide and bovine serum albumin.

PubMed

Zhang, Qiu-Ju; Liu, Bao-Sheng; Li, Gai-Xia; Han, Rong

2016-08-01

At different temperatures (298, 310 and 318 K), the interaction between gliclazide and bovine serum albumin (BSA) was investigated using fluorescence quenching spectroscopy, resonance light scattering spectroscopy and UV/vis absorption spectroscopy. The first method studied changes in the fluorescence of BSA on addition of gliclazide, and the latter two methods studied the spectral change in gliclazide while BSA was being added. The results indicated that the quenching mechanism between BSA and gliclazide was static. The binding constant (Ka ), number of binding sites (n), thermodynamic parameters, binding forces and Hill's coefficient were calculated at three temperatures. Values for the binding constant obtained using resonance light scattering and UV/vis absorption spectroscopy were much greater than those obtained from fluorescence quenching spectroscopy, indicating that methods monitoring gliclazide were more accurate and reasonable. In addition, the results suggest that other residues are involved in the reaction and the mode 'point to surface' existed in the interaction between BSA and gliclazide. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Survey of the occurrence of desiccation-induced quenching of basal fluorescence in 28 species of green microalgae.

PubMed

Wieners, Paul Christian; Mudimu, Opayi; Bilger, Wolfgang

2018-05-30

Desiccation-induced chlorophyll fluorescence quenching seems to be an indispensable part of desiccation resistance in the surveyed 28 green microalgal species. Lichens are desiccation tolerant meta-organisms. In the desiccated state photosynthesis is inhibited rendering the photobionts potentially sensitive to photoinhibition. As a photoprotective mechanism, strong non-radiative dissipation of absorbed light leading to quenching of chlorophyll fluorescence has been proposed. Desiccation-induced quenching affects not only variable fluorescence, but also the so-called basal fluorescence, F 0 . This phenomenon is well-known for intact lichens and some free living aero-terrestrial algae, but it was often absent in isolated lichen algae. Therefore, a thorough screening for the appearance of desiccation-induced quenching was undertaken with 13 different aero-terrestrial microalgal species and lichen photobionts. They were compared with 15 aquatic green microalgal species, among them also three marine species. We asked the following questions: Do isolated lichen algae show desiccation-induced quenching? Are aero-terrestrial algae different in this respect to aquatic algae and is the potential for desiccation-induced quenching coupled to desiccation tolerance? How variable is desiccation-induced quenching among species? Most of the aero-terrestrial algae, including all lichen photobionts, showed desiccation-induced quenching, although highly variable in extent, whereas most of the aquatic algae did not. All algae displaying quenching were also desiccation tolerant, whereas all algae unable to perform desiccation-induced quenching were desiccation intolerant. Desiccation-induced fluorescence quenching seems to be an indispensable part of desiccation resistance in the investigated species.

DNA-length-dependent quenching of fluorescently labeled iron oxide nanoparticles with gold, graphene oxide and MoS2 nanostructures.

PubMed

Balcioglu, Mustafa; Rana, Muhit; Robertson, Neil; Yigit, Mehmet V

2014-08-13

We controlled the fluorescence emission of a fluorescently labeled iron oxide nanoparticle using three different nanomaterials with ultraefficient quenching capabilities. The control over the fluorescence emission was investigated via spacing introduced by the surface-functionalized single-stranded DNA molecules. DNA molecules were conjugated on different templates, either on the surface of the fluorescently labeled iron oxide nanoparticles or gold and nanographene oxide. The efficiency of the quenching was determined and compared with various fluorescently labeled iron oxide nanoparticle and nanoquencher combinations using DNA molecules with three different lengths. We have found that the template for DNA conjugation plays significant role on quenching the fluorescence emission of the fluorescently labeled iron oxide nanoparticles. We have observed that the size of the DNA controls the quenching efficiency when conjugated only on the fluorescently labeled iron oxide nanoparticles by setting a spacer between the surfaces and resulting change in the hydrodynamic size. The quenching efficiency with 12mer, 23mer and 36mer oligonucleotides decreased to 56%, 54% and 53% with gold nanoparticles, 58%, 38% and 32% with nanographene oxide, 46%, 38% and 35% with MoS2, respectively. On the other hand, the presence, not the size, of the DNA molecules on the other surfaces quenched the fluorescence significantly with different degrees. To understand the effect of the mobility of the DNA molecules on the nanoparticle surface, DNA molecules were attached to the surface with two different approaches. Covalently immobilized oligonucleotides decreased the quenching efficiency of nanographene oxide and gold nanoparticles to ∼22% and ∼21%, respectively, whereas noncovalently adsorbed oligonucleotides decreased it to ∼25% and ∼55%, respectively. As a result, we have found that each nanoquencher has a powerful quenching capability against a fluorescent nanoparticle, which can be tuned with surface functionalized DNA molecules.

Selective detection of Co2+ by fluorescent nano probe: Diagnostic approach for analysis of environmental samples and biological activities

NASA Astrophysics Data System (ADS)

Mahajan, Prasad G.; Dige, Nilam C.; Desai, Netaji K.; Patil, Shivajirao R.; Kondalkar, Vijay V.; Hong, Seong-Karp; Lee, Ki Hwan

2018-06-01

Nowadays scientist over the world are engaging to put forth improved methods to detect metal ion in an aqueous medium based on fluorescence studies. A simple, selective and sensitive method was proposed for detection of Co2+ ion using fluorescent organic nanoparticles. We synthesized a fluorescent small molecule viz. 4,4‧-{benzene-1,4-diylbis-[(Z)methylylidenenitrilo]}dibenzoic acid (BMBA) to explore its suitability as sensor for Co2+ ion and biocompatibility in form of nanoparticles. Fluorescence nanoparticles (BMBANPs) prepared by simple reprecipitation method. Aggregation induced enhanced emission of BMBANPs exhibits the narrower particle size of 68 nm and sphere shape morphology. The selective fluorescence quenching was observed by addition of Co2+ and does not affected by presence of other coexisting ion solutions. The photo-physical properties, viz. UV-absorption, fluorescence emission, and lifetime measurements are in support of ligand-metal interaction followed by static fluorescence quenching phenomenon in emission of BMBANPs. Finally, we develop a simple analytical method for selective and sensitive determination of Co2+ ion in environmental samples. The cell culture E. coli, Bacillus sps., and M. tuberculosis H37RV strain in the vicinity of BMBANPs indicates virtuous anti-bacterial and anti-tuberculosis activity which is of additional novel application shown by prepared nanoparticles.

Quenching of photoexcited states of the proteins chromophores and introduced into the protein macromolecules fluorescent probes by heavy metal ions

NASA Astrophysics Data System (ADS)

Melnikov, A. G.; Dyachuk, O. A.; Melnikov, G. V.

2015-03-01

We have studied the processes of quenching of photoexcited states of fluorescent probes and quenching of the fluorescence of the chromophores of human serum albumin (HSA) by heavy metal ions (HM): cations Tl+, Pb2+, Cu2+, Cd2+, and the anion of iodine (I-). We used the dye from xanthene series - eosin as a fluorescent probe. By quenching of the fluorescence of protein chromophores we found an influence of HM on the structure of proteins, resulting in a shift of the peak of the fluorescence of HSA tryptophanyl. This can be explained by proteins denaturation under the influence of heavy metals and penetration of water into the inner environment of HSA tryptophan. It was established that the constant of the quenching of the probe phosphorescence is much higher than the fluorescence, which is explained by significantly longer lifetime of the photoexcited states of fluorescent probes in the triplet state than in the singlet.

Optical and Electrochemical Aptasensors for Sensitive Detection of Streptomycin in Blood Serum and Milk.

PubMed

Ramezani, Mohammad; Abnous, Khalil; Taghdisi, Seyed Mohammad

2017-01-01

Detection and quantitation of antibiotic residues in blood serum and foodstuffs are in great demand. We have developed aptasensors for detection of streptomycin using electrochemical and optical methods. In the first method, an electrochemical aptasensor was developed for sensitive and selective detection of streptomycin, based on combination of exonuclease I (Exo I), complementary strand of aptamer (CS), arch shaped structure of aptamer (Apt)-CS conjugate, and gold electrode. The designed electrochemical aptasensor exhibited high selectivity toward streptomycin with a limit of detection (LOD) as low as 11.4 nM. Moreover, the developed electrochemical aptasensor was successfully used to detect streptomycin in milk and serum with LODs of 14.1 and 15.3 nM, respectively. In the second method, fluorescence quenching and colorimetric aptasensors were designed for detection of streptomycin based on aqueous gold nanoparticles (AuNPs) and double-stranded DNA (dsDNA). In the absence of streptomycin, aptamer/FAM-labeled complementary strand dsDNA is stable, resulting in the aggregation of AuNPs by salt bridge and an obvious color change from red to blue and strong emission of fluorescence. The colorimetric and fluorescence quenching aptasensors showed excellent selectivity toward streptomycin with limit of detections as low as 73.1 and 47.6 nM, respectively. The presented aptasensors were successfully used to detect streptomycin in milk and serum. For serum, LODs were determined to be 58.2 and 102.4 nM for fluorescence quenching and colorimetric aptasensors, respectively. For milk, LODs were calculated to be 56.2 and 108.7 nM for fluorescence quenching and colorimetric aptasensors, respectively.

Structural and photophysical properties of (2E)-3-[4-(dimethylamino) phenyl]-1-(naphthalen-1-yl) prop-2-en-1-one (DPNP) in different media.

PubMed

Pannipara, Mehboobali; Asiri, Abdullah M; Alamry, Khalid A; Salem, Ibrahim A; El-Daly, Samy A

2015-01-01

The spectral and photophysical properties of a new chalcone derivative (2E)-3-[4-(dimethylamino) phenyl]-1-(naphthalen-1-yl) prop-2-en-1-one (DPNP) containing donor-acceptor group has been synthesized and characterized on the basis of the spectral (IR, (1)HNMR & (13)C NMR) and X- ray crystallographic data. The effect of solvents on photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of DPNP have been investigated comprehensively. Significant red shift was observed in the emission spectrum of DPNP compared to the absorption spectrum upon increasing the solvent polarity, indicating a higher dipole moment in the excited state than in the ground state. The difference between the excited and ground state dipole moments (Δμ) were obtained from Lippert-Mataga and Reichardts correlations by means of solvatochromic shift method. The effects of medium acidity on the electronic absorption and emission spectra of DPNP were studied. The interaction of DPNP with colloidal silver nanoparticles (AgNPs) was also studied in ethanol and ethylene glycol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of DPNP by Ag NPs.

Chemical reactivation of quenched fluorescent protein molecules enables resin-embedded fluorescence microimaging

PubMed Central

Xiong, Hanqing; Zhou, Zhenqiao; Zhu, Mingqiang; Lv, Xiaohua; Li, Anan; Li, Shiwei; Li, Longhui; Yang, Tao; Wang, Siming; Yang, Zhongqin; Xu, Tonghui; Luo, Qingming; Gong, Hui; Zeng, Shaoqun

2014-01-01

Resin embedding is a well-established technique to prepare biological specimens for microscopic imaging. However, it is not compatible with modern green-fluorescent protein (GFP) fluorescent-labelling technique because it significantly quenches the fluorescence of GFP and its variants. Previous empirical optimization efforts are good for thin tissue but not successful on macroscopic tissue blocks as the quenching mechanism remains uncertain. Here we show most of the quenched GFP molecules are structurally preserved and not denatured after routine embedding in resin, and can be chemically reactivated to a fluorescent state by alkaline buffer during imaging. We observe up to 98% preservation in yellow-fluorescent protein case, and improve the fluorescence intensity 11.8-fold compared with unprocessed samples. We demonstrate fluorescence microimaging of resin-embedded EGFP/EYFP-labelled tissue block without noticeable loss of labelled structures. This work provides a turning point for the imaging of fluorescent protein-labelled specimens after resin embedding. PMID:24886825

An Iodine Fluorescence Quenching Clock Reaction

NASA Astrophysics Data System (ADS)

Weinberg, Richard B.

2007-05-01

A fluorescent clock reaction is described that is based on the principles of the Landolt iodine reaction but uses the potent fluorescence quenching properties of triiodide to abruptly extinguish the ultraviolet fluorescence of optical brighteners present in liquid laundry detergents. The reaction uses easily obtained household products. One variation illustrates the sequential steps and mechanisms of the reaction; other variations maximize the dramatic impact of the demonstration; and a variation that uses liquid detergent in the Briggs Rauscher reaction yields a striking oscillating luminescence. The iodine fluorescence quenching clock reaction can be used in the classroom to explore not only the principles of redox chemistry and reaction kinetics, but also the photophysics of fluorescent pH probes and optical quenching.

Determination of Cerium (IV) Using Rhodamine 6G Fluorescence Quenching

NASA Astrophysics Data System (ADS)

Zhao, Zh.; Sheng, L.; Su, B.; Tao, C.; Jing, W.

2017-11-01

The interaction between rhodamine 6G (Rh6G) and cerium sulfate was studied by the fluorescence quenching method. In a sulfuric acid medium, the interaction of Ce(IV) with Rh6G results in Rh6G fluorescence quenching. The maximum excitation wavelength (λex) and the maximum emission wavelength (λem) are 530 nm and 555 nm, respectively. A good linearity between the relative fl uorescence intensity (ΔF) and Ce(IV) was observed in the range 0.12-1.08 μg/mL. The detection limit was 1.4 × 10-3 μg/mL. The optimum reaction conditions, influencing factors, and effect of coexisting substances were investigated in the experiment. We found that the concentration of Rh6G was 3.2 × 10-6 mol/L, and the fl uorescence intensity was maximum.

A fluorometric aptasensor for methamphetamine based on fluorescence resonance energy transfer using cobalt oxyhydroxide nanosheets and carbon dots.

PubMed

Saberi, Zeinab; Rezaei, Behzad; Faroukhpour, Hossein; Ensafi, Ali Ashghar

2018-05-17

Cobalt oxyhydroxide (CoOOH) nanosheets are efficient fluorescence quenchers due to their specific optical properties and high surface area. The combination of CoOOH nanosheets and carbon dots (CDs) has not been used in any aptasensor based on fluorescence quenching so far. An aptamer based fluorometric assay is introduced that is making use of fluorescent CDs conjugated to the aptamer against methamphetamine (MTA), and of CoOOH nanosheets which reduce the fluorescence of the CDs as a quencher. The results revealed that the conjugated CDs with aptamers were able to enclose the CoOOH nanosheets. Consequently, fluorescence is quenched. If the aptamer on the CD binds MTA, the CDs are detached from CoOOH nanosheets. As a result, fluorescence is restored proportionally to zhe MTA concentration. The fluorometric limit of detection is 1 nM with a dynamic range from 5 to 156 nM. The method was validated by comparing the results obtained by the new method to those obtained by ion mobility spectroscopy. Theoretical studies showed that the distance between CoOOH nanosheet and C-Ds is approximately 7.6 Å which can illustrate the possibility of FRET phenomenon. The interactions of MTA and the aptamer were investigated using molecular dynamic simulation (MDS). Graphical abstract Carbon dots (C-Ds) were prepared from grape leaves, conjugated to aptamer, and adsorbed on CoOOH nanosheets. So, the fluorescence of C-Ds is quenched. On addition of MTA, fluorescence is restored.

Fluorescence ELISA based on glucose oxidase-mediated fluorescence quenching of quantum dots for highly sensitive detection of Hepatitis B.

PubMed

Wu, Yunqing; Zeng, Lifeng; Xiong, Ying; Leng, Yuankui; Wang, Hui; Xiong, Yonghua

2018-05-01

Herein, we present a novel sandwich fluorescence enzyme linked immunosorbent assay (ELISA) for highly sensitive detection of Hepatitis B virus surface antigen (HBsAg) based on glucose oxidase (GOx)-induced fluorescence quenching of mercaptopropionic acid-modified CdTe quantum dots (MPA-QDs). In this system, hydrogen peroxide (H 2 O 2 ) sensitive MPA-QDs was used as a signal output, and glucose oxidase (GOx) was used as label which can generate H 2 O 2 via catalytic oxidation of glucose. The proposed method showed dynamic linear detection of HBsAg both in the range of 47pgmL -1 ~ 380pgmL -1 and 0.75ngmL -1 ~ 12.12ngmL -1 . The detection limit of the proposed fluorescence ELISA was 1.16pgmL -1 , which was approximately 430-fold lower than that of horseradish peroxidase (HRP)-based conventional ELISA. The average recoveries for HBsAg-spiked serum samples ranged from 98.0% to 126.8% with the relative standard derivation below 10%, thus indicating acceptable precision and high reproducibility of the proposed fluorescence ELISA for HBsAg detection. Additionally, the developed method showed no false positive results analyzing 35 real HBsAg-negative serum samples, and exhibited excellent agreement (R 2 =0.9907) with a commercial time-resolved fluorescence immunoassay (TRFIA) kit for detecting 31 HBsAg-positive serum samples. In summary, the proposed method based on fluorescence quenching of H 2 O 2 sensitive QDs is considerably to be an excellent biodetection platform with ultrahigh sensitivity, good accuracy and excellent reliability. Copyright © 2018 Elsevier B.V. All rights reserved.

Detection of intra-brain cytoplasmic 1 (BC1) long noncoding RNA using graphene oxide-fluorescence beacon detector.

PubMed

Kim, Mee Young; Hwang, Do Won; Li, Fangyuan; Choi, Yoori; Byun, Jung Woo; Kim, Dongho; Kim, Jee-Eun; Char, Kookheon; Lee, Dong Soo

2016-03-21

Detection of cellular expression of long noncoding RNAs (lncRNAs) was elusive due to the ambiguity of exposure of their reactive sequences associated with their secondary/tertiary structures and dynamic binding of proteins around lncRNAs. Herein, we developed graphene-based detection techniques exploiting the quenching capability of graphene oxide (GO) flakes for fluorescent dye (FAM)-labeled single-stranded siRNAs and consequent un-quenching by their detachment from GO by matching lncRNAs. A brain cytoplasmic 1 (BC1) lncRNA expression was significantly decreased by a siRNA, siBC1-1. GO quenched the FAM-labeled siBC1-1 peptide nucleic acid (PNA) probe, and this quenching was recovered by BC1. While FAM-siBC1-1-PNA-GO complex transfected spontaneously mouse or human neural stem cells, fluorescence was recovered only in mouse cells having high BC1 expression. Fluorescent dye-labeled single-stranded RNA-GO probe could detect the reactive exposed nucleic acid sequence of a cytoplasmic lncRNA expressing in the cytoplasm, which strategy can be used as a detection method of lncRNA expression.

Evaluation of anthocyanins in Aronia melanocarpa/BSA binding by spectroscopic studies.

PubMed

Wei, Jie; Xu, Dexin; Zhang, Xiao; Yang, Jing; Wang, Qiuyu

2018-05-02

The interaction between Anthocyanins in Aronia melanocarpa (AMA) and bovine serum albumin (BSA) were studied in this paper by multispectral technology, such as fluorescence quenching titration, circular dichroism (CD) spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results of the fluorescence titration revealed that AMA could strongly quench the intrinsic fluorescence of BSA by static quenching. The apparent binding constants K SV and number of binding sites n of AMA with BSA were obtained by fluorescence quenching method. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS), were calculated to be 18.45 kJ mol -1  > 0 and 149.72 J mol -1  K -1  > 0, respectively, which indicated that the interaction of AMA with BSA was driven mainly by hydrophobic forces. The binding process was a spontaneous process of Gibbs free energy change. Based on Förster's non-radiative energy transfer theory, the distance r between the donor (BSA) and the receptor (AMA) was calculated to be 3.88 nm. Their conformations were analyzed using infrared spectroscopy and CD. The results of multispectral technology showed that the binding of AMA to BSA induced the conformational change of BSA.

Multimodal Sensing Strategy Using pH Dependent Fluorescence Switchable System

NASA Astrophysics Data System (ADS)

Muthurasu, A.; Ganesh, V.

2016-12-01

Biomolecules assisted preparation of fluorescent gold nanoparticles (FL-Au NPs) has been reported in this work using glucose oxidase enzyme as both reducing and stabilizing agent and demonstrated their application through multimodal sensing strategy for selective detection of cysteine (Cys). Three different methods namely fluorescence turn OFF-ON strategy, naked eye detection and electrochemical methods are used for Cys detection by employing FL-Au NPs as a common probe. In case of fluorescence turn-OFF method a strong interaction between Au NPs and thiol results in quenching of fluorescence due to replacement of glucose oxidase by Cys at neutral pH. Second mode is based on fluorescence switch-ON strategy where initial fluorescence is significantly quenched by either excess acid or base and further addition of Cys results in appearance of rosy-red and green fluorescence respectively. Visual colour change and fluorescence emission arises due to etching of Au atoms on the surface by thiol leading to formation of Au nanoclusters. Finally, electrochemical sensing of Cys is also carried out using cyclic voltammetry in 0.1 M PBS solution. These findings provide a suitable platform for Cys detection over a wide range of pH and concentration levels and hence the sensitivity can also be tuned accordingly.

Efficient fluorescence energy transfer system between CdTe-doped silica nanoparticles and gold nanoparticles for turn-on fluorescence detection of melamine.

PubMed

Gao, Feng; Ye, Qingqing; Cui, Peng; Zhang, Lu

2012-05-09

We here report an efficient and enhanced fluorescence energy transfer system between confined quantum dots (QDs) by entrapping CdTe into the mesoporous silica shell (CdTe@SiO₂) as donors and gold nanoparticles (AuNPs) as acceptors. At pH 6.50, the CdTe@SiO₂-AuNPs assemblies coalesce to form larger clusters due to charge neutralization, leading to the fluorescence quenching of CdTe@SiO₂ as a result of energy transfer. As compared with the energy transfer system between unconfined CdTe and AuNPs, the maximum fluorescence quenching efficiency of the proposed system is improved by about 27.0%, and the quenching constant, K(sv), is increased by about 2.4-fold. The enhanced quenching effect largely turns off the fluorescence of CdTe@SiO₂ and provides an optimal "off-state" for sensitive "turn-on" assay. In the present study, upon addition of melamine, the weak fluorescence system of CdTe@SiO₂-AuNPs is enhanced due to the strong interactions between the amino group of melamine and the gold nanoparticles via covalent bond, leading to the release of AuNPs from the surfaces of CdTe@SiO₂; thus, its fluorescence is restored. A "turn-on" fluorimetric method for the detection of melamine is proposed based on the restored fluorescence of the system. Under the optimal conditions, the fluorescence enhanced efficiency shows a linear function against the melamine concentrations ranging from 7.5 × 10⁻⁹ to 3.5 × 10⁻⁷ M (i.e., 1.0-44 ppb). The analytical sensitivity is improved by about 50%, and the detection limit is decreased by 5.0-fold, as compared with the analytical results using the CdTe-AuNPs system. Moreover, the proposed method was successfully applied to the determination of melamine in real samples with excellent recoveries in the range from 97.4 to 104.1%. Such a fluorescence energy transfer system between confined QDs and AuNPs may pave a new way for designing chemo/biosensing.

Quenching of cascade reaction between triplet and photochrome probes with nitroxide radicals. A novel labeling method in study of membranes and surface systems.

PubMed

Papper, V; Medvedeva, N; Fishov, I; Likhtenshtein, G I

2000-01-01

We proposed a new method for the study of molecular dynamics and fluidity of the living and model biomembranes and surface systems. The method is based on the measurements of the sensitized photoisomerization kinetics of a photochrome probe. The cascade triplet cis-trans photoisomerization of the excited stilbene derivative sensitized with the excited triplet Erythrosin B has been studied in a model liposome membrane. The photoisomerization reaction is depressed with nitroxide radicals quenching the excited triplet state of the sensitizer. The enhanced fluorescence polarization of the stilbene probe incorporated into liposome membranes indicates that the stilbene molecules are squeezed in a relatively viscous media of the phospholipids. Calibration of the "triple" cascade system is based on a previously proposed method that allows the measurement of the product of the quenching rate constant and the sensitizer's triplet lifetime, as well as the quantitative detection of the nitroxide radicals in the vicinity of the membrane surface. The experiment was conducted using the constant-illumination fluorescence technique. Sensitivity of the method using a standard commercial spectrofluorimeter is about 10(-12) mol of fluorescence molecules per sample and can be improved using an advanced fluorescence technique. The minimal local concentration of nitroxide radicals or any other quenchers being detected is about 10(-5) M. This method enables the investigation of any chemical and biological surface processes of microscopic scale when the minimal volume is about 10(-3) microL or less.

Selective fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene by nucleotides.

PubMed

Marquez, Cesar; Pischel, Uwe; Nau, Werner M

2003-10-16

[reaction: see text] The fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by nucleotides has been studied. The quenching mechanism was analyzed on the basis of deuterium isotope effects, tendencies for exciplex formation, and the quenching efficiency in the presence of a molecular container (cucurbit[7]uril). Exciplex-induced quenching appears to prevail for adenosine, cytidine, and uridine, while hydrogen abstraction becomes competitive for thymidine and guanosine. Compared to other fluorescent probes, DBO responds very selectively to the type of nucleotide.

Adenosine-derived doped carbon dots: From an insight into effect of N/P co-doping on emission to highly sensitive picric acid sensing.

PubMed

Li, Na; Liu, Shi Gang; Fan, Yu Zhu; Ju, Yan Jun; Xiao, Na; Luo, Hong Qun; Li, Nian Bing

2018-07-12

The various synthetic routes of carbon dots (C-dots) feature a considerable step toward their potential use in chemical sensors and biotechnology. Herein, by coupling phosphorus and nitrogen element introduction, the adenosine-derived N/P co-doped C-dots with fluorescence enhancement were achieved. By separately employing adenosine, adenosine monophosphate, adenosine diphosphate, and adenosine-5'-triphosphate as precursors, the effect of N/P co-doping on the fluorescence emission is discussed in detail. The formed C-dots with adenosine monophosphate exhibited strong blue fluorescence with a high quantum yield of 33.81%. Then the C-dots were employed as a fluorescent probe and utilized to develop a fast, sensitive, and selective picric acid sensor. The fluorescence of C-dots can be quenched by picric acid immediately, giving rise to a picric acid determination down to 30 nM. The possible mechanism of fluorescence quenching was discussed, which was proved to be inner filter effect and static quenching. Moreover, this method has the potential to detect picric acid in environmental water samples. Copyright © 2018 Elsevier B.V. All rights reserved.

One-step synthesis of fluorescein modified nano-carbon for Pd(II) detection via fluorescence quenching.

PubMed

Panchompoo, Janjira; Aldous, Leigh; Baker, Matthew; Wallace, Mark I; Compton, Richard G

2012-05-07

Carbon black (CB) nanoparticles modified with fluorescein, a highly fluorescent molecule, were prepared using a facile and efficient methodology. Simply stirring CB in aqueous solution containing fluorescein resulted in the strong physisorption of fluorescein onto the CB surface. The resulting Fluorescein/CB was then characterised by means of X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), fluorescence microscopy and fluorescence spectroscopy. The optimum experimental conditions for fluorescence of Fluorescein/CB viz. fluorescence excitation and emission wavelengths, O(2) removal and the amount of Fluorescein/CB used, were investigated. The Fluorescein/CB was used as a fluorescent probe for the sensitive detection of Pd(II) in water, based on fluorescence quenching. The results demonstrated that the fluorescence intensity of Fluorescein/CB decreased with increasing Pd(II) concentration, and the fluorescence quenching process could be described by the Stern-Volmer equation. The limit of detection (LOD) for the fluorescence quenching of Fluorescein/CB by Pd(II) in aqueous solution was found to be 1.07 μM (based on 3σ). Last, approaches were studied for the removal of Fe(III) which interferes with the fluorescence quenching of Fluorescein/CB. Complexation of Fe(III) with salicylic acid was used to enhance and control the selectivity of Fluorescein/CB sensor towards Pd(II) in the presence of Fe(III).

USE OF FLUORESCENT POLYCYLIC AROMATIC HYDROCARBON PROBES IN STUDYING THE IMPACT OF COLLOIDS ON POLLUTANT TRANSPORT IN GROUNDWATER

EPA Science Inventory

A fluorescence-quenching method was developed to assess the hydrophobic organic pollutant binding potential of organic colloids (OC) in unaltered natural waters. This method allows (1) direct assessment of the importance of OC-enhanced pollutant transport for environmental sam- p...

"Open-Box" Approach to Measuring Fluorescence Quenching Using an iPad Screen and Digital SLR Camera

ERIC Educational Resources Information Center

Koenig, Michael H.; Yi, Eun P.; Sandridge, Matthew J.; Mathew, Alexander S.; Demas, James N.

2015-01-01

Fluorescence quenching is an analytical technique and a common undergraduate laboratory exercise. Unfortunately, a typical quenching experiment requires the use of an expensive fluorometer that measures the relative fluorescence intensity of a single sample in a closed compartment unseen by the experimenter. To overcome these shortcomings, we…

Direct comparison of single- and multi-walled carbon nanotubes in fluorescence quenching phenomenon

NASA Astrophysics Data System (ADS)

Oura, Shusuke; Umemura, Kazuo

2018-03-01

Here, we report the fluorescence quenching ability of single-stranded DNA (ssDNA)-wrapped single- and multi-walled carbon nanotubes (ssDNA-SWNTs and ssDNA-MWNTs, respectively) using fluorescein dye-labeled ssDNA (Fluor-ssDNA). To compare the quenching abilities of SWNTs and MWNTs, we measured the quenching ratios of fluorescence emission from fluorescein when Fluor-ssDNA reacted with the hybrids of 30-mers of thymine (T30) and SWNTs or MWNTs (T30-SWNTs and T30-MWNTs, respectively). The fluorescence quenching ratios of Fluor-T30 in SWNT and MWNT samples were 28 ± 3.1 and 36 ± 2.0% relative to free fluorescein at the same concentration, respectively. On the other hand, those of Fluor-A30 with SWNT and MWNT hybrids were 11 ± 1.9 and 32 ± 1.9%, respectively. Our results suggest that although the fluorescence quenching ability of MWNT was greater than that of SWNT, SWNT quenching ratios were more sensitive to the base sequences of Fluor-ssDNA.

Nanostructure and Corresponding Quenching Efficiency of Fluorescent DNA Probes.

PubMed

Guo, Wenjuan; Wei, Yanhong; Dai, Zhao; Chen, Guangping; Chu, Yuanyuan; Zhao, Yifei

2018-02-09

Based on the fluorescence resonance energy transfer (FRET) mechanism, fluorescent DNA probes were prepared with a novel DNA hairpin template method, with SiO₂ coated CdTe (CdTe/SiO₂) core/shell nanoparticles used as the fluorescence energy donors and gold (Au) nanoparticles (AuNPs) as the energy acceptors. The nanostructure and energy donor/acceptor ratio in a probe were controlled with this method. The relationship between the nanostructure of the probes and FRET efficiency (quenching efficiency) were investigated. The results indicated that when the donor/acceptor ratios were 2:1, 1:1, and 1:2; the corresponding FRET efficiencies were about 33.6%, 57.5%, and 74.2%, respectively. The detection results indicated that the fluorescent recovery efficiency of the detecting system was linear when the concentration of the target DNA was about 0.0446-2.230 nmol/L. Moreover, the probes showed good sensitivity and stability in different buffer conditions with a low detection limit of about 0.106 nmol/L.

Nanostructure and Corresponding Quenching Efficiency of Fluorescent DNA Probes

PubMed Central

Guo, Wenjuan; Wei, Yanhong; Dai, Zhao; Chen, Guangping; Chu, Yuanyuan; Zhao, Yifei

2018-01-01

Based on the fluorescence resonance energy transfer (FRET) mechanism, fluorescent DNA probes were prepared with a novel DNA hairpin template method, with SiO2 coated CdTe (CdTe/SiO2) core/shell nanoparticles used as the fluorescence energy donors and gold (Au) nanoparticles (AuNPs) as the energy acceptors. The nanostructure and energy donor/acceptor ratio in a probe were controlled with this method. The relationship between the nanostructure of the probes and FRET efficiency (quenching efficiency) were investigated. The results indicated that when the donor/acceptor ratios were 2:1, 1:1, and 1:2; the corresponding FRET efficiencies were about 33.6%, 57.5%, and 74.2%, respectively. The detection results indicated that the fluorescent recovery efficiency of the detecting system was linear when the concentration of the target DNA was about 0.0446–2.230 nmol/L. Moreover, the probes showed good sensitivity and stability in different buffer conditions with a low detection limit of about 0.106 nmol/L. PMID:29425163

Quenching of fluorescence of conjugated poly(p-phenylene) polymers by benzil and dimethylaminobenzil molecules

NASA Astrophysics Data System (ADS)

Bagnich, S. A.; Knyukshto, V. N.

2006-11-01

We have studied the mechanisms for quenching of the fluorescence of conjugated poly(p-phenylene) polymers by benzil and dimethylaminobenzil molecules. We have shown that molecules in the diketone series are quenching agents for the fluorescence of the indicated polymers, and can serve as singlet-triplet converters capable of populating the triplet state of the polymer. We have observed that the efficiency of quenching of the fluorescence of the studied polymers depends considerably on the presence of bulky side groups in the polymer or in the activator molecules. Based on analysis of the data obtained, we conclude that in the case of a rigid planar structure for the polymer, a significant contribution to quenching of its fluorescence comes from not only singlet-singlet energy transfer but also charge transfer, leading to formation of intermolecular complexes (exciplexes).

Unambiguous detection of nitrated explosive vapours by fluorescence quenching of dendrimer films

NASA Astrophysics Data System (ADS)

Geng, Yan; Ali, Mohammad A.; Clulow, Andrew J.; Fan, Shengqiang; Burn, Paul L.; Gentle, Ian R.; Meredith, Paul; Shaw, Paul E.

2015-09-01

Unambiguous and selective standoff (non-contact) infield detection of nitro-containing explosives and taggants is an important goal but difficult to achieve with standard analytical techniques. Oxidative fluorescence quenching is emerging as a high sensitivity method for detecting such materials but is prone to false positives--everyday items such as perfumes elicit similar responses. Here we report thin films of light-emitting dendrimers that detect vapours of explosives and taggants selectively--fluorescence quenching is not observed for a range of common interferents. Using a combination of neutron reflectometry, quartz crystal microbalance and photophysical measurements we show that the origin of the selectivity is primarily electronic and not the diffusion kinetics of the analyte or its distribution in the film. The results are a major advance in the development of sensing materials for the standoff detection of nitro-based explosive vapours, and deliver significant insights into the physical processes that govern the sensing efficacy.

Unambiguous detection of nitrated explosive vapours by fluorescence quenching of dendrimer films.

PubMed

Geng, Yan; Ali, Mohammad A; Clulow, Andrew J; Fan, Shengqiang; Burn, Paul L; Gentle, Ian R; Meredith, Paul; Shaw, Paul E

2015-09-15

Unambiguous and selective standoff (non-contact) infield detection of nitro-containing explosives and taggants is an important goal but difficult to achieve with standard analytical techniques. Oxidative fluorescence quenching is emerging as a high sensitivity method for detecting such materials but is prone to false positives—everyday items such as perfumes elicit similar responses. Here we report thin films of light-emitting dendrimers that detect vapours of explosives and taggants selectively—fluorescence quenching is not observed for a range of common interferents. Using a combination of neutron reflectometry, quartz crystal microbalance and photophysical measurements we show that the origin of the selectivity is primarily electronic and not the diffusion kinetics of the analyte or its distribution in the film. The results are a major advance in the development of sensing materials for the standoff detection of nitro-based explosive vapours, and deliver significant insights into the physical processes that govern the sensing efficacy.

Unambiguous detection of nitrated explosive vapours by fluorescence quenching of dendrimer films

PubMed Central

Geng, Yan; Ali, Mohammad A.; Clulow, Andrew J.; Fan, Shengqiang; Burn, Paul L.; Gentle, Ian R.; Meredith, Paul; Shaw, Paul E.

2015-01-01

Unambiguous and selective standoff (non-contact) infield detection of nitro-containing explosives and taggants is an important goal but difficult to achieve with standard analytical techniques. Oxidative fluorescence quenching is emerging as a high sensitivity method for detecting such materials but is prone to false positives—everyday items such as perfumes elicit similar responses. Here we report thin films of light-emitting dendrimers that detect vapours of explosives and taggants selectively—fluorescence quenching is not observed for a range of common interferents. Using a combination of neutron reflectometry, quartz crystal microbalance and photophysical measurements we show that the origin of the selectivity is primarily electronic and not the diffusion kinetics of the analyte or its distribution in the film. The results are a major advance in the development of sensing materials for the standoff detection of nitro-based explosive vapours, and deliver significant insights into the physical processes that govern the sensing efficacy. PMID:26370931

Detection of DNA via the fluorescence quenching of Mn-doped ZnSe D-dots/doxorubicin/DNA ternary complexes system.

PubMed

Gao, Xue; Niu, Lu; Su, Xingguang

2012-01-01

This manuscript reports a method for the detection of double-stranded DNA, based on Mn:ZnSe d-dots and intercalating agent doxorubicin (DOX). DOX can quench the photoluminescence (PL) of Mn:ZnSe d-dots through photoinduced electron transfer process, after binding with Mn:ZnSe d-dots. The addition of DNA can result in the formation of the Mn:ZnSe d-dots-DOX-DNA ternary complexes, the fluorescence of the Mn:ZnSe d-dots-DOX complexes would be further quenched by the addition of DNA, thus allowing the detection of DNA. The formation mechanism of the Mn:ZnSe d-dots-DOX-DNA ternary complexes was studied in detail in this paper. Under optimal conditions, the quenched fluorescence intensity of Mn:ZnSe d-dots-DOX system are perfectly described by Stern-Volmer equation with the concentration of hsDNA ranging from 0.006 μg mL(-1) to 6.4 μg mL(-1). The detection limit (S/N = 3) for hsDNA is 0.5 ng mL(-1). The proposed method was successfully applied to the detection of DNA in synthetic samples and the results were satisfactory.

Fluorescence quenching effects of antibiotics on the main components of dissolved organic matter.

PubMed

Yan, Peng-Fei; Hu, Zhen-Hu; Yu, Han-Qing; Li, Wei-Hua; Liu, Li

2016-03-01

Dissolved organic matter (DOM) in wastewater can be characterized using fluorescence excitation-emission matrix and parallel factor (EEM-PARAFAC) analysis. Wastewater from animal farms or pharmaceutical plants usually contains high concentration of antibiotics. In this study, the quenching effect of antibiotics on the typical components of DOM was explored using fluorescence EEM-PARAFAC analysis. Four antibiotics (roxarsone, sulfaquinoxaline sodium, oxytetracycline, and erythromycin) at the concentration of 0.5∼4.0 mg/L and three typical components of DOM (tyrosine, tryptophan, and humic acid) were selected. Fluorescence quenching effects were observed with the addition of antibiotics. Among these four antibiotics, roxarsone (2.9∼20.2 %), sulfaquinoxaline sodium (0∼32.0 %), and oxytetracycline (0∼41.8 %) led to a stronger quenching effect than erythromycin (0∼8.0 %). From the side of DOM, tyrosine and tryptophan (0.5∼41.8 %) exhibited a similar quenching effect, but they were higher than humic acids (0∼20.2 %) at the same concentration of antibiotics. For humic acid, a significant quenching effect was observed only with the addition of roxarsone. This might be the first report about the fluorescence quenching effect caused by antibiotics. The results from this study confirmed the interference of antibiotics on the fluorescence intensity of the main components of DOM and highlighted the importance of correcting fluorescence data in the wastewater containing antibiotics.

Chemical reactivation of resin-embedded pHuji adds red for simultaneous two-color imaging with EGFP

PubMed Central

Guo, Wenyan; Liu, Xiuli; Liu, Yurong; Gang, Yadong; He, Xiaobin; Jia, Yao; Yin, Fangfang; Li, Pei; Huang, Fei; Zhou, Hongfu; Wang, Xiaojun; Gong, Hui; Luo, Qingming; Xu, Fuqiang; Zeng, Shaoqun

2017-01-01

The pH-sensitive fluorescent proteins enabling chemical reactivation in resin are useful tools for fluorescence microimaging. EGFP or EYFP is good for such applications. For simultaneous two-color imaging, a suitable red fluorescent protein is an urgent need. Here a pH-sensitive red fluorescent protein, pHuji, is selected and verified to remain pH-sensitive in HM20 resin. We observe 183% fluorescence intensity of pHuji in resin-embeded mouse brain and 29.08-fold fluorescence intensity of reactivated pHuji compared to the quenched state. pHuji and EGFP can be quenched and chemically reactivated simultaneously in resin, thus enabling simultaneous two-color micro-optical sectioning tomography of resin-embedded mouse brain. This method may greatly facilitate the visualization of neuronal morphology and neural circuits to promote understanding of the structure and function of the brain. PMID:28717566

Chemical reactivation of resin-embedded pHuji adds red for simultaneous two-color imaging with EGFP.

PubMed

Guo, Wenyan; Liu, Xiuli; Liu, Yurong; Gang, Yadong; He, Xiaobin; Jia, Yao; Yin, Fangfang; Li, Pei; Huang, Fei; Zhou, Hongfu; Wang, Xiaojun; Gong, Hui; Luo, Qingming; Xu, Fuqiang; Zeng, Shaoqun

2017-07-01

The pH-sensitive fluorescent proteins enabling chemical reactivation in resin are useful tools for fluorescence microimaging. EGFP or EYFP is good for such applications. For simultaneous two-color imaging, a suitable red fluorescent protein is an urgent need. Here a pH-sensitive red fluorescent protein, pHuji, is selected and verified to remain pH-sensitive in HM20 resin. We observe 183% fluorescence intensity of pHuji in resin-embeded mouse brain and 29.08-fold fluorescence intensity of reactivated pHuji compared to the quenched state. pHuji and EGFP can be quenched and chemically reactivated simultaneously in resin, thus enabling simultaneous two-color micro-optical sectioning tomography of resin-embedded mouse brain. This method may greatly facilitate the visualization of neuronal morphology and neural circuits to promote understanding of the structure and function of the brain.

Analysis of the binding interaction in uric acid - Human hemoglobin system by spectroscopic techniques

NASA Astrophysics Data System (ADS)

Makarska-Bialokoz, Magdalena

2017-05-01

The binding interaction between human hemoglobin and uric acid has been studied for the first time, by UV-vis absorption and steady-state, synchronous and three-dimensional fluorescence techniques. Characteristic effects observed for human hemoglobin intrinsic fluorescence during interaction with uric acid at neutral pH point at the formation of stacking non-covalent and non-fluorescent complexes. All the calculated parameters, the binding, fluorescence quenching and bimolecular quenching rate constants, as well as Förster resonance energy transfer parameters confirm the existence of static quenching. The results of synchronous fluorescence measurements indicate that the fluorescence quenching of human hemoglobin originates both from Trp and Tyr residues and that the addition of uric acid could significantly hinder the physiological functions of human hemoglobin.

A "turn-on" fluorescent copper biosensor based on DNA cleavage-dependent graphene-quenched DNAzyme.

PubMed

Liu, Meng; Zhao, Huimin; Chen, Shuo; Yu, Hongtao; Zhang, Yaobin; Quan, Xie

2011-06-15

A novel and promising "turn-on" fluorescent Cu(2+) biosensor is designed based on graphene-DNAzyme catalytic beacon. Due to the essential surface and quenching properties of two-dimensional graphene, it can function as both "scaffold" and "quencher" of the Cu(2+)-dependent DNAzyme, facilitating the formation of self-assembled graphene-quenched DNAzyme complex. However, Cu(2+)-induced catalytic reaction disturbs the graphene-DNAzyme conformation, which will produce internal DNA cleavage-dependent effect. In this case, the quenched fluorescence in graphene-DNAzyme is quickly recovered to a large extent in 15 min. Compared with common DNAzyme-based sensors, the presented graphene-based catalytic beacon greatly improves the signal-to-background ratio, hence increasing the sensitivity (LOD=0.365 nM). Furthermore, the controllable DNA cleavage reaction provides an original and alternative internal method to regulate the interaction between graphene and DNA relative to the previous external sequence-specific hybridization-dependent regulation, which will open new opportunities for nucleic studies and sensing applications in the future. Copyright © 2011 Elsevier B.V. All rights reserved.

Quantum dots as optical labels for ultrasensitive detection of polyphenols.

PubMed

Akshath, Uchangi Satyaprasad; Shubha, Likitha R; Bhatt, Praveena; Thakur, Munna Singh

2014-07-15

Considering the fact that polyphenols have versatile activity in-vivo, its detection and quantification is very much important for a healthy diet. Laccase enzyme can convert polyphenols to yield mono/polyquinones which can quench Quantum dots fluorescence. This phenomenon of charge transfer from quinones to QDs was exploited as optical labels to detect polyphenols. CdTe QD may undergo dipolar interaction with quinones as a result of broad spectral absorption due to multiple excitonic states resulting from quantum confinement effects. Thus, "turn-off" fluorescence method was applied for ultrasensitive detection of polyphenols by using laccase. We observed proportionate quenching of QDs fluorescence with respect to polyphenol concentration in the range of 100 µg to 1 ng/mL. Also, quenching of the photoluminescence was highly efficient and stable and could detect individual and total polyphenols with high sensitivity (LOD-1 ng/mL). Moreover, proposed method was highly efficient than any other reported methods in terms of sensitivity, specificity and selectivity. Therefore, a novel optical sensor was developed for the detection of polyphenols at a sensitive level based on the charge transfer mechanism. Copyright © 2014 Elsevier B.V. All rights reserved.

Carbon dots based fluorescent sensor for sensitive determination of hydroquinone.

PubMed

Ni, Pengjuan; Dai, Haichao; Li, Zhen; Sun, Yujing; Hu, Jingting; Jiang, Shu; Wang, Yilin; Li, Zhuang

2015-11-01

In this paper, a novel biosensor based on Carbon dots (C-dots) for sensitive detection of hydroquinone (H2Q) is reported. It is interesting to find that the fluorescence of the C-dots could be quenched by H2Q directly. The possible quenching mechanism is proposed, which shows that the quenching effect may be caused by the electron transfer from C-dots to oxidized H2Q-quinone. Based on the above principle, a novel C-dots based fluorescent probe has been successfully applied to detect H2Q. Under the optimal condition, detection limit down to 0.1 μM is obtained, which is far below U.S. Environmental Protection Agency estimated wastewater discharge limit of 0.5 mg/L. Moreover, the proposed method shows high selectivity for H2Q over a number of potential interfering species. Finally, several water samples spiked with H2Q are analyzed utilizing the sensing method with satisfactory recovery. The proposed method is simple with high sensitivity and excellent selectivity, which provides a new approach for the detection of various analytes that can be transformed into quinone. Copyright © 2015 Elsevier B.V. All rights reserved.

The causes of altered chlorophyll fluorescence quenching induction in the Arabidopsis mutant lacking all minor antenna complexes.

PubMed

Townsend, Alexandra J; Saccon, Francesco; Giovagnetti, Vasco; Wilson, Sam; Ungerer, Petra; Ruban, Alexander V

2018-03-13

Non-photochemical quenching (NPQ) of chlorophyll fluorescence is the process by which excess light energy is harmlessly dissipated within the photosynthetic membrane. The fastest component of NPQ, known as energy-dependent quenching (qE), occurs within minutes, but the site and mechanism of qE remain of great debate. Here, the chlorophyll fluorescence of Arabidopsis thaliana wild type (WT) plants was compared to mutants lacking all minor antenna complexes (NoM). Upon illumination, NoM exhibits altered chlorophyll fluorescence quenching induction (i.e. from the dark-adapted state) characterised by three different stages: (i) a fast quenching component, (ii) transient fluorescence recovery and (iii) a second quenching component. The initial fast quenching component originates in light harvesting complex II (LHCII) trimers and is dependent upon PsbS and the formation of a proton gradient across the thylakoid membrane (ΔpH). Transient fluorescence recovery is likely to occur in both WT and NoM plants, but it cannot be overcome in NoM due to impaired ΔpH formation and a reduced zeaxanthin synthesis rate. Moreover, an enhanced fluorescence emission peak at ~679 nm in NoM plants indicates detachment of LHCII trimers from the bulk antenna system, which could also contribute to the transient fluorescence recovery. Finally, the second quenching component is triggered by both ΔpH and PsbS and enhanced by zeaxanthin synthesis. This study indicates that minor antenna complexes are not essential for qE, but reveals their importance in electron stransport, ΔpH formation and zeaxanthin synthesis. Copyright © 2018 The Author(s). Published by Elsevier B.V. All rights reserved.

Fluorescence quenching of human orosomucoid. Accessibility to drugs and small quenching agents.

PubMed Central

Friedman, M L; Schlueter, K T; Kirley, T L; Halsall, H B

1985-01-01

The fluorescence behaviour of human orosomucoid was investigated. The intrinsic fluorescence was more accessible to acrylamide than to the slightly larger succinimide, indicating limited accessibility to part of the tryptophan population. Although I- showed almost no quenching, that of Cs+ was enhanced, and suggested a region of negative charge proximal to an emitting tryptophan residue. Removal of more than 90% of sialic acid from the glycan chains led to no change in the Cs+, I-, succinimide or acrylamide quenching, indicating that the negatively charged region originates with the protein core. Quenching as a function of pH and temperature supported this view. The binding of chlorpromazine monitored by fluorescence quenching, in the presence and in the absence of the small quenching probes (above), led to a model of its binding domain on orosomucoid that includes two tryptophan residues relatively shielded from the bulk solvent, with the third tryptophan residue being on the periphery of the domain, or affected allotopically and near the negatively charged field. PMID:4091825

Interactions of hemin with bovine serum albumin and human hemoglobin: A fluorescence quenching study

NASA Astrophysics Data System (ADS)

Makarska-Bialokoz, Magdalena

2018-03-01

The binding interactions between hemin (Hmi) and bovine serum albumin (BSA) or human hemoglobin (HHb), respectively, have been examined in aqueous solution at pH = 7.4, applying UV-vis absorption, as well as steady-state, synchronous and three-dimensional fluorescence spectra techniques. Representative results received for both BSA and HHb intrinsic fluorescence proceeding from the interactions with hemin suggest the formation of stacking non-covalent and non-fluorescent complexes in both the Hmi-BSA and Hmi-HHb systems, with highly possible concurrent formation of a coordinate bond between a group on the protein surface and the metal in Hmi molecule. All the values of calculated parameters, the binding, fluorescence quenching and bimolecular quenching rate constants point to the involvement of static quenching in both the systems studied. The blue shift in the synchronous fluorescence spectra imply the participation of both tryptophan and tyrosine residues in quenching of BSA and HHb intrinsic fluorescence. Depicted outcomes suggest that hemin is supposedly able to influence the physiological functions of BSA and HHb, the most important blood proteins, particularly in case of its overuse.

Investigation on interaction between Ligupurpuroside A and pepsin by spectroscopic and docking methods.

PubMed

Shen, Liangliang; Xu, Hong; Huang, Fengwen; Li, Yi; Xiao, Huafeng; Yang, Zhen; Hu, Zhangli; He, Zhendan; Zeng, Zheling; Li, Yinong

2015-01-25

Ligupurpuroside A is one of the major glycoside in Ku-Din-Cha, a type of Chinese functional tea. In order to better understand its digestion and metabolism in humans, the interaction between Ligupurpuroside A and pepsin has been investigated by fluorescence spectra, UV-vis absorption spectra and synchronous fluorescence spectra along with molecular docking method. The fluorescence experiments indicate that Ligupurpuroside A can effectively quench the intrinsic fluorescence of pepsin through a combined quenching way at the low concentration of Ligupurpuroside A, and a static quenching procedure at the high concentration. The binding constant, binding sites of Ligupurpuroside A with pepsin have been calculated. The thermodynamic analysis suggests that non-covalent reactions, including electrostatic force, hydrophobic interaction and hydrogen bond are the main forces stabilizing the complex. According to the Förster's non-radiation energy transfer theory, the binding distance between pepsin and Ligupurpuroside A was calculated to be 3.15 nm, which implies that energy transfer occurs between pepsin and Ligupurpuroside A. Conformation change of pepsin was observed from UV-vis absorption spectra and synchronous fluorescence spectra under experimental conditions. In addition, all these experimental results have been validated by the protein-ligand docking studies which show that Ligupurpuroside A is located in the cleft between the domains of pepsin. Copyright © 2014 Elsevier B.V. All rights reserved.

Two-dimensional fluorescence correlation spectroscopy: resolution of fluorescence of tryptophan residues in horse heart myoglobin.

PubMed

Nakashima, Kenichi; Yuda, Kazuki; Ozaki, Yukihiro; Noda, Isao

2003-11-01

Generalized two-dimensional (2D) fluorescence correlation spectroscopy has been used to resolve fluorescence of two tryptophan (Trp) residues in horse heart myoglobin. Fluorescence quenching is employed as a perturbation mode for causing intensity changes in the fluorescence (quenching perturbation). Two kinds of quenchers, iodide ion and acrylamide, are used for inducing fluorescence intensity change. This technique works because the Trp residue located at the 7th position (W7) is known to be easily accessible to the quencher, whereas that located at the 14th position (W14) is not. By this technique, the fluorescence spectra of the two Trp residues were clearly resolved. From asynchronous maps, it was also shown that the quenching of W7 fluorescence is brought about prior to the quenching of W14 fluorescence. This result is consistent with the structure of horse heart myoglobin that was proposed earlier. Furthermore, it was elucidated that the present 2D analysis is not interfered with by Raman bands of the solvents, which sometimes brings difficulty into conventional fluorescence analysis.

Sensitive detection of alkaline phosphatase by switching on gold nanoclusters fluorescence quenched by pyridoxal phosphate.

PubMed

Halawa, Mohamed Ibrahim; Gao, Wenyue; Saqib, Muhammad; Kitte, Shimeles Addisu; Wu, Fengxia; Xu, Guobao

2017-09-15

In this work, we designed highly sensitive and selective luminescent detection method for alkaline phosphatase using bovine serum albumin functionalized gold nanoclusters (BSA-AuNCs) as the nanosensor probe and pyridoxal phosphate as the substrate of alkaline phosphatase. We found that pyridoxal phosphate can quench the fluorescence of BSA-AuNCs and pyridoxal has little effect on the fluorescence of BSA-AuNCs. The proposed mechanism of fluorescence quenching by PLP was explored on the basis of data obtained from high-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), UV-vis spectrophotometry, fluorescence spectroscopy, fluorescence decay time measurements and circular dichroism (CD) spectroscopy. Alkaline phosphatase catalyzes the hydrolysis of pyridoxal phosphate to generate pyridoxal, restoring the fluorescence of BSA-AuNCs. Therefore, a recovery type approach has been developed for the sensitive detection of alkaline phosphatase in the range of 1.0-200.0U/L (R 2 =0.995) with a detection limit of 0.05U/L. The proposed sensor exhibit excellent selectivity among various enzymes, such as glucose oxidase, lysozyme, trypsin, papain, and pepsin. The present switch-on fluorescence sensing strategy for alkaline phosphatase was successfully applied in human serum plasma with good recoveries (100.60-104.46%), revealing that this nanosensor probe is a promising tool for ALP detection. Copyright © 2017 Elsevier B.V. All rights reserved.

Quenched substrates for live-cell labeling of SNAP-tagged fusion proteins with improved fluorescent background.

PubMed

Stöhr, Katharina; Siegberg, Daniel; Ehrhard, Tanja; Lymperopoulos, Konstantinos; Öz, Simin; Schulmeister, Sonja; Pfeifer, Andrea C; Bachmann, Julie; Klingmüller, Ursula; Sourjik, Victor; Herten, Dirk-Peter

2010-10-01

Recent developments in fluorescence microscopy raise the demands for bright and photostable fluorescent tags for specific and background free labeling in living cells. Aside from fluorescent proteins and other tagging methods, labeling of SNAP-tagged proteins has become available thereby increasing the pool of potentially applicable fluorescent dyes for specific labeling of proteins. Here, we report on novel conjugates of benzylguanine (BG) which are quenched in their fluorescence and become highly fluorescent upon labeling of the SNAP-tag, the commercial variant of the human O(6)-alkylguanosyltransferase (hAGT). We identified four conjugates showing a strong increase, i.e., >10-fold, in fluorescence intensity upon labeling of SNAP-tag in vitro. Moreover, we screened a subset of nine BG-dye conjugates in living Escherichia coli and found them all suited for labeling of the SNAP-tag. Here, quenched BG-dye conjugates yield a higher specificity due to reduced contribution from excess conjugate to the fluorescence signal. We further extended the application of these conjugates by labeling a SNAP-tag fusion of the Tar chemoreceptor in live E. coli cells and the eukaryotic transcription factor STAT5b in NIH 3T3 mouse fibroblast cells. Aside from the labeling efficiency and specificity in living cells, we discuss possible mechanisms that might be responsible for the changes in fluorescence emission upon labeling of the SNAP-tag, as well as problems we encountered with nonspecific labeling with certain conjugates in eukaryotic cells.

Highly Sensitive Ratiometric Fluorescent Sensor for Trinitrotoluene Based on the Inner Filter Effect between Gold Nanoparticles and Fluorescent Nanoparticles.

PubMed

Lu, Hongzhi; Quan, Shuai; Xu, Shoufang

2017-11-08

In this work, we developed a simple and sensitive ratiometric fluorescent assay for sensing trinitrotoluene (TNT) based on the inner filter effect (IFE) between gold nanoparticles (AuNPs) and ratiometric fluorescent nanoparticles (RFNs), which was designed by hybridizing green emissive carbon dots (CDs) and red emissive quantum dots (QDs) into a silica sphere as a fluorophore pair. AuNPs in their dispersion state can be a powerful absorber to quench CDs, while the aggregated AuNPs can quench QDs in the IFE-based fluorescent assays as a result of complementary overlap between the absorption spectrum of AuNPs and emission spectrum of RFNs. As a result of the fact that TNT can induce the aggregation of AuNPs, with the addition of TNT, the fluorescent of QDs can be quenched, while the fluorescent of CDs would be recovered. Then, ratiometric fluorescent detection of TNT is feasible. The present IFE-based ratiometric fluorescent sensor can detect TNT ranging from 0.1 to 270 nM, with a detection limit of 0.029 nM. In addition, the developed method was successfully applied to investigate TNT in water and soil samples with satisfactory recoveries ranging from 95 to 103%, with precision below 4.5%. The simple sensing approach proposed here could improve the sensitivity of colorimetric analysis by changing the ultraviolet analysis to ratiometric fluorescent analysis and promote the development of a dual-mode detection system.

Demonstration of thermal dissipation of absorbed quanta during energy-dependent quenching of chlorophyll fluorescence in photosynthetic membranes.

PubMed

Yahyaoui, W; Harnois, J; Carpentier, R

1998-11-27

When plant leaves or chloroplasts are exposed to illumination that exceeds their photosynthetic capacity, photoprotective mechanisms such as described by the energy-dependent (non-photochemical) quenching of chlorophyll fluorescence are involved. The protective action is attributed to an increased rate constant for thermal dissipation of absorbed quanta. We applied photoacoustic spectroscopy to monitor thermal dissipation in spinach thylakoid membranes together with simultaneous measurement of chlorophyll fluorescence in the presence of inhibitors of opposite action on the formation of delta pH across the thylakoid membrane (tentoxin and nigericin/valinomycin). A linear relationship between the appearance of fluorescence quenching during formation of the delta pH and the reciprocal variation of thermal dissipation was demonstrated. Dicyclohexylcarbodiimide, which is known to prevent protonation of the minor light-harvesting complexes of photosystem II, significantly reduced the formation of fluorescence quenching and the concurrent increase in thermal dissipation. However, the addition of exogenous ascorbate to activate the xanthophyll de-epoxidase increased non-photochemical fluorescence quenching without affecting the measured thermal dissipation. It is concluded that a portion of energy-dependent fluorescence quenching that is independent of de-epoxidase activity can be readily measured by photoacoustic spectroscopy as an increase in thermal deactivation processes.

The Rate Constant for Fluorescence Quenching

ERIC Educational Resources Information Center

Legenza, Michael W.; Marzzacco, Charles J.

1977-01-01

Describes an experiment that utilizes fluorescence intensity measurements from a Spectronic 20 to determine the rate constant for the fluorescence quenching of various aromatic hydrocarbons by carbon tetrachloride in an ethanol solvent. (MLH)

Sensitive and selective detection of Hg2+ and Cu2+ ions by fluorescent Ag nanoclusters synthesized via a hydrothermal method

NASA Astrophysics Data System (ADS)

Liu, Jing; Ren, Xiangling; Meng, Xianwei; Fang, Zheng; Tang, Fangqiong

2013-09-01

An easily prepared fluorescent Ag nanoclusters (Ag NCs) probe for the sensitive and selective detection of Hg2+ and Cu2+ ions was developed here. The Ag NCs were synthesized by using polymethacrylic acid sodium salt as a template via a convenient hydrothermal process. The as-prepared fluorescent Ag NCs were monodispersed, uniform and less than 2 nm in diameter, and can be quenched in the presence of mercury (Hg2+) or copper (Cu2+) ions. Excellent linear relationships existed between the quenching degree of the Ag NCs and the concentrations of Hg2+ or Cu2+ ions in the range of 10 nM to 20 μM or 10 nM to 30 μM, respectively. By using ethylenediaminetetraacetate (EDTA) as the masking agent of Cu2+, Hg2+ was exclusively detected in coexistence with Cu2+ with high sensitivity (LOD = 10 nM), which also provided a reusable detection method for Cu2+. Furthermore, the different quenching phenomena caused by the two metals ions such as changes in visible colour, shifts of UV absorbance peaks and changes in size of Ag NCs make it easy to distinguish between them. Therefore the easily synthesized fluorescent Ag NCs may have great potential as Hg2+ and Cu2+ ions sensors.An easily prepared fluorescent Ag nanoclusters (Ag NCs) probe for the sensitive and selective detection of Hg2+ and Cu2+ ions was developed here. The Ag NCs were synthesized by using polymethacrylic acid sodium salt as a template via a convenient hydrothermal process. The as-prepared fluorescent Ag NCs were monodispersed, uniform and less than 2 nm in diameter, and can be quenched in the presence of mercury (Hg2+) or copper (Cu2+) ions. Excellent linear relationships existed between the quenching degree of the Ag NCs and the concentrations of Hg2+ or Cu2+ ions in the range of 10 nM to 20 μM or 10 nM to 30 μM, respectively. By using ethylenediaminetetraacetate (EDTA) as the masking agent of Cu2+, Hg2+ was exclusively detected in coexistence with Cu2+ with high sensitivity (LOD = 10 nM), which also provided a reusable detection method for Cu2+. Furthermore, the different quenching phenomena caused by the two metals ions such as changes in visible colour, shifts of UV absorbance peaks and changes in size of Ag NCs make it easy to distinguish between them. Therefore the easily synthesized fluorescent Ag NCs may have great potential as Hg2+ and Cu2+ ions sensors. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03329e

Synthesis, spectral behaviour and photophysics of donor-acceptor kind of chalcones: Excited state intramolecular charge transfer and fluorescence quenching studies

NASA Astrophysics Data System (ADS)

Pannipara, Mehboobali; Asiri, Abdullah M.; Alamry, Khalid A.; Arshad, Muhammad N.; El-Daly, Samy A.

2015-02-01

The spectral and photophysical properties of two chalcones containing electron donating and accepting groups with intramolecular charge transfer characteristics were synthesized and characterized by 1H NMR, 13C NMR and X-ray crystallography. Both compounds show very strong solvent polarity dependent changes in their photophysical characteristics, namely, remarkable red shift in the emission spectra with increasing solvent polarity, large change in Stokes shift, significant reduction in the fluorescence quantum yield; indicating that the fluorescence states of these compounds are of intramolecular charge transfer (ICT) character. The solvent effect on the photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of both compounds have been investigated comprehensively. For both dyes, Lippert-Mataga and Reichardt's correlations were used to estimate the difference between the excited and ground state dipole moments (Δμ). The interactions of dyes with colloidal silver nanoparticles (Ag NPs) were also studied in ethanol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of dyes by Ag NPs.

Size dependent studies of metal nanoparticles with bio-fluorophores

NASA Astrophysics Data System (ADS)

Patil, Ajeetkumar; Ballary, Steffy; George, Sajan D.; Chidangil, Santhosh

2017-06-01

Interaction of noble metal nanoparticles (NPs) with fluorophores has been an important research area in the field of material science and biomedical field. In the proximity of a metal nanoparticle, there is a quenching or enhancement in the intrinsic fluorescence of the fluorophore . The conditional quenching of the fluorescence can be used for negative sensing whereas enhancement in the fluorescence can be used to gain greater sensitivity and high signal to noise ratio in the molecular sensing/imaging. The current work deals with the systematic studies to understand the fluorescence quenching for few bio-fluorophores (NADH and FAD) when interacted with different sized silver nano-particles of (10nm, 40nm and 100nm). Home assembled Laser Induced Fluorescence (LIF) set-up was used to study the fluorescence quenching of NADH and FAD for different sized silver nanoparticles.

Improving sensitivity of gold nanoparticle based fluorescence quenching and colorimetric aptasensor by using water resuspended gold nanoparticle.

PubMed

Liu, Jinchuan; Guan, Zheng; Lv, Zhenzhen; Jiang, Xiaoling; Yang, Shuming; Chen, Ailiang

2014-02-15

Gold nanoparticles (AuNPs) based fluorescence quenching or colorimetric aptasensor have been developed for many analytes recently largely because of the ease of detection, high sensitivity, and potential for high-throughput analysis. However, the effects of remnant non-AuNPs components in the colloid gold solution on these assays performance remain unclear. For the first time, we demonstrated that the remnant sodium citrate and the reaction products of three acids play counteractive roles in AuNPs based fluorescence quenching and colorimetric aptasensor in three ways in this study. First, the remnant sodium citrate in the colloid gold solution could increase the fluorescence intensity of FAM labeled on the aptamer that reduce the efficiency of AuNPs fluorescent quenching. Second, the reaction products of citric acid, HCl and ketoglutaric acid reduce the fluorescence recovery by quenching the fluorescence of FAM labeled on the aptamer dissociated from the surface of AuNPs upon addition of target. Lastly, the reaction products of three acids reduce the pH value of the colloid gold solution that reduce the sensitivity of AuNPs based colorimetric aptasensor by increasing the adsorption of aptamer to surface of AuNPs. With sulfadimethoxine and thrombin as model analytes, we found that water resuspended AuNPs can significantly increase the sensitivity by more than 10-fold for AuNPs based fluorescence quenching aptasensor. In the AuNPs based colorimetric aptasensor for sulfadimethoxine using the water resuspended AuNPs, the sensitivity also was increased by 10-fold compared with that of original AuNPs. The findings in this study provide theoretical guidance for further improving AuNPs based fluorescent quenching and colorimetric aptasensor by adjusting the composition of AuNPs solution. © 2013 Elsevier B.V. All rights reserved.

Novel biosensor system model based on fluorescence quenching by a fluorescent streptavidin and carbazole-labeled biotin.

PubMed

Zhu, Xianwei; Shinohara, Hiroaki; Miyatake, Ryuta; Hohsaka, Takahiro

2016-10-01

In the present study, a novel molecular biosensor system model was designed by using a couple of the fluorescent unnatural mutant streptavidin and the carbazole-labeled biotin. BODIPY-FL-aminophenylalanine (BFLAF), a fluorescent unnatural amino acid was position-specifically incorporated into Trp120 position of streptavidin by four-base codon method. On the other hand, carbazole-labeled biotin was synthesized as a quencher for the fluorescent Trp120BFLAF mutant streptavidin. The fluorescence of fluorescent Trp120BFLAF mutant streptavidin was decreased as we expected when carbazole-labeled biotin was added into the mutant streptavidin solution. Furthermore, the fluorescence decrease of Trp120BFLAF mutant streptavidin with carbazole-labeled biotin (100 nM) was recovered by the competitive addition of natural biotin. This result demonstrated that by measuring the fluorescence quenching and recovery, a couple of the fluorescent Trp120BFLAF mutant streptavidin and the carbazole-labeled biotin were successfully applicable for quantification of free biotin as a molecular biosensor system. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Selective colorimetric and fluorescent quenching determination of uranyl ion via its complexation with curcumin

NASA Astrophysics Data System (ADS)

Zhu, Jing-Hui; Zhao, Xin; Yang, Jidong; Tan, Yu-Ting; Zhang, Lei; Liu, Shao-Pu; Liu, Zhong-Fang; Hu, Xiao-Li

2016-04-01

Under pH 4.0 HAc-NaAc buffer medium, curcumin alone possesses extraordinary weak fluorescence emission. Nevertheless, the introduction of Triton X-100 micelles can largely enhance the fluorescence intensity of curcumin. Uranyl ions can complex with micelles-capped curcumin, along with the slight red shift of curcumin fluorescence (about 1-7 nm), a clear decrement of absorbance (424 nm) and fluorescence (507 nm) intensities, and a distinct color change from bright yellow to orange. The fluorescence decrements (ΔF, 507 nm) are positively correlated to the amount of uranyl ions in the concentration range of 3.7 × 10- 6-1.4 × 10- 5 mol L- 1. The detection limit of this fluorescence quenching methods is 3.7 × 10- 6 mol L- 1, which is nearly 9000 times lower than the maximum allowable level in drinking water proposed by World Health Organization. Good selectivity is achieved because of a majority of co-existing substances (such as Ce4 +, La3 +, and Th4 +) do not affect the detection. The content of uranyl ions in tap water samples was determined by the proposed method with satisfactory results.

