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Sample records for absolute fluorescence quantum

  1. Absolute excited-state absorption cross section and fluorescence quantum efficiency of Cr/sup 3 +/: gadolinium scandium gallium garnet

    SciTech Connect

    Seelert, W.; Strauss, E.

    1987-10-01

    Excited-state properties of the laser material Cr/sup 3 +/:Gd/sub 3/Sc/sub 2/(GaO/sub 4/)/sub 3/ were determined by a photocaloric technique. The excited-state absorption cross section at 650 nm is (3.6 +- 0.6)10/sup -20/ cm/sup 2/, and the fluorescence quantum efficiency at ambient temperature is (91 +- 1)%.

  2. Quantum Cloning for Absolute Radiometry

    SciTech Connect

    Sanguinetti, Bruno; Pomarico, Enrico; Sekatski, Pavel; Zbinden, Hugo; Gisin, Nicolas

    2010-08-20

    In the quantum regime information can be copied with only a finite fidelity. This fidelity gradually increases to 1 as the system becomes classical. In this Letter we show how this fact can be used to directly measure the amount of radiated power. We demonstrate how these principles can be used to build a practical primary standard.

  3. Absolute quantum yield measurement of powder samples.

    PubMed

    Moreno, Luis A

    2012-05-12

    Measurement of fluorescence quantum yield has become an important tool in the search for new solutions in the development, evaluation, quality control and research of illumination, AV equipment, organic EL material, films, filters and fluorescent probes for bio-industry. Quantum yield is calculated as the ratio of the number of photons absorbed, to the number of photons emitted by a material. The higher the quantum yield, the better the efficiency of the fluorescent material. For the measurements featured in this video, we will use the Hitachi F-7000 fluorescence spectrophotometer equipped with the Quantum Yield measuring accessory and Report Generator program. All the information provided applies to this system. Measurement of quantum yield in powder samples is performed following these steps: 1. Generation of instrument correction factors for the excitation and emission monochromators. This is an important requirement for the correct measurement of quantum yield. It has been performed in advance for the full measurement range of the instrument and will not be shown in this video due to time limitations. 2. Measurement of integrating sphere correction factors. The purpose of this step is to take into consideration reflectivity characteristics of the integrating sphere used for the measurements. 3. Reference and Sample measurement using direct excitation and indirect excitation. 4. Quantum Yield calculation using Direct and Indirect excitation. Direct excitation is when the sample is facing directly the excitation beam, which would be the normal measurement setup. However, because we use an integrating sphere, a portion of the emitted photons resulting from the sample fluorescence are reflected by the integrating sphere and will re-excite the sample, so we need to take into consideration indirect excitation. This is accomplished by measuring the sample placed in the port facing the emission monochromator, calculating indirect quantum yield and correcting the direct

  4. Absolute fluorescence measurements > 1000 nm: setup design, calibration and standards (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Resch-Genger, Ute; Würth, Christian; Pauli, Jutta; Hatami, Soheil; Kaiser, Martin

    2016-03-01

    There is an increasing interest in optical reporters like semiconductor quantum dots and upconversion nanophosphors with emission < 1000 nm for bioanalysis, medical diagnostics, and safety barcodes and hence, in reliable fluorescence measurements in this wavelength region, e.g., for the comparison of material performance and the rational design of new nanomaterials with improved properties [1-4]. The performance of fluorescence measurements < 800 nm and especially < 1000 nm is currently hampered by the lack of suitable methods and standards for the simple determination of the wavelength-dependent spectral responsivity of fluorescence measuring systems and the control of measured emission spectra and intensities [3-5]. This is of special relevance for nanocrystalline emitters like quantum dots and rods as well as for upconversion nanocrystals, where surface states and the accessibility of emissive states by quenchers largely control accomplishable quantum yields and hence, signal sizes and detection sensitivities from the reporter side. Here, we present the design of an integrating sphere setup for the absolute measurement of emission spectra and quantum yields in the wavelength region of 650 to 1600 nm and its calibration as well as examples for potential fluorescence standards from different reporter classes for the control of the reliability of such measurements [5]. This includes new spectral fluorescence standards for the wavelength region of 650 nm to 1000 nm as well as a set of quantum yield standards covering the wavelength region from 400 nm to 1000 nm.

  5. Measurement of the fluorescence quantum yield of bis-MSB

    NASA Astrophysics Data System (ADS)

    Ding, Xue-Feng; Wen, Liang-Jian; Zhou, Xiang; Ding, Ya-Yun; Ye, Xing-Chen; Zhou, Li; Liu, Meng-Chao; Cai, Hao; Cao, Jun

    2015-12-01

    The fluorescence quantum yield of bis-MSB, a widely used liquid scintillator wavelength shifter, was measured to study the photon absorption and re-emission processes in a liquid scintillator. The re-emission process affects the photoelectron yield and distribution, especially in a large liquid scintillator detector, thus must be understood to optimize the liquid scintillator for good energy resolution and to precisely simulate the detector with Monte Carlo. In this study, solutions of different bis-MSB concentration were prepared for absorption and fluorescence emission measurements to cover a broad range of wavelengths. Harmane was used as a standard reference to obtain the absolution fluorescence quantum yield. For the first time we measured the fluorescence quantum yield of bis-MSB up to 430 nm as inputs required by Monte Carlo simulation, which is 0.926±0.053 at λex=350 nm. Supported by National Natural Science Foundation of China (11205183, 11225525, 11390381)

  6. Biodetection using fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

    Speckman, Donna M.; Jennings, Travis L.; LaLumondiere, Steven D.; Klimcak, Charles M.; Moss, Steven C.; Loper, Gary L.; Beck, Steven M.

    2002-07-01

    Multi-pathogen biosensors that take advantage of sandwich immunoassay detection schemes and utilize conventional fluorescent dye reporter molecules are difficult to make into extremely compact and autonomous packages. The development of a multi-pathogen, immunoassay-based, fiber optic detector that utilizes varying sized fluorescent semiconductor quantum dots (QDs) as the reporter labels has the potential to overcome these problems. In order to develop such a quantum dot-based biosensor, it is essential to demonstrate that QDs can be attached to antibody proteins, such that the specificity of the antibody is maintained. We have been involved in efforts to develop a reproducible method for attaching QDs to antibodies for use in biodetection applications. We have synthesized CdSe/ZnS core-shell QDs of differing size, functionalized their surfaces with several types of organic groups for water solubility, and covalently attached these functionalized QDs to rabbit anti-ovalbumin antibody protein. We also demonstrated that these labeled antibodies exhibit selective binding to ovalbumin antigen. We characterized the QDs at each step in the overall synthesis by UV-VIS absorption spectroscopy and by picosecond (psec) transient photoluminescence (TPL) spectroscopy. TPL spectroscopy measurements indicate that QD lifetime depends on the size of the QD, the intensity of the optical excitation source, and whether or not they are functionalized and conjugated to antibodies. We describe details of these experiments and discuss the impact of our results on our biosensor development program.

  7. Fluorescent Quantum Dots for Biological Labeling

    NASA Technical Reports Server (NTRS)

    McDonald, Gene; Nadeau, Jay; Nealson, Kenneth; Storrie-Lomardi, Michael; Bhartia, Rohit

    2003-01-01

    Fluorescent semiconductor quantum dots that can serve as "on/off" labels for bacteria and other living cells are undergoing development. The "on/off" characterization of these quantum dots refers to the fact that, when properly designed and manufactured, they do not fluoresce until and unless they come into contact with viable cells of biological species that one seeks to detect. In comparison with prior fluorescence-based means of detecting biological species, fluorescent quantum dots show promise for greater speed, less complexity, greater sensitivity, and greater selectivity for species of interest. There are numerous potential applications in medicine, environmental monitoring, and detection of bioterrorism.

  8. Absolute 1* quantum yields for the ICN A state by diode laser gain versus absorption spectroscopy

    NASA Technical Reports Server (NTRS)

    Hess, Wayne P.; Leone, Stephen R.

    1987-01-01

    Absolute I* quantum yields were measured as a function of wavelength for room temperature photodissociation of the ICN A state continuum. The temperature yields are obtained by the technique of time-resolved diode laser gain-versus-absorption spectroscopy. Quantum yields are evaluated at seven wavelengths from 248 to 284 nm. The yield at 266 nm is 66.0 +/- 2% and it falls off to 53.4 +/- 2% and 44.0 +/- 4% at 284 and 248 respectively. The latter values are significantly higher than those obtained by previous workers using infrared fluorescence. Estimates of I* quantum yields obtained from analysis of CN photofragment rotational distributions, as discussed by other workers, are in good agreement with the I* yields. The results are considered in conjunction with recent theoretical and experimental work on the CN rotational distributions and with previous I* yield results.

  9. Quantum bath refrigeration towards absolute zero: challenging the unattainability principle.

    PubMed

    Kolář, M; Gelbwaser-Klimovsky, D; Alicki, R; Kurizki, G

    2012-08-31

    A minimal model of a quantum refrigerator, i.e., a periodically phase-flipped two-level system permanently coupled to a finite-capacity bath (cold bath) and an infinite heat dump (hot bath), is introduced and used to investigate the cooling of the cold bath towards absolute zero (T=0). Remarkably, the temperature scaling of the cold-bath cooling rate reveals that it does not vanish as T→0 for certain realistic quantized baths, e.g., phonons in strongly disordered media (fractons) or quantized spin waves in ferromagnets (magnons). This result challenges Nernst's third-law formulation known as the unattainability principle.

  10. The new Absolute Quantum Gravimeter (AQG): first results and perspectives

    NASA Astrophysics Data System (ADS)

    Bonvalot, Sylvain; Le Moigne, Nicolas; Merlet, Sebastien; Desruelle, Bruno; Lautier-Gaud, Jean; Menoret, Vincent; Vermeulen, Pierre

    2016-04-01

    Cold atom gravimetry represents one of the most innovative evolution in gravity instrumentation since the last 20 years. The concept of measuring the gravitational acceleration by dropping atoms and the development of the first instrumental devices during this last decade quickly revealed the promising perspectives of this new generation of gravity meters enabling accurate and absolute measurements of the Earth's gravity field for a wide range of applications (geophysics, geodesy, metrology, etc.). The Absolute Quantum Gravimeter (AQG) gravity meter, developed by MUQUANS (Talence, France - http://www.muquans.com/) with the support of RESIF, the French Seismologic and Geodetic Network (http://www.resif.fr/) belongs to this new generation of instruments. It also represents the first commercial device based on the utilization of advanced matter-wave interferometry techniques, which allow to characterize precisely the vertical acceleration experienced by a cloud of cold atoms. Recently, the first operational unit (AQG01) has been achieved as a compact transportable gravimeter with the aim of satisfying absolute gravity measurements in laboratory conditions under the following specifications: measurements the μGal level at a few Hz cycling frequency, sensitivity of 50μGal/√Hz, immunity to ground vibrations, easy and quickness of operation, automated continuous data acquisition for several months, etc. In order to evaluate the current performances of the AQG01, several experiments are carried out in collaboration between RESIF user's teams and the MUQUANS manufacturer on different reference gravity sites and laboratories in France. These measurements performed in indoor conditions including simultaneous observations with classical reference gravity instruments (corner-cube absolute gravity meters, relative superconducting meters) as well with the Cold Atom Gravity meter (CAG) developed by LNE-SYRTE, lead to a first objective characterization of the performances of

  11. STED nanoscopy with fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

    Hanne, Janina; Falk, Henning J.; Görlitz, Frederik; Hoyer, Patrick; Engelhardt, Johann; Sahl, Steffen J.; Hell, Stefan W.

    2015-05-01

    The widely popular class of quantum-dot molecular labels could so far not be utilized as standard fluorescent probes in STED (stimulated emission depletion) nanoscopy. This is because broad quantum-dot excitation spectra extend deeply into the spectral bands used for STED, thus compromising the transient fluorescence silencing required for attaining super-resolution. Here we report the discovery that STED nanoscopy of several red-emitting commercially available quantum dots is in fact successfully realized by the increasingly popular 775 nm STED laser light. A resolution of presently ~50 nm is demonstrated for single quantum dots, and sub-diffraction resolution is further shown for imaging of quantum-dot-labelled vimentin filaments in fibroblasts. The high quantum-dot photostability enables repeated STED recordings with >1,000 frames. In addition, we have evidence that the tendency of quantum-dot labels to blink is largely suppressed by combined action of excitation and STED beams. Quantum-dot STED significantly expands the realm of application of STED nanoscopy, and, given the high stability of these probes, holds promise for extended time-lapse imaging.

  12. Absolute I(asterisk) quantum yields for the ICN A state by diode laser gain-vs-absorption spectroscopy

    NASA Technical Reports Server (NTRS)

    Hess, Wayne P.; Leone, Stephen R.

    1987-01-01

    Absolute I(asterisk) quantum yields have been measured as a function of wavelength for room temperature photodissociation of the ICN A state continuum. The yields are obtained by the technique of time-resolved diode laser gain-vs-absorption spectroscopy. Quantum yields are evaluated at seven wavelengths from 248 to 284 nm. The yield at 266 nm is 66.0 + or - 2 percent and it falls off to 53.4 + or - 2 percent and 44.0 + or - 4 percent at 284 and 248 nm, respectively. The latter values are significantly higher than those obtained by previous workers using infrared fluorescence. Estimates of I(asterisk) quantum yields obtained from analysis of CN photofragment rotational distributions, as discussed by other workers, are in good agreement with the I(asterisk) yields reported here. The results are considered in conjunction with recent theoretical and experimental work on the CN rotational distributions and with previous I(asterisk) quantum yield results.

  13. Absolute quantum cutting efficiency of Tb3+-Yb3+ co-doped glass

    NASA Astrophysics Data System (ADS)

    Duan, Qianqian; Qin, Feng; Zhao, Hua; Zhang, Zhiguo; Cao, Wenwu

    2013-12-01

    The absolute quantum cutting efficiency of Tb3+-Yb3+ co-doped glass was quantitatively measured by an integrating sphere detection system, which is independent of the excitation power. As the Yb3+ concentration increases, the near infrared quantum efficiency exhibited an exponential growth with an upper limit of 13.5%, but the visible light efficiency was reduced rapidly. As a result, the total quantum efficiency monotonically decreases rather than increases as theory predicted. In fact, the absolute quantum efficiency was far less than the theoretical value due to the low radiative efficiency of Tb3+ (<61%) and significant cross-relaxation nonradiative loss between Yb3+ ions.

  14. Experimental feasibility of the airborne measurement of absolute oil fluorescence spectral conversion efficiency

    NASA Technical Reports Server (NTRS)

    Hoge, F. E.; Swift, R. N.

    1983-01-01

    Airborne lidar oil spill experiments carried out to determine the practicability of the AOFSCE (absolute oil fluorescence spectral conversion efficiency) computational model are described. The results reveal that the model is suitable over a considerable range of oil film thicknesses provided the fluorescence efficiency of the oil does not approach the minimum detection sensitivity limitations of the lidar system. Separate airborne lidar experiments to demonstrate measurement of the water column Raman conversion efficiency are also conducted to ascertain the ultimate feasibility of converting such relative oil fluorescence to absolute values. Whereas the AOFSCE model is seen as highly promising, further airborne water column Raman conversion efficiency experiments with improved temporal or depth-resolved waveform calibration and software deconvolution techniques are thought necessary for a final determination of suitability.

  15. Combinatorial Approach to Studying Metal Enhanced Fluorescence from Quantum Dots

    NASA Astrophysics Data System (ADS)

    Le, Nguyet; Corrigan, Timothy; Norton, Michael; Neff, David

    2013-03-01

    Fluorescence is extensively used in biochemistry for determining the concentration or purity of molecules in a biological environment. In metal-enhanced fluorescence (MEF), the fluorescence molecules separated from a metal surface by several nanometers can be enhanced. The fluorescent enhancement is dependent on the size and spacing of the nanoparticles, as has been shown previously for a number of fluorophore molecules. Fluorescence from quantum dots is of particular interest because the quantum dots do not lose fluorescence ability when exposed to light and they have higher intensity of fluorescence. The purpose of this study is to determine the effect of size and spacing on fluorescence intensity when coupling gold nano-particles with quantum dots. We employ a combinatorial approach, depositing gold particles ranging in diameter from 30 nm to 130 nm with varied spacings onto the substrate, followed by a protein spacer-layer and quantum dots. The fluorescence signal from the metal enhanced quantum dots were determined by confocal microscopy.

  16. Quantum Efficient Detectors for Use in Absolute Calibration

    NASA Technical Reports Server (NTRS)

    Faust, Jessica; Eastwood, Michael; Pavri, Betina; Raney, James

    1998-01-01

    The trap or quantum efficient detector has a quantum efficiency of greater than 0.98 for the region from 450 to 900 nm. The region of flattest response is from 600 to 900 nm. The QED consists of three windowless Hamamatsu silicon detectors. The QED was mounted below AVIRIS to monitor the Spectralon panel for changes in radiance during radiometric calibration. The next step is to permanently mount the detector to AVIRIS and monitor the overall radiance of scenes along with calibration.

  17. Highly Fluorescent Noble Metal Quantum Dots

    PubMed Central

    Zheng, Jie; Nicovich, Philip R.; Dickson, Robert M.

    2009-01-01

    Highly fluorescent, water-soluble, few-atom noble metal quantum dots have been created that behave as multi-electron artificial atoms with discrete, size-tunable electronic transitions throughout the visible and near IR. These “molecular metals” exhibit highly polarizable transitions and scale in size according to the simple relation, Efermi/N1/3, predicted by the free electron model of metallic behavior. This simple scaling indicates that fluorescence arises from intraband transitions of free electrons and that these conduction electron transitions are the low number limit of the plasmon – the collective dipole oscillations occurring when a continuous density of states is reached. Providing the “missing link” between atomic and nanoparticle behavior in noble metals, these emissive, water-soluble Au nanoclusters open new opportunities for biological labels, energy transfer pairs, and light emitting sources in nanoscale optoelectronics. PMID:17105412

  18. The Absolute, Relative and Multi-Wavelength Calibration of the Pierre Auger Observatory Fluorescence Detectors

    SciTech Connect

    Knapik, R.; Bauleo, P.; Becker, B.R.; Brack, J.; Caruso, R.; Fratte, C.Delle; Dorofeev, A.; Harton, J.; Insolia, A.; Matthews, J.A.J.; Menshikov, A.

    2007-08-01

    Absolute calibration of the Pierre Auger Observatory fluorescence detectors uses a 375 nm light source at the telescope aperture. This end-to-end technique accounts for the combined effects of all detector components in a single measurement. The relative response has been measured at wavelengths of 320, 337, 355, 380 and 405 nm, defining a spectral response curve which has been normalized to the absolute calibration. Before and after each night of data taking a relative calibration of the phototubes is performed. This relative calibration is used to track both short and long term changes in the detector's response. A cross check of the calibration in some phototubes is performed using an independent laser technique. Overall uncertainties, current results and future plans are discussed.

  19. On quantum harmonic oscillator being subjected to absolute potential state

    NASA Astrophysics Data System (ADS)

    Nityayogananda, Swami

    2017-01-01

    In a quantum harmonic oscillator (QHO), the energy of the oscillator increases with increased frequency. In this paper, assuming a boundary condition that the product of momentum and position, or the product of energy density and position remains constant in the QHO, it is established that a particle subjected to increasing frequencies becomes gradually subtler to transform into a very high dormant potential energy. This very high dormant potential energy is referred to as `like-potential' energy in this paper. In the process a new wave function is generated. This new function, which corresponds to new sets of particles, has scope to raise the quantum oscillator energy (QOE) up to infinity. It is proposed to show that this high energy does not get cancelled but remains dormant. Further, it is proposed that the displacement about the equilibrium goes to zero when the vibration of the oscillator stops and then the QOE becomes infinity - this needs further research. The more the QOE, the greater will be the degree of dormancy. A simple mathematical model has been derived here to discuss the possibilities that are involved in the QHO under the above-mentioned boundary conditions.

  20. Absolutely continuous spectrum implies ballistic transport for quantum particles in a random potential on tree graphs

    NASA Astrophysics Data System (ADS)

    Aizenman, Michael; Warzel, Simone

    2012-09-01

    We discuss the dynamical implications of the recent proof that for a quantum particle in a random potential on a regular tree graph absolutely continuous (ac) spectrum occurs non-perturbatively through rare fluctuation-enabled resonances. The main result is spelled in the title.

  1. Absolutely continuous spectrum implies ballistic transport for quantum particles in a random potential on tree graphs

    SciTech Connect

    Aizenman, Michael; Warzel, Simone

    2012-09-15

    We discuss the dynamical implications of the recent proof that for a quantum particle in a random potential on a regular tree graph absolutely continuous (ac) spectrum occurs non-perturbatively through rare fluctuation-enabled resonances. The main result is spelled in the title.

  2. Fluorescence correlation spectroscopy using quantum dots: advances, challenges and opportunities.

    PubMed

    Heuff, Romey F; Swift, Jody L; Cramb, David T

    2007-04-28

    Semiconductor nanocrystals (quantum dots) have been increasingly employed in measuring the dynamic behavior of biomacromolecules using fluorescence correlation spectroscopy. This poses a challenge, because quantum dots display their own dynamic behavior in the form of intermittent photoluminescence, also known as blinking. In this review, the manifestation of blinking in correlation spectroscopy will be explored, preceded by an examination of quantum dot blinking in general.

  3. Carbon Quantum Dots for Zebrafish Fluorescence Imaging

    NASA Astrophysics Data System (ADS)

    Kang, Yan-Fei; Li, Yu-Hao; Fang, Yang-Wu; Xu, Yang; Wei, Xiao-Mi; Yin, Xue-Bo

    2015-07-01

    Carbon quantum dots (C-QDs) are becoming a desirable alternative to metal-based QDs and dye probes owing to their high biocompatibility, low toxicity, ease of preparation, and unique photophysical properties. Herein, we describe fluorescence bioimaging of zebrafish using C-QDs as probe in terms of the preparation of C-QDs, zebrafish husbandry, embryo harvesting, and introduction of C-QDs into embryos and larvae by soaking and microinjection. The multicolor of C-QDs was validated with their imaging for zebrafish embryo. The distribution of C-QDs in zebrafish embryos and larvae were successfully observed from their fluorescence emission. the bio-toxicity of C-QDs was tested with zebrafish as model and C-QDs do not interfere to the development of zebrafish embryo. All of the results confirmed the high biocompatibility and low toxicity of C-QDs as imaging probe. The absorption, distribution, metabolism and excretion route (ADME) of C-QDs in zebrafish was revealed by their distribution. Our work provides the useful information for the researchers interested in studying with zebrafish as a model and the applications of C-QDs. The operations related zebrafish are suitable for the study of the toxicity, adverse effects, transport, and biocompatibility of nanomaterials as well as for drug screening with zebrafish as model.

  4. Carbon Quantum Dots for Zebrafish Fluorescence Imaging

    PubMed Central

    Kang, Yan-Fei; Li, Yu-Hao; Fang, Yang-Wu; Xu, Yang; Wei, Xiao-Mi; Yin, Xue-Bo

    2015-01-01

    Carbon quantum dots (C-QDs) are becoming a desirable alternative to metal-based QDs and dye probes owing to their high biocompatibility, low toxicity, ease of preparation, and unique photophysical properties. Herein, we describe fluorescence bioimaging of zebrafish using C-QDs as probe in terms of the preparation of C-QDs, zebrafish husbandry, embryo harvesting, and introduction of C-QDs into embryos and larvae by soaking and microinjection. The multicolor of C-QDs was validated with their imaging for zebrafish embryo. The distribution of C-QDs in zebrafish embryos and larvae were successfully observed from their fluorescence emission. the bio-toxicity of C-QDs was tested with zebrafish as model and C-QDs do not interfere to the development of zebrafish embryo. All of the results confirmed the high biocompatibility and low toxicity of C-QDs as imaging probe. The absorption, distribution, metabolism and excretion route (ADME) of C-QDs in zebrafish was revealed by their distribution. Our work provides the useful information for the researchers interested in studying with zebrafish as a model and the applications of C-QDs. The operations related zebrafish are suitable for the study of the toxicity, adverse effects, transport, and biocompatibility of nanomaterials as well as for drug screening with zebrafish as model. PMID:26135470

  5. On determining absolute entropy without quantum theory or the third law of thermodynamics

    NASA Astrophysics Data System (ADS)

    Steane, Andrew M.