Determination of tannin in green tea infusion by flow-injection analysis based on quenching the fluorescence of 3-aminophthalate.

PubMed

Chen, Richie L C; Lin, Chun-Hsun; Chung, Chien-Yu; Cheng, Tzong-Jih

2005-11-02

A flow-injection analytical system was developed to determine tannin content in green tea infusions. The flow-injection system is based on measuring the quenching effect of tannin on the fluorescence of 3-aminophthalate. Fluorophore was obtained by auto-oxidation of luminol during solution preparation. System performance was satisfactory for routine analysis (sample throughput >20 h(-1); linear dynamic range for tannic acid, 0.005-0.3 mg/mL; linear dynamic range for green tea tannin, 0.02-1.0 mg/mL; CV < 3%). The flow-injection method is immune from interference by coexisting ascorbate in green tea infusion. Analytical results were verified by the ferrous tartrate method, the Japanese official analytical method.

Detection of trace tetracycline in fish via synchronous fluorescence quenching with carbon quantum dots coated with molecularly imprinted silica

NASA Astrophysics Data System (ADS)

Yang, Ji; Lin, Zheng-Zhong; Nur, A.-Zha; Lu, Yan; Wu, Ming-Hui; Zeng, Jun; Chen, Xiao-Mei; Huang, Zhi-Yong

2018-02-01

A novel fluorescence-based sensor combining synchronous fluorescence spectroscopy (SFS) with molecularly imprinted polymers (MIPs) was fabricated with reverse microemulsion method. Tetracycline (TC), (3-aminopropyl) triethoxysilane (APTES), tetraethyl orthosilicate (TEOS) and carbon quantum dots (CDs) were used as template, functional monomer, cross-linker and signal sources respectively in the probe preparation. A synchronous fluorescence emission (λem) at 355 nm was observed for the prepared MIP-coated CDs (MIP@CDs) particles when the wavelength interval (Δλ) was set as 70 nm, and the synchronous fluorescence intensity could be rapidly and efficiently quenched by TC based on inner filter effect (IFE). The quenching efficiencies of synchronous fluorescence intensity was linearly fitted with tetracycline (TC) concentrations ranging from 0.1 to 50 μmol L- 1 with a detection limit (DL) of 9 nmol L- 1 (3σ, n = 9). The MIP@CDs was used as a probe to detect TC in fish samples with the recoveries ranging from 98.4% to 103.1% and the relative standard deviation less than 6.0%. The results illustrated that the as-prepared MIP@CDs could be applied to the detection of trace TC in fish samples with rapidity, high sensitivity and accuracy.

Specific detection of Vibrio parahaemolyticus by fluorescence quenching immunoassay based on quantum dots.

PubMed

Wang, Ling; Zhang, Junxian; Bai, Haili; Li, Xuan; Lv, Pintian; Guo, Ailing

2014-07-01

In this study, anti-Vibrio parahaemolyticus polyclonal and monoclonal antibodies were prepared through intradermal injection immune and lymphocyte hybridoma technique respectively. CdTe quantum dots (QDs) were synthesized at pH 9.3, 98 °C for 1 h with stabilizer of 2.7:1. The fluorescence intensity was 586.499, and the yield was 62.43%. QD probes were successfully prepared under the optimized conditions of pH 7.4, 37 °C for 1 h, 250 μL of 50 mg/mL EDC · HCl, 150 μL of 4 mg/mL NHS, buffer system of Na2HPO4-citric acid, and 8 μL of 2.48 mg/mL polyclonal antibodies. As gold nanoparticles could quench fluorescence of quantum dots, the concentration of V. parahaemolyticus could be detected through measuring the reduction of fluorescence intensity in immune sandwich reaction composed of quantum dot probe, gold-labeled antibody, and the sample. For pure culture, fluorescence intensity of the system was proportional with logarithm concentration of antigen, and the correlation coefficient was 99.764%. The fluorescence quenching immunoassay based on quantum dots is established for the first time to detect Vibrio parahaemolyticus. This method may be used as rapid testing procedure due to its high simplicity and sensitivity.

Selective recognition of 6-mercaptopurine based on luminescent metal-organic frameworks Fe-MIL-88NH₂.

PubMed

Sun, Zhengjuan; Liu, Yali; Li, Yuanfang

2015-03-15

A novel and rapid spectrofluorometry method for the recognition of 6-mercaptopurine (6-MP) has been developed based on luminescent metal-organic frameworks Fe-MIL-88NH2 as fluorescent probe. The strong fluorescence of Fe-MIL-88NH2 at 430 nm could be quenched by 6-MP directly, and the Fe-MIL-88NH2 shows high selectivity for 6-MP compared to other thiol-containing amino acids such as homocysteine (Hcy), cysteine (Cys), glutathione (GSH), etc. Under optimal conditions, the relative fluorescence intensity was linearly proportional to the concentration of 6-MP in the range of 5-600 μM with the detection limit at 1.17 μM (S/N=3). Furthermore, the present approach has been successfully applied to the determination of 6-MP in human serum samples. The possible fluorescence quenching mechanism has also been investigated, where it is revealed that the quenching was attributed to competition of absorption of the light source energy as well as electron transfer between Fe-MIL-88NH2 and 6-MP. Copyright © 2014 Elsevier B.V. All rights reserved.

Binding of mitomycin C to blood proteins: A spectroscopic analysis and molecular docking

NASA Astrophysics Data System (ADS)

Jang, Jongchol; Liu, Hui; Chen, Wei; Zou, Guolin

2009-06-01

Mitomycin C (MMC) was the first recognized bioreductive alkylating agent, and has been widely used clinically for antitumor therapy. The binding of MMC to two human blood proteins, human serum albumin (HSA) and human hemoglobin (HHb), have been investigated by fluorescence quenching, synchronous fluorescence, circular dichroism (CD) spectroscopy and molecular docking methods. The fluorescence data showed that binding of MMC to proteins caused strong fluorescence quenching of proteins through a static quenching way, and each protein had only one binding site for the drug. The binding constants of MMC to HSA and HHb at 298 K were 2.71 × 10 4 and 2.56 × 10 4 L mol -1, respectively. Thermodynamic analysis suggested that both hydrophobic interaction and hydrogen bonding played major roles in the binding of MMC to HSA or HHb. The CD spectroscopy indicated that the secondary structures of the two proteins were not changed in the presence of MMC. The study of molecular docking showed that MMC was located in the entrance of site I of HSA, and in the central cavity of HHb.

Determination of uranium in natural waters

USGS Publications Warehouse

Barker, Franklin Butt; Johnson, J.O.; Edwards, K.W.; Robinson, B.P.

1965-01-01

A method is described for the determination of very low concentrations of uranium in water. The method is based on the fluorescence of uranium in a pad prepared by fusion of the dried solids from the water sample with a flux of 10 percent NaF 45.5 percent Na2CO3 , and 45.5 percent K2CO3 . This flux permits use of a low fusion temperature and yields pads which are easily removed from the platinum fusion dishes for fluorescence measurements. Uranium concentrations of less than 1 microgram per liter can be determined on a sample of 10 milliliters, or less. The sensitivity and accuracy of the method are dependent primarily on the purity of reagents used, the stability and linearity of the fluorimeter, and the concentration of quenching elements in the water residue. A purification step is recommended when the fluorescence is quenched by more than 30 percent. Equations are given for the calculation of standard deviations of analyses by this method. Graphs of error functions and representative data are also included.

Quick and simple estimation of bacteria using a fluorescent paracetamol dimer-Au nanoparticle composite

NASA Astrophysics Data System (ADS)

Sahoo, Amaresh Kumar; Sharma, Shilpa; Chattopadhyay, Arun; Ghosh, Siddhartha Sankar

2012-02-01

Rapid, simple and sensitive detection of bacterial contamination is critical for safeguarding public health and the environment. Herein, we report an easy method of detection as well as enumeration of the bacterial cell number on the basis of fluorescence quenching of a non-antibacterial fluorescent nanocomposite, consisting of paracetamol dimer (PD) and Au nanoparticles (NPs), in the presence of bacteria. The composite was synthesized by reaction of paracetamol (p-hydroxyacetanilide) with HAuCl4. The Au NPs of the composite were characterized using UV-Vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction and selected area electron diffraction analysis. The paracetamol dimer in the composite showed emission peak at 435 nm when excited at 320 nm. The method successfully detected six bacterial strains with a sensitivity of 100 CFU mL-1. The Gram-positive and Gram-negative bacteria quenched the fluorescence of the composite differently, making it possible to distinguish between the two. The TEM analysis showed interaction of the composite with bacteria without any apparent damage to the bacteria. The chi-square test established the accuracy of the method. Quick, non-specific and highly sensitive detection of bacteria over a broad range of logarithmic dilutions within a short span of time demonstrates the potential of this method as an alternative to conventional methods.Rapid, simple and sensitive detection of bacterial contamination is critical for safeguarding public health and the environment. Herein, we report an easy method of detection as well as enumeration of the bacterial cell number on the basis of fluorescence quenching of a non-antibacterial fluorescent nanocomposite, consisting of paracetamol dimer (PD) and Au nanoparticles (NPs), in the presence of bacteria. The composite was synthesized by reaction of paracetamol (p-hydroxyacetanilide) with HAuCl4. The Au NPs of the composite were characterized using UV-Vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction and selected area electron diffraction analysis. The paracetamol dimer in the composite showed emission peak at 435 nm when excited at 320 nm. The method successfully detected six bacterial strains with a sensitivity of 100 CFU mL-1. The Gram-positive and Gram-negative bacteria quenched the fluorescence of the composite differently, making it possible to distinguish between the two. The TEM analysis showed interaction of the composite with bacteria without any apparent damage to the bacteria. The chi-square test established the accuracy of the method. Quick, non-specific and highly sensitive detection of bacteria over a broad range of logarithmic dilutions within a short span of time demonstrates the potential of this method as an alternative to conventional methods. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr11837h

Interactions of hemin with bovine serum albumin and human hemoglobin: A fluorescence quenching study.

PubMed

Makarska-Bialokoz, Magdalena

2018-03-15

The binding interactions between hemin (Hmi) and bovine serum albumin (BSA) or human hemoglobin (HHb), respectively, have been examined in aqueous solution at pH=7.4, applying UV-vis absorption, as well as steady-state, synchronous and three-dimensional fluorescence spectra techniques. Representative results received for both BSA and HHb intrinsic fluorescence proceeding from the interactions with hemin suggest the formation of stacking non-covalent and non-fluorescent complexes in both the Hmi-BSA and Hmi-HHb systems, with highly possible concurrent formation of a coordinate bond between a group on the protein surface and the metal in Hmi molecule. All the values of calculated parameters, the binding, fluorescence quenching and bimolecular quenching rate constants point to the involvement of static quenching in both the systems studied. The blue shift in the synchronous fluorescence spectra imply the participation of both tryptophan and tyrosine residues in quenching of BSA and HHb intrinsic fluorescence. Depicted outcomes suggest that hemin is supposedly able to influence the physiological functions of BSA and HHb, the most important blood proteins, particularly in case of its overuse. Copyright © 2017 Elsevier B.V. All rights reserved.

Insights into in vitro binding of parecoxib to human serum albumin by spectroscopic methods.

PubMed

Shang, Shujun; Liu, Qingling; Gao, Jiandong; Zhu, Yulin; Liu, Jingying; Wang, Kaiyan; Shao, Wei; Zhang, Shudong

2014-10-01

Herein, we report the effect of parecoxib on the structure and function of human serum albumin (HSA) by using fluorescence, circular dichroism (CD), Fourier transforms infrared (FTIR), three-dimensional (3D) fluorescence spectroscopy, and molecular docking techniques. The Stern-Volmer quenching constants K(SV) and the corresponding thermodynamic parameters ΔH, ΔG, and ΔS have been estimated by the fluorescence quenching method. The results indicated that parecoxib binds spontaneously with HSA through van der Waals forces and hydrogen bonds with binding constant of 3.45 × 10(4) M(-1) at 298 K. It can be seen from far-UV CD spectra that the α-helical network of HSA is disrupted and its content decreases from 60.5% to 49.6% at drug:protein = 10:1. Protein tertiary structural alterations induced by parecoxib were also confirmed by FTIR and 3D fluorescence spectroscopy. The molecular docking study indicated that parecoxib is embedded into the hydrophobic pocket of HSA. © 2014 Wiley Periodicals, Inc.

Binding of dicamba to soluble and bound extracellular polymeric substances (EPS) from aerobic activated sludge: a fluorescence quenching study.

PubMed

Pan, Xiangliang; Liu, Jing; Zhang, Daoyong; Chen, Xi; Song, Wenjuan; Wu, Fengchang

2010-05-15

Binding of dicamba to soluble EPS (SEPS) and bound EPS (BEPS) from aerobic activated sludge was investigated using fluorescence spectroscopy. Two protein-like fluorescence peaks (peak A with Ex/Em=225 nm/342-344 nm and peak B with Ex/Em=275/340-344 nm) were identified in SEPS and BEPS. Humic-like fluorescence peak C (Ex/Em=270-275 nm/450-460 nm) was only found in BEPS. Fluorescence of the peaks A and B for SEPS and peak A for BEPS were markedly quenched by dicamba at all temperatures whereas fluorescence of peaks B and C for BEPS was quenched only at 298 K. A dynamic process dominated the fluorescence quenching of peak A of both SEPS and BEPS. Fluorescence quenching of peak B and C was governed a static process. The effective quenching constants (logK(a)) were 4.725-5.293 for protein-like fluorophores of SEPS and 4.23-5.190 for protein-like fluorophores of BEPS, respectively. LogK(a) for humic-like substances was 3.85. Generally, SEPS had greater binding capacity for dicamba than BEPS, and protein-like substances bound dicamba more strongly than humic-like substances. Binding of dicamba to SEPS and BEPS was spontaneous and exothermic. Electrostatic force and hydrophobic interaction forces play a crucial role in binding of dicamba to EPS. Copyright © 2010 Elsevier Inc. All rights reserved.

Sensitive determination of enoxacin in pharmaceutical formulations by its quench effect on the fluorescence of glutathione-capped CdTe quantum dots.

PubMed

Yang, Qiong; Tan, Xuanping; Yang, Jidong

2016-02-01

A sensitive and simple method for the determination of enoxacin (ENX) was developed based on the fluorescence quenching effect of ENX for glutathione (GSH)-capped CdTe quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 4.333 × 10(-9)  mol⋅L(-1) to 1.4 × 10(-5)  mol⋅L(-1) with a correlation coefficient (R) of 0.9987, and the detection limit (3σ/K) was 1.313 × 10(-9)  mol⋅L(-1). The corresponding mechanism has been proposed on the basis of electron transfer supported by ultraviolet-visible (UV) light absorption, fluorescence spectroscopy, and the measurement of fluorescence lifetime. The method has been applied to the determination of ENX in pharmaceutical formulations (enoxacin gluconate injections and commercial tablets) with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation. Copyright © 2015 John Wiley & Sons, Ltd.

Simple and Sensitive Molecularly Imprinted Polymer - Mn-Doped ZnS Quantum Dots Based Fluorescence Probe for Cocaine and Metabolites Determination in Urine.

PubMed

Chantada-Vázquez, María Pilar; Sánchez-González, Juan; Peña-Vázquez, Elena; Tabernero, María Jesús; Bermejo, Ana María; Bermejo-Barrera, Pilar; Moreda-Piñeiro, Antonio

2016-03-01

A new molecularly imprinted polymer (MIP)-based fluorescent artificial receptor has been prepared by anchoring a selective MIP for cocaine (COC) on the surface of polyethylene glycol (PEG) modified Mn-doped ZnS quantum dots (QDs). The prepared material combines the high selectivity attributed to MIPs and the sensitive fluorescent property of the Mn-doped ZnS QDs. Simple and low cost methods have therefore been optimized for assessing cocaine abuse in urine by monitoring the fluorescence quenching when the template (COC) and also metabolites from COC [benzoylecgonine (BZE) and ecgonine methyl ester (EME)] are present. Fluorescence quenching was not observed when performing experiments with other drugs of abuse (and their metabolites) or when using nonimprinted polymer (NIP)-coated QDs. Under optimized operating conditions (1.5 mL of 200 mg L(-1) MIP-coated QDs solution, pH 5.5, and 15 min before fluorescence scanning) two analytical methods were developed/validated. One of the procedures (direct method) consisted of urine sample 1:20 dilution before fluorescence measurements. The method has been found to be fast, precise, and accurate, but the standard addition technique for performing the analysis was required because of the existence of matrix effect. The second procedure performed a solid phase extraction (SPE) first, avoiding matrix effect and allowing external calibration. The limits of detection of the methods were 0.076 mg L(-1) (direct method) and 0.0042 mg L(-1) (SPE based method), which are lower than the cutoff values for confirmative conclusions regarding cocaine abuse.

Identification of antisense nucleic acid hybridization sites in mRNA molecules with self-quenching fluorescent reporter molecules

PubMed Central

Gifford, Lida K.; Opalinska, Joanna B.; Jordan, David; Pattanayak, Vikram; Greenham, Paul; Kalota, Anna; Robbins, Michelle; Vernovsky, Kathy; Rodriguez, Lesbeth C.; Do, Bao T.; Lu, Ponzy; Gewirtz, Alan M.

2005-01-01

We describe a physical mRNA mapping strategy employing fluorescent self-quenching reporter molecules (SQRMs) that facilitates the identification of mRNA sequence accessible for hybridization with antisense nucleic acids in vitro and in vivo, real time. SQRMs are 20–30 base oligodeoxynucleotides with 5–6 bp complementary ends to which a 5′ fluorophore and 3′ quenching group are attached. Alone, the SQRM complementary ends form a stem that holds the fluorophore and quencher in contact. When the SQRM forms base pairs with its target, the structure separates the fluorophore from the quencher. This event can be reported by fluorescence emission when the fluorophore is excited. The stem–loop of the SQRM suggests that SQRM be made to target natural stem–loop structures formed during mRNA synthesis. The general utility of this method is demonstrated by SQRM identification of targetable sequence within c-myb and bcl-6 mRNA. Corresponding antisense oligonucleotides reduce these gene products in cells. PMID:15718294

Unusual solvent effects on the fluorescence quenching rate constants of a thioxanthone derivative by n-butylamine and isoprene

NASA Astrophysics Data System (ADS)

Burget, D.; Jacques, P.

1998-07-01

The fluorescence quenching rate constants of a thioxanthone derivative by two electron donors ( n-butylamine and isoprene) were studied in eighteen solvents of different polarity. Both the empirical polarity parameter ET(30) and the more elaborate solvatochromic comparative method (SCM) π*, α, β (used without any precautions) failed to explain the relevant data. However, when in the frame of the SCM the sequential procedure is applied, unexpected solvent effects were revealed for hydroxylic solvents. These effects can be well accounted for by introducing a parameter χ for the whole set of solvents studied, equal to one or zero, depending on whether OH groups are involved or not in the quenching mechanism. A clue to the introduction of the parameter χ is presented.

Fluorescence resonance energy-transfer affects the determination of the affinity between ligand and proteins obtained by fluorescence quenching method

NASA Astrophysics Data System (ADS)

Xiao, Jianbo; Wei, Xinlin; Wang, Yuanfeng; Liu, Chunxi

2009-11-01

The interaction between esculin and serum albumins was investigated to illustrate that the fluorescence resonance energy-transfer (FRET) affects the determination of the binding constants obtained by fluorescence quenching method. The binding constants ( Ka) obtained by the double-logarithm curve for esculin-BSA and esculin-HSA were 1.02 × 10 7 and 2.07 × 10 4 L/mol, respectively. These results from synchronous fluorescence showed that the Tyr and Trp residues of HSA were affected more deeply than those in BSA. The excitation profile of esculin showed that in the presence of BSA and HSA, the S 0 → S 1 transition of esculin ( λexmax≈340 nm) appears, which is similar to the λemmax of BSA and HSA. The critical distance ( R0) between BSA and esculin is higher than that of HSA, which showed that the affinity of esculin and HSA should be higher than that of BSA. After centrifugation, the concentrations of esculin bound to albumins were determined by means of the fluorescence of esculin. It was found that much more esculin was bound to HSA than to BSA. However, the bound models for BSA and HSA are almost the same. The concentration of esculin bound to serum albumin at first decreased with the addition of esculin and then increased. From above results, it can be concluded that the affinity of esculin and HSA should be higher than that of esculin and BSA. This example showed that in the presence of FRET, the binding constants between ligands and proteins based on fluorescence quenching might be deviated.

Fluorescence resonance energy-transfer affects the determination of the affinity between ligand and proteins obtained by fluorescence quenching method.

PubMed

Xiao, Jianbo; Wei, Xinlin; Wang, Yuanfeng; Liu, Chunxi

2009-11-01

The interaction between esculin and serum albumins was investigated to illustrate that the fluorescence resonance energy-transfer (FRET) affects the determination of the binding constants obtained by fluorescence quenching method. The binding constants (K(a)) obtained by the double-logarithm curve for esculin-BSA and esculin-HSA were 1.02x10(7) and 2.07x10(4)L/mol, respectively. These results from synchronous fluorescence showed that the Tyr and Trp residues of HSA were affected more deeply than those in BSA. The excitation profile of esculin showed that in the presence of BSA and HSA, the S(0)-->S(1) transition of esculin (lambda(ex)(max) approximately 340nm) appears, which is similar to the lambda(em)(max) of BSA and HSA. The critical distance (R(0)) between BSA and esculin is higher than that of HSA, which showed that the affinity of esculin and HSA should be higher than that of BSA. After centrifugation, the concentrations of esculin bound to albumins were determined by means of the fluorescence of esculin. It was found that much more esculin was bound to HSA than to BSA. However, the bound models for BSA and HSA are almost the same. The concentration of esculin bound to serum albumin at first decreased with the addition of esculin and then increased. From above results, it can be concluded that the affinity of esculin and HSA should be higher than that of esculin and BSA. This example showed that in the presence of FRET, the binding constants between ligands and proteins based on fluorescence quenching might be deviated.

Fluorescence-quenching of a Liposomal-encapsulated Near-infrared Fluorophore as a Tool for In Vivo Optical Imaging

PubMed Central

Rabenhold, Markus; Steiniger, Frank; Fahr, Alfred; Hilger, Ingrid

2015-01-01

Optical imaging offers a wide range of diagnostic modalities and has attracted a lot of interest as a tool for biomedical imaging. Despite the enormous number of imaging techniques currently available and the progress in instrumentation, there is still a need for highly sensitive probes that are suitable for in vivo imaging. One typical problem of available preclinical fluorescent probes is their rapid clearance in vivo, which reduces their imaging sensitivity. To circumvent rapid clearance, increase number of dye molecules at the target site, and thereby reduce background autofluorescence, encapsulation of the near-infrared fluorescent dye, DY-676-COOH in liposomes and verification of its potential for in vivo imaging of inflammation was done. DY-676 is known for its ability to self-quench at high concentrations. We first determined the concentration suitable for self-quenching, and then encapsulated this quenching concentration into the aqueous interior of PEGylated liposomes. To substantiate the quenching and activation potential of the liposomes we use a harsh freezing method which leads to damage of liposomal membranes without affecting the encapsulated dye. The liposomes characterized by a high level of fluorescence quenching were termed Lip-Q. We show by experiments with different cell lines that uptake of Lip-Q is predominantly by phagocytosis which in turn enabled the characterization of its potential as a tool for in vivo imaging of inflammation in mice models. Furthermore, we use a zymosan-induced edema model in mice to substantiate the potential of Lip-Q in optical imaging of inflammation in vivo. Considering possible uptake due to inflammation-induced enhanced permeability and retention (EPR) effect, an always-on liposome formulation with low, non-quenched concentration of DY-676-COOH (termed Lip-dQ) and the free DY-676-COOH were compared with Lip-Q in animal trials. PMID:25591069

In vivo tumor-targeted dual-modal fluorescence/CT imaging using a nanoprobe co-loaded with an aggregation-induced emission dye and gold nanoparticles.

PubMed

Zhang, Jimei; Li, Chan; Zhang, Xu; Huo, Shuaidong; Jin, Shubin; An, Fei-Fei; Wang, Xiaodan; Xue, Xiangdong; Okeke, C I; Duan, Guiyun; Guo, Fengguang; Zhang, Xiaohong; Hao, Jifu; Wang, Paul C; Zhang, Jinchao; Liang, Xing-Jie

2015-02-01

As an intensely studied computed tomography (CT) contrast agent, gold nanoparticle has been suggested to be combined with fluorescence imaging modality to offset the low sensitivity of CT. However, the strong quenching of gold nanoparticle on fluorescent dyes requires complicated design and shielding to overcome. Herein, we report a unique nanoprobe (M-NPAPF-Au) co-loading an aggregation-induced emission (AIE) red dye and gold nanoparticles into DSPE-PEG(2000) micelles for dual-modal fluorescence/CT imaging. The nanoprobe was prepared based on a facile method of "one-pot ultrasonic emulsification". Surprisingly, in the micelles system, fluorescence dye (NPAPF) efficiently overcame the strong fluorescence quenching of shielding-free gold nanoparticles and retained the crucial AIE feature. In vivo studies demonstrated the nanoprobe had superior tumor-targeting ability, excellent fluorescence and CT imaging effects. The totality of present studies clearly indicates the significant potential application of M-NPAPF-Au as a dual-modal non-invasive fluorescence/X-ray CT nanoprobe for in vivo tumor-targeted imaging and diagnosis. Copyright © 2014 Elsevier Ltd. All rights reserved.

Detection of bisphenol A in food packaging based on fluorescent conjugated polymer PPESO3 and enzyme system.

PubMed

Huang, Hui; Li, Yongxin; Liu, Jintong; Tong, Jin; Su, Xingguang

2015-10-15

Bisphenol A (BPA) is a kind of carcinogen, which can interfere with the body's endocrine system. In this paper, a new kind of fluorescent sensor for BPA detection was established based on the fluorescent conjugated polymer PPESO3. The oxidative product of BPA is able to quench PPESO3 in the presence of HRP and H2O2, and the quenched PL intensity of PPESO3 was proportionally to the concentration of BPA in the range of 1-100 μmol/L with a detection limit of 4 × 10(-7) mol/L. The proposed method has been applied to detect BPA in eight food packaging samples with satisfactory results. The proposed method has the potential for the assay of BPA in food or food packaging samples. Copyright © 2015 Elsevier Ltd. All rights reserved.

Halide (Cl(super -)) Quenching of Quinine Sulfate Fluorescence: A Time-Resolved Fluorescence Experiment for Physical Chemistry

ERIC Educational Resources Information Center

Gutow, Jonathan H.

2005-01-01

The time-resolved fluorescence experiment investigating the halide quenching of fluorescence from quinine sulfate in water is described. The objectives of the experiment include reinforcing student understanding of the kinetics of competing pathways, making connections with microscopic theories of kinetics through comparison of experimental and…

Tryptophan and ATTO 590: mutual fluorescence quenching and exciplex formation.

PubMed

Bhattacharjee, Ujjal; Beck, Christie; Winter, Arthur; Wells, Carson; Petrich, Jacob W

2014-07-24

Investigation of fluorescence quenching of probes, such as ATTO dyes, is becoming an increasingly important topic owing to the use of these dyes in super-resolution microscopies and in single-molecule studies. Photoinduced electron transfer is their most important nonradiative pathway. Because of the increasing frequency of the use of ATTO and related dyes to investigate biological systems, studies are presented for inter- and intramolecular quenching of ATTO 590 with tryptophan. In order to examine intramolecular quenching, an ATTO 590-tryptophan conjugate was synthesized. It was determined that tryptophan is efficiently quenching ATTO 590 fluorescence by excited-state charge transfer and two charge transfer complexes are forming. In addition, it was discovered that an exciplex (whose lifetime is 5.6 ns) can be formed between tryptophan and ATTO 590, and it is suggested that the possibility of such exciplex formation should be taken into account when protein fluorescence is monitored in a system tagged with ATTO dyes.

Fast Decomposition of Three-Component Spectra of Fluorescence Quenching by White and Grey Methods of Data Modeling.

PubMed

Kałka, Andrzej J; Turek, Andrzej M

2018-04-03

'White' and 'grey' methods of data modeling have been employed to resolve the heterogeneous fluorescence from a fluorophore mixture of 9-cyanoanthracene (CNA), 10-chloro-9-cyanoanthracene (ClCNA) and 9,10-dicyanoanthracene (DCNA) into component individual fluorescence spectra. The three-component spectra of fluorescence quenching in methanol were recorded for increasing amounts of lithium bromide used as a quencher. The associated intensity decay profiles of differentially quenched fluorescence of single components were modeled on the basis of a linear Stern-Volmer plot. These profiles are necessary to initiate the fitting procedure in both 'white' and 'grey' modeling of the original data matrices. 'White' methods of data modeling, called also 'hard' methods, are based on chemical/physical laws expressed in terms of some well-known or generally accepted mathematical equations. The parameters of these models are not known and they are estimated by least squares curve fitting. 'Grey' approaches to data modeling, also known as hard-soft modeling techniques, make use of both hard-model and soft-model parts. In practice, the difference between 'white' and 'grey' methods lies in the way in which the 'crude' fluorescence intensity decays of the mixture components are estimated. In the former case they are given in a functional form while in the latter as digitized curves which, in general, can only be obtained by using dedicated techniques of factor analysis. In the paper, the initial values of the Stern-Volmer constants of pure components were evaluated by both 'point-by-point' and 'matrix' versions of the method making use of the concept of wavelength dependent intensity fractions as well as by the rank annihilation factor analysis applied to the data matrices of the difference fluorescence spectra constructed in two ways: from the spectra recorded for a few excitation lines at the same concentration of a fluorescence quencher or classically from a series of the spectra measured for one selected excitation line but for increasing concentration of the quencher. The results of multiple curve resolution obtained by all types of the applied methods have been scrutinized and compared. In addition, the effect of inadequacy of sample preparation and increasing instrumental noise on the shape of the resolved spectral profiles has been studied on several datasets mimicking the measured data matrices. Graphical Abstract ᅟ.

The G-BHQ synergistic effect: Improved double quenching molecular beacons based on guanine and Black Hole Quencher for sensitive simultaneous detection of two DNAs.

PubMed

Xiang, Dongshan; Li, Fengquan; Wu, Chenyi; Shi, Boan; Zhai, Kun

2017-11-01

We designed two double quenching molecular beacons (MBs) with simple structure based on guanine (G base) and Black Hole Quencher (BHQ), and developed a new analytical method for sensitive simultaneous detection of two DNAs by synchronous fluorescence analysis. In this analytical method, carboxyl fluorescein (FAM) and tetramethyl-6-carboxyrhodamine (TAMRA) were respectively selected as fluorophore of two MBs, Black Hole Quencher 1 (BHQ-1) and Black Hole Quencher 2 (BHQ-2) were respectively selected as organic quencher, and three continuous nucleotides with G base were connected to organic quencher (BHQ-1 and BHQ-2). In the presence of target DNAs, the two MBs hybridize with the corresponding target DNAs, the fluorophores are separated from organic quenchers and G bases, leading to recovery of fluorescence of FAM and TAMRA. Under a certain conditions, the fluorescence intensities of FAM and TAMRA all exhibited good linear dependence on their concentration of target DNAs (T1 and T2) in the range from 4 × 10 -10 to 4 × 10 -8 molL -1 (M). The detection limit (3σ, n = 13) of T1 was 3 × 10 -10 M and that of T2 was 2×10 -10 M, respectively. Compared with the existing analysis methods for multiplex DNA with MBs, this proposed method based on double quenching MBs is not only low fluorescence background, short analytical time and low detection cost, but also easy synthesis and good stability of MB probes. Copyright © 2017 Elsevier B.V. All rights reserved.

A Simple and Sensitive Method for Auramine O Detection Based on the Binding Interaction with Bovin Serum Albumin.

PubMed

Yan, Jingjing; Huang, Xin; Liu, Shaopu; Yang, Jidong; Yuan, Yusheng; Duan, Ruilin; Zhang, Hui; Hu, Xiaoli

2016-01-01

A simple, rapid and effective method for auramine O (AO) detection was proposed by fluorescence and UV-Vis absorption spectroscopy. In the BR buffer system (pH 7.0), AO had a strong quenching ability to the fluorescence of bovin serum albumin (BSA) by dynamic quenching. In terms of the thermodynamic parameters calculated as ΔH > 0 and ΔS > 0, the resulting binding of BSA and AO was mainly attributed to the hydrophobic interaction forces. The linearity of this method was in the concentration range from 0.16 to 50 μmol L(-1) with a detection limit of 0.05 μmol L(-1). Based on fluorescence resonance energy transfer (FRET), the distance r (1.36 nm) between donor (BSA) and acceptor (AO) was obtained. Furthermore, the effects of foreign substances and ionic strength were evaluated under the optimum reaction conditions. BSA as a selective probe could be applied to the analysis of AO in medicines with satisfactory results.

Analytical investigation of the influence of ornidazole on the native protein fluorescence.

PubMed

Ali, Hazim M; El-Hashemy, Mohammed A

2018-05-03

A novel spectrofluorimetric method for the determination of ornidazole (ORN) in pure form and dosage forms was developed based on the influence of ORN on the native fluorescence of bovine serum albumin (BSA) in a stimulated physiological environment. The obtained data reveal that the presence of ORN has a strong quenching effect on the fluorescence of BSA through both a dynamic and a static process. The parameters of the binding of ORN to BSA were calculated at different temperatures. Thermodynamic parameters values suggest a role of electrostatic and hydrophobic forces in the binding of ORN to BSA. The investigated method for the determination of ORN is accurate, precise and sensitive with a detection limit of 0.106 μg/mL and a quantification limit of 0.353 μg/mL. The quenching method was applied successfully in the determination of ORN in pure form and dosage forms. Copyright © 2018 Elsevier B.V. All rights reserved.

A fluorescence study of the molecular interactions of harmane with the nucleobases, their nucleosides and mononucleotides.

PubMed

Balón, M; Muñoz, M A; Carmona, C; Guardado, P; Galán, M

1999-07-19

Fluorescence binding studies of harmane to the elemental components of the nucleic acids were undertaken to investigate the origin of the interaction between the drug and DNA. Most of the tested substrates have been found to induce hypochromism in the absorption spectrum of harmane and to quench its fluorescence. The quenching process induced by the nucleobases and their nucleosides is mainly due to the formation of ground state 1:1 complexes. However, in the case of the mononucleotides a dynamic quenching component is also observed. This quenching component is likely due to the excited state interaction of harmane with the phosphate group of the nucleotides. UV-vis spectral changes and quenching measurements have been used to quantify the ground state association constants of the complexes and the quenching rate constants.

Investigation of common fluorophores for the detection of nitrated explosives by fluorescence quenching.

PubMed

Meaney, Melissa S; McGuffin, Victoria L

2008-03-03

Previous studies have indicated that nitrated explosives may be detected by fluorescence quenching of pyrene and related compounds. The use of pyrene, however, invokes numerous health and waste disposal hazards. In the present study, ten safer fluorophores are identified for quenching detection of target nitrated compounds. Initially, Stern-Volmer constants are measured for each fluorophore with nitrobenzene and 4-nitrotoluene to determine the sensitivity of the quenching interaction. For quenching constants greater than 50 M(-1), sensitivity and selectivity are investigated further using an extended set of target quenchers. Nitromethane, nitrobenzene, 4-nitrotoluene, and 2,6-dinitrotoluene are chosen to represent nitrated explosives and their degradation products; aniline, benzoic acid, and phenol are chosen to represent potential interfering compounds. Among the fluorophores investigated, purpurin, malachite green, and phenol red demonstrate the greatest sensitivity and selectivity for nitrated compounds. Correlation of the quenching rate constants for these fluorophores to Rehm-Weller theory suggests an electron-transfer quenching mechanism. As a result of the large quenching constants, purpurin, malachite green, and phenol red are the most promising for future detection of nitrated explosives via fluorescence quenching.

Advances in Surface-Enhanced Fluorescence

PubMed Central

Lakowicz, Joseph R.; Geddes, Chris D.; Gryczynski, Ignacy; Malicka, Joanna; Gryczynski, Zygmunt; Aslan, Kadir; Lukomska, Joanna; Matveeva, Evgenia; Zhang, Jian; Badugu, Ramachandram; Huang, Jun

2009-01-01

We report recent achievements in metal-enhanced fluorescence from our laboratory. Several fluorophore systems have been studied on metal particle-coated surfaces and in colloid suspensions. In particular, we describe a distance dependent enhancement on silver island films (SIFs), release of self-quenching of fluorescence near silver particles, and the applications of fluorescence enhancement near metalized surfaces to bioassays. We discuss a number of methods for various shaped silver particle deposition on surfaces. PMID:15617385

Multicolor fluorescent biosensor for multiplexed detection of DNA.

PubMed

Hu, Rong; Liu, Tao; Zhang, Xiao-Bing; Huan, Shuang-Yan; Wu, Cuichen; Fu, Ting; Tan, Weihong

2014-05-20

Development of efficient methods for highly sensitive and rapid screening of specific oligonucleotide sequences is essential to the early diagnosis of serious diseases. In this work, an aggregated cationic perylene diimide (PDI) derivative was found to efficiently quench the fluorescence emission of a variety of anionic oligonucleotide-labeled fluorophores that emit at wavelengths from the visible to NIR region. This broad-spectrum quencher was then adopted to develop a multicolor biosensor via a label-free approach for multiplexed fluorescent detection of DNA. The aggregated perylene derivative exhibits a very high quenching efficiency on all ssDNA-labeled dyes associated with biosensor detection, having efficiency values of 98.3 ± 0.9%, 97 ± 1.1%, and 98.2 ± 0.6% for FAM, TAMRA, and Cy5, respectively. An exonuclease-assisted autocatalytic target recycling amplification was also integrated into the sensing system. High quenching efficiency combined with autocatalytic target recycling amplification afforded the biosensor with high sensitivity toward target DNA, resulting in a detection limit of 20 pM, which is about 50-fold lower than that of traditional unamplified homogeneous fluorescent assay methods. The quencher did not interfere with the catalytic activity of nuclease, and the biosensor could be manipulated in either preaddition or postaddition manner with similar sensitivity. Moreover, the proposed sensing system allows for simultaneous and multicolor analysis of several oligonucleotides in homogeneous solution, demonstrating its potential application in the rapid screening of multiple biotargets.

Study on the interaction between cinnamic acid and lysozyme

NASA Astrophysics Data System (ADS)

Zhang, Hong-Mei; Chen, Jian; Zhou, Qiu-Hua; Shi, Yue-Qin; Wang, Yan-Qing

2011-02-01

The interaction between lysozyme and cinnamic acid was investigated systematically by ultraviolet-vis absorbance, circular dichroism, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques at pH 7.40. The binding constants, quenching mechanism, and the number of binding sites were determined by the quenching of lysozyme fluorescence in presence of cinnamic acid. The results showed that the fluorescence quenching of lysozyme by cinnamic acid was a result of the formation of cinnamic acid-lysozyme complex. The hydrophobic and electrostatic interactions played major roles in stabilizing the complex; the distance r between donor and acceptor was obtained to be 2.07 nm according to Förster's theory; the effect of cinnamic acid on the conformation of lysozyme was analyzed using synchronous fluorescence, circular dichroism and three-dimensional fluorescence spectra.

Direct interaction of the major light-harvesting complex II and PsbS in nonphotochemical quenching

PubMed Central

Wilk, Laura; Grunwald, Matthias; Liao, Pen-Nan; Walla, Peter Jomo; Kühlbrandt, Werner

2013-01-01

The photosystem II (PSII) subunit S (PsbS) plays a key role in nonphotochemical quenching, a photoprotective mechanism for dissipation of excess excitation energy in plants. The precise function of PsbS in nonphotochemical quenching is unknown. By reconstituting PsbS together with the major light-harvesting complex of PSII (LHC-II) and the xanthophyll zeaxanthin (Zea) into proteoliposomes, we have tested the individual contributions of PSII complexes and Zea to chlorophyll (Chl) fluorescence quenching in a membrane environment. We demonstrate that PsbS is stable in the absence of pigments in vitro. Significant Chl fluorescence quenching of reconstituted LHC-II was observed in the presence of PsbS and Zea, although neither Zea nor PsbS alone was sufficient to induce the same quenching. Coreconstitution with PsbS resulted in the formation of LHC-II/PsbS heterodimers, indicating their direct interaction in the lipid bilayer. Two-photon excitation measurements on liposomes containing LHC-II, PsbS, and Zea showed an increase of electronic interactions between carotenoid S1 and Chl states, , that correlated directly with Chl fluorescence quenching. These findings are in agreement with a carotenoid-dependent Chl fluorescence quenching by direct interactions of LHCs of PSII with PsbS monomers. PMID:23509270

Stable and Size-Tunable Aggregation-Induced Emission Nanoparticles Encapsulated with Nanographene Oxide and Applications in Three-Photon Fluorescence Bioimaging.

PubMed

Zhu, Zhenfeng; Qian, Jun; Zhao, Xinyuan; Qin, Wei; Hu, Rongrong; Zhang, Hequn; Li, Dongyu; Xu, Zhengping; Tang, Ben Zhong; He, Sailing

2016-01-26

Organic fluorescent dyes with high quantum yield are widely applied in bioimaging and biosensing. However, most of them suffer from a severe effect called aggregation-caused quenching (ACQ), which means that their fluorescence is quenched at high molecular concentrations or in the aggregation state. Aggregation-induced emission (AIE) is a diametrically opposite phenomenon to ACQ, and luminogens with this feature can effectively solve this problem. Graphene oxide has been utilized as a quencher for many fluorescent dyes, based on which biosensing can be achieved. However, using graphene oxide as a surface modification agent of fluorescent nanoparticles is seldom reported. In this article, we used nanographene oxide (NGO) to encapsulate fluorescent nanoparticles, which consisted of a type of AIE dye named TPE-TPA-FN (TTF). NGO significantly improved the stability of nanoparticles in aqueous dispersion. In addition, this method could control the size of nanoparticles' flexibly as well as increase their emission efficiency. We then used the NGO-modified TTF nanoparticles to achieve three-photon fluorescence bioimaging. The architecture of ear blood vessels in mice and the distribution of nanoparticles in zebrafish could be observed clearly. Furthermore, we extended this method to other AIE luminogens and showed it was widely feasible.

Ultratrace analysis of transuranic actinides by laser-induced fluorescence

DOEpatents

Miller, S.M.

1983-10-31

Ultratrace quantities of transuranic actinides are detected indirectly by their effect on the fluorescent emissions of a preselected fluorescent species. Transuranic actinides in a sample are coprecipitated with a host lattice material containing at least one preselected fluorescent species. The actinide either quenches or enhances the laser-induced fluorescence of the preselected fluorescent species. The degree of enhancement or quenching is quantitatively related to the concentration of actinide in the sample.

Characterization of humic acids by two-dimensional correlation fluorescence spectroscopy

NASA Astrophysics Data System (ADS)

Nakashima, K.; Xing, Shaoyong; Gong, Yongkuan; Miyajima, Toru

2008-07-01

We have investigated interaction between humic acids and heavy metal ions by fluorescence spectroscopy. The humic acids examined are Aldrich humic acid (AHA) and Dando humic acid (DHA), and heavy metal ions are Cu 2+ and Pb 2+. The binding constants between the humic acids and the heavy metal ions are obtained by a conventional fluorescence quenching technique. The two prominent bands in the fluorescence spectra of the humic acids give different binding constants, implying that the two bands are originated from different fluorescent species in the matrices of the humic acids. This was confirmed by two-dimensional correlation analysis based on the quenching perturbation on the fluorescence spectra. Two prominent cross peaks corresponding to the two fluorescence bands are obtained in the asynchronous maps, indicating that the two fluorescence bands belong to different species. The order of the response of the two fluorescence bands to the quenching perturbation is also elucidated based on Noda's rule.

Quenching of fluorescence of phenolic compounds and modified humic acids by cadmium ions.

PubMed

Tchaikovskaya, O N; Nechaev, L V; Yudina, N V; Mal'tseva, E V

2016-08-01

The interaction of a number of phenolic compounds, being 'model fragments' of humic acids, with cadmium ions was investigated. The fluorescence quenching method was used to determine the complexation constants of these compounds with cadmium ions. It was established that bonding of phenolic compounds by cadmium ions at рН 7 is weak and reaches a maximum value of 15% for interaction with resorcinol. It was demonstrated that modification of humic acids by the mechanoactivation method increases by three times bonding of cadmium ions, which is caused by strengthening the acid properties of carboxyl and hydroxyl groups at the aromatic ring. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Investigation of the binding affinity in vitamin B12-Bovine serum albumin system using various spectroscopic methods

NASA Astrophysics Data System (ADS)

Makarska-Bialokoz, Magdalena

2017-09-01

The binding affinity between vitamin B12 (VitB12) and bovine serum albumin (BSA) has been investigated in aqueous solution at pH = 7.4, employing UV-vis absorption and steady-state, synchronous and three-dimensional fluorescence spectra techniques. Representative effects noted for BSA intrinsic fluorescence resulting from the interactions with VitB12 confirm the formation of π-π stacked non-covalent and non-fluorescent complexes in the system VitB12-BSA. All the determined parameters, the binding, fluorescence quenching and bimolecular quenching rate constants (of the order of 104 L mol- 1, 103 L mol- 1 and 1011 L mol- 1 s- 1, respectively), as well as Förster resonance energy transfer parameters validate the mechanism of static quenching. The interaction with VitB12 induces folding of the polypeptide chains around Trp residues of BSA, resulting in a more hydrophobic surrounding. Presented outcomes suggest that the addition of VitB12 can lead to the more organized BSA conformation and its more folded tertiary structure, what could influence the physiological functions of bovine serum albumin, notably in case of its overuse or abnormal metabolism.

In vitro study on binding interaction of quinapril with bovine serum albumin (BSA) using multi-spectroscopic and molecular docking methods.

PubMed

Shi, Jie-Hua; Pan, Dong-Qi; Jiang, Min; Liu, Ting-Ting; Wang, Qi

2017-08-01

The binding interaction between quinapril (QNPL) and bovine serum albumin (BSA) in vitro has been investigated using UV absorption spectroscopy, steady-state fluorescence spectroscopic, synchronous fluorescence spectroscopy, 3D fluorescence spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and molecular docking methods for obtaining the binding information of QNPL with BSA. The experimental results confirm that the quenching mechanism of the intrinsic fluorescence of BSA induced by QNPL is static quenching based on the decrease in the quenching constants of BSA in the presence of QNPL with the increase in temperature and the quenching rates of BSA larger than 10 10  L mol -1  s -1 , indicating forming QNPL-BSA complex through the intermolecular binding interaction. The binding constant for the QNPL-BSA complex is in the order of 10 5  M -1 , indicating there is stronger binding interaction of QNPL with BSA. The analysis of thermodynamic parameters together with molecular docking study reveal that the main binding forces in the binding process of QNPL with BSA are van der Waal's forces and hydrogen bonding interaction. And, the binding interaction of BSA with QNPL is an enthalpy-driven process. Based on Förster resonance energy transfer, the binding distance between QNPL and BSA is calculated to be 2.76 nm. The results of the competitive binding experiments and molecular docking confirm that QNPL binds to sub-domain IIA (site I) of BSA. It is confirmed there is a slight change in the conformation of BSA after binding QNPL, but BSA still retains its secondary structure α-helicity.

Chiral recognition of naproxen enantiomers based on fluorescence quenching of bovine serum albumin-stabilized gold nanoclusters

NASA Astrophysics Data System (ADS)

Jafari, Marzieh; Tashkhourian, Javad; Absalan, Ghodratollah

2017-10-01

A simple, fast and green method for chiral recognition of S- and R-naproxen has been introduced. The method was based on quenching of the fluorescence intensity of bovine serum albumin-stabilized gold nanoclusters in the presence of naproxen enantiomers. The quenching intensity in the presence of S-naproxen was higher than R-naproxen when phosphate buffer solution at pH 7.0 was used. The chiral recognition occurred due to steric effect between bovine serum albumin conformation and naproxen enantiomers. Two linear determination range were established as 7.4 × 10-7-9.1 × 10-6 and 9.1 × 10-6-3.1 × 10-5 mol L-1 for both enantiomers and detection limits of 7.4 × 10-8 mol L- 1 and 9.5 × 10-8 mol L-1 were obtained for S- and R-naproxen, respectively. The developed method showed good repeatability and reproducibility for the analysis of a synthetic sample. To make the procedure applicable to biological samples, the removal of heavy metals from the sample is suggested before any analytical attempt.

Investigation of trypsin-CdSe quantum dot interactions via spectroscopic methods and effects on enzymatic activity.

PubMed

Kaur, Gurvir; Tripathi, S K

2015-01-05

The paper presents the interactions between trypsin and water soluble cadmium selenide (CdSe) quantum dots investigated by spectrophotometric methods. CdSe quantum dots have strong ability to quench the intrinsic fluorescence of trypsin by a static quenching mechanism. The quenching has been studied at three different temperatures where the results revealed that electrostatic interactions exist between CdSe quantum dots and trypsin and are responsible to stabilize the complex. The Scatchard plot from quenching revealed 1 binding site for quantum dots by trypsin, the same has been confirmed by making isothermal titrations of quantum dots against trypsin. The distance between donor and acceptor for trypsin-CdSe quantum dot complexes is calculated to be 2.8 nm by energy transfer mechanisms. The intrinsic fluorescence of CdSe quantum dots has also been enhanced by the trypsin, and is linear for concentration of trypsin ranging 1-80 μl. All the observations evidence the formation of trypsin-CdSe quantum dot conjugates, where trypsin retains the enzymatic activity which in turn is temperature and pH dependent. Copyright © 2014 Elsevier B.V. All rights reserved.

Fluorometric immunoassay for human serum albumin based on its inhibitory effect on the immunoaggregation of quantum dots with silver nanoparticles

NASA Astrophysics Data System (ADS)

Marukhyan, Seda S.; Gasparyan, Vardan K.

2017-02-01

Quantitative determination of HSA was conducted by competitive immunoassay. Inhibition of aggregation of antibody conjugated quantum dots (QD) with albumin conjugated silver nanoparticles (AgNPs) in the presence of HSA was conducted. If antibody-loaded CdSe QDs aggregate with HSA-coated silver nanoparticles the distance between the two kinds of nanoparticles will be reduced enough to cause fluorescence resonance energy transfer (FRET). In this case the yellow fluorescence of the Ab-QDs is quenched. However if HSA (antigen) is added to the Ab-QDs their surface will be blocked and they cannot aggregate any longer with the HSA-AgNPs. Hence, fluorescence will not be quenched. The drop of the intensity of fluorescence (peaking at 570 nm) is inversely correlated with the concentration of HSA in the sample. The method allows to determine HSA in the 30-600 ng·mL-1 concentration range.

Multi-Phenotypic subtyping of circulating tumor cells using sequential fluorescent quenching and restaining

NASA Astrophysics Data System (ADS)

Adams, Daniel L.; Alpaugh, R. Katherine; Tsai, Susan; Tang, Cha-Mei; Stefansson, Steingrimur

2016-09-01

In tissue biopsies formalin fixed paraffin embedded cancer blocks are micro-sectioned producing multiple semi-identical specimens which are analyzed and subtyped proteomically, and genomically, with numerous biomarkers. In blood based biopsies (BBBs), blood is purified for circulating tumor cells (CTCs) and clinical utility is typically limited to cell enumeration, as only 2-3 positive fluorescent markers and 1 negative marker can be used. As such, increasing the number of subtyping biomarkers on each individual CTC could dramatically enhance the clinical utility of BBBs, allowing in depth interrogation of clinically relevant CTCs. We describe a simple and inexpensive method for quenching the specific fluors of fluorescently stained CTCs followed by sequential restaining with additional biomarkers. As proof of principle a CTC panel, immunosuppression panel and stem cell panel were used to sequentially subtype individual fluorescently stained patient CTCs, suggesting a simple and universal technique to analyze multiple clinically applicable immunomarkers from BBBs.

Enzyme-catalyzed Michael addition for the synthesis of warfarin and its determination via fluorescence quenching of L-tryptophan

NASA Astrophysics Data System (ADS)

Yuan, Yusheng; Yang, Liu; Liu, Shaopu; Yang, Jidong; Zhang, Hui; Yan, Jingjing; Hu, Xiaoli

2017-04-01

A sensitive fluorescence sensor for warfarin was proposed via quenching the fluorescence of L-tryptophan due to the interaction between warfarin and L-tryptophan. Warfarin, as one of the most effective anticoagulants, was designed and synthesized via lipase from porcine pancreas (PPL) as a biocatalyst to catalyze the Michael addition of 4-hydroxycoumarin to α, β-unsaturated enones in organic medium in the presence of water. Furthermore, the spectrofluorometry was used to detect the concentration of warfarin with a linear range and detection limit (3σ/k) of 0.04-12.0 μmol L- 1 (R2 = 0.994) and 0.01 μmol L- 1, respectively. Herein, this was the first application of bio-catalytic synthesis and fluorescence for the determination of warfarin. The proposed method was applied to determine warfarin of the drug in tablets with satisfactory results.

Extended Fluorescent Resonant Energy Transfer in DNA Constructs

NASA Astrophysics Data System (ADS)

Oh, Taeseok

This study investigates the use of surfactants and metal cations for the enhancement of long range fluorescent resonant energy transfer (FRET) and the antenna effect in DNA structures with multiple fluorescent dyes. Double-stranded (ds) DNA structures were formed by hybridization of 21mer DNA oligonucleotides with different arrangements of three fluorescent TAMRA donor dyes with two different complementary 21mer oligonucleotides with one fluorescent TexasRed acceptor dye. In such DNA structures, hydrophobic interactions between the fluorescent dyes in close proximity produces dimerization which along with other quenching mechanisms leads to significant reduction of fluorescent emission properties. Addition of the surfactants Triton X-100, cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) along with sodium cations (Na+) and divalent magnesium cations (Mg 2+) were tested for their ability to reduce quenching of the fluorescent dyes and improve overall fluorescent emission, the long range FRET and the antenna effect properties. When the neutral (uncharged) surfactant Triton X-100 was added to the FRET ds-DNA hybrid structures with three TAMRA donors and one TexasRed acceptor, dye dimerization and emission quenching remained unaffected. However, for the positively charged CTAB surfactant at concentrations of 100 uM or higher, the neutralization of the negatively charged ds-DNA backbone by the cationic surfactant micelles was found to reduce TAMRA dye dimerization and emission quenching and improve TexasRed quantum yield, resulting in much higher FRET efficiencies and an enhanced antenna effect. This improvement is likely due to the CTAB molecules covering or sheathing the fluorescent donor and acceptor dyes which breaks up the dimerized dye complexes and prevents further quenching from interactions with water molecules and guanine bases in the DNA structure. While the negatively charged SDS surfactant alone was not able to reduce dimerization and emission quenching due to repulsive forces between DNA and SDS micelles, the addition of cations such as sodium ions (Na+) and divalent magnesium ions (Mg2+) did lead to a significant reduction in the dimerization and emission quenching resulting in much higher FRET efficiency and an enhanced antenna effect. It appears that when the repulsive electrostatic forces are screened by the cations (Mg2+ in particular), the SDS micelles can approach the FRET ds-DNA structures thereby sheathing or insulating the TAMRA and TexasRed dyes. Overall, the study provides a viable strategy for using combinations of surfactants and cations to reduce adverse fluorescent dye and other quenching mechanisms and improve the overall long distance FRET efficiency and the antenna effect in DNA structures with multi-donor and single acceptor fluorescent dye groups.

Complete suppression of the fluorophore fluorescence by combined effect of multiple fluorescence quenching groups: A fluorescent sensor for Cu²⁺ with zero background signals.

PubMed

Long, Lingliang; Wu, Yanjun; Wang, Lin; Gong, Aihua; Hu, Rongfeng; Zhang, Chi

2016-02-18

The reaction-based fluorescent sensors have attracted increasing attention in the past decades. However, the application of these sensors for accurate sensing was significantly retarded by the background fluorescence from the sensors themselves. In this work, we demonstrated a novel strategy that the background fluorescence of the sensor could be completely eliminated by the combined effect of multiple fluorescence quenching groups. Based on this new strategy, as proof-of-principle study, a fluorescent sensor (CuFS) for Cu(2+) was judiciously developed. In CuFS, three types of fluorescence quenching groups were directly tethered to a commonly used coumarin fluorophore. The fluorescence of coumarin fluorophore in CuFS was completely suppressed by the combined effect of these fluorescence quenching groups. Upon treatment with 22 μM Cu(2+), sensor CuFS achieved a dramatic fluorescence enhancement (fluorescence intensity enhanced up to 811-fold) centered at 469 nm. The detection limits was determined to be 12.3 nM. The fluorescence intensity enhancement also showed a good linearity with the Cu(2+) concentration in the range of 12.3 nM to 2 μM. By fabricating test strips, sensor CuFS can be utilized as a simple tool to detect Cu(2+) in water samples. Furthermore, the fluorescent sensor was successfully applied in detecting different concentration of Cu(2+) in living cells. Copyright © 2015 Elsevier B.V. All rights reserved.

A Graphene Oxide-Based Fluorescent Aptasensor for the Turn-on Detection of CCRF-CEM.

PubMed

Tan, Jie; Lai, Zongqiang; Zhong, Liping; Zhang, Zhenghua; Zheng, Rong; Su, Jing; Huang, Yong; Huang, Panpan; Song, Hui; Yang, Nuo; Zhou, Sufang; Zhao, Yongxiang

2018-04-01

A convenient, low-cost, and highly sensitive fluorescent aptasensor for detection of leukemia has been developed based on graphene oxide-aptamer complex (GO-apt). Graphene oxide (GO) can absorb carboxyfluorescein-labeled Sgc8 aptamer (FAM-apt) by π-π stacking and quench the fluorescence through fluorescence resonance energy transfer (FRET). In the absence of Sgc8 target cell CCRF-CEM, the fluorescence is almost all quenched. Conversely, when the CCRF-CEM cells are added, the quenched fluorescence can be recovered rapidly and significantly. Therefore, based on the change of fluorescence signals, we can detect the number of CCRF-CEM cells in a wide range from 1 × 10 2 to 1 × 10 7  cells/mL with a limit of detection (LOD) of 10 cells/mL. Therefore, this strategy of graphene oxide-based fluorescent aptasensor may be promising for the detection of cancer.

Suppression of Red Blood Cell Autofluorescence for Immunocytochemistry on Fixed Embryonic Mouse Tissue.

PubMed

Whittington, Niteace C; Wray, Susan

2017-10-23

Autofluorescence is a problem that interferes with immunofluorescent staining and complicates data analysis. Throughout the mouse embryo, red blood cells naturally fluoresce across multiple wavelengths, spanning the emission and excitation spectra of many commonly used fluorescent reporters, including antibodies, dyes, stains, probes, and transgenic proteins, making it difficult to distinguish assay fluorescence from endogenous fluorescence. Several tissue treatment methods have been developed to bypass this issue with varying degrees of success. Sudan Black B dye has been commonly used to quench autofluorescence, but can also introduce background fluorescence. Here we present a protocol for an alternative called TrueBlack Lipofuscin Autofluorescence Quencher. The protocol described in this unit demonstrates how TrueBlack efficiently quenches red blood cell autofluorescence across red and green wavelengths in fixed embryonic tissue without interfering with immunofluorescent signal intensity or introducing background staining. We also identify optimal incubation, concentration, and multiple usage conditions for routine immunofluorescence microscopy. © 2017 by John Wiley & Sons, Inc. Copyright © 2017 John Wiley & Sons, Inc.

Liposomal encapsulation of a near-infrared fluorophore enhances fluorescence quenching and reliable whole body optical imaging upon activation in vivo.

PubMed

Tansi, Felista L; Rüger, Ronny; Rabenhold, Markus; Steiniger, Frank; Fahr, Alfred; Kaiser, Werner A; Hilger, Ingrid

2013-11-11

In the past decade, there has been significant progress in the development of water soluble near-infrared fluorochromes for use in a wide range of imaging applications. Fluorochromes with high photo and thermal stability, sensitivity, adequate pharmacological properties and absorption/emission maxima within the near infrared window (650-900 nm) are highly desired for in vivo imaging, since biological tissues show very low absorption and auto-fluorescence at this spectrum window. Taking these properties into consideration, a myriad of promising near infrared fluorescent probes has been developed recently. However, a hallmark of most of these probes is a rapid clearance in vivo, which hampers their application. It is hypothesized that encapsulation of the near infrared fluorescent dye DY-676-COOH, which undergoes fluorescence quenching at high concentrations, in the aqueous interior of liposomes will result in protection and fluorescence quenching, which upon degradation by phagocytes in vivo will lead to fluorescence activation and enable imaging of inflammation. Liposomes prepared with high concentrations of DY-676-COOH reveal strong fluorescence quenching. It is demonstrated that the non-targeted PEGylated fluorescence-activatable liposomes are taken up predominantly by phagocytosis and degraded in lysosomes. Furthermore, in zymosan-induced edema models in mice, the liposomes are taken up by monocytes and macrophages which migrate to the sites of inflammation. Opposed to free DY-676-COOH, prolonged stability and retention of liposomal-DY-676-COOH is reflected in a significant increase in fluorescence intensity of edema. Thus, protected delivery and fluorescence quenching make the DY-676-COOH-loaded liposomes a highly promising contrast agent for in vivo optical imaging of inflammatory diseases. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carbon-Dots-Based Lab-On-a-Nanoparticle Approach for the Detection and Differentiation of Antibiotics.

PubMed

Qiao, Li'na; Qian, Sihua; Wang, Yuhui; Yan, Shifeng; Lin, Hengwei

2018-03-26

Fluorescent carbon dots (CDs) have received considerable attention in recent years due to their superior optical properties. To take further advantages of these unique features, herein, a CDs-based "lab-on-a-nanoparticle" approach for the detection and discrimination of antibiotics is developed. The sensing platform was designed based on the different channel's fluorescence recoveries or further quenching of the full-color emissive CDs (F-CDs) and metal ion ensembles upon the addition of antibiotics. The F-CDs exhibited unusually comparable emission intensity nearly across the entire visible spectrum even as the excitation wavelength is shifted, making it very suitable for the construction of multi-channel sensing systems. The sensing platform was fabricated on the basis of the competing interaction of metal ions with the F-CDs and antibiotics. Three metal ions (i.e., Cu 2+ , Ce 3+ and Eu 3+ ) can efficiently quench the fluorescence of the F-CDs. Upon the addition of antibiotics, the fluorescent intensities either recovered at different emission wavelengths or were further quenched to various degrees. The fluorescence response patterns at different emission wavelength were characteristic for each antibiotic and can be quantitatively differentiated by standard statistical methods (e.g., hierarchical clustering analysis and principal component analysis). Moreover, as an example, the proposed method was applied for quantitative detection of oxytetracycline with a limit of detection to be 0.06 μm. Finally, the sensing system was successfully employed for residual antibiotics detection and identification in real food samples. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Trace Hg2+ analysis via quenching of the fluorescence of a CdS-encapsulated DNA nanocomposite.

PubMed

Long, Yunfei; Jiang, Dianlu; Zhu, Xu; Wang, Jianxiu; Zhou, Feimeng

2009-04-01

A novel fluorescent CdS-encapsulated DNA nanocomposite was synthesized via alternate adsorption of Cd(2+) and S(2-) onto the DNA template affixed inside an agarose gel. Confining DNA molecules in the gel matrix reduces the flexibility of the DNA strand, which facilitates the formation of a uniform coating of CdS onto the DNA template. The resultant rod-shaped nanocomposite (40-90 nm in width and 200-300 nm in length) is well dispersed in solution and fluoresces at 330 nm upon excitation at either 228 or 280 nm. The fluorescence is attributed to tiny particles present in the CdS coating. It was found that the fluorescence can be significantly quenched by trace amount of Hg(2+). The high selectivity toward Hg(2+) and the apparent change in the CdS coating upon exposure to Hg(2+) indicate that Hg(2+) has reacted with the CdS coating through formation of the much more insoluble HgS and the bridging S-Hg-S bonds at the surface. The extent of quenching is dependent on the concentration of Hg(2+) in the range of 0.04-13 microM, and a remarkable detection limit (8.6 nM at 30 degrees C and 4.3 nM at 50 degrees C) can be achieved. The feasibility of the method for the analysis of Hg(2+) in a wastewater sample was demonstrated with an excellent relative standard deviation (RSD, 3.4%). The method described herein is simple, selective, and sensitive and obviates the need of extensive sample pretreatment or special instrumentation.

Conjugated polymer nanoparticles-based fluorescent biosensor for ultrasensitive detection of hydroquinone.

PubMed

Liu, Yuan; Wang, Yu-Min; Zhu, Wu-Yang; Zhang, Chong-Hua; Tang, Hao; Jiang, Jian-Hui

2018-07-05

This work describes a simple and sensitive fluorescent method for detection of hydroquinone utilizing conjugated polymer nanoparticles (CPNs). The CPNs serve both as a catalyst to accelerate the conversion of hydroquinone to benzoquinone and a fluorescent probe. In the presence of hydroquinone, the fluorescence of CPNs can be effectively quenched by benzoquinone. The detection limit of hydroquinone was down to 5 nM and excellent selectivity toward possible interferences was obtained. This method was successfully applied for hydroquinone detection in lake water and satisfactory results were achieved. Copyright © 2018 Elsevier B.V. All rights reserved.

[Determination of iron(III) in Chinese herbal medicine and tea based on fluorescence quenching of 2,4-dichro-phenylfluorone].

PubMed

Dai, Gang; Aodeng, Gao-wa

2004-07-01

A new spectrofluorimetric method for the determination of trace amount of Fe(III) has been developed. This method is based on the fluorescence quenching of 2,4-dichro-phenylfluorone due to the formation of complex Fe(III)-DCIPF. In pH 5.2-5.9 buffer solution, Fe (III) and DCIPF react on each other to form a red complex. Its composition was established by method of continuous variations and molar-ratio as Fe(III): DCIPF = 1:4, the excitation and emission wavelengths were found to be 282 and 560 nm, respectively. There is a linear relationship in the range 4-24 ng x mL(-1) for Fe(III). This method is simple and rapid, and has been applied to the determination of trace iron in Chinese herbal medicine and tea samples with satisfactory results.

Combined spectroscopies and molecular docking approach to characterizing the binding interaction of enalapril with bovine serum albumin.

PubMed

Pan, Dong-Qi; Jiang, Min; Liu, Ting-Ting; Wang, Qi; Shi, Jie-Hua

2017-06-01

The binding interaction between bovine serum albumin (BSA) and enalapril (ENPL) at the imitated physiological conditions (pH = 7.4) was investigated using UV-vis absorption spectroscopy (UV-vis), fluorescence emission spectroscopy (FES), synchronous fluorescence spectroscopy (SFS), Fourier transform infrared spectroscopy (FT-IR), circular dichroism (CD) and molecular docking methods. It can be deduced from the experimental results from the steady-state fluorescence spectroscopic titration that the intrinsic BSA fluorescence quenching mechanism induced by ENPL is static quenching, based on the decrease in the BSA quenching constants in the presence of ENPL with increase in temperature and BSA quenching rates >10 10  L mol -1  sec -1 . This result indicates that the ENPL-BSA complex is formed through an intermolecular interaction of ENPL with BSA. The main bonding forces for interaction of BSA and ENPL are van der Waal's forces and hydrogen bonding interaction based on negative values of Gibbs free energy change (ΔG 0 ), enthalpic change (ΔH 0 ) and entropic change (ΔS 0 ). The binding of ENPL with BSA is an enthalpy-driven process due to |ΔH°| > |TΔS°| in the binding process. The results of competitive binding experiments and molecular docking confirm that ENPL binds in BSA sub-domain IIA (site I) and results in a slight change in BSA conformation, but BSA still retains its α-helical secondary structure. Copyright © 2016 John Wiley & Sons, Ltd.

Study of fluorescence quenching of Barley α-amylase

NASA Astrophysics Data System (ADS)

Bakkialakshmi, S.; Shanthi, B.; Bhuvanapriya, T.

2012-05-01

The fluorescence quenching of Barley α-amylase by acrylamide and succinimide has been studied in water using steady-state and time-resolved fluorescence techniques. The steady-state fluorescence quenching technique has been performed in three different pHs (i.e., 6, 7 and 8) of water. Ground state and excited state binding constants (Kg &Ke) have been calculated. From the calculated binding constants (Kg &Ke) the free energy changes for the ground (ΔGg) and excited (ΔGe) states have been calculated and are presented in tables. UV and FTIR spectra have also been recorded to prove the binding of Barley α-amylase with acrylamide and succinimide.

Exciplexes and conical intersections lead to fluorescence quenching in π-stacked dimers of 2-aminopurine with natural purine nucleobases†

PubMed Central

Liang, JingXin; Nguyen, Quynh L.; Matsika, Spiridoula

2016-01-01

Fluorescent analogues of the natural DNA bases are useful in the study of nucleic acids’ structure and dynamics. 2-Aminopurine (2AP) is a widely used analogue with environmentally sensitive fluorescence behavior. The quantum yield of 2AP has been found to be significantly decreased when engaged in π-stacking interactions with the native bases. We present a theoretical study on fluorescence quenching mechanisms in dimers of 2AP π-stacked with adenine or guanine as in natural DNA. Relaxation pathways on the potential energy surfaces of the first excited states have been computed and reveal the importance of exciplexes and conical intersections in the fluorescence quenching process. PMID:23625036

Determination of berberine and the study of fluorescence quenching mechanism between berberine and enzyme-catalyzed product

NASA Astrophysics Data System (ADS)

Wang, Huaiyou; Zhang, Miao; Lv, Qingluan; Yue, Ningning; Gong, Bin

2009-08-01

A new method for determining berberine has been established based on the principle of fluorescence quenching. The calibration curve was found to be linear between F0/ F and the concentration of berberine with the range of 3.00-20.0 μg mL -1. The detection limit was 0.51 μg mL -1 and the relative standard derivative was 0.18%. Effects of pH, foreign ions and the optimization of variables on the determination of berberine have been examined. The mechanism of the fluorescence quenching has been discussed. The binding constant and the number of binding sites were 1.70 × 10 6 L mol -1 and 1.14, respectively. The data, Δ H = 42.71 kJ mol -1, Δ S = 264.3 J K -1 mol -1 and the mean value Δ G = -39.65 kJ mol -1 were estimated which showed that the reaction was spontaneous and endothermic. The main binding force was hydrophobic force because both Δ H and Δ S were positive.

Detection of Thrombin Based on Fluorescence Energy Transfer between Semiconducting Polymer Dots and BHQ-Labelled Aptamers.

PubMed

Liu, Yizhang; Jiang, Xuekai; Cao, Wenfeng; Sun, Junyong; Gao, Feng

2018-02-14

Carboxyl-functionalized semiconducting polymer dots (Pdots) were synthesized as an energy donor by the nanoprecipitation method. A black hole quenching dye (BHQ-labelled thrombin aptamers) was used as the energy acceptor, and fluorescence resonance energy transfer between the aptamers and Pdots was used for fluorescence quenching of the Pdots. The addition of thrombin restored the fluorescence intensity. Under the optimized experimental conditions, the fluorescence of the system was restored to the maximum when the concentration of thrombin reached 130 nM, with a linear range of 0-50 nM (R² = 0.990) and a detection limit of 0.33 nM. This sensor was less disturbed by impurities, showing good specificity and signal response to thrombin, with good application in actual samples. The detection of human serum showed good linearity in the range of 0-30 nM (R² = 0.997), with a detection limit of 0.56 nM and a recovery rate of 96.2-104.1%, indicating that this fluorescence sensor can be used for the detection of thrombin content in human serum.

Combining Graphical and Analytical Methods with Molecular Simulations To Analyze Time-Resolved FRET Measurements of Labeled Macromolecules Accurately

PubMed Central

2017-01-01

Förster resonance energy transfer (FRET) measurements from a donor, D, to an acceptor, A, fluorophore are frequently used in vitro and in live cells to reveal information on the structure and dynamics of DA labeled macromolecules. Accurate descriptions of FRET measurements by molecular models are complicated because the fluorophores are usually coupled to the macromolecule via flexible long linkers allowing for diffusional exchange between multiple states with different fluorescence properties caused by distinct environmental quenching, dye mobilities, and variable DA distances. It is often assumed for the analysis of fluorescence intensity decays that DA distances and D quenching are uncorrelated (homogeneous quenching by FRET) and that the exchange between distinct fluorophore states is slow (quasistatic). This allows us to introduce the FRET-induced donor decay, εD(t), a function solely depending on the species fraction distribution of the rate constants of energy transfer by FRET, for a convenient joint analysis of fluorescence decays of FRET and reference samples by integrated graphical and analytical procedures. Additionally, we developed a simulation toolkit to model dye diffusion, fluorescence quenching by the protein surface, and FRET. A benchmark study with simulated fluorescence decays of 500 protein structures demonstrates that the quasistatic homogeneous model works very well and recovers for single conformations the average DA distances with an accuracy of < 2%. For more complex cases, where proteins adopt multiple conformations with significantly different dye environments (heterogeneous case), we introduce a general analysis framework and evaluate its power in resolving heterogeneities in DA distances. The developed fast simulation methods, relying on Brownian dynamics of a coarse-grained dye in its sterically accessible volume, allow us to incorporate structural information in the decay analysis for heterogeneous cases by relating dye states with protein conformations to pave the way for fluorescence and FRET-based dynamic structural biology. Finally, we present theories and simulations to assess the accuracy and precision of steady-state and time-resolved FRET measurements in resolving DA distances on the single-molecule and ensemble level and provide a rigorous framework for estimating approximation, systematic, and statistical errors. PMID:28709377

Investigating structure-property relationships of biomineralized calcium phosphate compounds as fluorescent quenching-recovery platform

NASA Astrophysics Data System (ADS)

Wang, Liuzheng; He, Xiang; Zhang, Wei; Liu, Yong; Banks, Craig E.; Zhang, Ying

2018-02-01

The structure-property relationship between biomineralized calcium phosphate compounds upon a fluorescent quenching-recovery platform and their distinct crystalline structure and surficial functional groups are investigated. A fluorescence-based sensing platform is shown to be viable for the sensing of 8-hydroxy-2-deoxy-guanosine in simulated systems.

Ensemble and Single-Molecule Studies on Fluorescence Quenching in Transition Metal Bipyridine-Complexes

PubMed Central

Brox, Dominik; Kiel, Alexander; Wörner, Svenja Johanna; Pernpointner, Markus; Comba, Peter; Martin, Bodo; Herten, Dirk-Peter

2013-01-01

Beyond their use in analytical chemistry fluorescent probes continuously gain importance because of recent applications of single-molecule fluorescence spectroscopy to monitor elementary reaction steps. In this context, we characterized quenching of a fluorescent probe by different metal ions with fluorescence spectroscopy in the bulk and at the single-molecule level. We apply a quantitative model to explain deviations from existing standard models for fluorescence quenching. The model is based on a reversible transition from a bright to a dim state upon binding of the metal ion. We use the model to estimate the stability constants of complexes with different metal ions and the change of the relative quantum yield of different reporter dye labels. We found ensemble data to agree widely with results from single-molecule experiments. Our data indicates a mechanism involving close molecular contact of dye and quenching moiety which we also found in molecular dynamics simulations. We close the manuscript with a discussion of possible mechanisms based on Förster distances and electrochemical potentials which renders photo-induced electron transfer to be more likely than Förster resonance energy transfer. PMID:23483966

Chemical reactivation of fluorescein isothiocyanate immunofluorescence-labeled resin-embedded samples

NASA Astrophysics Data System (ADS)

Li, Longhui; Rao, Gong; Lv, Xiaohua; Chen, Ruixi; Cheng, Xiaofeng; Wang, Xiaojun; Zeng, Shaoqun; Liu, Xiuli

2018-02-01

Resin embedding is widely used and facilitates microscopic imaging of biological tissues. In contrast, quenching of fluorescence during embedding process hinders the application of resin embedding for imaging of fluorescence-labeled samples. For samples expressing fluorescent proteins, it has been demonstrated that the weakened fluorescence could be recovered by reactivating the fluorophore with alkaline buffer. We extended this idea to immunofluorescence-labeling technology. We showed that the fluorescence of pH-sensitive fluorescein isothiocyanate (FITC) was quenched after resin embedding but reactivated after treating by alkaline buffer. We observed 138.5% fluorescence preservation ratio of reactivated state, sixfold compared with the quenched state in embedding resin, which indicated its application for fluorescence imaging of high signal-to-background ratio. Furthermore, we analyzed the chemical reactivation mechanism of FITC fluorophore. This work would show a way for high-resolution imaging of immunofluorescence-labeled samples embedded in resin.

Azide–Alkyne Click Conjugation on Quantum Dots by Selective Copper Coordination

PubMed Central

Mann, Victor R.; Powers, Alexander S.; Tilley, Drew C.; Sack, Jon T.; Cohen, Bruce E.

2018-01-01

Functionalization of nanocrystals is essential for their practical application, but synthesis on nanocrystal surfaces is limited by incompatibilities with certain key reagents. The copper-catalyzed azide-alkyne cycloaddition (CuAAC) is among the most useful methods for ligating molecules to surfaces, but has been largely useless for semiconductor quantum dots (QDs) because Cu+ ions quickly and irreversibly quench QD fluorescence. To discover non-quenching synthetic conditions for Cu-catalyzed click reactions on QD surfaces, we developed a combinatorial fluorescence assay to screen >2000 reaction conditions to maximize cycloaddition efficiency while minimizing QD quenching. We identify conditions for complete coupling without significant quenching, which are compatible with common QD polymer surfaces and various azide/alkyne pairs. Based on insight from the combinatorial screen and mechanistic studies of Cu coordination and quenching, we find that superstoichiometric concentrations of Cu can promote full coupling if accompanied by ligands that selectively compete the Cu from the QD surface but allow it to remain catalytically active. Applied to the conjugation of a K+ channel-specific peptidyl toxin to CdSe/ZnS QDs, we synthesize unquenched QD conjugates and image their specific and voltage-dependent affinity for K+ channels in live cells. PMID:29608274

Effect of the Semiconductor Quantum Dot Shell Structure on Fluorescence Quenching by Acridine Ligand

NASA Astrophysics Data System (ADS)

Linkov, P. A.; Vokhmintcev, K. V.; Samokhvalov, P. S.; Laronze-Cochard, M.; Sapi, J.; Nabiev, I. R.

2018-02-01

The main line of research in cancer treatment is the development of methods for early diagnosis and targeted drug delivery to cancer cells. Fluorescent semiconductor core/shell nanocrystals of quantum dots (e.g., CdSe/ZnS) conjugated with an anticancer drug, e.g., an acridine derivative, allow real-time tracking and control of the process of the drug delivery to tumors. However, linking of acridine derivatives to a quantum dot can be accompanied by quantum dot fluorescence quenching caused by electron transfer from the quantum dot to the organic molecule. In this work, it has been shown that the structure of the shell of the quantum dot plays the decisive role in the process of photoinduced charge transfer from the quantum dot to the acridine ligand, which is responsible for fluorescence quenching. It has been shown that multicomponent ZnS/CdS/ZnS shells of CdSe cores of quantum dots, which have a relatively small thickness, make it possible to significantly suppress a decrease in the quantum yield of fluorescence of quantum dots as compared to both the classical ZnS thin shell and superthick shells of the same composition. Thus, core/multicomponent shell CdSe/ZnS/CdS/ZnS quantum dots can be used as optimal fluorescent probes for the development of systems for diagnosis and treatment of cancer with the use of anticancer compounds based on acridine derivatives.

A graphene oxide-based fluorescent aptasensor for the turn-on detection of epithelial tumor marker mucin 1.

PubMed

He, Yue; Lin, Yi; Tang, Hongwu; Pang, Daiwen

2012-03-21

Mucin 1 (MUC1) which presents in epithelial malignancies, is a well-known tumor biomarker. In this paper, a highly sensitive and selective fluorescent aptasensor for Mucin 1 (MUC1) detection is constructed, utilizing graphene oxide (GO) as a quencher which can quench the fluorescence of single-stranded dye-labeled MUC1 specific aptamer. In the absence of MUC1, the adsorption of the dye-labeled aptamer on GO brings the dyes in close proximity to the GO surface resulting in high efficiency quenching of dye fluorescence. Therefore, the fluorescence of the designed aptasensor is completely quenched by GO, and the system shows very low background fluorescence. Conversely, and very importantly, upon the adding of MUC1, the quenched fluorescence is recovered significantly, and MUC1 can be detected in a wide range of 0.04-10 μM with a detection limit of 28 nM and good selectivity. Moreover, the results have also been verified for real sample application by testing 2% serum containing buffer solution spiked with a series of concentrations of MUC1. This journal is © The Royal Society of Chemistry 2012

Study on interaction between curcumin and pepsin by spectroscopic and docking methods.

PubMed

Ying, Ming; Huang, Fengwen; Ye, Haidong; Xu, Hong; Shen, Liangliang; Huan, Tianwen; Huang, Shitong; Xie, Jiangfeng; Tian, Shengli; Hu, Zhangli; He, Zhendan; Lu, Jun; Zhou, Kai

2015-08-01

The interaction between curcumin and pepsin was investigated by fluorescence, synchronous fluorescence, UV-vis absorption, circular dichroism (CD), and molecular docking. Under physiological pH value in stomach, the fluorescence of pepsin can be quenched effectively by curcumin via a combined quenching process. Binding constant (Ka) and binding site number (n) of curcumin to pepsin were obtained. According to the theory of Förster's non-radiation energy transfer, the distance r between pepsin and curcumin was found to be 2.45 nm within the curcumin-pepsin complex, which implies that the energy transfer occurs between curcumin and pepsin, leading to the quenching of pepsin fluorescence. Fluorescence experiments also suggest that curcumin is located more closely to tryptophan residues than tyrosine residues. CD spectra together with UV-vis absorbance studies show that binding of curcumin to pepsin results in the extension of peptide strands of pepsin with loss of some β-sheet structures. Thermodynamic parameters calculated from the binding constants at different temperatures reveal that hydrophobic force plays a major role in stabilizing the curcumin-pepsin complex. In addition, docking results support the above experimental findings and suggest the possible hydrogen bonds of curcumin with Thr-77, Thr-218, and Glu-287 of pepsin, which help further stabilize the curcumin-pepsin complex. Copyright © 2015 Elsevier B.V. All rights reserved.

Self-organization, interfacial interaction and photophysical properties of gold nanoparticle complexes derived from resilin-mimetic fluorescent protein rec1-resilin.

PubMed

Mayavan, Sundar; Dutta, Naba K; Choudhury, Namita R; Kim, Misook; Elvin, Christopher M; Hill, Anita J

2011-04-01

In this investigation we report the synthesis of optically coupled hybrid architectures based on a new biomimetic fluorescent protein rec1-resilin and nanometer-scale gold nanoparticles (AuNPs) in a one-step method using a non-covalent mode of binding protocol. The presence of uniformly distributed fluorophore sequences, -Ser(Thr)-Tyr-Gly- along the molecular structure of rec1-resilin provides significant opportunity to synthesize fluorophore-modified AuNPs bioconjugates with unique photophysical properties. The detailed analyses of the AuNP-bioconjugates, synthesized under different experimental conditions using spectroscopic, microscopic and scattering techniques demonstrate the organizational pathways and the electronic and photophysical properties of the developed AuNP-rec1-resilin bioconjugates. The calculation of the bimolecular quenching constant using the Stern-Volmer equation confirms that the dominant mechanism involved in quenching of fluorescence of rec1-resilin in the presence of AuNP is static. Photoacoustic infrared spectroscopy was employed to understand the nature of the interfacial interaction between the AuNP and rec1-resilin and its evolution with pH. In such bioconjugates the quenched emission of fluorescence by AuNP on the fluorophore moiety of rec1-resilin in the immediate vicinity of the AuNP has significant potential for fluorescence-based detection schemes, sensors and also can be incorporated into nanoparticle-based devices. Copyright © 2011 Elsevier Ltd. All rights reserved.

Carbon dots as fluorescent probes for "off-on" detection of Cu2+ and L-cysteine in aqueous solution.

PubMed

Zong, Jie; Yang, Xiaoling; Trinchi, Adrian; Hardin, Simon; Cole, Ivan; Zhu, Yihua; Li, Chunzhong; Muster, Tim; Wei, Gang

2014-01-15

Copper ion (Cu(2+)) and L-cysteine (L-Cys) detection is critically important since an abnormal level of Cu(2+) or L-Cys is an indicator for many diseases. In this paper, we demonstrate an "off-on" approach for highly sensitive and selective detection of Cu(2+) and L-Cys using carbon dots (CDs) as fluorescent probes. CDs were prepared by using mesoporous silica (MS) spheres as nanoreactors. The binding ability of CDs towards metal ions was examined by comparing the fluorescence intensities of CDs before and after the addition of the metal ions. The addition of Cu(2+) cations leads to their absorption on the surface of CDs and the significant fluorescence quench of CDs (turn-off). The resulting in CDs-Cu(2+) system was found to be sensitive to L-Cys. The addition of L-Cys not only serves to shelter the CDs effectively from being quenched, but also to reverse the quenching and restore the fluorescence (turn-on) due to its ability to remove Cu(2+) from the surface of CDs. This method is facile, rapid, low cost, and environment-friendly. A detection limit as low as 2.3×10(-8) M for Cu(2+) and 3.4×10(-10) M for L-Cys is obtained, which is promising for biological applications. © 2013 Elsevier B.V. All rights reserved.

Fluorescence study on the interaction of human serum albumin with Butein in liposomes

NASA Astrophysics Data System (ADS)

Toprak, Mahmut

2016-02-01

The interaction of Butein with human serum albumin in L-egg lecithin phosphatidycholine (PC) liposome has been investigated by fluorescence and absorption spectroscopy. The results of the fluorescence measurement indicated that Butein effectively quenched the intrinsic fluorescence of HSA via static quenching. The Stern-Volmer plots in all the liposome solutions showed a positive deviation from the linearity. According to the thermodynamic parameters, the hydrophobic interactions appeared be the major interaction forces between Butein and HSA. The effect of Butein on the conformation of HSA was also investigated by the synchronous fluorescence under the same experimental conditions. In addition, the partition coefficient of the Butein in the PC liposomes was also determined by using the fluorescence quenching process. The obtained results can be of biological significance in pharmacology and clinical medicine.

Label-free turn-on fluorescent detection of melamine based on the anti-quenching ability of Hg 2+ to gold nanoclusters.

PubMed

Dai, Haichao; Shi, Yan; Wang, Yilin; Sun, Yujing; Hu, Jingting; Ni, Pengjuan; Li, Zhuang

2014-03-15

In this work, we proposed a facile, environmentally friendly and cost-effective assay for melamine with BSA-stabilized gold nanoclusters (AuNCs) as a fluorescence reader. Melamine, which has a multi-nitrogen heterocyclic ring, is prone to coordinate with Hg(2+). This property causes the anti-quenching ability of Hg(2+) to AuNCs through decreasing the metallophilic interaction between Hg(2+) and Au(+). By this method, detection limit down to 0.15 µM is obtained, which is approximately 130 times lower than that of the US food and Drug Administration estimated melamine safety limit of 20 µM. Furthermore, several real samples spiked with melamine, including raw milk and milk powder, are analyzed using the sensing system with excellent recoveries. This gold-nanocluster-based fluorescent method could find applications in highly sensitive detection of melamine in real samples. © 2013 Elsevier B.V. All rights reserved.

Quenching mechanism of Zn(salicylaldimine) by nitroaromatics.

PubMed

Germain, Meaghan E; Vargo, Thomas R; McClure, Beth Anne; Rack, Jeffrey J; Van Patten, P Gregory; Odoi, Michael; Knapp, Michael J

2008-07-21

Nitroaromatics and nitroalkanes quench the fluorescence of Zn(Salophen) (H2Salophen = N,N'-phenylene-bis-(3,5-di- tert-butylsalicylideneimine); ZnL(R)) complexes. A structurally related family of ZnL(R) complexes (R = OMe, di-tBu, tBu, Cl, NO2) were prepared, and the mechanisms of fluorescence quenching by nitroaromatics were studied by a combined kinetics and spectroscopic approach. The fluorescent quantum yields for ZnL(R) were generally high (Phi approximately 0.3) with sub-nanosecond fluorescence lifetimes. The fluorescence of ZnL(R) was quenched by nitroaromatic compounds by a mixture of static and dynamic pathways, reflecting the ZnL(R) ligand bulk and reduction potential. Steady-state Stern-Volmer plots were curved for ZnL(R) with less-bulky substituents (R = OMe, NO2), suggesting that both static and dynamic pathways were important for quenching. Transient Stern-Volmer data indicated that the dynamic pathway dominated quenching for ZnL(R) with bulky substituents (R = tBu, DtBu). The quenching rate constants with varied nitroaromatics (ArNO2) followed the driving force dependence predicted for bimolecular electron transfer: ZnL* + ArNO2 --> ZnL(+) + ArNO2(-). A treatment of the diffusion-corrected quenching rates with Marcus theory yielded a modest reorganization energy (lambda = 25 kcal/mol), and a small self-exchange reorganization energy for ZnL*/ZnL(+) (ca. 20 kcal/mol) was estimated from the Marcus cross-relation, suggesting that metal phenoxyls may be robust biological redox cofactors. Electronic structure calculations indicated very small changes in bond distances for the ZnL --> ZnL(+) oxidation, suggesting that solvation was the dominant contributor to the observed reorganization energy. These mechanistic insights provide information that will be helpful to further develop ZnL(R) as sensors, as well as for potential photoinduced charge transfer chemistry.

Magnetite nanoparticle-induced fluorescence quenching of adenosine triphosphate-BODIPY Conjugates: application to adenosine triphosphate and pyrophosphate sensing.

PubMed

Yu, Cheng-Ju; Wu, Su-Mei; Tseng, Wei-Lung

2013-09-17

We report that magnetite nanoparticles (Fe3O4 NPs) act as an efficient quencher for boron dipyrromethene-conjugated adenosine 5'-triphosphate (BODIPY-ATP) that is highly fluorescent in bulk solution. BODIPY-ATP molecules attached to the surface of Fe3O4 NPs through the coordination between the triphosphate group of BODIPY-ATP and Fe(3+)/Fe(2+) on the NP surface. The formed complexes induced an apparent reduction in the BODIPY-ATP fluorescence resulting from an oxidative-photoinduced electron transfer (PET) from the BODIPY-ATP excited state to an unfilled d shell of Fe(3+)/Fe(2+) on the NP surface. A comparison of the Stern-Volmer quenching constant between Fe(3+) and Fe(2+) suggests that Fe(3+) on the NP surface dominantly controls this quenching process. The efficiency for Fe3O4 NP-induced fluorescence quenching of the BODIPY-ATP was enhanced by increasing the concentration of Fe3O4 NPs and lowering the pH of the solution to below 6.0. We found that pyrophosphate and ATP compete with BODIPY-ATP for binding to Fe3O4 NPs. Thus, we amplified BODIPY-ATP fluorescence in the presence of increasing the pyrophosphate and ATP concentration; the detection limits at a signal-to-noise ratio of 3 for pyrophosphate and ATP were determined to be 7 and 30 nM, respectively. The Fe3O4 NP-based competitive binding assay detected ATP and pyrophosphate in only 5 min. The selectivity of this assay for ATP over metal ions, amino acids, and adenosine analogues is particularly high. The practicality of using the developed method to determine ATP in a single drop of blood is also validated.

Interactions between natural organic ligands and trace metals studied by fluorescence lifetime and fluorescence quenching

NASA Astrophysics Data System (ADS)

Nouhi, Ayoub; Hajjoul, Houssam; Redon, Roland; Gagné, Jean-Pierre; Mounier, Stéphane

2017-04-01

Improved insight on the interactions between natural organic ligands and trace metals is of paramount importance for better understanding transport and toxicity pathways of metal ions in the environment. Fluorescence spectroscopy allows introspecting ligands-metals interactions. Time-resolved laser fluorescence spectroscopy (TRLFS) measures fluorophore lifetime probing the local molecular environment. Excitation Emission Fluorescence Matrices (EEFMs) and their statistical treatment : parallel factor analysis (PARAFAC) using PROGMEEF Matlab homemade program, can give insight on the number or nature of organic fluorophores involved in the interactions. Quenching of fluorescence by metals can occur following two processes: dynamic and static quenching (Lakowicz, 2013). In the first case, quenching is caused by physical collisions among molecules and in the second case fluorophores can form nonfluorescent complexes with quenchers. It is possible to identify the different mechanisms because each type of quenching corresponds to a different mathematical model (Lakowicz, 2013; Valeur and Berberan-Santos, 2012). In TRLFS, the study of fluorescence decay's laws induced by nanosecond pulsed laser will allow to exactly qualify the type of interaction. The crucial point of the temporal deconvolution will be the evaluation of the best fitting between the different physical models and the decays measured. From the most suitable time decay model, it will be possible to deduce the quenching which modifies the fluorescence. The aim of this study was to characterize interactions between natural organic ligands and trace metals using fluorescence tools to evaluate the fluorescence lifetime of the fluorophore, the occurrence of quenching in presence of metal, discuss its mechanism and estimate conditional stability constants if a complex organic ligand-metal is formed. This study has been done in two steps. First, we have examined the interactions between salicylic acid and copper in order to calibrate our assays and compare our results with literature. Several studies have shown that static quenching occurs in that case (Brun and Schröder, 1975; Lavrik and Mulloev, 2010; Ventry et al., 1991; Babko, 1968). Indeed, after processing the EEFMs and TRLFS data, we found a fluorescence intensity decay by about 50% and a constant lifetime for the fluorophore suggesting a static quenching, in agreement with the literature. In the second step, we have studied the interactions between metal and different types of natural organic matters. In this case, EEMFs and TRLFS experiments were done on samples prepared by dissolving copper in four different fractions of organic matter extracted from estuarine water (St. Lawrence Estuary, Canada). Organic matter was obtained using DAX-8 and XAD-4 resins in series. Humic and fulvic acids are obtained following the IHSS protocol. The results of interaction between humic substances and copper gathered after processing data on PROGMEEF have shown a fluorescence intensity decay by about 57% for the first component and 88% for the second component. The fluorescence lifetime for both components were close to 2 ns and 6 ns respectively and the pH range was stable and close to 6. This means that a static quenching takes place in this case in agreement with the literature. Our study also focused on the investigation of complexation of organic matter by other metals in particular Aluminum, Arsenic, Europium and Uranium.

Direct determination of uranium in seawater by laser fluorimetry.

PubMed

Kumar, Sanjukta A; Shenoy, Niyoti S; Pandey, Shailaja; Sounderajan, Suvarna; Venkateswaran, G

2008-10-19

A method for estimation of uranium in seawater by using steady state laser flourimetry is described. Uranium present in seawater, in concentration of approximately 3 ng ml(-1) was estimated without prior separation of matrix. Quenching effect of major ions (Cl(-), Na(+), SO(4)(-), Mg(+), Ca(+), K(+), HCO(3)(-), Br(-)) present in seawater on fluorescence intensity of uranium was studied. The concentration of phosphoric acid required for maximum enhancement of fluorescence intensity was optimized and was found to be 5%. Similarly the volume of concentrated nitric acid required to eliminate the quenching effect of chloride and bromide completely from 5 ml of seawater were optimized and was found to be 3 ml. A simple equation was derived using steady state fluorescence correction method and was used for calculation of uranium concentration in seawater samples. The method has a precesion of 1% (1s, n=3). The values obtained from laser fluorimetry were validated by analyzing the same samples by linear sweep adsorptive stripping voltametry (LSASV) of the uranium-chloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone) complex. Both the values are well in agreement.

Highly Tunable Aptasensing Microarrays with Graphene Oxide Multilayers

NASA Astrophysics Data System (ADS)

Jung, Yun Kyung; Lee, Taemin; Shin, Eeseul; Kim, Byeong-Su

2013-11-01

A highly tunable layer-by-layer (LbL)-assembled graphene oxide (GO) array has been devised for high-throughput multiplex protein sensing. In this array, the fluorescence of different target-bound aptamers labeled with dye is efficiently quenched by GO through fluorescence resonance energy transfer (FRET), and simultaneous multiplex target detection is performed by recovering the quenched fluorescence caused by specific binding between an aptamer and a protein. Thin GO films consisting of 10 bilayers displayed a high quenching ability, yielding over 85% fluorescence quenching with the addition of a 2 μM dye-labeled aptamer. The limit for human thrombin detection in the 6- and 10-bilayered GO array is estimated to be 0.1 and 0.001 nM, respectively, indicating highly tunable nature of LbL assembled GO multilayers in controlling the sensitivity of graphene-based FRET aptasensor. Furthermore, the GO chip could be reused up to four times simply by cleaning it with distilled water.

Forster resonance energy transfer in the system of human serum albumin-xanthene dyes

NASA Astrophysics Data System (ADS)

Kochubey, V. I.; Pravdin, A. B.; Melnikov, A. G.; Konstantinova, I.; Alonova, I. V.

2016-04-01

The processes of interaction of fluorescent probes: eosin and erythrosine with human serum albumin (HSA) were studied by the methods of absorption and fluorescence spectroscopy. Extinction coefficients of probes were determined. Critical transfer radius and the energy transfer efficiency were defined by fluorescence quenching of HSA. Analysis of the excitation spectra of HSA revealed that the energy transfer process is carried out mainly between tryptophanyl and probes.

A novel immunoassay based on the dissociation of immunocomplex and fluorescence quenching by gold nanoparticles.

PubMed

Peng, Zhaofeng; Chen, Zhaopeng; Jiang, Jianhui; Zhang, Xiaobing; Shen, Guoli; Yu, Ruqin

2007-01-30

This study reports a novel, simple and sensitive immunoassay using fluorescence quenching caused by gold nanoparticles coated with antibody. The method is based on a non-competitive heterogeneous immunoassay of human IgG conducted by the typical procedure of sandwich immunocomplex formation. Goat anti-human IgG was first adsorbed on polystyrene microwells, and human IgG analyte was captured by the primary antibody and then sandwiched by antibody labeled with gold nanoparticles. The sandwich-type immunocomplex was subsequently dissociated by the mixed solution of sodium hydroxide and trisodium citrate, the solution obtained, which contains gold nanoparticles coated with antibody, was used to quench fluorescence. The fluorescence intensity of fluorescein at 517 nm was inversely proportional to the logarithm of the concentration of human IgG in the dynamic range of 10-5000 ng mL(-1) with a detection limit of 4.7 ng mL(-1). The electrochemical experiments and the UV-vis measurements were applied to demonstrate whether the immunogold was dissociated completely and whether the gold nanoparticles aggregated after being dissociated, respectively. The proposed system can be extended to detect target molecules such as other kinds of antigen and DNA strands, and has broad potential applications in disease diagnosis.

[Effect of quantum dots CdSe/ZnS's concentration on its fluorescence].

PubMed

Jin, Min; Huang, Yu-hua; Luo, Ji-xiang

2015-02-01

The authors measured the absorption and the fluorescence spectra of the quantum dots CdSe/ZnS with 4 nm in size at different concentration with the use of the UV-Vis absorption spectroscopy and fluorescence spectrometer. The effect of quantum dots CdSe/ZnS's concentration on its fluorescence was especially studied and its physical mechanism was analyzed. It was observed that the optimal concentration of the quantum dots CdSe/ZnS for fluorescence is 2 micromole x L(-1). When the quantum dot's concentration is over 2 micromol x L(-1), the fluorescence is decreased with the increase in the concentration. While the quantum dot's concentration is less than 2 micromol x L(-1), the fluorescence is decreased with the decrease in the concentration. There are two main reasons: (1) fluorescence quenching and 2) the competition between absorption and fluorescence. When the quantum dot's concentration is over 2 micromol x L(-1), the distance between quantum dots is so close that the fluorescence quenching is induced. The closer the distance between quantum dots is, the more serious the fluorescence quenching is induced. Also, in this case, the absorption is so large that some of the quantum dots can not be excited because the incident light can not pass through the whole sample. As a result, the fluorescence is decreased with the increase in the quantum dot's concentration. As the quantum dot's concentration is below 2 micromol x L(-1), the distance between quantum dots is far enough that no more fluorescence quenching is induced. In this case, the fluorescence is determined by the particle number per unit volume. More particle number per unit volume produces more fluorescence. Therefore, the fluorescence is decreased with the decrease in the quantum dot's concentration.

Efficiency of the intermolecular interaction of salicylic acid neutral form and monoanion with Cd2 + ion studied by methods of absorption and fluorescence

NASA Astrophysics Data System (ADS)

Lavrik, N. L.; Mulloev, N. U.

2018-02-01

The methods of absorption and fluorescence were used to study the efficiency of the interaction between salicylic acid derivatives SAD (neutral SA form and SA monoanion) and Cd2 + ions (in CdBr2 salt) within the range pH = 1.5 ÷ 8. The efficiency was determined from the change in both the absorption band contour and the fluorescence intensity of various SAD forms. It has been established that depending on the SAD form, the addition of CdBr2 to a starting solution leads to the formation of additional absorption for both the shorter wave lengths in the absorption spectrum of the neutral form (at pH < 3) and the longer wave lengths in the absorption spectrum for the HSal- monoanion (at pH > 4). In the fluorescence spectra, the intensity was observed to increase for the neutral SAD form (at pH < 3) and to decrease for the HSal- monoanion (at pH > 4) after addition of CdBr2. The spectral changes were interpreted in the framework of common notions about the effect of three physicochemical factors that determine the interaction between the SAD and the Cd2 + ion and affect the parameters of absorption and fluorescence spectra. These factors are: (1) the decrease in pH after addition of CdBr2 to the SAD solution, (2) the decrease in the efficiency of the H-bonding of SAD molecules to the water ones, and (3) the existence of electrostatic ion-ion interaction between the HSal- monoanion and the Cd2 + ion. The bimolecular fluorescence quenching constants Kq of HSal- monoanion fluorescence quenching by the Cd2 + ion appeared to be substantially less than those of the quenching which would follow either the dynamic (diffusion) or the concentration (static) mechanisms.

Iron specificity of a biosensor based on fluorescent pyoverdin immobilized in sol-gel glass

PubMed Central

2011-01-01

Two current technologies used in biosensor development are very promising: 1. The sol-gel process of making microporous glass at room temperature, and 2. Using a fluorescent compound that undergoes fluorescence quenching in response to a specific analyte. These technologies have been combined to produce an iron biosensor. To optimize the iron (II or III) specificity of an iron biosensor, pyoverdin (a fluorescent siderophore produced by Pseudomonas spp.) was immobilized in 3 formulations of porous sol-gel glass. The formulations, A, B, and C, varied in the amount of water added, resulting in respective R values (molar ratio of water:silicon) of 5.6, 8.2, and 10.8. Pyoverdin-doped sol-gel pellets were placed in a flow cell in a fluorometer and the fluorescence quenching was measured as pellets were exposed to 0.28 - 0.56 mM iron (II or III). After 10 minutes of exposure to iron, ferrous ion caused a small fluorescence quenching (89 - 97% of the initial fluorescence, over the range of iron tested) while ferric ion caused much greater quenching (65 - 88%). The most specific and linear response was observed for pyoverdin immobilized in sol-gel C. In contrast, a solution of pyoverdin (3.0 μM) exposed to iron (II or III) for 10 minutes showed an increase in fluorescence (101 - 114%) at low ferrous concentrations (0.45 - 2.18 μM) while exposure to all ferric ion concentrations (0.45 - 3.03 μM) caused quenching. In summary, the iron specificity of pyoverdin was improved by immobilizing it in sol-gel glass C. PMID:21554740

Investigation into the interaction of methylparaben and erythromycin with human serum albumin using multispectroscopic methods.

PubMed

Naik, Keerti M; Nandibewoor, Sharanappa T

2016-03-01

In this paper, the interaction of methylparaben and erythromycin with human serum albumin (HSA) was studied for the first time using spectroscopic methods including Fourier transform infrared (FTIR) spectroscopy and UV absorption spectroscopy in combination with fluorescence quenching under physiological conditions. The binding parameters were evaluated using a fluorescence quenching method. Based on Förster's theory of non-radiation energy transfer, the binding average distance, r between the donor (HSA) and the acceptor (methylparaben and erythromycin) was evaluated. UV/vis absorption, FTIR, synchronous and 3D spectral results showed that the conformation of HSA was changed in the presence of methylparaben and erythromycin. The thermodynamic parameters were calculated according to the van't Hoff equation and are discussed. The effect of some biological metal ions and site probes on the binding of methylparaben and erythromycin to HSA were further examined. Copyright © 2015 John Wiley & Sons, Ltd.

Poly(o-phenylenediamine) colloid-quenched fluorescent oligonucleotide as a probe for fluorescence-enhanced nucleic acid detection.

PubMed

Tian, Jingqi; Li, Hailong; Luo, Yonglan; Wang, Lei; Zhang, Yingwei; Sun, Xuping

2011-02-01

In this Letter, we demonstrate that chemical oxidation polymerization of o-phenylenediamine (OPD) by potassium bichromate at room temperature results in the formation of submicrometer-scale poly(o-phenylenediamine) (POPD) colloids. Such colloids can absorb and quench dye-labeled single-stranded DNA (ssDNA) very effectively. In the presence of a target, a hybridization event occurs, which produces a double-stranded DNA (dsDNA) that detaches from the POPD surface, leading to recovery of dye fluorescence. With the use of an oligonucleotide (OND) sequence associated with human immunodeficiency virus (HIV) as a model system, we demonstrate the proof of concept that POPD colloid-quenched fluorescent OND can be used as a probe for fluorescence-enhanced nucleic acid detection with selectivity down to single-base mismatch.

Evaluation of the binding interaction between bovine serum albumin and dimethyl fumarate, an anti-inflammatory drug by multispectroscopic methods

NASA Astrophysics Data System (ADS)

Jattinagoudar, Laxmi; Meti, Manjunath; Nandibewoor, Sharanappa; Chimatadar, Shivamurti

2016-03-01

The information of the quenching reaction of bovine serum albumin with dimethyl fumarate is obtained by multi-spectroscopic methods. The number of binding sites, n and binding constants, KA were determined at different temperatures. The effect of increasing temperature on Stern-Volmer quenching constants (KD) indicates that a dynamic quenching mechanism is involved in the interaction. The analysis of thermodynamic quantities namely, ∆H° and ∆S° suggested hydrophobic forces playing a major role in the interaction between dimethyl fumarate and bovine serum albumin. The binding site of dimethyl fumarate on bovine serum albumin was determined by displacement studies, using the site probes viz., warfarin, ibuprofen and digitoxin. The determination of magnitude of the distance of approach for molecular interactions between dimethyl fumarate and bovine serum albumin is calculated according to the theory of Förster energy transfer. The CD, 3D fluorescence spectra, synchronous fluorescence measurements and FT-IR spectral results were indicative of the change in secondary structure of the protein. The influence of some of the metal ions on the binding interaction was also studied.

A novel monodisperse SiO2@C-dot for the rapid and facile identification of latent fingermarks using self-quenching resistant solid-state fluorescence.

PubMed

Peng, Di; Liu, Xiang; Huang, Mengjun; Wang, Dan; Liu, Renlong

2018-04-24

Solid powder fluorescence shows great potential for application in medicine, biology, and engineering, especially in the identification of latent fingermarks in forensic science. However, conventional developing methods suffer from some drawbacks, such as low contrast, low sensitivity, low selectivity, and high toxicity. To conquer these challenges, novel SiO2@C-dot microspheres were prepared via a facile one-pot hydrothermal method by using citric acid as a carbon source and aminosilane as a nitrogen source. Interestingly, the results showed that the resultant powders possess good monodispersity, high fluorescence emission, and resistance to self-quenching. Additionally, the mechanism for the solid-state fluorescence of SiO2@C-dot compounds was also investigated. More importantly, the fingermarks on various surfaces, including transparent glasses, ceramic tiles, transparent plastics, aluminum alloys, plastic cards, painted woods, artificial leathers, and Chinese paper money, developed by the powders have indicated well-defined papillary ridges under a 365 nm UV lamp. The novel strategy of using monodisperse SiO2@C-dot microspheres as a fluorescent label for developing latent fingermarks showed greater advantages compared to conventional methods, which was also demonstrated using the automatic fingerprint identification system. It is simple, rapid, low-cost, nontoxic, and effective, and is expected to be a promising alternative for the development of latent fingerprints in forensic science.

"Turn-off" fluorescent data array sensor based on double quantum dots coupled with chemometrics for highly sensitive and selective detection of multicomponent pesticides.

PubMed

Fan, Yao; Liu, Li; Sun, Donglei; Lan, Hanyue; Fu, Haiyan; Yang, Tianming; She, Yuanbin; Ni, Chuang

2016-04-15

As a popular detection model, the fluorescence "turn-off" sensor based on quantum dots (QDs) has already been successfully employed in the detections of many materials, especially in the researches on the interactions between pesticides. However, the previous studies are mainly focused on simple single track or the comparison based on similar concentration of drugs. In this work, a new detection method based on the fluorescence "turn-off" model with water-soluble ZnCdSe and CdSe QDs simultaneously as the fluorescent probes is established to detect various pesticides. The fluorescence of the two QDs can be quenched by different pesticides with varying degrees, which leads to the differences in positions and intensities of two peaks. By combining with chemometrics methods, all the pesticides can be qualitative and quantitative respectively even in real samples with the limit of detection was 2 × 10(-8) mol L(-1) and a recognition rate of 100%. This work is, to the best of our knowledge, the first report on the detection of pesticides based on the fluorescence quenching phenomenon of double quantum dots combined with chemometrics methods. What's more, the excellent selectivity of the system has been verified in different mediums such as mixed ion disruption, waste water, tea and water extraction liquid drugs. Copyright © 2016 Elsevier B.V. All rights reserved.

Monitoring the Photosynthetic Apparatus During Space Flight: Interspecific Variation in Chlorophyll Fluorescence Signatures Induced by Different Root Zone Stresses

NASA Technical Reports Server (NTRS)

Bubenheim, David L.; Patterson, Mark T.; Kliss, Mark H. (Technical Monitor)

1996-01-01

Chlorophyll fluorescence has been used extensively as a tool to indicate stress to the photosynthetic apparatus in green plants. A rise in fluorescence has been attributed to the blockage of photosystem II photochemistry, and patterns of fluorescence decay (quenching) from dark adapted leaves can be related to specific photochemical and non-photochemical deexcitation pathways of light trapped by the photosynthetic apparatus and thus result in characteristically different fluorescence signatures. Four distantly related plant species, Hypocharis radicata (Asteraceae), Brassica rapa (Brassicaceae), Spinacea oleracea (Chenopodiaceae) and Triticum aestivum (Poaceae), were grown hydroponically for three weeks before the initiation of three different root zone stresses (10 mM Cu, 100 mM NaCl and nitrogen deficient nutrition). After 10 days, characteristic fluorescence signatures for each stress could be noted although the degree varied between species. Fast kinetics analysis showed a reduction in plastoquinone pool size for copper and nitrogen stress for all species but a more species specific result with NaCl stress. Photochemical quenching kinetics varied between species and stress treatments from no quenching in S. oleracea in copper treatments to increased photochemical quenching in NaCl treatments. Non-photochemical quenching kinetics demonstrated a distinct pattern between stresses for all species. Copper treatments characteristically exhibited a shallow, flat non-photochemical quenching profile suggesting a general blockage of electron transport whereas NaCl treatments exhibited a slow rising profile that suggested damage to thylakoid acidification kinetics and nitrogen deficiency exhibited a fast rising and declining profile that suggested an altered state 1-state 2 transition regulated by the phosphorylation of LHCII. These results demonstrate characteristic fluorescence signatures for specific plant stresses that may be applied to different, unrelated plant species. In addition, the potential use of chlorophyll fluorescence for both basic research and diagnostic physiology in space biology is presented.

One-step synthesis of nitrogen, boron co-doped fluorescent carbon nanoparticles for glucose detection.

PubMed

Liang, Meijuan; Ren, Yi; Zhang, Haijuan; Ma, Yunxia; Niu, Xiaoying; Chen, Xingguo

2017-09-01

Heteroatom-doped carbon nanoparticles (CNPs) have attracted considerable attention due to an effective improvement in their intrinsic properties. Here, a facile and simple synthesis of nitrogen, boron co-doped carbon nanoparticles (NB-CNPs) from a sole precursor, 3-aminophenylboronic acid, was performed via a one-step solid-phase approach. Because of the presence of boronic acid, NB-CNPs can be used directly as a fluorescent probe for glucose. Based on a boronic acid-triggered specific reaction, we developed a simple NB-CNP probe without surface modification for the detection of glucose. When glucose was introduced, the fluorescence of NB-CNPs was suppressed through a surface-quenching states mechanism. Obvious fluorescence quenching allowed the highly sensitive determination of glucose with a limit of detection of 1.8 μM. Moreover, the proposed method has been successfully used to detect glucose in urine from people with diabetes, suggesting potential application in sensing glucose. Copyright © 2017 John Wiley & Sons, Ltd.

Free energy gap laws for the pulse-induced and stationary fluorescence quenching by reversible charge transfer in polar solutions.

PubMed

Khokhlova, Svetlana S; Burshtein, Anatoly I

2011-01-21

The Stern-Volmer constants for either pulse-induced or stationary fluorescence being quenched by a contact charge transfer are calculated and their free energy dependencies (the free energy gap laws) are specified. The reversibility of charge transfer is taken into account as well as spin conversion in radical ion pairs, followed by their recombination in either singlet or triplet neutral products. The natural decay of triplets as well as their impurity quenching by ionization are accounted for when estimating the fluorescence quantum yield and its free energy dependence.

Investigation on Fluorescence Quenching Mechanism of Perylene Diimide Dyes by Graphene Oxide.

PubMed

Zhao, Yuzhen; Li, Kexuan; He, Zemin; Zhang, Yongming; Zhao, Yang; Zhang, Haiquan; Miao, Zongcheng

2016-11-30

Perylene diimide derivatives were used as probes to investigate the effect of the molecular structures on the fluorescence quenching mechanism in a perylene diimide/graphene oxide system. The electrons transferred from the excited state of dyes to the conductive band of graphene oxide with different concentrations were determined by fluorescence spectra. The results indicated that the quenching efficiency of perylene diimides by graphene oxide was not only dependent on the difference between the lowest unoccupied molecular orbital level of dyes and the conduction band of the graphene oxide, but also mainly on the difference in the molecular structures.

The efficiency of non-photochemical fluorescence quenching by cation radicals in photosystem II reaction centers.

PubMed

Paschenko, V Z; Churin, A A; Gorokhov, V V; Grishanova, N P; Korvatovskii, B N; Maksimov, E G; Mamedov, M D

2016-12-01

In a direct experiment, the rate constants of photochemical k p and non-photochemical k p + quenching of the chlorophyll fluorescence have been determined in spinach photosystem II (PS II) membrane fragments, oxygen-evolving PS II core, as well as manganese-depleted PS II particles using pulse fluorimetry. In the dark-adapted reaction center(s) (RC), the fluorescence decay kinetics of the antenna were measured at low-intensity picosecond pulsed excitation. To create a "closed" P680 + Q A - state, RCs were illuminated by high-intensity actinic flash 8 ns prior to the measuring flash. The obtained data were approximated by the sum of two decaying exponents. It was found that the antennae fluorescence quenching efficiency by the oxidized photoactive pigment of RC P680 + was about 1.5 times higher than that of the neutral P680 state. These results were confirmed by a single-photon counting technique, which allowed to resolve the additional slow component of the fluorescence decay. Slow component was assigned to the charge recombination of P680 + Pheo - in PS II RC. Thus, for the first time, the ratio k p + /k p  ≅ 1.5 was found directly. The mechanism of the higher efficiency of non-photochemical quenching comparing to photochemical quenching is discussed.

A base-modified PNA-graphene oxide platform as a turn-on fluorescence sensor for the detection of human telomeric repeats

NASA Astrophysics Data System (ADS)

Sabale, Pramod M.; George, Jerrin Thomas; Srivatsan, Seergazhi G.

2014-08-01

Given the biological and therapeutic significance of telomeres and other G-quadruplex forming sequences in human genome, it is highly desirable to develop simple methods to study these structures, which can also be implemented in screening formats for the discovery of G-quadruplex binders. The majority of telomere detection methods developed so far are laborious and use elaborate assay and instrumental setups, and hence, are not amenable to discovery platforms. Here, we describe the development of a simple homogeneous fluorescence turn-on method, which uses a unique combination of an environment-sensitive fluorescent nucleobase analogue, the superior base pairing property of PNA, and DNA-binding and fluorescence quenching properties of graphene oxide, to detect human telomeric DNA repeats of varying lengths. Our results demonstrate that this method, which does not involve a rigorous assay setup, would provide new opportunities to study G-quadruplex structures.Given the biological and therapeutic significance of telomeres and other G-quadruplex forming sequences in human genome, it is highly desirable to develop simple methods to study these structures, which can also be implemented in screening formats for the discovery of G-quadruplex binders. The majority of telomere detection methods developed so far are laborious and use elaborate assay and instrumental setups, and hence, are not amenable to discovery platforms. Here, we describe the development of a simple homogeneous fluorescence turn-on method, which uses a unique combination of an environment-sensitive fluorescent nucleobase analogue, the superior base pairing property of PNA, and DNA-binding and fluorescence quenching properties of graphene oxide, to detect human telomeric DNA repeats of varying lengths. Our results demonstrate that this method, which does not involve a rigorous assay setup, would provide new opportunities to study G-quadruplex structures. Electronic supplementary information (ESI) available. Figures, tables, experimental procedures and NMR spectra. See DOI: 10.1039/c4nr00878b

A naphthalimide fluorophore with efficient intramolecular PET and ICT processes: application in molecular logic.

PubMed

Wang, Haixia; Wu, Haixia; Xue, Lin; Shi, Yan; Li, Xiyou

2011-08-07

A novel 4-amino-1,8-naphthalimide (NDI) with two different metal cation receptors connected at 4-amino or imide nitrogen positions respectively was designed and prepared. Significant internal charge transfer (ICT) as well as photoinduced electron transfer (PET) from the receptors to NDI is revealed by the shifted UV-vis absorption spectra and significant fluorescence quenching. Both Zn(2+) and Cu(2+) can coordinate selectively with the two cation receptors in this molecule with different affinities. The coordination of Zn(2+) with the receptor at imide nitrogen hindered the PET process and accordingly restored the quenched fluorescence of NDI. But the coordination of Zn(2+) at 4-amino position blocked the ICT process and caused significant blue-shift on the absorption peak with the fluorescence intensity unaffected. Similarly, coordination of Cu(2+) with the receptor at imide nitrogen can block the PET process, but can not restore the quenched fluorescence of compound 3 due to the paramagnetic properties of Cu(2+), which quench the fluorescence significantly instead. With Cu(2+) and Zn(2+) as two chemical inputs and absorption or fluorescence as output, several logic gate operations, such as OR, NOR and INHIBIT, can be achieved.

A signal-on fluorosensor based on quench-release principle for sensitive detection of antibiotic rapamycin.

PubMed

Jeong, Hee-Jin; Itayama, Shuya; Ueda, Hiroshi

2015-03-26

An antibiotic rapamycin is one of the most commonly used immunosuppressive drugs, and also implicated for its anti-cancer activity. Hence, the determination of its blood level after organ transplantation or tumor treatment is of great concern in medicine. Although there are several rapamycin detection methods, many of them have limited sensitivity, and/or need complicated procedures and long assay time. As a novel fluorescent biosensor for rapamycin, here we propose "Q'-body", which works on the fluorescence quench-release principle inspired by the antibody-based quenchbody (Q-body) technology. We constructed rapamycin Q'-bodies by linking the two interacting domains FKBP12 and FRB, whose association is triggered by rapamycin. The fusion proteins were each incorporated position-specifically with one of fluorescence dyes ATTO520, tetramethylrhodamine, or ATTO590 using a cell-free translation system. As a result, rapid rapamycin dose-dependent fluorescence increase derived of Q'-bodies was observed, especially for those with ATTO520 with a lowest detection limit of 0.65 nM, which indicates its utility as a novel fluorescent biosensor for rapamycin.

A Signal-On Fluorosensor Based on Quench-Release Principle for Sensitive Detection of Antibiotic Rapamycin

PubMed Central

Jeong, Hee-Jin; Itayama, Shuya; Ueda, Hiroshi

2015-01-01

An antibiotic rapamycin is one of the most commonly used immunosuppressive drugs, and also implicated for its anti-cancer activity. Hence, the determination of its blood level after organ transplantation or tumor treatment is of great concern in medicine. Although there are several rapamycin detection methods, many of them have limited sensitivity, and/or need complicated procedures and long assay time. As a novel fluorescent biosensor for rapamycin, here we propose “Q’-body”, which works on the fluorescence quench-release principle inspired by the antibody-based quenchbody (Q-body) technology. We constructed rapamycin Q’-bodies by linking the two interacting domains FKBP12 and FRB, whose association is triggered by rapamycin. The fusion proteins were each incorporated position-specifically with one of fluorescence dyes ATTO520, tetramethylrhodamine, or ATTO590 using a cell-free translation system. As a result, rapid rapamycin dose-dependent fluorescence increase derived of Q’-bodies was observed, especially for those with ATTO520 with a lowest detection limit of 0.65 nM, which indicates its utility as a novel fluorescent biosensor for rapamycin. PMID:25822756

Time-resolved laser fluorescence spectroscopy of organic ligands by europium: Fluorescence quenching and lifetime properties

NASA Astrophysics Data System (ADS)

Nouhi, A.; Hajjoul, H.; Redon, R.; Gagné, J. P.; Mounier, S.

2018-03-01

Time-resolved Laser Fluorescence Spectroscopy (TRLFS) has proved its usefulness in the fields of biophysics, life science and geochemistry to characterize the fluorescence probe molecule with its chemical environment. The purpose of this study is to demonstrate the applicability of this powerful technique combined with Steady-State (S-S) measurements. A multi-mode factor analysis, in particular CP/PARAFAC, was used to analyze the interaction between Europium (Eu) and Humic substances (HSs) extracted from Saint Lawrence Estuary in Canada. The Saint Lawrence system is a semi-enclosed water stream with connections to the Atlantic Ocean and is an excellent natural laboratory. CP/PARAFAC applied to fluorescence S-S data allows introspecting ligands-metal interactions and the one-site 1:1 modeling gives information about the stability constants. From the spectral signatures and decay lifetimes data given by TRLFS, one can deduce the fluorescence quenching which modifies the fluorescence and discuss its mechanisms. Results indicated a relatively strong binding ability between europium and humic substances samples (Log K value varies from 3.38 to 5.08 at pH 7.00). Using the Stern-Volmer plot, it has been concluded that static and dynamic quenching takes places in the case of salicylic acid and europium interaction while for HSs interaction only a static quenching is observed.

Some fluorescence properties of dimethylaminochalcone and its novel cyclic analogues

NASA Astrophysics Data System (ADS)

Tomečková, Vladimíra; Poškrobová, Martina; Štefanišinová, Miroslava; Perjési, Pál

2009-12-01

This paper demonstrates the basic character (polarity, solubility, colour, absorption and fluorescence quantum yield) of synthetic dimethylaminochalcone ( 1) and its cyclic analogues measured in toluene, chloroform, dimethylsulfoxide and ethanol, which have been studied by absorption and fluorescence spectroscopy. The biologically active dye 4'-dimethylaminochalcone ( 1b) and its less flexible analogues 4-dimethylaminoindanone ( 2b), -tetralone ( 3b), and -benzosuberone ( 4b) are lipophilic molecules that displayed the best solubility in toluene and chloroform. The highest fluorescence and quantum yields of compounds 1 and 2 have been obtained in DMSO and chloroform. Quenching effect of fluorescence compounds ( 1- 4) has been studied in the mixture of the most polar organic solvents DMSO and water. In the presence of water, fluorescence of compound 1 has been quenched the best from all studied chalcones and emission maxima of molecules 1- 4 have been shifted to the longer wavelengths. Quenching effect of fluorescence by water was in order 1 > 2 > 3 > 4.

Fluorescence self-quenching assay for the detection of target collagen sequences using a short probe peptide.

PubMed

Nian, Linge; Hu, Yue; Fu, Caihong; Song, Chen; Wang, Jie; Xiao, Jianxi

2018-01-01

The development of novel assays to detect collagen fragments is of utmost importance for diagnostic, prognostic and therapeutic decisions in various collagen-related diseases, and one essential question is to discover probe peptides that can specifically recognize target collagen sequences. Herein we have developed the fluorescence self-quenching assay as a convenient tool to screen the capability of a series of fluorescent probe peptides of variable lengths to bind with target collagen peptides. We have revealed that the targeting ability of probe peptides is length-dependent, and have discovered a relatively short probe peptide FAM-G(POG) 8 capable to identify the target peptide. We have further demonstrated that fluorescence self-quenching assay together with this short probe peptide can be applied to specifically detect the desired collagen fragment in complex biological media. Fluorescence self-quenching assay provides a powerful new tool to discover effective peptides for the recognition of collagen biomarkers, and it may have great potential to identify probe peptides for various protein biomarkers involved in pathological conditions. Copyright © 2017 Elsevier B.V. All rights reserved.

Radiative decay engineering 5: metal-enhanced fluorescence and plasmon emission

PubMed Central

Lakowicz, Joseph R.

2009-01-01

Metallic particles and surfaces display diverse and complex optical properties. Examples include the intense colors of noble metal colloids, surface plasmon resonance absorption by thin metal films, and quenching of excited fluorophores near the metal surfaces. Recently, the interactions of fluorophores with metallic particles and surfaces (metals) have been used to obtain increased fluorescence intensities, to develop assays based on fluorescence quenching by gold colloids, and to obtain directional radiation from fluorophores near thin metal films. For metal-enhanced fluorescence it is difficult to predict whether a particular metal structure, such as a colloid, fractal, or continuous surface, will quench or enhance fluorescence. In the present report we suggest how the effects of metals on fluorescence can be explained using a simple concept, based on radiating plasmons (RPs). The underlying physics may be complex but the concept is simple to understand. According to the RP model, the emission or quenching of a fluorophore near the metal can be predicted from the optical properties of the metal structures as calculated from electrodynamics, Mie theory, and/or Maxwell’s equations. For example, according to Mie theory and the size and shape of the particle, the extinction of metal colloids can be due to either absorption or scattering. Incident energy is dissipated by absorption. Far-field radiation is created by scattering. Based on our model small colloids are expected to quench fluorescence because absorption is dominant over scattering. Larger colloids are expected to enhance fluorescence because the scattering component is dominant over absorption. The ability of a metal’s surface to absorb or reflect light is due to wavenumber matching requirements at the metal–sample interface. Wavenumber matching considerations can also be used to predict whether fluorophores at a given distance from a continuous planar surface will be emitted or quenched. These considerations suggest that the so called “lossy surface waves” which quench fluorescence are due to induced electron oscillations which cannot radiate to the far-field because wavevector matching is not possible. We suggest that the energy from the fluorophores thought to be lost by lossy surface waves can be recovered as emission by adjustment of the sample to allow wavevector matching. The RP model provides a rational approach for designing fluorophore–metal configurations with the desired emissive properties and a basis for nanophotonic fluorophore technology. PMID:15691498

Ternary Interactions and Energy Transfer between Fluorescein Isothiocyanate, Adenosine Triphosphate, and Graphene Oxide Nanocarriers.

PubMed

Ratajczak, Katarzyna; Stobiecka, Magdalena

2017-07-20

The interactions of fluorescent probes and biomolecules with nanocarriers are of key importance to the emerging targeted drug delivery systems. Graphene oxide nanosheets (GONs) as the nanocarriers offer biocompatibility and robust drug binding capacity. The interactions of GONs with fluorophores lead to strong fluorescence quenching, which may interfere with fluorescence bioimaging and biodetection. Herein, we report on the interactions and energy transfers in a model ternary system: GONs-FITC-ATP, where FITC is a model fluorophore (fluorescein isothiocyanate) and ATP is a common biomolecule (adenosine-5'-triphosphate). We have found that FITC fluorescence is considerably quenched by ATP (the quenching constant K SV = 113 ± 22 M -1 ). The temperature coefficient of K SV is positive (α T = 4.15 M -1 deg -1 ). The detailed analysis of a model for internal self-quenching of FITC indicates that the temperature dependence of the net quenching efficiency η for the FITC-ATP pair is dominated by FITC internal self-quenching modes with their contribution estimated at 79%. The quenching of FITC by GONs is much stronger (K SV = 598 ± 29 M -1 ) than that of FITC-ATP and is associated with the formation of supramolecular assemblies bound with hydrogen bonding and π-π stacking interactions. For the analysis of the complex behavior of the ternary system GONs-FITC-ATP, a model of chemisorption of ATP on GONs, with partial blocking of FITC quenching, has been developed. Our results indicate that ATP acts as a moderator for FITC quenching by GONs. The interactions between ATP, FITC, and GONs have been corroborated using molecular dynamics and quantum mechanical calculations.

Bioanalytical Applications of Fluorenscence Quenching.

DTIC Science & Technology

1986-02-10

fluorescence is observed. Thus, ’ the enzymes (in this case phosphorylase C) which can hydrolyze the lecithin , can be determined by measuring the released...encapsulated in lecithin liposomes. In this manner the fluorescence is self-quenched. When the liposomes are disrupted, the dye is released and

Substrate-based near-infrared imaging sensors enable fluorescence lifetime contrast via built-in dynamic fluorescence quenching elements.

PubMed

Kumar, Anand T N; Rice, William L; López, Jessica C; Gupta, Suresh; Goergen, Craig J; Bogdanov, Alexei A

2016-04-22

Enzymatic activity sensing in fluorescence lifetime (FLT) mode with "self-quenched" macromolecular near-infrared (NIR) sensors is a highly promising strategy for in vivo imaging of proteolysis. However, the mechanisms of FLT changes in such substrate-based NIR sensors have not yet been studied. We synthesized two types of sensors by linking the near-infrared fluorophore IRDye 800CW to macromolecular graft copolymers of methoxy polyethylene glycol and polylysine (MPEG-gPLL) with varying degrees of MPEGylation and studied their fragmentation induced by trypsin, elastase, plasmin and cathepsins (B,S,L,K). We determined that the efficiency of such NIR sensors in FLT mode depends on sensor composition. While MPEG-gPLL with a high degree of MPEGylation showed rapid (τ 1/2 =0.1-0.2 min) FLT increase (Δτ=0.25 ns) upon model proteinase-mediated hydrolysis in vivo , lower MPEGylation density resulted in no such FLT increase. Temperature-dependence of fluorescence de-quenching of NIR sensors pointed to a mixed dynamic/static-quenching mode of MPEG-gPLL-linked fluorophores. We further demonstrated that although the bulk of sensor-linked fluorophores were de-quenched due to the elimination of static quenching, proteolysis-mediated deletion of a fraction of short (8-10kD) negatively charged fragments of highly MPEGylated NIR sensor is the most likely event leading to a rapid FLT increase phenomenon in quenched NIR sensors. Therefore, the optimization of "built-in" dynamic quenching elements of macromolecular NIR sensors is a potential avenue for improving their response in FLT mode.

Pre-recombination quenching of the radiation induced fluorescence as the approach to study kinetics of ion-molecular reactions

NASA Astrophysics Data System (ADS)

Borovkov, V. I.; Ivanishko, I. S.

2011-04-01

This study deals with the geminate ion recombination in the presence of bulk scavengers, that is the so-called scavenger problem, as well as with the effect of the scavenging reaction on the radiation-induced recombination fluorescence. Borovkov and Velizhanin (2004) have proposed a method to determine the rate constant of the bulk reaction between neutral scavengers and one of the geminate ions if the ion-molecular reaction prevented the formation of electronically excited states upon recombination involving a newly formed ion. If such pre-recombination quenching of the radiation-induced fluorescence took place, it manifested itself as a progressive decrease in the decay of the fluorescence intensity. The relative change in the fluorescence decay as caused by the scavengers was believed to be closely related to the kinetics of the scavenging reaction. The goal of the present study is to support this method, both computationally and experimentally because there are two factors, which cast doubt on the intuitively obvious approach to the scavenger problem: spatial correlations between the particles involved and the drift of the charged reagent in the electric field of its geminate partner. Computer simulation of geminate ions recombination with an explicit modeling of the motion trajectories of scavengers has been performed for media of low dielectric permittivity, i.e. for the maximal Coulomb interaction between the ions. The simulation has shown that upon continuous diffusion of the particles involved, the joint effect of the two above factors can be considered as insignificant with a high accuracy. Besides, it is concluded then that the method of pre-recombination quenching could be applied to study parallel and consecutive reactions where the yields of excited states in the reaction pathways are different with the use of very simple analytical relations of the formal chemical kinetics. The conclusion has been confirmed experimentally by the example of the reactions of electron transfer from the diphenylacetylene radical anion to dibromoethane and hexafluorobenzene in n-dodecane solutions.

A universal label-free fluorescent aptasensor based on Ru complex and quantum dots for adenosine, dopamine and 17β-estradiol detection.

PubMed

Huang, Hailiang; Shi, Shuo; Gao, Xing; Gao, Ruru; Zhu, Ying; Wu, Xuewen; Zang, Ruimin; Yao, Tianming

2016-05-15

Based on specific aptamer binding properties, a strategy for adenosine, dopamine and 17β-estradiol detection was realised by employing Ru complex and quantum dots (QDs) as fluorescence probes. Ru complex, which could quench the fluorescence of QDs, preferred to bind with aptamer DNA and resulted in the fluorescence rise of QDs. When the aptamer DNA was incubated with the target first, it could not bind with Ru complex and the fluorescence of QDs was quenched. Under the optimal condition, the fluorescence intensity was linearly proportional to the concentration of adenosine, dopamine and 17β-estradiol with a limit of detection (LOD) of 101 nM, 19 nM and 37 nM, respectively. The experiments in fetal bovine serum were also carried out with good results. This universal method was rapid, label-free, low-cost, easy-operating and highly repeatable for the detection of adenosine, dopamine and 17β-estradiol. Qualitative detection by naked eyes was also available without complex instruments. It could also be extended to detect various analytes, such as metal ions, proteins and small molecules by using appropriate aptamers. Copyright © 2015 Elsevier B.V. All rights reserved.

Real-time Detection and Monitoring of Loop Mediated Amplification (LAMP) Reaction Using Self-quenching and De-quenching Fluorogenic Probes.

PubMed

Gadkar, Vijay J; Goldfarb, David M; Gantt, Soren; Tilley, Peter A G

2018-04-03

Loop-mediated isothermal amplification (LAMP) is an isothermal nucleic acid amplification (iNAAT) technique known for its simplicity, sensitivity and speed. Its low-cost feature has resulted in its wide scale application, especially in low resource settings. The major disadvantage of LAMP is its heavy reliance on indirect detection methods like turbidity and non-specific dyes, which often leads to the detection of false positive results. In the present work, we have developed a direct detection approach, whereby a labelled loop probe quenched in its unbound state, fluoresces only when bound to its target (amplicon). Henceforth, referred to as Fluorescence of Loop Primer Upon Self Dequenching-LAMP (FLOS-LAMP), it allows for the sequence-specific detection of LAMP amplicons. The FLOS-LAMP concept was validated for rapid detection of the human pathogen, Varicella-zoster virus, from clinical samples. The FLOS-LAMP had a limit of detection of 500 copies of the target with a clinical sensitivity and specificity of 96.8% and 100%, respectively. The high level of specificity is a major advance and solves one of the main shortcomings of the LAMP technology, i.e. false positives. Self-quenching/de-quenching probes were further used with other LAMP primer sets and different fluorophores, thereby demonstrating its versatility and adaptability.

Insight into the interaction of antitubercular and anticancer compound clofazimine with human serum albumin: spectroscopy and molecular modelling.

PubMed

Ajmal, Mohammad Rehan; Zaidi, Nida; Alam, Parvez; Nusrat, Saima; Siddiqi, Mohd Khursheed; Badr, Gamal; Mahmoud, Mohamed H; Khan, Rizwan Hasan

2017-01-01

The binding of clofazimine to human serum albumin (HSA) was investigated by applying optical spectroscopy and molecular docking methods. Fluorescence quenching data revealed that clofazimine binds to protein with binding constant in the order of 10 4  M -1 , and with the increase in temperature, Stern-Volmer quenching constants gradually decreased indicating quenching mode to be static. The UV-visible spectra showed increase in absorbance upon interaction of HSA with clofazimine which further reveals formation of the drug-albumin complex. Thermodynamic parameters obtained from fluorescence data indicate that the process is exothermic and spontaneous. Forster distance (R o ) obtained from fluorescence resonance energy transfer is found to be 2.05 nm. Clofazimine impelled rise in α-helical structure in HSA as observed from far-UV CD spectra while there are minor alterations in tertiary structure of the protein. Clofazimine interacts strongly with HSA inducing secondary structure in the protein and slight alterations in protein topology as suggested by dynamic light scattering results. Moreover, docking results indicate that clofazimine binds to hydrophobic pocket near to the drug site II in HSA.