    2016-04-01

    We employ classical thermodynamics to gain information about absolute entropy, without recourse to statistical methods, quantum mechanics or the third law of thermodynamics. The Gibbs-Duhem equation yields various simple methods to determine the absolute entropy of a fluid. We also study the entropy of an ideal gas and the ionization of a plasma in thermal equilibrium. A single measurement of the degree of ionization can be used to determine an unknown constant in the entropy equation, and thus determine the absolute entropy of a gas. It follows from all these examples that the value of entropy at absolute zero temperature does not need to be assigned by postulate, but can be deduced empirically.

  6. Fluorescent carbon nano dots from lignite: unveiling the impeccable evidence for quantum confinement.

    PubMed

    Kumar Thiyagarajan, Senthil; Raghupathy, Suresh; Palanivel, Dharmalingam; Raji, Kaviyarasan; Ramamurthy, Perumal

    2016-04-28

    Synthesizing nano carbon from its bulk precursors is of recent research interest. In this report, luminescent carbon nanoparticles (CNPs) with tunable particle size and surface functionality are fabricated from lignite using ethylenediamine as the reactive solvent and surface passivating agent via different experimental methods. From the steady-state and time-resolved photophysical studies of these differently sized CNPs, it is unveiled that the energy of the excitons generated after photoexcitation is quantum confined, and it influences the observed photophysical behaviour significantly only when the particle size is less than 10 nm. A larger size of the CNPs and less surface functionalization lead to aggregation, and quenching of the fluorescence. But by dispersing smaller size CNPs in sodium sulfate matrix exhibits fluorescence in the solid state with an absolute fluorescence quantum yield of ∼34%. The prospective application of this hybrid material in sensing and removal of moisture in the atmosphere is illustrated.

  7. Wavelength dependence of the fluorescence and singlet oxygen quantum yields of new photosensitizers

    NASA Astrophysics Data System (ADS)

    Lavi, Adina; Johnson, Fred M.; Ehrenberg, Benjamin

    1994-12-01

    The photophysical properties of Mg and Zn tetrabenzoporphyrins and Cd-texaphyrin are presented. These sensitizers have strong absorption bands in the red and near-IR regions that make them good candidates for biological photosensitization. Singlet oxygen quantum yields which were determined in an absolute manner, in several solvents, are reported. We show an unusual behavior regarding adherence to Kasha's and Vavilov's rules: upon excitation to different electronic states, different values of singlet oxygen quantum yields were obtained. We also show an unusual wavelength dependence of singlet oxygen and fluorescence yields upon excitation to different vibrational levels within the same electronic state.

  8. Variations in fluorescence quantum yield of basic fuchsin with silver nanoparticles prepared by femtosecond laser ablation.

    PubMed

    Pathrose, Bini; Sahira, H; Nampoori, V P N; Radhakrishnan, P; Mujeeb, A

    2014-07-15

    Nano structured noble metals have very important applications in diverse fields such as photovoltaics, catalysis, electronic and magnetic devices, etc. In the present work, the application of dual beam thermal lens technique is employed for the determination of the absolute fluorescence quantum yield of the triaminotriphenylmethane dye, basic fuchsin in the presence of silver sol is studied. Silver sol is prepared by femtosecond laser ablation. It is observed that the presence of silver sol decreases the fluorescence quantum efficiency. The observed results are in line with the conclusion that the reduction in quantum yield in the quenching region is essentially due to the non-radiative relaxation of the absorbed energy. It is also observed that the presence of silver sol enhances the thermal lens signal which makes its detection easier at any concentration.

  9. Assignment of absolute stereostructures through quantum mechanics electronic and vibrational circular dichroism calculations.

    PubMed

    Dai, Peng; Jiang, Nan; Tan, Ren-Xiang

    2016-01-01

    Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.

  10. Peptide-Decorated Tunable-Fluorescence Graphene Quantum Dots.

    PubMed

    Sapkota, Bedanga; Benabbas, Abdelkrim; Lin, Hao-Yu Greg; Liang, Wentao; Champion, Paul; Wanunu, Meni

    2017-03-22

    We report here the synthesis of graphene quantum dots with tunable size, surface chemistry, and fluorescence properties. In the size regime 15-35 nm, these quantum dots maintain strong visible light fluorescence (mean quantum yield of 0.64) and a high two-photon absorption (TPA) cross section (6500 Göppert-Mayer units). Furthermore, through noncovalent tailoring of the chemistry of these quantum dots, we obtain water-stable quantum dots. For example, quantum dots with lysine groups bind strongly to DNA in solution and inhibit polymerase-based DNA strand synthesis. Finally, by virtue of their mesoscopic size, the quantum dots exhibit good cell permeability into living epithelial cells, but they do not enter the cell nucleus.

  11. Absolute Density Calibration Cell for Laser Induced Fluorescence Erosion Rate Measurements

    NASA Technical Reports Server (NTRS)

    Domonkos, Matthew T.; Stevens, Richard E.

    2001-01-01

    Flight qualification of ion thrusters typically requires testing on the order of 10,000 hours. Extensive knowledge of wear mechanisms and rates is necessary to establish design confidence prior to long duration tests. Consequently, real-time erosion rate measurements offer the potential both to reduce development costs and to enhance knowledge of the dependency of component wear on operating conditions. Several previous studies have used laser-induced fluorescence (LIF) to measure real-time, in situ erosion rates of ion thruster accelerator grids. Those studies provided only relative measurements of the erosion rate. In the present investigation, a molybdenum tube was resistively heated such that the evaporation rate yielded densities within the tube on the order of those expected from accelerator grid erosion. This work examines the suitability of the density cell as an absolute calibration source for LIF measurements, and the intrinsic error was evaluated.

  12. Approximating relational observables by absolute quantities: a quantum accuracy-size trade-off

    NASA Astrophysics Data System (ADS)

    Miyadera, Takayuki; Loveridge, Leon; Busch, Paul

    2016-05-01

    The notion that any physical quantity is defined and measured relative to a reference frame is traditionally not explicitly reflected in the theoretical description of physical experiments where, instead, the relevant observables are typically represented as ‘absolute’ quantities. However, the emergence of the resource theory of quantum reference frames as a new branch of quantum information science in recent years has highlighted the need to identify the physical conditions under which a quantum system can serve as a good reference. Here we investigate the conditions under which, in quantum theory, an account in terms of absolute quantities can provide a good approximation of relative quantities. We find that this requires the reference system to be large in a suitable sense.

  13. Fluorophore discrimination by tracing quantum interference in fluorescence microscopy

    SciTech Connect

    De, Arijit Kumar; Roy, Debjit; Goswami, Debabrata

    2011-01-15

    We show fluorescence-detected quantum interference in a microscope setup and demonstrate selective enhancement or suppression of fluorophores using femtosecond pulse-pair excitation with periodic modulation of the interpulse phase.

  14. Ion Coulomb crystals: from quantum technology to chemistry close to the absolute zero point

    NASA Astrophysics Data System (ADS)

    Dulieu, O.; Willitsch, S.

    2017-03-01

    Ion Coulomb crystals are ordered structures of atomic or molecular ions stored in ion traps at temperatures close to the absolute zero point. These unusual "crystals" form the basis of extremely accurate clocks, provide an environment for precise studies of chemical reactions and enable advanced implementations of the technology for a quantum computer. In this article, we discuss the techniques for generating atomic and molecular Coulomb crystals and highlight some of their applications.

  15. Toward quantitatively fluorescent carbon-based "quantum" dots.

    PubMed

    Anilkumar, Parambath; Wang, Xin; Cao, Li; Sahu, Sushant; Liu, Jia-Hui; Wang, Ping; Korch, Katerina; Tackett, Kenneth N; Parenzan, Alexander; Sun, Ya-Ping

    2011-05-01

    Carbon-based "quantum" dots (or "carbon dots") are generally defined as surface-passivated small carbon nanoparticles that are brightly fluorescent. Apparently, the carbon particle surface passivation in carbon dots is critical to their fluorescence performance. An effective way to improve the surface passivation is to dope the surface of the precursor carbon nanoparticles with an inorganic salt, followed by the typical functionalization with organic molecules. In this work we passivated small carbon nanoparticles by a combination of the surface-doping with nanoscale semiconductors and the organic functionalization, coupled with gel column fractionation to harvest the most fluorescent carbon dots, which exhibited fluorescence emission quantum yields of up to 78%. Experimental and mechanistic issues relevant to potentially further improve the performance of carbon dots toward their being quantitatively fluorescent are discussed.

  16. Full counting statistics of quantum dot resonance fluorescence

    PubMed Central

    Matthiesen, Clemens; Stanley, Megan J.; Hugues, Maxime; Clarke, Edmund; Atatüre, Mete

    2014-01-01

    The electronic energy levels and optical transitions of a semiconductor quantum dot are subject to dynamics within the solid-state environment. In particular, fluctuating electric fields due to nearby charge traps or other quantum dots shift the transition frequencies via the Stark effect. The environment dynamics are mapped directly onto the fluorescence under resonant excitation and diminish the prospects of quantum dots as sources of indistinguishable photons in optical quantum computing. Here, we present an analysis of resonance fluorescence fluctuations based on photon counting statistics which captures the underlying time-averaged electric field fluctuations of the local environment. The measurement protocol avoids dynamic feedback on the electric environment and the dynamics of the quantum dot's nuclear spin bath by virtue of its resonant nature and by keeping experimental control parameters such as excitation frequency and external fields constant throughout. The method introduced here is experimentally undemanding. PMID:24810097

  17. Using star tracks to determine the absolute pointing of the Fluorescence Detector telescopes of the Pierre Auger Observatory

    SciTech Connect

    De Donato, Cinzia; Sanchez, Federico; Santander, Marcos; Natl.Tech.U., San Rafael; Camin, Daniel; Garcia, Beatriz; Grassi, Valerio; /Milan U. /INFN, Milan

    2005-05-01

    To accurately reconstruct a shower axis from the Fluorescence Detector data it is essential to establish with high precision the absolute pointing of the telescopes. To d that they calculate the absolute pointing of a telescope using sky background data acquired during regular data taking periods. The method is based on the knowledge of bright star's coordinates that provide a reliable and stable coordinate system. it can be used to check the absolute telescope's pointing and its long-term stability during the whole life of the project, estimated in 20 years. They have analyzed background data taken from January to October 2004 to determine the absolute pointing of the 12 telescopes installed both in Los Leones and Coihueco. The method is based on the determination of the mean-time of the variance signal left by a star traversing a PMT's photocathode which is compared with the mean-time obtained by simulating the track of that star on the same pixel.

  18. Absolute Configuration Determination by Quantum Mechanical Calculation of Chiroptical Spectra: Basics and Applications to Fungal Metabolites.

    PubMed

    Superchi, Stefano; Scafato, Patrizia; Górecki, Marcin; Pescitelli, Gennaro

    2017-03-10

    The application of quantum mechanical simulation of chiroptical properties, i.e. electronic circular dichroism (ECD), optical rotation (OR), and vibrational circular dichroism (VCD), to the assignment of the absolute configuration of chiral naturally occurring metabolites of fungal origin, is reviewed. The fundamentals of such chiroptical spectroscopies as well as the specific experimental and computational issues allied to the application of their ab initio calculation is reported. Some examples, related to the use of the ECD, VCD, and OR techniques and highlighting the practical application of the methods, are also described.

  19. Colloidal quantum dots for fluorescent labels of proteins

    NASA Astrophysics Data System (ADS)

    Gladyshev, P.; Kouznetsov, V.; Martinez Bonilla, C.; Dezhurov, S.; Krilsky, D.; Vasiliev, A.; Morenkov, O.; Vrublevskaya, V.; Tsygankov, P.; Ibragimova, S.; Rybakova, A.

    2016-10-01

    The work is devoted to the synthesis of colloidal quantum dots (QDs) and their bioconjugates with proteins. Various QDs were obtained as well with synthesis method in an organic solvent followed by hydrophilization and functionalization or synthesis in aqueous phase provides obtaining hydrophilic QDs directly. Particular attention is paid to the synthesis of QDs as fluorescent tags in the near infrared where minimum absorption occurs and the fluorescence of biological tissue and synthetic materials used in analytical systems. A method for the QDs synthesis of type fluorescent core/shell CdTeSe/CdS/CdZnS-PolyT with mixed telluride, selenide cadmium core with a high quantum yield and high resistance to photoaging. It is shown that these quantum dots may be effectively used in the immunoassay.

  20. Semiconductor Quantum Rods as Single Molecule FluorescentBiological Labels

    SciTech Connect

    Fu, Aihua; Gu, Weiwei; Boussert, Benjamine; Koski, Kristie; Gerion, Daniele; Manna, Liberato; Le Gros, Mark; Larabell, Carolyn; Alivisatos, A. Paul

    2006-05-29

    In recent years, semiconductor quantum dots have beenapplied with great advantage in a wide range of biological imagingapplications. The continuing developments in the synthesis of nanoscalematerials and specifically in the area of colloidal semiconductornanocrystals have created an opportunity to generate a next generation ofbiological labels with complementary or in some cases enhanced propertiescompared to colloidal quantum dots. In this paper, we report thedevelopment of rod shaped semiconductor nanocrystals (quantum rods) asnew fluorescent biological labels. We have engineered biocompatiblequantum rods by surface silanization and have applied them fornon-specific cell tracking as well as specific cellular targeting. Theproperties of quantum rods as demonstrated here are enhanced sensitivityand greater resistance for degradation as compared to quantum dots.Quantum rods have many potential applications as biological labels insituations where their properties offer advantages over quantumdots.

  1. Atomistic Model of Fluorescence Intermittency of Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Voznyy, O.; Sargent, E. H.

    2014-04-01

    Optoelectronic applications of colloidal quantum dots demand a high emission efficiency, stability in time, and narrow spectral bandwidth. Electronic trap states interfere with the above properties but understanding of their origin remains lacking, inhibiting the development of robust passivation techniques. Here we show that surface vacancies improve the fluorescence yield compared to vacancy-free surfaces, while dynamic vacancy aggregation can temporarily turn fluorescence off. We find that infilling with foreign cations can stabilize the vacancies, inhibiting intermittency and improving quantum yield, providing an explanation of recent experimental observations.

  2. Fluorescent carbon nanomaterials: "quantum dots" or nanoclusters?

    PubMed

    Dekaliuk, Mariia O; Viagin, Oleg; Malyukin, Yuriy V; Demchenko, Alexander P

    2014-08-14

    Despite many efforts, the mechanisms of light absorption and emission of small fluorescent carbon nanoparticles (C-dots) are still unresolved and are a subject of active discussion. In this work we address the question as to whether the fluorescence is a collective property of these nanoparticles or they are composed of assembled individual emitters. Selecting three types of C-dots with "violet", "blue" and "green" emissions and performing a detailed study of fluorescence intensity, lifetime and time-resolved anisotropy as a function of excitation and emission wavelengths together with the effect of viscogen and dynamic fluorescence quencher, we demonstrate that the C-dots represent assemblies of surface-exposed fluorophores. They behave as individual emitters, display electronic anisotropy, do not exchange their excited-state energies via homo-FRET and possibly display sub-nanosecond intra-particle mobility.

  3. Fluorescence Quantum Yield Measurements of Fluorescent Proteins: A Laboratory Experiment for a Biochemistry or Molecular Biophysics Laboratory Course

    ERIC Educational Resources Information Center

    Wall, Kathryn P.; Dillon, Rebecca; Knowles, Michelle K.

    2015-01-01

    Fluorescent proteins are commonly used in cell biology to assess where proteins are within a cell as a function of time and provide insight into intracellular protein function. However, the usefulness of a fluorescent protein depends directly on the quantum yield. The quantum yield relates the efficiency at which a fluorescent molecule converts…

  4. Quantum process tomography by 2D fluorescence spectroscopy

    SciTech Connect

    Pachón, Leonardo A.; Marcus, Andrew H.; Aspuru-Guzik, Alán

    2015-06-07

    Reconstruction of the dynamics (quantum process tomography) of the single-exciton manifold in energy transfer systems is proposed here on the basis of two-dimensional fluorescence spectroscopy (2D-FS) with phase-modulation. The quantum-process-tomography protocol introduced here benefits from, e.g., the sensitivity enhancement ascribed to 2D-FS. Although the isotropically averaged spectroscopic signals depend on the quantum yield parameter Γ of the doubly excited-exciton manifold, it is shown that the reconstruction of the dynamics is insensitive to this parameter. Applications to foundational and applied problems, as well as further extensions, are discussed.

  5. Supramolecular spectrally encoded microgels with double strand probes for absolute and direct miRNA fluorescence detection at high sensitivity.

    PubMed

    Causa, Filippo; Aliberti, Anna; Cusano, Angela M; Battista, Edmondo; Netti, Paolo A

    2015-02-11

    We present novel microgels as a particle-based suspension array for direct and absolute microRNA (miRNA) detection. The microgels feature a flexible molecular architecture, antifouling properties, and enhanced sensitivity with a large dynamic range of detection. Specifically, they possess a core-shell molecular architecture with two different fluorescent dyes for multiplex spectral analyses and are endowed with a fluorescent probe for miRNA detection. Encoding and detection fluorescence signals are distinguishable by nonoverlapping emission spectra. Tunable fluorescence probe conjugation and emission confinement on single microgels allow for ultrasensitive miRNA detection. Indeed, the suspension array has high selectivity and sensitivity with absolute quantification, a detection limit of 10(-15) M, a dynamic range from 10(-9) to 10(-15) M, and higher accuracy than qRT-PCR. The antifouling properties of the microgels also permit the direct measurement of miRNAs in serum, without sample pretreatment or target amplification. A multiplexed assay has been tested for a set of miRNAs chosen as cancer biomarkers.

  6. A study of the valence shell absolute photoabsorption, photoionisation and photodissociation cross sections and the photoionisation quantum efficiency of carbonyl sulphide

    NASA Astrophysics Data System (ADS)

    Holland, D. M. P.; Shaw, D. A.

    2016-11-01

    The absolute photoabsorption, photoionisation and photodissociation cross sections and the photoionisation quantum efficiency of carbonyl sulphide have been measured using a double ion chamber and synchrotron radiation in the energy range from the ionisation threshold to 24 eV. In addition to the absorption bands associated with well established Rydberg series, some previously unassigned features have been tentatively attributed to an f-type Rydberg series converging onto the B ˜ 2Σ+ state ionisation threshold. Structure appearing in the photodissociation spectrum has been correlated with that observed in earlier fluorescence yields for emission, due mainly to the CS photofragment, occurring between 160 and 300 nm. The photoionisation quantum efficiency reaches a plateau value close to unity for energies above ∼16 eV. The predissociation of Rydberg states into neutral fragments does not appear to affect the photoionisation quantum efficiency of carbonyl sulphide to the extent that is commonly observed in other small molecules. A sum rule analysis has been carried out by combining the present absolute photoabsorption measurements with similar data covering the remaining energy regions.

  7. Ultraviolet photolysis of HCHO: absolute HCO quantum yields by direct detection of the HCO radical photoproduct.

    PubMed

    Carbajo, Paula Gorrotxategi; Smith, Shona C; Holloway, Anne-Louise; Smith, Carina A; Pope, Francis D; Shallcross, Dudley E; Orr-Ewing, Andrew J

    2008-12-04

    Absolute quantum yields for the radical (H + HCO) channel of HCHO photolysis, Phi(HCO), have been measured for the tropospherically relevant range of wavelengths (lambda) between 300 and 330 nm. The HCO photoproduct was directly detected by using a custom-built, combined ultra-violet (UV) absorption and cavity ring down (CRD) detection spectrometer. This instrument was previously employed for high-resolution (spectral resolution approximately 0.0035 nm) measurements of absorption cross-sections of HCHO, sigma(HCHO)(lambda), and relative HCO quantum yields. Absolute Phi(HCO) values were measured at seven wavelengths, lambda = 303.70, 305.13, 308.87, 314.31, 320.67, 325.59, and 329.51 nm, using an independent calibration technique based on the simultaneous UV photolysis of HCHO and Cl(2). These Phi(HCO) measurements display greater variability as a function of wavelength than the current NASA-JPL recommendations for Phi(HCO). The absolute Phi(HCO)(lambda) determinations and previously measured sigma(HCHO)(lambda) were used to scale an extensive set of relative HCO yield measurements. The outcome of this procedure is a full suite of data for the product of the absolute radical quantum yield and HCHO absorption cross-section, Phi(HCO)(lambda)sigma(HCHO)(lambda), at wavelengths from 302.6 to 331.0 nm with a wavelength resolution of 0.005 nm. This product of photochemical parameters is combined with high-resolution solar photon flux data to calculate the integrated photolysis rate of HCHO to the radical (H + HCO) channel, J(HCO). Comparison with the latest NASA-JPL recommendations, reported at 1 nm wavelength resolution, suggests an increased J(HCO) of 25% at 0 degrees solar zenith angle (SZA) increasing to 33% at high SZA (80 degrees). The differences in the calculated photolysis rate compared with the current HCHO data arise, in part, from the higher wavelength resolution of the current data set and highlight the importance of using high-resolution spectroscopic

  8. Fluorescent carbon 'quantum' dots from thermochemical functionalization of carbon nanoparticles

    NASA Astrophysics Data System (ADS)

    Rednic, Monica I.; Lu, Zhuomin; Wang, Ping; LeCroy, Gregory E.; Yang, Fan; Liu, Yun; Qian, Haijun; Terec, Anamaria; Veca, L. Monica; Lu, Fushen; Sun, Ya-Ping

    2015-10-01

    Fluorescent carbon 'quantum' dots are generally obtained by deliberate chemical functionalization of carbon nanoparticles or by 'one-pot' carbonization processing. For brightly fluorescent carbon dots with optoelectronic polymers, a hybrid approach was developed to use pre-processed and selected carbon nanoparticles as precursor for surface passivation by poly(9-vinylcarbazole) (PVK) in one-pot thermochemical processing, thus taking advantage of the more controllable feature from the deliberate functionalization and also the versatility associated with the one-pot synthesis. The PVK-carbon dots were characterized by optical spectroscopy, microscopy, and other techniques. The broad applicability of the hybrid approach is discussed.

  9. Fluorescence quantum yield measurements of fluorescent proteins: a laboratory experiment for a biochemistry or molecular biophysics laboratory course.

    PubMed

    Wall, Kathryn P; Dillon, Rebecca; Knowles, Michelle K

    2015-01-01

    Fluorescent proteins are commonly used in cell biology to assess where proteins are within a cell as a function of time and provide insight into intracellular protein function. However, the usefulness of a fluorescent protein depends directly on the quantum yield. The quantum yield relates the efficiency at which a fluorescent molecule converts absorbed photons into emitted photons and it is necessary to know for assessing what fluorescent protein is the most appropriate for a particular application. In this work, we have designed an upper-level, biochemistry laboratory experiment where students measure the fluorescence quantum yields of fluorescent proteins relative to a standard organic dye. Four fluorescent protein variants, enhanced cyan fluorescent protein (ECFP), enhanced green fluorescent protein (EGFP), mCitrine, and mCherry, were used, however the methods described are useful for the characterization of any fluorescent protein or could be expanded to fluorescent quantum yield measurements of organic dye molecules. The laboratory is designed as a guided inquiry project and takes two, 4 hr laboratory periods. During the first day students design the experiment by selecting the excitation wavelength, choosing the standard, and determining the concentration needed for the quantum yield experiment that takes place in the second laboratory period. Overall, this laboratory provides students with a guided inquiry learning experience and introduces concepts of fluorescence biophysics into a biochemistry laboratory curriculum.

  10. Carbon dots with high fluorescence quantum yield: the fluorescence originates from organic fluorophores

    NASA Astrophysics Data System (ADS)

    Shi, Lei; Yang, Jian Hai; Zeng, Hai Bo; Chen, Yong Mei; Yang, Sheng Chun; Wu, Chao; Zeng, Hao; Yoshihito, Osada; Zhang, Qiqing

    2016-07-01

    In this contribution, we have shown that the organic fluorophores, 5-oxo-3,5-dihydro-2H-thiazolo [3,2-a] pyridine-3,7-dicarboxylic acid (TPDCA) and 5-oxo-3,5-dihydro-2H-thiazolo [3,2-a] pyridine-7-carboxylic acid (TPCA), are the main ingredients and fluorescence origins of N,S-CDs via systematic analyses. It inspires us to deeply analyze and understand the fluorescence origins of carbon dots with high fluorescence quantum yields, which will expand their applications.In this contribution, we have shown that the organic fluorophores, 5-oxo-3,5-dihydro-2H-thiazolo [3,2-a] pyridine-3,7-dicarboxylic acid (TPDCA) and 5-oxo-3,5-dihydro-2H-thiazolo [3,2-a] pyridine-7-carboxylic acid (TPCA), are the main ingredients and fluorescence origins of N,S-CDs via systematic analyses. It inspires us to deeply analyze and understand the fluorescence origins of carbon dots with high fluorescence quantum yields, which will expand their applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00451b

  11. Fluorescence from a quantum dot and metallic nanosphere hybrid system

    NASA Astrophysics Data System (ADS)

    Schindel, Daniel G.; Singh, Mahi R.

    2014-03-01

    We present energy absorption and interference in a quantum dot-metallic nanosphere system embedded on a dielectric substrate. A control field is applied to induce dipole moments in the nanosphere and the quantum dot, and a probe field is applied to monitor absorption. Dipole moments in the quantum dot or the metal nanosphere are induced, both by the external fields and by each other's dipole fields. Thus, in addition to direct polarization, the metal nanosphere and the quantum dot will sense one another via the dipole-dipole interaction. The density matrix method was used to show that the absorption spectrum can be split from one peak to two peaks by the control field, and this can also be done by placing the metal sphere close to the quantum dot. When the two are extremely close together, a self-interaction in the quantum dot produces an asymmetry in the absorption peaks. In addition, the fluorescence efficiency can be quenched by the addition of a metal nanosphere. This hybrid system could be used to create ultra-fast switching and sensing nanodevices.

  12. Long-Term Retention of Fluorescent Quantum Dots In Vivo

    NASA Astrophysics Data System (ADS)

    Ballou, Byron; Ernst, Lauren A.; Andreko, Susan; Eructiez, Marcel P.; Lagerholm, B. Christoffer; Waggoner, Alan S.

    Quantum dots that emit in the near-infrared can be used in vivo to follow circulation, to target the reticuloendothelial system, and to map lymphatic drainage from normal tissues and tumors. We have explored the role of surface charge and passivation by polyethylene glycol in determining circulating lifetimes and sites of deposition. Use of long polyethylene glycol polymers increases circulating lifetime. Changing surface charge can partially direct quantum dots to the liver and spleen, or the lymph nodes. Quantum dots are cleared in the order liver > spleen > bone marrow > lymph nodes. Quantum dots retained by lymph nodes maintained fluorescence for two years, suggesting either that the coating is extremely stable or that some endosomes preserve quantum dot function. We also explored migration from tumors to sentinel lymph nodes using tumor models in mice; surface charge and size make little difference to transport from tumors. Antibody and Fab-conjugates of polymer-coated quantum dots failed to target tumors in vivo, probably because of size.

  13. Use of quantum dots as mass and fluorescence labels in microarray biosensing.

    PubMed

    Finetti, Chiara; Plavisch, Lauren; Chiari, Marcella

    2016-01-15

    In this work, we demonstrate the efficacy of a Quantum Dot (QD) mass label strategy to enhance sensitivity in an interferometric technique called interferometric reflectance imaging sensor (IRIS). This biomass detection platform confers the advantage of absolute mass quantification and lower cost, easily implementable equipment. We discuss the advantages of this label when used in parallel with fluorescence detection. QDs represent a unique opportunity to improve sensitivity in both mass-label detection methods due to their large detectable mass, as well as in fluorescence detection, as they fluoresce without quenching. Streptavidin-conjugated QDs (SA-QDs) have been investigated as such a dual-role probe because of their large shape and mass, their 655nm emission peak for fluorescent detection platforms, and their robust insensitivity to photobleaching and quenching. In particular we explored their dual role in a microarrays immunoassay designed to detect antibodies against β-lactoglobulin, a common milk allergen. The SA-QDs formed a large detectable monolayer of 6.2ng/mm(2) in the saturation conditions, a mass signal corroborated by previous studies by Platt et al..

  14. Photoacoustic analysis of proteins: volumetric signals and fluorescence quantum yields.

    PubMed Central

    Kurian, E; Prendergast, F G; Small, J R

    1997-01-01

    A series of proteins has been examined using time-resolved, pulsed-laser volumetric photoacoustic spectroscopy. Photoacoustic waveforms were collected to measure heat release for calculation of fluorescence quantum yields, and to explore the possibility of photoinduced nonthermal volume changes occurring in these protein samples. The proteins studied were the green fluorescent protein (GFP); intestinal fatty acid binding protein (IFABP), and adipocyte lipid-binding protein (ALBP), each labeled noncovalently with 1-anilinonaphthalene-8-sulfonate (1,8-ANS) and covalently with 6-acryloyl-2-(dimethylamino)naphthalene (acrylodan); and acrylodan-labeled IFABP and ALBP with added oleic acid. Of this group of proteins, only the ALBP labeled with 1,8-ANS showed significant nonthermal volume changes at the beta = 0 temperature (approximately 3.8 degrees C) for the buffer used (10 mM Tris-HCI, pH 7.5) (beta is the thermal cubic volumetric expansion coefficient). For all of the proteins except for acrylodan-labeled IFABP, the fluorescence quantum yields calculated assuming simple energy conservation were anomalously high, i.e., the apparent heat signals were lower than those predicted from independent fluorescence measurements. The consistent anomalies suggest that the low photoacoustic signals may be characteristic of fluorophores buried in proteins, and that photoacoustic signals derive in part from the microenvironment of the absorbing chromophore. Images FIGURE 1 PMID:9199809

  15. Fluorescence and Bonding of Quantum Dots on DNA Origami Constructs

    NASA Astrophysics Data System (ADS)

    Kessinger, Matthew; Corrigan, Timothy; Neff, David; Norton, Michael; Concord University Collaboration; Marshall University Collaboration

    2015-03-01

    Semiconductor quantum dots (QDots) have historically been of interest to the scientific community since their creation for various applications ranging from solar energy to optical labeling. In this study, bioconjugated CdSe/ZnS core/shell QDots were synthesized and functionalized with 3-mercaptopropionic acid using both traditional ligand exchange as well as newly developed in situ functionalization techniques used to increase the quantum yield of the QDots. Their fluorescence and bonding to both gold as well as DNA origami were investigated for use in self assembled DNA constructs. It is believed that controlling the attachment and spacing of these nanoparticles on DNA origami could be used in a variety of optical labeling and sensing applications. Commercially available biotin and streptavidin functionalized quantum dots were also examined, and subject to the same experiments with gold nanoparticles as the MPA functionalized QDots.

  16. CH3O(A-X) fluorescence from photodissociation of dimethyl ether

    NASA Technical Reports Server (NTRS)

    Suto, Masako; Ye, Chao; Lee, L. C.

    1988-01-01

    The paper reports the quantitative photoabsorption and fluorescence cross sections of dimethyl ether (DME) measured with synchrotron radiation. Determinations were also made of the absolute fluorescence cross sections, the fluorescence quantum yield, and the radiative lifetime.

  17. Fluorescence quantum yield measurement in nanoparticle-fluorophore systems by thermal lens spectroscopy

    NASA Astrophysics Data System (ADS)

    Ferreira, M.; Piscitelli, V.

    2016-04-01

    Metallic nanoparticles have been used as a way to tailor the fluorescence properties like quantum yield, but regular fluorescence quantum yield measurements have to counter the reflection and dispersion of a sample for an accurate result. Thermal lens spectroscopy is a good alternative to resolve this problem because doesn't measure the fluorescence intensity but the heat generated by absorption. We studied the changes induced by silver nanoparticles, generated by laser ablation, in the fluorescence peak and quantum yield of Rhodamine B. We fund that the silver nanoparticles lowered the fluorescence peak and quenched the fluorescence of the Rhodamine B and how much is quenched also depends on its concentration.

  18. Binding phenomena and fluorescence quenching. I: Descriptive quantum principles of fluorescence quenching using a supermolecule approach

    NASA Astrophysics Data System (ADS)

    Callis, Patrik R.

    2014-12-01

    Principal aspects of fluorescence and quenching are placed on an equal footing consistent with microscopic quantum concepts familiar to all who use fluorescence in the study of association of ligands with proteins. Quenching of fluorophores involved in determination of ligand binding to proteins is described in terms of generic quantum principles using a framework in which the fluorophore and quencher are together considered a “supermolecule”. Quenching then becomes just another form of internal conversion, which in turn leads to new language for defining “dynamic” and “static” quenching, for which there exist disparate definitions. The benefit of casting quenching in this manner, and citing relevant literature, has been to expand the vocabulary and mental imagery associated with quenching.

  19. Excitation power dependent population pathways and absolute quantum yields of upconversion nanoparticles in different solvents.

    PubMed

    Würth, C; Kaiser, M; Wilhelm, S; Grauel, B; Hirsch, T; Resch-Genger, U

    2017-03-23

    The rational design of brighter upconversion nanoparticles (UCNPs) requires a better understanding of the radiationless deactivation pathways in these materials. Here, we demonstrate the potential of excitation power density (P)-dependent studies of upconversion (UC) luminescence intensities, slope factors, and absolute quantum yields (ΦUC) of popular β-NaYF4:20% Yb(3+),2% Er(3+) UCNPs of different surface chemistries in organic solvents, D2O, and water as a tool to gain deeper insight into the UC mechanism including population and deactivation pathways particularly of the red emission. Our measurements, covering a P regime of three orders of magnitude, reveal a strong difference of the P-dependence of the ratio of the green and red luminescence bands (Ig/r) in water and organic solvents and P-dependent population pathways of the different emissive energy levels of Er(3+). In summary, we provide experimental evidence for three photon processes in UCNPs, particularly for the red emission. Moreover, we demonstrate changes in the excited population dynamics via bi- and triphotonic processes dependent on the environment, surface chemistry, and P, and validate our findings theoretically.

  20. Spin-resolved quantum-dot resonance fluorescence

    NASA Astrophysics Data System (ADS)

    Nick Vamivakas, A.; Zhao, Yong; Lu, Chao-Yang; Atatüre, Mete

    2009-03-01

    Confined spins in self-assembled semiconductor quantum dots promise to serve both as probes for studying mesoscopic physics in the solid state and as stationary qubits for quantum-information science. Moreover, the excitations of self-assembled quantum dots can interact with near-infrared photons, providing an interface between stationary and `flying' qubits. Here, we report the observation of spin-selective photon emission from a resonantly driven quantum-dot transition. The Mollow triplet in the scattered photon spectrum-the hallmark of resonance fluorescence when an optical transition is driven resonantly-is presented as a natural way to spectrally isolate the photons of interest from the original driving field. We also demonstrate that the relative frequencies of the two spin-tagged photon states can be tuned independent of an applied magnetic field through the spin-selective dynamic Stark effect, induced by the same driving laser. This demonstration should be a step towards the realization of challenging tasks such as electron-spin readout, heralded single-photon generation for linear-optics quantum computing and spin-photon entanglement.

  1. pH-Responsive fluorescent graphene quantum dots for fluorescence-guided cancer surgery and diagnosis.

    PubMed

    Fan, Zetan; Zhou, Shixin; Garcia, Cesar; Fan, Louzhen; Zhou, Jiangbing

    2017-04-03

    Cancer remains a major cause of morbidity and mortality around the world. Improved cancer treatment requires enhancement of cancer diagnosis and detection. To achieve this goal, here we report a novel imaging probe, pH-responsive fluorescent graphene quantum dots (pRF-GQDs). pRF-GQDs were prepared by electrolysis of graphite rods in sodium p-toluenesulfonate acetonitrile solution. The resulting pRF-GQDs, which have minimal toxicity, display a sharp fluorescence transition between green and blue at pH 6.8, a pH matching the acidic extracellular microenvironment in solid tumors. We found that this unique fluorescence switch property allows tumors to be distinguished from normal tissues. In addition to fluorescence, pRF-GQDs also exhibit upconversion photoluminescence (UCPL). We demonstrate that the combination of UCPL and fluorescence switch enables detection of solid tumors of different origin at an early developmental stage. Therefore, pRF-GQDs have great potential to be used as a universal probe for fluorescence-guided cancer surgery and cancer diagnosis.

  2. Fluorescence quenching of CdSe quantum dots on graphene

    SciTech Connect

    Guo, Xi Tao; Hua Ni, Zhen Yan Nan, Hai; Hui Wang, Wen; Yan Liao, Chun; Zhang, Yan; Wei Zhao, Wei

    2013-11-11

    We studied systematically the fluorescence quenching of CdSe quantum dots (QDs) on graphene and its multilayers, as well as graphene oxide (GO) and reduced graphene oxide (rGO). Raman intensity of QDs was used as a quantitatively measurement of its concentration in order to achieve a reliable quenching factor (QF). It was found that the QF of graphene (∼13.1) and its multilayers is much larger than rGO (∼4.4), while GO (∼1.5) has the lowest quenching efficiency, which suggests that the graphitic structure is an important factor for quenching the fluorescence of QDs. It was also revealed that the QF of graphene is not strongly dependent on its thicknesses.

  3. Synchrotron measurements of the absolute x-ray quantum efficiency of CsI-coated microchannel plates

    NASA Astrophysics Data System (ADS)

    Rideout, Rob M.; Pearson, James F.; Fraser, George W.; Lees, John E.; Brunton, Adam N.; Bannister, N. P.; Kenter, Almus T.; Kraft, Ralph P.

    1998-11-01

    Two identical CsI-coated, low noise microchannel plate (MCP) detectors were taken to the Daresbury Synchrotron Radiation Source (SRS) to measure their quantum efficiencies over two different energy ranges - 450 eV to 1200 eV and 4.5 eV to 9.5 eV. The SRS was run in low ring current with the beam flux monitored using single wire gas proportional counters. We present accurate measurements of edge-related absolute quantum efficiency features due to the CsI photocathodes. This data will be incorporated into the calibration program of the Advanced X-ray Astrophysical Facility High Resolution Camera.

  4. Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes

    NASA Astrophysics Data System (ADS)

    Gromova, Yulia A.; Orlova, Anna O.; Maslov, Vladimir G.; Fedorov, Anatoly V.; Baranov, Alexander V.

    2013-10-01

    Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed.

  5. Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes.

    PubMed

    Gromova, Yulia A; Orlova, Anna O; Maslov, Vladimir G; Fedorov, Anatoly V; Baranov, Alexander V

    2013-10-31

    Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed.

  6. Quantum dot-containing polymer particles with thermosensitive fluorescence

    NASA Astrophysics Data System (ADS)

    Generalova, Alla N.; Oleinikov, Vladimir A.; Sukhanova, Alyona; Artemyev, Mikhail V.; Zubov, Vitaly P.; Nabiev, Igor

    2012-10-01

    In the past decades, increasing attention has been paid to the preparation of "smart" functionalized polymer particles reversibly responding to slight environmental changes, such as variations in temperature, pH, and ionic strength. The composite polymer particles consisting of a solid poly(acrolein-co-styrene) core and a poly(N-vinylcaprolactam) (PVCL) polymer shell doped with CdSe/ZnS semiconductor quantum dots (QDs) were prepared. The thermosensitive response of the composite particles was observed as a decrease in their hydrodynamic diameter upon heating above the lower critical solution temperature of the thermosensitive PVCL polymer used as a shell. Embedding QDs in the PVCL shell makes it possible to obtain particles whose fluorescence is sensitive to temperature changes. The temperature-dependent fluorescence of particles was determined by reversible variation of the distances between QDs in the PVCL shell as a result of temperature-driven conformational changes in this polymer. In addition, these particles can be used as carriers of biomolecule (e.g., bovine serum albumin, BSA) characterized by reversibly temperature-dependent fluorescence, which can serve as the basis for optical detection methods in bioassays, such as the measurement of local temperature in nanovolumes, biosensing, etc.

  7. Atom-chip based quantum gravimetry for the precise determination of absolute local gravity

    NASA Astrophysics Data System (ADS)

    Abend, S.

    2015-12-01

    We present a novel technique for the precise measurement of absolute local gravity based on cold atom interferometry. Atom interferometry utilizes the interference of matter waves interrogated by laser light to read out inertial forces. Today's generation of these devices typically operate with test mass samples, that consists of ensembles of laser cooled atoms. Their performance is limited by the velocity spread and finite-size of the test masses that impose systematic uncertainties at the level of a few μGal. Rather than laser cooled atoms we employ quantum degenerate ensembles, so called Bose-Einstein condensates, as ultra-sensitive probes for gravity. These sources offer unique properties in temperature as well as in ensemble size that will allow to overcome the current limitations with the next generation of sensors. Furthermore, atom-chip technologies offer the possibility to generate Bose-Einstein condensates in a fast and reliable way. We show a lab-based prototype that uses the atom-chip itself to retro-reflect the interrogation laser and thus serving as inertial reference inside the vacuum. With this setup it is possible to demonstrate all necessary steps to measure gravity, including the preparation of the source, spanning an interferometer as well as the detection of the output signal, within an area of 1 cm3 right below the atom-chip and to analyze relevant systematic effects. In the framework of the center of excellence geoQ a next generation device is under construction at the Institut für Quantenoptik, that will allow for in-field measurements. This device will feature a state-of-the-art atom-chip source with a high-flux of ultra-cold atoms at a repetition rate of 1-2 Hz. In cooperation with the Müller group at the Institut für Erdmessung the sensor will be characterized in the laboratory first, to be ultimately employed in campaigns to measure the Fennoscandian uplift at the level of 1 μGal. The presented work is part of the center of

  8. Effects of external fields, dimension and polarization on the resonance fluorescence of quantum dots

    NASA Astrophysics Data System (ADS)

    Vaseghi, B.; Razavi, S. M.

    2017-02-01

    In this paper simultaneous effects of external electric and magnetic fields, dimension and polarization on the resonance fluorescence spectrum and photon statistics of a spherical quantum dot with parabolic confinement are investigated. With special attention to the optical scattering processes resonance fluorescence spectrum and second-order correlation function are calculated and plotted for different external parameters. Our results show the occurrence of resonance fluorescence similar to atomic systems and considerable effects of external fields, quantum confinement and light polarization on the resonance fluorescence spectrum and second-order correlation function in the quantum dot systems. The existence of Mollow triplets and photon antibunching are strongly depend on these external agents.

  9. Fluorescence of quantum dots on e-beam patterned and DNA origami substrates

    NASA Astrophysics Data System (ADS)

    Corrigan, Timothy D.; Kessinger, Matthew; Kidd, Jesse; Neff, David; Rahman, Masudur; Norton, Michael L.

    2015-05-01

    Attachment of quantum dots or fluorescent molecules to gold nanoparticles has a variety of optical labeling and sensory applications. In this study, we use both e-beam lithography and DNA origami to examine the fluorescence enhancement of fluorescent molecules and quantum dots with a systematic approach to understanding the contribution of gold nanoparticle size and interparticle spacing. The unique design of our patterns allows us to study the effects of size and spacing of the gold nanoparticles on the enhancement of fluorescence in one quick study with constant conditions - removing undesirable effects such as differences in concentration of quantum dots or other chemistry differences that plague multiple experiments. We also discuss the fluorescence and bonding of CdSe/ZnS quantum dots to both gold as well as DNA for use in self assembled DNA constructs. Specifically, bioconjugated CdSe/ZnS core/shell quantum dots were synthesized and functionalized with MPA using both traditional ligand exchange as well as newly developed in situ functionalization techniques used to increase the quantum yield of the quantum dots. We will present fluorescent images showing results of optimal size and spacing for fluorescence as well as demonstrating attachment chemistry of the quantum dots.

  10. Fluorescence-enhanced gadolinium-doped zinc oxide quantum dots for magnetic resonance and fluorescence imaging.

    PubMed

    Liu, Yanlan; Ai, Kelong; Yuan, Qinghai; Lu, Lehui

    2011-02-01

    We report here the development of Gd-doped ZnO quantum dots (QDs) as dual modal fluorescence and magnetic resonance imaging nanoprobes. They are fabricated in a simple, versatile and environmentally friendly method, not only decreasing the difficulty and complexity, but also avoiding the increase of particle's size brought about by silica coating procedure in the synthesis of nanoprobes reported previously. These nanoprobes, with exceptionally small size and enhanced fluorescence resulting from the Gd doping, can label successfully the HeLa cells in short time and present no evidence of toxicity or adverse affect on cell growth even at the concentration up to 1 mm. These results show that such nanoprobes have low toxicity, especially in comparison with the traditional PEGylated CdSe/ZnS or CdSe/CdS QDs. In MRI studies, they exert strong positive contrast effect with a large longitudinal relaxivity (r(1)) of water proton of 16 mm(-1) s(-1). Their capability of imaging HeLa cells with MRI implies that they have great potential as MRI contrast agents. Combining the high sensitivity of fluorescence imaging with high spatial resolution of MRI, We expect that the as-prepared Gd-doped Zno QDs can provide a better reliability of the collected data and find promising applications in biological, medical and other fields.

  11. HEPES is not suitable for fluorescence detection of HClO: a novel probe for HClO in absolute PBS.

    PubMed

    Xing, Panfei; Gao, Kuo; Wang, Beng; Gao, Jian; Yan, Hui; Wen, Jia; Li, Weisi; Xu, Yongqian; Li, Hongjuan; Chen, Jianxin; Wang, Wei; Sun, Shiguo

    2016-04-11

    HEPES is not suitable for fluorescence detection of HClO because it can be oxidized by HClO. A novel probe for HClO, which can selectively and sensitively detect HClO in absolute PBS, was developed on the basis of an oxidation reaction with an azo moiety. Furthermore, it works well in live mouse imaging.

  12. Data analysis considerations in probing single quantum dot fluorescence intermittency

    NASA Astrophysics Data System (ADS)

    Krogmeier, Jeffrey R.; Hwang, Jeeseong

    2005-04-01

    The fluorescence intermittency of single, bare, CdSe/ZnS quantum dots was probed using single molecule confocal microscopy and found to demonstrate power law kinetics. Various threshold values and line fitting parameters are employed in the data analysis and their effects on the extracted power law exponents, moff and mon, are presented. The threshold is found to be critical in determining moff while having no significant effect on mon. The mean plus 2σ threshold, calculated from the background noise in the measurement, results in a more negative moff slope in comparison to the mean plus 3σ or mean plus 4σ thresholds. This is likely due to the mean plus 2σ threshold lying within the background noise outliers which mimic short on events. In contrast, the mean plus 4σ threshold is above 99.99% of the background noise while adequately below the fluorescence signal. Additionally, it is found that fitting only the ten most probable data points rather than all the data points in the log-log probability density graphs results in no significant change in moff and mon.

  13. Water-Soluble Quantum Dots for Multiphoton Fluorescence Imaging in Vivo

    NASA Astrophysics Data System (ADS)

    Larson, Daniel R.; Zipfel, Warren R.; Williams, Rebecca M.; Clark, Stephen W.; Bruchez, Marcel P.; Wise, Frank W.; Webb, Watt W.

    2003-05-01

    The use of semiconductor nanocrystals (quantum dots) as fluorescent labels for multiphoton microscopy enables multicolor imaging in demanding biological environments such as living tissue. We characterized water-soluble cadmium selenide-zinc sulfide quantum dots for multiphoton imaging in live animals. These fluorescent probes have two-photon action cross sections as high as 47,000 Goeppert-Mayer units, by far the largest of any label used in multiphoton microscopy. We visualized quantum dots dynamically through the skin of living mice, in capillaries hundreds of micrometers deep. We found no evidence of blinking (fluorescence intermittency) in solution on nanosecond to millisecond time scales.