Characteristics of the isomeric flavonoids apigenin and genistein binding to hemoglobin by spectroscopic methods

NASA Astrophysics Data System (ADS)

Yuan, Jiang-Lan; Liu, Hui; Kang, Xu; Lv, Zhong; Zou, Guo-Lin

2008-11-01

Apigenin (Ap) and genistein (Ge), a couple of isomeric flavonoids with extensive bioactivities, are the most common dietary ingredients. They have been widely investigated due to their potential therapeutic actions for some diseases. In our work, binding characteristics of Ap and Ge to hemoglobin (Hb) were analyzed with fluorescence spectroscopy, circular dichroism (CD) and UV-vis absorption spectroscopy. The results indicated that Ap and Ge caused strong fluorescence quenching of Hb by static quenching mechanism, but their quenching efficiency and mechanisms were different. The binding site n suggested that there was a single binding site in Hb for Ap and Ge. The results of synchronous fluorescence showed that the microenvironment around Tyr residues of Hb had a slight trend of polarity decreasing, but the polarity around Trp residues increased by adding Ap. Results of CD indicated that the Ap and Ge did not changed the secondary structure of Hb. According to the theory of Förster resonance energy transfer, the binding distance r between Trp 37 and Ap/Ge was predicted to be 3.4 nm and 3.32 nm, respectively. The affinity of Ge toward Hb was higher than that of Ap.

Spectroscopic analyses on interaction of o-Vanillin- D-Phenylalanine, o-Vanillin- L-Tyrosine and o-Vanillin- L-Levodopa Schiff Bases with bovine serum albumin (BSA)

NASA Astrophysics Data System (ADS)

Gao, Jingqun; Guo, Yuwei; Wang, Jun; Wang, Zhiqiu; Jin, Xudong; Cheng, Chunping; Li, Ying; Li, Kai

2011-04-01

In this work, three o-Vanillin Schiff Bases (o-VSB: o-Vanillin- D-Phenylalanine (o-VDP), o-Vanillin- L-Tyrosine (o-VLT) and o-Vanillin- L-Levodopa (o-VLL)) with alanine constituent were synthesized by direct reflux method in ethanol solution, and then were used to study the interaction to bovine serum albumin (BSA) molecules by fluorescence spectroscopy. Based on the fluorescence quenching calculation, the bimolecular quenching constant ( Kq), apparent quenching constant ( Ksv), effective binding constant ( KA) and corresponding dissociation constant ( KD) as well as binding site number ( n) were obtained. In addition, the binding distance ( r) was also calculated according to Foster's non-radioactive energy transfer theory. The results show that these three o-VSB can efficiently bind to BSA molecules, but the binding array order is o-VDP-BSA > o-VLT-BSA > o-VLL-BSA. Synchronous fluorescence spectroscopy indicates that the o-VDP is more accessibility to tryptophan (Trp) residues of BSA molecules than to tyrosine (Tyr) residues. Nevertheless, the o-VLT and o-VLL are more accessibility to Tyr residues than to Trp residues.

Spectroscopic analyses on interaction of o-Vanillin-D-Phenylalanine, o-Vanillin-L-Tyrosine and o-Vanillin-L-Levodopa Schiff Bases with bovine serum albumin (BSA).

PubMed

Gao, Jingqun; Guo, Yuwei; Wang, Jun; Wang, Zhiqiu; Jin, Xudong; Cheng, Chunping; Li, Ying; Li, Kai

2011-04-01

In this work, three o-Vanillin Schiff Bases (o-VSB: o-Vanillin-D-Phenylalanine (o-VDP), o-Vanillin-L-Tyrosine (o-VLT) and o-Vanillin-L-Levodopa (o-VLL)) with alanine constituent were synthesized by direct reflux method in ethanol solution, and then were used to study the interaction to bovine serum albumin (BSA) molecules by fluorescence spectroscopy. Based on the fluorescence quenching calculation, the bimolecular quenching constant (K(q)), apparent quenching constant (K(sv)), effective binding constant (K(A)) and corresponding dissociation constant (K(D)) as well as binding site number (n) were obtained. In addition, the binding distance (r) was also calculated according to Foster's non-radioactive energy transfer theory. The results show that these three o-VSB can efficiently bind to BSA molecules, but the binding array order is o-VDP-BSA>o-VLT-BSA>o-VLL-BSA. Synchronous fluorescence spectroscopy indicates that the o-VDP is more accessibility to tryptophan (Trp) residues of BSA molecules than to tyrosine (Tyr) residues. Nevertheless, the o-VLT and o-VLL are more accessibility to Tyr residues than to Trp residues. Copyright © 2010 Elsevier B.V. All rights reserved.

Versatile Molecular Functionalization for Inhibiting Concentration Quenching of Thermally Activated Delayed Fluorescence.

PubMed

Lee, Jiyoung; Aizawa, Naoya; Numata, Masaki; Adachi, Chihaya; Yasuda, Takuma

2017-01-01

Concentration quenching of thermally activated delayed fluorescence is found to be dominated by electron-exchange interactions, as described by the Dexter energy-transfer model. Owing to the short-range nature of the electron-exchange interactions, even a small modulation in the molecular geometric structure drastically affects the concentration-quenching, leading to enhanced solid-state photoluminescence and electroluminescence quantum efficiencies. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

An Iodine Fluorescence Quenching Clock Reaction

ERIC Educational Resources Information Center

Weinberg, Richard B.; Muyskens, Mark

2007-01-01

Clock reactions based upon competing oxidation and reduction reactions of iodine and starch as the most popular type of chemistry example is presented to illustrate the redox phenomena, reaction kinetics, and principles of chemical titration. The examination of the photophysical principles underlying the iodine fluorescence quenching clock…

Does Cu(acac)2 Quench Benzene Fluorescence? A Physical Chemistry Experiment.

ERIC Educational Resources Information Center

Marciniak, Bronislaw

1986-01-01

Describes a laboratory experiment in which benzene fluorescence is quenched by bis(acetylacetonato) copper(II). Discusses how this experiment can demonstrate a special technique used in the field of photochemistry. Provides an outline of the experimental procedure and discusses its results. (TW)

Structure-matched Phthalocyanine Ion Pair as a Red-emitting Fluorescent Optical Probe for the Analysis of Sodium Dodecylbenzenesulfonate with High Specificity and Sensitivity.

PubMed

Yu, Fei; Guo, Menglin; Deng, Yabin; Lu, Yin; Chen, Lin; Huang, Ping; Li, Donghui

2016-01-01

We have found that a positively charged cationic copper phthalocyanine, Alcian blue (Alcian blue 8GX), can efficiently quench the fluorescence of an oppositely charged red fluorescent phthalocyanine compound with a matched molecular structure, tetrasulfonated aluminum phthalocyanine (AlS4Pc), because of the formation of an ion pair complex (AlS4Pc-Alcian blue 8GX) that exhibits almost no fluorescence. An investigation was carried out on the fluorescence recovery of AlS4Pc-Alcian blue 8GX caused by a series of anionic surfactants containing a sulfonic group (sodium dodecylbenzenesulfonate (SDBS), sodium lauryl sulfate (SLS), and sodium dodecyl sulfate (SDS)). The results showed that SDBS exhibited a significant response, and the highest sensitivity among the surfactants. Due to its high efficiency of fluorescence quenching and the high level of fluorescence recovery, direct observes can even be performed by the naked eye. The results revealed that the Alcian blue 8GX-AlS4Pc ion-pair complex fluorescent probe only responded to SDBS in the low-concentration range. Based on the new founding, this study proposed a novel principle and method of fluorescence enhancement to specifically measure the concentration of SDBS, thereby achieving a highly sensitive and highly specific determination of SDBS. Under the optimal conditions, the fluorescence intensity (I(f)) of the system and the concentration of SDBS in the range of 1 × 10(-7) - 1 × 10(-5) mol/dm(3) exhibited a good linear relationship. This method is highly sensitive, and the operation is simple and rapid. It had been applied for the quantitative analysis of SDBS in environmental water, while achieving satisfactory results compared with those of the standard method. This study developed a new application of the fluorescent phthalocyanine compounds used as molecular probes in analytical sciences.

Which model based on fluorescence quenching is suitable to study the interaction between trans-resveratrol and BSA?

NASA Astrophysics Data System (ADS)

Wei, Xin Lin; Xiao, Jian Bo; Wang, Yuanfeng; Bai, Yalong

2010-01-01

There are several models by means of quenching fluorescence of BSA to determine the binding parameters. The binding parameters obtained from different models are quite different from each other. Which model is suitable to study the interaction between trans-resveratrol and BSA? Herein, twelve models based fluorescence quenching of BSA were compared. The number of binding sites increasing with increased binding constant for similar compounds binding to BSA maybe one approach to resolve this question. For example, here eleven flavonoids were tested to illustrate that the double logarithm regression curve is suitable to study binding polyphenols to BSA.

Effect of perfluorooctane sulfonate on the conformation of wheat germ acid phosphatase.

PubMed

Xu, Dongmei; Jin, Jianchang; Shen, Tong; Wang, Yanhua

2013-11-01

Fluorescence spectroscopy was used to study the quenching mechanism, the type of force and the binding sites of perfluorooctane sulfonate (PFOS) on wheat germ acid phosphatase (ACPase). The results showed that the quenching effect of PFOS on ACPase was mainly due to a static quenching mechanism that occurred via the formation of hydrogen bonds and van der Waals forces. The results from synchronous fluorescence spectroscopy demonstrated that PFOS interacts with ACPase close to the tryptophan residues. In addition, synchronous fluorescence spectroscopy also showed that PFOS increases the hydrophobicity of the microenvironment of the tyrosine residues, hence decreasing the local polarity.

Interpenetrated Binary Supramolecular Nanofibers for Sensitive Fluorescence Detection of Six Classes of Explosives.

PubMed

Xiong, Wei; Zhu, Qijian; Gong, Yanjun; Wang, Chen; Che, Yanke; Zhao, Jincai

2018-04-03

In this work, we develop a sequential self-assembly approach to fabricate interpenetrated binary supramolecular nanofibers consisting of carbazole oligomer 1-cobalt(II) (1-Co 2+ ) coordination nanofibers and oligomer 2 nanofibers for the sensitive detection of six classes of explosives. When exposed to peroxide explosives (e.g., H 2 O 2 ), Co 2+ in 1-Co 2+ coordination nanofibers can be reduced to Co + that can transfer an electron to the excited 2 nanofibers and thereby quench their fluorescence. On the other hand, when exposed to the other five classes of explosives, the excited 2 nanofibers can transfer an electron to explosives to quench their fluorescence. On the basis of the distinct fluorescence quenching mechanisms, six classes of explosives can be sensitively detected. Herein, we provide a new strategy to design broad-band fluorescence sensors for a rich identification of threats.

Interaction of Chelerythrine with Keyhole Limpet Hemocyanin: a Fluorescence Spectroscopy and Molecular Docking Study

NASA Astrophysics Data System (ADS)

Zhong, M.; Long, R. Q.; Wang, Y. H.; Chen, C. L.

2018-05-01

The quenching mechanism between chelerythrine (CHE) and keyhole limpet hemocyanin (KLH) was investigated using fluorescence spectroscopy and molecular docking. The experiments were conducted at three different temperatures (293, 298, and 303 K). The results revealed that the intrinsic fluorescence of KLH was strongly quenched by CHE through a static quenching mechanism. The thermodynamic parameters (ΔG, ΔH, and ΔS) of the interaction were calculated, indicating that the interaction between CHE and KLH was spontaneous and that van der Waals forces and hydrogen bond formation played major roles in the binding process. The intrinsic fluorescence of the tyrosine and tryptophan residues in KLH was studied by synchronous fluorescence, which suggested that CHE changed the conformation of KLH. Finally, molecular docking was used to obtain detailed information on the binding sites and binding affinities between CHE and KLH.

Blending DNA binding dyes to improve detection in real-time PCR.

PubMed

Jansson, Linda; Koliana, Marianne; Sidstedt, Maja; Hedman, Johannes

2017-03-01

The success of real-time PCR (qPCR) analysis is partly limited by the presence of inhibitory compounds in the nucleic acid samples. For example, humic acid (HA) from soil and aqueous sediment interferes with amplification and also quenches the fluorescence of double-stranded (ds) DNA binding dyes, thus hindering amplicon detection. We aimed to counteract the HA fluorescence quenching effect by blending complementary dsDNA binding dyes, thereby elevating the dye saturation levels and increasing the fluorescence signals. A blend of the four dyes EvaGreen, ResoLight, SYBR Green and SYTO9 gave significantly higher fluorescence intensities in the presence and absence of HA, compared with the dyes applied separately and two-dye blends. We propose blending of dyes as a generally applicable means for elevating qPCR fluorescence signals and thus enabling detection in the presence of quenching substances.

Quenching of the fluorescence of NO2

NASA Technical Reports Server (NTRS)

Braslavsky, S.; Heicklen, J.

1972-01-01

The fluorescence yield of NO2 was monitored at 25 C with incident wavelengths of 4047, 4358, and 4800A at fluorescence wavelengths of 4860, 5577, and 6300A. The NO2 pressure was varied between 0.004 and 0.080 torr. Measurements were taken both in the absence of foreign gases and in the presence of up to 30 torr. He, N2, and O2 at each NO2 pressure. In the absence of foreign gases, the self quenching follows a Stern-Volmer quenching mechanism, but foreign-gas quenching shows marked deviations from this mechanism. Both from lifetime and kinetic considerations, it is argued that the electronic state formed by absorption of the radiation cannot be the emitting state. Emission occurs from several vibrational levels of the emitting state, the various vibrational levels being formed by collisional cascade reactions. The appropriate quenching rate constant ratios were measured and tabulated. Even the two electronic state mechanism is insufficient to explain all the observations.

Quantitative Imaging in Laboratory: Fast Kinetics and Fluorescence Quenching

ERIC Educational Resources Information Center

Cumberbatch, Tanya; Hanley, Quentin S.

2007-01-01

The process of quantitative imaging, which is very commonly used in laboratory, is shown to be very useful for studying the fast kinetics and fluorescence quenching of many experiments. The imaging technique is extremely cheap and hence can be used in many absorption and luminescence experiments.

Intermolecular interaction of fosinopril with bovine serum albumin (BSA): The multi-spectroscopic and computational investigation.

PubMed

Zhou, Kai-Li; Pan, Dong-Qi; Lou, Yan-Yue; Shi, Jie-Hua

2018-04-16

The intermolecular interaction of fosinopril, an angiotensin converting enzyme inhibitor with bovine serum albumin (BSA), has been investigated in physiological buffer (pH 7.4) by multi-spectroscopic methods and molecular docking technique. The results obtained from fluorescence and UV absorption spectroscopy revealed that the fluorescence quenching mechanism of BSA induced by fosinopril was mediated by the combined dynamic and static quenching, and the static quenching was dominant in this system. The binding constant, K b , value was found to lie between 2.69 × 10 3 and 9.55 × 10 3  M -1 at experimental temperatures (293, 298, 303, and 308 K), implying the low or intermediate binding affinity between fosinopril and BSA. Competitive binding experiments with site markers (phenylbutazone and diazepam) suggested that fosinopril preferentially bound to the site I in sub-domain IIA on BSA, as evidenced by molecular docking analysis. The negative sign for enthalpy change (ΔH 0 ) and entropy change (ΔS 0 ) indicated that van der Waals force and hydrogen bonds played important roles in the fosinopril-BSA interaction, and 8-anilino-1-naphthalenesulfonate binding assay experiments offered evidence of the involvements of hydrophobic interactions. Moreover, spectroscopic results (synchronous fluorescence, 3-dimensional fluorescence, and Fourier transform infrared spectroscopy) indicated a slight conformational change in BSA upon fosinopril interaction. Copyright © 2018 John Wiley & Sons, Ltd.

Direct detection of RDX vapor using a conjugated polymer network.

PubMed

Gopalakrishnan, Deepti; Dichtel, William R

2013-06-05

1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) is a principal component of plastic explosives used in acts of terrorism and within improvised explosive devices, among others. Approaches to detect RDX compatible with remote, "stand-off" sampling that do not require preconcentration strategies, such as the swabs commonly employed in airports, will benefit military and civilian security. Such detection remains a significant challenge because RDX is 10(3) less volatile than 1,3,5-trinitrotoluene (TNT), corresponding to a parts-per-trillion vapor pressure under ambient conditions. Therefore, while fluorescence quenching of conjugated polymers is sufficiently sensitive to detect TNT vapors, RDX vapor detection is undemonstrated. Here we report a cross-linked phenylene vinylene polymer network whose fluorescence is quenched by trace amounts of RDX introduced from solution or the vapor phase. Fluorescence quenching is reduced, but remains significant, when partially degraded RDX is employed, suggesting that the polymer responds to RDX itself. The polymer network also responds to TNT and PETN similarly introduced from solution or the vapor phase. Pure solvents, volatile amines, and the outgassed vapors from lipstick or sunscreen do not quench polymer fluorescence. The established success of TNT sensors based on fluorescence quenching makes this a material of interest for real-world explosive sensors and will motivate further interest in cross-linked polymers and framework materials for sensing applications.

Fluorescent properties of a hybrid cadmium sulfide-dendrimer nanocomposite and its quenching with nitromethane.

PubMed

Campos, Bruno B; Algarra, Manuel; Esteves da Silva, Joaquim C G

2010-01-01

A fluorescent hybrid cadmium sulphide quantum dots (QDs) dendrimer nanocomposite (DAB-CdS) synthesised in water and stable in aqueous solution is described. The dendrimer, DAB-G5 dendrimer (polypropylenimine tetrahexacontaamine) generation 5, a diaminobutene core with 64 amine terminal primary groups. The maximum of the excitation and emission spectra, Stokes' shift and the emission full width of half maximum of this nanocomposite are, respectively: 351, 535, 204 and 212 nm. The fluorescence time decay was complex and a four component decay time model originated a good fit (chi = 1.20) with the following lifetimes: tau (1) = 657 ps; tau (2) = 10.0 ns; tau (3) = 59.42 ns; and tau (4) = 265 ns. The fluorescence intensity of the nanocomposite is markedly quenched by the presence of nitromethane with a dynamic Stern-Volmer constant of 25 M(-1). The quenching profiles show that about 81% of the CdS QDs are located in the external layer of the dendrimer accessible to the quencher. PARAFAC analysis of the excitation emission matrices (EEM) acquired as function of the nitromethane concentration showed a trilinear data structure with only one linearly independent component describing the quenching which allows robust estimation of the excitation and emission spectra and of the quenching profiles. This water soluble and fluorescent nanocomposite shows a set of favourable properties to its use in sensor applications.

[Study of the interaction mechanism between brodifacoum and DNA by spectroscopy].

PubMed

Duan, Yun-qing; Min, Shun-geng

2009-04-01

The interaction between brodifacoum (3-[3-(4'-bromophenyl-4) 1,2,3,4-tetralin-10]-4-hydroxyl-coumarin) (BDF), an anticoagulant rodenticide, and calf thymus DNA (ct-DNA) was studied by UV spectrum and fluorescence spectrum. The results were summarized as follows: There was a hypochromic effect of low concentration ct-DNA on the UV spectra. The fluorescence quenching studies showed a regular decrease in the fluorescence intensity after addition of ct-DNA by the static quenching mode with a quenching constant (Ksv) of 1.21 x 10(4) L x mol(-1) at 27 degrees C. The BDF possibly bonded to ct-DNA mainly via Van der Waals forces by the corresponding thermodynamics parameter. KI quenching experiment found that there was not obvious protection of ct-DNA to BDF. The fluorescence intensity of BDF/ct-DNA system changed with the variation in ionic strength Quenching of ct-DNA on the fluorescence of BDF/beta-CD inclusion complex was reduced in contrast with the free BDF, which showed that beta-CD could provide BDF with protection. So the comprehensive interaction mode of BDF with ct-DNA may be the groove binding by the above results. It was indicated that there had been static-electro interaction between BDF and ct-DNA at the same time. The conjunct action of Van der Waals forces and electrostatic attraction favorably provide BDF bonding interaction in the groove of ct-DNA.

PsbS protein modulates non-photochemical chlorophyll fluorescence quenching in membranes depleted of photosystems.

PubMed

Ware, Maxwell A; Giovagnetti, Vasco; Belgio, Erica; Ruban, Alexander V

2015-11-01

Plants with varying levels of PsbS protein were grown on lincomycin. Enhanced levels of non-photochemical fluorescence quenching (NPQ) in over-expressers of the protein have been observed. This was accompanied by increased amplitude of the irreversible NPQ component, qI, previously considered to reflect mainly photoinhibition of PSII reaction centres (RCII). However, since RCIIs were largely absent the observed qI is likely to originate from the LHCII antenna. In chloroplasts of over-expressers of PsbS grown on lincomycin an abnormally large NPQ (∼7) was characterised by a 0.34 ns average chlorophyll fluorescence lifetime. Yet the lifetime in the Fm state was similar to that of wild-type plants. 77K fluorescence emission spectra revealed a specific 700 nm peak typical of LHCII aggregates as well as quenching of the PSI fluorescence at 730 nm. The aggregated state manifested itself as a clear change in the distance between LHCII complexes detected by freeze-fracture electron microscopy. Grana thylakoids in the quenched state revealed 3 times more aggregated LHCII particles compared to the dark-adapted state. Overall, the results directly demonstrate the importance of LHCII aggregation in the NPQ mechanism and show that the PSII supercomplex structure plays no role in formation of the observed quenching. Copyright © 2015 Elsevier B.V. All rights reserved.

Ultrasensitive detection of lead (II) based on fluorescent aptamer-functionalized carbon nanotubes.

PubMed

Taghdisi, Seyed Mohammad; Emrani, Somayeh Sarreshtehdar; Tabrizian, Kaveh; Ramezani, Mohammad; Abnous, Khalil; Emrani, Ahmad Sarreshtehdar

2014-05-01

Lead contamination is a serious environmental problem with toxic effects in human. Here, we developed a simple and sensitive sensing method employing ATTO 647N/aptamer-SWNT ensemble for detection of Pb(2+). This method is based on the super quenching capability of single-walled carbon nanotubes (SWNTs), high affinity of the aptamer toward Pb(2+) and different propensities of ATTO 647N-aptamer and ATTO 647N-aptamer/Pb(2+) complex for adsorption on SWNTs. In the absence of Pb(2+), the fluorescence of ATTO 647N-aptamer is efficiently quenched by SWNTs. Upon addition of Pb(2+), the aptamer binds to its target, leading to the formation of a G-quadruplex/Pb(2+) complex and does not interact with SWNTs and ATTO 647N-aptamer starts fluorescing. This sensor exhibited a high selectivity toward Pb(2+) and a limit of detection (LOD) as low as 0.42 nM was obtained. Also this sensor could be applied for detection of Pb(2+) ions in tap water and biological sample like serum with high sensitivity. Copyright © 2014 Elsevier B.V. All rights reserved.

Determination of amantadine and rimantadine using a sensitive fluorescent probe

NASA Astrophysics Data System (ADS)

Wang, Guang-Quan; Qin, Yan-Fang; Du, Li-Ming; Li, Jun-Fei; Jing, Xu; Chang, Yin-Xia; Wu, Hao

2012-12-01

Amantadine hydrochloride (AMA) and rimantadine hydrochloride (RIM) are non-fluorescent in aqueous solutions. This property makes their determination through direct fluorescent method difficult. The competing reactions and the supramolecular interaction mechanisms between the two drugs and coptisine (COP) as they fight for occupancy of the cucurbit[7]uril (CB[7]) cavity, were studied using spectrofluorimetry, 1H NMR, and molecular modeling calculations. Based on the significant quenching of the supramolecular complex fluorescence intensity, a fluorescent probe method of high sensitivity and selectivity was developed to determine AMA or RIM in their pharmaceutical dosage forms and in urine samples with good precision and accuracy. The linear range of the method was from 0.0040 to 1.0 μg mL-1 with a detection limit ranging from 0.0012 to 0.0013 μg mL-1. This shows that the proposed method has promising potential for therapeutic monitoring and pharmacokinetics and for clinical application.

The interaction of C.I. acid red 27 with human hemoglobin in solution.

PubMed

Wang, Yan-Qing; Zhang, Hong-Mei; Tang, Bo-Ping

2010-08-02

The nature of the interaction between human hemoglobin and C.I. acid red 27 was investigated systematically by ultraviolet-vis absorbance, circular dichroism, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques at pH 7.40. The quenching mechanism, binding constants, and the number of binding sites were determined by the quenching of human hemoglobin fluorescence in presence of C.I. acid red 27. The results showed that the nature of the quenching was of static type and the process of binding acid red 27 on human hemoglobin was a spontaneous molecular interaction procedure. The electrostatic and hydrophobic interactions played a major role in stabilizing the complex; The distance r between donor and acceptor was obtained to be 4.40 nm according to Förster's theory; The effect of acid red 27 on the conformation of human hemoglobin was analyzed using synchronous fluorescence, circular dichroism and three-dimensional fluorescence spectra. 2010 Elsevier B.V. All rights reserved.

Real-time PCR detection of Plasmodium directly from whole blood and filter paper samples

PubMed Central

2011-01-01

Background Real-time PCR is a sensitive and specific method for the analysis of Plasmodium DNA. However, prior purification of genomic DNA from blood is necessary since PCR inhibitors and quenching of fluorophores from blood prevent efficient amplification and detection of PCR products. Methods Reagents designed to specifically overcome PCR inhibition and quenching of fluorescence were evaluated for real-time PCR amplification of Plasmodium DNA directly from blood. Whole blood from clinical samples and dried blood spots collected in the field in Colombia were tested. Results Amplification and fluorescence detection by real-time PCR were optimal with 40× SYBR® Green dye and 5% blood volume in the PCR reaction. Plasmodium DNA was detected directly from both whole blood and dried blood spots from clinical samples. The sensitivity and specificity ranged from 93-100% compared with PCR performed on purified Plasmodium DNA. Conclusions The methodology described facilitates high-throughput testing of blood samples collected in the field by fluorescence-based real-time PCR. This method can be applied to a broad range of clinical studies with the advantages of immediate sample testing, lower experimental costs and time-savings. PMID:21851640

The mechanism of interactions between tea polyphenols and porcine pancreatic alpha‐amylase: Analysis by inhibition kinetics, fluorescence quenching, differential scanning calorimetry and isothermal titration calorimetry

PubMed Central

Sun, Lijun; Gidley, Michael J.

2017-01-01

Scope This study aims to use a combination of biochemical and biophysical methods to derive greater mechanistic understanding of the interactions between tea polyphenols and porcine pancreatic α‐amylase (PPA). Methods and results The interaction mechanism was studied through fluorescence quenching (FQ), differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC) and compared with inhibition kinetics. The results showed that a higher quenching effect of polyphenols corresponded to a stronger inhibitory activity against PPA. The red‐shift of maximum emission wavelength of PPA bound with some polyphenols indicated a potential structural unfolding of PPA. This was also suggested by the decreased thermostability of PPA with these polyphenols in DSC thermograms. Through thermodynamic binding analysis of ITC and inhibition kinetics, the equilibrium of competitive inhibition was shown to result from the binding of particularly galloylated polyphenols with specific sites on PPA. There were positive linear correlations between the reciprocal of competitive inhibition constant (1/K ic), quenching constant (K FQ) and binding constant (K itc). Conclusion The combination of inhibition kinetics, FQ, DSC and ITC can reasonably characterize the interactions between tea polyphenols and PPA. The galloyl moiety is an important group in catechins and theaflavins in terms of binding with and inhibiting the activity of PPA. PMID:28618113

Theoretical study of the initial non-radiative 1 Bu → 2 Ag transition in the fluorescence quenching of s-trans-butadiene: Electronic structure methods and quantum dynamics

NASA Astrophysics Data System (ADS)

Komainda, A.; Lefrancois, D.; Dreuw, A.; Köppel, H.

2017-01-01

The photodynamics of s-trans-butadiene in the 6 eV excitation energy range is investigated by ab initio quantum dynamical methods, paying particular attention to the nonadiabatic coupling between the 1Bu and 2Ag singlet excited states. The existence of a conical intersection between their potential energy surfaces is confirmed. Key parameters of the system, like the energy gap between the interacting states and their coupling strength, are critically assessed. Up to eight nuclear degrees of freedom are considered in the dynamical treatment and are shown to lead to a more realistic description of the interactions. The gas phase (jet) UV absorption spectrum is well reproduced. The related ultrafast nonradiative population transfer from 1Bu to 2Ag is the initial processes leading to fluorescence quenching of trans-butadiene.

Investigation on the pH-dependent binding of benzocaine and lysozyme by fluorescence and absorbance

NASA Astrophysics Data System (ADS)

Li, Shihui; Li, Daojin

2011-11-01

The interaction mechanism between benzocaine (BZC) and lysozyme (Lys) has been investigated by fluorescence, synchronous fluorescence, ultraviolet-vis (UV) absorption spectra, and three-dimensional fluorescence (3-D) in various pH medium. The observations of fluorescence spectra were mainly rationalized in terms of a static quenching process at lower concentration of BZC ( CBZC/ CLys < 9) and a combined quenching process at higher concentration of BZC ( CBZC/ CLys > 9) at pH 7.4 and 8.4. However, the fluorescence quenching was mainly arisen from static quenching by complex formation in all studied drug concentrations at pH 3.5. The structural characteristics of BZC and Lys were probed, and their binding affinities were determined under different pH conditions (pH 3.5, 7.4, and 8.4). The results indicated that the binding abilities of BZC to Lys decreased at the pH below and above the simulative physiological condition (pH 7.4) due to the alterations of the protein secondary and tertiary structures or the structural change of BZC. The effect of BZC on the conformation of Lys was analyzed using UV, synchronous fluorescence and three-dimensional fluorescence under different pH conditions. These results indicate that the binding of BZC to Lys causes apparent change in the secondary and tertiary structures of Lys. The effect of Zn 2+ on the binding constant of BZC with Lys under various pH conditions (pH 3.5, 7.4, and 8.4) was also studied.

Unusual Fluorescent Responses of Morpholine-functionalized Fluorescent Probes to pH via Manipulation of BODIPY’s HOMO and LUMO Energy Orbitals for Intracellular pH Detection

PubMed Central

Zhang, Jingtuo; Yang, Mu; Mazi, Wafa; Adhikari, Kapil; Fang, Mingxi; Xie, Fei; Valenzano, Loredana; Tiwari, Ashutosh; Luo, Fen-Tair; Liu, Haiying

2016-01-01

Three uncommon morpholine-based fluorescent probes (A, B and C) for pH were prepared by introducing morpholine residues to BODIPY dyes at 4,4’- and 2,6-positions, respectively. In contrast to morpholine-based fluorescent probes for pH reported in literature, these fluorescent probes display high fluorescence in a basic condition while they exhibit very weak fluorescence in an acidic condition. The theoretical calculation confirmed that morpholine is unable to function as either an electron donor or an electron acceptor to quench the BODIPY fluorescence in the neutral and basic condition via photo-induced electron transfer (PET) mechanism because the LUMO energy of morpholine is higher than those of the BODIPY dyes while its HOMO energy is lower than those of the BODIPY dyes. However, the protonation of tertiary amines of the morpholine residues in an acidic environment leads to fluorescence quenching of the BODIPY dyes via d-PET mechanism. The fluorescence quenching is because the protonation effectively decreases the LUMO energy which locates between the HOMO and LUMO energies of the BODIPY dyes. Fluorescent probe C with deep-red emission has been successfully used to detect pH changes in mammalian cells. PMID:27547822

Characterization of a recombinant humanized anti-cocaine monoclonal antibody and its Fab fragment.

PubMed

Kirley, Terence L; Norman, Andrew B

2015-01-01

Variations of post-translational modifications are important for stability and in vivo behavior of therapeutic antibodies. A recombinant humanized anti-cocaine monoclonal antibody (h2E2) was characterized for heterogeneity of N-linked glycosylation and disulfide bonds. In addition, charge heterogeneity, which is partially due to the presence or absence of C-terminal lysine on the heavy chains, was examined. For cocaine overdose therapy, Fab fragments may be therapeutic, and thus, a simplified method of generation, purification, and characterization of the Fab fragment generated by Endoproteinase Lys-C digestion was devised. Both the intact h2E2 antibody and purified Fab fragments were analyzed for their affinities for cocaine and 2 of its metabolites, benzoylecgonine and cocaethylene, by fluorescence quenching of intrinsic antibody tyrosine and tryptophan fluorescence resulting from binding of these drugs. Binding constants obtained from fluorescence quenching measurements are in agreement with recently published radioligand and ELISA binding assays. The dissociation constants determined for the h2E2 monoclonal and its Fab fragment are approximately 1, 5, and 20 nM for cocaethylene, cocaine, and benzoylecgonine, respectively. Tryptophan fluorescence quenching (emission at 330 nm) was measured after either excitation of tyrosine and tryptophan (280 nm) or selective excitation of tryptophan alone (295 nm). More accurate binding constants are obtained using tryptophan selective excitation at 295 nm, likely due to interfering absorption of cocaine and metabolites at 280 nm. These quenching results are consistent with multiple tryptophan and tyrosine residues in or near the predicted binding location of cocaine in a previously published 3-D model of this antibody's variable region.

Real-time fluorescence assay of alkaline phosphatase in living cells using boron-doped graphene quantum dots as fluorophores.

PubMed

Chen, Li; Yang, Guancao; Wu, Ping; Cai, Chenxin

2017-10-15

This work reports a convenient and real-time assay of alkaline phosphatase (ALP) in living cells based on a fluorescence quench-recovery process at a physiological pH using the boron-doped graphene quantum dots (BGQDs) as fluorophore. The fluorescence of BGQDs is found to be effectively quenched by Ce 3+ ions because of the coordination of Ce 3+ ions with the carboxyl group of BGQDs. Upon addition of adenosine triphosphate (ATP) into the system, the quenched fluorescence can be recovered by the ALP-positive expressed cells (such as MCF-7 cells) due to the removal of Ce 3+ ions from BGQDs surface by phosphate ions, which are generated from ATP under catalytic hydrolysis of ALP that expressed in cells. The extent of fluorescence signal recovery depends on the level of ALP in cells, which establishes the basis of ALP assay in living cells. This approach can also be used for specific discrimination of the ALP expression levels in different type of cells and thus sensitive detection of those ALP-positive expressed cells (for example MCF-7 cells) at a very low abundance (10±5 cells mL -1 ). The advantages of this approach are that it has high sensitivity because of the significant suppression of the background due to the Ce 3+ ion quenching the fluorescence of BGQDs, and has the ability of avoiding false signals arising from the nonspecific adsorption of non-target proteins because it operates via a fluorescence quench-recovery process. In addition, it can be extended to other enzyme systems, such as ATP-related kinases. Copyright © 2017 Elsevier B.V. All rights reserved.

Fluorescence and visual detection of fluoride ions using a photoluminescent graphene oxide paper sensor

NASA Astrophysics Data System (ADS)

Chen, Xiaochun; Yu, Shaoming; Yang, Liang; Wang, Jianping; Jiang, Changlong

2016-07-01

The instant and on-site detection of trace aqueous fluoride ions is still a challenge for environmental monitoring and protection. This work demonstrates a new analytical method and its utility of a paper sensor for visual detection of F- on the basis of the fluorescence resonance energy transfer (FRET) between photoluminescent graphene oxide (GO) and silver nanoparticles (AgNPs) through the formation of cyclic esters between phenylborinic acid and diol. The fluorescence of GO was quenched by the AgNPs, and trace F- can recover the fluorescence of the quenched photoluminescent GO. The increase in fluorescence intensity is proportional to the concentration of F- in the range of 0.05-0.55 nM, along with a limit of detection (LOD) as low as 9.07 pM. Following the sensing mechanism, a paper-based sensor for the visual detection of aqueous F- has been successfully developed. The paper sensor showed high sensitivity for aqueous F-, and the LOD could reach as low as 0.1 μM as observed by the naked eye. The very simple and effective strategy reported here could be extended to the visual detection of a wide range of analytes in the environment by the construction of highly efficient FRET nanoprobes.The instant and on-site detection of trace aqueous fluoride ions is still a challenge for environmental monitoring and protection. This work demonstrates a new analytical method and its utility of a paper sensor for visual detection of F- on the basis of the fluorescence resonance energy transfer (FRET) between photoluminescent graphene oxide (GO) and silver nanoparticles (AgNPs) through the formation of cyclic esters between phenylborinic acid and diol. The fluorescence of GO was quenched by the AgNPs, and trace F- can recover the fluorescence of the quenched photoluminescent GO. The increase in fluorescence intensity is proportional to the concentration of F- in the range of 0.05-0.55 nM, along with a limit of detection (LOD) as low as 9.07 pM. Following the sensing mechanism, a paper-based sensor for the visual detection of aqueous F- has been successfully developed. The paper sensor showed high sensitivity for aqueous F-, and the LOD could reach as low as 0.1 μM as observed by the naked eye. The very simple and effective strategy reported here could be extended to the visual detection of a wide range of analytes in the environment by the construction of highly efficient FRET nanoprobes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02878k

A G-quadruplex based fluorescent oligonucleotide turn-on probe towards iodides detection in real samples.

PubMed

Li, Qian; Li, Shuaihua; Chen, Xiu; Bian, Liujiao

2017-09-01

A basket-type G-quadruplex (GQ) fluorescent oligonucleotide (OND) probe is designed to detect iodides dependent on thymine-Hg(II)-thymine (T-Hg(II)-T) base pairs and the intrinsic fluorescence quenching capacity of GQ. In the presence of Hg(II) ions (Hg 2+ ), the two hexachloro-fluorescein-labeled ONDs form a hairpin structure and the fluorophores are dragged close to the GQ, leading to fluorescence quenching of the probe due to photoinduced electron transfer. Upon addition of iodide anions, Hg 2+ are extracted from T-Hg(II)-T complexes which attributes to the stronger binding with iodide anions, resulting in the fluorescence recovery. Through performing the fluorescence quenching and recovery processes, this probe developed a fluorescence turn-on sensor for iodide anions determination over a linear range of 20-200nmol/L with a limit of detection of 5nmol/L. The practical use of the turn-on technology was demonstrated by its application in determination of iodides in water, food, pharmaceutical products and biological samples. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fluorescence quenching of protonated β-carbolines in water and microemulsions: evidence for heavy-atom and electron-transfer mechanisms.

PubMed

Mousa, Souad A; Douglas, Peter; Burrows, Hugh D; Fonseca, Sofia M

2013-09-01

The fluorescence quenching of protonated β-carbolines has been investigated in acidic aqueous solutions and in w/o microemulsions using I(-), Br(-), Cu(2+), SCN(-), and Pb(2+) as quenchers. It was found that fluorescence quenching by these compounds is much more efficient in water than in microemulsions since quenching in microemulsions depends on the simultaneous occupancy of the water droplets by both fluorophore and quencher. Linear Stern-Volmer plots were obtained in all cases, leading to quenching rate constants of ca. 10(8)-10(10) M(-1) s(-1) in water and ca. 10(7)-10(8) M(-1) s(-1) in microemulsions. In the case of quenching by SCN(-), ns flash photolysis studies indicate formation of (SCN)2(˙-) showing that at least part of the quenching process involves an electron transfer mechanism. This indicates that the singlet excited states of the protonated β-carbolines can act as relatively strong oxidants (E° > 1.6 V), capable of oxidizing many species, including the biologically relevant DNA base guanine. The observation of the (SCN)2(˙-) transient in microemulsions demonstrates that it is possible to have the protonated β-carboline and at least two thiocyanate ions in the same water pool.

Structural Implications of Fluorescence Quenching in the Shaker K+ Channel

PubMed Central

Cha, Albert; Bezanilla, Francisco

1998-01-01

When attached to specific sites near the S4 segment of the nonconducting (W434F) Shaker potassium channel, the fluorescent probe tetramethylrhodamine maleimide undergoes voltage-dependent changes in intensity that correlate with the movement of the voltage sensor (Mannuzzu, L.M., M.M. Moronne, and E.Y. Isacoff. 1996. Science. 271:213–216; Cha, A., and F. Bezanilla. 1997. Neuron. 19:1127–1140). The characteristics of this voltage-dependent fluorescence quenching are different in a conducting version of the channel with a different pore substitution (T449Y). Blocking the pore of the T449Y construct with either tetraethylammonium or agitoxin removes a fluorescence component that correlates with the voltage dependence but not the kinetics of ionic activation. This pore-mediated modulation of the fluorescence quenching near the S4 segment suggests that the fluorophore is affected by the state of the external pore. In addition, this modulation may reflect conformational changes associated with channel opening that are prevented by tetraethylammonium or agitoxin. Studies of pH titration, collisional quenchers, and anisotropy indicate that fluorophores attached to residues near the S4 segment are constrained by a nearby region of protein. The mechanism of fluorescence quenching near the S4 segment does not involve either reorientation of the fluorophore or a voltage-dependent excitation shift and is different from the quenching mechanism observed at a site near the S2 segment. Taken together, these results suggest that the extracellular portion of the S4 segment resides in an aqueous protein vestibule and is influenced by the state of the external pore. PMID:9758859

Determination of polycyclic aromatic hydrocarbons by four-way parallel factor analysis in presence of humic acid.

PubMed

Yang, Ruifang; Zhao, Nanjing; Xiao, Xue; Yu, Shaohui; Liu, Jianguo; Liu, Wenqing

2016-01-05

There is not effective method to solve the quenching effect of quencher in fluorescence spectra measurement and recognition of polycyclic aromatic hydrocarbons in aquatic environment. In this work, a four-way dataset combined with four-way parallel factor analysis is used to identify and quantify polycyclic aromatic hydrocarbons in the presence of humic acid, a fluorescent quencher and an ubiquitous substance in aquatic system, through modeling the quenching effect of humic acid by decomposing the four-way dataset into four loading matrices corresponding to relative concentration, excitation spectra, emission spectra and fluorescence quantum yield, respectively. It is found that Phenanthrene, pyrene, anthracene and fluorene can be recognized simultaneously with the similarities all above 0.980 between resolved spectra and reference spectra. Moreover, the concentrations of them ranging from 0 to 8μgL(-1) in the test samples prepared with river water could also be predicted successfully with recovery rate of each polycyclic aromatic hydrocarbon between 100% and 120%, which were higher than those of three-way PARAFAC. These results demonstrate that the combination of four-way dataset with four-way parallel factor analysis could be a promising method to recognize the fluorescence spectra of polycyclic aromatic hydrocarbons in the presence of fluorescent quencher from both qualitative and quantitative perspective. Copyright © 2015 Elsevier B.V. All rights reserved.

Highly selective and sensitive fluorescent paper sensor for nitroaromatic explosive detection.

PubMed

Ma, Yingxin; Li, Hao; Peng, Shan; Wang, Leyu

2012-10-02

Rapid, sensitive, and selective detection of explosives such as 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP), especially using a facile paper sensor, is in high demand for homeland security and public safety. Although many strategies have been successfully developed for the detection of TNT, it is not easy to differentiate the influence from TNP. Also, few methods were demonstrated for the selective detection of TNP. In this work, via a facile and versatile method, 8-hydroxyquinoline aluminum (Alq(3))-based bluish green fluorescent composite nanospheres were successfully synthesized through self-assembly under vigorous stirring and ultrasonic treatment. These polymer-coated nanocomposites are not only water-stable but also highly luminescent. Based on the dramatic and selective fluorescence quenching of the nanocomposites via adding TNP into the aqueous solution, a sensitive and robust platform was developed for visual detection of TNP in the mixture of nitroaromatics including TNT, 2,4-dinitrotoluene (DNT), and nitrobenzene (NB). Meanwhile, the fluorescence intensity is proportional to the concentration of TNP in the range of 0.05-7.0 μg/mL with the 3σ limit of detection of 32.3 ng/mL. By handwriting or finger printing with TNP solution as ink on the filter paper soaked with the fluorescent nanocomposites, the bluish green fluorescence was instantly and dramatically quenched and the dark patterns were left on the paper. Therefore, a convenient and rapid paper sensor for TNP-selective detection was fabricated.

Label free selective detection of estriol using graphene oxide-based fluorescence sensor

NASA Astrophysics Data System (ADS)

Kushwaha, H. S.; Sao, Reshma; Vaish, Rahul

2014-07-01

Water-soluble and fluorescent Graphene oxide (GO) is biocompatible, easy, and economical to synthesize. Interestingly, GO is also capable of quenching fluorescence. On the basis of its fluorescence and quenching abilities, GO has been reported to serve as an energy acceptor in a fluorescence resonance energy transfer (FRET) sensor. GO-based FRET biosensors have been widely reported for sensing of proteins, nucleic acid, ATP (Adenosine triphosphate), etc. GO complexes with fluorescent dyes and enzymes have been used to sense metal ions. Graphene derivatives have been used for sensing endocrine-disrupting chemicals like bisphenols and chlorophenols with high sensitivity and good reproducibility. On this basis, a novel GO based fluorescent sensor has been successfully designed to detect estriol with remarkable selectivity and sensitivity. Estriol is one of the three estrogens in women and is considered to be medically important. Estriol content of maternal urine or plasma acts as an important screening marker for estimating foetal growth and development. In addition, estriol is also used as diagnostic marker for diseases like breast cancer, osteoporosis, neurodegenerative and cardiovascular diseases, insulin resistance, lupus erythematosus, endometriosis, etc. In this present study, we report for the first time a rapid, sensitive with detection limit of 1.3 nM, selective and highly biocompatible method for label free detection of estriol under physiological conditions using fluorescence assay.

Oxygen optical gas sensing by reversible fluorescence quenching in photo-oxidized poly(9,9-dioctylfluorene) thin films.

PubMed

Anni, M; Rella, R

2010-02-04

We investigated the fluorescence (FL) dependence on the environment oxygen content of poly(9,9-dioctylfluorene) (PF8) thin films. We show that the PF8 interactions with oxygen are not limited to the known irreversible photo-oxidation, resulting in the formation of Keto defects, but also reversible FL quenching is observed. This effect, which is stronger for the Keto defects than for the PF8, has been exploited for the realization of a prototype oxygen sensor based on FL quenching. The sensing sensitivity of Keto defects is comparable with the state of the art organic oxygen sensors based on phosphorescence quenching.

Dynamic quenching study of 2-amino-3-bromo-1,4-naphthoquinone by titanium dioxide nano particles in solution (methanol).

PubMed

Pushpam, S; Kottaisamy, M; Ramakrishnan, V

2013-10-01

The dependence of fluorescence emission of 2-amino-3-bromo-1,4-naphthoquinone on titanium dioxide (TiO2) in methanol has been investigated. The increase in TiO2 concentration causes a decrease in the fluorescence intensity of 2-amino-3-bromo-1,4-naphthoquinone. A linear Stern-Volmer plot in this study indicates the presence of dynamic quenching. The quenching and association constants have been calculated. The quenching process is due to the electron transfer from 2-amino-3-bromo-1,4-naphthoquinone to TiO2. Copyright © 2013 Elsevier B.V. All rights reserved.

Lifetime and linewidth of individual quantum dots interfaced with graphene.

PubMed

Miao, Xin; Gosztola, David J; Sumant, Anirudha V; Grebel, Haim

2018-04-19

We report on luminescence lifetimes and linewidths from an array of individual quantum dots (QDs) that were either interfaced with graphene surface guides or dispersed on aluminum electrodes. The observed fluorescence quenching is consistent with screening by charge carriers. Fluorescence quenching is typically mentioned as a sign that chromophores are interfacing with a conductive surface (metal or graphene); we find that the QDs interfaced with the metal film exhibit shortened lifetime and line-broadening but not necessarily fluorescence quenching as the latter may be impacted by molecular concentration, reflectivity and conductor imperfections. We also comment on angle-dependent lifetime measurements, which we postulate depend on the specifics of the local density-of-states involved.

Spectrofluorimetric determination of cefixime using terbium-danofloxacin probe

PubMed Central

Manzoori, Jamshid L.; Amjadi, Mohammad; Soltani, Naser; Jouyban, Abolghasem

2014-01-01

Objective(s): Cefixime (Cfx), is a semi-synthetic third-generation oral cephalosporin antibiotic that is prescribed for the treatment of susceptible infections. There are some procedures for the determination of Cfx in pharmaceutical formulations and biological samples. Herein a spectrofluorimetric method was proposed for Cfx determination based on the fluorescence quenching of terbium-danofloxacin (Tb3+-Dano) in the presence of Cfx. Materials and Methods: Cfx was detected based on fluorescence quenching of terbium-danofloxacin (Tb3+-Dano) in the presence of Cfx with maximum excitation and emission wavelengths at 347 nm and 545 nm, respectively. The quenched fluorescence intensity of Tb3+- Dano system is proportional to the concentration of Cfx. The optimum conditions for the determination of Cfx were studied. Results: The maximum response was achieved under optimum conditions of [Tris buffer]= 0.008 mol/l (pH 6.5), [Tb3+]=1×10-4 mol/l and [Dano]=1×10-4 mol/l. The developed method was evaluated in terms of accuracy, precision and limit of detection. The linear concentration ranges for quantification of Cfx were 8.8×10-8-8.8×10-7 mol/l and 1.1×10-7-8.8×10-7 mol/l in standard and human serum samples with the detection limits (S/N=3) of 2.8×10-8 mol/l and 3.9×10-8 mol/l, respectively. The Cfx was determined in pharmaceutical tablets and spiked serum samples and the results were satisfactory. Conclusion: This method is simple, practical and relatively interference-free for determination of Cfx in pharmaceutical tablets and serum samples. PMID:24904718

Reversible intermolecular energy transfer between saturated amines and benzene in non-polar solution

NASA Astrophysics Data System (ADS)

Halpern, Arthur M.; Wryzykowska, Krystyna

1981-01-01

Excitation of a mixture of dimethylethylamine (DEMA) and benzene in n-hexane at 222 nm primarily produces excited amine, while at 261 nm excited benzene predominantly results. The fluorescence spectra appreciably overlap. With 222 nm excitation, DEMA fluorescence is quenched by benzene at the diffusion-controlled rate; this quenching results with nearly unit efficiency in sensitized benzene fluorescence. With 261 nm excitation, some sensitized DEMA fluorescence is observed: the rate constant for tins process is ≈ 2.6 × 10 9 M -1 s -1.

Hemoglobin detection using carbon dots as a fluorescence probe.

PubMed

Barati, Ali; Shamsipur, Mojtaba; Abdollahi, Hamid

2015-09-15

Herein, we have described the application of high fluorescent carbon dots (CDs) without any surface modification as a simple and fast responding fluorescence probe for sensitive and selective determination of hemoglobin (Hb) in the presence of H2O2. Although Hb itself was able to quench the fluorescence of CDs, based on the inner filter effect (IFE) of the protein that affects both excitation and emission spectra of CDs, the presence of H2O2 resulted in further improvement of the sensitivity of Hb detection. The assay is based on the reaction of Hb with H2O2 that generates reactive oxygen species including hydroxyl (OH•) and superoxide (O2(•-)) radicals under heme degradation and/or iron release from Hb and the subsequent reaction of hydroxyl radicals, as strong oxidizing agents, with CDs resulting in high fluorescence quenching. The proposed probe was used for determination of Hb in concentration range of 1-100 nM with a detection limit of 0.4 nM. The method was successfully applied to the determination of Hb in human blood samples. Copyright © 2015 Elsevier B.V. All rights reserved.

[Fluorescence Resonance Energy Transfer Detection of Cobalt Ions by Silver Triangular Nanoplates and Rhodamine 6G].

PubMed

Zhang, Xiu-qing; Peng, Jun; Ling, Jian; Liu, Chao-juan; Cao, Qiu-e; Ding, Zhong-tao

2015-04-01

In the present paper, the authors studied fluorescence resonance energy transfer (FRET) phenomenon between silver triangular nanoplates and bovine serum albumin (BSA)/Rhodamine 6G fluorescence complex, and established a fluorescence method for the detection of cobalt ions. We found that when increasing the silver triangular nanoplates added to certain concentrations of fluorescent bovine serum albumin (BSA)/Rhodamine 6G complex, the fluorescence of Rhodamine 6G would be quenched up to 80% due to the FRET between the quencher and donor. However, in the presence of cobalt ions, the disassociation of the fluorescent complex from silver triangular nanoplates occurred and the fluorescence of the Rhodamine 6G recovered. The recovery of fluorescence intensity rate (I/I0) has a good relationship with the cobalt ion concentration (cCO2+) added. Thus, the authors developed a fluorescence method for the detection of cobalt ions based on the FRET of silver triangular nanoplates and Rhodamine 6G.

New effects in Langmuir and Langmuir-Blodgett monolayers from fluorescently labelled phospholipids and their possible use for water quality control

NASA Astrophysics Data System (ADS)

Ivanov, G. R.; Geshev, N. I.

2016-02-01

Secondary water contamination poses significant challenges to the sensitivity and selectivity of sensors used for its detection and monitoring. Currently only lab tests can detect these contaminants and by the time this happens the contaminated water has entered the city water supply system. Fluorescent chromophore NitroBenzoxaDiazole (NBD) is very suitable and had been successfully used in biosensor applications due to its high sensitivity to close proximity polarity of the medium. Over the years we have discovered 3 new effects in NBD- labelled phospholipids which can significantly improve the performance of biosensors. The phospholipid matrix provides flexible biocompatible environment for immobilization of selectively reacting enzymes, microorganisms, DNA, immunoagents, whole cells. Use of single layer (3.1 nm thickness) films at the air-water interface (Langmuir films) or deposited on solid support as Langmuir-Blodgett (LB) film gives fast response times for real time monitoring (no slow diffusion processes) and precise molecule ordering and orientation. The first new effect was fluorescence self-quenching in Langmuir and LB films. In the liquid phase films exhibit normal fluorescence. Upon transition to solid phase fluorescence intensity is almost completely self-quenched and fluorescence lifetimes in the nanosecond region decrease 2 times. This is easily measured. Usually large heavy metal atoms quench fluorescence. We observed the opposite new effect when LB film is deposited in the solid phase from a subphase containing heavy metals. The third new effect is the obtaining of nanosized cylinders with bilayer thickness, which remain stable at least for months, when LB monolayer is deposited in the phase coexistence region at thermodynamic equilibrium. This greatly increases reacting surface and sensitivity of possible sensors. Almost all possible optical experimental methods were used for this research. This includes polarized ATR FTIR and polarized UV-VIS spectroscopies, Fluorescence Lifetime Imaging Microscopy (FLIM), Scanning Near-field Optical Microscopy (SNOM).

Single molecule detection of nitric oxide enabled by d(AT)15 DNA adsorbed to near infrared fluorescent single-walled carbon nanotubes.

PubMed

Zhang, Jingqing; Boghossian, Ardemis A; Barone, Paul W; Rwei, Alina; Kim, Jong-Ho; Lin, Dahua; Heller, Daniel A; Hilmer, Andrew J; Nair, Nitish; Reuel, Nigel F; Strano, Michael S

2011-01-26

We report the selective detection of single nitric oxide (NO) molecules using a specific DNA sequence of d(AT)(15) oligonucleotides, adsorbed to an array of near-infrared fluorescent semiconducting single-walled carbon nanotubes (AT(15)-SWNT). While SWNT suspended with eight other variant DNA sequences show fluorescence quenching or enhancement from analytes such as dopamine, NADH, L-ascorbic acid, and riboflavin, d(AT)(15) imparts SWNT with a distinct selectivity toward NO. In contrast, the electrostatically neutral polyvinyl alcohol enables no response to nitric oxide, but exhibits fluorescent enhancement to other molecules in the tested library. For AT(15)-SWNT, a stepwise fluorescence decrease is observed when the nanotubes are exposed to NO, reporting the dynamics of single-molecule NO adsorption via SWNT exciton quenching. We describe these quenching traces using a birth-and-death Markov model, and the maximum likelihood estimator of adsorption and desorption rates of NO is derived. Applying the method to simulated traces indicates that the resulting error in the estimated rate constants is less than 5% under our experimental conditions, allowing for calibration using a series of NO concentrations. As expected, the adsorption rate is found to be linearly proportional to NO concentration, and the intrinsic single-site NO adsorption rate constant is 0.001 s(-1) μM NO(-1). The ability to detect nitric oxide quantitatively at the single-molecule level may find applications in new cellular assays for the study of nitric oxide carcinogenesis and chemical signaling, as well as medical diagnostics for inflammation.

On-off QD switch that memorizes past recovery from quenching by diazonium salts.

PubMed

Liras, Marta; González-Béjar, María; Scaiano, J C

2010-09-07

The understanding of the interaction of CdSe/ZnS semiconductor quantum dots (QD) with their chemical environment is fundamental, yet far from being fully understood. p-Methylphenyldiazonium tetrafluoroborate has been used to get some insight into the effect of diazonium salts on the spectroscopy of QD. Our study reveals that the surface of CdSe/ZnS quantum dots can be modified by diazonium salts (although not functionalized), showing and on-off fluorescence behaviour that memorizes past quenching recoveries. Facile modification of the surface confers protection against quenching by new molecules of diazonium salt and other known quenchers such as 4-amino-TEMPO. The reaction mechanism has been explored in detail by using different spectroscopic techniques. At the first time after addition of diazonium salt over QD the fluorescent is turned off with Stern-Volmer behaviour; the fluorescence recovers following irradiation. Subsequent additions of diazonium salts do not cause the same degree of quenching. We have noted that the third addition (following two cycles of addition and irradiation) is unable to quench the fluorescence. Monitoring the process using NMR techniques reveals the formation of p-difluoroborane toluene as a result of the irradiation of diazonium-treated QD; the treatment leads to the fluorination of the QD surface.

Determination of phenformin hydrochloride employing a sensitive fluorescent probe

NASA Astrophysics Data System (ADS)

Shi, Lin; Xie, Jian-Hong; Du, Li-Ming; Chang, Yin-xia; Wu, Hao

2016-06-01

A complexation of non-fluorescent phenformin hydrochloride (PFH) with cucurbit [7]uril (CB [7]) in aqueous solution was investigated using the fluorescent probe of palmatine (PAL) coupled with CB [7]. The fluorescent probe of CB [7]-PAL exhibited strong fluorescence in aqueous solution, which was quenched gradually with the increase of PFH. This effect is observed because when PFH was added to the host-guest system of CB [7]-PAL, PFH and PAL competed to occupy the CB [7] cavity. Portions of the PAL molecule were expelled from the CB [7] cavity owing to the introduction of PFH. Based on the significant quenching of the supramolecular complex fluorescence intensity, a fluorescence method of high sensitivity and selectivity was developed to determine PFH with good precision and accuracy for the first time. The linear range of the method was 0.005-1.9 μg mL- 1 with a detection limit of 0.003 μg mL- 1. In this work, association constants (K) of PFH with CB [7] were also determined. KCB [7]-PFH = (2.52 ± 0.05) × 105 L mol- 1. The ability of PFH to bind with CB [7] is stronger than that of PAL. The results of a density functional theory calculation authenticated that the moiety of PFH was embedded in the hydrophobic cavity of CB [7] tightly, and the nitrogen atom is located in the vicinity of a carbonyl-laced portal in the energy-minimized structure. The molecular modelling of the interaction between PFH and CB [7] was also confirmed by 1H NMR spectra (Bruker 600 MHz).

Binding analysis for interaction of diacetylcurcumin with β-casein nanoparticles by using fluorescence spectroscopy and molecular docking calculations

NASA Astrophysics Data System (ADS)

Mehranfar, Fahimeh; Bordbar, Abdol-Khalegh; Fani, Najme; Keyhanfar, Mehrnaz

2013-11-01

The interaction of diacetylcurcumin (DAC), as a novel synthetic derivative of curcumin, with bovine β-casein (an abundant milk protein that is highly amphiphilic and self assembles into stable micellar nanoparticles in aqueous solution) was investigated using fluorescence quenching experiments, Forster energy transfer measurements and molecular docking calculations. The fluorescence quenching measurements revealed the presence of a single binding site on β-casein for DAC with the binding constant value equals to (4.40 ± 0.03) × 104 M-1. Forster energy transfer measurements suggested that the distance between bound DAC and Trp143 residue is higher than the respective critical distance, hence, the static quenching is more likely responsible for fluorescence quenching other than the mechanism of non-radiative energy transfer. Our results from molecular docking calculations indicated that binding of DAC to β-casein predominantly occurred through hydrophobic contacts in the hydrophobic core of protein. Additionally, in vitro investigation of the cytotoxicity of free DAC and DAC-β-casein complex in human breast cancer cell line MCF7 revealed the higher cytotoxic effect of DAC-β-casein complex.

Femtogram detection of explosive nitroaromatics: fluoranthene-based fluorescent chemosensors.

PubMed

Venkatramaiah, N; Kumar, Shiv; Patil, Satish

2012-11-12

Herein we report a novel fluoranthene-based fluorescent fluorophore 7,10-bis(4-bromophenyl)-8,9-bis[4-(hexyloxy)phenyl]fluoranthene (S(3)) and its remarkable properties in applications of explosive detection. The sensitivity towards the detection of nitroaromatics (NACs) was evaluated through fluorescence quenching in solution, vapor, and contact mode approaches. The contact mode approach using thin-layer silica chromatographic plates exhibited a femtogram (1.15 fg cm(-2)) detection limit for trinitrotoluene (TNT) and picric acid (PA), whereas the solution-phase quenching showed PA detection at the 2-20 ppb level. Fluorescence lifetime measurements revealed that the quenching is static in nature and the quenching process is fully reversible. Binding energies between model binding sites of the S(3) and analyte compounds reveal that analyte molecules enter into the cavity created by substituted phenyl rings of fluoranthene and are stabilized by strong intermolecular interactions with alkyl chains. It is anticipated that the sensor S(3) could be a promising material for the construction of portable optical devices for the detection of onsite explosive nitroaromatics. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of gold nanoparticles on the fluorescence excitation spectrum of α-fetoprotein: Local environment dependent fluorescence quenching

NASA Astrophysics Data System (ADS)

Li, Jian-jun; Chen, Yu; Wang, A.-qing; Zhu, Jian; Zhao, Jun-wu

2011-01-01

The effect of colloid gold nanoparticles (AuNPs) on the fluorescence excitation spectrum of α-fetoprotein (AFP) has been investigated experimentally. The excitation spectral peaks of AFP with low concentration from 0.01 ng ml -1 to 12 ng ml -1 increase monotonically with increasing of AFP concentration. When some gold colloids were added to the AFP solution, the excitation peak at 285 nm decreases distinctly. By comparing the excitation peak intensity of AFP solution with gold colloids and without gold colloids at different AFP concentrations, the quenching effect from gold nanoparticle was more effective at lower AFP concentration. So the range of concentration from 0.01 ng ml -1 to 0.09 ng ml -1 will be the potential range of applications because of the higher sensitivity. The physical origin based on local field effect was investigated to illuminate this local environment dependent fluorescence quenching. The changing extent of quenching with different AFP concentrations can be attributed to the nonlinear decreasing of the local field factor of gold nanoparticles as a function of environmental dielectric constant.

Fluorescent film sensors based on SAMs of pyrene derivatives for detecting nitroaromatics in aqueous solutions

NASA Astrophysics Data System (ADS)

Zhang, Shujuan; Ding, Liping; Lü, Fengting; Liu, Taihong; Fang, Yu

2012-11-01

The detection of nitroaromatics in aqueous solutions by a novel pyrene-functionalized film has been investigated in the present study. The pyrene moieties were attached on the glass surface via a long flexible spacer based on self-assembled monolayer technique. Steady-state fluorescence measurements revealed that these surface-attached pyrene moieties exhibited both monomer and excimer emission. Nitroaromatics such as 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, and 2,4,6-trinitrophenol (picric acid) were found to efficiently quench the fluorescence emission of this film. The quenching results demonstrated that the excimer emission of these surface-confined pyrene moieties is more sensitive to the presence of nitroaromatics than the monomer emission. The quenching mechanism was examined through fluorescence lifetime measurement and it revealed that the quenching is static in nature and may be caused by electron transfer from the polycyclic aromatics to the nitroaromatics. Furthermore, the response of the film to nitroaromatics is fast and reversible, and the obtained film shows promising potentials in detecting explosives in aqueous environment.

Green preparation of carbon dots with mangosteen pulp for the selective detection of Fe3+ ions and cell imaging

NASA Astrophysics Data System (ADS)

Yang, Rui; Guo, Xiangfeng; Jia, Lihua; Zhang, Yu; Zhao, Zhenlong; Lonshakov, Fedor

2017-11-01

A simple method was developed in the synthesis of fluorescent carbon dots (referred to as M-CDs), calcined treatment of mangosteen pulp in air, without the assistance of any chemical reagent. The M-CDs possess good-solubility, satisfactory chemical stability and can be applied as the fluorescent temperature probe. More strikingly, the fluorescence of M-CDs can be fleetly and selectively quenched by Fe3+ ions. The phenomenon was used to develop a fluorescent method for facile detection of Fe3+ with a linear range of 0-0.18 mM and a detection limit of 52 nM. Eventually, the M-CDs were applied for cell imaging, demonstrating their potential toward diverse applications.

Intrinsic Fluorescence as a Spectral Probe for Protein Denaturation Studies in the Presence of Honey

NASA Astrophysics Data System (ADS)

Wong, Y. H.; Kadir, H. A.; Tayyab, S.

2015-11-01

Honey was found to quench the intrinsic fluorescence of bovine serum albumin (BSA) in a concentration dependent manner, showing complete quenching in the presence of 5% (w/v) honey. Increasing the protein concentration up to 5.0 μM did not lead to the recovery of the protein fluorescence. Urea denaturation of BSA, which otherwise shows a two-step, three-state transition, using intrinsic fluorescence of the protein as the probe failed to produce any result in the presence of 5% (w/v) honey. Thus, intrinsic fluorescence cannot be used as a spectral probe for protein denaturation studies in the presence of honey.

Green Tea Catechins Quench the Fluorescence of Bacteria-Conjugated Alexa Fluor Dyes

PubMed Central

Zhao, Lin; Li, Wei; Zhu, Shu; Tsai, Sheena; Li, Jianhua; Tracey, Kevin J.; Wang, Ping; Fan, Saijun; Sama, Andrew E.; Wang, Haichao

2013-01-01

Accumulating evidence suggests that Green tea polyphenolic catechins, especially the (-)-epigallocatechin gallate (EGCG), can be cross-linked to many proteins, and confer a wide range of anti-bacterial activities possibly by damaging microbial cytoplasmic lipids and proteins. At the doses that conferred protection against lethal polymicrobial infection (induced by cecal ligation and puncture), EGCG significantly reduced bacterial loads particularly in the liver and lung. To elucidate its bactericidal mechanisms, we determined whether EGCG affected the fluorescence intensities of bacteria-conjugated Alexa Fluor 488 or 594 dyes. When mixed with unconjugated Alexa Fluor 488 or 594 dyes, EGCG or analogs did not affect the fluorescence intensity of these dyes. In a sharp contrast, EGCG and some analogs (e.g., Catechin Gallate, CG), markedly reduced the fluorescence intensity of Gram-positive Staphylococcus aureus-conjugated Alexa 594 and Gram-negative Escherichia coli-conjugated Alexa 488. Interestingly, co-treatment with ethanol impaired the EGCG-mediated fluorescence quenching of the G+ S. aureus, but not of the G- E. coli-conjugated Alexa Flour dyes. In light of the notion that Alexa Fluor dyes can be quenched by aromatic amino acids, it is plausible that EGCG exerts anti-microbial activities possibly by altering microbial protein conformations and functions. This possibility can now be explored by screening other fluorescence-quenching agents for possible antimicrobial activities. PMID:24011199

Non-covalent interactions between thio-caffeine derivatives and water-soluble porphyrin in ethanol-water environment

NASA Astrophysics Data System (ADS)

Lipke, Agnieszka; Makarska-Bialokoz, Magdalena; Sierakowska, Arleta; Jasiewicz, Beata

2018-03-01

To determine the binding interactions and ability to form the non-covalent systems, the association process between 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21H,23H-porphine tetra-p-tosylate (H2TTMePP) and a series of five structurally diverse thio-caffeine analogues has been studied in ethanol and ethanol-water solutions, analyzing its absorption and steady-state fluorescence spectra. The porphyrin fluorescence lifetimes in the systems studied were established as well. During the titration with thio-caffeine compounds the slight bathochromic effect and considerable hypochromicity of the porphyrin Soret band maximum can be noted. The fluorescence quenching effect observed for interactions in H2TTMePP - thio-caffeine derivative systems, as well as the order of binding and fluorescence quenching constants (of 105-103 mol- 1) suggest the existence of the mechanism of static quenching due to the formation of non-covalent and non-fluorescent stacking complexes. In all the systems studied the phenomenon of the fractional accessibility of the fluorophore for the quencher was observed as well. Additionally, the specific binding interactions, due to the changes in reaction environment polarity, can be observed. It was found that thio-caffeine compounds can quench the porphyrin fluorescence according to the structure of thio-substituent in caffeine molecule. The obtained results can be potentially useful from scientific, therapeutic or environmental points of view.

Investigation on the pH-dependent binding of benzocaine and lysozyme by fluorescence and absorbance.

PubMed

Li, Shihui; Li, Daojin

2011-11-01

The interaction mechanism between benzocaine (BZC) and lysozyme (Lys) has been investigated by fluorescence, synchronous fluorescence, ultraviolet-vis (UV) absorption spectra, and three-dimensional fluorescence (3-D) in various pH medium. The observations of fluorescence spectra were mainly rationalized in terms of a static quenching process at lower concentration of BZC (C(BZC)/C(Lys)<9) and a combined quenching process at higher concentration of BZC (C(BZC)/C(Lys)>9) at pH 7.4 and 8.4. However, the fluorescence quenching was mainly arisen from static quenching by complex formation in all studied drug concentrations at pH 3.5. The structural characteristics of BZC and Lys were probed, and their binding affinities were determined under different pH conditions (pH 3.5, 7.4, and 8.4). The results indicated that the binding abilities of BZC to Lys decreased at the pH below and above the simulative physiological condition (pH 7.4) due to the alterations of the protein secondary and tertiary structures or the structural change of BZC. The effect of BZC on the conformation of Lys was analyzed using UV, synchronous fluorescence and three-dimensional fluorescence under different pH conditions. These results indicate that the binding of BZC to Lys causes apparent change in the secondary and tertiary structures of Lys. The effect of Zn(2+) on the binding constant of BZC with Lys under various pH conditions (pH 3.5, 7.4, and 8.4) was also studied. Copyright © 2011 Elsevier B.V. All rights reserved.