  14. Water-soluble quantum dots for multiphoton fluorescence imaging in vivo.

    PubMed

    Larson, Daniel R; Zipfel, Warren R; Williams, Rebecca M; Clark, Stephen W; Bruchez, Marcel P; Wise, Frank W; Webb, Watt W

    2003-05-30

    The use of semiconductor nanocrystals (quantum dots) as fluorescent labels for multiphoton microscopy enables multicolor imaging in demanding biological environments such as living tissue. We characterized water-soluble cadmium selenide-zinc sulfide quantum dots for multiphoton imaging in live animals. These fluorescent probes have two-photon action cross sections as high as 47,000 Goeppert-Mayer units, by far the largest of any label used in multiphoton microscopy. We visualized quantum dots dynamically through the skin of living mice, in capillaries hundreds of micrometers deep. We found no evidence of blinking (fluorescence intermittency) in solution on nanosecond to millisecond time scales.

  15. Rigidifying Fluorescent Linkers by Metal-Organic Framework Formation for Fluorescence Blue Shift and Quantum Yield Enhancement

    SciTech Connect

    Wei, ZW; Gu, ZY; Arvapally, RK; Chen, YP; McDougald, RN; Ivy, JF; Yakovenko, AA; Feng, DW; Omary, MA; Zhou, HC

    2014-06-11

    We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal-organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 +/- 0.5%) under Ar, representing ca. 3600 cm(-1) blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity.

  16. Rigidifying Fluorescent Linkers by Metal–Organic Framework Formation for Fluorescence Blue Shift and Quantum Yield Enhancement

    SciTech Connect

    Wei, Zhangwen; Gu, Zhi-Yuan; Arvapally, Ravi K.; Chen, Ying-Pin; Ivy, Joshua F.; Yakovenko, Andrey A.; Feng, Dawei; Omary, Mohammad A.; Zhou, Hong-Cai

    2014-06-11

    We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal–organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 ± 0.5%) under Ar, representing ca. 3600 cm⁻¹ blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity.

  17. Sensitive fluorescence response of ZnSe(S) quantum dots: an efficient fluorescence probe

    NASA Astrophysics Data System (ADS)

    Saikia, K.; Deb, P.; Kalita, E.

    2013-06-01

    An efficient fluorescence probe based on ZnSe(S) alloyed quantum dots (QDs) has been reported here. The alloyed QDs were prepared through an aqueous route, where 3-mercaptopropionic acid (MPA) was employed as the effective precursor for both the sulfur source and stabilizer in the development of the alloyed system. Five-fold quantum yield (QY) enhancement was obtained for the ZnSe(S) QDs compared to the ZnSe QDs, formed in the initial stage of the refluxing process. The ultimate alloyed systems retained their high biocompatibility characteristics similar to the conventional ZnSe QDs. The photoluminescence of the ZnSe(S) QDs showed pH dependence, which was also evidenced in mammalian lymphocyte cells suspended in biological buffer over a wide pH range of 4.00-12.00. These characteristics make our prepared ZnSe(S) an efficient system for development of cell tracking, monitoring and sensing intracellular nanoprobes and devices.

  18. Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes

    PubMed Central

    2013-01-01

    Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed. PMID:24172215

  19. Glutathione-functionalized graphene quantum dots as selective fluorescent probes for phosphate-containing metabolites

    NASA Astrophysics Data System (ADS)

    Liu, Jing-Jing; Zhang, Xiao-Long; Cong, Zhong-Xiao; Chen, Zhi-Tao; Yang, Huang-Hao; Chen, Guo-Nan

    2013-02-01

    Bright blue fluorescent glutathione-functionalized graphene quantum dots (GQDs@GSH) were prepared by a one-step pyrolysis method with a fluorescence quantum yield as high as 33.6%. Futhermore, the obtained GQDs@GSH can be used as a probe to estimate the ATP level in cell lysates and human blood serum.Bright blue fluorescent glutathione-functionalized graphene quantum dots (GQDs@GSH) were prepared by a one-step pyrolysis method with a fluorescence quantum yield as high as 33.6%. Futhermore, the obtained GQDs@GSH can be used as a probe to estimate the ATP level in cell lysates and human blood serum. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr33794d

  20. Resonance fluorescence from an asymmetric quantum dot dressed by a bichromatic electromagnetic field

    NASA Astrophysics Data System (ADS)

    Kryuchkyan, G. Yu.; Shahnazaryan, V.; Kibis, O. V.; Shelykh, I. A.

    2017-01-01

    We present the theory of resonance fluorescence from an asymmetric quantum dot driven by a two-component electromagnetic field with two different frequencies, polarizations, and amplitudes (bichromatic field) in the regime of strong light-matter coupling. It follows from the elaborated theory that the broken inversion symmetry of the driven quantum system and the bichromatic structure of the driving field result in unexpected features of the resonance fluorescence, including the infinite set of Mollow triplets, the quench of fluorescence peaks induced by the dressing field, and the oscillating behavior of the fluorescence intensity as a function of the dressing field amplitude. These quantum phenomena are of general physical nature and, therefore, can take place in various double-driven quantum systems with broken inversion symmetry.

  1. Emerging applications of fluorescent nanocrystals quantum dots for micrometastases detection.

    PubMed

    Mahmoud, Wael; Sukhanova, Alyona; Oleinikov, Vladimir; Rakovich, Yury P; Donegan, John F; Pluot, Michel; Cohen, Jacques H M; Volkov, Yuri; Nabiev, Igor

    2010-02-01

    The occurrence of metastases is one of the main causes of death in many cancers and the main cause of death for breast cancer patients. Micrometastases of disseminated tumour cells and circulating tumour cells are present in more than 30% of breast cancer patients without any clinical or even histopathological signs of metastasis. Low abundance of these cell types in clinical diagnostic material dictates the necessity of their enrichment prior to reliable detection. Current micrometastases detection techniques are based on immunocytochemical and molecular methods suffering from low efficiency of tumour cells enrichment and observer-dependent interpretation. The use of highly fluorescent semiconductor nanocrystals, also known as "quantum dots" and nanocrystal-encoded microbeads tagged with a wide panel of antibodies against specific tumour markers offers unique possibilities for ultra-sensitive micrometastases detection in patients' serum and tissues. The nanoparticle-based diagnostics provides an opportunity for highly sensitive parallel quantification of specific proteins in a rapid and low-cost method, thereby providing a link between the primary tumour and the micrometastases for early diagnosis.

  2. Absolutely classical spin states

    NASA Astrophysics Data System (ADS)

    Bohnet-Waldraff, F.; Giraud, O.; Braun, D.

    2017-01-01

    We introduce the concept of "absolutely classical" spin states, in analogy to absolutely separable states of bipartite quantum systems. Absolutely classical states are states that remain classical (i.e., a convex sum of projectors on coherent states of a spin j ) under any unitary transformation applied to them. We investigate the maximal size of the ball of absolutely classical states centered on the maximally mixed state and derive a lower bound for its radius as a function of the total spin quantum number. We also obtain a numerical estimate of this maximal radius and compare it to the case of absolutely separable states.

  3. A Microfluidic Microbeads Fluorescence Assay with Quantum Dots-Bead-DNA Probe.

    PubMed

    Ankireddy, S R; Kim, Jongsung

    2016-03-01

    A microfluidic bead-based nucleic acid sensor for the detection of tumor causing N-Ras genes using quantum dots has been developed. Presently, quantum dots-bead-DNA probe based hybridization detection methods are often called as 'bead based assays' and their success is substantially influenced by the dispensing and manipulation capability of the microfluidic technology. This study reports the detection of N-Ras cancer gene by fluorescence quenching of quantum dots immobilized on the surface of polystyrene beads. A microfluidic chip was constructed in which the quantum dots-bead-DNA probes were packed in the channel. The target DNA flowed across the beads and hybridized with immobilized probe sequences. The target DNA can be detected by the fluorescence quenching of the quantum dots due to their transfer of emission energy to intercalation dye after DNA hybridization. The mutated gene also induces fluorescence quenching but with less degree than the perfectly complementary target DNA.

  4. The effect of a gas environment on the fluorescence intensity of quantum-dot composite systems

    NASA Astrophysics Data System (ADS)

    Danilov, V. V.; Khrebtovb, A. I.; Shtrom, I. V.; Tsyrlin, G. E.; Samsonenko, Yu. B.

    2016-09-01

    The fluorescence kinetics of a composite structure based on colloidal CdSe/ZnS core-shell quantum dots deposited on an array of GaAs nanowires in atmospheres of different gases is studied upon excitation by cw laser radiation. It is suggested that the fluorescence enhancement mechanism consists in the transfer of part of the vibrational energy of quantum dots to surrounding gas molecules due to inelastic collisions.

  5. Inkjet printed fluorescent nanorod layers exhibit superior optical performance over quantum dots

    NASA Astrophysics Data System (ADS)

    Halivni, Shira; Shemesh, Shay; Waiskopf, Nir; Vinetsky, Yelena; Magdassi, Shlomo; Banin, Uri

    2015-11-01

    Semiconductor nanocrystals exhibit unique fluorescence properties which are tunable in size, shape and composition. The high quantum yield and enhanced stability have led to their use in biomedical imaging and flat panel displays. Here, semiconductor nanorod based inkjet inks are presented, overcoming limitations of the commonly reported quantum dots in printing applications. Fluorescent seeded nanorods were found to be outstanding candidates for fluorescent inks, due to their low particle-particle interactions and negligible self-absorption. This is manifested by insignificant emission shifts upon printing, even in highly concentrated printed layers and by maintenance of a high fluorescence quantum yield, unlike quantum dots which exhibit fluorescence wavelength shifts and quenching effects. This behavior results from the reduced absorption/emission overlap, accompanied by low energy transfer efficiencies between the nanorods as supported by steady state and time resolved fluorescence measurements. The new seeded nanorod inks enable patterning of thin fluorescent layers, for demanding light emission applications such as signage and displays.Semiconductor nanocrystals exhibit unique fluorescence properties which are tunable in size, shape and composition. The high quantum yield and enhanced stability have led to their use in biomedical imaging and flat panel displays. Here, semiconductor nanorod based inkjet inks are presented, overcoming limitations of the commonly reported quantum dots in printing applications. Fluorescent seeded nanorods were found to be outstanding candidates for fluorescent inks, due to their low particle-particle interactions and negligible self-absorption. This is manifested by insignificant emission shifts upon printing, even in highly concentrated printed layers and by maintenance of a high fluorescence quantum yield, unlike quantum dots which exhibit fluorescence wavelength shifts and quenching effects. This behavior results from the

  6. Control of fluorescence in quantum emitter and metallic nanoshell hybrids for medical applications

    NASA Astrophysics Data System (ADS)

    Singh, Mahi R.; Guo, Jiaohan; J. Cid, José M.; De Hoyos Martinez, Jesús E.

    2017-03-01

    We study the light emission from a quantum emitter and double metallic nanoshell hybrid systems. Quantum emitters act as local sources which transmit their light efficiently due to a double nanoshell near field. The double nanoshell consists of a dielectric core and two outer nanoshells. The first nanoshell is made of a metal, and the second spacer nanoshell is made of a dielectric material or human serum albumin. We have calculated the fluorescence emission for a quantum emitter-double nanoshell hybrid when it is injected in an animal or a human body. Surface plasmon polariton resonances in the double nanoshell are calculated using Maxwell's equations in the quasi-static approximation, and the fluorescence emission is evaluated using the density matrix method in the presence of dipole-dipole interactions. We have compared our theory with two fluorescence experiments in hybrid systems in which the quantum emitter is Indocyanine Green or infrared fluorescent molecules. The outer spacer nanoshell of double metallic nanoshells consists of silica and human serum albumin with variable thicknesses. Our theory explains the enhancement of fluorescence spectra in both experiments. We find that the thickness of the spacer nanoshell layer increases the enhancement when the fluorescence decreases. The enhancement of the fluorescence depends on the type of quantum emitter, spacer layer, and double nanoshell. We also found that the peak of the fluorescence spectrum can be shifted by changing the shape and the size of the nanoshell. The fluorescence spectra can be switched from one peak to two peaks by removing the degeneracy of excitonic states in the quantum emitter. Hence, using these properties, one can use these hybrids as sensing and switching devices for applications in medicine.

  7. Excitation-emission spectra and fluorescence quantum yields for fresh and aged biogenic secondary organic aerosols.

    PubMed

    Lee, Hyun Ji Julie; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A

    2013-06-04

    Certain biogenic secondary organic aerosols (SOA) become absorbent and fluorescent when exposed to reduced nitrogen compounds such as ammonia, amines, and their salts. Fluorescent SOA may potentially be mistaken for biological particles by detection methods relying on fluorescence. This work quantifies the spectral distribution and effective quantum yields of fluorescence of water-soluble SOA generated from two monoterpenes, limonene and α-pinene, and two different oxidants, ozone (O3) and hydroxyl radical (OH). The SOA was generated in a smog chamber, collected on substrates, and aged by exposure to ∼100 ppb ammonia in air saturated with water vapor. Absorption and excitation-emission matrix (EEM) spectra of aqueous extracts of aged and control SOA samples were measured, and the effective absorption coefficients and fluorescence quantum yields (∼0.005 for 349 nm excitation) were determined from the data. The strongest fluorescence for the limonene-derived SOA was observed for λexcitation = 420 ± 50 nm and λemission = 475 ± 38 nm. The window of the strongest fluorescence shifted to λexcitation = 320 ± 25 nm and λemission = 425 ± 38 nm for the α-pinene-derived SOA. Both regions overlap with the EEM spectra of some of the fluorophores found in primary biological aerosols. Despite the low quantum yield, the aged SOA particles may have sufficient fluorescence intensities to interfere with the fluorescence detection of common bioaerosols.

  8. Excitation-emission spectra and fluorescence quantum yields for fresh and aged biogenic secondary organic aerosols

    SciTech Connect

    Lee, Hyun Ji; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A.

    2013-05-10

    Certain biogenic secondary organic aerosols (SOA) become absorbent and fluorescent when exposed to reduced nitrogen compounds such as ammonia, amines and their salts. Fluorescent SOA may potentially be mistaken for biological particles by detection methods relying on fluorescence. This work quantifies the spectral distribution and effective quantum yields of fluorescence of SOA generated from two monoterpenes, limonene and a-pinene, and two different oxidants, ozone (O3) and hydroxyl radical (OH). The SOA was generated in a smog chamber, collected on substrates, and aged by exposure to ~100 ppb ammonia vapor in air saturated with water vapor. Absorption and excitation-emission matrix (EEM) spectra of aqueous extracts of aged and control SOA samples were measured, and the effective absorption coefficients and fluorescence quantum yields (~0.005 for 349 nm excitation) were determined from the data. The strongest fluorescence for the limonene-derived SOA was observed for excitation = 420+- 50 nm and emission = 475 +- 38 nm. The window of the strongest fluorescence shifted to excitation = 320 +- 25 nm and emission = 425 +- 38 nm for the a-pinene-derived SOA. Both regions overlap with the excitation-emission matrix (EEM) spectra of some of the fluorophores found in primary biological aerosols. Our study suggests that, despite the low quantum yield, the aged SOA particles should have sufficient fluorescence intensities to interfere with the fluorescence detection of common bioaerosols.

  9. Effect of silver nano particles on the fluorescence quantum yield of Rhodamine 6G determined using dual beam thermal lens method.

    PubMed

    Santhi, A; Umadevi, M; Ramakrishnan, V; Radhakrishnan, P; Nampoori, V P N

    2004-04-01

    Nano structured noble metals have very important applications in diverse fields as photovoltaics, catalysis, electronic and magnetic devices, etc. Here, we report the application of dual beam thermal lens technique for the determination of the effect of silver sol on the absolute fluorescence quantum yield (FQY) of the laser dye rhodamine 6G. A 532 nm radiation from a diode pumped solid state laser was used as the excitation source. It has been observed that the presence of silver sol decreases the fluorescence quantum efficiency. This is expected to have a very important consequence in enhancing Raman scattering which is an important spectrochemical tool that provides information on molecular structures. We have also observed that the presence of silver sol can enhance the thermal lens signal which makes the detection of the signal easier at any concentration.

  10. Selective recognition of Glutamate based on fluorescence enhancement of graphene quantum dot

    NASA Astrophysics Data System (ADS)

    Hosseini, Morteza; Khabbaz, Hossein; Dezfoli, Amin Shiralizadeh; Ganjali, Mohammad Reza; Dadmehr, Mehdi

    2015-02-01

    Graphene quantum dots (GQDs) have successfully been utilized as an efficient nano-sized fluorescence chemosensor to detect selectively Glutamate (Glu) in Tris-HCl buffer solution (pH = 9). The fluorescence emission spectrum of graphene quantum dots was at about 430 nm. The study showed that fluorescence intensity of the quantum dot gradually enhanced with increase in concentration of Glutamate and any change in fluorescence intensity was directly proportional to the concentration of Glutamate. Under optimum conditions, the linear range for the detection of Glutamate was 1.6 × 10-7 M to 1.0 × 10-5 M with a detection limit of 5.2 × 10-8 M. The sensor showed high selectivity toward Glutamate in comparison with other amino acids.

  11. Shielding of quantum dots using diblock copolymers: implementing copper catalyzed click chemistry to fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

    Merkl, Jan-Philip; Ostermann, Johannes; Schmidtke, Christian; Kloust, Hauke; Eggers, Robin; Feld, Artur; Wolter, Christopher; Kreuziger, Anna-Marlena; Flessau, Sandra; Mattoussi, Hedi; Weller, Horst

    2014-03-01

    We describe the design and optimization of an amphiphilic diblock copolymer and its use to provide surface functionalization of colloidal semiconductor nanoparticles (quantum dots, QDs). This polymer coating promotes hydrophilicity of the nanocrystals while providing numerous functional groups ideally suited for biofunctionalization of the QDs using copper-catalyzed azide alkyne Husigen 1,3-cyloaddition (i.e., cupper catalyzed "click" reaction). Copper ions are known to quench the fluorescence of QDs in solution. Thus effective shielding of the nanocrystal surface is essential to apply copper-catalyzed reactions to luminescent QDs without drastically quenching their emission. We have applied a strategy based on micellar encapsulation within poly(isoprene-block- ethylene oxide) diblock-copolymers (PI-b-PEO), where three critical factors promote and control the effectiveness of the shielding of copper ion penetration: 1) The excess of PI-b-PEO, 2) the size of PI-b-PEO and 3) insertion of an additional PS-shell grown via seeded emulsion polymerization (EP) reaction. Due to the amphiphilic character of the block-copolymer, this approach provides a shielding layer surrounding the particles, preventing metal ions from reaching the QD surfaces and maintaining high photoluminescence. The effective shielding allowed the use of copper-catalyzed azide-alkyne 1,3-cycloaddition (CuAAC) to hydrophilic and highly fluorescent QDs, opening up great possibilities for the bio functionalization of QDs.

  12. Control of photoinduced fluorescence enhancement of colloidal quantum dots using metal oxides

    NASA Astrophysics Data System (ADS)

    Sadeghi, Seyed M.; Wing, Waylin J.; Patty, Kira; Campbell, Quinn

    2015-10-01

    It is well known that irradiation of colloidal quantum dots can dramatically enhance their emission efficiencies, leading to so-called photoinduced fluorescence enhancement (PFE). This process is the result of the photochemical and photophysical properties of quantum dots and the way they interact with the environment in the presence of light. It has been shown that such properties can be changed significantly using metal oxides. Using spectroscopic techniques, in this paper we investigate emission of different types of quantum dots (with and without shell) in the presence of metal oxides with opposing effects. We observed significant increase of PFE when quantum dots are deposited on about one nanometer of aluminum oxide, suggesting such oxide can profoundly increase quantum yield of such quantum dots. On the other hand, copper oxide can lead to significant suppression of emission of quantum dots, making them nearly completely dark instantly.

  13. Highly luminescent N-doped carbon quantum dots as an effective multifunctional fluorescence sensing platform.

    PubMed

    Qian, Zhaosheng; Ma, Juanjuan; Shan, Xiaoyue; Feng, Hui; Shao, Linxiang; Chen, Jianrong

    2014-02-17

    The doping of carbon quantum dots with nitrogen provides a promising direction to improve fluorescence performance and broaden their applications in sensing systems. Herein we report a one-pot solvothermal synthesis of N-doped carbon quantum dots (NCQDs) and the synthesis of a series of NCQDs with different nitrogen contents. The as-prepared NCQDs were compared with carbon quantum dots (CQDs); the introduction of nitrogen atoms largely increased the quantum yield of NCQDs and highest emission efficiency is up to 36.3 %. The fluorescence enhancement may originate from more polyaromatic structures induced by incorporated nitrogen atoms and protonation of nitrogen atoms on dots. It was found that NCQDs can act as a multifunctional fluorescence sensing platform because they can be used to detect pH values, Ag(I), and Fe(III) in aqueous solution. The fluorescence intensity of NCQDs is inversely proportional to pH values across a broad range from 5.0 to 13.5, which indicates that NCQDs can be devised as an effective pH indicator. Selective detection of Ag(I) and Fe(III) was achieved based on their distinctive fluorescence influence because Ag(I) can significantly enhance the fluorescence whereas Fe(III) can greatly quench the fluorescence. The quantitative determination of Ag(I) can be accomplished with NCQDs by using the linear relationship between fluorescence intensity of NCQDs and concentration of Ag(I). The sensitive detection of H2O2 was developed by taking advantage of the distinct quenching ability of Fe(III) and Fe(II) toward the fluorescence of NCQDs. Cellular toxicity test showed NCQDs still retain low toxicity to cells despite the introduction of a great deal of nitrogen atoms. Moreover, bioimaging experiments demonstrated that NCQDs have stronger resistance to photobleaching than CQDs and more excellent fluorescence labeling performance.

  14. Structure-guided evolution of cyan fluorescent proteins towards a quantum yield of 93%

    PubMed Central

    Goedhart, Joachim; von Stetten, David; Noirclerc-Savoye, Marjolaine; Lelimousin, Mickaël; Joosen, Linda; Hink, Mark A.; van Weeren, Laura; Gadella, Theodorus W.J.; Royant, Antoine

    2012-01-01

    Cyan variants of green fluorescent protein are widely used as donors in Förster resonance energy transfer experiments. The popular, but modestly bright, Enhanced Cyan Fluorescent Protein (ECFP) was sequentially improved into the brighter variants Super Cyan Fluorescent Protein 3A (SCFP3A) and mTurquoise, the latter exhibiting a high-fluorescence quantum yield and a long mono-exponential fluorescence lifetime. Here we combine X-ray crystallography and excited-state calculations to rationalize these stepwise improvements. The enhancement originates from stabilization of the seventh β-strand and the strengthening of the sole chromophore-stabilizing hydrogen bond. The structural analysis highlighted one suboptimal internal residue, which was subjected to saturation mutagenesis combined with fluorescence lifetime-based screening. This resulted in mTurquoise2, a brighter variant with faster maturation, high photostability, longer mono-exponential lifetime and the highest quantum yield measured for a monomeric fluorescent protein. Together, these properties make mTurquoise2 the preferable cyan variant of green fluorescent protein for long-term imaging and as donor for Förster resonance energy transfer to a yellow fluorescent protein. PMID:22434194

  15. Redox heme-proteins mediated fluorescence of CdSe/ZnS quantum dots.

    PubMed

    Qin, Lixia; He, Luwei; Ji, Congcong; Li, Xiangqing; Kang, Shi-Zhao; Mu, Jin

    2014-04-05

    The redox properties of cytochrome c (Cyt c), hemoglobin (Hb) and myoglobin (Mb) were studied based on electrostatic interactions between Thioglycolic acid (TGA) capped CdSe/ZnS quantum dots (QDs) and proteins. Results indicated that only Cyt c quenched the fluorescence of the QDs at pH>8.0. Under the optimized conditions, a significant fluorescence recovery of the QDs' system was observed when the reduced form of Cyt c incubated with TGA capped QDs, however, the reduced state of Hb and Mb resulted in a more fluorescence quenching on the same size of QDs. Interestingly, the fluorescence changes of QDs-proteins could be switched by modulating the redox potentials of proteins-attached QDs. Moreover, only the oxidized Cyt c form was reduced by the generated O2(-) that significantly enhanced the fluorescence of the QDs' system, which was also demonstrated by fluorescence imaging in HeLa cells.

  16. A type of novel fluorescent magnetic carbon quantum dots for cells imaging and detection.

    PubMed

    Su, Xi; Xu, Yi; Che, Yulan; Liao, Xin; Jiang, Yan

    2015-12-01

    A new type of multifunctional fluorescent magnetic carbon quantum dots SPIO@CQDs(n) ([superparamagnetic iron oxide nanoparticles (SPIO), carbon quantum dots, (CQDs)]) with magnetic and fluorescence properties was designed and prepared through layer-by-layer self-assembly method. The as-synthesized SPIO@CQDs(n) exhibited different emission colors including blue, green, and red when they were excited at different excitation wavelengths, and its fluorescent intensity increased as the increase of CQD layer (n). SPIO@CQDs(n) with quite low toxicity could mark cytoplasm with fluorescence by means of nonimmune markers. The mixture sample of liver cells L02 and hepatoma carcinoma cells HepG2 was taken as an example, and HepG2 cells were successfully separated and detected effectively by SPIO@CQDs(n), with a separation rate of 90.31%. Importantly, the designed and prepared SPIO@CQDs( n ) are certified to be wonderful biological imaging and magnetic separation regents.

  17. Charge-driven feedback loop in the resonance fluorescence of a single quantum dot

    NASA Astrophysics Data System (ADS)

    Merkel, B.; Kurzmann, A.; Schulze, J.-H.; Strittmatter, A.; Geller, M.; Lorke, A.

    2017-03-01

    We demonstrate a feedback loop that manifests itself in a strong hysteresis and bistability of the exciton resonance fluorescence signal. Field ionization of photogenerated quantum dot excitons leads to the formation of a charged interface layer that drags the emission line along over a frequency range of more than 30 GHz . These measurements are well described by a rate equation model. With a time-resolved resonance fluorescence measurement we determined the buildup times for the hole gas in the orders of milliseconds. This internal charge-driven feedback loop could be used to reduce the spectral wandering in the emission spectra of single self-assembled quantum dots.

  18. Fluorescence assay based on aptamer-quantum dot binding to Bacillus thuringiensis spores.

    PubMed

    Ikanovic, Milada; Rudzinski, Walter E; Bruno, John G; Allman, Amity; Carrillo, Maria P; Dwarakanath, Sulatha; Bhahdigadi, Suneetha; Rao, Poornima; Kiel, Johnathan L; Andrews, Carrie J

    2007-03-01

    A novel assay was developed for the detection of Bacillus thuringiensis (BT) spores. The assay is based on the fluorescence observed after binding an aptamer-quantum dot conjugate to BT spores. The in vitro selection and amplification technique called SELEX (Systematic Evolution of Ligands by EXponential enrichment) was used in order to identify the DNA aptamer sequence specific for BT. The 60 base aptamer was then coupled to fluorescent zinc sulfide-capped, cadmium selenide quantum dots (QD). The assay is semi-quantitative, specific and can detect BT at concentrations of about 1,000 colony forming units/ml.

  19. Easy Absolute Values? Absolutely

    ERIC Educational Resources Information Center

    Taylor, Sharon E.; Mittag, Kathleen Cage

    2015-01-01

    The authors teach a problem-solving course for preservice middle-grades education majors that includes concepts dealing with absolute-value computations, equations, and inequalities. Many of these students like mathematics and plan to teach it, so they are adept at symbolic manipulations. Getting them to think differently about a concept that they…

  20. Fluorescence Assay Based on Aptamer-Quantum Dot Binding to Bacillus thuringiensis Spores

    DTIC Science & Technology

    2007-01-01

    Binding to Bacillus thuringiensis 5a. CONTRACT NUMBER N/A Spores 5b. GRANT NUMBER N/A 5c. PROGRAM ELEMENT NUMBER 62202F 6. AUTHOR(S) Milada...assay was developed for the detection of Bacillus thuringiensis (BT) spores. The assay is based on the fluorescence observed after binding an aptamer...units/ml. 15. SUBJECT TERMS Bacillus thuringiensis , Aptamer, Quantum dots, SELEX, Fluorescence 16. SECURITY CLASSIFICATION OF: Unclassified U

  1. Highly fluorescent magnetic quantum dotprobe with superior colloidal stability

    NASA Astrophysics Data System (ADS)

    Basiruddin, Sk; Saha, Arindam; Sarkar, Rupa; Majumder, Moumita; Jana, Nikhil R.

    2010-12-01

    A magnetic quantum dot (MQD) based cellular nanoprobe, composed of a magnetic oxidenanoparticle component and a quantum dot component, has been synthesized and used for both imaging and separation. The successful synthesis is based on a reverse micelle based polyacrylate coating in the presence of component nanoparticles, followed by their functionalization viaconjugation chemistry.A magnetic quantum dot (MQD) based cellular nanoprobe, composed of a magnetic oxidenanoparticle component and a quantum dot component, has been synthesized and used for both imaging and separation. The successful synthesis is based on a reverse micelle based polyacrylate coating in the presence of component nanoparticles, followed by their functionalization viaconjugation chemistry. Electronic supplementary information (ESI) available: Details of the experimental procedure, MQD characterization via magnetic measurements, EDX, TEM, FTIR, fluorescamine test and control celllabeling data. See DOI: 10.1039/c0nr00501k

  2. Bright Multicolor Bandgap Fluorescent Carbon Quantum Dots for Electroluminescent Light-Emitting Diodes.

    PubMed

    Yuan, Fanglong; Wang, Zhibin; Li, Xiaohong; Li, Yunchao; Tan, Zhan'ao; Fan, Louzhen; Yang, Shihe

    2017-01-01

    Multicolor bandgap fluorescent carbon quantum dots (MCBF-CQDs) from blue to red with quantum yield up to 75% are synthesized using a solvothermal method. For the first time, monochrome electroluminescent light-emitting diodes (LEDs) with MCBF-CQDs directly as an active emission layer are fabricated. The maximum luminance of blue LEDs reaches 136 cd m(-2) , which is the best performance for CQD-based monochrome electroluminescent LEDs.

  3. A novel turn-on fluorescent strategy for sensing ascorbic acid using graphene quantum dots as fluorescent probe.

    PubMed

    Liu, Hua; Na, Weidan; Liu, Ziping; Chen, Xueqian; Su, Xingguang

    2017-06-15

    In this paper, a facile and rapid fluorescence turn-on assay for fluorescent detection of ascorbic acid (AA) was developed by using the orange emission graphene quantum dots (GQDs). In the presence of horse radish peroxidase (HRP) and hydrogen peroxide (H2O2), catechol can be oxidized by hydroxyl radicals and converted to o-benzoquinone, which can significantly quench the fluorescence of GQDs. However, when AA present in the system, it can consume part of H2O2 and hydroxyl radicals to inhibit the generation of o-benzoquinone, resulting in fluorescence recovery. Under the optimized experimental conditions, the fluorescence intensity was linearly correlated with the concentration of H2O2 in the range of 3.33-500µM with a detection limit of 1.2µM. The linear detection for AA was in the range from 1.11 to 300µM with a detection limit of 0.32µM. The proposed method was applied to the determination of AA in human serum samples with satisfactory results.

  4. Correlative fluorescence and electron microscopy of quantum dot labeled proteins on whole cells in liquid.

    PubMed

    Peckys, Diana B; Dukes, Madeline J; de Jonge, Niels

    2014-01-01

    Correlative fluorescence microscopy and scanning transmission electron microscopy (STEM) of cells fully immersed in liquid is a new methodology with many application areas. Proteins, in live cells immobilized on microchips, are labeled with fluorescent quantum dot (QD) nanoparticles. In this protocol, the epidermal growth factor receptor (EGFR) is labeled. The cells are fixed after a selected labeling time, for example, 5 min as needed to form EGFR dimers. The microchip with cells is then imaged with fluorescence microscopy. Thereafter, the microchip with the labeled cells and one with a spacer are assembled in a special microfluidic device and imaged with STEM.

  5. Functional surface engineering of quantum dot hydrogels for selective fluorescence imaging of extracellular lactate release.

    PubMed

    Zhang, Xiaomeng; Ding, Shushu; Cao, Sumei; Zhu, Anwei; Shi, Guoyue

    2016-06-15

    Selective and sensitive detection of extracellular lactate is of fundamental significance for studying the metabolic alterations in tumor progression. Here we report the rational design and synthesis of a quantum-dot-hydrogel-based fluorescent probe for biosensing and bioimaging the extracellular lactate. By surface engineering the destabilized quantum dot sol with Nile Blue, the destabilized Nile-Blue-functionalized quantum dot sol cannot only self-assemble forming quantum dot hydrogel but also monitor lactate in the presence of nicotinamide adenine dinucleotide cofactor and lactate dehydrogenase through fluorescence resonance energy transfer. Notably, the surface engineered quantum dot hydrogel show high selectivity toward lactate over common metal ions, amino acids and other small molecules that widely coexist in biological system. Moreover, the destabilized Nile-Blue-functionalized quantum dots can encapsulate isolated cancer cells when self-assembled into a hydrogel and thus specifically detect and image the extracellular lactate metabolism. By virtue of these properties, the functionalized quantum dot hydrogel was further successfully applied to monitor the effect of metabolic agents.

  6. Light propagation and fluorescence quantum yields in liquid scintillators

    NASA Astrophysics Data System (ADS)

    Buck, C.; Gramlich, B.; Wagner, S.

    2015-09-01

    For the simulation of the scintillation and Cherenkov light propagation in large liquid scintillator detectors a detailed knowledge about the absorption and emission spectra of the scintillator molecules is mandatory. Furthermore reemission probabilities and quantum yields of the scintillator components influence the light propagation inside the liquid. Absorption and emission properties are presented for liquid scintillators using 2,5-Diphenyloxazole (PPO) and 4-bis-(2-Methylstyryl)benzene (bis-MSB) as primary and secondary wavelength shifter. New measurements of the quantum yields for various aromatic molecules are shown.

  7. A Brief History of Fluorescence and Phosphorescence before the Emergence of Quantum Theory

    ERIC Educational Resources Information Center

    Valeur, Bernard; Berberan-Santos, Mario N.

    2011-01-01

    Fluorescence and phosphorescence are two forms of photoluminescence used in modern research and in practical applications. The early observations of these phenomena, before the emergence of quantum theory, highlight the investigation into the mechanism of light emission. In contrast to incandescence, photoluminescence does not require high…

  8. Charge Effect on the Quantum Dots-Peptide Self-Assembly Using Fluorescence Coupled Capillary Electrophoresis.

    PubMed

    Wang, Jianhao; Li, Jingyan; Teng, Yiwan; Bi, Yanhua; Hu, Wei; Li, Jinchen; Wang, Cheli; Qiu, Lin; Jiang, Pengju

    2016-04-01

    We present a molecular characterization of metal-affinity driven self-assembly between CdSe-ZnS quantum dots and a series of hexahistidine peptides with different charges. In particular, we uti- lized fluorescence coupled capillary electrophoresis to test the self-assembly process of quantum dots with peptides in solution. Four peptides with different charges can be efficiently separated by fluorescence coupled capillary electrophoresis. The migration time appeared to be influenced by the charges of the peptide. In addition, the kinetics of self-assembly process of quantum dots with one of the peptides manifested a bi-phasic kinetics followed by a saturating stage. This work revealed that there exist two types of binding sites on the surface of quantum dots for peptide 1: one type termed "high priority" binding site and a "low priority" site which is occupied after the first binding sites are fully occupied. The total self-assembly process finishes in solution within 80 s. Our work represents the systematic investigation of the details of self-assembly kinetics utilizing high-resolution fluorescence coupled capillary electrophoresis. The charge effect of peptide coating quantum dots provides a new way of preparing bioprobes.

  9. Fluoroimmunoassay for antigen based on fluorescence quenching between quantum dots and gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Huang, Peng; Wang, Kan; Pandoli, Omar; Zhang, Xueqing; Gao, Feng; Shao, Jun; You, Xiaogang; He, Rong; Song, Hua; Cui, Daxiang

    2010-11-01

    A unique, sensitive, and highly specific fluoroimmunoassay system for antigen detection using gold and quantum dot nanoparticles has been developed. The assay is based on the fluorescence quenching of quantum dots caused by gold nanoparticles coated with antibody. To demonstrate its analytical capabilities, the CdTe quantum dots were coated with anti-HBsAg monoclonal antibodies (QDs-MAb1) and gold nanoparticles coated with another anti-HBsAg monoclonal antibodies (GNPs-MAb2) which specifically bound with HBsAg could sandwich the HBsAg captured by the immunoreactions. The sandwich-type immunocomplex was formed and the fluorescence intensity of quantum dots was measured. The results showed that the fluorescence intensity of quantum dots at 570 nm was negative linear proportional to the HBsAg concentration logarithm, and the limit of detection of the HBsAg was 0.928 ng/mL. This new system can be extended to detect target molecules with matched antibodies and has broad potential applications in immunoassay and disease diagnosis.

  10. Do the cations in clay and the polymer matrix affect quantum dot fluorescent properties?

    PubMed

    Wei, Wenjun; Liu, Cui; Liu, Jiyan; Liu, Xueqing; Zou, Linling; Cai, Shaojun; Shi, Hong; Cao, Yuan-Cheng

    2016-06-01

    This paper studied the effects of cations and polymer matrix on the fluorescent properties of quantum dots (QDs). The results indicated that temperature has a greater impact on fluorescence intensity than clay cations (mainly K(+) and Na(+) ). Combined fluorescence lifetime and steady-state spectrometer tests showed that QD lifetimes all decreased when the cation concentration was increased, but the quantum yields were steady at various cation concentrations of 0, 0.05, 0.5 and 1 M. Poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA) and diepoxy resin were used to study the effects of polymers on QD lifetime and quantum yield. The results showed that the lifetime for QDs 550 nm in PEO and PVA was 17.33 and 17.12 ns, respectively; for the epoxy resin, the lifetime was 0.74 ns, a sharp decrease from 24.47 ns. The quantum yield for QDs 550 nm changed from 34.22% to 7.45% and 7.81% in PEO and PVA, respectively; for the epoxy resin the quantum yield was 2.25%. QDs 580 nm and 620 nm showed the same results as QDs 550 nm. This study provides useful information on the design, synthesis and application of QDs-polymer luminescent materials. Copyright © 2015 John Wiley & Sons, Ltd.

  11. Investigation of pH-dependent photophysical properties of quantum nanocrystals by fluorescence correlation spectroscopy.

    PubMed

    Oura, Makoto; Yamamoto, Johtaro; Jin, Takashi; Kinjo, Masataka

    2017-01-23

    Quantum dot (QD) and quantum rod (QR) nanocrystals are widely used non-organic nanocrystals. Their strong fluorescence and photostability make them suitable for biomedical imaging applications. However, their pH-dependence and antibunching properties have not been studied much, especially in aqueous conditions. In this report, we used fluorescence correlation spectroscopy (FCS) with high temporal resolution to demonstrate that the fluorescent blinking and antibunching of QDs/QRs can be changed by varying the pH of their solutions. Furthermore, herein, we reported the relationship between the aggregation and antibunching relaxation time of QDs/QRs for the first time. The findings of this study suggest that FCS can be used to discover novel environmental indicators via observing nanosecond and microsecond phenomena.

  12. Fluorescence lifetimes and quantum yields of rhodamine derivatives: new insights from theory and experiment.

    PubMed

    Savarese, Marika; Aliberti, Anna; De Santo, Ilaria; Battista, Edmondo; Causa, Filippo; Netti, Paolo A; Rega, Nadia

    2012-07-19

    Although lifetimes and quantum yields of widely used fluorophores are often largely characterized, a systematic approach providing a rationale of their photophysical behavior on a quantitative basis is still a challenging goal. Here we combine methods rooted in the time-dependent density functional theory and fluorescence lifetime imaging microscopy to accurately determine and analyze fluorescence signatures (lifetime, quantum yield, and band peaks) of several commonly used rhodamine and pyronin dyes. We show that the radiative lifetime of rhodamines can be correlated to the charge transfer from the phenyl toward the xanthene moiety occurring upon the S(0) ← S(1) de-excitation, and to the xanthene/phenyl relative orientation assumed in the S(1) minimum structure, which in turn is variable upon the amino and the phenyl substituents. These findings encourage the synergy of experiment and theory as unique tool to design finely tuned fluorescent probes, such those conceived for modern optical sensors.

  13. Cyclodextrin capped CdTe quantum dots as versatile fluorescence sensors for nitrophenol isomers.

    PubMed

    Zhang, Zhixing; Zhou, Jie; Liu, Yun; Tang, Jian; Tang, Weihua

    2015-12-14

    Cyclodextrin (CD) capped CdTe quantum dots (QDs) were prepared with uniform dimension (average diameter ∼5 nm) and high quantum yield (ca. 65%). By taking advantage of the inclusion complexation of CD, β-CD-CdTe QDs exhibited strong fluorescence quenching in a linear relationship with the concentration of o-, m- and p-nitrophenol in the range of 20-100 μM. The detection limit reached 0.05 μM for o-/p-nitrophenol and 0.3 μM for m-nitrophenol. The fluorescence decay study revealed the stabilization effect of CD covering on CdTe QDs and fine-tuning of the fluorescence for selective ultrasensitive detection of nitrophenol isomers.

  14. Fluorescence quantum yield of Yb3+-doped tellurite glasses determined by thermal lens spectroscopy

    NASA Astrophysics Data System (ADS)

    Lima, S. M.; Souza, A. K. R.; Langaro, A. P.; Silva, J. R.; Costa, F. B.; Moraes, J. C. S.; Figueiredo, M. S.; Santos, F. A.; Baesso, M. L.; Nunes, L. A. O.; Andrade, L. H. C.

    2017-01-01

    In this work, the combination of three different thermal lens spectroscopic methodologies was used to better determine the fluorescence quantum yield and to observe the concentration quenching in Yb3+-doped binary tellurite glasses (in mol%, 80TeO2 - 20Li2O and 80TeO2 - 20WO3). The samples were synthesized by the conventional melt-quenching method and then studied using optical spectroscopy and thermal lens spectroscopy (TLS). These characterizations enabled investigation of the radiative and nonradiative processes involved in the ytterbium doped systems. High fluorescence quantum yield was obtained for low Yb3+ doping (>90%), and in both glasses the Yb3+ presented concentration quenching mainly caused by impurities, host-ion interaction and OH- vibrations. The observations suggested that there is a possibility of doping the glasses with higher Yb concentration (>1.6 × 1021 ions/cm3) with low reduction of the quantum yield.

  15. Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host.

    PubMed

    Lukishova, Svetlana G; Bissell, Luke J; Winkler, Justin; Stroud, C R

    2012-04-01

    Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.

  16. The inhibition of fluorescence resonance energy transfer between quantum dots for glucose assay.

    PubMed

    Hu, Bo; Zhang, Li-Pei; Chen, Mei-Ling; Chen, Ming-Li; Wang, Jian-Hua

    2012-02-15

    Fluorescence resonance energy transfer (FRET) between two quantum dots of different sizes causes fluorescence quenching. Hereby a binding site pre-blocking approach is proposed to avoid this effect. Pre-binding of glucose on the donor occupies the binding sites and thus blocks resonance energy transfer between the two quantum dots, protecting the fluorescence from being quenched. A glucose assay is developed based on this approach. The glucose content is correlated with the fluorescence difference in the absence and in the presence of glucose. In practice, Green QDs-Con A conjugates are used as donors and Red QDs-NH(2)-glu conjugates as acceptors to form FRET system. The inhibition of fluorescence quenching is then measured in the presence of glucose. A linear calibration graph is achieved within 0.1-2.0 mmolL(-1), along with a detection limit of 0.03 mmolL(-1) and a RSD of 2.1% (1.0 mmolL(-1)). 91-105% of glucose in serum and urine samples is recovered. It is worth mentioning that the present glucose assay approach also generates a fluorescence chromatic difference imaging, and the color display clearly identifies the glucose contents by visual detection with a distinguishing ability of ca. 0.5 mmolL(-1). The present approach can potentially be used for the clinical determination of glucose in biological samples which can be further developed into a glucose sensor.

  17. Strategy for high recovery of fluorescence from quencher assembled quantum-dot donor

    NASA Astrophysics Data System (ADS)

    Kim, Joong Hyun; Ozkan, Mihrimah

    2014-05-01

    We fabricated 1.4 nm nanogold and molecular dark quencher assembled quantum dot for estimating their performances in a target specific conformal changing molecular event. For the assembling, we immobilized each acceptor linked molecular beacons using interaction between biotin at molecular beacon and streptavidins on quantum dot. Through optical analysis of the purified hybrids of the acceptors and quantum dots, we could estimate numbers of the assembled acceptors per quantum dot and their efficiency of energy transfer depending on conformal changes of molecular beacons. We obtained maximum 95 % and 78% of energy transfer efficiency with 17 metallic nanocrystals and 41 black hole quencher 2, the molecular dark quencher per single quantum dote, respectively. Molecular beacons form linear helix from a hair-pin structure by hybridizing with complementary DNA. In the presence of target DNA, energy transfer efficiency of the organic quencher was 22 % while only 2 % decreased efficiency was obtained with the nanogold, indicating higher fluorescence recovery with the ordinary organic quencher. Considering the relatively low assembled number and the large size, a steric hindrance might be attributed to the low fluorescence recovery. Since the energy transfer efficiency obtained with the nanogold at a fixed distance is high enough, it would be still effective to apply nanogold a system, where nanogold is removed permanently from quantum dots.

  18. Absolute Doppler shift calibration of laser induced fluorescence signals using optogalvanic measurements in a hollow cathode lamp

    NASA Technical Reports Server (NTRS)

    Ruyten, Wilhelmus M.; Keefer, Dennis

    1992-01-01

    The paper investigates the use of optogalvanic (OG) measurements on the neutral 3P1 and 3P2 levels of argon in a hollow cathode lamp for the purpose of calibrating Doppler shifts of laser-induced fluorescence signals from an arcjet plume. It is shown that, even with non-Doppler-free OG detection, accuracy to better than 10 MHz is possible but that, depending on the experiment geometry, corrections of 10-35 MHz may be necessary to offset small axial drift velocities of neutral atoms in the hollow cathode lamp.

  19. Probing dynamic fluorescence properties of single and clustered quantum dots toward quantitative biomedical imaging of cells.

    PubMed

    Kang, Hyeong-Gon; Tokumasu, Fuyuki; Clarke, Matthew; Zhou, Zhenping; Tang, Jianyong; Nguyen, Tinh; Hwang, Jeeseong

    2010-01-01

    We present results on the dynamic fluorescence properties of bioconjugated nanocrystals or quantum dots (QDs) in different chemical and physical environments. A variety of QD samples was prepared and compared: isolated individual QDs, QD aggregates, and QDs conjugated to other nanoscale materials, such as single-wall carbon nanotubes (SWCNTs) and human erythrocyte plasma membrane proteins. We discuss plausible scenarios to explain the results obtained for the fluorescence characteristics of QDs in these samples, especially for the excitation time-dependent fluorescence emission from clustered QDs. We also qualitatively demonstrate enhanced fluorescence emission signals from clustered QDs and deduce that the band 3 membrane proteins in erythrocytes are clustered. This approach is promising for the development of QD-based quantitative molecular imaging techniques for biomedical studies involving biomolecule clustering.

  20. 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%.