Non-invasive Photoacoustic and Fluorescence Sentinel Lymph Node Identification using Dye-loaded Perfluorocarbon Nanoparticles

PubMed Central

Akers, Walter J.; Kim, Chulhong; Berezin, Mikhail; Guo, Kevin; Fuhrhop, Ralph; Lanza, Gregory M.; Fischer, Georg M.; Daltrozzo, Ewald; Zumbusch, Andreas; Cai, Xin; Wang, Lihong V.; Achilefu, Samuel

2010-01-01

The contrast mechanisms used for photoacoustic tomography (PAT) and fluorescence imaging differ in subtle but significant ways. Design of contrast agents for each or both modalities requires an understanding of the spectral characteristics as well as intra- and intermolecular interactions that occur during formulation. We found that fluorescence quenching that occurs in the formulation of near infrared (NIR) fluorescent dyes in nanoparticles results in enhanced contrast for PAT. The ability of the new PAT method to utilize strongly absorbing chromophores for signal generation allowed us to convert a highly fluorescent dye into an exceptionally high PA contrast material. Spectroscopic characterization of the developed NIR dye-loaded perfluorocarbon-based nanoparticles for combined fluorescence and PA imaging revealed distinct dye-dependent photophysical behavior. We demonstrate that the enhanced contrast allows detection of regional lymph nodes of rats in vivo with time-domain optical and photoacoustic imaging methods. The results further show that the use of fluorescence lifetime (FLT) imaging, which is less dependent on fluorescence intensity, provides a strategic approach to bridge the disparate contrast reporting mechanisms of fluorescence and PA imaging methods. PMID:21171567

A novel fluorescent retrograde neural tracer: cholera toxin B conjugated carbon dots

NASA Astrophysics Data System (ADS)

Zhou, Nan; Hao, Zeyu; Zhao, Xiaohuan; Maharjan, Suraj; Zhu, Shoujun; Song, Yubin; Yang, Bai; Lu, Laijin

2015-09-01

The retrograde neuroanatomical tracing method is a key technique to study the complex interconnections of the nervous system. Traditional tracers have several drawbacks, including time-consuming immunohistochemical or immunofluorescent staining procedures, rapid fluorescence quenching and low fluorescence intensity. Carbon dots (CDs) have been widely used as a fluorescent bio-probe due to their ultrasmall size, excellent optical properties, chemical stability, biocompatibility and low toxicity. Herein, we develop a novel fluorescent neural tracer: cholera toxin B-carbon dot conjugates (CTB-CDs). It can be taken up and retrogradely transported by neurons in the peripheral nervous system of rats. Our results show that CTB-CDs possess high photoluminescence intensity, good optical stability, a long shelf-life and non-toxicity. Tracing with CTB-CDs is a direct and more economical way of performing retrograde labelling experiments. Therefore, CTB-CDs are reliable fluorescent retrograde tracers.The retrograde neuroanatomical tracing method is a key technique to study the complex interconnections of the nervous system. Traditional tracers have several drawbacks, including time-consuming immunohistochemical or immunofluorescent staining procedures, rapid fluorescence quenching and low fluorescence intensity. Carbon dots (CDs) have been widely used as a fluorescent bio-probe due to their ultrasmall size, excellent optical properties, chemical stability, biocompatibility and low toxicity. Herein, we develop a novel fluorescent neural tracer: cholera toxin B-carbon dot conjugates (CTB-CDs). It can be taken up and retrogradely transported by neurons in the peripheral nervous system of rats. Our results show that CTB-CDs possess high photoluminescence intensity, good optical stability, a long shelf-life and non-toxicity. Tracing with CTB-CDs is a direct and more economical way of performing retrograde labelling experiments. Therefore, CTB-CDs are reliable fluorescent retrograde tracers. Electronic supplementary information (ESI) available: PL spectra of CTB; absorption spectra of dialysate; fluorescence signal and immunohistochemical staining of CTB-CDs in L4 DRG. See DOI: 10.1039/c5nr04361a

Water-Soluble Nonconjugated Polymer Nanoparticles with Strong Fluorescence Emission for Selective and Sensitive Detection of Nitro-Explosive Picric Acid in Aqueous Medium.

PubMed

Liu, Shi Gang; Luo, Dan; Li, Na; Zhang, Wei; Lei, Jing Lei; Li, Nian Bing; Luo, Hong Qun

2016-08-24

Water-soluble nonconjugated polymer nanoparticles (PNPs) with strong fluorescence emission were prepared from hyperbranched poly(ethylenimine) (PEI) and d-glucose via Schiff base reaction and self-assembly in aqueous phase. Preparation of the PEI-d-glucose (PEI-G) PNPs was facile (one-pot reaction) and environmentally friendly under mild conditions. Also, PEI-G PNPs showed a high fluorescence quantum yield in aqueous solution, and the fluorescence properties (such as concentration- and solvent-dependent fluorescence) and origin of intrinsic fluorescence were investigated and discussed. PEI-G PNPs were then used to develop a fluorescent probe for fast, selective, and sensitive detection of nitro-explosive picric acid (PA) in aqueous medium, because the fluorescence can be easily quenched by PA whereas other nitro-explosives and structurally similar compounds only caused negligible quenching. A wide linear range (0.05-70 μM) and a low detection limit (26 nM) were obtained. The fluorescence quenching mechanism was carefully explored, and it was due to a combined effect of electron transfer, resonance energy transfer, and inner filter effect between PA and PEI-G PNPs, which resulted in good selectivity and sensitivity for PA. Finally, the developed sensor was successfully applied to detection of PA in environmental water samples.

Fluorescent trimethyl-substituted naphthyridine as a label-free signal reporter for one-step and highly sensitive fluorescent detection of DNA in serum samples.

PubMed

Wang, Jiamian; Wang, Xiuyun; Wu, Shuo; Che, Ruping; Luo, Pinchen; Meng, Changgong

2017-01-15

A facile label-free sensing method is developed for the one-step and highly sensitive fluorescent detection of DNA, which couples the specific C-C mismatch bonding and fluorescent quenching property of a trimethyl-substituted naphthyridine dye (ATMND) with the exonuclease III (Exo III) assisted cascade target recycling amplification strategy. In the absence of target DNA, the DNA hairpin probe with a C-C mismatch in the stem and more than 4 bases overhung at the 3' terminus could entrap and quench the fluorescence of ATMND and resist the digestion of Exo III, thus showing a low fluorescence background. In the presence of the target, however, the hybridization event between the two protruding segments and the target triggers the digestion reaction of Exo III, recycles the initial target, and simultaneously releases both the secondary target analogue and the ATMND caged in the stem. The released initial and secondary targets take part in another cycle of digestion, thus leading to the release of a huge amount of free ATMND for signal transducing. Based on the fluorescence recovery, the as-proposed label-free fluorescent sensing strategy shows very good analytical performances towards DNA detection, such as a wide linear range from 10pM to 1μM, a low limit of detection of 6pM, good selectivity, and a facile one-step operation at room temperature. Practical sample analysis in serum samples indicates the method has good precision and accuracy, which may thus have application potentials for point-of-care screening of DNA in complex clinical and environmental samples. Copyright © 2016 Elsevier B.V. All rights reserved.

Optimized optical clearing method for imaging central nervous system

NASA Astrophysics Data System (ADS)

Yu, Tingting; Qi, Yisong; Gong, Hui; Luo, Qingming; Zhu, Dan

2015-03-01

The development of various optical clearing methods provides a great potential for imaging entire central nervous system by combining with multiple-labelling and microscopic imaging techniques. These methods had made certain clearing contributions with respective weaknesses, including tissue deformation, fluorescence quenching, execution complexity and antibody penetration limitation that makes immunostaining of tissue blocks difficult. The passive clarity technique (PACT) bypasses those problems and clears the samples with simple implementation, excellent transparency with fine fluorescence retention, but the passive tissue clearing method needs too long time. In this study, we not only accelerate the clearing speed of brain blocks but also preserve GFP fluorescence well by screening an optimal clearing temperature. The selection of proper temperature will make PACT more applicable, which evidently broaden the application range of this method.

Spectroscopic studies on the interaction of a water-soluble cationic porphyrin with proteins

NASA Astrophysics Data System (ADS)

Ma, Hong-Min; Chen, Xin; Zhang, Nuo; Han, Yan-Yan; Wu, Dan; Du, Bin; Wei, Qin

2009-04-01

The interaction of a water-soluble cationic porphyrin, meso-tetrakis (4- N, N, N-trimethylanilinium) porphyrin (TMAP), with two proteins, bovine serum albumin (BSA) and human serum albumin (HSA), was studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, fluorescence anisotropy and synchronous fluorescence spectroscopy at neutral aqueous solutions. Free base TMAP bound to proteins as monomers and no aggregation was observed. The binding of TMAP quenched the fluorescence of the protein. On the contrary, the fluorescence of TMAP was enhanced and the fluorescence anisotropy increased due to the binding. The direct static binding mechanism could account for the quenching by TMAP and the binding constants were calculated. TMAP showed a higher quenching efficiency and binding constant of HSA than BSA. The binding of TMAP had no obvious effect on the molecular conformation of the protein. There was only one binding site for TMAP and it was located on the surface of the protein molecule. Electrostatic force played an important role in the binding due to the opposite charges on porphyrin and the proteins.

Spectroscopic studies on the interaction of a water-soluble cationic porphyrin with proteins.

PubMed

Ma, Hong-Min; Chen, Xin; Zhang, Nuo; Han, Yan-Yan; Wu, Dan; Du, Bin; Wei, Qin

2009-04-01

The interaction of a water-soluble cationic porphyrin, meso-tetrakis (4-N,N,N-trimethylanilinium) porphyrin (TMAP), with two proteins, bovine serum albumin (BSA) and human serum albumin (HSA), was studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, fluorescence anisotropy and synchronous fluorescence spectroscopy at neutral aqueous solutions. Free base TMAP bound to proteins as monomers and no aggregation was observed. The binding of TMAP quenched the fluorescence of the protein. On the contrary, the fluorescence of TMAP was enhanced and the fluorescence anisotropy increased due to the binding. The direct static binding mechanism could account for the quenching by TMAP and the binding constants were calculated. TMAP showed a higher quenching efficiency and binding constant of HSA than BSA. The binding of TMAP had no obvious effect on the molecular conformation of the protein. There was only one binding site for TMAP and it was located on the surface of the protein molecule. Electrostatic force played an important role in the binding due to the opposite charges on porphyrin and the proteins.

Investigations on the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene by certain flavonoids.

PubMed

Anbazhagan, V; Kalaiselvan, A; Jaccob, M; Venuvanalingam, P; Renganathan, R

2008-05-29

The fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by seven flavonoids namely flavone, flavanone, quercetin, rutin, genistein, diadzein and chrysin has been investigated in acetonitrile and dichloromethane solvents. The bimolecular quenching rate constants lie in the range of 0.09-5.75 x 10(9)M(-1)s(-1) and are explained in terms of structure of the flavonoids studied. The reactivity of flavonoids are in the order: quercetin>rutin>genistein>diadzein>chrysin>flavone>flavanone. The quenching rate constants (k(q)) increase with increase in the number of -OH groups. The endergonic thermodynamic values of DeltaG(et) reveal that electron transfer quenching mechanism can be ruled out. Bond dissociation enthalpy calculations reveal that the position of -OH is important. Further in vitro-antioxidant activities of flavonoids were evaluated with rat liver catalase by gel electrophoresis. The deuterium isotope effect thus observed in this work provides evidence for hydrogen abstraction involved in the quenching process of singlet excited DBO by flavonoids. The data suggest the involvement of direct hydrogen atom transfer (radical scavenging) in the fluorescence quenching of DBO. Bond dissociation enthalpy calculation performed at B3LYP/6-31G(p')//B3LYP/3-21G level are in excellent agreement with the above observations and further reveal that the number OH groups and position of them decide the quenching ability of the flavonoids.

Photophysical Characterization of Enhanced 6-Methylisoxanthopterin Fluorescence in Duplex DNA.

PubMed

Moreno, Andrew; Knee, J L; Mukerji, Ishita

2016-12-08

The structure and dynamic motions of bases in DNA duplexes and other constructs are important for understanding mechanisms of selectivity and recognition of DNA-binding proteins. The fluorescent guanine analogue, 6-methylisoxanthopterin 6-MI, is well suited to this purpose as it exhibits an unexpected 3- to 4-fold increase in relative quantum yield upon duplex formation when incorporated into the following sequences: ATFAA, AAFTA, or ATFTA (where F represents 6-MI). To better understand some of the factors leading to the 6-MI fluorescence increase upon duplex formation, we characterized the effect of local sequence and structural perturbations on 6-MI photophysics through temperature melts, quantum yield measurements, fluorescence quenching assays, and fluorescence lifetime measurements. By examining 21 sequences we have determined that the duplex-enhanced fluorescence (DEF) depends on the composition of bases adjacent to 6-MI and the presence of adenines at locations n ± 2 from the probe. Investigation of duplex stability and local solvent accessibility measurements support a model in which the DEF arises from a constrained geometry of 6-MI in the duplex, which remains H-bonded to cytosine, stacked with adjacent bases and inaccessible to quenchers. Perturbation of DNA structure through the introduction of an unpaired base 3' to 6-MI or a mismatched basepair increases 6-MI dynamic motion leading to fluorescence quenching and a reduction in quantum yield. Molecular dynamics simulations suggest the enhanced fluorescence results from a greater degree of twist at the X-F step relative to the quenched duplexes examined. These results point to a model where adenine residues located at n ± 2 from 6-MI induce a structural geometry with greater twist in the duplex that hinders local motion reducing dynamic quenching and producing an increase in 6-MI fluorescence.

Hydrophobic interactions in donor-disulphide-acceptor (DSSA) probes looking beyond fluorescence resonance energy transfer theory.

PubMed

Sanjeeva, Shilpa Kammaradi; Korrapati, Swathi; Nair, Chandrasekhar B; Rao, P V Subba; Pullela, Phani Kumar; Vijayalakshmi, U; Siva, Ramamoorthy

2014-07-01

Donor-linker-acceptor (DSSA) is a concept in fluorescence chemistry with acceptor being a fluorescent compound (FRET) or quencher. The DSSA probes used to measure thiol levels in vitro and in vivo. The reduction potential of these dyes are in the range of -0.60 V, much lower than the best thiol reductant reported in literature, the DTT (-0.33 V). DSSA disulphide having an unusually low reduction potential compared to the typical thiol reductants is a puzzle. Secondly, DSSA probes have a cyclized rhodamine ring as acceptor which does not have any spectral overlap with fluorescein, but quenches its absorbance and fluorescence. To understand the structural features of DSSA probes, we have synthesized DSSANa and DSSAOr. The calculated reduction potential of these dyes suggest that DSSA probes have an alternate mechanism from the FRET based quenching, namely hydrophobic interaction or dye to dye quenching. The standard reduction potential change with increasing complexity and steric hindrance of the molecule is small, suggesting that ultra- low Eo' has no contribution from the disulphide linker and is based on structural interactions between fluorescein and cyclized rhodamine. Our results help to understand the DSSA probe quenching mechanism and provide ways to design fluorescent probes.

Al-based metal-organic gels for selective fluorescence recognition of hydroxyl nitro aromatic compounds

NASA Astrophysics Data System (ADS)

Guo, Mao Xia; Yang, Liu; Jiang, Zhong Wei; Peng, Zhe Wei; Li, Yuan Fang

2017-12-01

The novel class of luminescent Al3 +-based metal-organic gels (Al-MOGs) have been developed by mix 4-[2,2‧:6‧,2″-terpyridine]-4‧-ylbenzoic acid (Hcptpy) with Al3 + under mild condition. The as-prepared Al-MOGs have not only multiple stimuli-responsive properties, but selective recognition of hydroxyl nitro aromatic compounds, which can quench the fluorescence of the Al-MOGs, while other nitro aromatic analogues without hydroxyl substitutes cannot. The fluorescence of Al-MOGs at 467 nm was seriously quenched by picric acid (PA) whose lowest unoccupied molecular orbital (LUMO) energy levels are lower than those of three other hydroxyl nitro aromatic compounds including 4-nitrophenol (4-NP), 3,5-dinitrosalicylic acid (3,5-DNTSA) and 2,4-dinitrophenol (2,4-DNP). Thus, PA was chosen as a model compound under optimal conditions and the relative fluorescence intensity of Al-MOGs was proportional to the concentration of PA in the range of 5.0-320.0 μM with a detection limit of 4.64 μM. Furthermore, the fluorescence quenching mechanism has also been investigated and revealed that the quenching was attributed to inner filter effects (IFEs), as well as electron transfer (ET) between Al-MOGs and PA.

Al-based metal-organic gels for selective fluorescence recognition of hydroxyl nitro aromatic compounds.

PubMed

Guo, Mao Xia; Yang, Liu; Jiang, Zhong Wei; Peng, Zhe Wei; Li, Yuan Fang

2017-12-05

The novel class of luminescent Al 3+ -based metal-organic gels (Al-MOGs) have been developed by mix 4-[2,2':6',2″-terpyridine]-4'-ylbenzoic acid (Hcptpy) with Al 3+ under mild condition. The as-prepared Al-MOGs have not only multiple stimuli-responsive properties, but selective recognition of hydroxyl nitro aromatic compounds, which can quench the fluorescence of the Al-MOGs, while other nitro aromatic analogues without hydroxyl substitutes cannot. The fluorescence of Al-MOGs at 467nm was seriously quenched by picric acid (PA) whose lowest unoccupied molecular orbital (LUMO) energy levels are lower than those of three other hydroxyl nitro aromatic compounds including 4-nitrophenol (4-NP), 3,5-dinitrosalicylic acid (3,5-DNTSA) and 2,4-dinitrophenol (2,4-DNP). Thus, PA was chosen as a model compound under optimal conditions and the relative fluorescence intensity of Al-MOGs was proportional to the concentration of PA in the range of 5.0-320.0μM with a detection limit of 4.64μM. Furthermore, the fluorescence quenching mechanism has also been investigated and revealed that the quenching was attributed to inner filter effects (IFEs), as well as electron transfer (ET) between Al-MOGs and PA. Copyright © 2017 Elsevier B.V. All rights reserved.

Preparation of carbon quantum dots from cigarette filters and its application for fluorescence detection of Sudan I.

PubMed

Anmei, Su; Qingmei, Zhong; Yuye, Chen; Yilin, Wang

2018-09-06

Carbon quantum dots (CQDs) with quantum yield of 14% were successfully synthesized via a simple, low-cost, and green hydrothermal treatment using cigarette filters as carbon source for the first time. The obtained CQDs showed a strong emission at the wavelength of 465 nm, with an optimum excitation of 365 nm.Sudan I with maximum absorption wavelength at 477 nm could selectively quench the fluorescence of CQDs. Based on this principle, a fluorescence probe was developed for Sudan I determination. Furthermore, the quenching mechanism of the CQDs was elucidated. A linear relationship was found in the range of 2.40-104.0 μmol/L Sudan I with the detection limit (3σ/k) of 0.95 μmol/L. Satisfactory results were achieved when the method was submitted to the determination of Sudan I in food samples. Copyright © 2018 Elsevier B.V. All rights reserved.

Antibacterial potential of rutin conjugated with thioglycolic acid capped cadmium telluride quantum dots (TGA-CdTe QDs)

NASA Astrophysics Data System (ADS)

Ananth, Devanesan Arul; Rameshkumar, Angappan; Jeyadevi, Ramachandran; Jagadeeswari, Sivanadanam; Nagarajan, Natarajan; Renganathan, Rajalingam; Sivasudha, Thilagar

2015-03-01

Quantum dots not only act as nanocarrier but also act as stable and resistant natural fluorescent bio markers used in various in vitro and in vivo photolabelling and biological applications. In this study, the antimicrobial potential of TGA-CdTe QDs and commercial phenolics (rutin and caffeine) were investigated against Escherichiacoli. UV absorbance and fluorescence quenching study of TGA-CdTe QDs with rutin and caffeine complex was measured by spectroscopic technique. QDs-rutin conjugate exhibited excellent quenching property due to the -OH groups present in the rutin structure. But the same time caffeine has not conjugated with QDs because of lacking of -OH group in its structure. Photolabelling of E. coli with QDs-rutin and QDs-caffeine complex was analyzed by fluorescent microscopic method. Microbe E. coli cell membrane damage was assessed by atomic force (AFM) and confocal microscopy. Based on the results obtained, it is suggested that QDs-rutin conjugate enhance the antimicrobial activity more than the treatment with QDs, rutin and caffeine alone.

Mechanistic and conformational studies on the interaction of food dye amaranth with human serum albumin by multispectroscopic methods.

PubMed

Zhang, Guowen; Ma, Yadi

2013-01-15

The mechanism of interaction between food dye amaranth and human serum albumin (HSA) in physiological buffer (pH 7.4) was investigated by fluorescence, UV-vis absorption, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopy. Results obtained from analysis of fluorescence spectra indicated that amaranth had a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The negative value of enthalpy change and positive value of entropy change elucidated that the binding of amaranth to HSA was driven mainly by hydrophobic and hydrogen bonding interactions. The surface hydrophobicity of HSA increased after binding with amaranth. The binding distance between HSA and amaranth was estimated to be 3.03 nm and subdomain IIA (Sudlow site I) was the primary binding site for amaranth on HSA. The results of CD and FT-IR spectra showed that binding of amaranth to HSA induced conformational changes of HSA. Copyright © 2012 Elsevier Ltd. All rights reserved.

Reconsideration of the Detection and Fluorescence Mechanism of a Pyrene-Based Chemosensor for TNT.

PubMed

Lu, Meiheng; Zhou, Panwang; Ma, Yinhua; Tang, Zhe; Yang, Yanqiang; Han, Keli

2018-02-08

The rapid detection of chemical explosives is crucial for national security and public safety, and the investigation of sensing mechanisms is important for designing highly efficient chemosensors. This study theoretically investigates the detection and fluorescence mechanism of a newly synthesized pyrene-based chemosensor for the detection of trinitrotoluene (TNT) through density-functional-theory (DFT) and time-dependent density-functional-theory (TDDFT) methods and suggests a different interaction product of the probe and TNT from previously reported ones [ Mosca et al. J. Am. Chem. Soc. 2015 , 137 , 7967 ]. Instead of forming Meisenheimer complexes, the energies of which are beyond those of the reactants, a low-energy product generated by a π-π-stacking interaction is more rational and favorable. The fluorescence-quenching property further confirms that the π-π-stacking product is the predicted one rather than luminescent Meisenheimer complexes. Frontier-molecular-orbital (FMO)-analysis results show that photoinduced electron transfer (PET) is the mechanism underlying the luminescence quenching of the probe upon exposure to TNT.

Enhanced solubilization of curcumin in mixed surfactant vesicles.

PubMed

Kumar, Arun; Kaur, Gurpreet; Kansal, S K; Chaudhary, Ganga Ram; Mehta, S K

2016-05-15

Self-assemblies of equimolar double and single chain mixed ionic surfactants, with increasing numbers of carbon atoms of double chain surfactant, were analyzed on the basis of fluorescence and conductivity results. Attempts were also made to enhance the solubilization of curcumin in aqueous equimolar mixed surfactant systems. Mixed surfactant assembly was successful in retarding the degradation of curcumin in alkaline media (only 25-28 40% degraded in 10h at pH 13). Fluorescence spectroscopy and fluorescence quenching methods were employed to predict the binding position and mechanism of curcumin with self-assemblies. Results indicate that the interactions take place according to both dynamic and static quenching mechanisms and curcumin was distributed in a palisade layer of mixed aggregates. Antioxidant activity (using DPPH radical) and biocompatibility (using calf-thymus DNA) of curcumin-loaded mixed surfactant formulations were also evaluated. The prepared systems improved the stability, solubility and antioxidant activity of curcumin and additionally are biocompatible. Copyright © 2015 Elsevier Ltd. All rights reserved.

Calorimetric and spectroscopic studies of the interaction between zidovudine and human serum albumin

NASA Astrophysics Data System (ADS)

Pîrnău, Adrian; Mic, Mihaela; Neamţu, Silvia; Floare, Călin G.; Bogdan, Mircea

2018-02-01

A quantitative analysis of the interaction between zidovudine (AZT) and human serum albumin (HSA) was achieved using Isothermal titration calorimetry (ITC) in combination with fluorescence and 1H NMR spectroscopy. ITC directly measure the heat during a biomolecular binding event and gave us thermodynamic parameters and the characteristic association constant. By fluorescence quenching, the binding parameters of AZT-HSA interaction was determined and location to binding site I of HSA was confirmed. Via T1 NMR selective relaxation time measurements the drug-protein binding extent was evaluated as dissociation constants Kd and the involvement of azido moiety of zidovudine in molecular complex formation was put in evidence. All three methods indicated a very weak binding interaction. The association constant determined by ITC (3.58 × 102 M- 1) is supported by fluorescence quenching data (2.74 × 102 M- 1). The thermodynamic signature indicates that at least hydrophobic and electrostatic type interactions played a main role in the binding process.

A sensor based on blue luminescent graphene quantum dots for analysis of a common explosive substance and an industrial intermediate, 2,4,6-trinitrophenol.

PubMed

Li, Zhuo; Wang, Yong; Ni, Yongnian; Kokot, Serge

2015-02-25

A rapid and effective sensor for the analysis of nitrophenol-based explosive substances, represented by trinitrophenol (TNP), has been developed with the use of the blue luminescent graphene quantum dots (GQDs); these GQDs are derived from citric acid by a pyrolysis procedure. They emit strong blue fluorescence at 450 nm after excitation at 365 nm, and TNP can quench this fluorescence because a fluorescence resonance energy transfer occurs. The quenching ratio (F0-F)/F0 was related linearly to the concentration of TNP in the range of 0.1-15 μmol L(-1) with a detection limit of 0.091 μmol L(-1) (S/N=3). The developed method exhibits high sensitivity, good linearity and reliable reproducibility for the quantitative analysis of TNP in water samples. The GQDs were used directly without any further treatment or complicated modification. Copyright © 2014 Elsevier B.V. All rights reserved.

Studies on the interaction between 7-(dimethyl amino)-4-(trifluoromethyl)-2H-1-benzopyran-2-one and cadmium sulfide quantum dots

NASA Astrophysics Data System (ADS)

Kuriakose, Alina C.; Pradeep, C.; Nampoori, V. P. N.; Thomas, Sheenu

2018-04-01

Quantum dots (QDs) are well known for their optical properties which differ from those of bulk semiconductors. Herein, we have created an energy transfer platform that combines CdS QDs with a coumarin based dye C485 [7-(dimethyl amino)-4-(trifluoromethyl)-2H-1-benzopyran-2-one]. Spectroscopic studies of energy transfer between the dye donor and CdS QDs as acceptors reveal the occurrence of dynamic quenching. Analysis of the steady-state and time resolved fluorescence measurements of C485 in the presence of CdS QDs infers fluorescence resonance (Förster type) energy transfer (FRET) as responsible for the quenching phenomena. The energy transfer efficiency as well as energy transfer distance for the donor-acceptor pair is calculated using steady-state fluorescence method. Luminescence enhancement of CdS QDs play a critical role in device performance for solar applications and also in the field of biological applications.

A ratiometric fluorescent quantum dots based biosensor for organophosphorus pesticides detection by inner-filter effect.

PubMed

Yan, Xu; Li, Hongxia; Han, Xiaosong; Su, Xingguang

2015-12-15

In this work, we develop a novel and sensitive sensor for the detection of organophosphorus pesticides based on the inner-filter effect (IFE) between gold nanoparticles (AuNPs) and ratiometric fluorescent quantum dots (RF-QDs). The RF-QDs has been designed by hybridizing two differently colored CdTe QDs, in which the red emissive QDs entrapped in the silica sphere acting as the reference signal, and the green emissive QDs covalently attached on the silica surface serving as the response signal.The fluorescence of RF-QDs could be quenched by AuNPs based on IFE. Protamine could effectively turn on the fluorescence due to the electrostatic attraction between protamine and AuNPs. Trypsin can easily hydrolyze protamine, leading to the quench of the fluorescence. Then, the fluorescence could be recovered again by the addition of parathion-methyl (PM) which could inhibit the activity of trypsin. By measuring the fluorescence of RF-QDs, the inhibition efficiency of PM to trypsin activity was evaluated. Under the optimized conditions, the inhibition efficiency was proportional to the logarithm of PM concentration in the range of 0.04-400 ng mL(-1), with a detection limit of 0.018 ng mL(-1). Furthermore, the simple and convenient method had been used for PM detection in environmental and agricultural samples with satisfactory results. Copyright © 2015 Elsevier B.V. All rights reserved.

Experimental, computational and chemometrics studies of BSA-vitamin B6 interaction by UV-Vis, FT-IR, fluorescence spectroscopy, molecular dynamics simulation and hard-soft modeling methods.

PubMed

Manouchehri, Firouzeh; Izadmanesh, Yahya; Aghaee, Elham; Ghasemi, Jahan B

2016-10-01

The interaction of pyridoxine (Vitamin B6) with bovine serum albumin (BSA) is investigated under pseudo-physiological conditions by UV-Vis, fluorescence and FTIR spectroscopy. The intrinsic fluorescence of BSA was quenched by VB6, which was rationalized in terms of the static quenching mechanism. According to fluorescence quenching calculations, the bimolecular quenching constant (kq), dynamic quenching (KSV) and static quenching (KLB) at 310K were obtained. The efficiency of energy transfer and the distance between the donor (BSA) and the acceptor (VB6) were calculated by Foster's non-radiative energy transfer theory and were equal to 41.1% and 2.11nm. The collected UV-Vis and fluorescence spectra were combined into a row-and column-wise augmented matrix and resolved by multivariate curve resolution-alternating least squares (MCR-ALS). MCR-ALS helped to estimate the stoichiometry of interactions, concentration profiles and pure spectra for three species (BSA, VB6 and VB6-BSA complex) existed in the interaction procedure. Based on the MCR-ALS results, using mass balance equations, a model was developed and binding constant of complex was calculated using non-linear least squares curve fitting. FT-IR spectra showed that the conformation of proteins was altered in presence of VB6. Finally, the combined docking and molecular dynamics (MD) simulations were used to estimate the binding affinity of VB6 to BSA. Five-nanosecond MD simulations were performed on bovine serum albumin (BSA) to study the conformational features of its ligand binding site. From MD results, eleven BSA snapshots were extracted, at every 0.5ns, to explore the binding affinity (GOLD score) of VB6 using a docking procedure. MD simulations indicated that there is a considerable flexibility in the structure of protein that affected ligand recognition. Structural analyses and docking simulations indicated that VB6 binds to site I and GOLD score values depend on the conformations of both BSA and ligand. Molecular modeling results showed that VB6-BSA complex formed not only on the basis of electrostatic forces, but also on the basis of π-π staking and hydrogen bond. There was an excellent agreement between the experimental and computational results. The results presented in this paper, will offer a reference for detailed and systematic studies on the biological effects and action mechanism of small molecules with proteins. Copyright © 2016 Elsevier Inc. All rights reserved.

[Quenched fluorescein: a reference dye for instrument response function of TCSPC].

PubMed

Pan, Hai-feng; Ding, Jing-xin; Liang, Rong-rong; Tao, Zhan-dong; Liu, Meng-wei; Zhang, San-jun; Xu, Jian-hua

2014-08-01

Measuring the instrument response function (IRF) and fitting by reconvolution algorithms are routines to improve time resolution in fluorescence lifetime measurements. Iodide ions were successfully used to quench the fluorescence of fluorescein in this study. By systematically adding saturated NaI water solution in basic fluorescein solution, the lifetimes of fluorescein were reduced from 4 ns to 24 ps. The quenched lifetime of fluorescein obtained from the analysis of Time-Correlated Single Photon Counting (TCSPC) measurement agrees well with that from femtosecond frequency up-conversion measurement. In time resolved excitation spectra measurements, the IRF should be measured at various detection wavelengths providing scattring materials are used. This study could not only reduce the complexity of IRF measurement, but also avoid the existing color effect in system. This study should have wide applications in time resolved fluorescence spectroscopy and fluorescence lifetime imaging.

Quenching of graphene quantum dots fluorescence by alkaline phosphatase activity in the presence of hydroquinone diphosphate.

PubMed

Pereira da Silva Neves, Marta Maria; González-García, María Begoña; Pérez-Junquera, Alejandro; Hernández-Santos, David; Fanjul-Bolado, Pablo

2018-05-01

In this work, a turn-off photoluminescent sensing proof-of-concept based on blue luminescent graphene quantum dots (GQDs) as the fluorescent probe was developed. For that purpose, GQDs optical response was related with the catalytic enzymatic activity of alkaline phosphatase (ALP), in the presence of hydroquinone diphosphate (HQDP). The hydrolysis of HQDP by ALP generated hydroquinone (HQ). The oxidation of HQ, enzymatically produced, to p-benzoquinone (BQ) resulted in the quenching of GQDs fluorescence (FL). Therefore, the developed luminescent sensing mechanism allowed the FL quenching with ALP activity to be related and thus quantified the concentration of ALP down to 0.5 nM of enzyme. This innovative design principle appears as a promising tool for the development of enzymatic sensors based on ALP labeling with fluorescent detection or even for direct ALP luminescent quantification in an easy, fast and sensitive manner. Copyright © 2018 John Wiley & Sons, Ltd.

Fluorescent studies on the interaction of DNA and ternary lanthanide complexes with cinnamic acid-phenanthroline and antibacterial activities testing.

PubMed

Sun, Hui-Juan; Wang, Ai-Ling; Chu, Hai-Bin; Zhao, Yong-Liang

2015-03-01

Twelve lanthanide complexes with cinnamate (cin(-) ) and 1,10-phenanthroline (phen) were synthesized and characterized. Their compositions were assumed to be RE(cin)3 phen (RE(3+)  = La(3+) , Pr(3+) , Nd(3+) , Sm(3+) , Eu(3+) , Gd(3+) , Tb(3+) , Dy(3+) , Ho(3+) , Tm(3+) , Yb(3+) , Lu(3+) ). The interaction mode between the complexes and DNA was investigated by fluorescence quenching experiment. The results indicated the complexes could bind to DNA and the main binding mode is intercalative binding. The fluorescence quenching constants of the complexes increased from La(cin)3 phen to Lu(cin)3 phen. Additionally, the antibacterial activity testing showed that the complexes exhibited excellent antibacterial ability against Escherichia coli, and the changes of antibacterial ability are in agreement with that of the fluorescence quenching constants. Copyright © 2014 John Wiley & Sons, Ltd.

Measuring Norfloxacin Binding to Trypsin Using a Fluorescence Quenching Assay in an Upper-Division, Integrated Laboratory Course

ERIC Educational Resources Information Center

Hicks, Katherine A.

2016-01-01

Fluorescence quenching assays are often used to measure dissociation constants that quantify the binding affinity between small molecules and proteins. In an upper-division undergraduate laboratory course, where students work on projects using a guided inquiry-based approach, a binding titration experiment at physiological pH is performed to…

Fluorescence Aggregation-Caused Quenching versus Aggregation-Induced Emission: A Visual Teaching Technology for Undergraduate Chemistry Students

ERIC Educational Resources Information Center

Ma, Xiaofeng; Sun, Rui; Cheng, Jinghui; Liu, Jiaoyan; Gou, Fei; Xiang, Haifeng; Zhou, Xiangge

2016-01-01

A laboratory experiment visually exploring two opposite basic principles of fluorescence of aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE) is demonstrated. The students would prepared two salicylaldehyde-based Schiff bases through a simple one-pot condensation reaction of one equiv of 1,2-diamine with 2 equiv of…

The Use Of Fluorescence Quenching To Measure Oxygen Concentration

NASA Astrophysics Data System (ADS)

Cox, M. E.; Dunn, B.

1986-01-01

The method of fluorescence quenching is used to measure the concentration of molecular oxygen. The method is rapid, reversible, and does not consume oxygen. The method may provide the basis for a unique biomedical sensor. The key to developing such a device lies in the choice of a fluorophor/polymer composite matrix having the desired optical and transport properties. Experimental results will be presented for certain parameters essential for assessing device development. The properties of interest include the kinetics of fluorescence quenching, the biomolecular rate constants, the temperature dependence of oxygen solubility and diffusivity in the composite matrix, and the oxygen diffusion coefficient. Poly(dimethyl siloxane) [PDMS] was chosen as the polymer host because it is biocompatible, hydrophobic, has a high diffusivity for the simple gases, and is easily bonded to fused silica. 9,10-diphenyl anthracene [9,10-D] was selected since it is readily soluble in a number of organic solvents, has an excitation spectrum in the near UV, an emission spectrum in the visible, a long fluorescence lifetime, and a high quantum yield. When incorporated into PDMS, the optical spectra of 9,10-D does not alter appreciably. The response time of the device is determined by the solution/diffusion kinetics of oxygen in PDMS. The solubility of oxygen in PDMS decreases with increasing temperature and an enthalpy of solution of off = -3.0 kcal/mole. (1) The diffusion of oxyzen in PDMS is found to obey an Arrhenius relation over the temperature range of 5'C to 450C with D = Do exp (-ED/RT) (2) where Do = 0.115 cm2/s (3) and ED = 4.77 kcal/mole. (4) Results of these studies indicate that an appropriate device, based on a fluorophor/polymer composite, for the measurement of oxygen concentration should be sensitive over those ranges which are important for physiological monitoring.

Detection of DNA damage by using hairpin molecular beacon probes and graphene oxide.

PubMed

Zhou, Jie; Lu, Qian; Tong, Ying; Wei, Wei; Liu, Songqin

2012-09-15

A hairpin molecular beacon tagged with carboxyfluorescein in combination with graphene oxide as a quencher reagent was used to detect the DNA damage by chemical reagents. The fluorescence of molecular beacon was quenched sharply by graphene oxide; while in the presence of its complementary DNA the quenching efficiency decreased because their hybridization prevented the strong adsorbability of molecular beacon on graphene oxide. If the complementary DNA was damaged by a chemical reagent and could not form intact duplex structure with molecular beacon, more molecular beacon would adsorb on graphene oxide increasing the quenching efficiency. Thus, damaged DNA could be detected based on different quenching efficiencies afforded by damaged and intact complementary DNA. The damage effects of chlorpyrifos-methyl and three metabolites of styrene such as mandelieaeids, phenylglyoxylieaeids and epoxystyrene on DNA were studied as models. The method for detection of DNA damage was reliable, rapid and simple compared to the biological methods. Copyright © 2012 Elsevier B.V. All rights reserved.

Fluorescent Metal-Organic Framework (MOF) as a Highly Sensitive and Quickly Responsive Chemical Sensor for the Detection of Antibiotics in Simulated Wastewater.

PubMed

Zhu, Xian-Dong; Zhang, Kun; Wang, Yu; Long, Wei-Wei; Sa, Rong-Jian; Liu, Tian-Fu; Lü, Jian

2018-02-05

A Zn(II)-based fluorescent metal-organic framework (MOF) was synthesized and applied as a highly sensitive and quickly responsive chemical sensor for antibiotic detection in simulated wastewater. The fluorescent chemical sensor, denoted FCS-1, exhibited enhanced fluorescence derived from its highly ordered, 3D MOF structure as well as excellent water stability in the practical pH range of simulated antibiotic wastewater (pH = 3.0-9.0). Remarkably, FCS-1 was able to effectively detect a series of sulfonamide antibiotics via photoinduced electron transfer that caused detectable fluorescence quenching, with fairly low detection limits. Two influences impacting measurements related to wastewater treatment and water quality monitoring, the presence of heavy-metal ions and the pH of solutions, were studied in terms of fluorescence quenching, which was nearly unaffected in sulfonamide-antibiotic detection. Additionally, the effective detection of sulfonamide antibiotics was rationalized by the theoretical computation of the energy bands of sulfonamide antibiotics, which revealed a good match between the energy bands of FCS-1 and sulfonamide antibiotics, in connection with fluorescence quenching in this system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Zongchao; Wang, Fengqin, E-mail: wangfengqin@tjpu.edu.cn; Lin, Xiangyi

Metal-organic frameworks (MOFs) are porous crystalline materials with high potential for applications in fluorescence sensors. In this work, two solvent-induced Zn(II)–based metal-organic frameworks, Zn{sub 3}L{sub 3}(DMF){sub 2} (1) and Zn{sub 3}L{sub 3}(DMA){sub 2}(H{sub 2}O){sub 3} (2) (L=4,4′-stilbenedicarboxylic acid), were investigated as selective sensing materials for detection of nitroaromatic compounds and metal ions. The sensing experiments show that 1 and 2 both exhibit selective fluorescence quenching toward nitroaniline with a low detection limit. In addition, 1 exhibits high selectivity for detection of Fe{sup 3+} and Al{sup 3+} by significant fluorescence quenching or enhancement effect. While for 2, it only exhibits significantmore » fluorescence quenching effect for Fe{sup 3+}. The results indicate that 1 and 2 are both promising fluorescence sensors for detecting and recognizing nitroaniline and metal ions with high sensitivity and selectivity. - Graphical abstract: Two MOFs have been selected as the fluorescence sensing materials for selectively sensing mitroaromatic compounds and metal ions. The high selectivity makes them promising fluorescence sensors for detecting and recognizing nitroaniline and Fe{sup 3+} or Al{sup 3+}.« less

Binding of the bioactive component Aloe dihydroisocoumarin with human serum albumin

NASA Astrophysics Data System (ADS)

Zhang, Xiu-Feng; Xie, Ling; Liu, Yang; Xiang, Jun-Feng; Tang, Ya-Lin

2008-11-01

Aloe dihydroisocoumarin, one of new components isolated from Aloe vera, can scavenge reactive oxygen species. In order to explore the mechanism of drug action at a molecular level, the binding of Aloe dihydroisocoumarin with human serum albumin (HSA) has been investigated by using fluorescence, ultraviolet (UV), circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy, fluorescence dynamics, and molecular dynamic docking for the first time. We observed a quenching of fluorescence of HSA in the presence of Aloe dihydroisocoumarin and also analyzed the quenching results using the Stern-Volmer equation and obtained high affinity binding to HSA. An isoemissive point at 414 nm is seen, indicating that the quenching of HSA fluorescence depends on the formation of Aloe dihydroisocoumarin-HSA complex, which is further confirmed by fluorescence dynamic result. From the CD and FT-IR results, it is apparent that the interaction of Aloe dihydroisocoumarin with HSA causes a conformational change of the protein, with the gain of α-helix, β-sheet and random coil stability and the loss of β-turn content. Data obtained by fluorescence spectroscopy, fluorescence dynamics, CD, and FTIR experiments along with the docking studies suggest that Aloe dihydroisocoumarin binds to residues located in subdomain IIA of HSA.

Exciton-controlled fluorescence: application to hybridization-sensitive fluorescent DNA probe.

PubMed

Okamoto, Akimitsu; Ikeda, Shuji; Kubota, Takeshi; Yuki, Mizue; Yanagisawa, Hiroyuki

2009-01-01

A hybridization-sensitive fluorescent probe has been designed for nucleic acid detection, using the concept of fluorescence quenching caused by the intramolecular excitonic interaction of fluorescence dyes. We synthesized a doubly thiazole orange-labeled nucleotide showing high fluorescence intensity for a hybrid with the target nucleic acid and effective quenching for the single-stranded state. This exciton-controlled fluorescent probe was applied to living HeLa cells using microinjection to visualize intracellular mRNA localization. Immediately after injection of the probe into the cell, fluorescence was observed from the probe hybridizing with the target RNA. This fluorescence rapidly decreased upon addition of a competitor DNA. Multicoloring of this probe resulted in the simple simultaneous detection of plural target nucleic acid sequences. This probe realized a large, rapid, reversible change in fluorescence intensity in sensitive response to the amount of target nucleic acid, and facilitated spatiotemporal monitoring of the behavior of intracellular RNA.

Donor-acceptor-pair emission in fluorescent 4H-SiC grown by PVT method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xi, E-mail: liuxi@mail.sic.ac.cn; Zhuo, Shi-Yi; Gao, Pan

Fluorescent SiC, which contains donor and acceptor impurities with optimum concentrations, can work as a phosphor for visible light emission by donor-acceptor-pair (DAP) recombination. In this work, 3 inch N-B-Al co-doped fluorescent 4H-SiC crystals are prepared by PVT method. The p-type fluorescent 4H-SiC with low aluminum doping concentration can show intensive yellow-green fluorescence at room temperature. N-B DAP peak wavelength shifts from 578nm to 525nm and weak N-Al DAP emission occurred 403/420 nm quenches, when the temperature increases from 4K to 298K. The aluminum doping induces higher defect concentration in the fluorescent crystal and decreases optical transmissivity of the crystalmore » in the visible light range. It triggers more non-radiative recombination and light absorption losses in the crystal.« less

Quenching-induced deactivation of photosensitizer by nanoencapsulation to improve phototherapy of cancer.

PubMed

Zeisser-Labouèbe, Magali; Mattiuzzo, Marc; Lange, Norbert; Gurny, Robert; Delie, Florence

2009-09-01

Photodynamic therapy has emerged as a promising alternative to current cancer treatment. However, conventional photosensitizers have several limitations due to their unsuitable pharmaceutical formulations and lack of selectivity. Our strategy was to exploit the advantages of nanoparticles and the quenching-induced deactivation of the model photosensitizer hypericin to produce "activatable" drug delivery systems. Efficient fluorescence and activity quenching were achieved by increasing the drug-loading rate of nanoparticles. In vitro assays confirmed the reversibility of hypericin deactivation, as the hypericin fluorescence and photodynamic activity were recovered upon cell internalization.

Studies on the binding behavior of prodigiosin with bovine hemoglobin by multi-spectroscopic techniques

NASA Astrophysics Data System (ADS)

Tang, Jing; Yang, Chao; Zhou, Lin; Ma, Fei; Liu, Shuchao; Wei, Shaohua; Zhou, Jiahong; Zhou, Yanhuai

2012-10-01

In this article, the interaction mechanism of prodigiosin (PG) with bovine hemoglobin (BHb) is studied in detail using various spectroscopic technologies. UV-vis absorption and fluorescence spectra demonstrate the interaction process. The Stern-Volmer plot and the time-resolved fluorescence study suggest the quenching mechanism of fluorescence of BHb by PG is a static quenching procedure, and the hydrophobic interactions play a major role in binding of PG to BHb. Furthermore, synchronous fluorescence studies, Fourier transform infrared (FTIR) and circular dichroism (CD) spectra reveal that the conformation of BHb is changed after conjugation with PG.

Method of determining the optimal dilution ratio for fluorescence fingerprint of food constituents.

PubMed

Trivittayasil, Vipavee; Tsuta, Mizuki; Kokawa, Mito; Yoshimura, Masatoshi; Sugiyama, Junichi; Fujita, Kaori; Shibata, Mario

2015-01-01

Quantitative determination by fluorescence spectroscopy is possible because of the linear relationship between the intensity of emitted fluorescence and the fluorophore concentration. However, concentration quenching may cause the relationship to become nonlinear, and thus, the optimal dilution ratio has to be determined. In the case of fluorescence fingerprint (FF) measurement, fluorescence is measured under multiple wavelength conditions and a method of determining the optimal dilution ratio for multivariate data such as FFs has not been reported. In this study, the FFs of mixed solutions of tryptophan and epicatechin of different concentrations and composition ratios were measured. Principal component analysis was applied, and the resulting loading plots were found to contain useful information about each constituent. The optimal concentration ranges could be determined by identifying the linear region of the PC score plotted against total concentration.

Quenching characteristics of bathocuproinedisulfonic acid, disodium salt in aqueous solution and copper sulfate plating solution

NASA Astrophysics Data System (ADS)

Koga, Toshiaki; Hirakawa, Chieko; Takeshita, Michinori; Terasaki, Nao

2018-04-01

Bathocuproinedisulfonic acid, disodium salt (BCS) is generally used to detect Cu(I) through a color reaction. We newly found BCS fluorescence in the visible blue region in an aqueous solution. However, the fluorescence mechanism of BCS is not well known, so we should investigate its fundamental information. We confirmed that the characteristics of fluorescence are highly dependent on the molecular concentration and solvent properties. In particular, owing to the presence of the copper compound, the fluorescence intensity extremely decreases. By fluorescence quenching, we observed that a copper compound concentration of 10-6 mol/L or less could easily be measured in an aqueous solution. We also observed BCS fluorescence in copper sulfate plating solution and the possibility of detecting monovalent copper by fluorescence reabsorption.

Spectral Fluorescence Properties of an Anionic Oxacarbocyanine Dye in Complexes with Human Serum Albumin

NASA Astrophysics Data System (ADS)

Pronkin, P. G.; Tatikolov, A. S.

2015-07-01

The spectral fluorescence properties of the anionic oxacarbocyanine dye 3,3'-di-(γ-sulfopropyl)-5,5'-diphenyl-9-ethyloxacarbocyanine betaine (OCC) were studied in solutions and in complexes with human serum albumin (HSA). Interaction with HSA leads to a significant increase in the fluorescence of the dye. We studied quenching of the fluorescence of OCC in a complex with HSA by ibuprofen and warfarin. Data on quenching of fluorescence by ibuprofen indicate binding of the dye to binding site II of subdomain IIIA in the HSA molecule. Synchronous fluorescence spectra of human serum albumin in the presence of OCC showed that complexation with OCC does not lead to appreciable rearrangement of the protein molecule at the binding site.

Light-up fluorescent probes utilizing binding behavior of perylenediimide derivatives to a hydrophobic pocket within DNA.

PubMed

Takada, Tadao; Yamaguchi, Kosato; Tsukamoto, Suguru; Nakamura, Mitsunobu; Yamana, Kazushige

2014-08-21

Here we study the binding behavior of perylenediimide () derivatives to a hydrophobic pocket created inside DNA and their photochemical properties capable of designing a light-up fluorescent sensor for short single-stranded DNA or RNA. The perylenediimide derivative with alkoxy groups () suppressing electron transfer quenching was examined. The bound randomly to DNA showed negligible fluorescence due to the aggregation-induced quenching, whereas the bound to the pocket as a monomeric form showed more than 100-fold fluorescence enhancement. Switching the binding states of the corresponded to a change in the fluorescence response for the hybridization event, which allowed us to design a fluorescent sensor of nucleic acids with a nanomolar detection limit.

Teaching about photosynthesis with simple equipment: analysis of light-induced changes in fluorescence and reflectance of plant leaves.

PubMed

Björn, Lars Olof; Li, Shaoshan

2013-10-01

Solar energy absorbed by plants results in either reflection or absorption. The latter results in photosynthesis, fluorescence, or heat. Measurements of fluorescence changes have been used for monitoring processes associated with photosynthesis. A simple method to follow changes in leaf fluorescence and leaf reflectance associated with nonphotochemical quenching and light acclimation of leaves is described. The main equipment needed consists of a green-light emitting laser pointer, a digital camera, and a personal computer equipped with the camera acquisition software and the programs ImageJ and Excel. Otherwise, only commonly available cheap materials are required.

A novel fluorescence biosensor for sensitivity detection of tyrosinase and acid phosphatase based on nitrogen-doped graphene quantum dots.

PubMed

Qu, Zhengyi; Na, Weidan; Liu, Xiaotong; Liu, Hua; Su, Xingguang

2018-01-02

In this paper, we developed a sensitive fluorescence biosensor for tyrosinase (TYR) and acid phosphatase (ACP) activity detection based on nitrogen-doped graphene quantum dots (N-GQDs). Tyrosine could be catalyzed by TYR to generate dopaquinone, which could efficiently quench the fluorescence of N-GQDs, and the degree of fluorescence quenching of N-GQDs was proportional to the concentration of TYR. In the presence of ACP, l-Ascorbic acid-2-phosphate (AAP) was hydrolyzed to generate ascorbic acid (AA), and dopaquinone was reduced to l-dopa, resulting in the fluorescence recovery of the quenched fluorescence by dopaquinone. Thus, a novel fluorescence biosensor for the detection of TYR and ACP activity based on N-GQDs was constructed. Under the optimized experimental conditions, the fluorescence intensity was linearly correlated with the concentration of TYR and ACP in the range of 0.43-3.85 U mL -1 and 0.04-0.7 mU mL -1 with a detection limit of 0.15 U mL -1 and 0.014 mU mL -1 , respectively. The feasibility of the proposed biosensor in real samples assay was also studied and satisfactory results were obtained. Copyright © 2017 Elsevier B.V. All rights reserved.

Quenching Enhancement of the Singlet Excited State of Pheophorbide-a by DNA in the Presence of the Quinone Carboquone

PubMed Central

Díaz-Espinosa, Yisaira; Crespo-Hernández, Carlos E.; Alegría, Antonio E.; García, Carmelo; Arce, Rafael

2011-01-01

Changes in the emission fluorescence intensity of pheophorbide-a (PHEO) in the presence of carboquone (CARBOQ) were used to obtain the association constant, the number of CARBOQ molecules interacting with PHEO, and the fluorescence quantum yield of the complex. Excitation spectra of mixtures of PHEO and CARBOQ in ethanol (EtOH) show an unresolved doublet in the red-most excitation band of PHEO, indicating the formation of a loose ground-state complex. The 1:1 CARBOQ–PHEO complex shows a higher fluorescence quantum yield in EtOH (0.41 ± 0.02) than in buffer solution (0.089 ± 0.002), which is also higher than that of the PHEO monomer (0.28). Quenching of the PHEO fluorescence by DNA nucleosides and double-stranded oligonucleotides was also observed and the bimolecular quenching rate constants were determined. The quenching rate constant increase as the oxidation potential of the DNA nucleoside increases. Larger quenching constants were obtained in the presence of CARBOQ suggesting that CARBOQ enhances DNA photo-oxidation, presumably by inhibiting the back–electron-transfer reaction from the photoreduced PHEO to the oxidized base. Thus, the enhanced DNA-base photosensitized oxidation by PHEO in the presence of CARBOQ may be related to the large extent by which this quinone covalently binds to DNA, as previously reported. PMID:21138440

Spectroscopic studies on the interaction of bovine serum albumin with surfactants and apigenin

NASA Astrophysics Data System (ADS)

Zhao, Xu-Na; Liu, Yi; Niu, Li-Yuan; Zhao, Chen-Ping

The binding of apigenin (Ap) to bovine serum albumin (BSA) has been studied using the methods of fluorescence spectroscopy and UV-vis absorption spectroscopy. The spectroscopic analysis of the quenching mechanism indicates that the quenching constants are inversely correlated with the temperatures and the quenching process could result from a static interaction. The type of interaction force was discussed and the binding site of Ap was in site I (subdomain IIA) of BSA. The thermodynamic parameters ΔH and ΔS are -42.02 kJ mol-1 and -48.31 J mol-1 K-1, respectively and the negative ΔG implying that the binding interaction was spontaneous. The distance r between BSA and Ap was calculated according to Förster's theory and the value is 3.44 nm. The synchronous and three-dimensional fluorescence spectra show that the binding of Ap to BSA could lead to the changes in the conformation and microenvironment of BSA. At the same time, the effects of ionic surfactants on the interaction of Ap and BSA have also been investigated.

Photoprotective Energy Dissipation in Higher Plants Involves Alteration of the Excited State Energy of the Emitting Chlorophyll(s) in the Light Harvesting Antenna II (LHCII)*

PubMed Central

Johnson, Matthew P.; Ruban, Alexander V.

2009-01-01

Non-photochemical quenching (NPQ), a mechanism of energy dissipation in higher plants protects photosystem II (PSII) reaction centers from damage by excess light. NPQ involves a reduction in the chlorophyll excited state lifetime in the PSII harvesting antenna (LHCII) by a quencher. Yet, little is known about the effect of the quencher on chlorophyll excited state energy and dynamics. Application of picosecond time-resolved fluorescence spectroscopy demonstrated that NPQ involves a red-shift (60 ± 5 cm−1) and slight enhancement of the vibronic satellite of the main PSII lifetime component present in intact chloroplasts. Whereas this fluorescence red-shift was enhanced by the presence of zeaxanthin, it was not dependent upon it. The red-shifted fluorescence of intact chloroplasts in the NPQ state was accompanied by red-shifted chlorophyll a absorption. Nearly identical absorption and fluorescence changes were observed in isolated LHCII complexes quenched in a low detergent media, suggesting that the mechanism of quenching is the same in both systems. In both cases, the extent of the fluorescence red-shift was shown to correlate with the lifetime of a component. The alteration in the energy of the emitting chlorophyll(s) in intact chloroplasts and isolated LHCII was also accompanied by changes in lutein 1 observed in their 77K fluorescence excitation spectra. We suggest that the characteristic red-shifted fluorescence emission reflects an altered environment of the emitting chlorophyll(s) in LHCII brought about by their closer interaction with lutein 1 in the quenching locus. PMID:19567871

Photoprotective energy dissipation in higher plants involves alteration of the excited state energy of the emitting chlorophyll(s) in the light harvesting antenna II (LHCII).

PubMed

Johnson, Matthew P; Ruban, Alexander V

2009-08-28

Non-photochemical quenching (NPQ), a mechanism of energy dissipation in higher plants protects photosystem II (PSII) reaction centers from damage by excess light. NPQ involves a reduction in the chlorophyll excited state lifetime in the PSII harvesting antenna (LHCII) by a quencher. Yet, little is known about the effect of the quencher on chlorophyll excited state energy and dynamics. Application of picosecond time-resolved fluorescence spectroscopy demonstrated that NPQ involves a red-shift (60 +/- 5 cm(-1)) and slight enhancement of the vibronic satellite of the main PSII lifetime component present in intact chloroplasts. Whereas this fluorescence red-shift was enhanced by the presence of zeaxanthin, it was not dependent upon it. The red-shifted fluorescence of intact chloroplasts in the NPQ state was accompanied by red-shifted chlorophyll a absorption. Nearly identical absorption and fluorescence changes were observed in isolated LHCII complexes quenched in a low detergent media, suggesting that the mechanism of quenching is the same in both systems. In both cases, the extent of the fluorescence red-shift was shown to correlate with the lifetime of a component. The alteration in the energy of the emitting chlorophyll(s) in intact chloroplasts and isolated LHCII was also accompanied by changes in lutein 1 observed in their 77K fluorescence excitation spectra. We suggest that the characteristic red-shifted fluorescence emission reflects an altered environment of the emitting chlorophyll(s) in LHCII brought about by their closer interaction with lutein 1 in the quenching locus.

Variation among slash pine families in chlorophyll fluorescence traits

Treesearch

Anita C. Koehn; James H. Roberds; Robert L. Doudrick

2003-01-01

Abstract: Photochemical quenching, nonphotochemical quenching, and yield of photosystem II were measured on seedlings of full-sibling, open-, and self-pollinated slash pine (Pinus elliottii Engelm. var. elliottii) families. Our results reveal that genetic variation in photochemical quenching and yield of...

Ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine and N-acetyltryptophan in aqueous solution: proton-coupled electron transfer versus electron transfer.

PubMed

Zhang, Ying; Yuan, Shuwei; Lu, Rong; Yu, Anchi

2013-06-20

We studied the ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine (AcTyr) and N-acetyltryptophan (AcTrp) in aqueous solution with femtosecond transient absorption spectroscopy. We found that the charge-transfer rate between Atto655 and AcTyr is about 240 times smaller than that between Atto655 and AcTrp. The pH value and D2O dependences of the excited-state decay kinetics of Atto655 in the presence of AcTyr and AcTrp reveal that the quenching of Atto655 fluorescence by AcTyr in aqueous solution is via a proton-coupled electron-transfer (PCET) process and that the quenching of Atto655 fluorescence by AcTrp in aqueous solution is via an electron-transfer process. With the version of the semiclassical Marcus ET theory, we derived that the electronic coupling constant for the PCET reaction between Atto655 and AcTyr in aqueous solution is 8.3 cm(-1), indicating that the PCET reaction between Atto655 and AcTyr in aqueous solution is nonadiabatic.

Multispectroscopic and bioimaging approach for the interaction of rhodamine 6G capped gold nanoparticles with bovine serum albumin.

PubMed

Manjubaashini, N; Kesavan, Mookkandi Palsamy; Rajesh, Jegathalaprathaban; Daniel Thangadurai, T

2018-06-01

Binding interaction of Bovine Serum Albumin (BSA) with newly prepared rhodamine 6G-capped gold nanoparticles (Rh6G-Au NPs) under physiological conditions (pH 7.2) was investigated by a wide range of photophysical techniques. Rh6G-Au NPs caused the static quenching of the intrinsic fluorescence of BSA that resulted from the formation of ground-state complex between BSA and Rh6G-Au NPs. The binding constant from fluorescence quenching method (K a  = 1.04 × 10 4  L mol -1 ; LoD = 14.0 μM) is in accordance with apparent association constant (K app  = 1.14 × 10 1  M -1 ), which is obtained from absorption spectral studies. Förster resonance energy transfer (FRET) efficiency between the tryptophan (Trp) residue of BSA and fluorophore of Rh6G-Au NPs during the interaction was calculated to be 90%. The free energy change (ΔG = -23.07 kJ/mol) of BSA-Rh6G-Au NPs complex was calculated based on modified Stern-Volmer Plot. The time-resolved fluorescence analysis confirmed that quenching of BSA follows static mechanism through the formation of ground state complex. Furthermore, synchronous and three-dimensional fluorescence measurement, Raman spectral analysis and Circular Dichroism spectrum results corroborate the strong binding between Rh6G-Au NPs and BSA, which causes the conformational changes on BSA molecule. In addition, fluorescence imaging experiments of BSA in living human breast cancer (HeLa) cells was successfully demonstrated, which articulated the value of Rh6G-Au NPs practical applications in biological systems. Copyright © 2018. Published by Elsevier B.V.

Quantitative and discriminative analysis of nucleic acid samples using luminometric nonspecific nanoparticle methods

NASA Astrophysics Data System (ADS)

Pihlasalo, S.; Mariani, L.; Härmä, H.

2016-03-01

Homogeneous simple assays utilizing luminescence quenching and time-resolved luminescence resonance energy transfer (TR-LRET) were developed for the quantification of nucleic acids without sequence information. Nucleic acids prevent the adsorption of a protein to europium nanoparticles which is detected as a luminescence quenching of europium nanoparticles with a soluble quencher or as a decrease of TR-LRET from europium nanoparticles to the acceptor dye. Contrary to the existing methods based on fluorescent dye binding to nucleic acids, equal sensitivities for both single- (ssDNA) and double-stranded DNA (dsDNA) were measured and a detection limit of 60 pg was calculated for the quenching assay. The average coefficient of variation was 5% for the quenching assay and 8% for the TR-LRET assay. The TR-LRET assay was also combined with a nucleic acid dye selective to dsDNA in a single tube assay to measure the total concentration of DNA and the ratio of ssDNA and dsDNA in the mixture. To our knowledge, such a multiplexed assay is not accomplished with commercially available assays.Homogeneous simple assays utilizing luminescence quenching and time-resolved luminescence resonance energy transfer (TR-LRET) were developed for the quantification of nucleic acids without sequence information. Nucleic acids prevent the adsorption of a protein to europium nanoparticles which is detected as a luminescence quenching of europium nanoparticles with a soluble quencher or as a decrease of TR-LRET from europium nanoparticles to the acceptor dye. Contrary to the existing methods based on fluorescent dye binding to nucleic acids, equal sensitivities for both single- (ssDNA) and double-stranded DNA (dsDNA) were measured and a detection limit of 60 pg was calculated for the quenching assay. The average coefficient of variation was 5% for the quenching assay and 8% for the TR-LRET assay. The TR-LRET assay was also combined with a nucleic acid dye selective to dsDNA in a single tube assay to measure the total concentration of DNA and the ratio of ssDNA and dsDNA in the mixture. To our knowledge, such a multiplexed assay is not accomplished with commercially available assays. Electronic supplementary information (ESI) available: The labeling of amino modified polystyrene nanoparticles with Eu3+ chelate and the experimental details and results for the optimization of nucleic acid binding protein and for the ratiometric measurement of DNA and RNA with quenching assay. See DOI: 10.1039/c5nr09252c

Determination of phenformin hydrochloride employing a sensitive fluorescent probe.

PubMed

Shi, Lin; Xie, Jian-Hong; Du, Li-Ming; Chang, Yin-xia; Wu, Hao

2016-06-05

A complexation of non-fluorescent phenformin hydrochloride (PFH) with cucurbit [7]uril (CB [7]) in aqueous solution was investigated using the fluorescent probe of palmatine (PAL) coupled with CB [7]. The fluorescent probe of CB [7]-PAL exhibited strong fluorescence in aqueous solution, which was quenched gradually with the increase of PFH. This effect is observed because when PFH was added to the host-guest system of CB [7]-PAL, PFH and PAL competed to occupy the CB [7] cavity. Portions of the PAL molecule were expelled from the CB [7] cavity owing to the introduction of PFH. Based on the significant quenching of the supramolecular complex fluorescence intensity, a fluorescence method of high sensitivity and selectivity was developed to determine PFH with good precision and accuracy for the first time. The linear range of the method was 0.005-1.9 μg mL(-1) with a detection limit of 0.003 μg mL(-1). In this work, association constants (K) of PFH with CB [7] were also determined. KCB [7]-PFH=(2.52±0.05)×10(5) L mol(-1). The ability of PFH to bind with CB [7] is stronger than that of PAL. The results of a density functional theory calculation authenticated that the moiety of PFH was embedded in the hydrophobic cavity of CB [7] tightly, and the nitrogen atom is located in the vicinity of a carbonyl-laced portal in the energy-minimized structure. The molecular modelling of the interaction between PFH and CB [7] was also confirmed by (1)H NMR spectra (Bruker 600 MHz). Copyright © 2016 Elsevier B.V. All rights reserved.

Light-dependent quenching of chlorophyll fluorescence in pea chloroplasts induced by adenosine 5'-triphosphate.

PubMed

Horton, P; Black, M T

1981-03-12

Addition of ATP to chloroplasts causes a reversible 25-30% decrease in chlorophyll fluorescence. This quenching is light-dependent, uncoupler insensitive but inhibited by DCMU and electron acceptors and has a half-time of 3 minutes. Electron donors to Photosystem I can not overcome the inhibitory effect of DCMU, suggesting that light activation depends on the reduced state of plastoquinone. Fluorescence emission spectra recorded at -196 degrees C indicate that ATP treatment increases the amount of excitation energy transferred to Photosystem I. Examination of fluorescence induction curves indicate that ATP treatment decreases both the initial (F0) and variable (Fv) fluorescence such that the ratio of Fv to the maximum (Fm) yield is unchanged. The initial sigmoidal phase of induction is slowed down by ATP treatment and is quenched 3-fold more than the exponential slow phase, the rate of which is unchanged. A plot of Fv against area above the induction curve was identical plus or minus ATP. Thus ATP treatment can alter quantal distribution between Photosystems II and I without altering Photosystem II-Photosystem II interaction. The effect of ATP strongly resembles in its properties the phosphorylation of the light-harvesting complex by a light activated, ATP-dependent protein kinase found in chloroplast membranes and could be the basis of physiological mechanisms which contribute to slow fluorescence quenching in vivo and regulate excitation energy distribution between Photosystem I and II. It is suggested that the sensor for this regulation is the redox state of plastoquinone.

Fluorescent biosensor for the detection of hyaluronidase: intensity-based ratiometric sensing and fluorescence lifetime-based sensing using a long lifetime azadioxatriangulenium (ADOTA) fluorophore.

PubMed

Chib, Rahul; Mummert, Mark; Bora, Ilkay; Laursen, Bo W; Shah, Sunil; Pendry, Robert; Gryczynski, Ignacy; Borejdo, Julian; Gryczynski, Zygmunt; Fudala, Rafal

2016-05-01

In this report, we have designed a rapid and sensitive, intensity-based ratiometric sensing as well as lifetime-based sensing probe for the detection of hyaluronidase activity. Hyaluronidase expression is known to be upregulated in various pathological conditions. We have developed a fluorescent probe by heavy labeling of hyaluronic acid with a new orange/red-emitting organic azadioxatriangulenium (ADOTA) fluorophore, which exhibits a long fluorescence lifetime (∼20 ns). The ADOTA fluorophore in water has a peak fluorescence lifetime of ∼20 ns and emission spectra centered at 560 nm. The heavily ADOTA-labeled hyaluronic acid (HA-ADOTA) shows a red shift in the peak emission wavelength (605 nm), a weak fluorescence signal, and a shorter fluorescence lifetime (∼4 ns) due to efficient self-quenching and formation of aggregates. In the presence of hyaluronidase, the brightness and fluorescence lifetime of the sample increase with a blue shift in the peak emission to its original wavelength at 560 nm. The ratio of the fluorescence intensity of the HA-ADOTA probe at 560 and 605 nm can be used as the sensing method for the detection of hyaluronidase. The cleavage of the hyaluronic acid macromolecule reduces the energy migration between ADOTA molecules, as well as the degree of self-quenching and aggregation. This probe can be efficiently used for both intensity-based ratiometric sensing as well as fluorescence lifetime-based sensing of hyaluronidase. The proposed method makes it a rapid and sensitive assay, useful for analyzing levels of hyaluronidase in relevant clinical samples like urine or plasma. Graphical Abstract Scheme showing cleavage of HA-ADOTA probe by hyaluronidase and the change in the emission spectrum of HA-ADOTA probe before and after cleavage by hyaluronidase.