  1. Horseradish peroxidase-driven fluorescent labeling of nanotubes with quantum dots.

    PubMed

    Didenko, Vladimir V; Baskin, David S

    2006-03-01

    We describe the first enzyme-driven technique for fluorescent labeling of single-walled carbon nanotubes (SWNTs). The labeling was performed via enzymatic biotinylation of nanotubes in the tyramide-horseradish peroxidase (HRP) reaction. Both direct and indirect fuorescent labeling of SWNTs was achieved using either biotinyl tyramide or fluorescently tagged tyramides. Biotinylated SWNTs later reacted with streptavidin-conjugated fluorophores. Linking semiconductor nanocrystals, quantum dots (Q-dots), to the surface of nanotubes resulted in their fluorescent visualization, whereas conventional fluorophores bound to SWNTs directly or through biotin-streptavidin linkage, were completely quenched. Enzymatic biotinylation permits fluorescent visualization of carbon nanotubes, which could be useful for a number of biomedical applications. In addition, other organic molecules such as proteins, antibodies, or DNA can be conjugated to biotinylated SWNTs using this approach.

  2. Photoinduced fluorescence enhancement in CdSe /ZnS quantum dot monolayers: Influence of substrate

    NASA Astrophysics Data System (ADS)

    Uematsu, Takafumi; Maenosono, Shinya; Yamaguchi, Yukio

    2006-07-01

    Photoinduced fluorescence enhancement (PFE) of CdSe /ZnS core/shell quantum dot (QD) films on SiOx substrates was investigated. The fluorescence intensity of the QD film on SiO1.9 was greatly enhanced by continuous irradiation in vacuum, while the same QD film on SiO0.6 showed a small enhancement of the fluorescence intensity. After irradiation, the rate of fluorescence decay of the QD film on SiO0.6 was smaller than that of the QD film on SiO1.9. Our results suggest that the origin of PFE derives from the photoejection of electrons into the substrate, and that the oxygen-excess-related defects work as trap sites for the electrons.

  3. 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%.

  4. Assay of ceftazidime and cefepime based on fluorescence quenching of carbon quantum dots.

    PubMed

    Huang, Yu; Zhang, Ying; Yan, Zhengyu; Liao, Shenghua

    2015-11-01

    A novel and sensitive method for the determination of ceftazidime and cefepime in an active pharmaceutical ingredient (API) has been developed based on the fluorescence quenching of poly(ethylene glycol) (PEG)2000-capped carbon quantum dots (CQDs) prepared using a chemical oxidation method. The quenching of fluorescence intensity is proportional to the concentration of ceftazidime and cefepime over the range of 0.33-3.30 and 0.24-2.40 µg/mL, respectively. The mode of interaction between PEG2000-capped CQDs and ceftazidime/cefepime in aqueous solutions was investigated using a fluorescence, UV/Vis and Fourier transform infrared spectrometry (FTIR) at physiological pH. UV/Vis and FTIR spectra demonstrated that ground state compounds were formed through hydrophobic interaction the fluorescence quenching of CQDs caused by ceftazidime and cefepime. The quenching constants decreased with increases in temperature, which was consistent with static quenching.

  5. Quantum dot-sized organic fluorescent dots for long-term cell tracing

    NASA Astrophysics Data System (ADS)

    Li, Kai; Tang, Ben Zhong; Liu, Bin

    2014-03-01

    Fluorescence techniques have been extensively employed to develop non-invasive methodologies for tracking and understanding complex biological processes both in vitro and in vivo, which is of high importance in modern life science research. Among a variety of fluorescent probes, inorganic semiconductor quantum dots (QDs) have shown advantages in terms of better photostability, larger Stokes shift and more feasible surface functionalization. However, their intrinsic toxic heavy metal components and unstable fluorescence at low pH greatly impede the applications of QDs in in vivo studies. In this work, we developed novel fluorescent probes that can outperform currently available QD based probes in practice. Using conjugated oligomer with aggregation-induced emission characteristics as the fluorescent domain and biocompatible lipid-PEG derivatives as the encapsulation matrix, the obtained organic dots have shown higher brightness, better stability in biological medium and comparable size and photostability as compared to their counterparts of inorganic QDs. More importantly, unlike QD-based probes, the organic fluorescent dots do not blink, and also do not contain heavy metal ions that could be potentially toxic when applied for living biosubstrates. Upon surface functionalization with a cell-penetrating peptide, the organic dots greatly outperform inorganic quantum dots in both in vitro and in vivo long-term cell tracing studies, which will be beneficial to answer crucial questions in stem cell/immune cell therapies. Considering the customized fluorescent properties and surface functionalities of the organic dots, a series of biocompatible organic dots will be developed to serve as a promising platform for multifarious bioimaging tasks in future.

  6. Quantum-confined emission and fluorescence blinking of individual exciton complexes in CdSe nanowires.

    PubMed

    Franz, Dennis; Reich, Aina; Strelow, Christian; Wang, Zhe; Kornowski, Andreas; Kipp, Tobias; Mews, Alf

    2014-11-12

    One-dimensional semiconductor nanostructures combine electron mobility in length direction with the possibility of tailoring the physical properties by confinement effects in radial direction. Here we show that thin CdSe quantum nanowires exhibit low-temperature fluorescence spectra with a specific universal structure of several sharp lines. The structure strongly resembles the pattern of bulk spectra but show a diameter-dependent shift due to confinement effects. Also the fluorescence shows a pronounced complex blinking behavior with very different blinking dynamics of different emission lines in one and the same spectrum. Time- and space-resolved optical spectroscopy are combined with high-resolution transmission electron microscopy of the very same quantum nanowires to establish a detailed structure-property relationship. Extensive numerical simulations strongly suggest that excitonic complexes involving donor and acceptor sites are the origin of the feature-rich spectra.

  7. Optical properties of fluorescent zigzag graphene quantum dots derived from multi-walled carbon nanotubes

    SciTech Connect

    Chen, Wei; Li, Fushan Wu, Chaoxing; Guo, Tailiang

    2014-02-10

    Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating electronic and optical properties due to their quantum confinement and edge effect. In this paper, GQDs were synthesized by using acid treatment and chemical exfoliation of multi-walled carbon nanotubes (MWCNTs). The structure of the GQDs was investigated by transmission electron microscope. The GQDs have a uniform size distribution, zigzag edge structure and two-dimensional morphology. The results indicated that the GQDs have bright blue emission upon UV excitation. The highly fluorescent GQDs exhibited high water solubility and good stability. It is shown that the acid treatment of MWCNTs leads to the formation of the functional group in zigzag sites, which results in the pH-dependent fluorescence of the GQDs.

  8. Monte-Carlo simulations of photoinduced fluorescence enhancement in semiconductor quantum dot arrays

    NASA Astrophysics Data System (ADS)

    Maenosono, Shinya

    2005-03-01

    Photoinduced fluorescence enhancement (PFE) in semiconductor quantum dot (QD) arrays is simulated by a Monte-Carlo method based on the distributed tunneling model. PFE, a property of a QD ensemble, is directly related to the blinking behavior of single QDs. The origin of PFE is attributed not to an increase in the emission intensity during the 'on' period, but to the prolongation of average 'on' time.

  9. Fluorescence Imaging Assisted Photodynamic Therapy Using Photosensitizer-Linked Gold Quantum Clusters.

    PubMed

    Nair, Lakshmi V; Nazeer, Shaiju S; Jayasree, Ramapurath S; Ajayaghosh, Ayyappanpillai

    2015-06-23

    Fluorescence imaging assisted photodynamic therapy (PDT) is a viable two-in-one clinical tool for cancer treatment and follow-up. While the surface plasmon effect of gold nanorods and nanoparticles has been effective for cancer therapy, their emission properties when compared to gold nanoclusters are weak for fluorescence imaging guided PDT. In order to address the above issues, we have synthesized a near-infrared-emitting gold quantum cluster capped with lipoic acid (L-AuC with (Au)18(L)14) based nanoplatform with excellent tumor reduction property by incorporating a tumor-targeting agent (folic acid) and a photosensitizer (protoporphyrin IX), for selective PDT. The synthesized quantum cluster based photosensitizer PFL-AuC showed 80% triplet quantum yield when compared to that of the photosensitizer alone (63%). PFL-AuC having 60 μg (0.136 mM) of protoporphyrin IX was sufficient to kill 50% of the tumor cell population. Effective destruction of tumor cells was evident from the histopathology and fluorescence imaging, which confirm the in vivo PDT efficacy of PFL-AuC.

  10. Analysis of quantum dot fluorescence stability in primary blood mononuclear cells.

    PubMed

    Summers, Huw D; Holton, Mark D; Rees, Paul; Williams, Paul M; Thornton, Catherine A

    2010-10-01

    A quantitative assessment of fluorescence signal generation and persistence in blood cells, measured at multiple points over a time course, is presented. Quantum dots (QDs) are inorganic fluorophores that are photostable and nonmetabolized and so can provide quantitative measures of cell biology over multiple cell generations. However, if the potential of these nanoparticles for long-term reporting is to be realized, an understanding of the stability of their fluorescence in living cells is essential. CdTe/ZnS and CdSe/ZnS core/shell dots with peak emission wavelengths of 705 nm and 585 nm, respectively, were loaded, via endocytosis into mononuclear cells extracted from primary blood and flow cytometry used to measure the average fluorescence intensity per cell within populations >10⁴. Time-based study showed a saturation-limited uptake of QDs with a characteristic time of 20 min and a maximum fluorescence signal that is linearly proportional to dot solution concentration. The fluorescence signal decreases after attachment and internalization within cells and is accurately described by a biexponential decay with a rapid initial decay followed by a much slower signal loss with characteristic times of 435 and 7,000 min respectively. Comparison with control samples indicates that interaction with the culture media is a major contributory factor to the initial signal decay. These results provide phenomenological descriptions of the evolving QD fluorescence within live cells with associated analytical equations that allow quantitative assessment of QD-based assays.

  11. "Turn off-on" fluorescent sensor for platinum drugs-DNA interactions based on quantum dots.

    PubMed

    Zhao, Dan; Li, Jiaotian; Yang, Tianming; He, Zhike

    2014-02-15

    A "turn off-on" mode has been established by using the interaction between platinum anticancer drugs and DNA as input signal and the fluorescence reversible change of quantum dots (QDs) as output signal. The QDs fluorescence can be quenched by platinum anticancer drugs via photo-induced electron transfer process, rendering the system into "turn off" status, and the system can then be "turned on" when fluorescence is restored due to covalent conjugation between DNA and platinum anticancer drugs. This dual-directional fluorescence change realized the detection of cisplatin and DNA, overcoming the selectivity problem commonly existed in the traditional mono-directional fluorescence detection mode. The reversible fluorescent "turn off-on" mode has been further employed to study the interactions between DNA and different platinum anticancer drugs (cisplatin, oxaliplatin and carboplatin). Furthermore, the impacts of different types of DNAs (different in base sequence, chain length and ssDNA/dsDNA) on the mode are also explored. This simple, fast and convenient spectroscopic method owns promising applications in the study on interaction between medical molecules and DNA, and in biochemical detections.

  12. Dissecting the Factors Affecting the Fluorescence Stability of Quantum Dots in Live Cells.

    PubMed

    Wang, Zhi-Gang; Liu, Shu-Lin; Hu, Yuan-Jun; Tian, Zhi-Quan; Hu, Bin; Zhang, Zhi-Ling; Pang, Dai-Wen

    2016-04-06

    Labeling and imaging of live cells with quantum dots (QDs) has attracted great attention in the biomedical field over the past two decades. Maintenance of the fluorescence of QDs in a biological environment is crucial for performing long-term cell tracking to investigate the proliferation and functional evolution of cells. The cell-penetrating peptide transactivator of transcription (TAT) is a well-studied peptide to efficiently enhance the transmembrane delivery. Here, we used TAT peptide-conjugated QDs (TAT-QDs) as a model system to examine the fluorescence stability of QDs in live cells. By confocal microscopy, we found that TAT-QDs were internalized into cells by endocytosis, and transported into the cytoplasm via the mitochondria, Golgi apparatus, and lysosomes. More importantly, the fluorescence of TAT-QDs in live cells was decreased mainly by cell proliferation, and the low pH value in the lysosomes could also lower the fluorescence intensity of intracellular QDs. Quantitative analysis of the amount of QDs in the extracellular region and whole cells indicated that the exocytosis was not the primary cause of fluorescence decay of intracellular QDs. This work facilitates a better understanding of the fluorescence stability of QDs for cell imaging and long-term tracking in live cells. Also, it provides insights into the utility of TAT for transmembrane transportation, and the preparation and modification of QDs for cell imaging and tracking.

  13. A single-wavelength-emitting ratiometric probe based on phototriggered fluorescence switching of graphene quantum dots.

    PubMed

    Qu, Zhi-bei; Zhang, Min; Zhou, Tianshu; Shi, Guoyue

    2014-10-13

    Ratiometric fluorescent probes are of great importance in research, because a built-in correction for environmental effects can be provided to reduce background interference. However, the traditional ratiometric fluorescent probes require two luminescent materials with different emission bands. Herein a novel ratiometric probe based on a single-wavelength-emitting material is reported. The probe works by regulating the luminescent property of graphene quantum dots with UV illumination as activator. The ratiometric sensor shows high sensitivity and specificity for iron ions. Moreover, the ratiometric sensor was successfully employed to monitor ferritin levels in Sprague Dawley rats with chemical-induced acute liver damage. The proposed single-wavelength ratiometric fluorescent probe may greatly broaden the applicability of ratiometric sensors in diagnostic devices, medical applications, and analytical chemistry.

  14. Quantum dots (QDs) based fluorescence probe for the sensitive determination of kaempferol

    NASA Astrophysics Data System (ADS)

    Tan, Xuanping; Liu, Shaopu; Shen, Yizhong; He, Youqiu; Yang, Jidong

    2014-12-01

    In this work, using the quenching of fluorescence of thioglycollic acid (TGA)-capped CdTe quantum dots (QDs), a novel method for the determination of kaempferol (KAE) has been developed. Under optimum conditions, a linear calibration plot of the quenched fluorescence intensity at 552 nm against the concentration of KAE was observed in the range of 4-44 μg mL-1 with a detection limit (3σ/K) of 0.79 μg mL-1. In addition, the detailed reaction mechanism has also been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-vis) absorption and fluorescence (FL) spectroscopy. The method has been applied for the determination of KAE in pharmaceutical preparations with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

  15. Stability of fluorescent labels in PLGA polymeric nanoparticles: Quantum dots versus organic dyes.

    PubMed

    Abdel-Mottaleb, Mona M A; Beduneau, Arnaud; Pellequer, Yann; Lamprecht, Alf

    2015-10-15

    Polymeric nanoparticles (NPs) are currently being investigated for various therapeutic, diagnostic and drug delivery applications. The study of their interactions and fate in biological systems is frequently performed via their fluorescent labeling and following them using fluorescent microscopy. Quantum dots are proposed as stable fluorescent label and compared to other organic dyes (Nile red and DiI) in terms of their entrapment, diffusion in different aqueous or lipophilic media and photostability. In vitro transfer to hydrophilic PBS solution showed that after 8h, 4.2±2.2, 15.5±2.0 and 0.9±0.02% was released from the QDs, NR and DiI nanoparticles, respectively. However, higher diffusion rates were observed in the lipophilic medium chain triglyceride and artificial sebum for all the dyes used. Fluorescent intensity of the three different markers was found to be stable over a period of 24h. Continuous illumination with laser beam using a confocal laser scanning microscopy indicated the superior stability of quantum dots compared to the other organic dyes. Skin permeation experiments have shown that QDs were the most representative marker for the polymeric nanoparticles skin penetration.

  16. Scanning single quantum emitter fluorescence lifetime imaging: quantitative analysis of the local density of photonic states.

    PubMed

    Schell, Andreas W; Engel, Philip; Werra, Julia F M; Wolff, Christian; Busch, Kurt; Benson, Oliver

    2014-05-14

    Their intrinsic properties render single quantum systems as ideal tools for quantum enhanced sensing and microscopy. As an additional benefit, their size is typically on an atomic scale that enables sensing with very high spatial resolution. Here, we report on utilizing a single nitrogen vacancy center in nanodiamond for performing three-dimensional scanning-probe fluorescence lifetime imaging microscopy. By measuring changes of the single emitter's lifetime, information on the local density of optical states is acquired at the nanoscale. Three-dimensional ab initio discontinuous Galerkin time-domain simulations are used in order to verify the results and to obtain additional insights. This combination of experiment and simulations to gather quantitative information on the local density of optical states is of direct relevance for the understanding of fundamental quantum optical processes as well as for the engineering of novel photonic and plasmonic devices.

  17. Photoinduced fluorescence enhancement in colloidal CdSeTe /ZnS core/shell quantum dots

    NASA Astrophysics Data System (ADS)

    Yuan, C. T.; Chou, W. C.; Chuu, D. S.; Chen, Y. N.; Lin, C. A.; Chang, W. H.

    2008-05-01

    Photoinduced fluorescence enhancement (PFE) in colloidal CdSeTe /ZnS core/shell quantum dots (QDs) was investigated by monitoring ensemble fluorescence and single-QD fluorescence blinking behavior upon illumination. Ensemble fluorescence was increased in air and in vacuum with different enhanced factors. At the single-QD levels, fluorescence was also enhanced for some individual QDs. Relatively long on times, high quantum yields within the on times, and multilevel on states were found in fluorescence time traces. We suggest that the PFE origin from single-QD viewpoint is attributed to the contributions of surface passivation by photoinduced charged carriers and the formation of neutral core/charged shell QD states.

  18. Whole-body, real-time preclinical imaging of quantum dot fluorescence with time-gated detection.

    PubMed

    May, Andrzej; Bhaumik, Srabani; Gambhir, Sanjiv S; Zhan, Chun; Yazdanfar, Siavash

    2009-01-01

    We describe a wide-field preclinical imaging system optimized for time-gated detection of quantum dot fluorescence emission. As compared to continuous wave measurements, image contrast was substantially improved by suppression of short-lifetime background autofluorescence. Real-time (8 frames/s) biological imaging of subcutaneous quantum dot injections is demonstrated simultaneously in multiple living mice.

  19. Quantum dots based mesoporous structured imprinting microspheres for the sensitive fluorescent detection of phycocyanin.

    PubMed

    Zhang, Zhong; Li, Jinhua; Wang, Xiaoyan; Shen, Dazhong; Chen, Lingxin

    2015-05-06

    Phycocyanin with important physiological/environmental significance has attracted increasing attention; versatile molecularly imprinted polymers (MIPs) have been applied to diverse species, but protein imprinting is still quite difficult. Herein, using phycocyanin as template via a sol-gel process, we developed a novel fluorescent probe for specific recognition and sensitive detection of phycocyanin by quantum dots (QDs) based mesoporous structured imprinting microspheres (SiO2@QDs@ms-MIPs), obeying electron-transfer-induced fluorescence quenching mechanism. When phycocyanin was present, a Meisenheimer complex would be produced between phycocyanin and primary amino groups of QDs surface, and then the photoluminescent energy of QDs would be transferred to the complex, leading to the fluorescence quenching of QDs. As a result, the fluorescent intensity of the SiO2@QDs@ms-MIPs was significantly decreased within 8 min, and accordingly a favorable linearity within 0.02-0.8 μM and a high detectability of 5.9 nM were presented. Excellent recognition specificity for phycocyanin over its analogues was displayed, with a high imprinting factor of 4.72. Furthermore, the validated probe strategy was successfully applied to seawater and lake water sample analysis, and high recoveries in the range of 94.0-105.0% were attained at three spiking levels of phycocyanin, with precisions below 5.3%. The study provided promising perspectives to develop fluorescent probes for convenient, rapid recognition and sensitive detection of trace proteins from complex matrices, and further pushed forward protein imprinting research.

  20. Carbon quantum dots as fluorescence resonance energy transfer sensors for organophosphate pesticides determination.

    PubMed

    Wu, Xiaoli; Song, Yang; Yan, Xu; Zhu, Chengzhou; Ma, Yongqiang; Du, Dan; Lin, Yuehe

    2017-03-07

    Carbon quantum dots (CQDs) obtained from natural organics attract significant attention due to the abundance of carbon sources, varieties of heteroatom doping (such as N, S, P) and good biocompatibility of precursor. In this study, tunable fluorescence emission CQDs originated from chlorophyll were synthesized and characterized. The fluorescence emission can be effectively quenched by gold nanoparticles (Au NPs) via fluorescence resonance energy transfer (FRET). Thiocholine, which was produced from acetylthiocholine (ATC) by the hydrolysis of butyrylcholinesterase (BChE), could cause the aggregation of Au NPs and the corresponding recovery of FRET-quenched fluorescence emission. The catalytic activity of BChE could be irreversibly inhibited by organophosphorus pesticides (OPs), thus, the recovery effect was reduced. By evaluating the fluorescence emission intensity of CQDs, a FRET-based sensing platform for OPs determination was established. Paraoxon was studied as an example of OPs. The sensing platform displayed a linear relationship with the logarithm of the paraoxon concentrations in the range of 0.05-50μgL(-1) and the limit of detection (LOD) was 0.05μgL(-1). Real sample study in tap and river water revealed that this sensing platform was repeatable and accurate. The results indicate that the OP sensor is promising for applications in food safety and environmental monitoring.

  1. Lipidots: competitive organic alternative to quantum dots for in vivo fluorescence imaging

    NASA Astrophysics Data System (ADS)

    Gravier, Julien; Navarro, Fabrice P.; Delmas, Thomas; Mittler, Frédérique; Couffin, Anne-Claude; Vinet, Françoise; Texier, Isabelle

    2011-09-01

    The use of fluorescent nanostructures can bring several benefits on the signal to background ratio for in vitro microscopy, in vivo small animal imaging, and image-guided surgery. Fluorescent quantum dots (QDs) display outstanding optical properties, with high brightness and low photobleaching rate. However, because of their toxic element core composition and their potential long term retention in reticulo-endothelial organs such as liver, their in vivo human applications seem compromised. The development of new dye-loaded (DiO, DiI, DiD, DiR, and Indocyanine Green (ICG)) lipid nanoparticles for fluorescence imaging (lipidots) is described here. Lipidot optical properties quantitatively compete with those of commercial QDs (QTracker®705). Multichannel in vivo imaging of lymph nodes in mice is demonstrated for doses as low as 2 pmols of particles. Along with their optical properties, fluorescent lipidots display very low cytotoxicity (IC50 > 75 nM), which make them suitable tools for in vitro, and especially in vivo, fluorescence imaging applications.

  2. Ultrasensitive fluorescence detection of heparin based on quantum dots and a functional ruthenium polypyridyl complex.

    PubMed

    Cao, Yanlin; Shi, Shuo; Wang, Linlin; Yao, Junliang; Yao, Tianming

    2014-05-15

    A new strategy for the detection of heparin is developed by utilizing quantum dots (QDs) and a functional ruthenium polypyridyl complex [Ru(phen)2(dppz-idzo)](2+) (phen=1,10-phenanthroline, dppz-idzo=dipyrido-[3,2-a:2',3'-c] phenazine-imidazolone). The emission of CdTe QDs is found to be quenched by Ru complex due to electron transfer. Upon addition of the polyanionic heparin, it could remove the quencher (Ru complex) from the surface of QDs owing to the electrostatic and/or hydrogen bonding interactions between heparin and Ru complex, which led to significant fluorescence recovery of CdTe QDs. The fluorescence intensity enhanced with the increase of heparin and a linear relationship was observed in the range of 21-77 nM for heparin detection in buffer solution and the limit of detection (LOD) is 0.38 nM. Moreover, the strategy was successfully applied to detect heparin as low as 0.68 nM with a linear range of 35-98 nM in fetal bovine serum samples. The selectivity results of the fluorescence assay revealed that our system displayed excellent fluorescence selectivity towards heparin over its analogues, such as chondroitin 4-sulfate (Chs) or hyaluronic acid (Hya). This fluorescence "switch on" assay for heparin is label-free, convenient, sensitive and selective, which can be used to detect heparin in biological systems even with the naked eyes.