Spectroscopic analysis on the resveratrol-DNA binding interactions at physiological pH

NASA Astrophysics Data System (ADS)

Zhang, Shufang; Sun, Xuejun; Jing, Zhihong; Qu, Fengli

2011-11-01

The interaction of resveratrol with calf thymus deoxyribonucleic acid (ctDNA) under physiological conditions (Tris-HCl buffer solutions, pH 7.4) was studied by spectroscopy, fluorescence spectroscopy and viscosity measurement method, respectively. Results indicated that a complex of resveratrol with ctDNA was formed with a binding constant of K17 °C = 5.49 × 10 3 L mol -1 and K37 °C = 1.90 × 10 4 L mol -1. The fluorescence quenching mechanism of acridine orange (AO)-ctDNA by resveratrol was shown to be a static quenching type. The thermodynamic parameters of the complex were calculated by a double reciprocal method: ΔHms=4.64×10 J mol, ΔSms=231.8 J K mol and ΔGms=-2.54×10 J mol (37 °C). Spectroscopic techniques together with viscosity determination provided evidences of intercalation mode of binding for the interaction between resveratrol and ctDNA.

Mechanism of Dimercaptosuccinic Acid Coated Superparamagnetic Iron Oxide Nanoparticles with Human Serum Albumin.

PubMed

Zhao, Lining; Song, Wei; Wang, Jing; Yan, Yunxing; Chen, Jiangwei; Liu, Rutao

2015-12-01

To research the mechanism of dimercaptosuccinic acid coated-superparamagnetic iron oxide nanoparticles (SPION) with human serum albumin (HSA), the methods of spectroscopy, molecular modeling calculation, and calorimetry were used in this paper. The inner filter effect of the fluorescence intensity was corrected to obtain the accurate results. Ultraviolet-visible absorption and circular dichroism spectra reflect that SPION changed the secondary structure with a loss of α-helix and loosened the protein skeleton of HSA; the activity of the protein was also affected by the increasing exposure of SPION. Fluorescence lifetime measurement indicates that the quenching mechanism type of this system was static quenching. The isothermal titration calorimetry measurement and molecular docking calculations prove that the predominant force of this system was the combination of Van der Waals' force and hydrogen bonds. © 2015 Wiley Periodicals, Inc.

Selective detection of dopamine in the presence of ascorbic acid via fluorescence quenching of InP/ZnS quantum dots.

PubMed

Ankireddy, Seshadri Reddy; Kim, Jongsung

2015-01-01

Dopamine is a neurotransmitter of the catecholamine family and has many important roles, especially in human brain. Several diseases of the nervous system, such as Parkinson's disease, attention deficit hyperactivity disorder, restless legs syndrome, are believed to be related to deficiency of dopamine. Several studies have been performed to detect dopamine by using electrochemical analysis. In this study, quantum dots (QDs) were used as sensing media for the detection of dopamine. The surface of the QDs was modified with l-cysteine by coupling reaction to increase the selectivity of dopamine. The fluorescence of cysteine-capped indium phosphide/zinc sulfide QDs was quenched by dopamine with various concentrations in the presence of ascorbic acid. This method shows good selectivity for dopamine detection, and the detection limit was 5 nM.

The investigation of the interaction between NCP-EDA and bovine serum albumin by spectroscopic approaches

NASA Astrophysics Data System (ADS)

Yu, Xianyong; Lu, Shiyu; Yang, Ying; Li, Xiaofang; Yi, Pinggui

2011-12-01

The fluorescence and ultraviolet spectroscopies were explored to study the interaction between N-confused porphyrins-edaravone diad (NCP-EDA) and bovine serum albumin (BSA) under simulative physiological condition at different temperatures. The experimental results show that the fluorescence quenching mechanism between NCP-EDA and BSA is a combined quenching (dynamic and static quenching). The binding constants, binding sites and the corresponding thermodynamic parameters (Δ G, Δ H, and Δ S) of the interaction system were calculated at different temperatures. According to Förster non-radiation energy transfer theory, the binding distance between NCP-EDA and BSA was calculated to be 3.63 nm. In addition, the effect of NCP-EDA on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy.

A metal-organic framework based on nanosized hexagonal channels as fluorescent indicator for detection of nitroaromatic explosives

NASA Astrophysics Data System (ADS)

Hu, Xiao-Li; Wang, Xin-Long; Su, Zhong-Min

2018-02-01

A novel Zn-MOF (metal organic framework) [Zn3(NTB)2(DMA)2]·12DMA (NTB = 4,4‧,4″-nitrilotrisbenzoic acid; DMA = N,N-dimethylacetamide) (1) was obtained under solvothermal condition. The resulted MOF which is based on {Zn3} SBU displays an interesting (3,6)-connected three-dimensional net with nanosized, hexagonal channels. Additionally, 1 can be a useful fluorescent indicator for the detection of nitroaromatic explosives qualitatively and quantitatively via a strong quenching effect, especially for picric acid (PA). With increasing - NO2 groups, energy transfer from the electron-donating framework to high electron deficiency becomes more, making the effect of fluorescence quenching more obvious. The result demonstrates that the photo-induced electron transfer (PET) is responsible for the emission quenching.

Simple replacement of violaxanthin by zeaxanthin in LHC-II does not cause chlorophyll fluorescence quenching.

PubMed

Dreuw, Andreas; Wormit, Michael

2008-03-01

Recently, a mechanism for the energy-dependent component (qE) of non-photochemical quenching (NPQ), the fundamental photo-protection mechanism in green plants, has been suggested. Replacement of violaxanthin by zeaxanthin in the binding pocket of the major light harvesting complex LHC-II may be sufficient to invoke efficient chlorophyll fluorescence quenching. Our quantum chemical calculations, however, show that the excited state energies of violaxanthin and zeaxanthin are practically identical when their geometry is constrained to the naturally observed structure of violaxanthin in LHC-II. Therefore, since violaxanthin does not quench LHC-II, zeaxanthin should not either. This theoretical finding is nicely in agreement with experimental results obtained by femtosecond spectroscopy on LHC-II complexes containing violaxanthin or zeaxanthin.

Fluorescence and visual detection of fluoride ions using a photoluminescent graphene oxide paper sensor.

PubMed

Chen, Xiaochun; Yu, Shaoming; Yang, Liang; Wang, Jianping; Jiang, Changlong

2016-07-14

The instant and on-site detection of trace aqueous fluoride ions is still a challenge for environmental monitoring and protection. This work demonstrates a new analytical method and its utility of a paper sensor for visual detection of F(-) on the basis of the fluorescence resonance energy transfer (FRET) between photoluminescent graphene oxide (GO) and silver nanoparticles (AgNPs) through the formation of cyclic esters between phenylborinic acid and diol. The fluorescence of GO was quenched by the AgNPs, and trace F(-) can recover the fluorescence of the quenched photoluminescent GO. The increase in fluorescence intensity is proportional to the concentration of F(-) in the range of 0.05-0.55 nM, along with a limit of detection (LOD) as low as 9.07 pM. Following the sensing mechanism, a paper-based sensor for the visual detection of aqueous F(-) has been successfully developed. The paper sensor showed high sensitivity for aqueous F(-), and the LOD could reach as low as 0.1 μM as observed by the naked eye. The very simple and effective strategy reported here could be extended to the visual detection of a wide range of analytes in the environment by the construction of highly efficient FRET nanoprobes.

Interactions between polyphenols in thinned young apples and porcine pancreatic α-amylase: Inhibition, detailed kinetics and fluorescence quenching.

PubMed

Sun, Lijun; Chen, Weiqi; Meng, Yonghong; Yang, Xingbin; Yuan, Li; Guo, Yurong; Warren, Frederick J; Gidley, Michael J

2016-10-01

Young apple polyphenols (YAP) and nine types of phenolic compounds were investigated regarding the inhibitory activity against porcine pancreatic α-amylase (PPA) in vitro. Tannic acid, chlorogenic acid and caffeic acid in YAP showed relatively high inhibition with the IC50 values of 0.30, 1.96 and 3.69mg/mL, respectively. A detailed kinetics of inhibition study revealed that YAP and tannic acid were competitive inhibitors of PPA, whereas chlorogenic acid and caffeic acid were mixed inhibitors, exhibiting both competitive and uncompetitive characteristics. The fluorescence of PPA could be significantly quenched by YAP and the three polyphenols, and their quenching constants were determined. The results showed that for the polyphenols investigated, the order of the apparent static quenching constants (KFQ) was in agreement with that of the reciprocal competitive inhibition constants (1/Kic) (tannic acid>chlorogenic acid>caffeic acid>epicatechin); both of the parameters were contrary to the order of the IC50 values. Thus, combining detailed kinetics and fluorescence quenching studies can be applied to characterise the interactions between polyphenols in young apples and α-amylase. Copyright © 2016 Elsevier Ltd. All rights reserved.

Hydrogen bond strengthening induces fluorescence quenching of PRODAN derivative by turning on twisted intramolecular charge transfer

NASA Astrophysics Data System (ADS)

Yang, Yonggang; Li, Donglin; Li, Chaozheng; Liu, YuFang; Jiang, Kai

2017-12-01

Researchers have proposed different effective mechanisms of hydrogen bonding (HB) on the fluorescence of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and its derivatives. Herein, excited state transition and dynamics analysis confirm that the fluorescence of PD (a derivative of PRODAN with ethyl replaced by 3-hydroxy-2,2-dimethylpropan) emits from the planar intramolecular charge transfer (PICT) state rather than twist ICT (TICT) state, because the fluorescence emission and surface hopping from the TICT state to the twist ground (T-S0) state is energy forbidden. Nevertheless, the strengthening of intramolecular-HB (intra-HB) and intermolecular-HB (inter-HB) of PD-(methanol)2 smooth the pathway of surface hopping from TICT to T-S0 state and the external conversion going to planar ground state by decreasing the energy difference of the two states. This smoothing changes the fluorescence state of PD-(methanol)2 to the TICT state in which fluorescence emission does not occur but surface hopping, leading to the partial fluorescence quenching of PD in methanol solvent. This conclusion is different from previous related reports. Moreover, the inter-HB strengthening of PD-methanol in PICT state induces the cleavage of intra-HB and a fluorescence red-shift of 54 nm compared to PD. This red-shift increases to 66 nm for PD-(methanol)2 for the strengthening of the one intra-HB and two inter-HBs. The dipole moments of PD-methanol and PD-(methanol)2 respectively increase about 10.3D and 8.1D in PICT state compared to PD. The synergistic effect of intra-HB and inter-HB induces partial quenching of PD in methanol solvent by turning on the TICT state and fluorescence red-shift. This work gives a reasonable description on the fluorescence red-shift and partial quenching of PD in methanol solvent, which will bring insight into the study of spectroscopic properties of molecules owning better spectral characteristics.

Hydrogen bond strengthening induces fluorescence quenching of PRODAN derivative by turning on twisted intramolecular charge transfer.

PubMed

Yang, Yonggang; Li, Donglin; Li, Chaozheng; Liu, YuFang; Jiang, Kai

2017-12-05

Researchers have proposed different effective mechanisms of hydrogen bonding (HB) on the fluorescence of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and its derivatives. Herein, excited state transition and dynamics analysis confirm that the fluorescence of PD (a derivative of PRODAN with ethyl replaced by 3-hydroxy-2,2-dimethylpropan) emits from the planar intramolecular charge transfer (PICT) state rather than twist ICT (TICT) state, because the fluorescence emission and surface hopping from the TICT state to the twist ground (T-S 0 ) state is energy forbidden. Nevertheless, the strengthening of intramolecular-HB (intra-HB) and intermolecular-HB (inter-HB) of PD-(methanol) 2 smooth the pathway of surface hopping from TICT to T-S 0 state and the external conversion going to planar ground state by decreasing the energy difference of the two states. This smoothing changes the fluorescence state of PD-(methanol) 2 to the TICT state in which fluorescence emission does not occur but surface hopping, leading to the partial fluorescence quenching of PD in methanol solvent. This conclusion is different from previous related reports. Moreover, the inter-HB strengthening of PD-methanol in PICT state induces the cleavage of intra-HB and a fluorescence red-shift of 54nm compared to PD. This red-shift increases to 66nm for PD-(methanol) 2 for the strengthening of the one intra-HB and two inter-HBs. The dipole moments of PD-methanol and PD-(methanol) 2 respectively increase about 10.3D and 8.1D in PICT state compared to PD. The synergistic effect of intra-HB and inter-HB induces partial quenching of PD in methanol solvent by turning on the TICT state and fluorescence red-shift. This work gives a reasonable description on the fluorescence red-shift and partial quenching of PD in methanol solvent, which will bring insight into the study of spectroscopic properties of molecules owning better spectral characteristics. Copyright © 2017 Elsevier B.V. All rights reserved.

Mixed ligand two dimensional Cd(ii)/Ni(ii) metal organic frameworks containing dicarboxylate and tripodal N-donor ligands: Cd(ii) MOF is an efficient luminescent sensor for detection of picric acid in aqueous media.

PubMed

Rachuri, Yadagiri; Parmar, Bhavesh; Bisht, Kamal Kumar; Suresh, Eringathodi

2016-05-04

Two dimensional metal organic frameworks (MOFs) [Cd(5-BrIP)(TIB)]n () and [Ni2(5-BrIP)2(TIB)2]n (), involving the aromatic polycarboxylate ligand 5-bromo isophthalic acid (H2BrIP), flexible tripodal ligand 1,3,5-tris(imidazol-1-ylmethyl)benzene (TIB) and Cd(ii)/Ni(ii) metal nodes have been synthesized by different methods. These compounds were characterized by various analytical methods, and variable temperature X-ray diffraction data showed thermal stability of both MOFs up to 350 °C. Phase purity as well as water stability of the MOFs were established by powder X-ray diffraction, and the structural diversity of the compounds were investigated by single-crystal X-ray diffraction. Both the MOFs are mixed ligand 2D nets, and the topology of the network can be described as a binodal 3,5-c connected net with 3,5L2 topology having the point symbol {4(2)·6(7)·8}{4(2)·6}. Sensing of picric acid [2,4,6-trinitrophenol, TNP] by luminescence quenching among a large range of nitroanalytes in aqueous phase by the Cd(ii) luminescent MOF (LMOF) were been investigated. Structural studies on 1 : 1 co-crystals () of TIB and TNP were carried out. The selective and sensitive fluorescence quenching response of towards electron-deficient TNP over other nitro analytes in aqueous phase was demonstrated by fluorescence quenching titration. Concomitant occurrence of electron transfer/energy transfer processes and electrostatic interaction favours the selective sensing of TNP. A Cd(ii) LMOF ()-coated paper strip that we developed demonstrated fast and selective response to TNP, by the complete quenching of the blue fluorescence upon excitation of the paper strip at 365 nm radiation in its presence.

Polyfluorophore Labels on DNA: Dramatic Sequence Dependence of Quenching

PubMed Central

Teo, Yin Nah; Wilson, James N.

2010-01-01

We describe studies carried out in the DNA context to test how a common fluorescence quencher, dabcyl, interacts with oligodeoxynu-cleoside fluorophores (ODFs)—a system of stacked, electronically interacting fluorophores built on a DNA scaffold. We tested twenty different tetrameric ODF sequences containing varied combinations and orderings of pyrene (Y), benzopyrene (B), perylene (E), dimethylaminostilbene (D), and spacer (S) monomers conjugated to the 3′ end of a DNA oligomer. Hybridization of this probe sequence to a dabcyl-labeled complementary strand resulted in strong quenching of fluorescence in 85% of the twenty ODF sequences. The high efficiency of quenching was also established by their large Stern–Volmer constants (KSV) of between 2.1 × 104 and 4.3 × 105M−1, measured with a free dabcyl quencher. Interestingly, quenching of ODFs displayed strong sequence dependence. This was particularly evident in anagrams of ODF sequences; for example, the sequence BYDS had a KSV that was approximately two orders of magnitude greater than that of BSDY, which has the same dye composition. Other anagrams, for example EDSY and ESYD, also displayed different responses upon quenching by dabcyl. Analysis of spectra showed that apparent excimer and exciplex emission bands were quenched with much greater efficiency compared to monomer emission bands by at least an order of magnitude. This suggests an important role played by delocalized excited states of the π stack of fluorophores in the amplified quenching of fluorescence. PMID:19780115

Low-temperature collisional quenching of NO A{sup 2}Σ{sup +}(v′ = 0) by NO(X{sup 2}Π) and O{sub 2} between 34 and 109 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sánchez-González, R.; Eveland, W. D.; West, N. A.

2014-08-21

We present measurements of collisional fluorescence quenching cross sections of NO(A{sup 2}Σ{sup +}, v′ = 0) by NO(X{sup 2}Π) and O{sub 2} between 34 and 109 K using a pulsed converging-diverging nozzle gas expansion, extending the temperature range of previous measurements. The thermally averaged fluorescence quenching cross sections for both species show a monotonic increase as temperature decreases in this temperature range, consistent with earlier observations. These new measurements, however, allow discrimination between predictions obtained by extrapolating fits of previous data using different functional forms that show discrepancies exceeding 120% for NO and 160% for O{sub 2} at 34 K.more » The measured self-quenching cross section is 52.9 Å{sup 2} near 112 K and increases to 64.1 Å{sup 2} at 35 K, whereas the O{sub 2} fluorescence quenching cross section is 42.9 Å{sup 2} at 109 K and increases to 58.3 Å{sup 2} at 34 K. Global fits of the quenching cross section temperature dependence show that, when including our current measurements, the low temperature behavior of the quenching cross sections for NO and O{sub 2} is better described by a parameterization that accounts for the long-range interactions leading to the collisional deactivation via an inverse power law model.« less

Elucidation of Prion Protein Conformational Changes Associated with Infectivity by Fluorescence Spectroscopy

DTIC Science & Technology

2007-06-01

developed the β-spiral model for PrPSc structure by using molecular dynamics simulations with the sequence of human PrPC (residues 90-231) under...SUPPLEMENTARY NOTES exerpts from thesis of Jessica Gilbert 14. ABSTRACT Steady state and lifetime fluorescence measurements were made on 12...lieu of F. We tried both methods. See Ms. Jessica Gilbert’s MS thesis for details, which is included. 6 Figure 4. Acrylamide quenching of Trp

Synthesis, surface modification and biological imaging of aggregation-induced emission (AIE) dye doped silica nanoparticles

NASA Astrophysics Data System (ADS)

Mao, Liucheng; Liu, Meiying; Xu, Dazhuang; Wan, Qing; Huang, Qiang; Jiang, Ruming; Shi, Yingge; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

2017-05-01

Fluorescent silica nanoparticles (FSNPs) have been extensively investigated for various biomedical applications in recently years. However, the aggregation of organic dyes in silica nanoparticles also leads the significant fluorescence quenching owing to the aggregation caused quenching effects of organic dyes. Herein, we developed a rather facile strategy to fabricate FSNPs with desirable fluorescent properties through non-covalent incorporation of fluorophores with aggregation-induced emission (AIE) feature into silica nanoparticles, which were subsequently modified with functional polymers. The resultant FSNPs polymer nanocomposites (named as FSNPs-poly(IA-co-PEGMA)) exhibited uniform spherical morphology, high water dispersiity, and bright red fluorescence. Cytotoxicity results indicate that FSNPs-poly(IA-co-PEGMA) possess excellent biocompatibility. Cell uptake behavior suggests FSNPs-poly(IA-co-PEGMA) are of great potential for biological imaging applications. Taken together, we have reported a facile method for the fabrication of FSNPs through non-covalent encapsulation using an AIE-active dye. These FSNPs can be further functionalized with functional polymers through ring-opening reaction and the resultant FSNPs-poly(IA-co-PEGMA) showed great potential for biological imaging. More importantly, we believe that many other functional components could also be integrated into these FSNPs through the facile ring-opening reaction. Therefore, this method should be a facile and general tool for fabrication of polymer functionalized AIE-active FSNPs.

Gold nanocluster-based ratiometric fluorescent probes for hydrogen peroxide and enzymatic sensing of uric acid.

PubMed

Yang, Dongqin; Luo, Minchuan; Di, Junwei; Tu, Yifeng; Yan, Jilin

2018-05-18

A method is described for ratiometric fluorometric assays of H 2 O 2  by using two probes that have distinct response profiles. Under the catalytic action of ferrous ion, the 615 nm emission of protein-stabilized gold nanoclusters (under 365 nm photoexcitation) is quenched by H 2 O 2 , while an increased signal is generated with a peak at 450 nm by oxidizing coumarin with the H 2 O 2 /Fe(II) system to form a blue emitting fluorophore. These decrease/increase responses give a ratiometric signal. The ratio of the fluorescences at the two peaks are linearly related to the concentration of H 2 O 2 in the range from 0.05 to 10 μM, with a 7.7 nM limit of detection. The detection scheme was further coupled to the urate oxidase catalyzed oxidation of uric acid which proceeds under the formation of H 2 O 2 . This method provides an simple and effective means for the construction of ratiometric fluorometric (enzymatic) assays that involve the detection of H 2 O 2 . Graphical abstract Under catalysis by ferrous ion, hydrogen peroxide quenches the luminescence of gold nanoclusters (AuNCs) and oxidizes coumarin into a fluorescent derivative, which rendered fluorescence ON and OFF at two distinct wavelengths for ratiometric measurements.

Studying the association complex formation of atomoxetine and fluvoxamine with eosin Y and its application in their fluorimetric determination

NASA Astrophysics Data System (ADS)

Derayea, Sayed M.; Omar, Mahmoud A.; Abu-hassan, Ahmed A.

2018-03-01

A simple, sensitive and non-extractive spectrofluorimetric method has been developed and validated for the determination of two psychoanaleptic drugs, atomoxetine and fluvoxamine, in pure forms and pharmaceutical dosage forms. The proposed method is based on the formation of binary complexes between eosin Y and the studied drugs in the presence of a Teorell-Stenhagen buffer. The quenching of the native fluorescence of eosin Y due to complex formation with the studied drugs was measured spectrofluorimetrically at 545 nm after excitation at 302 nm. At the optimum reaction conditions, the fluorescence quenching values (ΔF) and concentrations were rectilinear over the concentration ranges of 0.2-2.2 and 0.3-2.2 µg ml-1 for atomoxetine and fluvoxamine, respectively. The developed method was successfully applied for the determination of the studied drugs in their pharmaceutical formulations with average percentage recoveries of 100.13 ± 0.66 and 99.69 ± 0.44 for atomoxetine and fluvoxamine, respectively (n = 5), without interference from common excipients.

Studying the association complex formation of atomoxetine and fluvoxamine with eosin Y and its application in their fluorimetric determination

PubMed Central

Omar, Mahmoud A.; Abu-hassan, Ahmed A.

2018-01-01

A simple, sensitive and non-extractive spectrofluorimetric method has been developed and validated for the determination of two psychoanaleptic drugs, atomoxetine and fluvoxamine, in pure forms and pharmaceutical dosage forms. The proposed method is based on the formation of binary complexes between eosin Y and the studied drugs in the presence of a Teorell–Stenhagen buffer. The quenching of the native fluorescence of eosin Y due to complex formation with the studied drugs was measured spectrofluorimetrically at 545 nm after excitation at 302 nm. At the optimum reaction conditions, the fluorescence quenching values (ΔF) and concentrations were rectilinear over the concentration ranges of 0.2–2.2 and 0.3–2.2 µg ml−1 for atomoxetine and fluvoxamine, respectively. The developed method was successfully applied for the determination of the studied drugs in their pharmaceutical formulations with average percentage recoveries of 100.13 ± 0.66 and 99.69 ± 0.44 for atomoxetine and fluvoxamine, respectively (n = 5), without interference from common excipients. PMID:29657744

False HDAC Inhibition by Aurone Compound.

PubMed

Itoh, Yukihiro; Suzuki, Miki; Matsui, Taiji; Ota, Yosuke; Hui, Zi; Tsubaki, Kazunori; Suzuki, Takayoshi

2016-01-01

Fluorescence assays are useful tools for estimating enzymatic activity. Their simplicity and manageability make them suitable for screening enzyme inhibitors in drug discovery studies. However, researchers need to pay attention to compounds that show auto-fluorescence and quench fluorescence, because such compounds lower the accuracy of the fluorescence assay systems by producing false-positive or negative results. In this study, we found that aurone compound 7, which has been reported as a histone deacetylase (HDAC) inhibitor, gave false-positive results. Although compound 7 was identified by an in vitro HDAC fluorescence assay, it did not show HDAC inhibitory activity in a cell-based assay, leading us to suspect its in vitro HDAC inhibitory activity. As a result of verification experiments, we found that compound 7 interferes with the HDAC fluorescence assay by quenching the HDAC fluorescence signal. Our findings underscore the faults of fluorescence assays and call attention to careless interpretation.

Binding of Sulpiride to Seric Albumins

PubMed Central

da Silva Fragoso, Viviane Muniz; de Morais Coura, Carla Patrícia; Hoppe, Luanda Yanaan; Soares, Marília Amável Gomes; Silva, Dilson; Cortez, Celia Martins

2016-01-01

The aim of this work was to study the interaction of sulpiride with human serum albumin (HSA) and bovine serum albumin (BSA) through the fluorescence quenching technique. As sulpiride molecules emit fluorescence, we have developed a simple mathematical model to discriminate the quencher fluorescence from the albumin fluorescence in the solution where they interact. Sulpiride is an antipsychotic used in the treatment of several psychiatric disorders. We selectively excited the fluorescence of tryptophan residues with 290 nm wavelength and observed the quenching by titrating HSA and BSA solutions with sulpiride. Stern-Volmer graphs were plotted and quenching constants were estimated. Results showed that sulpiride form complexes with both albumins. Estimated association constants for the interaction sulpiride–HSA were 2.20 (±0.08) × 104 M−1, at 37 °C, and 5.46 (±0.20) × 104 M−1, at 25 °C. Those for the interaction sulpiride-BSA are 0.44 (±0.01) × 104 M−1, at 37 °C and 2.17 (±0.04) × 104 M−1, at 25 °C. The quenching intensity of BSA, which contains two tryptophan residues in the peptide chain, was found to be higher than that of HSA, what suggests that the primary binding site for sulpiride in albumin should be located next to the sub domain IB of the protein structure. PMID:26742031

Interaction of carboxylated single-walled carbon nanotubes with bovine serum albumin

NASA Astrophysics Data System (ADS)

Li, Lili; Lin, Rui; He, Hua; Jiang, Li; Gao, Mengmeng

2013-03-01

Carboxylated single-walled carbon nanotubes (c-SWNTs) were synthesized prosperously in order to improve dispersion of raw carbon nanotubes. Then, bovine serum albumin (BSA) was used as the template protein to study the biocompatibility of c-SWNTs by UV-Vis, fluorescence and circular dichroism (CD) spectroscopic methods at the molecular level. Results from fluorescence spectrum showed obvious decreases in fluorescence intensity of BSA induced by c-SWNTs, indicating the occurrence of interaction between BSA and c-SWNTs. Static quenching effect of c-SWNTs was verified by linear Stern-Volmer plots and KSV values. Thermodynamic parameters at different temperatures demonstrated that the interaction between c-SWNTs and BSA was mainly favored by hydrophobic force. In addition, Na+ interfered with the quenching effect of c-SWNTs, which revealed that electrostatic force played a role in binding roles of BSA to c-SWNTs simultaneously. The results of UV and synchronous fluorescence spectrum validated that hydrophobicity of amino acid residues expressly increased with the addition of c-SWNTs. The content of α-helix structure in BSA decreased by 14.06% with c-SWNTs viewed from CD spectrum. Effect of SWNTs on the conformation of BSA could be controlled by the surface chemistry of SWNTs.

Synthesizing a nano-composite of BSA-capped Au nanoclusters/graphitic carbon nitride nanosheets as a new fluorescent probe for dopamine detection.

PubMed

Guo, Xinrong; Wu, Fangying; Ni, Yongnian; Kokot, Serge

2016-10-26

A strong red fluorescent nanocomposite, consisting of graphite-like carbon nitride nanosheets (g-C 3 N 4 NSs) and serum albumin-capped Au nanoclusters (AuNCs), was synthesized. Dopamine (DA) can quench the red fluorescence of the nanocomposite, based on the Forster resonance energy transfer (FRET) mechanism. In this quenching process, the energy is transferred from the fluorescent g-C 3 N 4 NSs-AuNCs to the oxidized DA quinine molecules (DA is easily oxidated to form DA quinine in air). The red fluorescence emission at 420 nm decreases dramatically and the quenching ratio (F 0 - F)/F 0 is linearly related to the concentration of DA in the range of 0.05-8.0 μmol L -1 with a detection limit of 0.018 μmol L -1  (S/N = 3). Additionally, this sensor has a potential of application to assay the DA in the real samples, such as human serum and human urine. Copyright © 2016 Elsevier B.V. All rights reserved.

Fluorescent component and complexation mechanism of extracellular polymeric substances during dye wastewater biotreatment by anaerobic granular sludge

NASA Astrophysics Data System (ADS)

Li, Na; Wei, Dong; Sun, Qunqun; Han, Xiao; Du, Bin; Wei, Qin

2018-02-01

In this study, methylene blue (MB) wastewater was biotreated by anaerobic granular sludge (AnGS), and the fluorescent components of extracellular polymeric substances (EPS) and complexation mechanism were evaluated. Based on the experimental data, the sorption of MB by both live and inactivated AnGS followed the pseudo-second-order model, and the adsorption isotherm conformed well to the Langmuir model. It was shown that the difference in the sorption of live and inactivated AnGS was not significant, indicating that the sorption is mainly a physical-chemical process and metabolically mediated diffusion is negligible. The interaction between EPS and MB was proved by three-dimensional excitation-emission matrix (3D-EEM) and synchronous fluorescence spectra. 3D-EEM indicated that protein (PN)-like substances were the main peaks of EPS, and gradually quenched with increase of MB concentrations. According to synchronous fluorescence spectra, the main fluorescence quenching was caused by PN-like and humic-like fractions, and belonged to the static type of quenching. FTIR spectra demonstrated that hydroxyl and amino groups played a major role in MB sorption.

Connecting active to passive fluorescence with photosynthesis: a method for evaluating remote sensing measurements of Chl fluorescence.

PubMed

Magney, Troy S; Frankenberg, Christian; Fisher, Joshua B; Sun, Ying; North, Gretchen B; Davis, Thomas S; Kornfeld, Ari; Siebke, Katharina

2017-09-01

Recent advances in the retrieval of Chl fluorescence from space using passive methods (solar-induced Chl fluorescence, SIF) promise improved mapping of plant photosynthesis globally. However, unresolved issues related to the spatial, spectral, and temporal dynamics of vegetation fluorescence complicate our ability to interpret SIF measurements. We developed an instrument to measure leaf-level gas exchange simultaneously with pulse-amplitude modulation (PAM) and spectrally resolved fluorescence over the same field of view - allowing us to investigate the relationships between active and passive fluorescence with photosynthesis. Strongly correlated, slope-dependent relationships were observed between measured spectra across all wavelengths (F λ , 670-850 nm) and PAM fluorescence parameters under a range of actinic light intensities (steady-state fluorescence yields, F t ) and saturation pulses (maximal fluorescence yields, F m ). Our results suggest that this method can accurately reproduce the full Chl emission spectra - capturing the spectral dynamics associated with changes in the yields of fluorescence, photochemical (ΦPSII), and nonphotochemical quenching (NPQ). We discuss how this method may establish a link between photosynthetic capacity and the mechanistic drivers of wavelength-specific fluorescence emission during changes in environmental conditions (light, temperature, humidity). Our emphasis is on future research directions linking spectral fluorescence to photosynthesis, ΦPSII, and NPQ. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Green synthesis of carbon dots from pork and application as nanosensors for uric acid detection

NASA Astrophysics Data System (ADS)

Zhao, Chunxi; Jiao, Yang; Hu, Feng; Yang, Yaling

2018-02-01

In this work, a green, simple, economical method was developed in the synthesis of fluorescent carbon dots using pork as carbon source. The as-prepared carbon dots exhibit exceptional advantages including high fluorescent quantum yield (17.3%) and satisfactory chemical stability. The fluorescence of carbon dots based nanosensor can be selectively and efficiently quenched by uric acid. This phenomenon was used to develop a fluorescent method for facile detection of uric acid within a linear range of 0.1-100 μM and 100-500 μM, with a detection limit of 0.05 μM (S/N = 3). Finally, the proposed method was successfully applied in the determination of uric acid in human serum and urine samples with satisfactory recoveries, which suggested that the new nanosensors have great prospect toward the detection of uric acid in human fluids.

One pot synthesis of intriguing fluorescent carbon dots for sensing and live cell imaging.

PubMed

Jana, Jayasmita; Ganguly, Mainak; Das, Bodhisatwa; Dhara, Santanu; Negishi, Yuichi; Pal, Tarasankar

2016-04-01

We report a simple one-pot synthesis of highly fluorescent carbon dots (CDs) via modified hydrothermal (MHT) treatment of alkaline solution of dopamine and cysteine. These CDs (λex=320 nm, λem=390 nm, and quantum yield ∼ 5.1%) are of ∼ 2-3 nm in diameter. Further attempt of synthesizing CDs in some common water-miscible solvents ends up the fact that the MHT product from acetone medium is nonfluorescent. However, CDs, produced in aqueous medium, are so stable that they can be dried as a deliverable solid (WCD) without any alteration of fluorescing property if reversibly dispersed in water. Fluorescence of WCD is quenched selectively in acetone. Quenching occurs presumably due to the disruption of radiative recombination along with the hindrance in quantum confinement of the emissive energy traps to the particle surface. Successive quenching of fluorescence of WCD in different acetone concentration admixed in water paves the way to selective acetone sensing (LOD=8.75 × 10(-7) M). The synthesized CDs (in aqueous medium) are cytocompatible and are efficient fluorescent probe for cell imaging. Only living cells are recognized exclusively from fluorescence imaging leaving aside dead cells, while cells are treated with CDs. Copyright © 2015 Elsevier B.V. All rights reserved.

Combination of a Copper-Ion Selective Electrode and Fluorometric Titration for the Determination of Copper(II) Ion Conditional Stability Constants of Humic Substances.

PubMed

Chen, Juan; Chen, Hao; Zhang, Xing-wen; Lei, Kun; Kenny, Jonathan E

2015-11-01

A fluorescence quenching model using copper(II) ion (Cu(2+)) ion selective electrode (Cu-ISE) is developed. It uses parallel factor analysis (PARAFAC) to model fluorescence excitation-emission matrices (EEMs) of humic acid (HA) samples titrated with Cu(2+) to resolve fluorescence response of fluorescent components to Cu(2+) titration. Meanwhile, Cu-ISE is employed to monitor free Cu(2+) concentration ([Cu]) at each titration step. The fluorescence response of each component is fit individually to a nonlinear function of [Cu] to find the Cu(2+) conditional stability constant for that component. This approach differs from other fluorescence quenching models, including the most up-to-date multi-response model that has a problematic assumption on Cu(2+) speciation, i.e., an assumption that total Cu(2+) present in samples is a sum of [Cu] and those bound by fluorescent components without taking into consideration the contribution of non-fluorescent organic ligands and inorganic ligands to speciation of Cu(2+). This paper employs the new approach to investigate Cu(2+) binding by Pahokee peat HA (PPHA) at pH values of 6.0, 7.0, and 8.0 buffered by phosphate or without buffer. Two fluorescent components (C1 and C2) were identified by PARAFAC. For the new quenching model, the conditional stability constants (logK1 and logK2) of the two components all increased with increasing pH. In buffered solutions, the new quenching model reported logK1 = 7.11, 7.89, 8.04 for C1 and logK2 = 7.04, 7.64, 8.11 for C2 at pH 6.0, 7.0, and 8.0, respectively, nearly two log units higher than the results of the multi-response model. Without buffer, logK1 and logK2 decreased but were still high (>7) at pH 8.0 (logK1 = 7.54, logK2 = 7.95), and all the values were at least 0.5 log unit higher than those (4.83 ~ 5.55) of the multi-response model. These observations indicate that the new quenching model is more intrinsically sensitive than the multi-response model in revealing strong fluorescent binding sites of PPHA in different experimental conditions. The new model was validated by testing it with a mixture of two fluorescing Cu(2+) chelating organic compounds, i.e., l-tryptophan and salicylic acid mixed with one non-fluorescent binding compound oxalic acid titrated with Cu(2+) at pH 5.0.

Analyses of procyanidins in foods using Diol phase HPLC

USDA-ARS?s Scientific Manuscript database

Separation of procyanidins using silica-based HPLC suffered from poor resolution for higher oligomers and low sensitivity due to the fluorescence quenching effects of methylene chloride in the mobile phase. Optimization of a published Diol-phase HPLC method resulted in near baseline separation for p...

Optical detection of organophosphorus compounds based on Mn-doped ZnSe d-dot enzymatic catalytic sensor.

PubMed

Gao, Xue; Tang, Guangchao; Su, Xingguang

2012-01-01

In this paper, we report a sensitive and selective method for detection of organophosphorus compounds (OPs) based on Mn:ZnSe d-dots-enzyme-hydrogen peroxide (H(2)O(2)) fluorescence quenching system. Acetylcholine esterase (AChE) can hydrolyze acetylcholine (ACh) to choline. Subsequently, choline oxidase (ChOx) oxidizes choline to generate H(2)O(2). The enzyme-generated H(2)O(2) can quench the fluorescence of Mn:ZnSe d-dots. When paraoxon are introduced in solution, it can interact with the active centers of AChE and decrease the enzyme activity. This leads to the decrease of the H(2)O(2) production and then the fluorescence quenching rate of Mn:ZnSe d-dots. Experimental results showed that the enzyme inhibition percentage of Mn:ZnSe d-dots-ChOx-AChE-ACh system was proportional to the logarithm of paraoxon in the range 4.84×10(-11) to 4.84×10(-6) mol/L with the detection limit (S/N=3) of 1.31×10(-11) mol/L. The proposed biosensor has been employed for quick determination of paraoxon in tap water and milk samples with satisfactory reproducibility and accuracy. This nano-biosensor was proved to be sensitive, rapid, simple and tolerance of most interfering substances. Copyright © 2012 Elsevier B.V. All rights reserved.

Visualization of nucleic acids with synthetic exciton-controlled fluorescent oligonucleotide probes.

PubMed

Wang, Dan Ohtan; Okamoto, Akimitsu

2015-01-01

Engineered probes to adapt new photochemical properties upon recognition of target nucleic acids offer powerful tools to DNA and RNA visualization technologies. Herein, we describe a rapid and effective visualization method of nucleic acids in both fixed and living cells with hybridization-sensitive fluorescent oligonucleotide probes. These probes are efficiently quenched in an aqueous environment due to the homodimeric, excitonic interactions between fluorophores but become highly fluorescent upon hybridization to DNA or RNA with complementary sequences. The fast hybridization kinetics and quick fluorescence activation of the new probes allow applications to simplify the conventional fluorescent in situ hybridization protocols and reduce the amount of time to process the samples. Furthermore, hybridization-sensitive fluorescence emission of the probes allows monitoring dynamic behaviors of RNA in living cells.

MEH-PPV film thickness influenced fluorescent quenching of tip-coated plastic optical fiber sensors

NASA Astrophysics Data System (ADS)

Yusufu, A. M.; Noor, A. S. M.; Tamchek, N.; Abidin, Z. Z.

2017-12-01

The performance of plastic optical fiber sensors in detecting nitro aromatic explosives 1,4-dinitrobenzene (DNB) have been investigated by fluorescence spectroscopy and analyzed by using fluorescence quenching technique. The plastic optical fiber utilized is 90 degrees cut tip and dip-coated with conjugated polymer MEH-PPV poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] thin films for detection conjugants. The thicknesses of the MEH-PPV coating were varied to improvise the sensitivity whilst slowly reducing the fluorescence intensity. It was shown that fluorescence intensity from thinner film decreased by (82% in 40 s) in the presence of DNB signifying an improvement of 28% reduction with time 13 s less than that of the thicker film.

Detection of residual rifampicin in urine via fluorescence quenching of gold nanoclusters on paper.

PubMed

Chatterjee, Krishnendu; Kuo, Chiung Wen; Chen, Ann; Chen, Peilin

2015-06-26

Rifampicin or rifampin (R) is a common drug used to treat inactive meningitis, cholestatic pruritus and tuberculosis (TB), and it is generally prescribed for long-term administration under regulated dosages. Constant monitoring of rifampicin is important for controlling the side effects and preventing overdose caused by chronic medication. In this study, we present an easy to use, effective and less costly method for detecting residual rifampicin in urine samples using protein (bovine serum albumin, BSA)-stabilized gold nanoclusters (BSA-Au NCs) adsorbed on a paper substrate in which the concentration of rifampicin in urine can be detected via fluorescence quenching. The intensity of the colorimetric assay performed on the paper-based platforms can be easily captured using a digital camera and subsequently analyzed. The decreased fluorescence intensity of BSA-Au NCs in the presence of rifampicin allows for the sensitive detection of rifampicin in a range from 0.5 to 823 µg/mL. The detection limit for rifampicin was measured as 70 ng/mL. The BSA-Au NCs were immobilized on a wax-printed paper-based platform and used to conduct real-time monitoring of rifampicin in urine. We have developed a robust, cost-effective, and portable point-of-care medical diagnostic platform for the detection of rifampicin in urine based on the ability of rifampicin to quench the fluorescence of immobilized BSA-Au NCs on wax-printed papers. The paper-based assay can be further used for the detection of other specific analytes via surface modification of the BSA in BSA-Au NCs and offers a useful tool for monitoring other diseases.

Oligofluorenes as polymeric model compounds for providing insight into the triplets of ketone and ketylimine derivatives.

PubMed

Robert, Patricia; Bolduc, Andréanne; Skene, W G

2012-09-20

A series of oligofluorenes ranging between one and three repeating units were prepared as structurally well-defined representative models of polyfluorenes. The photophysics of the oligofluorene models were investigated both by laser flash photolysis and steady-state fluorescence. The effects of the ketone and ketylimine functional groups in the 9-position on the photophysical properties, notably the triplet quantum yield (Φ(TT)) by intersystem crossing and the absolute fluorescence quantum yields (Φ(fl)), were investigated. The singlet depletion method was used to determine both the Φ(TT) and molar absorption coefficients of the observed triplets (ε(TT)). Meanwhile, the absolute Φ(fl) were determined using an integrating sphere. It was found that both the ketone and ketylimine substituents and the degree of oligomerization contributed to quenching the oligofluorene fluorescence. For example, the Φ(fl) was quenched 5-fold with the ketylimine and ketone substituents for the bifluorenyl derivatives compared to their corresponding 9,9-dihexyl bifluorenyl counterparts. Meanwhile, the Φ(fl) quenching increased 14 times with the trifluorenyl ketone and ketylimine derivatives. Measured Φ(TT) values ranged between 22 and 43% for the difluorenyl derivatives with ε(TT) on the order of 13 000 cm(-1) M(-1). The Φ(TT) decreased to <10% concomitant with doubling of the ε(TT) when the degree of oligomerization was increased to 3. A new fluorescence emission at 545 nm formed at low temperatures for the ketone and ketylimine oligofluorene derivatives. The emission intensity was dependent on the temperature, and it disappeared at room temperature.

Fluorescent Zn-PDC/Tb3+ Coordination Polymer Nanostructure: A Candidate for Highly Selective Detections of Cefixime Antibiotic and Acetone in Aqueous System.

PubMed

Pan, Hong; Wang, Sufan; Dao, Xiaoyao; Ni, Yonghong

2018-02-05

Tb 3+ -doped zinc-based coordination polymer nanospindle bundles (Zn-PDC/Tb 3+ , or [Zn(2,5-PDC)(H 2 O) 2 ]·H 2 O/Tb 3+ ) were synthesized by a simple solution precipitation route at room temperature, employing Zn(NO 3 ) 2 , Tb(NO 3 ) 3 , and 2,5-Na 2 PDC as the initial reactants, and a mixture of water and ethanol with the volume ratio of 10:10 as the solvent. The as-obtained nanostructures presented strong fluorescent emission under the excitation of 298 nm light, which was attributed to the characteristic emission of the Tb 3+ ion. It was found that the above-mentioned strong fluorescence of the nanostructures could be selectively quenched by cefixime (CFX) in aqueous solution. The other common antibiotics hardly interfered. Thus, as-obtained Zn-PDC/Tb 3+ nanostructures could be prepared as a highly sensitive fluorescence probe for selective detection of CFX in an aqueous system. The corresponding detection limit reached 72 ppb. The theoretic calculation and UV-vis absorption experiments confirmed that the fluorescence quenching of Zn-PDC/Tb 3+ nanostructures toward CFX should be attributed to the electron transfer and the fluorescence inner filter effect between the fluorescent matter and the analyte. In addition, the strong fluorescence of the nanostructures could also be selectively quenched by acetone in the water system.

Sensitive Pb(2+) probe based on the fluorescence quenching by graphene oxide and enhancement of the leaching of gold nanoparticles.

PubMed

Shi, Xinhao; Gu, Wei; Peng, Weidong; Li, Bingyu; Chen, Ningning; Zhao, Kai; Xian, Yuezhong

2014-02-26

A novel strategy was developed for fluorescent detection of Pb(2+) in aqueous solution based on the fact that graphene oxide (GO) could quench the fluorescence of amino pyrene (AP)-grafted gold nanoparticles (AP-AuNPs) and Pb(2+) could accelerate the leaching rate of AuNPs in the presence of S2O3(2-). In this system, fluorescence reporter AP was grafted on AuNPs through the Au-N bond. In the presence of GO, the system shows fluorescence quenching because of π-π stacking between AP and GO. With the addition of Pb(2+) and S2O3(2-), the system displays fluorescence recovery, which is attributed to the fact that Pb(2+) could accelerate the leaching of the AuNPs from GO surfaces and release of AP into aqueous solution. Interestingly, the concentration of GO could control the fluorescence "turn-off" or "turn-on" for Pb(2+) detection. In addition, GO is also an excellent promoter for the acceleration of the leaching of AuNPs and shortening the analytical time to ∼15 min. Under the optimal conditions, the fluorescence Pb(2+) sensor shows a linear range from 2.0 × 10(-9) to 2.3 × 10(-7) mol/L, with a detection limit of 1.0 × 10(-10) mol/L.

Substrate-Triggered Exosite Binding: Synergistic Dendrimer/Folic Acid Action for Achieving Specific, Tight-Binding to Folate Binding Protein.

PubMed

Chen, Junjie; van Dongen, Mallory A; Merzel, Rachel L; Dougherty, Casey A; Orr, Bradford G; Kanduluru, Ananda Kumar; Low, Philip S; Marsh, E Neil G; Banaszak Holl, Mark M

2016-03-14

Polymer-ligand conjugates are designed to bind proteins for applications as drugs, imaging agents, and transport scaffolds. In this work, we demonstrate a folic acid (FA)-triggered exosite binding of a generation five poly(amidoamine) (G5 PAMAM) dendrimer scaffold to bovine folate binding protein (bFBP). The protein exosite is a secondary binding site on the protein surface, separate from the FA binding pocket, to which the dendrimer binds. Exosite binding is required to achieve the greatly enhanced binding constants and protein structural change observed in this study. The G5Ac-COG-FA1.0 conjugate bound tightly to bFBP, was not displaced by a 28-fold excess of FA, and quenched roughly 80% of the initial fluorescence. Two-step binding kinetics were measured using the intrinsic fluorescence of the FBP tryptophan residues to give a KD in the low nanomolar range for formation of the initial G5Ac-COG-FA1.0/FBP* complex, and a slow conversion to the tight complex formed between the dendrimer and the FBP exosite. The extent of quenching was sensitive to the choice of FA-dendrimer linker chemistry. Direct amide conjugation of FA to G5-PAMAM resulted in roughly 50% fluorescence quenching of the FBP. The G5Ac-COG-FA, which has a longer linker containing a 1,2,3-triazole ring, exhibited an ∼80% fluorescence quenching. The binding of the G5Ac-COG-FA1.0 conjugate was compared to poly(ethylene glycol) (PEG) conjugates of FA (PEGn-FA). PEG2k-FA had a binding strength similar to that of FA, whereas other PEG conjugates with higher molecular weight showed weaker binding. However, no PEG conjugates gave an increased degree of total fluorescence quenching.

Rose bengal in poly(2-hydroxyethyl methacrylate) thin films: self-quenching by photoactive energy traps

NASA Astrophysics Data System (ADS)

Ezquerra Riega, Sergio D.; Rodríguez, Hernán B.; San Román, Enrique

2017-03-01

The effect of dye concentration on the fluorescence,ΦF, and singlet molecular oxygen,ΦΔ, quantum yields of rose bengal loaded poly(2-hydroxyethyl methacrylate) thin films (∼200 nm thick) was investigated, with the aim of understanding the effect of molecular interactions on the photophysical properties of dyes in crowded constrained environments. Films were characterized by absorption and fluorescence spectroscopy, singlet molecular oxygen (1O2) production was quantified using a chemical monitor, and the triplet decay was determined by laser flash-photolysis. For the monomeric dilute dye, ΦF = 0.05 ± 0.01 and ΦΔ = 0.76 ± 0.14. The effect of humidity and the photostability of the dye were also investigated. Spectral changes in absorption and fluorescence in excess of 0.05 M and concentration self-quenching after 0.01 M are interpreted in the context of a quenching radius model. Calculations of energy migration and trapping rates were performed assuming random distribution of the dye. Best fits of fluorescence quantum yields with concentration are obtained in the whole concentration range with a quenching radius r Q = 1.5 nm, in the order of molecular dimensions. Agreement is obtained only if dimeric traps are considered photoactive, with an observed fluorescence quantum yield ratio ΦF,trap/ΦF,monomer ≈ 0.35. Fluorescent traps are capable of yielding triplet states and 1O2. Results show that the excited state generation efficiency, calculated as the product between the absorption factor and the fluorescence quantum yield, is maximized at around 0.15 M, a very high concentration for random dye distributions. Relevant information for the design of photoactive dyed coatings is provided.

A nanocluster-based fluorescent sensor for sensitive hemoglobin detection.

PubMed

Yang, Dongqin; Meng, Huijie; Tu, Yifeng; Yan, Jilin

2017-08-01

In this report, a fluorescence sensor for sensitive detection of hemoglobin was developed. Gold nanoclusters were first synthesized with bovine serum albumin. It was found that both hydrogen peroxide and hemoglobin could weakly quench the fluorescence from the gold nanoclusters, but when these two were applied onto the nanolcusters simultaneously, a much improved quenching was resulted. This enhancing effect was proved to come from the catalytic generation of hydroxyl radical by hemoglobin. Under an optimized condition, the quenching linearly related to the concentration of hemoglobin in the range of 1-250nM, and a limit of detection as low as 0.36nM could be obtained. This provided a sensitive means for the quantification of Hb. The sensor was then successfully applied for blood analyses with simple sample pretreatment. Copyright © 2017 Elsevier B.V. All rights reserved.

Investigation on the Interaction of Norgestrel with Human Serum Albumin Using Spectroscopy and Molecular-Docking Method.

PubMed

Ma, Xiangling; Wang, Qing; Wang, Lili; Huang, Yanmei; Liao, Xiaoxiang; Li, Hui

2016-06-01

The interaction of norgestrel with human serum albumin (HSA) was investigated by spectroscopy and molecular-docking methods. Results of spectroscopy methods suggested that the quenching mechanism of norgestrel on HSA was static quenching and that the quenching process was spontaneous. Negative values of thermodynamic parameters (ΔG, ΔH, and ΔS) indicated that hydrogen bonding and van der Waals forces dominated the binding between norgestrel and HSA. Three-dimensional fluorescence spectrum and circular dichroism spectrum showed that the HSA structure was slightly changed by norgestrel. Norgestrel mainly bound with Sudlow site I based on a probe study, as confirmed by molecular-docking results. Competition among similar structures indicated that ethisterone and norethisterone affected the binding of norgestrel with HSA. CH3 in R1 had little effect on norgestrel binding with HSA. The surface hydrophobicity properties of HSA, investigated using 8-anilino-1-naphthalenesulfonic acid, was changed with norgestrel addition. © 2016 Wiley Periodicals, Inc.

Quantifying exciton hopping in disordered media with quenching sites: Application to arrays of quantum dots

NASA Astrophysics Data System (ADS)

Miyazaki, Jun

2013-10-01

We present an analytical method for quantifying exciton hopping in an energetically disordered system with quenching sites. The method is subsequently used to provide a quantitative understanding of exciton hopping in a quantum dot (QD) array. Several statistical quantities that characterize the dynamics (survival probability, average number of distinct sites visited, average hopping distance, and average hopping rate in the initial stage) are obtained experimentally by measuring time-resolved fluorescence intensities at various temperatures. The time evolution of these quantities suggests in a quantitative way that at low temperature an exciton tends to be trapped at a local low-energy site, while at room temperature, exciton hopping occurs repeatedly, leading to a large hopping distance. This method will serve to facilitate highly efficient optoelectronic devices using QDs such as photovoltaic cells and light-emitting diodes, since exciton hopping is considered to strongly influence their operational parameters. The presence of a dark QD (quenching site) that exhibits fast decay is also quantified.

Interaction of sulpiride and serum albumin: Modeling from spectrofluorimetric data

NASA Astrophysics Data System (ADS)

Fragoso, Viviane Muniz da Silva; Silva, Dilson

2015-12-01

We have applied the fluorescence quenching modeling to study the process of interaction of sulpiride with human serum albumin (HSA) and bovine (BSA). Albumin is more abundant protein in blood and it emits fluorescence when excited by 260-295 nm. Sulpiride is an atypical antipsychotic used in the treatment of many psychiatric disorders. As sulpiride is fluorescent, we developed a mathematical model to analyzing the interaction of two fluorescent substances. This model was able to separate the albumin fluorescence from the quencher fluorescence. Results have shown that sulpiride quenches the fluorescence of both albumins by a static process, due to the complex formation drugalbumin. The association constants calculated for sulpiride-HSA was 2.20 (± 0.08) × 104 M-1 at 37° C, and 5.46 (± 0.20) × 104 M-1, 25 ° C, and the primary binding site to sulpiride in the albumin is located closer to the subdomain IB.

Distinct roles of the photosystem II protein PsbS and zeaxanthin in the regulation of light harvesting in plants revealed by fluorescence lifetime snapshots.

PubMed

Sylak-Glassman, Emily J; Malnoë, Alizée; De Re, Eleonora; Brooks, Matthew D; Fischer, Alexandra Lee; Niyogi, Krishna K; Fleming, Graham R

2014-12-09

The photosystem II (PSII) protein PsbS and the enzyme violaxanthin deepoxidase (VDE) are known to influence the dynamics of energy-dependent quenching (qE), the component of nonphotochemical quenching (NPQ) that allows plants to respond to fast fluctuations in light intensity. Although the absence of PsbS and VDE has been shown to change the amount of quenching, there have not been any measurements that can detect whether the presence of these proteins alters the type of quenching that occurs. The chlorophyll fluorescence lifetime probes the excited-state chlorophyll relaxation dynamics and can be used to determine the amount of quenching as well as whether two different genotypes with the same amount of NPQ have similar dynamics of excited-state chlorophyll relaxation. We measured the fluorescence lifetimes on whole leaves of Arabidopsis thaliana throughout the induction and relaxation of NPQ for wild type and the qE mutants, npq4, which lacks PsbS; npq1, which lacks VDE and cannot convert violaxanthin to zeaxanthin; and npq1 npq4, which lacks both VDE and PsbS. These measurements show that although PsbS changes the amount of quenching and the rate at which quenching turns on, it does not affect the relaxation dynamics of excited chlorophyll during quenching. In addition, the data suggest that PsbS responds not only to ΔpH but also to the Δψ across the thylakoid membrane. In contrast, the presence of VDE, which is necessary for the accumulation of zeaxanthin, affects the excited-state chlorophyll relaxation dynamics.

Distinct roles of the photosystem II protein PsbS and zeaxanthin in the regulation of light harvesting in plants revealed by fluorescence lifetime snapshots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sylak-Glassman, Emily J.; Malnoë, Alizée; De Re, Eleonora

2014-11-24

The photosystem II (PSII) protein PsbS and the enzyme violaxanthin deepoxidase (VDE) are known to influence the dynamics of energy-dependent quenching (qE), the component of nonphotochemical quenching (NPQ) that allows plants to respond to fast fluctuations in light intensity. Although the absence of PsbS and VDE has been shown to change the amount of quenching, there have not been any measurements that can detect whether the presence of these proteins alters the type of quenching that occurs. The chlorophyll fluorescence lifetime probes the excited-state chlorophyll relaxation dynamics and can be used to determine the amount of quenching as well asmore » whether two different genotypes with the same amount of NPQ have similar dynamics of excited-state chlorophyll relaxation. We measured the fluorescence lifetimes on whole leaves of Arabidopsis thaliana throughout the induction and relaxation of NPQ for wild type and the qE mutants, npq4, which lacks PsbS; npq1, which lacks VDE and cannot convert violaxanthin to zeaxanthin; and npq1 npq4, which lacks both VDE and PsbS. These measurements show that although PsbS changes the amount of quenching and the rate at which quenching turns on, it does not affect the relaxation dynamics of excited chlorophyll during quenching. In addition, the data suggest that PsbS responds not only to ΔpH but also to the Δψ across the thylakoid membrane. In contrast, the presence of VDE, which is necessary for the accumulation of zeaxanthin, affects the excited-state chlorophyll relaxation dynamics.« less

Molecular quenching and relaxation in a plasmonic tunable system

NASA Astrophysics Data System (ADS)

Baffou, Guillaume; Girard, Christian; Dujardin, Erik; Colas Des Francs, Gérard; Martin, Olivier J. F.

2008-03-01

Molecular fluorescence decay is significantly modified when the emitting molecule is located near a plasmonic structure. When the lateral sizes of such structures are reduced to nanometer-scale cross sections, they can be used to accurately control and amplify the emission rate. In this Rapid Communication, we extend Green’s dyadic method to quantitatively investigate both radiative and nonradiative decay channels experienced by a single fluorescent molecule confined in an adjustable dielectric-metal nanogap. The technique produces data in excellent agreement with current experimental work.

Using Bio-Optics to Reveal Phytoplankton Physiology from a Wirewalker Autonomous Platform

NASA Technical Reports Server (NTRS)

Omand, M. M.; Cetinic, I.; Lucas, A. J.

2017-01-01

Rapid, wave-powered profiling of bio-optical properties from an autonomous Wirewalker platform provides useful insights into phytoplankton physiology, including the patterns of diel growth, phytoplankton mortality, nonphotochemical quenching of chlorophyll a fluorescence, and natural (sun-induced) fluorescence of mixed communities. Methods are proposed to quantify each of these processes. Such autonomous measurements of phytoplankton physiological rates and responses open up new possibilities for studying phytoplankton in situ, over longer periods, and under a broader range of environmental conditions.

Spectral dependence of irreversible light-induced fluorescence quenching: Chlorophyll forms with maximal emission at 700-702 and 705-710nm as spectroscopic markers of conformational changes in the core complex.

PubMed

Nematov, Sherzod; Casazza, Anna Paola; Remelli, William; Khuvondikov, Vakhobjon; Santabarbara, Stefano

2017-07-01

The spectral dependence of the irreversible non-photochemical fluorescence quenching associated with photoinhibition in vitro has been comparatively investigated in thylakoid membranes, PSII enriched particles and PSII core complexes isolated from spinach. The analysis of the fluorescence emission spectra of dark-adapted and quenched samples as a function of the detection temperature in the 280-80K interval, indicates that Chlorophyll spectral forms having maximal emission in the 700-702nm and 705-710nm ranges gain relative intensity in concomitance with the establishment of irreversible light-induced quenching, acting thereby as spectroscopic markers. The relative enhancement of the 700-702nm and 705-710nm forms emission could be due either to an increase of their stoichiometric abundance or to their intrinsically low fluorescence quantum yields. These two factors, that can also coexist, need to be promoted by light-induced alterations in chromophore-protein as well as chromophore-chromophore interactions. The bands centred at about 701 and 706nm are also observed in the PSII core complex, suggesting their, at least partial, localisation in proximity to the reaction centre, and the occurrence of light-induced conformational changes in the core subunits. Copyright © 2017 Elsevier B.V. All rights reserved.

A fluorescence turn-on sensor for iodide based on a thymine-Hg(II)-thymine complex.

PubMed

Ma, Boling; Zeng, Fang; Zheng, Fangyuan; Wu, Shuizhu

2011-12-23

Iodide plays a vital role in many biological processes, including neurological activity and thyroid function. Due to its physiological relevance, a method for the rapid, sensitive, and selective detection of iodide in food, pharmaceutical products, and biological samples such as urine is of great importance. Herein, we demonstrate a novel and facile strategy for constructing a fluorescence turn-on sensor for iodide based on a T-Hg(II)-T complex (T=thymine). A fluorescent anthracene-thymine dyad (An-T) was synthesized, the binding of which to a mercury(II) ion lead to the formation of a An-T-Hg(II)-T-An complex, thereby quenching the fluorescent emission of this dyad. In this respect, the dyad An-T constituted a fluorescence turn-off sensor for mercury(II) ions in aqueous media. More importantly, it was found that upon addition of iodide, the mercury(II) ion was extracted from the complex due to the even stronger binding between mercury(II) ions and iodide, leading to the release of the free dyad and restoration of the fluorescence. By virtue of this fluorescence quenching and recovery process, the An-T-Hg(II)-T-An complex constitutes a fluorescence turn-on sensor for iodide with a detection limit of 126 nM. Moreover, this sensor is highly selective for iodide over other common anions, and can be used in the determination of iodide in drinking water and biological samples such as urine. This strategy may provide a new approach for sensing some other anions. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly sensitive fluorescence and SERS detection of azide through a simple click reaction of 8-chloroquinoline and phenylacetylene.

PubMed

Zeng, Qing; Ye, Lingling; Ma, Lu; Yin, Wenqing; Li, Tingsheng; Liang, Aihui; Jiang, Zhiliang

2015-05-01

In 0.19 mol/L acetic acid (HAc), a click reaction of 8-chloroquinoline/azide/phenylacetylene take places in aqueous solution without Cu(I) as a catalyst. 8-Chloroquinoline (CQN) exhibited a strong fluorescence peak at 430 nm that was quenched linearly as the concentration of azide increased from 20 to 1000 ng/mL. This quenching was due to consumption of CQN in the click reaction and a decrease in the number of efficiently excited photons due to the presence of triazole-quinoline ramification molecules with strong hydrophobicity. Using blue nanosilver sol as the substrate, CQN absorbed onto the surface of nanosilver particles, showing a strong surface-enhanced Raman scattering (SERS) peak at 1585 cm(-1) that decreased linearly as the azide concentration increased from 8 to 500 ng/mL; the detection limit was 4 ng/mL. Thus, two new, simple and sensitive fluorescence and SERS methods have been developed for the determination of azide via the click reaction. Copyright © 2014 John Wiley & Sons, Ltd.

Effect of ion pairing on the fluorescence of berberine, a natural isoquinoline alkaloid

NASA Astrophysics Data System (ADS)

Megyesi, Mónika; Biczók, László

2007-10-01

Effect of association with chloride or perchlorate anions on the fluorescence properties of berberine, a cationic isoquinoline alkaloid, has been studied. Interaction with Cl - caused more efficient fluorescence quenching; it significantly accelerated the radiationless deactivation and slowed down the radiative transition. Combined analysis of spectrophotometric, steady-state and time-resolved fluorescence results provided 1.5 × 10 5 M -1 for the equilibrium constant of ion pairing with Cl - in CH 2Cl 2. Both ion pairing and enrichment of the microenvironment of berberine in ions led to excited state quenching in solvents of medium polarity, but only the latter effect was observed in the presence of perchlorates in butyronitrile.

Protein-targeted corona phase molecular recognition

PubMed Central

Bisker, Gili; Dong, Juyao; Park, Hoyoung D.; Iverson, Nicole M.; Ahn, Jiyoung; Nelson, Justin T.; Landry, Markita P.; Kruss, Sebastian; Strano, Michael S.

2016-01-01

Corona phase molecular recognition (CoPhMoRe) uses a heteropolymer adsorbed onto and templated by a nanoparticle surface to recognize a specific target analyte. This method has not yet been extended to macromolecular analytes, including proteins. Herein we develop a variant of a CoPhMoRe screening procedure of single-walled carbon nanotubes (SWCNT) and use it against a panel of human blood proteins, revealing a specific corona phase that recognizes fibrinogen with high selectivity. In response to fibrinogen binding, SWCNT fluorescence decreases by >80% at saturation. Sequential binding of the three fibrinogen nodules is suggested by selective fluorescence quenching by isolated sub-domains and validated by the quenching kinetics. The fibrinogen recognition also occurs in serum environment, at the clinically relevant fibrinogen concentrations in the human blood. These results open new avenues for synthetic, non-biological antibody analogues that recognize biological macromolecules, and hold great promise for medical and clinical applications. PMID:26742890

Selective detection of dopamine in the presence of ascorbic acid via fluorescence quenching of InP/ZnS quantum dots

PubMed Central

Ankireddy, Seshadri Reddy; Kim, Jongsung

2015-01-01

Dopamine is a neurotransmitter of the catecholamine family and has many important roles, especially in human brain. Several diseases of the nervous system, such as Parkinson’s disease, attention deficit hyperactivity disorder, restless legs syndrome, are believed to be related to deficiency of dopamine. Several studies have been performed to detect dopamine by using electrochemical analysis. In this study, quantum dots (QDs) were used as sensing media for the detection of dopamine. The surface of the QDs was modified with l-cysteine by coupling reaction to increase the selectivity of dopamine. The fluorescence of cysteine-capped indium phosphide/zinc sulfide QDs was quenched by dopamine with various concentrations in the presence of ascorbic acid. This method shows good selectivity for dopamine detection, and the detection limit was 5 nM. PMID:26347250

Fluorescence Manipulation by Gold Nanoparticles: From Complete Quenching to Extensive Enhancement

PubMed Central

2011-01-01

Background When a fluorophore is placed in the vicinity of a metal nanoparticle possessing a strong plasmon field, its fluorescence emission may change extensively. Our study is to better understand this phenomenon and predict the extent of quenching and/or enhancement of fluorescence, to beneficially utilize it in molecular sensing/imaging. Results Plasmon field intensities on/around gold nanoparticles (GNPs) with various diameters were theoretically computed with respect to the distance from the GNP surface. The field intensity decreased rapidly with the distance from the surface and the rate of decrease was greater for the particle with a smaller diameter. Using the plasmon field strength obtained, the level of fluorescence alternation by the field was theoretically estimated. For experimental studies, 10 nm GNPs were coated with polymer layer(s) of known thicknesses. Cypate, a near infrared fluorophore, was placed on the outermost layer of the polymer coated GNPs, artificially separated from the GNP at known distances, and its fluorescence levels were observed. The fluorescence of Cypate on the particle surface was quenched almost completely and, at approximately 5 nm from the surface, it was enhanced ~17 times. The level decreased thereafter. Theoretically computed fluorescence levels of the Cypate placed at various distances from a 10 nm GNP were compared with the experimental data. The trend of the resulting fluorescence was similar. The experimental results, however, showed greater enhancement than the theoretical estimates, in general. The distance from the GNP surface that showed the maximum enhancement in the experiment was greater than the one theoretically predicted, probably due to the difference in the two systems. Conclusions Factors affecting the fluorescence of a fluorophore placed near a GNP are the GNP size, coating material on GNP, wavelengths of the incident light and emitted light and intrinsic quantum yield of the fluorophore. Experimentally, we were able to quench and enhance the fluorescence of Cypate, by changing the distance between the fluorophore and GNP. This ability of artificially controlling fluorescence can be beneficially used in developing contrast agents for highly sensitive and specific optical sensing and imaging. PMID:21569249

Effective binding of perhalogenated closo-borates to serum albumins revealed by spectroscopic and ITC studies

NASA Astrophysics Data System (ADS)

Kuperman, Marina V.; Losytskyy, Mykhaylo Yu.; Bykov, Alexander Yu.; Yarmoluk, Sergiy M.; Zhizhin, Konstantin Yu.; Kuznetsov, Nikolay T.; Varzatskii, Oleg A.; Gumienna-Kontecka, Elzbieta; Kovalska, Vladyslava B.

2017-08-01

The interactions of boron cluster compounds closo-borates with biomolecules are widely studied due to their efficiency as agents for boron neutron capture therapy of cancer. In present work the binding abilities of anionic halogen closo-borates [B10Hal10]2- (Hal = Cl, Br, I) and [B12Hal12]2- (Hal = Cl, I) towards bovine and human serum albumins were investigated by spectroscopic and isothermal titration calorimetry (ITC) methods. The protein fluorescence quenching method and ITC studies confirmed the complex formation. The degree of protein fluorescence quenching increased from chlorine to iodine boron derivatives that is attributed to external heavy atom effect. The ITC data point on the existence in the protein structure of two types of binding sites: with higher and lower affinity to closo-borates. Albumin-closo-borate complex binding ratio, n (4-5 anions per protein molecule) is higher than for the parent hydrogen closo-borates (2 anions per protein molecule). Binding constants estimated by fluorescent and ITC methods indicate higher affinity of halogen closo-borates to albumins (K in the range of 104-106 M-1) comparing to that of the hydrogen closo-borate (K about 103 M-1). Due to their high affinity and high binding ratio to albumins halogen closo-borates are proposed for further studies as agents for boron neutron capture therapy.

Sensitive fluorimetric assays for α-glucosidase activity and inhibitor screening based on β-cyclodextrin-coated quantum dots.

PubMed

Liu, Si-Yao; Wang, Huan; He, Tian; Qi, Liang; Zhang, Zhi-Qi

2016-02-01

A fluorescence method was established for a α-glucosidase activity assay and inhibitor screening based on β-cyclodextrin-coated quantum dots. p-Nitrophenol, the hydrolysis product of the α-glucosidase reaction, could quench the fluorescence of β-cyclodextrin-coated quantum dots via an electron transfer process, leading to fluorescence turn-off, whereas the fluorescence of the system turned on in the presence of α-glucosidase inhibitors. Taking advantage of the excellent properties of quantum dots, this method provided a very simple, rapid and sensitive screening method for α-glucosidase inhibitors. Two α-glucosidase inhibitors, 2,4,6-tribromophenol and acarbose, were used to evaluate the feasibility of this screening model, and IC50 values of 24 μM and 0.55 mM were obtained respectively, which were lower than those previously reported. The method may have potential application in screening α-glucosidase inhibitors. Copyright © 2015 John Wiley & Sons, Ltd.

Spectroscopic study of binding of chlorogenic acid with the surface of ZnO nanoparticles

NASA Astrophysics Data System (ADS)

Belay, Abebe; Kim, Hyung Kook; Hwang, Yoon-Hwae

2017-09-01

Understanding the interaction properties of biological materials with ZnO NPs is fundamental interest in the field of biotechnological applications as well as in the formation of optoelectronic devices. In this research, the binding of ZnO NPs and chlorogenic acid (CGA) were investigated using fluorescence quenching, UV-Vis absorption spectroscopy, Fourier transform infrared (FTIR), Raman spectroscopy, scanning electron microscopy (TEM), and dynamic light scattering (DLS) techniques. The study results indicated the fluorescence quenching between ZnO NPs and CGA rationalized in terms of static quenching mechanism or the formation of nonfluorescent CGA-ZnO. From fluorescence quenching spectral analysis the binding constant ( K a ), number of binding sites ( n), and thermodynamic properties, were determined. The quenching constants ( K sv) and binding constant ( K a ), decrease with increasing the temperature and their binding sites n are 2. The thermodynamic parameters determined using Van't Hoff equation indicated binding occurs spontaneously involving the hydrogen bond and van der Walls forces played the major role in the reaction of ZnO NPs with CGA. The Raman, SEM, DLS, and Zeta potential measurements were also indicated the differences in the structure, morphology and sizes of CGA, ZnO NPs, and their corresponding CGA-ZnO due to adsorption of CGA on the surface of ZnO NPs

Template-directed synthesis of silica nanotubes for explosive detection.

PubMed

Yildirim, Adem; Acar, Handan; Erkal, Turan S; Bayindir, Mehmet; Guler, Mustafa O

2011-10-01

Fluorescent porous organic-inorganic thin films are of interest of explosive detection because of their vapor phase fluorescence quenching property. In this work, we synthesized fluorescent silica nanotubes using a biomineralization process through self-assembled peptidic nanostructures. We designed and synthesized an amyloid-like peptide self-assembling into nanofibers to be used as a template for silica nanotube formation. The amine groups on the peptide nanofibrous system were used for nucleation of silica nanostructures. Silica nanotubes were used to prepare highly porous surfaces, and they were doped with a fluorescent dye by physical adsorption for explosive sensing. These porous surfaces exhibited fast, sensitive, and highly selective fluorescence quenching against nitro-explosive vapors. The materials developed in this work have vast potential in sensing applications due to enhanced surface area. © 2011 American Chemical Society

Label-Free Platform for MicroRNA Detection Based on the Fluorescence Quenching of Positively Charged Gold Nanoparticles to Silver Nanoclusters.

PubMed

Miao, Xiangmin; Cheng, Zhiyuan; Ma, Haiyan; Li, Zongbing; Xue, Ning; Wang, Po

2018-01-16

A novel strategy was developed for microRNA-155 (miRNA-155) detection based on the fluorescence quenching of positively charged gold nanoparticles [(+)AuNPs] to Ag nanoclusters (AgNCs). In the designed system, DNA-stabilized Ag nanoclusters (DNA/AgNCs) were introduced as fluorescent probes, and DNA-RNA heteroduplexes were formed upon the addition of target miRNA-155. Meanwhile, the (+)AuNPs could be electrostatically adsorbed on the negatively charged single-stranded DNA (ssDNA) or DNA-RNA heteroduplexes to quench the fluorescence signal. In the presence of duplex-specific nuclease (DSN), DNA-RNA heteroduplexes became a substrate for the enzymatic hydrolysis of the DNA strand to yield a fluorescence signal due to the diffusion of AgNCs away from (+)AuNPs. Under the optimal conditions, (+)AuNPs displayed very high quenching efficiency to AgNCs, which paved the way for ultrasensitive detection with a low detection limit of 33.4 fM. In particular, the present strategy demonstrated excellent specificity and selectivity toward the detection of target miRNA against control miRNAs, including mutated miRNA-155, miRNA-21, miRNA-141, let-7a, and miRNA-182. Moreover, the practical application value of the system was confirmed by the evaluation of the expression levels of miRNA-155 in clinical serum samples with satisfactory results, suggesting that the proposed sensing platform is promising for applications in disease diagnosis as well as the fundamental research of biochemistry.

Target-cancer cell specific activatable fluorescence imaging Probes: Rational Design and in vivo Applications

PubMed Central

Kobayashi, Hisataka; Choyke, Peter L.

2010-01-01

CONSPECTUS Conventional imaging methods, such as angiography, computed tomography, magnetic resonance imaging and radionuclide imaging, rely on contrast agents (iodine, gadolinium, radioisotopes) that are “always on”. While these agents have proven clinically useful, they are not sufficiently sensitive because of the inadequate target to background ratio. A unique aspect of optical imaging is that fluorescence probes can be designed to be activatable, i.e. only “turned on” under certain conditions. These probes can be designed to emit signal only after binding a target tissue, greatly increasing sensitivity and specificity in the detection of disease. There are two basic types of activatable fluorescence probes; 1) conventional enzymatically activatable probes, which exist in the quenched state until activated by enzymatic cleavage mostly outside of the cells, and 2) newly designed target-cell specific activatable probes, which are quenched until activated in targeted cells by endolysosomal processing that results when the probe binds specific cell-surface receptors and is subsequently internalized. Herein, we present a review of the rational design and in vivo applications of target-cell specific activatable probes. Designing these probes based on their photo-chemical (e.g. activation strategy), pharmacological (e.g. biodistribution), and biological (e.g. target specificity) properties has recently allowed the rational design and synthesis of target-cell specific activatable fluorescence imaging probes, which can be conjugated to a wide variety of targeting molecules. Several different photo-chemical mechanisms have been utilized, each of which offers a unique capability for probe design. These include: self-quenching, homo- and hetero-fluorescence resonance energy transfer (FRET), H-dimer formation and photon-induced electron transfer (PeT). In addition, the repertoire is further expanded by the option for reversibility or irreversibility of the signal emitted using the aforementioned mechanisms. Given the wide range of photochemical mechanisms and properties, target-cell specific activatable probes possess considerable flexibility and can be adapted to specific diagnostic needs. Herein, we summarize the chemical, pharmacological, and biological basis of target-cell specific activatable imaging probes and discuss methods to successfully design such target-cell specific activatable probes for in vivo cancer imaging. PMID:21062101

Enhancement of fluorescence quenching and exciplex formation in DNA major groove by double incorporation of modified fluorescent deoxyuridines.

PubMed

Tanaka, Makiko; Oguma, Kazuhiro; Saito, Yoshio; Saito, Isao

2012-06-15

5-(1-Naphthalenylethynyl)-2'-deoxyuridine ((N)U) and 5-[(4-cyano-1-naphthalenyl)ethynyl]-2'-deoxyuridine ((CN)U) were synthesized and incorporated into oligodeoxynucleotides. Fluorescence emissions of modified duplexes containing double (N)U were efficiently quenched depending upon the sequence pattern of the naphthalenes in DNA major groove, as compared to the duplex possessing single (N)U. When one of the naphthalene moieties has a cyano substituent, the exciplex emission from the chromophores in DNA major groove was observed at longer wavelength. Copyright © 2012 Elsevier Ltd. All rights reserved.

Photophysical properties and fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene in zeolites

NASA Astrophysics Data System (ADS)

Pischel, Uwe; Galletero, Maria S.; García, Hermenegildo; Miranda, Miguel A.; Nau, Werner M.

2002-06-01

2,3-Diazabicyclo[2.2.2]oct-2-ene (DBO) was used as a long-lived fluorescent probe in zeolites (NaY, Na-mordenite, Na-ZSM-5, H-ZSM-5) and related oxide materials (all silica MCM-41, silica, silica-alumina, γ-alumina). The photophysical properties are dominated by a hydroxylic environment, caused by the inorganic framework and co-adsorbed water. The quenching of DBO by oxygen was strongly dependent on the type of zeolite. In ZSM-5 zeolites, the fluorescence decays were not monoexponential in the presence of oxygen (air).

Preassembled Fluorescent Multivalent Probes for the Imaging of Anionic Membranes.

PubMed

Roland, Felicia M; Peck, Evan M; Rice, Douglas R; Smith, Bradley D

2017-04-19

A new self-assembly process known as Synthavidin (synthetic avidin) technology was used to prepare targeted probes for near-infrared fluorescence imaging of anionic membranes and cell surfaces, a hallmark of many different types of disease. The probes were preassembled by threading a tetralactam macrocycle with six appended zinc-dipicolylamine (ZnDPA) targeting units onto a linear scaffold with one or two squaraine docking stations to produce hexavalent or dodecavalent fluorescent probes. A series of liposome titration experiments showed that multivalency promoted stronger membrane binding by the dodecavalent probe. In addition, the dodecavalent probe exhibited turn-on fluorescence due to probe unfolding during fluorescence microscopy at the membrane surface. However, the dodecavalent probe also had a higher tendency to self-aggregate after membrane binding, leading to probe self-quenching under certain conditions. This self-quenching effect was apparent during fluorescence microscopy experiments that recorded low fluorescence intensity from anionic dead and dying mammalian cells that were saturated with the dodecavalent probe. Conversely, probe self-quenching was not a factor with anionic microbial surfaces, where there was intense fluorescence staining by the dodecavalent probe. A successful set of rat tumor imaging experiments confirmed that the preassembled probes have sufficient mechanical stability for effective in vivo imaging. The results demonstrate the feasibility of this general class of preassembled fluorescent probes for multivalent targeting, but fluorescence imaging performance depends on the specific physical attributes of the biomarker target, such as the spatial distance between different copies of the biomarker and the propensity of the probe-biomarker complex to self-aggregate.

Polydopamine Nanotubes as an Effective Fluorescent Quencher for Highly Sensitive and Selective Detection of Biomolecules Assisted with Exonuclease III Amplification.

PubMed

Fan, Daoqing; Zhu, Xiaoqing; Zhai, Qingfeng; Wang, Erkang; Dong, Shaojun

2016-09-20

In this work, the effective fluorescence quenching ability of polydopamine nanotubes (PDANTs) toward various fluorescent dyes was studied and further applied to fluorescent biosensing for the first time. The PDANTs could quench the fluorophores with different emission frequencies, aminomethylcoumarin acetate (AMCA), 6-carboxyfluorescein (FAM), 6-carboxytetramethylrhodamine (TAMRA), and Cy5. All the quenching efficiencies reached to more than 97%. Taking advantage of PDANTs' different affinities toward ssDNA and dsDNA and utilizing the complex of FAM-labeled ssDNA and PDANTs as a sensing platform, we achieved highly sensitive and selective detection of human immunodeficiency virus (HIV) DNA and adenosine triphosphate (ATP) assisted with Exonuclease III amplification. The limits of detection (LODs) of HIV DNA and ATP reached to 3.5 pM and 150 nM, respectively, which were all lower than that of previous nanoquenchers with Exo III amplification, and the platform also presented good applicability in biological samples. Fluorescent sensing applications of this nanotube enlightened other targets detection based upon it and enriched the building blocks of fluorescent sensing platforms. This polydopamine nanotube also possesses excellent biocompatibility and biodegradability, which is suitable for future drug delivery, cell imaging, and other biological applications.

Effects of iron on optical properties of dissolved organic matter.

PubMed

Poulin, Brett A; Ryan, Joseph N; Aiken, George R

2014-09-02

Iron is a source of interference in the spectroscopic analysis of dissolved organic matter (DOM); however, its effects on commonly employed ultraviolet and visible (UV-vis) light adsorption and fluorescence measurements are poorly defined. Here, we describe the effects of iron(II) and iron(III) on the UV-vis absorption and fluorescence of solutions containing two DOM fractions and two surface water samples. In each case, regardless of DOM composition, UV-vis absorption increased linearly with increasing iron(III). Correction factors were derived using iron(III) absorption coefficients determined at wavelengths commonly used to characterize DOM. Iron(III) addition increased specific UV absorbances (SUVA) and decreased the absorption ratios (E2:E3) and spectral slope ratios (SR) of DOM samples. Both iron(II) and iron(III) quenched DOM fluorescence at pH 6.7. The degree and region of fluorescence quenching varied with the iron:DOC concentration ratio, DOM composition, and pH. Regions of the fluorescence spectra associated with greater DOM conjugation were more susceptible to iron quenching, and DOM fluorescence indices were sensitive to the presence of both forms of iron. Analyses of the excitation-emission matrices using a 7- and 13-component parallel factor analysis (PARAFAC) model showed low PARAFAC sensitivity to iron addition.

Effects of iron on optical properties of dissolved organic matter

USGS Publications Warehouse

Poulin, Brett; Ryan, Joseph N.; Aiken, George R.

2014-01-01

Iron is a source of interference in the spectroscopic analysis of dissolved organic matter (DOM); however, its effects on commonly employed ultraviolet and visible (UV–vis) light adsorption and fluorescence measurements are poorly defined. Here, we describe the effects of iron(II) and iron(III) on the UV–vis absorption and fluorescence of solutions containing two DOM fractions and two surface water samples. In each case, regardless of DOM composition, UV–vis absorption increased linearly with increasing iron(III). Correction factors were derived using iron(III) absorption coefficients determined at wavelengths commonly used to characterize DOM. Iron(III) addition increased specific UV absorbances (SUVA) and decreased the absorption ratios (E2:E3) and spectral slope ratios (SR) of DOM samples. Both iron(II) and iron(III) quenched DOM fluorescence at pH 6.7. The degree and region of fluorescence quenching varied with the iron:DOC concentration ratio, DOM composition, and pH. Regions of the fluorescence spectra associated with greater DOM conjugation were more susceptible to iron quenching, and DOM fluorescence indices were sensitive to the presence of both forms of iron. Analyses of the excitation–emission matrices using a 7- and 13-component parallel factor analysis (PARAFAC) model showed low PARAFAC sensitivity to iron addition.

Synthesis, characterization and photophysical properties of ferrocenyl and mixed sandwich cobaltocenyl ester linked meso-triaryl corrole dyads

NASA Astrophysics Data System (ADS)

Achary, B. Shivaprasad; Ramya, A. R.; Trivedi, Rajiv; Bangal, P. R.; Giribabu, L.

We report here the design and synthesis of corrole-metallocene dyads consisting of a metallocene (either ferrocene (Dyad 1) or mixed sandwich η5-[C5H4(COOH)]Co(η4-C4Ph4) (Dyad 2)) connected via an ester linkage at meso phenyl position. Both the dyads were characterized by 1H NMR, MALDI-TOF, UV-visible, fluorescence spectroscopies (steady-state, picosecond time-resolved), femtosecond transient absorption spectroscopy (fs-TA) and electrochemical methods. The absorption spectra of these dyads showed slight broadening and splitting of the Soret band that indicates a weak ground state interaction between the corrole macrocycle and metallocene part of the present donor-acceptor (D-A) system. However, in both the dyad systems, fluorescence emission of the corrole was quenched in polar solvents as compared to its parent compound 10-(4-hydroxyphenyl)-5,15-bis-(pentafluorophenyl ) corrole (Ph-Corr). The quenching was more pronounced in ferrocene derivatives than in cobaltocenyl derivatives. Transient absorption studies confirm the absence of photoinduced electron transfer from metallocene to correl for these dyad systems and the quenching of singlet state of corrole is found to enhance intersystem crossing due to heavy atom effect. Corrole-ferrocene and corrole-mixed sandwich η5-[C5H4(COOH)]Co(η4-C4Ph4) dyads have been designed, synthesized and characterized by various spectroscopic techniques. Emission intensitiy of both dyads were quenched in polar solvents whereas transient absorption studies indicates that the quenching coule be due to the heavy atom effect.

Hairpin stabilized fluorescent silver nanoclusters for quantitative detection of NAD+ and monitoring NAD+/NADH based enzymatic reactions.

PubMed

Jain, Priyamvada; Chakma, Babina; Patra, Sanjukta; Goswami, Pranab

2017-03-01

A set of 90 mer long ssDNA candidates, with different degrees of cytosine (C-levels) (% and clusters) was analyzed for their function as suitable Ag-nanocluster (AgNC) nucleation scaffolds. The sequence (P4) with highest C-level (42.2%) emerged as the only candidate supporting the nucleation process as evident from its intense fluorescence peak at λ 660 nm . Shorter DNA subsets derived from P4 with only stable hairpin structures could support the AgNC formation. The secondary hairpin structures were confirmed by PAGE, and CD studies. The number of base pairs in the stem region also contributes to the stability of the hairpins. A shorter 29 mer sequence (Sub 3) (ΔG = -1.3 kcal/mol) with 3-bp in the stem of a 7-mer loop conferred highly stable AgNC. NAD + strongly quenched the fluorescence of Sub 3-AgNC in a concentration dependent manner. Time resolved photoluminescence studies revealed the quenching involves a combined static and dynamic interaction where the binding constant and number of binding sites for NAD + were 0.201 L mol -1 and 3.6, respectively. A dynamic NAD + detection range of 50-500 μM with a limit of detection of 22.3 μM was discerned. The NAD + mediated quenching of AgNC was not interfered by NADH, NADP + , monovalent and divalent ions, or serum samples. The method was also used to follow alcohol dehydrogenase and lactate dehydrogenase catalyzed physiological reactions in a turn-on and turn-off assay, respectively. The proposed method with ssDNA-AgNC could therefore be extended to monitor other NAD + /NADH based enzyme catalyzed reactions in a turn-on/turn-off approach. Copyright © 2016 Elsevier B.V. All rights reserved.

Multispectroscopic and molecular modeling studies on the interaction of copper-ibuprofenate complex with bovine serum albumin (BSA).

PubMed

Shiri, Farshad; Rahimi-Nasrabadi, Mehdi; Ahmadi, Farhad; Ehrlich, Hermann

2018-05-31

Bovine serum albumin (BSA) represents the well recognized model protein for investigations of diverse intermolecular reactions in studies on pharmacological activities of modern drugs. In the present work, the interaction between copper ibuprofenate ([Cu2(IBU)4]) and BSA under simulative physiological conditions was investigated by the using of diverse spectral methods including fluorescence, UV-vis absorption, CD spectroscopy and also molecular docking. The obtained results showed that there was a strong fluorescence quenching of BSA by [Cu2(IBU)4] (2.964E+4 M -1 at room temperature). Using the continuous variation method, a single class of binding sites, (1:1), for [Cu2(IBU)4] on BSA was put in evidence. The Stern-Volmer analysis of fluorescence quenching data shows the presence of the static quenching mechanism. The binding constants K b were calculated and the thermodynamic parameters ∆G°, ∆H° and ∆S° were given. The obtained thermodynamic values and the change observed in the alpha-helical content signature suggests that hydrogen bonding and hydrophobic forces play a major role in the [Cu2(IBU)4]-BSA binding interaction. Site marker competitive experiments indicated that the binding of [Cu2(IBU)4] to BSA primarily took place in sub-domain IIA that this observation were substantiated by molecular docking studies. The results of CD and UV-vis spectroscopy showed for the first time that the presence of [Cu2(IBU)4] increased the ɑ-helical content of BSA (from 48.56% to 55.71%) and conformational changes of BSA molecules. Copyright © 2017 Elsevier B.V. All rights reserved.

Spectroscopic and theoretical investigation of oxali-palladium interactions with β-lactoglobulin.

PubMed

Ghalandari, Behafarid; Divsalar, Adeleh; Saboury, Ali Akbar; Haertlé, Thomas; Parivar, Kazem; Bazl, Roya; Eslami-Moghadam, Mahbube; Amanlou, Massoud

2014-01-24

The possibility of using a small cheap dairy protein, β-lactoglobulin (β-LG), as a carrier for oxali-palladium for drug delivery was studied. Their binding in an aqueous solution at two temperatures of 25 and 37°C was investigated using spectroscopic techniques in combination with a molecular docking study. Fluorescence intensity changes showed combined static and dynamic quenching during β-LG oxali-palladium binding, with the static mode being predominant in the quenching mechanism. The binding and thermodynamic parameters were determined by analyzing the results of quenching and those of the van't Hoff equation. According to obtained results the binding constants at two temperatures of 25 and 37°C are 3.3×10(9) M(-1) and 18.4×10(6) M(-1) respectively. Fluorescence resonance energy transfer (FRET) showed that the experimental results and the molecular docking results were coherent. An absence change of β-LG secondary structure was confirmed by the CD results. Molecular docking results agreed fully with the experimental results since the fluorescence studies also revealed the presence of two binding sites with a negative value for the Gibbs free energy of binding of oxali-palladium to β-LG. Furthermore, molecular docking and experimental results suggest that the hydrophobic effect plays a critical role in the formation of the oxali-palladium complex with β-LG. This agreement between molecular docking and experimental results implies that docking studies may be a suitable method for predicting and confirming experimental results, as shown in this study. Hence, the combination of molecular docking and spectroscopy methods is an effective innovative approach for binding studies, particularly for pharmacophores. Copyright © 2013 Elsevier B.V. All rights reserved.

Design and fabrication of optical chemical sensor for detection of nitroaromatic explosives based on fluorescence quenching of phenol red immobilized poly(vinyl alcohol) membrane.

PubMed

Zarei, Ali Reza; Ghazanchayi, Behnam

2016-04-01

The present study developed a new optical chemical sensor for detection of nitroaromatic explosives in liquid phase. The method is based on the fluorescence quenching of phenol red as fluorophore in a poly(vinyl alcohol) (PVA) membrane in the presence of nitroaromatic explosives as quenchers, e.g., 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), 4-nitrotoluene (4-NT), 2,4,6-trinitrobenzene (TNB), and nitrobenzene (NB). For chemical immobilization of phenol red in PVA, phenol red reacted with formaldehyde to produce hydroxymethyl groups and then attached to PVA membrane through the hydroxymethyl groups. The optical sensor showed strong quenching of nitroaromatic explosives. A Stern-Volmer graph for each explosive was constructed and showed that the range of concentration from 5.0 × 10(-6) to 2.5 × 10(-4) mol L(-1) was linear for each explosive and sensitivity varied as TNB >TNT>2,4-DNT>NB>4-NT. The response time of the sensor was within 1 min. The proposed sensor showed good reversibility and reproducibility. Copyright © 2015 Elsevier B.V. All rights reserved.

[Study of scavenging activity of sorghum pigment to hydroxyl free radicals by fluorimetry].

PubMed

Zhang, Hai-rong; Wang, Wen-yan

2007-03-01

A natural product, sorghum pigment, consists of a number of important flavonoid derivatives, occurrs on the seed capsules or in the stems of many sorghums, and is widely applied in different fields of food, cosmetic and dyeing industries, It is important for scavenging hydroxyl free radicals and protection of human healthiness. Scavenging capacities of hydroxyl free radicals with sodium nitrite, quercetin and sorghum pigment were comparatively researched by fluorimetry, and the model of hydroxyl free radicals produced is based on the reaction of Cu2+ -catalyzed oxidation of ascorbic acid in the presence of hydrogen peroxide. The hydroxyl radicals react with benzoic acid, forming a fluorescent product, and the fluorescence intensity was determined by the concentration of hydroxybenzoic acid. The experimental results show that the sodium nitrite, quercetin and sorghum pigment have a quantity-effect relationship for scavenging hydroxyl free radicals, and sodium nitrite and quercetin in comparison with sorghum pigment have high antioxidant capacity. Finally, the quenching mechanisms were explored with sodium nitrite, sorghum pigment, and quercetin respectively. The sorghum pigment and sodium nitrite feature a dynamic quenching processes, while quercetin shows a static quenching processes. A reference method was provided for reasonable exploitation and utilization of sorghum pigment.

A chlorophyll fluorescence-based method for the integrated characterization of the photophysiological response to light stress.

PubMed

Serôdio, João; Schmidt, William; Frankenbach, Silja

2017-02-01

This work introduces a new experimental method for the comprehensive description of the physiological responses to light of photosynthetic organisms. It allows the integration in a single experiment of the main established manipulative chlorophyll fluorescence-based protocols. It enables the integrated characterization of the photophysiology of samples regarding photoacclimation state (generating non-sequential light-response curves of effective PSII quantum yield, electron transport rate or non-photochemical quenching), photoprotection capacity (running light stress-recovery experiments, quantifying non-photochemical quenching components) and the operation of photoinactivation and photorepair processes (measuring rate constants of photoinactivation and repair for different light levels and the relative quantum yield of photoinactivation). The new method is based on a previously introduced technique, combining the illumination of a set of replicated samples with spatially separated actinic light beams of different intensity, and the simultaneous measurement of the fluorescence emitted by all samples using an imaging fluorometer. The main novelty described here is the independent manipulation of light intensity and duration of exposure for each sample, and the control of the cumulative light dose applied. The results demonstrate the proof of concept for the method, by comparing the responses of cultures of Chlorella vulgaris acclimated to low and high light regimes, highlighting the mapping of light stress responses over a wide range of light intensity and exposure conditions, and the rapid generation of paired light-response curves of photoinactivation and repair rate constants. This approach represents a chlorophyll fluorescence 'protocol of everything', contributing towards the high throughput characterization of the photophysiology of photosynthetic organisms. © The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Quantum Dot-Fullerene Based Molecular Beacon Nanosensors for Rapid, Highly Sensitive Nucleic Acid Detection.

PubMed

Liu, Ye; Kannegulla, Akash; Wu, Bo; Cheng, Li-Jing

2018-05-15

Spherical fullerene (C 60 ) can quench the fluorescence of a quantum dot (QD) through energy transfer and charge transfer processes, with the quenching efficiency regulated by the number of proximate C 60 on each QD. With the quenching property and its small size compared with other nanoparticle-based quenchers, it is advantageous to group a QD reporter and multiple C 60 -labeled oligonucleotide probes to construct a molecular beacon (MB) probe for sensitive, robust nucleic acid detection. We demonstrated a rapid, high-sensitivity DNA detection method using the nanosensors composed of QD-C 60 based MBs carried by magnetic nanoparticles (MNPs). The assay was accelerated by first dispersing the nanosensors in analytes for highly efficient DNA capture resulting from short-distance 3-dimensional diffusion of targets to the sensor surface and then concentrating the nanosensors to a substrate by magnetic force to amplify the fluorescence signal for target quantification. The enhanced mass transport enabled a rapid detection (< 10 min) with a small sample volume (1-10 µl). The high signal-to-noise ratio produced by the QD-C 60 pairs and magnetic concentration yielded a detection limit of 100 fM (~106 target DNA copies for a 10 µl analyte). The rapid, sensitive, label-free detection method will benefit the applications in point-of-care molecular diagnostic technologies.

Fluorescence studies on binding of pyrene and its derivatives to humic acid

NASA Astrophysics Data System (ADS)

Nakashima, K.; Maki, M.; Ishikawa, F.; Yoshikawa, T.; Gong, Y.-K.; Miyajima, T.

2007-07-01

Binding of pyrene (PyH) and its derivatives to humic acid (HA) has been studied by fluorescence spectroscopy. The nature of the interaction between HA and pyrene derivatives are extensively investigated by employing three derivatives ranging from anionic to cationic compounds: 1-pyrenebutylic acid (PyA), 1-pyrenemethanol (PyM), and 1-pyrenebutyltrimethylammonium bromide (PyB). Binding constants between HA and PyX (X = H, A, M, B) are obtained by steady-state fluorescence quenching techniques, and it is found that PyB has a markedly large binding constant among the pyrene family. This is attributed to a strong electrostatic interaction between cationic PyB and anionic HA. The result suggests that an electrostatic interaction plays a dominant role in binding of pyrenes to humic acid. The importance of electrostatic interaction was also confirmed by a salt effect on the binding constant. Influence of collisional quenching on the binding constant, which causes overestimation of the binding constant, was examined by time-resolved fluorescence spectroscopy as well as temperature effect in steady-state fluorescence measurements. It is elucidated that collisional quenching does not much bring overestimation into the binding constants.

Smart coumarin-tagged imprinted polymers for the rapid detection of tamoxifen.

PubMed

Ray, Judith V; Mirata, Fosca; Pérollier, Celine; Arotcarena, Michel; Bayoudh, Sami; Resmini, Marina

2016-03-01

A signalling molecularly imprinted polymer was synthesised for easy detection of tamoxifen and its metabolites. 6-Vinylcoumarin-4-carboxylic acid (VCC) was synthesised from 4-bromophenol to give a fluorescent monomer, designed to switch off upon binding of tamoxifen. Clomiphene, a chlorinated analogue, was used as the template for the imprinting, and its ability to quench the coumarin fluorescence when used in a 1:1 ratio was demonstrated. Tamoxifen and 4-hydroxytamoxifen were also shown to quench coumarin fluorescence. Imprinted and non-imprinted polymers were synthesised using VCC, methacrylic acid as a backbone monomer and ethylene glycol dimethacrylate as cross-linker, and were ground and sieved to particle sizes ranging between 45 and 25 μm. Rebinding experiments demonstrate that the imprinted polymer shows very strong affinity for both clomiphene and tamoxifen, while the non-imprinted polymer shows negligible rebinding. The fluorescence of the imprinted polymer is quenched by clomiphene, tamoxifen and 4-hydroxytamoxifen. The switch off in fluorescence of the imprinted polymer under these conditions could also be detected under a UV lamp with the naked eye, making this matrix suitable for applications when coupled with a sample preparation system.

Enantioselective binding of L, D-phenylalanine to ct DNA

NASA Astrophysics Data System (ADS)

Zhang, Lijin; Xu, Jianhua; Huang, Yan; Min, Shungeng

2009-10-01

The enantioselective binding of L, D-phenylalanine to calf thymus DNA was studied by absorption, circular dichroism, fluorescence quenching, viscosity, salt effect and emission experiments. The results obtained from absorption, circular dichroism, fluorescence quenching and viscosity experiments excluded the intercalative binding and salt effect experiments did not support electrostatic binding. So the binding of L, D-phenylalanine to ct DNA should be groove binding. Furthermore, the emission spectra revealed that the binding is enantioselective.

Enantioselective binding of L,D-phenylalanine to ct DNA.

PubMed

Zhang, Lijin; Xu, Jianhua; Huang, Yan; Min, Shungeng

2009-10-15

The enantioselective binding of L,D-phenylalanine to calf thymus DNA was studied by absorption, circular dichroism, fluorescence quenching, viscosity, salt effect and emission experiments. The results obtained from absorption, circular dichroism, fluorescence quenching and viscosity experiments excluded the intercalative binding and salt effect experiments did not support electrostatic binding. So the binding of l,d-phenylalanine to ct DNA should be groove binding. Furthermore, the emission spectra revealed that the binding is enantioselective.

Photogalvanic cells driven by electron transfer quenching of excited singlet states

NASA Astrophysics Data System (ADS)

Creed, D.; Fawcett, N. C.

Photoreduction of oxonine by iron(II) sulfate in dilute acid is produced by quenching of the excited signlet state (S1). No induced intersystem crossing to the tripolet (T1) is observed by nanosecond flash photolysis. The photoreduction of oxonine (S1) by iron(II) was used in a totally illuminated thin layer photogalvanic cell. Power conversion efficiencies are, however, very low. The fluorescence of oxonine and thiazine dyes such as thionine is quenched by acids. Oxonine fluorescence is also quenched by hydroquinone and catechol sulfonates and related compounds. Eleven new thiazine dyes were synthesized. A few photogalvanic experiments were carried out using high concentrations of the water miscible dye and iron(II) in a TI/TL cell. Ferrophos, an iron phosphorus alloy, can be substituted for platinum or gold as a cathode in photogalvanic cells.

Interaction of promethazine and adiphenine to human hemoglobin: A comparative spectroscopic and computational analysis

NASA Astrophysics Data System (ADS)

Maurya, Neha; ud din Parray, Mehraj; Maurya, Jitendra Kumar; Kumar, Amit; Patel, Rajan

2018-06-01

The binding nature of amphiphilic drugs viz. promethazine hydrochloride (PMT) and adiphenine hydrochloride (ADP), with human hemoglobin (Hb) was unraveled by fluorescence, absorbance, time resolved fluorescence, fluorescence resonance energy transfer (FRET) and circular dichroism (CD) spectral techniques in combination with molecular docking and molecular dynamic simulation methods. The steady state fluorescence spectra indicated that both PMT and ADP quenches the fluorescence of Hb through static quenching mechanism which was further confirmed by time resolved fluorescence spectra. The UV-Vis spectroscopy suggested ground state complex formation. The activation energy (Ea) was observed more in the case of Hb-ADP than Hb-PMT interaction system. The FRET result indicates the high probability of energy transfer from β Trp37 residue of Hb to the PMT (r = 2.02 nm) and ADP (r = 2.33 nm). The thermodynamic data reveal that binding of PMT with Hb are exothermic in nature involving hydrogen bonding and van der Waal interaction whereas in the case of ADP hydrophobic forces play the major role and binding process is endothermic in nature. The CD results show that both PMT and ADP, induced secondary structural changes of Hb and unfold the protein by losing a large helical content while the effect is more pronounced with ADP. Additionally, we also utilized computational approaches for deep insight into the binding of these drugs with Hb and the results are well matched with our experimental results.

The identification of hydrophobic sites on the surface of proteins using absorption difference spectroscopy of bromophenol blue.

PubMed

Bertsch, M; Mayburd, A L; Kassner, R J

2003-02-15

Hydrophobic sites on the surface of protein molecules are thought to have important functional roles. The identification of such sites can provide information about the function and mode of interaction with other cellular components. While the fluorescence enhancement of polarity-sensitive dyes has been useful in identifying hydrophobic sites on a number of targets, strong intrinsic quenching of Nile red and ANSA dye fluorescence is observed on binding to a cytochrome c('). Fluorescence quenching is also observed to take place in the presence of a variety of other biologically important molecules which can compromise the quantitative determination of binding constants. Absorption difference spectroscopy is shown not to be sensitive to the presence of fluorescence quenchers but sensitive enough to measure binding constants. The dye BPB is shown to bind to the same hydrophobic sites on proteins as polarity-sensitive fluorescence probes. The absorption spectrum of BPB is also observed to be polarity sensitive. A binding constant of 3x10(6)M(-1) for BPB to BSA has been measured by absorption difference spectroscopy. An empirical correlation is observed between the shape of the absorption difference spectrum of BPB and the polarity of the environment. The results indicate that absorption difference spectroscopy of BPB provides a valuable supplement to fluorescence for determining the presence of hydrophobic sites on the surface of proteins as well as a method for measuring binding constants.

Interaction of promethazine and adiphenine to human hemoglobin: A comparative spectroscopic and computational analysis.

PubMed

Maurya, Neha; Ud Din Parray, Mehraj; Maurya, Jitendra Kumar; Kumar, Amit; Patel, Rajan

2018-06-15

The binding nature of amphiphilic drugs viz. promethazine hydrochloride (PMT) and adiphenine hydrochloride (ADP), with human hemoglobin (Hb) was unraveled by fluorescence, absorbance, time resolved fluorescence, fluorescence resonance energy transfer (FRET) and circular dichroism (CD) spectral techniques in combination with molecular docking and molecular dynamic simulation methods. The steady state fluorescence spectra indicated that both PMT and ADP quenches the fluorescence of Hb through static quenching mechanism which was further confirmed by time resolved fluorescence spectra. The UV-Vis spectroscopy suggested ground state complex formation. The activation energy (E a ) was observed more in the case of Hb-ADP than Hb-PMT interaction system. The FRET result indicates the high probability of energy transfer from β Trp37 residue of Hb to the PMT (r=2.02nm) and ADP (r=2.33nm). The thermodynamic data reveal that binding of PMT with Hb are exothermic in nature involving hydrogen bonding and van der Waal interaction whereas in the case of ADP hydrophobic forces play the major role and binding process is endothermic in nature. The CD results show that both PMT and ADP, induced secondary structural changes of Hb and unfold the protein by losing a large helical content while the effect is more pronounced with ADP. Additionally, we also utilized computational approaches for deep insight into the binding of these drugs with Hb and the results are well matched with our experimental results. Copyright © 2018 Elsevier B.V. All rights reserved.

Evaluation of OH laser-induced fluorescence techniques for supersonic combustion diagnostics

NASA Technical Reports Server (NTRS)

Quagliaroli, T. M.; Laufer, G.; Krauss, R. H.; Mcdaniel, J. C., Jr.

1992-01-01

The limitations on application of dye laser and narrowband tunable KrF excimer laser systems to planar OH fluorescence measurements in supersonic combustion test facilities are examined. Included in the analysis are effects of collisional quenching, beam absorption, fluorescence trapping, and signal strengths on achievable measurement accuracy using several excitation and detection options for either of the two laser systems. Dye-based laser systems are found to be the method of choice for imaging OH concentrations less than 10 exp 15 per cu cm, while the KrF based systems provide significant reduction in measurement ambiguity for concentrations in excess of 10 exp 15 per cu cm.

Exciplex formation accompanied with excitation quenching.

PubMed

Fedorenko, Stanislav G; Burshtein, Anatoly I

2010-04-08

The competence of the reversible exciplex formation and parallel quenching of excitation (by electron or energy transfer) was considered using a non-Markovian pi-forms approach, identical to integral encounter theory (IET). General equations accounting for the reversible quenching and exciplex formation are derived in the contact approximation. Their general solution was obtained and adopted to the most common case when the ground state particles are in great excess. Particular cases of only photoionization or just exciplex formation separately studied earlier by means of IET are reproduced. In the case of the irreversible excitation quenching, the theory allows specifying the yields of the fluorescence and exciplex luminescence, as well as the long time kinetics of excitation and exciplex decays, in the absence of quenching. The theory distinguishes between the alternative regimes of (a) fast equilibration between excitations and exciplexes followed by their decay with a common average rate and (b) the fastest and deep excitation decay followed by the weaker and slower delayed fluorescence, backed by exciplex dissociation.

Fluorescent probe for turn-on sensing of L-cysteine by ensemble of AuNCs and polymer protected AuNPs.

PubMed

Xu, Xiaozhe; Qiao, Juan; Li, Nan; Qi, Li; Zhang, Shufeng

2015-06-16

A new fluorescent probe based on ensemble of gold nanoclusters (AuNCs) and polymer protected gold nanoparticles (AuNPs) for turn-on sensing of L-cysteine was designed and prepared. The AuNCs were protected by bovine serum albumin and had strong fluorescence. The polymer protected AuNPs were synthesized by a facile in situ strategy at room temperature and could quench the fluorescence of AuNCs due to the Förster resonance energy transfer. Interestingly, it has been observed that the quenched fluorescence of AuNCs was recovered by L-cysteine, which could induce the aggregation of polymer protected AuNPs by sulfur group. Then the prepared fluorescent probe was successfully used for determination of L-Cys in human urines, which would have an evolving aspect and promote the subsequent exploration. Copyright © 2015 Elsevier B.V. All rights reserved.

Two-photon oxygen nanosensors based on a conjugated fluorescent polymer doped with platinum porphyrins.

PubMed

Wang, Xiao-Hui; Peng, Hong-Shang; Cheng, Kun; Liu, Xiao-Ming; Liu, Yuan-An; Yang, Wei

2018-04-27

Ratiometric fluorescent nanoparticles (NPs) under two-photon excitation are successfully developed for sensing dissolved oxygen. The NPs comprise the oxygen probe Pt(II)-porphyrins (PtTFPP) and fluorescent organic semiconducting polymer (PFO). PFO polymer acts as both a two-photon antenna and a reference dye, while PtTFPP absorbs the photonic energy transferred by the PFO under two-photon excitation at 740 nm to sense oxygen. The red fluorescence of PtTFPP is sensitive to oxygen with a quenching response of 88% from nitrogen saturation to oxygen saturation, and PFO gives oxygen-insensitive referenced blue fluorescence. The fluorescence quenching of the NPs against oxygen at two-photon excitation follows a linear Stern-Volmer behavior. The nanosensors exhibit low cytotoxic effects as well as effortless cellular uptake. When incorporated into cells, the ratio of the signals increases up to about 500% from oxygen-saturated to oxygen-free environment.

Use of induced fluorescence measurements to assess aluminum-organic interactions in acidified lakes

NASA Technical Reports Server (NTRS)

Vodacek, A.; Philpot, W. D.

1985-01-01

The application of laser fluorosensing to the tracing of metals in acid lakes is proposed. The effects of the metals on the dissolving organic carbon (DOC) fluorescence is studied using laboratory mixed water samples and natural water samples from Hamilton and Big Moose Lakes in New York. The operation of the laser fluorosensing system employed in the experiment is described. The DOC fluorescence was quenched by Al, Cu, and Fe, and the relation between pH and the quenching rate is examined. The humic substances fluorescence spectra are analyzed to estimate the concentrations of DOC in water and the relative concentration of Al. The interference problems caused by chemical competition between metal ions and ligands, and changes in the background DOC fluorescence are discussed. It is noted that an airborne laser fluorescence is useful for detecting elevated concentrations of metals.

Fluorescent probes for "off-on" highly sensitive detection of Hg²⁺ and L-cysteine based on nitrogen-doped carbon dots.

PubMed

Zhang, Yi; Cui, Peipei; Zhang, Feng; Feng, Xiaoting; Wang, Yaling; Yang, Yongzhen; Liu, Xuguang

2016-05-15

Fluorescent nitrogen-doped carbon dots (NCDs) were synthesized by a facile, and low-cost one-step hydrothermal strategy using citric acid as carbon source and ammonia solution as nitrogen source for the first time. The obtained NCDs show stable blue fluorescence with a high quantum yield of 35.4%, along with the fluorescence lifetime of ca. 6.75 ns. Most importantly, Hg(2+) can completely quench the fluorescence of NCDs as a result of the formation of a non-fluorescent stable NCDs-Hg(2+) complex. Static fluorescence quenching towards Hg(2+) is proved by the Stern-Volmer equation, ultraviolet-visible absorption spectra, temperature dependent quenching and fluorescence lifetime measurements. Subsequently, the fluorescence of the NCDs-Hg(2+) system is completely recovered with the addition L-cysteine (L-Cys) owing to the dissociation of NCDs-Hg(2+) complex to form a more stable Hg(2+)-L-Cys complex by Hg(2+)-S bonding. Therefore, such NCDs can be used as an effective fluorescent "turn-off" probe for rapid, rather highly selective and sensitive detection of Hg(2+), with a limit of detection (LOD) as low as 1.48 nM and a linear detection range of 0-10 μM. Interestingly, NCDs-Hg(2+) system can be conveniently employed as a fluorescent "turn-on" sensor for highly selective and sensitive detection of L-Cys with a low LOD of 0.79 nM and a wide linear detection range of 0-50 μM. Further, the sensitivity of NCDs to Hg(2+) is preserved in tap water with a LOD of 1.65 nM and a linear detection range of 0-10 μM. Copyright © 2016 Elsevier B.V. All rights reserved.

Two-photon fluorescence imaging super-enhanced by multishell nanophotonic particles, with application to subcellular pH.

PubMed

Ray, Aniruddha; Lee, Yong-Eun Koo; Kim, Gwangseong; Kopelman, Raoul

2012-07-23

A novel nanophotonic method for enhancing the two-photon fluorescence signal of a fluorophore is presented. It utilizes the second harmonic (SH) of the exciting light generated by noble metal nanospheres in whose near-field the dye molecules are placed, to further enhance the dye's fluorescence signal in addition to the usual metal-enhanced fluorescence phenomenon. This method enables demonstration, for the first time, of two-photon fluorescence enhancement inside a biological system, namely live cells. A multishell hydrogel nanoparticle containing a silver core, a protective citrate capping, which serves also as an excitation quenching inhibitor spacer, a pH indicator dye shell, and a polyacrylamide cladding are employed. Utilizing this technique, an enhancement of up to 20 times in the two-photon fluorescence of the indicator dye is observed. Although a significant portion of the enhanced fluorescence signal is due to one-photon processes accompanying the SH generation of the exciting light, this method preserves all the advantages of infrared-excited, two-photon microscopy: enhanced penetration depth, localized excitation, low photobleaching, low autofluorescence, and low cellular damage. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effect of concentration of guanidine hydrochloride on the sulfasalazine serum albumin complex

NASA Astrophysics Data System (ADS)

Sułkowska, A.; Równicka, J.; Pożycka, J.; Bojko, B.; Sułkowski, W. W.

2005-06-01

A detailed study of the effect of Gu·HCl concentration is presented in this work. Destabilization of the tertiary structure of BSA was observed by using fluorescence measurements of excitation wavelength of 280 and 295 nm. We ascertained that in terms of the effect on the fluorescence emission spectrum of BSA, Gu·HCl concentration falls into three regions: I, 0.1-1.6 M; II, 1.6-3 M and III, 3-6 M. The intermediate state of BSA denaturation for 1.6-1.7 M Gu·HCl was noticed. Quenching of the native BSA fluorescence by sulfasalazine (SSZ), a drug used in inflammatory bowel disease, was shown. In the presence of Gu·HCl, BSA fluorescence rises or decreases depending on the concentration region I or II, respectively. A similar effect of Gu·HCl on the fluorescence spectrum of BSA, quenched by sulfasalazine, can be found. However, Gu·HCl concentration-dependent reduction of the quenching effect of the SSZ points to the gradual loss of the binding properties. Binding and quenching constants for the SSZ-BSA complexes were calculated in the absence and presence of the denaturant. Since Gu·HCl at concentration 0.1-1.6 M increases and at concentration 1.6-3 M decreases the BSA fluorescence, the mechanism of the destabilization of the native structure of serum albumin differs for these two ranges of Gu·HCl concentration. The small concentration of the denaturant causes a disorder in the hydration layer of the albumin and the higher one causes the binding of the denaturant molecule close to the Trp 135 in the IB subdomain.

Binding of Cu(II) ions to peptides studied by fluorescence spectroscopy and isothermal titration calorimetry.

PubMed

Makowska, Joanna; Żamojć, Krzysztof; Wyrzykowski, Dariusz; Uber, Dorota; Wierzbicka, Małgorzata; Wiczk, Wiesław; Chmurzyński, Lech

2016-01-15

Steady-state and time-resolved fluorescence quenching measurements supported by Isothermal Titration Calorimetry (ITC) were used to study the interactions of Cu(2+) with four peptides. Two of them were taken from the N-terminal part of the FBP28 protein (formin binding protein) WW domain: Tyr-Lys-Thr-Ala-Asp-Gly-Lys-Thr-Tyr-NH2 (D9) and its mutant Tyr-Lys-Thr-Ala-Asn-Gly-Lys-Thr-Tyr-NH2 (D9_M) as well as two mutated peptides from the B3 domain of the immunoglobulin binding protein G derived from Streptococcus: Asp-Val-Ala-Thr-Tyr-Thr-NH2 (J1) and Glu-Val-Ala-Thr-Tyr-Thr-NH2 (J2). The measurements were carried out at 298.15K in 20mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer solution with a pH of 6. The fluorescence of all peptides was quenched by Cu(2+) ions. The stoichiometry, conditional stability constants and thermodynamic parameters for the interactions of the Cu(2+) ions with D9 and D9_M were determined from the calorimetric data. The values of the conditional stability constants were additionally determined from fluorescence quenching measurements and compared with those obtained from calorimetric studies. There was a good correlation between data obtained from the two techniques. On the other hand, the studies revealed that J1 and J2 do not exhibit an affinity towards metal ions. The obtained results prove that fluorescence quenching experiments may be successfully used in order to determine stability constants of complexes with fluorescent ligands. Finally, based on the obtained results, the coordinating properties of the peptides towards the Cu(2+) ions are discussed. Copyright © 2015 Elsevier B.V. All rights reserved.

Binding of naproxen enantiomers to human serum albumin studied by fluorescence and room-temperature phosphorescence

NASA Astrophysics Data System (ADS)

Lammers, Ivonne; Lhiaubet-Vallet, Virginie; Ariese, Freek; Miranda, Miguel A.; Gooijer, Cees

2013-03-01

The interaction of the enantiomers of the non-steroidal anti-inflammatory drug naproxen (NPX) with human serum albumin (HSA) has been investigated using fluorescence and phosphorescence spectroscopy in the steady-state and time-resolved mode. The absorption, fluorescence excitation, and fluorescence emission spectra of (S)-NPX and (R)-NPX differ in shape in the presence of HSA, indicating that these enantiomers experience a different environment when bound. In solutions containing 0.2 M KI, complexation with HSA results in a strongly increased NPX fluorescence intensity and a decreased NPX phosphorescence intensity due to the inhibition of the collisional interaction with the heavy atom iodide. Fluorescence intensity curves obtained upon selective excitation of NPX show 8-fold different slopes for bound and free NPX. No significant difference in the binding constants of (3.8 ± 0.6) × 105 M-1 for (S)-NPX and (3.9 ± 0.6) × 105 M-1 for (R)-NPX was found. Furthermore, the addition of NPX quenches the phosphorescence of the single tryptophan in HSA (Trp-214) based on Dexter energy transfer. The short-range nature of this mechanism explains the upward curvature of the Stern-Volmer plot observed for HSA: At low concentrations NPX binds to HSA at a distance from Trp-214 and no quenching occurs, whereas at high NPX concentrations the phosphorescence intensity decreases due to dynamic quenching by NPX diffusing into site I from the bulk solution. The dynamic quenching observed in the Stern-Volmer plots based on the longest phosphorescence lifetime indicates an overall binding constant to HSA of about 3 × 105 M-1 for both enantiomers.

Binding of Cu(II) ions to peptides studied by fluorescence spectroscopy and isothermal titration calorimetry

NASA Astrophysics Data System (ADS)

Makowska, Joanna; Żamojć, Krzysztof; Wyrzykowski, Dariusz; Uber, Dorota; Wierzbicka, Małgorzata; Wiczk, Wiesław; Chmurzyński, Lech

2016-01-01

Steady-state and time-resolved fluorescence quenching measurements supported by Isothermal Titration Calorimetry (ITC) were used to study the interactions of Cu2 + with four peptides. Two of them were taken from the N-terminal part of the FBP28 protein (formin binding protein) WW domain: Tyr-Lys-Thr-Ala-Asp-Gly-Lys-Thr-Tyr-NH2 (D9) and its mutant Tyr-Lys-Thr-Ala-Asn-Gly-Lys-Thr-Tyr-NH2 (D9_M) as well as two mutated peptides from the B3 domain of the immunoglobulin binding protein G derived from Streptococcus: Asp-Val-Ala-Thr-Tyr-Thr-NH2 (J1) and Glu-Val-Ala-Thr-Tyr-Thr-NH2 (J2). The measurements were carried out at 298.15 K in 20 mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer solution with a pH of 6. The fluorescence of all peptides was quenched by Cu2 + ions. The stoichiometry, conditional stability constants and thermodynamic parameters for the interactions of the Cu2 + ions with D9 and D9_M were determined from the calorimetric data. The values of the conditional stability constants were additionally determined from fluorescence quenching measurements and compared with those obtained from calorimetric studies. There was a good correlation between data obtained from the two techniques. On the other hand, the studies revealed that J1 and J2 do not exhibit an affinity towards metal ions. The obtained results prove that fluorescence quenching experiments may be successfully used in order to determine stability constants of complexes with fluorescent ligands. Finally, based on the obtained results, the coordinating properties of the peptides towards the Cu2 + ions are discussed.

Fluorimetric Studies of a Trans-Membrane Protein and Its Interactions with Differently Functionalized Silver Nanoparticles.

PubMed

Gambucci, Marta; Tarpani, Luigi; Zampini, Giulia; Massaro, Giuseppina; Nocchetti, Morena; Sassi, Paola; Latterini, Loredana

2018-06-18

Trans-membrane proteins play important roles in the inter-cellular signaling to regulate the interactions among adjacent cells and influence cell fate. The study of the interactions between membrane proteins and nanomaterials is paramount for the design of nanomaterial-based therapies. In the present work, the fluorescence properties of the trans-membrane receptor Notch2 have been investigated. In particular, steady state and time resolved fluorescence methods have been used to characterize the emission of tryptophan residues of Notch2 and then this emission is used to monitor the impact of silver colloids on protein behavior. To this aim, silver colloids are prepared with two different methods to make sure they bear hydrophilic (citrate ions, C-AgNPs) or hydrophobic (dodecanethiol molecules D-AgNPs) capping agents; the preparation procedures are tightly controlled in order to obtain metal cores with similar size distributions (7.4 ± 2.5 and 5.0 ± 0.8 nm, respectively), thus making easier the comparison of the results. The occurrence of strong interactions between Notch2 and D-AgNPs is suggested by the efficient and statistically relevant quenching of the stationary protein emission already at low nanoparticle concentrations (ca. 12% quenching with [D-AgNPs] = 0.6nM). The quenching becomes even more pronounced (ca. 60%) when [D-AgNPs] is raised to 8.72nM. On the other hand, the addition of increasing concentrations of C-AgNPs to Notch2 does not affect the protein fluorescence (intensity variations below 5%) indicating that negligible interactions are taking place. The fluorescence data, recorded in the presence of increasing concentrations of silver nanoparticles, are then analyzed through the Stern-Volmer equation and the sphere of action model to discuss the nature of the interactions. The effect of D-AgNPs on the fluorescence decay times of Notch2 is also investigated and a decrease of the average decay time is observed (from 4.64 to 3.42 ns). The observed variations of the stationary and time-resolved fluorescence behavior of the protein are discussed in terms of static and collisional interactions. These results document that the capping shell is able to drive the protein-particle interactions, which have likely a hydrophobic nature.

Probing the mechanism of interaction of metoprolol succinate with human serum albumin by spectroscopic and molecular docking analysis.

PubMed

Pawar, Suma K; Jaldappagari, Seetharamappa

2017-09-01

In the present work, the mechanism of the interaction between a β1 receptor blocker, metoprolol succinate (MS) and human serum albumin (HSA) under physiological conditions was investigated by spectroscopic techniques, namely fluorescence, Fourier transform infra-red spectroscopy (FT-IR), fluorescence lifetime decay and circular dichroism (CD) as well as molecular docking and cyclic voltammetric methods. The fluorescence and lifetime decay results indicated that MS quenched the intrinsic intensity of HSA through a static quenching mechanism. The Stern-Volmer quenching constants and binding constants for the MS-HSA system at 293, 298 and 303 K were obtained from the Stern-Volmer plot. Thermodynamic parameters for the interaction of MS with HSA were evaluated; negative values of entropy change (ΔG°) indicated the spontaneity of the MS and HSA interaction. Thermodynamic parameters such as negative ΔH° and positive ΔS° values revealed that hydrogen bonding and hydrophobic forces played a major role in MS-HSA interaction and stabilized the complex. The binding site for MS in HSA was identified by competitive site probe experiments and molecular docking studies. These results indicated that MS was bound to HSA at Sudlow's site I. The efficiency of energy transfer and the distance between the donor (HSA) and acceptor (MS) was calculated based on the theory of Fosters' resonance energy transfer (FRET). Three-dimensional fluorescence spectra and CD results revealed that the binding of MS to HSA resulted in an obvious change in the conformation of HSA. Cyclic voltammograms of the MS-HSA system also confirmed the interaction between MS and HSA. Furthermore, the effects of metal ions on the binding of MS to HSA were also studied. Copyright © 2017 John Wiley & Sons, Ltd.

Synthesis and characterization of new fluorescent styrene-containing carborane derivatives: the singular quenching role of a phenyl substituent.

PubMed

Ferrer-Ugalde, Albert; Juárez-Pérez, Emilio José; Teixidor, Francesc; Viñas, Clara; Sillanpää, Reijo; Pérez-Inestrosa, Ezequiel; Núñez, Rosario

2012-01-09

A set of neutral and anionic carborane derivatives in which the styrenyl fragment is introduced as a fluorophore group has been successfully synthesized and characterized. The reaction of the monolithium salts of 1-Ph-1,2-C(2)B(10)H(11), 1-Me-1,2-C(2)B(10)H(11) and 1,2-C(2)B(10)H(12) with one equivalent of 4-vinylbenzyl chloride leads to the formation of compounds 1-3, whereas the reaction of the dilithium salt of 1,2-C(2)B(10)H(12) with two equivalents of 4-vinylbenzyl chloride gives disubstituted compound 4. The closo clusters were degraded using the classical method, KOH in EtOH, to afford the corresponding nido species, which were isolated as tetramethylammonium salts. The crystal structure of the four closo compounds 1-4 were analyzed by X-ray diffraction. All compounds, except 1, display emission properties, with quantum yields dependent on the nature of the cluster (closo or nido) and the substituent on the second C(cluster) atom. In general, closo compounds 2-4 exhibit high fluorescence emission, whereas the presence of a nido cluster produces a decrease of the emission intensity. The presence of a phenyl group bonded to the C(cluster) results in an excellent electron-acceptor unit that produces a quenching of the fluorescence. DFT calculations have confirmed the charge-separation state in 1 to explain the quenching of the fluorescence and the key role of the carboranyl fragment in this luminescent process. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interaction of glutathione with bovine serum albumin: Spectroscopy and molecular docking.

PubMed

Jahanban-Esfahlan, Ali; Panahi-Azar, Vahid

2016-07-01

This study aims to investigate the interaction between glutathione and bovine serum albumin (BSA) using ultraviolet-visible (UV-vis) absorption, fluorescence spectroscopies under simulated physiological conditions (pH 7.4) and molecular docking methods. The results of fluorescence spectroscopy indicated that the fluorescence intensity of BSA was decreased considerably upon the addition of glutathione through a static quenching mechanism. The fluorescence quenching obtained was related to the formation of BSA-glutathione complex. The values of KSV, Ka and Kb for the glutathione and BSA interaction were in the order of 10(5). The thermodynamic parameters including enthalpy change (ΔH), entropy change (ΔS) and also Gibb's free energy (ΔG) were determined using Van't Hoff equation. These values showed that hydrogen bonding and van der Waals forces were the main interactions in the binding of glutathione to BSA and the stabilization of the complex. Also, the interaction of glutathione and BSA was spontaneous. The effects of glutathione on the BSA conformation were determined using UV-vis spectroscopy. Moreover, glutathione was docked in BSA using ArgusLab as a molecular docking program. It was recognized that glutathione binds within the sub-domain IIA pocket in domain II of BSA. Copyright © 2016 Elsevier Ltd. All rights reserved.

Spectroscopic profiling and computational study of the binding of tschimgine: A natural monoterpene derivative, with calf thymus DNA

NASA Astrophysics Data System (ADS)

Khajeh, Masoumeh Ashrafi; Dehghan, Gholamreza; Dastmalchi, Siavoush; Shaghaghi, Masoomeh; Iranshahi, Mehrdad

2018-03-01

DNA is a major target for a number of anticancer substances. Interaction studies between small molecules and DNA are essential for rational drug designing to influence main biological processes and also introducing new probes for the assay of DNA. Tschimgine (TMG) is a monoterpene derivative with anticancer properties. In the present study we tried to elucidate the interaction of TMG with calf thymus DNA (CT-DNA) using different spectroscopic methods. UV-visible absorption spectrophotometry, fluorescence and circular dichroism (CD) spectroscopies as well as molecular docking study revealed formation of complex between TMG and CT-DNA. Binding constant (Kb) between TMG and DNA was 2.27 × 104 M- 1, that is comparable to groove binding agents. The fluorescence spectroscopic data revealed that the quenching mechanism of fluorescence of TMG by CT-DNA is static quenching. Thermodynamic parameters (ΔH < 0 and ΔS < 0) at different temperatures indicated that van der Waals forces and hydrogen bonds were involved in the binding process of TMG with CT-DNA. Competitive binding assay with methylene blue (MB) and Hoechst 33258 using fluorescence spectroscopy displayed that TMG possibly binds to the minor groove of CT-DNA. These observations were further confirmed by CD spectral analysis, viscosity measurements and molecular docking.

Spectroscopic investigations on the interaction of thioacetamide with ZnO quantum dots and application for its fluorescence sensing

NASA Astrophysics Data System (ADS)

Saha, Dipika; Negi, Devendra P. S.

2018-01-01

The purpose of the present work was to develop a method for the sensing of thioacetamide by using spectroscopic techniques. Thioacetamide is a carcinogen and it is important to detect its presence in food-stuffs. Semiconductor quantum dots are frequently employed as sensing probes since their absorption and fluorescence properties are highly sensitive to the interaction with substrates present in the solution. In the present work, the interaction between thioacetamide and ZnO quantum dots has been investigated by using UV-visible, fluorescence and infrared spectroscopy. Besides, dynamic light scattering (DLS) has also been utilized for the interaction studies. UV-visible absorption studies indicated the bonding of the lone pair of sulphur atom of thioacetamide with the surface of the semiconductor. The fluorescence band of the ZnO quantum dots was found to be quenched in the presence of micromolar concentrations of thioacetamide. The quenching was found to follow the Stern-Volmer relationship. The Stern-Volmer constant was evaluated to be 1.20 × 105 M- 1. Infrared spectroscopic measurements indicated the participation of the sbnd NH2 group and the sulphur atom of thioacetamide in bonding with the surface of the ZnO quantum dots. DLS measurements indicated that the surface charge of the semiconductor was shielded by the thioacetamide molecules.

Synthesis, characterization, DNA/protein interaction and cytotoxicity studies of Cu(II) and Co(II) complexes derived from dipyridyl triazole ligands

NASA Astrophysics Data System (ADS)

Zhang, Wei; Yao, Di; Wei, Yi; Tang, Jie; Bian, He-Dong; Huang, Fu-Ping; Liang, Hong

2016-06-01

Four different transition metal complexes containing dipyridyl triazole ligands, namely [Cu(abpt)2Cl2]·2H2O (1), [Cu(abpt)2(ClO4)2] (2), [Co2(abpt)2(H2O)2Cl2]·Cl2·4H2O (3) and [Co2(Hbpt)2(CH3OH)2(NO3)2] (4) have been designed, synthesized and further structurally characterized by X-ray crystallography, ESI-MS, elemental analysis, IR and Raman spectroscopy. In these complexes, the both ligands act as bidentate ligands with N, N donors. DNA binding interactions with calf thymus DNA (ct-DNA) of the ligand and its complexes 1 ~ 4 were investigated via electronic absorption, fluorescence quenching, circular dichroism and viscosity measurements as well as confocal Laser Raman spectroscopy. The results show these complexes are able to bind to DNA via the non-covalent mode i.e. intercalation and groove binding or electrostatic interactions. The interactions with bovine serum albumin (BSA) were also studied using UV-Vis and fluorescence spectroscopic methods which indicated that fluorescence quenching of BSA by these compounds was the presence of both static and dynamic quenching. Moreover, the in vitro cytotoxic effects of the complexes against four cell lines SK-OV-3, HL-7702, BEL7404 and NCI-H460 showed the necessity of the coordination action on the biological properties on the respective complex and that all four complexes exhibited substantial cytotoxic activity.

Detection of ultra-low oxygen concentration based on the fluorescence blinking dynamics of single molecules

NASA Astrophysics Data System (ADS)

Wu, Ruixiang; Chen, Ruiyun; Zhou, Haitao; Qin, Yaqiang; Zhang, Guofeng; Qin, Chengbing; Gao, Yan; Gao, Yajun; Xiao, Liantuan; Jia, Suotang

2018-01-01

We present a sensitive method for detection of ultra-low oxygen concentrations based on the fluorescence blinking dynamics of single molecules. The relationship between the oxygen concentration and the fraction of time spent in the off-state, stemming from the population and depopulation of triplet states and radical cationic states, can be fitted with a two-site quenching model in the Stern-Volmer plot. The oxygen sensitivity is up to 43.42 kPa-1 in the oxygen partial pressure region as low as 0.01-0.25 kPa, which is seven times higher than that of the fluorescence intensity indicator. This method avoids the limitation of the sharp and non-ignorable fluctuations that occur during the measurement of fluorescence intensity, providing potential applications in the field of low oxygen-concentration monitoring in life science and industry.

Synthesis of positively charged CdTe quantum dots and detection for uric acid

NASA Astrophysics Data System (ADS)

Zhang, Tiliang; Sun, Xiangying; Liu, Bin

2011-09-01

The CdTe dots (QDs) coated with 2-Mercaptoethylamine was prepared in aqueous solution and characterized with fluorescence spectroscopy, UV-Vis absorption spectra, high-resolution transmission electron microscopy and infrared spectroscopy. When the λex = 350 nm, the fluorescence peak of positively charged CdTe quantum dots is at 592 nm. The uric acid is able to quench their fluorescence. Under optimum conditions, the change of fluorescence intensity is linearly proportional to the concentration of uric acid in the range 0.4000-3.600 μmol L -1, and the limit of detection calculated according to IUPAC definitions is 0.1030 μmol L -1. Compared with routine method, the present method determines uric acid in human serum with satisfactory results. The mechanism of this strategy is due to the interaction of the tautomeric keto/hydroxyl group of uric acid and the amino group coated at the CdTe QDs.

Characterization of flavonoid-protein interactions using fluorescence spectroscopy: Binding of pelargonidin to dairy proteins.

PubMed

Arroyo-Maya, Izlia J; Campos-Terán, José; Hernández-Arana, Andrés; McClements, David Julian

2016-12-15

In this study, the interaction between the flavonoid pelargonidin and dairy proteins: β-lactoglobulin (β-LG), whey protein (WPI), and caseinate (CAS) was investigated. Fluorescence experiments demonstrated that pelargonidin quenched milk proteins fluorescence strongly. However, the protein secondary structure was not significantly affected by pelargonidin, as judged from far-UV circular dichroism. Analysis of fluorescence data indicated that pelargonidin-induced quenching does not arise from a dynamical mechanism, but instead is due to protein-ligand binding. Therefore, quenching data were analyzed using the model of independent binding sites. Both β-LG and CAS, but not WPI, showed hyperbolic binding isotherms indicating that these proteins firmly bound pelargonidin at both pH 7.0 and 3.0 (binding constants ca. 1.0×10(5) at 25.0°C). To investigate the underlying thermodynamics, binding constants were determined at 25.0, 35.0, and 45.0°C. These results pointed to binding processes that depend on the structural conformation of the milk proteins. Copyright © 2016 Elsevier Ltd. All rights reserved.

A fluorescent paramagnetic Mn metal–organic framework based on semi-rigid pyrene tetra­carboxylic acid: sensing of solvent polarity and explosive nitroaromatics

PubMed Central

Bajpai, Alankriti; Mukhopadhyay, Arindam; Krishna, Manchugondanahalli Shivakumar; Govardhan, Savitha; Moorthy, Jarugu Narasimha

2015-01-01

An Mn metal–organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4 L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-L MOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt’s solvent polarity parameter (E T N). Further, the applicability of Mn-L to the sensing of nitroaromatics via fluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF. PMID:26306197

A novel single fluorophore-labeled double-stranded oligonucleotide probe for fluorescence-enhanced nucleic acid detection based on the inherent quenching ability of deoxyguanosine bases and competitive strand-displacement reaction.