  3. Fluorescent reversible regulation based on the interactions of topotecan hydrochloride, neutral red and quantum dots.

    PubMed

    Wang, Linlin; Shen, Yizhong; Liu, Shaopu; Yang, Jidong; Liang, Wanjun; Li, Dan; He, Youqiu

    2015-02-05

    The interactions of topotecan hydrochloride (THC), neutral red (NR) and thioglycolic acid (TGA) capped CdTe/CdS quantum dots (QDs) built a solid base for the controlling of the fluorescent reversible regulation of the system. This study was developed by means of ultraviolet-visible (UV-vis) absorption, fluorescence (FL), resonance Rayleigh scattering (RRS) spectroscopy and transmission electron microscopy (TEM). Corresponding experimental results revealed that the fluorescence of TGA-CdTe/CdS QDs could be effectively quenched by NR, while the RRS of the QDs enhanced gradually with the each increment of NR concentration. After the addition of THC, the strong covalent conjugation between NR and THC which was in carboxylate state enabled NR to be dissociated from the surface of TGA-CdTe/CdS QDs to form more stable complex with THC, thereby enhancing the fluorescence of the TGA-CdTe/CdS QDs-NR system. What is more, through analyzing the optical properties and experimental data of the reaction between TGA-CdTe/CdS QDs and NR, the possible reaction mechanism of the whole system was discussed. This combination of multiple spectroscopic techniques could contribute to the investigation for the fluorescent reversible regulation of QDs and a method could also be established to research the interactions between camptothecin drugs and dyes.

  4. Fluorescent reversible regulation based on the interactions of topotecan hydrochloride, neutral red and quantum dots

    NASA Astrophysics Data System (ADS)

    Wang, Linlin; Shen, Yizhong; Liu, Shaopu; Yang, Jidong; Liang, Wanjun; Li, Dan; He, Youqiu

    2015-02-01

    The interactions of topotecan hydrochloride (THC), neutral red (NR) and thioglycolic acid (TGA) capped CdTe/CdS quantum dots (QDs) built a solid base for the controlling of the fluorescent reversible regulation of the system. This study was developed by means of ultraviolet-visible (UV-vis) absorption, fluorescence (FL), resonance Rayleigh scattering (RRS) spectroscopy and transmission electron microscopy (TEM). Corresponding experimental results revealed that the fluorescence of TGA-CdTe/CdS QDs could be effectively quenched by NR, while the RRS of the QDs enhanced gradually with the each increment of NR concentration. After the addition of THC, the strong covalent conjugation between NR and THC which was in carboxylate state enabled NR to be dissociated from the surface of TGA-CdTe/CdS QDs to form more stable complex with THC, thereby enhancing the fluorescence of the TGA-CdTe/CdS QDs-NR system. What is more, through analyzing the optical properties and experimental data of the reaction between TGA-CdTe/CdS QDs and NR, the possible reaction mechanism of the whole system was discussed. This combination of multiple spectroscopic techniques could contribute to the investigation for the fluorescent reversible regulation of QDs and a method could also be established to research the interactions between camptothecin drugs and dyes.

  5. Probing of marker proteins in cancer tissue using quantum dots with Hadamard transform fluorescence imaging microscopy

    NASA Astrophysics Data System (ADS)

    Xu, Hao; Chen, Chuang; Li, Yan; Tang, Hong-Wu

    2009-08-01

    A domestic-made Hadamard transform spectral imaging microscope was employed to provide high-resolutional fluorescence spectrum and image of tiny samples such as single cells and tissues. By using agron laser line at 454 nm to excite fluorescence and based on immunostaining with quantum dots (QDs) at different wavelengths to tag and trace breast cancer biomarkers in human breast cancer tissues, in situ single-color and dual-color fluorescence imaging for human epidermal growth factor receptor 2 (HER2), estrogen receptor (ER) and proliferating cell nuclear antigen (PCNA) in tissues were realized, by using the Hadamard imaging microscope to capture the high S/N ratio fluorescence images. Moreover, through the comparative study of the differences between fluorescence spectra and images of positive samples and negative control, a method was proposed to evaluate tumor malignancy of the specimens based on the analysis of distribution of HER2, ER and PCNA in the tissues. The results show that the Hadamard transform spectral imaging technique can be applied to visualize and quantitatively measure the subcellular molecules inside the tumor tissues and has great potential in biology and medical diagnosis.

  6. Enhanced indistinguishability of in-plane single photons by resonance fluorescence on an integrated quantum dot

    NASA Astrophysics Data System (ADS)

    Kalliakos, Sokratis; Brody, Yarden; Bennett, Anthony J.; Ellis, David J. P.; Skiba-Szymanska, Joanna; Farrer, Ian; Griffiths, Jonathan P.; Ritchie, David A.; Shields, Andrew J.

    2016-10-01

    Integrated quantum light sources in photonic circuits are envisaged as the building blocks of future on-chip architectures for quantum logic operations. While semiconductor quantum dots have been proven to be the highly efficient emitters of quantum light, their interaction with the host material induces spectral decoherence, which decreases the indistinguishability of the emitted photons and limits their functionality. Here, we show that the indistinguishability of in-plane photons can be greatly enhanced by performing resonance fluorescence on a quantum dot coupled to a photonic crystal waveguide. We find that the resonant optical excitation of an exciton state induces an increase in the emitted single-photon coherence by a factor of 15. Two-photon interference experiments reveal a visibility of 0.80 ± 0.03, which is in good agreement with our theoretical model. Combined with the high in-plane light-injection efficiency of photonic crystal waveguides, our results pave the way for the use of this system for the on-chip generation and transmission of highly indistinguishable photons.

  7. Multicolor fluorescent light-emitting diodes based on cesium lead halide perovskite quantum dots

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Bai, Xue; Sun, Chun; Zhang, Xiaoyu; Zhang, Tieqiang; Zhang, Yu

    2016-08-01

    High quantum yield, narrow full width at half-maximum and tunable emission color of perovskite quantum dots (QDs) make this kind of material good prospects for light-emitting diodes (LEDs). However, the relatively poor stability under high temperature and air condition limits the device performance. To overcome this issue, the liquid-type packaging structure in combination with blue LED chip was employed to fabricate the fluorescent perovskite quantum dot-based LEDs. A variety of monochromatic LEDs with green, yellow, reddish-orange, and red emission were fabricated by utilizing the inorganic cesium lead halide perovskite quantum dots as the color-conversion layer, which exhibited the narrow full width at half-maximum (<35 nm), the relatively high luminous efficiency (reaching 75.5 lm/W), and the relatively high external quantum efficiency (14.6%), making it the best-performing perovskite LEDs so far. Compared to the solid state LED device, the liquid-type LED devices exhibited excellent color stability against the various working currents. Furthermore, we demonstrated the potential prospects of all-inorganic perovskite QDs for the liquid-type warm white LEDs.

  8. 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.

  9. Absolute atomic oxygen density measurements for nanosecond-pulsed atmospheric-pressure plasma jets using two-photon absorption laser-induced fluorescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Jiang, C.; Carter, C.

    2014-12-01

    Nanosecond-pulsed plasma jets that are generated under ambient air conditions and free from confinement of electrodes have become of great interest in recent years due to their promising applications in medicine and dentistry. Reactive oxygen species that are generated by nanosecond-pulsed, room-temperature non-equilibrium He-O2 plasma jets among others are believed to play an important role during the bactericidal or sterilization processes. We report here absolute measurements of atomic oxygen density in a 1 mm-diameter He/(1%)O2 plasma jet at atmospheric pressure using two-photon absorption laser-induced fluorescence spectroscopy. Oxygen number density on the order of 1013 cm-3 was obtained in a 150 ns, 6 kV single-pulsed plasma jet for an axial distance up to 5 mm above the device nozzle. Temporally resolved O density measurements showed that there are two maxima, separated in time by 60-70 µs, and a total pulse duration of 260-300 µs. Electrostatic modeling indicated that there are high-electric-field regions near the nozzle exit that may be responsible for the observed temporal behavior of the O production. Both the field-distribution-based estimation of the time interval for the O number density profile and a pulse-energy-dependence study confirmed that electric-field-dependent, direct and indirect electron-induced processes play important roles for O production.

  10. Effect of capsid proteins to ICG mass ratio on fluorescent quantum yield of virus-resembling optical nano-materials

    NASA Astrophysics Data System (ADS)

    Gupta, Sharad; Ico, Gerardo; Matsumura, Paul; Rao, A. L. N.; Vullev, Valentine; Anvari, Bahman

    2012-03-01

    We recently reported construction of a new type of optical nano-construct composed of genome-depleted plant infecting brome mosaic virus (BMV) doped with Indocyanine green (ICG), an FDA-approved chromophore. We refer to these constructs as optical viral ghosts (OVGs) since only the capsid protein (CP) subunits of BMV remain to encapsulate ICG. To utilize OVGs as effective nano-probes in fluorescence imaging applications, their fluorescence quantum yield needs to be maximized. In this study, we investigate the effect of altering the CP to ICG mass ratio on the fluorescent quantum yield of OVGs. Results of this study provide the basis for construction of OVGs with optimal amounts of CP and ICG to yield maximal fluorescence quantum yield.

  11. Fluorescent probe for detection of Cu2+ using core-shell CdTe/ZnS quantum dots.

    PubMed

    Bian, Wei; Wang, Fang; Zhang, Hao; Zhang, Lin; Wang, Li; Shuang, Shaomin

    2015-11-01

    Core-shell CdTe/ZnS quantum dots capped with 3-mercaptopropionic acid (MPA) were successfully synthesized in aqueous medium by hydrothermal synthesis. These quantum dots have advantages compared to traditional quantum dots with limited biological applications, high toxicity and tendency to aggregate. The concentration of Cu(2+) has a significant impact on the fluorescence intensity of quantum dots (QDs), therefore, a rapid sensitive and selective fluorescence probe has been proposed for the detection of Cu(2+) in aqueous solution. Under optimal conditions, the fluorescence intensity of CdTe/ZnS QDs was linearly proportional to the concentration of Cu(2+) in the range from 2.5 × 10(-9) M to 17.5 × 10(-7) M with the limit of 1.5 × 10(-9) M and relative standard deviation of 0.23%. The quenching mechanism is static quenching with recoveries of 97.30-102.75%.

  12. Fluorescence Determination of Warfarin Using TGA-capped CdTe Quantum Dots in Human Plasma Samples.

    PubMed

    Dehbozorgi, A; Tashkhourian, J; Zare, S

    2015-11-01

    In this study, some effort has been performed to provide low temperature, less time consuming and facile routes for the synthesis of CdTe quantum dots using ultrasound and water soluble capping agent thioglycolic acid. TGA-capped CdTe quantum dots were characterized through x-ray diffraction, transmission electron microscopy, Fourier transform infrared, ultraviolet-visible and fluorescence spectroscopy. The prepared quantum dots were used for warfarin determination based on the quenching of the fluorescence intensity in aqueous solution. Under the optimized conditions, the linear range of quantum dots fluorescence intensity versus the concentration of warfarin was 0.1-160.0 μM, with the correlation coefficient of 0.9996 and a limit of detection of 77.5 nM. There was no interference to coexisting foreign substances. The selectivity of the sensor was also tested and the results show that the developed method possesses a high selectivity for warfarin.

  13. LASERS IN MEDICINE: Quantum efficiency of the laser-excited singlet-oxygen-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine

    NASA Astrophysics Data System (ADS)

    Bashtanov, M. E.; Drozdova, N. N.; Krasnovskii, A. A.

    1999-12-01

    An investigation was made of the ratios of the intensity Idf of the singlet-oxygen(1O2)-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine (ZnTBPc), with the maximum at λ = 685 nm, to the intensity I1270 of the photosensitised phosphorescence of 1O2 with the maximum at λ = 1270 nm in deuterated benzene when excited with λ = 337 nm nitrogen-laser pulses. Depending on the energy density of the laser radiation (0.25 — 0.7 mJ cm-2) and on the concentration of ZnTBPc (0.06 — 3.4 μM), the ratio of the zero-time intensities of the delayed fluorescence of ZnTBPc and of the singlet-oxygen phosphorescence Idf0/I12700 varied from 0.01 to 0.2 in air-saturated solutions of ZnTBPc. The intensity Idf0 decreased fivefold as a result of saturation with oxygen of air-saturated solutions. The quantum efficiency of the delayed fluorescence was represented by the coefficient α =(Idf0/I12700)kr/(γf[1O2]0[ZnTBPc]), where [1O2]0 is the zero-time concentration of 1O2 after a laser shot; kr is the rate constant of radiative deactivation of 1O2 in the investigated solvent; γf is the quantum yield of the ZnTBPc fluorescence. It was established that in the case of air-saturated solutions of ZnTBPc this coefficient was approximately 200 times less than for metal-free tetra(4-tert-butyl)phthalocyanine and its absolute value was ~2 × 1011 M-2 s-1.

  14. Green synthesis of highly fluorescent carbon quantum dots from sugarcane bagasse pulp

    NASA Astrophysics Data System (ADS)

    Thambiraj, S.; Ravi Shankaran, D.

    2016-12-01

    Carbon quantum dots (CQDs) have great potential due to its advantageous characteristics of highly fluorescent nature and good stability. In this study, we aimed to develop a simple and efficient method for the green synthesis of fluorescent CQDs from sugarcane bagasse, a renewable and sustainable resource. The process involves the top down approach of chemical oxidation followed by exfoliation of sugarcane carbon. The synthesized CQDs was characterized by UV-vis absorption spectroscopy, Spectrofluorophotometry, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, X-ray photon spectroscopy (XPS), Atomic force microscopy (AFM) and High-resolution transmission electron microscopy (HR-TEM). The synthesized CQDs possess stable fluorescent properties, good bio-compatibility and high quantum yield. The CQDs are highly crystalline with longitudinal dimensions of 4.1 ± 0.17 nm with an average roughness of around 5 nm. The XRD and TEM analysis indicates that the synthesized CQDs possess face centred cubic crystal structure. The results suggest that the proposed CQDs could be utilized for bio-sensor, bio-imaging and drug delivery applications.

  15. Polymer-coated fluorescent CdSe-based quantum dots for application in immunoassay.

    PubMed

    Speranskaya, Elena S; Beloglazova, Natalia V; Lenain, Pieterjan; De Saeger, Sarah; Wang, Zhanhui; Zhang, Suxia; Hens, Zeger; Knopp, Dietmar; Niessner, Reinhard; Potapkin, Dmitry V; Goryacheva, Irina Yu

    2014-03-15

    The paper describes all stages of synthesis and characterization of biocompatible CdSe-based core/shell quantum dots (QDs) and their application as fluorescent label for immunoassay. Special attention was focused on development of maleic anhydride-based amphiphilic polymers for QDs solubilization in aqueous media. In this work two PEG-amines were tried for polymer modification: monoamine Jeffamine M 1000 used previously in some researches and diamine Jeffamine ED-2003 applied for the first time for QDs solubilization. The use of different Jeffamines allows us to obtain QDs with carboxyl or amine functional groups available for conjugation. The influence of polymer composition on optical properties of the nanocrystals and their stability in aqueous solutions as well as on their conjugation with biomolecules was studied. QDs with different coatings were used as biolabels in quantitative fluorescence microtiter plate immunoassay and qualitative on-site column test. It was found that quantum dots covered with amphiphilic polymer prepared from poly(maleic anhydride-alt-1-octadecene) and Jeffamine ED-2003 retained up to 90% of their initial brightness, easily conjugated with protein and showed low non-specific adsorption. In optimized conditions the obtained QDs were successfully used for determination of mycotoxin deoxynivalenol in wheat and maize samples by fluorescence microtiter plate immunoassay with an IC50 of 220 μg kg(-1) and by on-site column test with cut-off of 500 μg kg(-1).

  16. Fluorescence modulation in single CdSe quantum dots by moderate applied electric fields

    SciTech Connect

    LeBlanc, Sharonda J.; McClanahan, Mason R.; Moyer, Tully; Moyer, Patrick J.; Jones, Marcus

    2014-01-21

    Single molecule time-resolved fluorescence spectroscopy of CdSe/ZnS core-shell quantum dots (QDs) under the influence of moderate applied electric fields reveals distributed emission from states which are neither fully on nor off and pronounced changes in the excited state decay. The data suggest that a 54 kV/cm applied electric field causes small perturbations to the QD surface charge distribution, effectively increasing the surface trapping probability and resulting in the appearance of gray states. We present simultaneous blinking and fluorescence decay results for two sets of QDs, with and without an applied electric field. Further kinetic modeling analysis suggests that a single trapped charged cannot be responsible for a blinking off event.

  17. Suppressing the Fluorescence Blinking of Single Quantum Dots Encased in N-type Semiconductor Nanoparticles

    PubMed Central

    Li, Bin; Zhang, Guofeng; Wang, Zao; Li, Zhijie; Chen, Ruiyun; Qin, Chengbing; Gao, Yan; Xiao, Liantuan; Jia, Suotang

    2016-01-01

    N-type semiconductor indium tin oxide (ITO) nanoparticles are used to effectively suppress the fluorescence blinking of single near-infrared-emitting CdSeTe/ZnS core/shell quantum dots (QDs), where the ITO could block the electron transfer from excited QDs to trap states and facilitate more rapid regeneration of neutral QDs by back electron transfer. The average blinking rate of QDs is significantly reduced by more than an order of magnitude and the largest proportion of on-state is 98%, while the lifetime is not considerably reduced. Furthermore, an external electron transfer model is proposed to analyze the possible effect of radiative, nonradiative, and electron transfer pathways on fluorescence blinking. Theoretical analysis based on the model combined with measured results gives a quantitative insight into the blinking mechanism. PMID:27605471

  18. Suppressing the Fluorescence Blinking of Single Quantum Dots Encased in N-type Semiconductor Nanoparticles

    NASA Astrophysics Data System (ADS)

    Li, Bin; Zhang, Guofeng; Wang, Zao; Li, Zhijie; Chen, Ruiyun; Qin, Chengbing; Gao, Yan; Xiao, Liantuan; Jia, Suotang

    2016-09-01

    N-type semiconductor indium tin oxide (ITO) nanoparticles are used to effectively suppress the fluorescence blinking of single near-infrared-emitting CdSeTe/ZnS core/shell quantum dots (QDs), where the ITO could block the electron transfer from excited QDs to trap states and facilitate more rapid regeneration of neutral QDs by back electron transfer. The average blinking rate of QDs is significantly reduced by more than an order of magnitude and the largest proportion of on-state is 98%, while the lifetime is not considerably reduced. Furthermore, an external electron transfer model is proposed to analyze the possible effect of radiative, nonradiative, and electron transfer pathways on fluorescence blinking. Theoretical analysis based on the model combined with measured results gives a quantitative insight into the blinking mechanism.

  19. Polyvalent lactose-quantum dot conjugate for fluorescent labeling of live leukocytes.

    PubMed

    Yu, Min; Yang, Yang; Han, Rongcheng; Zheng, Qiang; Wang, Lijun; Hong, Yuankai; Li, Zhongjun; Sha, Yinlin

    2010-06-01

    Oligosaccharides play crucial roles in many biorecognition processes by the so-called "cluster glycosidic effect". We here report a facile synthesis of lactose-CdSeS/ZnS quantum dot conjugate (Lac-QDs) by use of 1-thiol-beta-D-lactose via ligand exchange, which exhibits significantly high affinity and specificity to leukocytes in contrast to the monovalent lactose. Structural analyses indicate that there are about 132 lactosyl molecules assembled on single QDs and the hydrodynamic diameter is small, close to 8.2 nm. Further, Lac-QDs display good fluorescence and physicochemical stability in physiological conditions, as well as extremely low cytotoxicity. These properties facilitate the use of Lac-QDs in fluorescent labeling of live leukocytes.

  20. Fluorescence thermometry enhanced by the quantum coherence of single spins in diamond

    PubMed Central

    Toyli, David M.; de las Casas, Charles F.; Christle, David J.; Dobrovitski, Viatcheslav V.; Awschalom, David D.

    2013-01-01

    We demonstrate fluorescence thermometry techniques with sensitivities approaching 10 mK⋅Hz−1/2 based on the spin-dependent photoluminescence of nitrogen vacancy (NV) centers in diamond. These techniques use dynamical decoupling protocols to convert thermally induced shifts in the NV center's spin resonance frequencies into large changes in its fluorescence. By mitigating interactions with nearby nuclear spins and facilitating selective thermal measurements, these protocols enhance the spin coherence times accessible for thermometry by 45-fold, corresponding to a 7-fold improvement in the NV center’s temperature sensitivity. Moreover, we demonstrate these techniques can be applied over a broad temperature range and in both finite and near-zero magnetic field environments. This versatility suggests that the quantum coherence of single spins could be practically leveraged for sensitive thermometry in a wide variety of biological and microscale systems. PMID:23650364

  1. A novel metronidazole fluorescent nanosensor based on graphene quantum dots embedded silica molecularly imprinted polymer.

    PubMed

    Mehrzad-Samarin, Mina; Faridbod, Farnoush; Dezfuli, Amin Shiralizadeh; Ganjali, Mohammad Reza

    2017-06-15

    A novel optical nanosensor for detection of Metronidazole in biological samples was reported. Graphene quantum dots embedded silica molecular imprinted polymer (GQDs-embedded SMIP) was synthesized and used as a selective fluorescent probe for Metronidazole detection. The new synthesized GQDs-embedded SMIP showed strong fluorescent emission at 450nm excited at 365nm which quenched in presence of Metronidazole as a template molecule.. The quenching was proportional to the concentration of Metronidazole in a linear range of at least 0.2μM to 15μM. The limit of detection for metronidazole determination was obtained 0.15μM. The nanosensor successfully worked in plasma matrixes.

  2. Enhanced fluorescence, morphological and thermal properties of CdSe/ZnS quantum dots incorporated in silicone resin.

    PubMed

    Trung, Nguyen Ngoc; Luu, Quynh-Phuong; Son, Bui Thanh; Sinh, Le Hoang; Bae, Jin-Young

    2013-01-01

    Our research focused on the morphological and optical properties of core/shell cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots incorporated in silicone resin. After dispersing ligand-coated quantum dots into Dow Corning two-component silicone resins (OE6630A and OE6630B at 1:4 mixing ratio by weight), the resins were cured at 150 degrees C for 1.5 hours to produce the quantum dot-silicone resin nanocomposites. The optical, morphological and thermal properties of the quantum dot incorporated in silicone resin were investigated by ultraviolet-visible, fluorescence, atomic force microscopy, field emission scanning electron microscopy, differential scanning calorimetry and thermogravimetric analysis. When the quantum dots, originally coated with trioctylamine ligand, were transferred from a chloroform solvent to methyl phenyl silicone oil and silicone resins of high viscosity, the quantum dots showed increased turbidity and lowered fluorescence intensity. Fluorescence enhancement was investigated by using various functional ligands such as poly(1, 1-dimethyl silazane) (multi-silazane), hexamethylenediamine (diamine), cysteamine (amino-thiol), triethylsilane (reactive hydrosilane), hexamethyldisilazane, nonamethyltrisilazane, octamethylcyclotetrasilazane (reactive amines). The results showed that the reactive amines were good additive ligands for enhancing the fluorescence of CdSe/ZnS quantum dots dispersed in the silicone resins, providing 1.2-2.48 Im/W and 4.2-5.56% higher luminous efficiency and photoluminescence conversion efficiency, respectively. We speculate that these reactive amines donate electrons to the surface electron traps, thereby reducing charge recombination. In addition, quantum dots aggregate to form quantum dot clusters with a relatively homogeneously dispersed in the silicone resin matrices, showing good emission properties due to surface passivation and good colloidal stability with the addition of silazane compounds to the resin

  3. Investigation of red blood cell antigens with highly fluorescent and stable semiconductor quantum dots.

    PubMed

    de Farias, Patrícia Maria Albuquerque; Santos, Beate Saegesser; de Menezes, Frederico Duarte; de Carvalho Ferreira, Ricardo; Barjas-Castro, Maria Lourdes; Castro, Vagner; Lima, Paulo Roberto Moura; Fontes, Adriana; Cesar, Carlos Lenz

    2005-01-01

    We report a new methodology for red blood cell antigen expression determination by a simple labeling procedure employing luminescent semiconductor quantum dots. Highly luminescent and stable core shell cadmium sulfide/cadmium hydroxide colloidal particles are obtained, with a predominant size of 9 nm. The core-shell quantum dots are functionalized with glutaraldehyde and conjugated to a monoclonal anti-A antibody to target antigen-A in red blood cell membranes. Erythrocyte samples of blood groups A+, A2+, and O+ are used for this purpose. Confocal microscopy images show that after 30 min of conjugation time, type A+ and A2+ erythrocytes present bright emission, whereas the O+ group cells show no emission. Fluorescence intensity maps show different antigen expressions for the distinct erythrocyte types. The results obtained strongly suggest that this simple labeling procedure may be employed as an efficient tool to investigate quantitatively the distribution and expression of antigens in red blood cell membranes.