PubMed

Zhang, Yingwei; Tian, Jingqi; Li, Hailong; Wang, Lei; Sun, Xuping

2012-01-01

We develop a novel single fluorophore-labeled double-stranded oligonucleotide (OND) probe for rapid, nanostructure-free, fluorescence-enhanced nucleic acid detection for the first time. We further demonstrate such probe is able to well discriminate single-base mutation in nucleic acid. The design takes advantage of an inherent quenching ability of guanine bases. The short strand of the probe is designed with an end-labeled fluorophore that is placed adjacent to two guanines as the quencher located on the long opposite strand, resulting in great quenching of dye fluorescence. In the presence of a target complementary to the long strand of the probe, a competitive strand-displacement reaction occurs and the long strand forms a more stable duplex with the target, resulting in the two strands of the probe being separated from each other. As a consequence of this displacement, the fluorophore and the quencher are no longer in close proximity and dye fluorescence increases, signaling the presence of target.

A fluorescent paramagnetic Mn metal-organic framework based on semi-rigid pyrene tetra-carboxylic acid: sensing of solvent polarity and explosive nitroaromatics.

PubMed

Bajpai, Alankriti; Mukhopadhyay, Arindam; Krishna, Manchugondanahalli Shivakumar; Govardhan, Savitha; Moorthy, Jarugu Narasimha

2015-09-01

An Mn metal-organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4 L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-L MOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt's solvent polarity parameter (E T (N)). Further, the applicability of Mn-L to the sensing of nitroaromatics via fluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF.

A spectroscopic study on the interaction between gold nanoparticles and hemoglobin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garabagiu, Sorina, E-mail: sgarabagiu@itim-cj.ro

2011-12-15

Highlights: Black-Right-Pointing-Pointer The interaction was studied using UV-vis and fluorescence spectroscopy. Black-Right-Pointing-Pointer Gold nanoparticles quench the fluorescence emission of hemoglobin solution. Black-Right-Pointing-Pointer The binding and thermodynamic constants were calculated. Black-Right-Pointing-Pointer Major impact: electrochemical applications of the complex onto a substrate. -- Abstract: The interaction between horse hemoglobin and gold nanoparticles was studied using optical spectroscopy. UV-vis and fluorescence spectra show that a spontaneous binding process occurred between hemoglobin and gold nanoparticles. The Soret band of hemoglobin in the presence of gold nanoparticles does not show significant changes, which proves that the protein retained its biological function. A shift to longermore » wavelengths appears in the plasmonic band of gold nanoparticles upon the attachment of hemoglobin molecules. Gold nanoparticles quench the fluorescence emission of tryptophan residues in the structure of hemoglobin. The Stern-Volmer quenching constant, the binding constant and the number of binding sites were also calculated. Thermodynamic parameters indicate that the binding was mainly due to hydrophobic interactions.« less

Experimental and theoretical investigation of the temperature dependent electronic quenching of O(1D) atoms in collisions with Kr

NASA Astrophysics Data System (ADS)

Nuñez-Reyes, Dianailys; Kłos, Jacek; Alexander, Millard H.; Dagdigian, Paul J.; Hickson, Kevin M.

2018-03-01

The kinetics and dynamics of the collisional electronic quenching of O(1D) atoms by Kr have been investigated in a joint experimental and theoretical study. The kinetics of quenching were measured over the temperature range 50-296 K using the Laval nozzle method. O(1D) atoms were prepared by 266 nm photolysis of ozone, and the decay of the O(1D) concentration was monitored through vacuum ultraviolet fluorescence at 115.215 nm, from which the rate constant was determined. To interpret the experiments, a quantum close-coupling treatment of the quenching transition from the 1D state to the 3Pj fine-structure levels in collisions with Kr, and also Ar and Xe, was carried out. The relevant potential energy curves and spin-orbit coupling matrix elements were obtained in electronic structure calculations. We find reasonable agreement between computed temperature-dependent O(1D)-Rg (Rg = Ar, Kr, Xe) quenching rate constants and the present measurements for Kr and earlier measurements. In particular, the temperature dependence is well described.

Spectrofluorimetric determination of thioridazine and flupentixol in dosage forms; application to content uniformity test.

PubMed

Attia, Tamer Z; Omar, Mahmoud A

2016-08-01

A reliable, sensitive, cheap and non-extractive spectrofluorimetric method has been developed and validated for determination of thioridazine and flupentixol based on ternary complex formation with eosin and lead(II) in the presence of methylcellulose as surfactant at pH 3.2. Under the optimum conditions, the quantitative quenching effect of investigated drugs on the native fluorescence of eosin has been investigated. The quenching of the eosin fluorescence was measured at 517 nm after excitation at 462 nm. The different experimental parameters affecting the development and stability of the reaction products were carefully studied and optimized, and the results were satisfactory. The calibration plots were constructed over the range of 0.5-3.0 µg mL(-1) . The developed method was successfully applied for determination of investigated drugs in commercial tablets without interference from common excipients. It was further applied for content uniformity testing of flupentixol in its tablets. Statistical comparisons of the results with those of the reference methods revealed excellent agreement and indicated no significant difference in accuracy and precision. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Characterization of the organic ligand shell of semiconductor quantum dots by fluorescence quenching experiments.

PubMed

Boldt, Klaus; Jander, Sebastian; Hoppe, Kathrin; Weller, Horst

2011-10-25

We present the characterization of the organic ligand shell of CdSe/Cd(x)Zn(1-x)S/ZnS nanoparticles by means of fluorescence quenching experiments. Both electron scavengers and acceptors for resonance energy transfer were employed as probes. Different quenching behavior for short and long chain thiol ligands in water was found. It could be shown that poly(ethylene oxide) (PEO)-capping of the particles comprises a densely packed inner shell and a loosely packed outer shell in which ions and small molecules diffuse unhindered. A quantitative uptake of quencher molecules into the PEO shell was observed, through which the particle volume including the ligand sphere could be determined.

New fluorescence techniques for high-throughput drug discovery.

PubMed

Jäger, S; Brand, L; Eggeling, C

2003-12-01

The rapid increase of compound libraries as well as new targets emerging from the Human Genome Project require constant progress in pharmaceutical research. An important tool is High-Throughput Screening (HTS), which has evolved as an indispensable instrument in the pre-clinical target-to-IND (Investigational New Drug) discovery process. HTS requires machinery, which is able to test more than 100,000 potential drug candidates per day with respect to a specific biological activity. This calls for certain experimental demands especially with respect to sensitivity, speed, and statistical accuracy, which are fulfilled by using fluorescence technology instrumentation. In particular the recently developed family of fluorescence techniques, FIDA (Fluorescence Intensity Distribution Analysis), which is based on confocal single-molecule detection, has opened up a new field of HTS applications. This report describes the application of these new techniques as well as of common fluorescence techniques--such as confocal fluorescence lifetime and anisotropy--to HTS. It gives experimental examples and presents advantages and disadvantages of each method. In addition the most common artifacts (auto-fluorescence or quenching by the drug candidates) emerging from the fluorescence detection techniques are highlighted and correction methods for confocal fluorescence read-outs are presented, which are able to circumvent this deficiency.

Fluorescence observations of LDEF exposed materials as an indicator of induced material reactions

NASA Technical Reports Server (NTRS)

Linton, Roger C.; Whitaker, Ann F.; Kamenetzky, Rachel R.

1993-01-01

Observations and measurements of induced changes in the fluorescent emission of materials exposed to the space environment on the Long Duration Exposure Facility (LDEF) have revealed systematic patterns of material-dependent behavior. These results have been supplemented by inspection of similar materials exposed on previous Space Shuttle Missions and in laboratory testing. The space environmental factors affecting the fluorescence of exposed materials have been found to include (but are not necessarily limited to) solar ultraviolet (UV) radiation, atomic oxygen (AO), thermal vacuum exposure, and synergistic combinations of these factors. Observed changes in material fluorescent behavior include stimulation, quenching, and spectral band shifts of emission. For example, the intrinsic yellow fluorescence of zinc oxide pigmented thermal control coatings undergoes quenching as a result of exposure, while coloration is stimulated in the fluorescent emission of several polyurethane coating materials. The changes in fluorescent behavior of these materials are shown to be a revealing indicator of induced material reactions as a result of space environmental exposure.

A trident dithienylethene-perylenemonoimide dyad with super fluorescence switching speed and ratio

NASA Astrophysics Data System (ADS)

Li, Chong; Yan, Hui; Zhao, Ling-Xi; Zhang, Guo-Feng; Hu, Zhe; Huang, Zhen-Li; Zhu, Ming-Qiang

2014-12-01

Photoswitchable fluorescent diarylethenes are promising in molecular optical memory and photonic devices. However, the performance of current diarylethenes is far from satisfactory because of the scarcity of high-speed switching capability and large fluorescence on-off ratio. Here we report a trident perylenemonoimide dyad modified by triple dithienylethenes whose photochromic fluorescence quenching ratio at the photostationary state exceeds 10,000 and the fluorescence quenching efficiency is close to 100% within seconds of ultraviolet irradiation. The highly sensitive fluorescence on/off switching of the trident dyad enables recyclable fluorescence patterning and all-optical transistors. The prototype optical device based on the trident dyad enables the optical switching of incident light and conversion from incident light wavelength to transmitted light wavelength, which is all-optically controlled, reversible and wavelength-convertible. In addition, the trident dyad-staining block copolymer vesicles are observed via optical nanoimaging with a sub-100 nm resolution, portending a potential prospect of the dithienylethene dyad in super-resolution imaging.

A trident dithienylethene-perylenemonoimide dyad with super fluorescence switching speed and ratio.

PubMed

Li, Chong; Yan, Hui; Zhao, Ling-Xi; Zhang, Guo-Feng; Hu, Zhe; Huang, Zhen-Li; Zhu, Ming-Qiang

2014-12-12

Photoswitchable fluorescent diarylethenes are promising in molecular optical memory and photonic devices. However, the performance of current diarylethenes is far from satisfactory because of the scarcity of high-speed switching capability and large fluorescence on-off ratio. Here we report a trident perylenemonoimide dyad modified by triple dithienylethenes whose photochromic fluorescence quenching ratio at the photostationary state exceeds 10,000 and the fluorescence quenching efficiency is close to 100% within seconds of ultraviolet irradiation. The highly sensitive fluorescence on/off switching of the trident dyad enables recyclable fluorescence patterning and all-optical transistors. The prototype optical device based on the trident dyad enables the optical switching of incident light and conversion from incident light wavelength to transmitted light wavelength, which is all-optically controlled, reversible and wavelength-convertible. In addition, the trident dyad-staining block copolymer vesicles are observed via optical nanoimaging with a sub-100 nm resolution, portending a potential prospect of the dithienylethene dyad in super-resolution imaging.

The design and application of fluorophore–gold nanoparticle activatable probes

PubMed Central

Swierczewska, Magdalena; Lee, Seulki; Chen, Xiaoyuan

2013-01-01

Fluorescence-based assays and detection techniques are among the most highly sensitive and popular biological tests for researchers. To match the needs of research and the clinic, detection limits and specificities need to improve, however. One mechanism is to decrease non-specific background signals, which is most efficiently done by increasing fluorescence quenching abilities. Reports in the literature of theoretical and experimental work have shown that metallic gold surfaces and nanoparticles are ultra-efficient fluorescence quenchers. Based on these findings, subsequent reports have described gold nanoparticle fluorescence-based activatable probes that were designed to increase fluorescence intensity based on a range of stimuli. In this way, these probes can detect and signify assorted biomarkers and changes in environmental conditions. In this review, we explore the various factors and theoretical models that affect gold nanoparticle fluorescence quenching, explore current uses of activatable probes, and propose an engineering approach for future development of fluorescence based gold nanoparticle activatable probes. PMID:21380462

A new s-adenosylhomocysteine hydrolase-linked method for adenosine detection based on DNA-templated fluorescent Cu/Ag nanoclusters.

PubMed

Ahn, Jun Ki; Kim, Hyo Yong; Baek, Songyi; Park, Hyun Gyu

2017-07-15

We herein describe a novel fluorescent method for the rapid and selective detection of adenosine by utilizing DNA-templated Cu/Ag nanoclusters (NCs) and employing s-adenosylhomocysteine hydrolase (SAHH). SAHH is allowed to promote hydrolysis reaction of s-adenosylhomocysteine (SAH) and consequently produces homocysteine, which would quench the fluorescence signal from DNA-templated Cu/Ag nanoclusters employed as a signaling probe in this study. On the other hand, adenosine significantly inhibits the hydrolysis reaction and prevent the formation of homocysteine. Consequently, highly enhanced fluorescence signal from DNA-Cu/Ag NCs is retained, which could be used to identify the presence of adenosine. By employing this design principle, adenosine was sensitively detected down to 19nM with high specificity over other adenosine analogs such as AMP, ADP, ATP, cAMP, guanosine, cytidine, and urine. Finally, the diagnostic capability of this method was successfully verified by reliably detecting adenosine present in a real human serum sample. Copyright © 2016 Elsevier B.V. All rights reserved.

A novel fluorescent biosensor for adrenaline detection and tyrosinase inhibitor screening.

PubMed

Liu, Ziping; Liu, Shasha

2018-04-17

In this work, a novel simple fluorescent biosensor for the highly sensitive and selective detection of adrenaline was established. Firstly, water-soluble CuInS 2 quantum dots (QDs) capped by L-Cys were synthesized via a hydrothermal synthesis method. Then, the positively charged adrenaline was assembled on the surface of CuInS 2 QDs due to the electrostatic interactions and hydrogen bonding, which led to the formation of adrenaline-CuInS 2 QD (Adr-CuInS 2 QD) electrostatic complexes. Tyrosinase (TYR) can catalyze adrenaline to generate H 2 O 2 , and additionally oxidize the adrenaline to adrenaline quinone. Both the H 2 O 2 and the adrenaline quinone can quench the fluorescence of the CuInS 2 QDs through the electron transfer (ET) process. Thus, the determination of adrenaline could be facilely achieved by taking advantage of the fluorescence "turn off" feature of CuInS 2 QDs. Under the optimum conditions, the fluorescence quenching ratio I f /I f0 (I f and I f0 were the fluorescence intensity of Adr-CuInS 2 QDs in the presence and absence of TYR, respectively) was proportional to the logarithm of adrenaline concentration in the range of 1 × 10 -8 -1 × 10 -4  mol L -1 with the detection limit of 3.6 nmol L -1 . The feasibility of the proposed biosensor in real sample assay was also studied and satisfactory results were obtained. Significantly, the proposed fluorescent biosensor can also be utilized to screen TYR inhibitors. Graphical abstract Schematic illustration of the fluorescent biosensor for adrenaline detection (A) and tyrosinase inhibitor screening (B).

Dummy molecularly imprinted polymers-capped CdTe quantum dots for the fluorescent sensing of 2,4,6-trinitrotoluene.

PubMed

Xu, Shoufang; Lu, Hongzhi; Li, Jinhua; Song, Xingliang; Wang, Aixiang; Chen, Lingxin; Han, Shaobo

2013-08-28

Molecularly imprinted polymers (MIPs) with trinitrophenol (TNP) as a dummy template molecule capped with CdTe quantum dots (QDs) were prepared using 3-aminopropyltriethoxy silane (APTES) as the functional monomer and tetraethoxysilane (TEOS) as the cross linker through a seed-growth method via a sol-gel process (i.e., DMIP@QDs) for the sensing of 2,4,6-trinitrotoluene (TNT) on the basis of electron-transfer-induced fluorescence quenching. With the presence and increase of TNT in sample solutions, a Meisenheimer complex was formed between TNT and the primary amino groups on the surface of the QDs. The energy of the QDs was transferred to the complex, resulting in the quenching of the QDs and thus decreasing the fluorescence intensity, which allowed the TNT to be sensed optically. DMIP@QDs generated a significantly reduced fluorescent intensity within less than 10 min upon binding TNT. The fluorescence-quenching fractions of the sensor presented a satisfactory linearity with TNT concentrations in the range of 0.8-30 μM, and its limit of detection could reach 0.28 μM. The sensor exhibited distinguished selectivity and a high binding affinity to TNT over its possibly competing molecules of 2,4-dinitrophenol (DNP), 4-nitrophenol (4-NP), phenol, and dinitrotoluene (DNT) because there are more nitro groups in TNT and therefore a stronger electron-withdrawing ability and because it has a high similarity in shape and volume to TNP. The sensor was successfully applied to determine the amount of TNT in soil samples, and the average recoveries of TNT at three spiking levels ranged from 90.3 to 97.8% with relative standard deviations below 5.12%. The results provided an effective way to develop sensors for the rapid recognition and determination of hazardous materials from complex matrices.

Fluorescence quenching near small metal nanoparticles.

PubMed

Pustovit, V N; Shahbazyan, T V

2012-05-28

We develop a microscopic model for fluorescence of a molecule (or semiconductor quantum dot) near a small metal nanoparticle. When a molecule is situated close to metal surface, its fluorescence is quenched due to energy transfer to the metal. We perform quantum-mechanical calculations of energy transfer rates for nanometer-sized Au nanoparticles and find that nonlocal and quantum-size effects significantly enhance dissipation in metal as compared to those predicted by semiclassical electromagnetic models. However, the dependence of transfer rates on molecule's distance to metal nanoparticle surface, d, is significantly weaker than the d(-4) behavior for flat metal surface with a sharp boundary predicted by previous calculations within random phase approximation.

Super-quenched Molecular Probe Based on Aggregation-Induced Emission and Photoinduced Electron Transfer Mechanisms for Formaldehyde Detection in Human Serum.

PubMed

Yang, Haitao; Wang, Fujia; Zheng, Jilin; Lin, Hao; Liu, Bin; Tang, Yi-Da; Zhang, Chong-Jing

2018-06-04

Energy transfer between fluorescent dyes and quenchers is widely used in the design of light-up probes. Although dual quenchers are more effective in offering lower background signals and higher turn-on ratios than one quencher, such probes are less explored in practice as they require both quenchers to be within the proximity of the fluorescent core. In this contribution, we utilized intramolecular motion and photoinduced electron transfer (PET) as quenching mechanisms to build super-quenched light-up probes based on fluorogens with aggregation-induced emission. The optimized light-up probe possesses negligible background and is able to detect not only free formaldehyde (FA) but also polymeric FA, with an unprecedented turn-on ratio of >4900. We envision that this novel dual quenching strategy will help to develop various light-up probes for analyte sensing. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

CdTe/ZnS quantum dots as fluorescent probes for ammonium determination.

PubMed

Yi, Kui-Yu

2016-06-01

Novel CdTe/ZnS quantum dot (QD) probes based on the quenching effect were proposed for the simple, rapid, and specific determination of ammonium in aqueous solutions. The QDs were modified using 3-mercaptopropionic acid, and the fluorescence responses of the CdTe/ZnS QD probes to ammonium were detected through regularity quenching. The quenching levels of the CdTe/ZnS QDs and ammonium concentration showed a good linear relationship between 4.0 × 10(-6) and 5.0 × 10(-4) mol/L; the detection limit was 3.0 × 10(-7) mol/L. Ammonium contents in synthetic explosion soil samples were measured to determine the practical applications of the QD probes and a probable quenching mechanism was described. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

[Studies on the action features between cefuroxime axetil and bovine serum albumin].

PubMed

Wu, Gang-ke; Yan, Cheng-nong; Liu, Yi

2008-09-01

Under different temperatures and physiological conditions, with cefuroxime axetil concentrations in the range of 1.959 X 10(-6) to 13.71 X 10(-6) mol x L(-1), and bovine serum albumin (BSA) concentrations at 2.0 X 10(-6) mol x L(-1), the interaction between cefuroxime axetil and BSA was studied by fluorescence spectroscopy, three-dimensional fluorescence spectrum, synchronous fluorescence spectrum and UV-Vis absorption spectroscopy. After analyzing and processing the fluorescence quenching data at different temperatures according to Sterm-Volmer equation, Lineweaver-Burk equation and thermodynamic equation, the average value of the apparent binding constant (K(LB): 3.907 X 10(6) L x mol(-1)), and thermodynamics parameters (enthalpy change delta H: -13.43 kJ x mol(-1), entropy change delta S: 81.90 J x K(-1) and standard Gibbs free energy change delta G0: -38.34 kJ x mol(-1)) were calculated, and the amounts of binding sites (n: 1.042)were measured. The fluorescence quenching mechanism of BSA after cefuroxime axetil was added was discussed. BSA was bound with cefuroxime axetil and formed a new compound. The quenching belonged to static fluorescence quenching. The thermodynamic parameters agree with delta H approximately 0, delta S > 0 and delta G0 < 0, and the binding reaction is mainly entropy-driven and electro-static interaction force plays a major role in the reaction. The maximum emission wavelength of Tyr and Trp had an obvious red shift in the synchronous fluorescence spectra, the fluorescence emission wavelength of two peaks had a blue shift in the three-dimensional fluorescence spectrum of BSA in the presence of cefuroxime axetil and the maximum absorbtion wavelenghs of three systems in the UV-Vis absorption spectra were obviously different. These showed that the changes in the micro-environment of Tyr and Trp and demonstrated that the conformation of BSA changed as cefuroxime axetil had been added. This provides important information for discussing the configuration modification of BSA because of the added cefuroxime axetil, and for elucidating the pharmacological effects of cefuroxime axetil and biological effects in the organism.

Evidence of bovine serum albumin-viologen herbicide binding interaction and associated structural modifications

NASA Astrophysics Data System (ADS)

Roy, Swarup; Saxena, Shailendra K.; Mishra, Suryakant; Yogi, Priyanka; Sagdeo, P. R.; Kumar, Rajesh

2017-07-01

The binding ability of viologen herbicide with bovine serum albumin (BSA) has been investigated to understand viologen associated hazards by investigating ethyl viologen's (EV) binding using various spectroscopies and in-silico molecular docking approaches. Apparent association constant (1.3 × 104 L/mol), calculated using UV-Vis spectra indicating a moderate complex formation between BSA and EV. A static mode of fluorescence quenching has been observed as evident from inverse temperature dependence of Stern-Volmer quenching constant which also confirms an EV-BSA complex formation. Emission and time resolved fluorescence studies reveal that the emission quenching of BSA with EV is initiated by static quenching mechanism. A moderately strong binding affinity between EV and BSA has been observed (binding constant value of 7.58 × 104 L/Mol) using fluorescence quenching titration, obtained at 298 K. Quantitative measurements of thermodynamic parameters like enthalpy and entropy changes clearly indicates hydrophobic force responsible for EV-BSA complex formation. The binding distance between EV and BSA was found to be 4.48 nm are involved in non-radiative energy transfer process. Furthermore, from the circular dichroism spectra it was observed that addition of EV is also found to change the secondary structure of BSA which leads to decrease in α-helix. Above mentioned results are found to be in consonance with molecular docking simulations and supports the EV-BSA binding.

A generalized model on the effects of nanoparticles on fluorophore fluorescence in solution

USDA-ARS?s Scientific Manuscript database

Nanoparticles (NP) can modify fluorophore fluorescence in solution through multiple pathways that include fluorescence inner filter effect (IFE), dynamic and static quenching, surface enhancement, and fluorophore quantum yield variation associated with structural and conformational modifications ind...

Method Of Signal Amplification In Multi-Chromophore Luminescence Sensors

DOEpatents

Levitsky, Igor A.; Krivoshlykov, Sergei G.

2004-02-03

A fluorescence-based method for highly sensitive and selective detection of analyte molecules is proposed. The method employs the energy transfer between two or more fluorescent chromophores in a carefully selected polymer matrix. In one preferred embodiment, signal amplification has been achieved in the fluorescent sensing of dimethyl methylphosphonate (DMMP) using two dyes, 3-aminofluoranthene (AM) and Nile Red (NR), in a hydrogen bond acidic polymer matrix. The selected polymer matrix quenches the fluorescence of both dyes and shifts dye emission and absorption spectra relative to more inert matrices. Upon DMMP sorption, the AM fluorescence shifts to the red at the same time the NR absorption shifts to the blue, resulting in better band overlap and increased energy transfer between chromophores. In another preferred embodiment, the sensitive material is incorporated into an optical fiber system enabling efficient excitation of the dye and collecting the fluorescent signal form the sensitive material on the remote end of the system. The proposed method can be applied to multichromophore luminescence sensor systems incorporating N-chromophores leading to N-fold signal amplification and improved selectivity. The method can be used in all applications where highly sensitive detection of basic gases, such as dimethyl methylphosphonate (DMMP), Sarin, Soman and other chemical warfare agents having basic properties, is required, including environmental monitoring, chemical industry and medicine.

Excitation of sensitized fluorescence of europium and curium in an aqueous solution of thenoyltrifluoroacetone by a nitrogen laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dem'yanova, T.A.; Stepanov, A.V.; Babaev, A.S.

1987-03-01

The fluorescence spectrum of trivalent europium in aqueous solutions of thenoyltrifluoroacetone, excited by a nitrogen laser with emission wavelength 337 nm, exhibits bands at 582, 593, 616, 650, and 695 nm. Two bands appear in the fluorescence spectrum of trivalent curium under the same conditions - at 598 and 607 nm. The times of quenching of the fluorescence of the ions of these elements were measured, both in H/sub 2/O medium and in D/sub 2/O. A linear relationship was found between the fluorescence intensity of europium and curium and their concentration in TTA solution. The limit of determination of europiummore » and curium by the fluorescent method with laser excitation using the bands at 615 and 607 nm proved equal to 0.3 and 0.07 ng/ml, respectively.« less

Spectroscopic and molecular modeling study on the separate and simultaneous bindings of alprazolam and fluoxetine hydrochloride to human serum albumin (HSA): With the aim of the drug interactions probing

NASA Astrophysics Data System (ADS)

Dangkoob, Faeze; Housaindokht, Mohmmad Reza; Asoodeh, Ahmad; Rajabi, Omid; Rouhbakhsh Zaeri, Zeinab; Verdian Doghaei, Asma

2015-02-01

The objective of the present research is to study the interaction of separate and simultaneous of alprazolam (ALP) and fluoxetine hydrochloride (FLX) with human serum albumin (HSA) in phosphate buffer (pH 7.4) using different kinds of spectroscopic, cyclic voltammetry and molecular modeling techniques. The absorbance spectra of protein, drugs and protein-drug showed complex formation between the drugs and HSA. Fluorescence analysis demonstrated that ALP and FLX could quench the fluorescence spectrum of HSA and demonstrated the conformational change of HSA in the presence of both drugs. Also, fluorescence quenching mechanism of HSA-drug complexes both separately and simultaneously was suggested as static quenching. The analysis of UV absorption data and the fluorescence quenching of HSA in the binary and ternary systems showed that FLX decreased the binding affinity between ALP and HSA. On the contrary, ALP increased the binding affinity of FLX and HSA. The results of synchronous fluorescence and three-dimensional fluorescence spectra indicated that the binding of drugs to HSA would modify the microenvironment around the Trp and Tyr residues and the conformation of HSA. The distances between Trp residue and the binding sites of the drugs were estimated according to the Förster theory, and it was demonstrated that non-radiative energy transfer from HSA to the drugs occurred with a high probability. Moreover, according to CV measurements, the decrease of peak current in the cyclic voltammogram of the both drugs in the presence of HSA revealed that they interacted with albumin and binding constants were calculated for binary systems which were in agreement with the binding constants obtained from UV absorption and fluorescence spectroscopy. The prediction of the best binding sites of ALP and FLX in binary and ternary systems in molecular modeling approach was done using of Gibbs free energy.

Spectroscopic and molecular modeling study on the separate and simultaneous bindings of alprazolam and fluoxetine hydrochloride to human serum albumin (HSA): with the aim of the drug interactions probing.

PubMed

Dangkoob, Faeze; Housaindokht, Mohmmad Reza; Asoodeh, Ahmad; Rajabi, Omid; Rouhbakhsh Zaeri, Zeinab; Verdian Doghaei, Asma

2015-02-25

The objective of the present research is to study the interaction of separate and simultaneous of alprazolam (ALP) and fluoxetine hydrochloride (FLX) with human serum albumin (HSA) in phosphate buffer (pH 7.4) using different kinds of spectroscopic, cyclic voltammetry and molecular modeling techniques. The absorbance spectra of protein, drugs and protein-drug showed complex formation between the drugs and HSA. Fluorescence analysis demonstrated that ALP and FLX could quench the fluorescence spectrum of HSA and demonstrated the conformational change of HSA in the presence of both drugs. Also, fluorescence quenching mechanism of HSA-drug complexes both separately and simultaneously was suggested as static quenching. The analysis of UV absorption data and the fluorescence quenching of HSA in the binary and ternary systems showed that FLX decreased the binding affinity between ALP and HSA. On the contrary, ALP increased the binding affinity of FLX and HSA. The results of synchronous fluorescence and three-dimensional fluorescence spectra indicated that the binding of drugs to HSA would modify the microenvironment around the Trp and Tyr residues and the conformation of HSA. The distances between Trp residue and the binding sites of the drugs were estimated according to the Förster theory, and it was demonstrated that non-radiative energy transfer from HSA to the drugs occurred with a high probability. Moreover, according to CV measurements, the decrease of peak current in the cyclic voltammogram of the both drugs in the presence of HSA revealed that they interacted with albumin and binding constants were calculated for binary systems which were in agreement with the binding constants obtained from UV absorption and fluorescence spectroscopy. The prediction of the best binding sites of ALP and FLX in binary and ternary systems in molecular modeling approach was done using of Gibbs free energy. Copyright © 2014 Elsevier B.V. All rights reserved.

Fluorescence of the various red antenna states in photosystem I complexes from cyanobacteria is affected differently by the redox state of P700.

PubMed

Schlodder, Eberhard; Hussels, Martin; Cetin, Marianne; Karapetyan, Navassard V; Brecht, Marc

2011-11-01

Photosystem I of cyanobacteria contains different spectral pools of chlorophylls called red or long-wavelength chlorophylls that absorb at longer wavelengths than the primary electron donor P700. We measured the fluorescence spectra at the ensemble and the single-molecule level at low temperatures in the presence of oxidized and reduced P700. In accordance with the literature, it was observed that the fluorescence is quenched by P700(+). However, the efficiency of the fluorescence quenching by oxidized P700(+) was found to be extremely different for the various red states in PS I from different cyanobacteria. The emission of the longest-wavelength absorbing antenna state in PS I trimers from Thermosynechococcus elongatus (absorption maximum at 5K: ≈ 719nm; emission maximum at 5K: ≈ 740nm) was found to be strongly quenched by P700(+) similar to the reddest state in PS I trimers from Arthrospira platensis emitting at 760nm at 5K. The fluorescence of these red states is diminished by more than a factor of 10 in the presence of oxidized P700. For the first time, the emission of the reddest states in A. platensis and T. elongatus has been monitored using single-molecule fluorescence techniques. 2011 Elsevier B.V. All rights reserved.

Preparation and preliminary characterization of crystallizing fluorescent derivatives of chicken egg white lysozyme

NASA Astrophysics Data System (ADS)

Sumida, John P.; Forsythe, Elizabeth L.; Pusey, Marc L.

2001-11-01

Fluorescence is one of the most versatile and powerful tools for the study of macromolecules. While most proteins are intrinsically fluorescent, working at crystallization concentrations require the use of covalently prepared derivatives added as tracers. This approach requires derivatives that do not markedly affect the crystal packing. We have prepared fluorescent derivatives of chicken egg white lysozyme with probes bound to one of two different sites on the protein molecule. Lucifer yellow and 5-(2-aminoethyl)aminonapthalene-1-sulfonic acid (EDANS) have been attached to the side chain carboxyl of Asp 101 using a carbodiimide coupling procedure. Asp 101 lies within the active site cleft, and it is believed that the probes are "buried" within that cleft. Lucifer yellow and EDANS probes with iodoacetamide reactive groups have been bound to His 15, located on the "back side" of the molecule relative to the active site. All the derivatives fluoresce in the solution and the crystalline states. Fluorescence characterization has focused on determination of binding effects on the probe quantum yield, lifetime, absorption and emission spectra, and quenching by added solutes. Quenching studies show that, as postulated, the Asp 101-bound probes are partially sheltered from the bulk solution by their location within the active site cleft. Probes bound to His 15 have quenching constants about equal to those for the free probes, indicating that this site is highly exposed to the bulk solution.

Fluorescence chemodosimeter for dopamine based on the inner filter effect of the in situ generation of silver nanoparticles and fluorescent dye

NASA Astrophysics Data System (ADS)

Uppa, Yuwapon; Ngamdee, Kessarin; Promarak, Vinich; Ngeontae, Wittaya

2018-07-01

A new strategy for the sensitive and selective detection of dopamine (DA) was proposed. The chemodosimeter design was based on the measurement of the fluorescent quenching of fluorescein dye caused by the in situ generation of silver nanoparticles (AgNPs). The AgNPs can be simply generated by a reaction between DA and Ag+ in the presence of polymethacrylic acid (PMAA). In addition, the generated AgNPs possess the maximum surface plasmon resonance (SPR) at 440 nm and an increase in the SPR intensity with an increasing DA concentration. Basically, fluorescein dye can emit the fluorescent intensity maximum at 513 nm with excitation at 487 nm. Thus, fluorescent quenching was achieved due to an inner filter effect from the overlap between the excitation spectrum of the fluorescein dye and the SPR spectrum of the generated AgNPs. The degree of fluorescent quenching linearly depends on the number of generated AgNPs that can be directly related to the concentration of DA. The proposed chemodosimeter can be used to detect DA in a working linear concentration range of 1.0-5.0 μM at a detection limit of 10.6 nM. This chemodosimeter was successfully applied to determine DA in a real urine sample and a dopamine injection formulation with satisfactory results.

Interaction and energy transfer studies between bovine serum albumin and CdTe quantum dots conjugates: CdTe QDs as energy acceptor probes.

PubMed

Kotresh, M G; Inamdar, L S; Shivkumar, M A; Adarsh, K S; Jagatap, B N; Mulimani, B G; Advirao, G M; Inamdar, S R

2017-06-01

In this paper, a systematic investigation of the interaction of bovine serum albumin (BSA) with water-soluble CdTe quantum dots (QDs) of two different sizes capped with carboxylic thiols is presented based on steady-state and time-resolved fluorescence measurements. Efficient Förster resonance energy transfer (FRET) was observed to occur from BSA donor to CdTe acceptor as noted from reduction in the fluorescence of BSA and enhanced fluorescence from CdTe QDs. FRET parameters such as Förster distance, spectral overlap integral, FRET rate constant and efficiency were determined. The quenching of BSA fluorescence in aqueous solution observed in the presence of CdTe QDs infers that fluorescence resonance energy transfer is primarily responsible for the quenching phenomenon. Bimolecular quenching constant (k q ) determined at different temperatures and the time-resolved fluorescence data provide additional evidence for this. The binding stoichiometry and various thermodynamic parameters are evaluated by using the van 't Hoff equation. The analysis of the results suggests that the interaction between BSA and CdTe QDs is entropy driven and hydrophobic forces play a key role in the interaction. Binding of QDs significantly shortened the fluorescence lifetime of BSA which is one of the hallmarks of FRET. The effect of size of the QDs on the FRET parameters are discussed in the light of FRET parameters obtained. Copyright © 2016 John Wiley & Sons, Ltd.

Fluorescent determination of chloride in nanoliter samples.

PubMed

García, N H; Plato, C F; Garvin, J L

1999-01-01

Measurements of Cl- in nanoliter samples, such as those collected during isolated, perfused tubule experiments, have been difficult, somewhat insensitive, and/or require custom-made equipment. We developed a technique using a fluorescent Cl- indicator, 6-methoxy-N-(3-sulfopropyl) quinolinium (SPQ), to make these measurements simple and reliable. This is a simple procedure that relies on the selectivity of the dye and the fact that Cl-quenches its fluorescence. To measure millimolar quantities of Cl- in nanoliter samples, we prepared a solution of 0.25 mm SPQ and loaded it into the reservoir of a continuous-flow ultramicrofluorometer, which can be constructed from commercially available components. Samples were injected with a calibrated pipette via an injection port, and the resultant peak fluorescent deflections were recorded. The deflections represent a decrease in fluorescence caused by the quenching effect of the Cl- injected. The method yielded a linear response with Cl- concentrations from 5 to 200 mm NaCl. The minimum detectable Cl- concentration was approximately 5 mm. The coefficient of variation between 5 and 200 mm was 1.7%. Resolution, defined as two times the standard error divided by the slope, between 10 and 50 mm and between 50 and 200 mm was 1 mm and 2.6 mm, respectively. Furosemide, diisothiocyanostilbene-2,2'-disulfonic acid and other nonchloride anions (HEPES, HCO3, SO4, and PO4) did not interfere with the assay, whereas 150 mm NaBr resulted in a peak height greater than 150 NaCl. In addition, the ability to measure Cl- did not vary with pH within the physiological range. We developed an easy, accurate, and sensitive method to measure Cl- concentration in small aqueous solution samples.

In depth analysis of the quenching of three fluorene-phenylene-based cationic conjugated polyelectrolytes by DNA and DNA bases.

PubMed

Davies, Matthew L; Douglas, Peter; Burrows, Hugh D; Martincigh, Bice; Miguel, Maria da Graça; Scherf, Ullrich; Mallavia, Ricardo; Douglas, Alastair

2014-01-16

The interaction of three cationic poly {9,9-bis[N,N-(trimethylammonium)hexyl]fluorene-co-1,4-phenylene} polymers with average chain lengths of ∼6, 12, and 100 repeat units (PFP-NR36(I),12(Br),100(Br)) with both double and single stranded, short and long, DNA and DNA bases have been studied by steady state and time-resolved fluorescence techniques. Fluorescence of PFP-NR3 polymers is quenched with high efficiency by DNA (both double and single stranded) and DNA bases. The resulting quenching plots are sigmoidal and are not accurately described by using a Stern-Volmer quenching mechanism. Here, the quenching mechanism is well modeled in terms of an equilibrium in which a PFP-NR3/DNA aggregate complex is formed which brings polymer chains into close enough proximity to allow interchain excitation energy migration and quenching at aggregate or DNA base traps. Such an analysis gives equilibrium constants of 8.4 × 10(6) (±1.2 × 10(6)) M(-1) for short-dsDNA and 8.6 × 10(6) (±1.7 × 10(6)) M(-1) for short-ssDNA with PFP-NR36(I).

Probing structure and dynamics of DNA with 2-aminopurine: effects of local environment on fluorescence.

PubMed

Rachofsky, E L; Osman, R; Ross, J B

2001-01-30

2-Aminopurine (2AP) is an analogue of adenine that has been utilized widely as a fluorescence probe of protein-induced local conformational changes in DNA. Within a DNA strand, this fluorophore demonstrates characteristic decreases in quantum yield and emission decay lifetime that vary sensitively with base sequence, temperature, and helix conformation but that are accompanied by only small changes in emission wavelength. However, the molecular interactions that give rise to these spectroscopic changes have not been established. To develop a molecular model for interpreting the fluorescence measurements, we have investigated the effects of environmental polarity, hydrogen bonding, and the purine and pyrimidine bases of DNA on the emission energy, quantum yield, and intensity decay kinetics of 2AP in simple model systems. The effects of environmental polarity were examined in a series of solvents of varying dielectric constant, and hydrogen bonding was investigated in binary mixtures of water with 1,4-dioxane or N,N-dimethylformamide (DMF). The effects of the purine and pyrimidine bases were studied by titrating 2AP deoxyriboside (d2AP) with the nucleosides adenosine (rA), cytidine (rC), guanosine (rG), and deoxythymidine (dT), and the nucleoside triphosphates ATP and GTP in neutral aqueous solution. The nucleosides and NTPs each quench the fluorescence of d2AP by a combination of static (affecting only the quantum yield) and dynamic (affecting both the quantum yield and the lifetime, proportionately) mechanisms. The peak wavelength and shape of the emission spectrum are not altered by either of these effects. The static quenching is saturable and has half-maximal effect at approximately 20 mM nucleoside or NTP, consistent with an aromatic stacking interaction. The rate constant for dynamic quenching is near the diffusion limit for collisional interaction (k(q) approximately 2 x 10(9) M(-1) s(-1)). Neither of these effects varies significantly between the various nucleosides and NTPs studied. In contrast, hydrogen bonding with water was observed to have a negligible effect on the emission wavelength, fluorescence quantum yield, or lifetime of 2AP in either dioxane or DMF. In nonpolar solvents, the fluorescence lifetime and quantum yield decrease dramatically, accompanied by significant shifts in the emission spectrum to shorter wavelengths. However, these effects of polarity do not coincide with the observed emission wavelength-independent quenching of 2AP fluorescence in DNA. Therefore, we conclude that the fluorescence quenching of 2AP in DNA arises from base stacking and collisions with neighboring bases only but is insensitive to base-pairing or other hydrogen bonding interactions. These results implicate both structural and dynamic properties of DNA in quenching of 2AP and constitute a simple model within which the fluorescence changes induced by protein-DNA binding or other perturbations may be interpreted.

Photophysical Diversity of Water-Soluble Fluorescent Conjugated Polymers Induced by Surfactant Stabilizers for Rapid and Highly Selective Determination of 2,4,6-Trinitrotoluene Traces.

PubMed

Alizadeh, Naader; Akbarinejad, Alireza; Ghoorchian, Arash

2016-09-21

The increasing application of fluorescence spectroscopy in development of reliable sensing platforms has triggered a lot of research interest for the synthesis of advanced fluorescent materials. Herein, we report a simple, low-cost strategy for the synthesis of a series of water-soluble conjugated polymer nanoparticles with diverse emission range using cationic (hexadecyltrimethylammonium bromide, CTAB), anionic (sodium dodecylbenzenesulfonate, SDBS), and nonionic (TX114) surfactants as the stabilizing agents. The role of surfactant type on the photophisical and sensing properties of resultant polymers has been investigated using dynamic light scattering (DLS), FT-IR, UV-vis, fluorescence, and energy dispersive X-ray (EDS) spectroscopies. The results show that the surface polarity, size, and spectroscopic and sensing properties of conjugated polymers could be well controlled by the proper selection of the stabilizer type. The fluorescent conjugated polymers exhibited fluorescence quenching toward nitroaromatic compounds. Further studies on the fluorescence properties of conjugated polymers revealed that the emission of the SDBS stabilized polymer, N-methylpolypyrrole-SDBS (NMPPY-SDBS), is strongly quenched by 2,4,6-trinitrotoluene molecule with a large Stern -Volmer constant of 59 526 M(-1) and an excellent detection limit of 100 nM. UV-vis and cyclic voltammetry measurements unveiled that fluorescence quenching occurs through a charge transfer mechanism between electron rich NMPPY-SDBS and electron deficient 2,4,6-trinitrotoluene molecules. Finally, the as-prepared conjugated polymer and approach were successfully applied to the determination of 2,4,6-trinitrotoluene in real water samples.

A supramolecular Tröger's base derived coordination zinc polymer for fluorescent sensing of phenolic-nitroaromatic explosives in water.

PubMed

Shanmugaraju, Sankarasekaran; Dabadie, Charlyne; Byrne, Kevin; Savyasachi, Aramballi J; Umadevi, Deivasigamani; Schmitt, Wolfgang; Kitchen, Jonathan A; Gunnlaugsson, Thorfinnur

2017-02-01

A V-Shaped 4-amino-1,8-napthalimide derived tetracarboxylic acid linker ( L ; bis-[ N -(1,3-benzenedicarboxylic acid)]-9,18-methano-1,8-naphthalimide-[ b , f ][1,5]diazocine) comprising the Tröger's base (TB) structural motif was rationally designed and synthesised to access a nitrogen-rich fluorescent supramolecular coordination polymer. By adopting the straight forward precipitation method, a new luminescent nanoscale Zn(ii) coordination polymer ( TB-Zn-CP ) was synthesized in quantitative yield using Zn(OAc) 2 ·2H 2 O and tetraacid linker L (1 : 0.5) in DMF at room temperature. The phase-purity of as-synthesised TB-Zn-CP was confirmed by X-ray powder diffraction analysis, infra-red spectroscopy, and elemental analysis. Thermogravimetric analysis suggests that TB-Zn-CP is thermally stable up to 330 °C and the morphological features of TB-Zn-CP was analysed by SEM and AFM techniques. The N 2 adsorption isotherm of thermally activated TB-Zn-CP at 77 K revealed a type-II reversible adsorption isotherm and the calculated Brunauer-Emmett-Teller (BET) surface area was found to be 72 m 2 g -1 . Furthermore, TB-Zn-CP displayed an excellent CO 2 uptake capacity of 76 mg g -1 at 273 K and good adsorption selectivity for CO 2 over N 2 and H 2 . The aqueous suspension of as-synthesized TB-Zn-CP showed strong green fluorescence ( λ max = 520 nm) characteristics due to the internal-charge transfer (ICT) transition and was used as a fluorescent sensor for the discriminative sensing of nitroaromatic explosives. The aqueous suspension of TB-Zn-CP showed the largest quenching responses with high selectivity for phenolic-nitroaromatics (4-NP, 2,4-DNP and PA) even in the concurrent presence of other potentially competing nitroaromatic analytes. The fluorescence titration studies also provide evidence that TB-Zn-CP detects picric acid as low as the parts per billion (26.3 ppb) range. Furthermore, the observed fluorescence quenching responses of TB-Zn-CP towards picric acid were highly reversible. The highly selective fluorescence quenching responses including the reversible detection efficiency make the nanoscale coordination polymer TB-Zn-CP a potential material for the discriminative fluorescent sensing of nitroaromatic explosives.

Type 2 pyoverdine from Pseudomonas aeruginosa strain BUP2 as turn-off biosensor for the rapid detection of iron and copper ions in contaminated water.

PubMed

Unni, Kizhakkepowathial Nair; Priji, Prakasan; Sajith, Sreedharan; Faisal, Panichikkal Abdul; Shainy, Karippayi Mattil; Joseph, Abraham; Babu, Moolath Girish; Benjamin, Sailas

2016-09-23

Employing fluorescent quenching mechanism, type 2 pyoverdine (PVD) purified from Pseudomonas aeruginosa strain BUP2 (new strain isolated from the rumen of Malabari goat) was used as a simple, convenient and inexpensive tool for the rapid detection of Fe and Cu ions in contaminated drinking water samples. The fluorescence emitted at λ 460 by PVD (in sterile water), mounted on a glass slide was efficiently quenched by the ions of heavy metals like Fe and Cu. The fluorescence quenching effect of PVD was monitored using UV trans-illuminator, and subsequently quantified and confirmed by spectrofluorimetry. Upon exposure for about 50 sec at 25 °C, this quenching efficiency could directly be assessed by naked eye with the aid of a UV trans-illuminator. The linear range of detection for Fe was 1 to 60 µM, while that of Cu was 1 to 20 µM. The limits of detection at µM concentration for Fe 3+ , Fe 2+ and Cu 2+ were 0.23, 0.24 and 0.38, respectively. The quenching of fluorescence was more pronounced in Fe-PVD system than Cu-PVD, and this observation was in corroboration with the Pearson acid base concept; being a hard acid, Fe 3+ effectively bound with the O-ligands and this ability was less in Cu 2+ , a border line acid. Briefly, this study proposed the use of type 2 PVD as a turn-off biosensor for the rapid screening of heavy metals like Fe and Cu in drinking water, at ppm levels only with the aid of UV trans-illuminator at 25 °C in 50 sec.

Complex-formation-enhanced fluorescence quenching effect for efficient detection of picric acid.

PubMed

Ding, Aixiang; Yang, Longmei; Zhang, Yuyang; Zhang, Gaobin; Kong, Lin; Zhang, Xuanjun; Tian, Yupeng; Tao, Xutang; Yang, Jiaxiang

2014-09-15

Amine-functionalized α-cyanostilbene derivatives (Z)-2-(4-aminophenyl)-3-(4-butoxyphenyl)acrylonitrile (ABA) and (Z)-3-(4-butoxyphenyl)-2-[4-(butylamino)phenyl]acrylonitrile (BBA) were designed for specific recognition of picric acid (PA), an environmental and biological pollutant. The 1:1 host-guest complexes formed between the chemosensors and PA enhanced fluorescence quenching, thus leading to sensitive and selective detection in aqueous media and the solid phase. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Double-wavelength overlapping resonance Rayleigh scattering technique for the simultaneous quantitative analysis of three β-adrenergic blockade

NASA Astrophysics Data System (ADS)

Tan, Xuanping; Yang, Jidong; Li, Qin; Yang, Qiong; Shen, Yizhong

2016-05-01

Four simple and accurate spectrophotometric methods were proposed for the simultaneous determination of three β-adrenergic blockade, e.g. atenolol, metoprolol and propranolol. The methods were based on the reaction of the three drugs with erythrosine B (EB) in a Britton-Robinson buffer solution at pH 4.6. EB could combine with the drugs to form three ion-association complexes, which resulted in the resonance Rayleigh scattering (RRS) intensity that is enhanced significantly with new RRS peaks that appeared at 337 nm and 370 nm, respectively. In addition, the fluorescence intensity of EB was also quenched. The enhanced scattering intensities of the two peaks and the fluorescence quenched intensity of EB were proportional to the concentrations of the drugs, respectively. What is more, the RRS intensity overlapped with the double-wavelength of 337 nm and 370 nm (so short for DW-RRS) was also proportional to the drugs concentrations. So, a new method with highly sensitive for simultaneous determination of three bisoprolol drugs was established. Finally, the optimum reaction conditions, influencing factors and spectral enhanced mechanism were investigated. The new DW-RRS method has been applied to simultaneously detect the three β-blockers in fresh serum with satisfactory results.

Quantification of Humic Substances in Natural Water Using Nitrogen-Doped Carbon Dots.

PubMed

Guan, Yan-Fang; Huang, Bao-Cheng; Qian, Chen; Yu, Han-Qing

2017-12-19

Dissolved organic matter (DOM) is ubiquitous in aqueous environments and plays a significant role in pollutant mitigation, transformation and organic geochemical circulation. DOM is also capable of forming carcinogenic byproducts in the disinfection treatment processes of drinking water. Thus, efficient methods for DOM quantification are highly desired. In this work, a novel sensor for rapid and selective detection of humic substances (HS), a key component of DOM, based on fluorescence quenching of nitrogen-doped carbon quantum dots was developed. The experimental results show that the HS detection range could be broadened to 100 mg/L with a detection limit of 0.2 mg/L. Moreover, the detection was effective within a wide pH range of 3.0 to 12.0, and the interferences of ions on the HS measurement were negligible. A good detection result for real surface water samples further validated the feasibility of the developed detection method. Furthermore, a nonradiation electron transfer mechanism for quenching the nitrogen-doped carbon-dots fluorescence by HS was elucidated. In addition, we prepared a test paper and proved its effectiveness. This work provides a new efficient method for the HS quantification than the frequently used modified Lowry method in terms of sensitivity and detection range.

Study of the rotational-level and temperature dependence of the quenching rate of OH fluorescence due to collisions with water molecules

NASA Technical Reports Server (NTRS)

Koker, Edmond B.

1995-01-01

The importance of the OH radical as an intermediate in many combustion reactions and in atmospheric photochemistry has led many researchers to use it as a diagnostic tool in these processes. The amount of data that has been acquired over the years for this radical is quite considerable. However, the quenching rate of OH with water molecules as a function of temperature and the rotational level of the excited state is not very well understood. The motivation of the studies undertaken is to bridge the gap between the low temperature measurements and the high temperature ones reported in the literature. The technique generally employed in these diagnostics is laser-induced fluorescence (LIF), through which rotational state selective excitation of the radical is possible. Furthermore, in a combustion medium, water is produced in abundance so that knowledge of the quenching rate of OH due to water molecules plays a crucial role in interpreting the data. In general, the precursor to an understanding of the collisional quenching rates of OH involves a characterization of the mode in which the radical is produced; the resulting rotational and translational distribution, followed by a measurement of the OH temperature; and ultimately obtaining the rate constants from the pressure dependence of the fluorescence signal. The experimental implementation of these measurements therefore involved, as a first step, the production of the OH radicals in a microwave discharge cell using water vapor as the source, wherein a hydrogen atom is abstracted from H2O. The second step involved the absorption of photons from the frequency-doubled output of a pulsed amplified, single-frequency cw ring dye laser. By tuning the laser to the peak of the transition and observing the fluorescence decay after the laser pulse, the lifetime of the OH in a particular rotational electronic state was determined (tau = 1.4 microseconds for Q(sub 1)(3)). Knowledge of this parameter led to a determination of the quenching rate. By varying the water vapor pressure in the cell and measuring the lifetime as a function of pressure a linear plot of the quenching rate as a function of pressure was obtained. Using this plot, the quenching cross section was deduced. It has therefore been possible to measure the local translational temperature and the quenching cross section with one laser system.

Flow-Tagging Velocimetry for Hypersonic Flows Using Fluorescence of Nitric Oxide

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; OByrne, Sean; Houwing, A. Frank P.; Fox, Jodie S.; Smith, Daniel R.

2003-01-01

We demonstrate a new variation of molecular-tagging velocimetry for hypersonic flows based on laser-induced fluorescence. A thin line of nitric-oxide molecules is excited with a laser beam and then, after a time delay, a fluorescence image of the displaced line is acquired. One component of velocity is determined from the time of flight. This method is applied to measure the velocity profile in a Mach 8.5 laminar, hypersonic boundary layer in the Australian National University s T2 free-piston shock tunnel. The single-shot velocity measurement uncertainty in the freestream was found to be 3.5%, based on 90% confidence. The method is also demonstrated in the separated flow region forward of a blunt fin attached to a flat plate in a Mach 7.4 flow produced by the Australian National University s T3 free-piston shock tunnel. The measurement uncertainty in the blunt fin experiment is approximately 30%, owing mainly to low fluorescence intensities, which could be improved significantly in future experiments. This velocimetry method is applicable to very high-speed flows that have low collisional quenching of the fluorescing species. It is particularly convenient in facilities where planar laser-induced fluorescence is already being performed.

Highly fluorescent carbon dots for visible sensing of doxorubicin release based on efficient nanosurface energy transfer.

PubMed

Wang, Beibei; Wang, Shujun; Wang, Yanfang; Lv, Yan; Wu, Hao; Ma, Xiaojun; Tan, Mingqian

2016-01-01

To prepare fluorescent carbon dots for loading cationic anticancer drug through donor-quenched nanosurface energy transfer in visible sensing of drug release. Highly fluorescent carbon dots (CDs) were prepared by a facile hydrothermal approach from citric acid and o-phenylenediamine. The obtained CDs showed a high quantum yield of 46 % and exhibited good cytocompatibility even at 1 mg/ml. The cationic anticancer drug doxorubicin (DOX) can be loaded onto the negatively charged CDs through electrostatic interactions. Additionally, the fluorescent CDs feature reversible donor-quenched mode nanosurface energy transfer. When loading the energy receptor DOX, the donor CDs' fluorescence was switched "off", while it turned "on" again after DOX release from the surface through endocytic uptake. Most DOX molecules were released from the CDs after 6 h incubation and entered cell nuclear region after 8 h, suggesting the drug delivery system may have potential for visible sensing in drug release.

A zinc fluorescent sensor used to detect mercury (II) and hydrosulfide.

PubMed

Jung, Jae Min; Lee, Jae Jun; Nam, Eunju; Lim, Mi Hee; Kim, Cheal; Harrison, Roger G

2017-05-05

A zinc sensor based on quinoline and morpholine has been synthesized. The sensor selectively fluoresces in the presence of Zn 2+ , while not for other metal ions. Absorbance changes in the 350nm region are observed when Zn 2+ binds, which binds in a 1:1 ratio. The sensor fluoresces due to Zn 2+ above pH values of 6.0 and in the biological important region. The Zn 2+ -sensor complex has the unique ability to detect both Hg 2+ and HS - . The fluorescence of the Zn 2+ -sensor complex is quenched when it is exposed to aqueous solutions of Hg 2+ with sub-micromolar detection levels for Hg 2+ . The fluorescence of the Zn 2+ -sensor complex is also quenched by aqueous solutions of hydrosulfide. The sensor was used to detect Zn 2+ and Hg 2+ in living cells. Copyright © 2017 Elsevier B.V. All rights reserved.

Interaction of the iron(II) cage complexes with proteins: protein fluorescence quenching study.

PubMed

Losytskyy, Mykhaylo Y; Kovalska, Vladyslava B; Varzatskii, Oleg A; Sergeev, Alexander M; Yarmoluk, Sergiy M; Voloshin, Yan Z

2013-09-01

Interaction of the iron(II) mono- and bis-clathrochelates with bovine serum albumin (BSA), β-lactoglobulin, lysozyme and insulin was studied by the steady-state and time-resolved fluorescent spectroscopies. These cage complexes do not make significant impact on fluorescent properties of β-lactoglobulin, lysozyme and insulin. At the same time, the monoclathrochelates strongly quench a fluorescence intensity of BSA and substantially decrease its excited state lifetime due to their binding to this protein. This occurs due to the excitation energy transfer from a tryptophan residue to a cage molecule or/and to the change of the tryptophan nearest environment caused by either clathrochelate binding or an alteration of the BSA conformation. The effect of the iron(II) bis-clathrochelate on BSA fluorescence is much weaker as compared to its monomacrobicyclic analogs as a result of an increase in its size.

Intrinsic fluorescence spectroscopy of glutamate dehydrogenase: Integrated behavior and deconvolution analysis

NASA Astrophysics Data System (ADS)

Pompa, P. P.; Cingolani, R.; Rinaldi, R.

2003-07-01

In this paper, we present a deconvolution method aimed at spectrally resolving the broad fluorescence spectra of proteins, namely, of the enzyme bovine liver glutamate dehydrogenase (GDH). The analytical procedure is based on the deconvolution of the emission spectra into three distinct Gaussian fluorescing bands Gj. The relative changes of the Gj parameters are directly related to the conformational changes of the enzyme, and provide interesting information about the fluorescence dynamics of the individual emitting contributions. Our deconvolution method results in an excellent fitting of all the spectra obtained with GDH in a number of experimental conditions (various conformational states of the protein) and describes very well the dynamics of a variety of phenomena, such as the dependence of hexamers association on protein concentration, the dynamics of thermal denaturation, and the interaction process between the enzyme and external quenchers. The investigation was carried out by means of different optical experiments, i.e., native enzyme fluorescence, thermal-induced unfolding, and fluorescence quenching studies, utilizing both the analysis of the “average” behavior of the enzyme and the proposed deconvolution approach.

A fluorescence detection of D-penicillamine based on Cu(2+)-induced fluorescence quenching system of protein-stabilized gold nanoclusters.

PubMed

Wang, Peng; Li, Bang Lin; Li, Nian Bing; Luo, Hong Qun

2015-01-25

In this contribution, a luminescent gold nanoclusters which were synthesized by bovine serum albumin as novel fluorescent probes were successfully utilized for the determination of D-penicillamine for the first time. Cupric ion was employed to quench the strong fluorescence of the gold nanoclusters, whereas the addition of D-penicillamine caused obvious restoration of fluorescence intensity of the Cu(2+)-gold nanoclusters system. Under optimum conditions, the increment in fluorescence intensity of Cu(2+)-gold nanoclusters system caused by D-penicillamine was linearly proportional to the concentration of D-penicillamine in the range of 2.0×10(-5)-2.39×10(-4) M. The detection limit for D-penicillamine was 5.4×10(-6) M. With the off-on fluorescence signal at 650 nm approaching the near-infrared region, the present sensor for D-penicillamine detection had high sensitivity and low spectral interference. Furthermore, the novel gold nanoclusters-based fluorescent sensor has been applied to the determination of D-penicillamine in real biological samples with satisfactory results. Copyright © 2014 Elsevier B.V. All rights reserved.

Interaction of residue tetracycline hydrochloride in milk with β-galactosidase protein by multi-spectrum methods and molecular docking

NASA Astrophysics Data System (ADS)

Gao, Xin; Bi, Hongna; Zuo, Huijun; Jia, Jingjing; Tang, Lin

2017-08-01

The purpose of this study was to explore the effect of residue tetracycline hydrochloride (TCH) in milk on molecular structure and activity of β-Gal. Inhibition kinetics assay showed the TCH inhibited β-Gal activity reversibly in a competitive manner. In addition, differences in the activity of β-Gal in the absence and presence of TCH as a function of pH and temperature were found although the optimum pH and temperature of β-Gal remained similar. Fluorescence experiment results showed that TCH effectively quenched the intrinsic fluorescence of β-Gal via static quenching. Thermodynamic parameters delineated the major roles of electrostatic forces played between β-Gal and TCH. Additionally, synchronous fluorescence and circular dichroism spectra (CD spectra) results indicated the secondary structure of β-Gal was changed due to the formation of β-Gal-TCH complexes. The molecular docking further revealed that TCH interacted with some amino acid residues of β-Gal, affecting the active site of the enzyme and thus leading to change in enzyme activity. These alterations in conformation and activity of β-Gal should be taken into consideration while using β-Gal for producing oligosaccharide prebiotics on dairy industries.

A highly sensitive and selective detection of Cr(VI) and ascorbic acid based on nitrogen-doped carbon dots.

PubMed

Zhang, Yuhua; Fang, Xian; Zhao, Hong; Li, Zengxi

2018-05-01

A highly sensitive and selective detection of hexavalent chromium (Cr(VI)) and ascorbic acid (AA) was proposed using nitrogen-doped carbon dots (N-CDs). In the absence of AA, the quantitative detection of Cr(VI) was realized through Cr(VI) acting as a quencher to quench the fluorescence of N-CDs by inner filter effect (IFE) and static quenching effect. Under the optimal conditions, the linear range for Cr(VI) detection was from 0.01 to 250μM with a detection limit of 5nM (S/N = 3). In the presence of AA, the fluorescence intensity could be rapidly enhanced compared with the fluorescence of N-CDs/Cr(VI) system since Cr(VI) can be reduced into trivalent chromium (Cr(III)) by AA. And a wide linear range for AA detection was obtained from 1 to 750μM. The detection limit was 0.3μM (S/N = 3). More importantly, this method can be successfully applied to the detection of Cr(VI) in real water samples, and AA in vitamins C tablets and human serum sample. Copyright © 2018 Elsevier B.V. All rights reserved.

Interaction of a dinuclear fluorescent Cd(II) complex of calix[4]arene conjugate with phosphates and its applicability in cell imaging.

PubMed

Sreenivasu Mummidivarapu, V V; Hinge, Vijaya Kumar; Rao, Chebrolu Pulla

2015-01-21

A triazole-linked hydroxyethylimino conjugate of calix[4]arene () and its cadmium complex have been synthesized and characterized, and their structures have been established. In the complex, both the Cd(2+) centers are bound by an N2O4 core, and one of it is a distorted octahedral, whereas the other is a trigonal anti-prism. The fluorescence intensity of the di-nuclear Cd(ii) complex is quenched only in the presence of phosphates and not with other anions studied owing to their binding affinities and the nature of the interaction of the phosphates with Cd(2+). These are evident even from their absorption spectra. Different phosphates exhibit changes in both their fluorescence as well as absorption spectra to varying extents, suggesting their differential interactions. Among the six phosphates, H2PO4(-) has higher fluorescence quenching even at low equivalents of this ion, whereas P2O7(4-) shows only 50% quenching even at 10 equivalents. The fluorescence quenching is considerable even at 20 ppb (0.2 μM) of H2PO4(-), whereas all other phosphates require a concentration of 50-580 ppb to exhibit the same effect on fluorescence spectra. Thus, the interaction of H2PO4(-) is more effective by ∼30 fold as compared to that of P2O7(4-). Fluorescence quenching by phosphate is due to the release of from its original cadmium complex via the formation of a ternary species followed by the capture of Cd(2+) by the phosphate, as delineated based on the combination of spectral techniques, such as absorption, emission, (1)H NMR and ESI MS. The relative interactive abilities of the six phosphates differ from each other. The removal of Cd(2+) is demonstrated to be reversible by the repeated addition of the phosphate followed by Cd(2+). The characteristics of the ternary species formed in each of these six phosphates have been computationally modeled using molecular mechanics. The computational study revealed that the coordination between cadmium and -CH2-CH2-OH breaks and new coordination is established through the phosphate oxygens, and as a result the Cd(2+) center acquires a distorted octahedral geometry. The utility of the complex was demonstrated in HeLa cells.

Enchanced methods of hydrophilized CdSe quantum dots synthesis

NASA Astrophysics Data System (ADS)

Potapkin, D. V.; Zharkova, I. S.; Goryacheva, I. Y.

2015-03-01

Quantum dots are bright and stable fluorescence signal sources, but for most of applications they need an additional hydrophilization step. Unfortunately, most of existing approaches lead to QD's fluorescence quenching, so there is a need for additional enhancing of hydrophilized QD's brightness like UV irradiation, which can be used both on water insoluble QD's with oleic acid ligands (in toluene) and on hydrophilized QD's covered with UV-stable polymer (in aqueous solution). For synthesis of bright water-soluble fluorescent labels CdSe/CdS/ZnS colloidal quantum dots were covered with PAMAM dendrimer and irradiated with UV lamp in quartz cuvettes for 3 hours at the room temperature and then compared with control sample.

Two-photon excitation of nitric oxide fluorescence as a temperature indicator in unsteady gas-dynamic processes

NASA Technical Reports Server (NTRS)

Mckenzie, R. L.; Gross, K. P.

1980-01-01

A laser induced fluorescence technique, suitable for measuring fluctuating temperatures in cold turbulent flows containing very low concentrations of nitric oxide is described. Temperatures below 300 K may be resolved with signal to noise ratios greater than 50 to 1 using high peak power, tunable dye lasers. The method relies on the two photon excitation of selected ro-vibronic transitions. The analysis includes the effects of fluorescence quenching and shows the technique to be effective at all densities below ambient. Signal to noise ratio estimates are based on a preliminary measurement of the two photon absorptivity for a selected rotational transition in the NO gamma (0,0) band.

A novel universal real-time PCR system using the attached universal duplex probes for quantitative analysis of nucleic acids.

PubMed

Yang, Litao; Liang, Wanqi; Jiang, Lingxi; Li, Wenquan; Cao, Wei; Wilson, Zoe A; Zhang, Dabing

2008-06-04

Real-time PCR techniques are being widely used for nucleic acids analysis, but one limitation of current frequently employed real-time PCR is the high cost of the labeled probe for each target molecule. We describe a real-time PCR technique employing attached universal duplex probes (AUDP), which has the advantage of generating fluorescence by probe hydrolysis and strand displacement over current real-time PCR methods. AUDP involves one set of universal duplex probes in which the 5' end of the fluorescent probe (FP) and a complementary quenching probe (QP) lie in close proximity so that fluorescence can be quenched. The PCR primer pair with attached universal template (UT) and the FP are identical to the UT sequence. We have shown that the AUDP technique can be used for detecting multiple target DNA sequences in both simplex and duplex real-time PCR assays for gene expression analysis, genotype identification, and genetically modified organism (GMO) quantification with comparable sensitivity, reproducibility, and repeatability with other real-time PCR methods. The results from GMO quantification, gene expression analysis, genotype identification, and GMO quantification using AUDP real-time PCR assays indicate that the AUDP real-time PCR technique has been successfully applied in nucleic acids analysis, and the developed AUDP real-time PCR technique will offer an alternative way for nucleic acid analysis with high efficiency, reliability, and flexibility at low cost.

Excited state complex formation between methyl glyoxal and some aromatic bio-molecules: a fluorescence quenching study

NASA Astrophysics Data System (ADS)

Banerjee, D.; Mandal, A.; Mukherjee, S.

2003-01-01

Fluorescence quenching of some important aromatic bio-molecules (ABM) such as 3-aminophthalhydrazide (luminol), tryptophan (Try), phenylalanine and tyrosine (Tyr) by methyl glyoxal (MG) has been studied employing different spectroscopic techniques. The interaction of MG with ABM in the excited state has been analysed using Stern-Volmer (S-V) mechanism. In the case of MG-luminol system time correlated single photon counting (TCSPC) technique has also been applied to explain the S-V mechanism. The bimolecular rate constants obtained are found to be higher than the rate constant for diffusion controlled process. A plausible explanation of the quenching mechanism has been discussed on the basis of hydrogen bonding, charge transfer and energy transfer interaction between the colliding species.

Affinity capillary electrophoresis and fluorescence spectroscopy for studying enantioselective interactions between omeprazole enantiomer and human serum albumin.

PubMed

Xu, Yujing; Hong, Tingting; Chen, Xueping; Ji, Yibing

2017-05-01

Baseline separation of omeprazole (OME) enantiomers was achieved by affinity capillary electrophoresis (ACE), using human serum albumin (HSA) as the chiral selector. The influence of several experimental variables such as HSA concentration, the type and content of organic modifiers, applied voltage and running buffer concentration on the separation was evaluated. The binding of esomeprazole (S-omeprazole, S-OME) and its R-enantiomer (R-omeprazole, R-OME) to HSA under simulated physiological conditions was studied by ACE and fluorescence spectroscopy which was considered as a reference method. ACE studies demonstrated that the binding constants of the two enantiomers and HSA were 3.18 × 10 3 M -1 and 5.36 × 10 3 M -1 , respectively. The binding properties including the fluorescence quenching mechanisms, binding constants, binding sites and the number of binding sites were obtained by fluorescence spectroscopy. Though the ACE method could not get enough data when compared with the fluorescence spectrum method, the separation and binding studies of chiral drugs could be achieved simultaneously via this method. This study is of great significance for the investigation and clinical application of chiral drugs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.