  4. Novel fluorescent CdTe quantum dot-thymine conjugate—synthesis, properties and possible application

    NASA Astrophysics Data System (ADS)

    Rodzik, Łucja; Lewandowska-Łańcucka, Joanna; Szuwarzyński, Michał; Szczubiałka, Krzysztof; Nowakowska, Maria

    2017-01-01

    Novel, highly fluorescent cadmium telluride quantum dots conjugated with thymine and stabilized with thioglycolic acid were obtained and characterized. Successful formation of the conjugate was confirmed by elemental analysis, and UV-vis, fluorescence and Fourier transform infrared spectroscopies. Crystal structure and composition of the conjugates were characterized with xray diffraction and x-ray photoelectron spectroscopy. The size of the conjugates was 4-6 nm as demonstrated using atomic force microscopy and high resolution transmission electron microscopy imaging. The plasmon resonance fluorescence band at 540 nm on excitation at 351 nm was observed for these nanoparticles. The intensity of this band increased with the increase in the amount of conjugated thymine with no shift in its position. Based on the fluorescence measurements it was found that the CdTe-thymine conjugate interacted efficiently and selectively not only with adenine, a nucleobase complementary to thymine, but also with adenine-containing modified nucleosides, i.e., 5‧-deoxy-5‧-(methylthio)adenosine and 2‧-O-methyladenosine, the urinary tumor markers which allow monitoring of the disease progression. To the best of our knowledge, as yet, there have been no studies presented in literature on that type of the interaction with CdTe-thymine conjugates. Therefore, the system presented can be considered as a working component of a selective adenine/adenosine biosensor with potential application in cancer diagnosis.

  5. Ratiometric fluorescence, electrochemiluminescence, and photoelectrochemical chemo/biosensing based on semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Wu, Peng; Hou, Xiandeng; Xu, Jing-Juan; Chen, Hong-Yuan

    2016-04-01

    Ratiometric fluorescent sensors, which can provide built-in self-calibration for correction of a variety of analyte-independent factors, have attracted particular attention for analytical sensing and optical imaging with the potential to provide a precise and quantitative analysis. A wide variety of ratiometric sensing probes using small fluorescent molecules have been developed. Compared with organic dyes, exploiting semiconductor quantum dots (QDs) in ratiometric fluorescence sensing is even more intriguing, owing to their unique optical and photophysical properties that offer significant advantages over organic dyes. In this review, the main photophysical mechanism for generating dual-emission from QDs for ratiometry is discussed and categorized in detail. Typically, dual-emission can be obtained either with energy transfer from QDs to dyes or with independent dual fluorophores of QDs and dye/QDs. The recent discovery of intrinsic dual-emission from Mn-doped QDs offers new opportunities for ratiometric sensing. Particularly, the signal transduction of QDs is not restricted to fluorescence, and electrochemiluminescence and photoelectrochemistry from QDs are also promising for sensing, which can be made ratiometric for correction of interferences typically encountered in electrochemistry. All these unique photophysical properties of QDs lead to a new avenue of ratiometry, and the recent progress in this area is addressed and summarized here. Several interesting applications of QD-based ratiometry are presented for the determination of metal ions, temperature, and biomolecules, with specific emphasis on the design principles and photophysical mechanisms of these probes.

  6. Resonance fluorescence beyond the dipole approximation of a quantum dot in a plasmonic nanostructure

    NASA Astrophysics Data System (ADS)

    Yang, Chun-Jie; An, Jun-Hong

    2016-05-01

    The mesoscopic characteristics of a quantum dot (QD), which make the dipole approximation (DA) break down, provide a new dimension to manipulate light-matter interaction [M. L. Andersen et al., Nat. Phys. 7, 215 (2011)], 10.1038/nphys1870. Here we investigate the power spectrum and the second-order correlation property of the fluorescence from a resonantly driven QD placed on a planar metal. It is revealed that due to the pronounced QD spatial extension and the dramatic variation of the triggered surface plasmon near the metal, the fluorescence has a notable contribution from the quadrupole moment. The π -rotation symmetry of the fluorescence to the QD orientation under the DA is broken. By manipulating the QD orientation and quadrupole moment, the spectrum can be switched between the Mollow triplet and a single peak, and the fluorescence characterized by the antibunching in the second-order correlation function can be changed from the weak to the strong radiation regime. Our result is instructive for utilizing the unique mesoscopic effects to develop nanophotonic devices.

  7. Silicon Quantum Dot-Based Fluorescence Turn-On Metal Ion Sensors in Live Cells.

    PubMed

    Dhenadhayalan, Namasivayam; Lee, Hsin-Lung; Yadav, Kanchan; Lin, King-Chuen; Lin, Yih-Tyng; Chang, A H H

    2016-09-14

    Multiple sensor systems are designed by varying aza-crown ether moiety in silicon quantum dots (SiQDs) for detecting individual Mg(2+), Ca(2+), and Mn(2+) metal ions with significant selectivity and sensitivity. The detection limit of Mg(2+), Ca(2+), and Mn(2+) can reach 1.81, 3.15, and 0.47 μM, respectively. Upon excitation of the SiQDs which are coordinated with aza-crown ethers, the photoinduced electron transfer (PET) takes place from aza-crown ether moiety to the valence band of SiQDs core such that the reduced probability of electron-hole recombination may diminish the subsequent fluorescence. The fluorescence suppression caused by such PET effect will be relieved after selective metal ion is added. The charge-electron binding force between the metal ion and aza-crown ether hinders the PET and thereby restores the fluorescence of SiQDs. The design of sensor system is based on the fluorescence "turn-on" of SiQDs while in search of the appropriate metal ion. For practical application, the sensing capabilities of metal ions in the live cells are performed and the confocal image results reveal their promising applicability as an effective and nontoxic metal ion sensor.

  8. Analysis of the Fluorescence Correlation Function of Quantum Rods with Different Lengths.

    PubMed

    Lee, Jaeran; Kim, Sok Won

    2015-11-01

    We built a polarization fluorescence correlation spectroscopy system to analyze the variation of the correlation function in rotational diffusion based on the length of rod-like fluorescent particles. Because the rotational diffusion of particles in liquid depends on the relative polarization states of the laser source and particle fluorescence, we compared the amplitudes of the rotational diffusion using the autocorrelation function in different polarization states. For experiments that depend on the length of the fluorescent particles, we prepared three kinds of quantum rod samples with a width of 6.5 ± 0.5 nm and lengths of 17 ± 3, 40 ± 3, and 46 ± 3 nm. Through the experiment, we obtained the hydrodynamic radii of each particle using the rotational diffusion coefficient: 10.7 ± 0.8, 13.4 ± 0.7, and 14.1 ± 0.4 nm with the length of the particles. All the obtained values for radii are 3 nm larger than the calculated equivalent radii of spheres with the same volume as the rod samples. Through a fraction analysis by polarization state, we confirmed that the ratio of rotational fraction for polarization increases with the aspect ratio of the actual particle.

  9. Cysteamine capped CdS quantum dots as a fluorescence sensor for the determination of copper ion exploiting fluorescence enhancement and long-wave spectral shifts

    NASA Astrophysics Data System (ADS)

    Boonmee, Chanida; Noipa, Tuanjai; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2016-12-01

    We described a turn-on fluorescence sensor for the determination of Cu2 + ions, utilizing the quantum confinement effect of cadmium sulfide quantum dots capped with cysteamine (Cys-CdS QDs). The fluorescence intensity of the Cys-CdS QDs was both enhanced and red shifted (from blue-green to yellow) in the presence of Cu2 +. Fluorescence enhancement was linearly proportional to the concentration of Cu2 + in the concentration range 2 to 10 μM. Other cations at the same concentration level did not significantly change the intensity and spectral maxima of Cys-CdS QDs, except Ag+. The limit of detection was 1.5 μM. The sensor was applied to the determination of Cu2 + in (spiked) real water samples and gave satisfactory results, with recoveries ranging from 96.7 to 108.2%, and with RSDs ranging from 0.3 to 2.6%.

  10. Field-induced control of universal fluorescence intermittency of a quantum dot light emitter

    NASA Astrophysics Data System (ADS)

    Lee, J. D.; Maenosono, S.

    2010-08-01

    With the nonstochastic quantum mechanical study of a quantum dot light emitter, we find that fluorescence intermittency statistics are universal and insensitive to the microscopic nature of the tunneling fluctuation between quantum dot and trapping state. We also investigate the power-law exponent θ and the crossover time τC of the on-time (τon) probability P(τon)∝τon-θ (for τon≲τC) and ∝e-Γτon (for τon≳τC) under an optical field of given energy and strength. For easy off-resonance excitation, it is found in both numerical and analytic ways that τC-1 is proportional to the intensity of the optical field (i.e., the square of the field strength) independent of the internal parameters of a quantum dot. Furthermore, it is also found that θ =2 in the limit of vanishing field strength is the upper bound of the exponent and θ becomes less than 2 as the field strength increases.

  11. Measuring the fluorescent quantum efficiency of indocyanine green encapsulated in nanocomposite particulates.

    PubMed

    Russin, T J; Altınoğlu, E İ; Adair, J H; Eklund, P C

    2010-08-25

    We present results of a fluorescent quantum efficiency (Φ(F)) study on the encapsulation of the near-infrared dye indocyanine green (ICG) in bioresorbable calcium phosphate nanoparticles (CPNPs). The Φ(F) (described as the ratio of photons emitted to photons absorbed) provides a quantitative means of describing the fluorescence of an arbitrary molecule. However, standard quantum efficiency measurement techniques provide only the Φ(F) of the smallest fluorescing unit-in the case of a nanoparticle suspension, the nanoparticle itself. This presents a problem in accurately describing the Φ(F) of fluorophores embedded in an inorganic nanoparticle. Combining the incidence of scattering with an evaluation of the differences in local electric field and photochemical environment, we have developed a method to determine the Φ(F) of the constituent fluorescent molecules embedded in such a nanoparticle, which provides a more meaningful comparison with the unencapsulated fluorophore. While applicable to generic systems, we present results obtained by our method for the ICG-CPNP in a phosphate buffered 0.15 M saline solution (PBS, pH 7.4)--specifically, Φ(F, free dye) = 0.027 ± 0.001, Φ(F, particle) = 0.053 ± 0.003, and for the individual encapsulated molecules, Φ(F, molecule) = 0.066 ± 0.004. The method developed also provides insight into the influences of encapsulation and key parameters to engineer resonant enhancement effects from the emission of the encapsulated fluorophores corresponding to an eigenmode of the embedding particle for tailored optical properties.

  12. High fluorescent and stable semiconductor quantum dots for red blood cells labeling

    NASA Astrophysics Data System (ADS)

    de Farias, Patricia M. A.; Santos, Beate S.; de Menezes, Frederico D.; Ferreira, Ricardo; Fontes, Adriana; Cesar, Carlos L.; Barjas Castro, Maria L.; Castro, Vagner; Lima, Paulo R. M.

    2005-04-01

    We present a simple and efficient method for marking living human red blood cells using CdS (Cadmium Sulfide) quantum dots (QDs). The nanocrystals were obtained via colloidal synthesis in aqueous medium with final pH=7 using sodium polyphosphate as the stabilizing agent. The methodology implementation is simple, do not requires additional capping layers nor narrow size QDs distribution. The synthesized nanoparticles were conjugated to monoclonal A anti-body. The resulting conjugates QDs/anti-A were incubated with human erythrocytes of blood groups A and O for 30 min at 37°C. The living cells in contact with the quantum dots maintained their properties for several days showing the low level of citotoxicity of the quantum dots. The conjugation of CdS QDs/anti-A show simultaneous red and green fluorescence when excited with 543 and 488 nm respectively. The efficiency of the conjugation QDs/anti-body to the erythrocytes, for each system, was monitored by confocal microscopy. The comparative analysis of the micrographs was done with the luminescence intensity maps of the samples obtained under constant capture conditions, such as, pinhole, filters, beam splitters and photomultiplier gain. The conjugates QDs/anti-A intensely marked group A erythrocytes and did not show any luminescence for group O erythrocytes, showing the sensitivity of the labeling procedure. In conclusion, we show the viability of the use of high luminescent and stable quantum dots as fluorescent labels for human erythrocytes with a methodology of simple implementation and the possibility to use them to distinguish different blood groups.

  13. Solid-phase single molecule biosensing using dual-color colocalization of fluorescent quantum dot nanoprobes

    NASA Astrophysics Data System (ADS)

    Liu, Jianbo; Yang, Xiaohai; Wang, Kemin; Wang, Qing; Liu, Wei; Wang, Dong

    2013-10-01

    The development of solid-phase surface-based single molecule imaging technology has attracted significant interest during the past decades. Here we demonstrate a sandwich hybridization method for highly sensitive detection of a single thrombin protein at a solid-phase surface based on the use of dual-color colocalization of fluorescent quantum dot (QD) nanoprobes. Green QD560-modified thrombin binding aptamer I (QD560-TBA I) were deposited on a positive poly(l-lysine) assembled layer, followed by bovine serum albumin blocking. It allowed the thrombin protein to mediate the binding of the easily detectable red QD650-modified thrombin binding aptamer II (QD650-TBA II) to the QD560-TBA I substrate. Thus, the presence of the target thrombin can be determined based on fluorescent colocalization measurements of the nanoassemblies, without target amplification or probe separation. The detection limit of this assay reached 0.8 pM. This fluorescent colocalization assay has enabled single molecule recognition in a separation-free detection format, and can serve as a sensitive biosensing platform that greatly suppresses the nonspecific adsorption false-positive signal. This method can be extended to other areas such as multiplexed immunoassay, single cell analysis, and real time biomolecule interaction studies.The development of solid-phase surface-based single molecule imaging technology has attracted significant interest during the past decades. Here we demonstrate a sandwich hybridization method for highly sensitive detection of a single thrombin protein at a solid-phase surface based on the use of dual-color colocalization of fluorescent quantum dot (QD) nanoprobes. Green QD560-modified thrombin binding aptamer I (QD560-TBA I) were deposited on a positive poly(l-lysine) assembled layer, followed by bovine serum albumin blocking. It allowed the thrombin protein to mediate the binding of the easily detectable red QD650-modified thrombin binding aptamer II (QD650-TBA II) to

  14. Chemically doped fluorescent carbon and graphene quantum dots for bioimaging, sensor, catalytic and photoelectronic applications

    NASA Astrophysics Data System (ADS)

    Du, Yan; Guo, Shaojun

    2016-01-01

    Doping fluorescent carbon dots (DFCDs) with heteroatoms have recently become of great interest compared to traditional fluorescent materials because it provides a feasible and new way to tune the intrinsic properties of carbon quantum dots (CQDs) and graphene quantum dots (GQDs) to achieve new applications for them in different fields. Since the first report on nitrogen (N) doped GQDs in 2012, more effort is being focused on exploring different procedures for making new types of DFCDs with different heteroatoms. This mini review will summarize recent research progress on DFCDs. It first reviews various doping categories achieved up to now, looking back on the synthesis method and comparing the differences in synthesis approaches between the DFCDs and the undoped ones. Then it focuses on the advances on how the doping affects the optical properties, especially DFCDs doped with N, which have been investigated the most. Finally, different applications of DFCDs involving bio-imaging, sensing, catalysis and photoelectronic devices will be discussed. This review will give new insights into how to use different synthetic methods for tuning the structure of DFCDs, understanding the correlation between the doping and properties, and achieving new applications.

  15. Fluorescent Carbon Quantum Dots as Single Light Converter for White LEDs

    NASA Astrophysics Data System (ADS)

    Feng, Xiaoting; Zhang, Feng; Wang, Yaling; Zhang, Yi; Yang, Yongzhen; Liu, Xuguang

    2016-06-01

    Synthesis of fluorescent carbon quantum dots (CQDs) as single light converter and their application in white light-emitting diodes (LEDs) are reported. CQDs were prepared by a one-step hydrothermal method using glucose and polyethylene glycol 200 as precursors. The structural and optical properties of the CQDs were investigated. The CQDs with uniform size of 4 nm possessed typical excitation-dependent emission wavelength and quantum yield of 3.5%. Under ultraviolet illumination, the CQDs in deionized water emitted bright blue fluorescence and produced broad visible-light emission with high red, green, and blue spectral component ratio of 63.5% (red-to-blue intensity to total intensity), suggesting great potential as single light converter for white LEDs. To demonstrate their potential, a white LED using CQDs as a single light converter was built. The device exhibited cool white light with corresponding color temperature of 5584 K and color coordinates of (0.32, 0.37), belonging to the white gamut. This research suggests that CQDs could be a promising candidate single light converter for white LEDs.

  16. Photodynamics and time-resolved fluorescence of azobenzene in solution: a mixed quantum-classical simulation.

    PubMed

    Cusati, Teresa; Granucci, Giovanni; Persico, Maurizio

    2011-04-06

    We have simulated the photodynamics of azobenzene by means of the Surface Hopping method. We have considered both the trans → cis and the cis → trans processes, caused by excitation in the n → π* band (S(1) state). To bring out the solvent effects on the excited state dynamics, we have run simulations in four different environments: in vacuo, in n-hexane, in methanol, and in ethylene glycol. Our simulations reproduce very well the measured quantum yields and the time dependence of the intensity and anisotropy of the transient fluorescence. Both the photoisomerization and the S(1) → S(0) internal conversion require the torsion of the N═N double bond, but the N-C bond rotations and the NNC bending vibrations also play a role. In the trans → cis photoconversion the N═N torsional motion and the excited state decay are delayed by increasing the solvent viscosity, while the cis → trans processes are less affected. The analysis of the simulation results allows the experimental observations to be explained in detail, and in particular the counterintuitive increase of the trans → cis quantum yield with viscosity, as well as the relationship between the excited state dynamics and the solvent effects on the fluorescence lifetimes and depolarization.

  17. Electronically excited states of membrane fluorescent probe 4-dimethylaminochalcone. Results of quantum chemical calculations.

    PubMed

    Romanov, Alexey N; Gularyan, Samvel K; Polyak, Boris M; Sakovich, Ruslan A; Dobretsov, Gennady E; Sarkisov, Oleg M

    2011-05-28

    Quantum-chemical calculations of ground and excited states for membrane fluorescent probe 4-dimethylaminochalcone (DMAC) in vacuum were performed. Optimized geometries and dipole moments for lowest-lying singlet and triplet states were obtained. The nature of these electronic transitions and the relaxation path in the excited states were determined; changes in geometry and charge distribution were assessed. It was shown that in vacuum the lowest existed level is of (n, π*) nature, and the closest to it is the level of (π, π*) nature; the energy gap between them is narrow. This led to an effective (1)(π, π*) →(1)(n, π*) relaxation. After photoexcitation the molecule undergoes significant transformations, including changes in bond orders, pyramidalization angle of the dimethylamino group, and planarity of the molecule. Its dipole moment rises from 5.5 Debye in the ground state to 17.1 Debye in the (1)(π, π*) state, and then falls to 2 Debye in the (1)(n, π*) state. The excited (1)(n, π*) state is a short living state; it has a high probability of intersystem crossing into the (3)(π, π*) triplet state. This relaxation path explains the low quantum yield of DMAC fluorescence in non-polar media. It is possible that (3)(π, π*) is responsible for observed DMAC phosphorescence.

  18. Ultrasmall Quantum Dots: A Tool for in Vitro and in Vivo Fluorescence Imaging

    NASA Astrophysics Data System (ADS)

    Linkov, Pavel; Vokhmintcev, Kirill V.; Samokhvalov, Pavel S.; Nabiev, Igor

    2017-01-01

    Fluorescence bioimaging is an increasingly popular approach in biomedical research and diagnosis, where semiconductor nanocrystals or quantum dots (QDs) have proved to be excellent fluorescent labels. The use of ultrasmall QDs in nanoprobes extends the possibilities of bioimaging owing to an enhanced capacity for penetrating through cell membranes. However, the QDs synthesis is accompanied by the rapid growth of nanocrystals in colloidal medium what prevents obtaining sufficiently small QDs prepared by conventional approaches. Here, a one-pot injection technique of QD synthesis in an organic medium, with the reaction terminated at an early crystal growth stage and excess precursors eliminated by gel permeation chromatography, is proposed. This technique yields defect-free cadmium selenide QD cores about 1.5 nm in size emitting at the wavelengths less than 500 nm. Coating of these QDs with epitaxial shells of different compositions ensures a photoluminescence quantum yield approaching 100%. The resultant ultrasmall QDs are promising components of nanoprobes to be used for imaging intracellular and intranuclear events down to the molecular level.

  19. Ultrasmall quantum dots for fluorescent bioimaging in vivo and in vitro

    NASA Astrophysics Data System (ADS)

    Linkov, P. A.; Vokhmintcev, K. V.; Samokhvalov, P. S.; Nabiev, I. R.

    2017-01-01

    Photoluminescent semiconductor quantum dots (QDs) are widely used in many branches of diagnostics and biomedicine. Using ultrasmall QDs for designing fluorescent nanoprobes increases their capacity for penetrating through cell membranes, which allows one to use them for tracking intracellular processes at the molecular level. Obtaining small-size QDs is usually impeded due to the fast kinetics of reactions of their formation and growth in a colloidal medium. We propose a method of synthesizing defectless CdSe QDs with a diameter of 1.5 nm based on the injection reaction in an organic medium, with superfast termination of the growth of QDs at the early stage of their formation. Separation of QDs by means of gel-permeation chromatography allows one to completely remove the excess of cadmium precursors not entering the reaction, which ensures the subsequent obtaining of QDs with a controllable fluorescence wavelength and high quantum yield in the process of depositing protective epitaxial shells of different compositions. The obtained ultrasmall QDs may find application in developing photoluminescent nanoprobes for visualizing intranuclear processes in cells.

  20. Mechanisms of fluorescence decays of colloidal CdSe-CdS/ZnS quantum dots unraveled by time-resolved fluorescence measurement.

    PubMed

    Xu, Hao; Chmyrov, Volodymyr; Widengren, Jerker; Brismar, Hjalmar; Fu, Ying

    2015-11-07

    By narrowing the detection bandpass and increasing the signal-to-noise ratio in measuring the time-resolved fluorescence decay spectrum of colloidal CdSe-CdS/ZnS quantum dots (QDs), we show that directly after the photoexcitation, the fluorescence decay spectrum is characterized by a single exponential decay, which represents the energy relaxation of the photogenerated exciton from its initial high-energy state to the ground exciton state. The fluorescence decay spectrum of long decay time is in the form of β/t(2), where β is the radiative recombination time of the ground-state exciton and t is the decay time. Our findings provide us with a direct and quantitative link between fluorescence decay measurement data and fundamental photophysics of QD exciton, thereby leading to a novel way of applying colloidal QDs to study microscopic, physical and chemical processes in many fields including biomedicine.

  1. Micro-RNA detection based on fluorescence resonance energy transfer of DNA-carbon quantum dots probes.

    PubMed

    Khakbaz, Faeze; Mahani, Mohamad

    2017-04-15

    Carbon quantum dots have been proposed as an effective platform for miRNA detection. Carbon dots were synthesized by citric acid. The synthesized dots were characterized by dynamic light scattering, UV-Vis spectrophotometry, spectrofluorimetry, transmission electron microscopy and FT-IR spectrophotometry. The fluorescence quantum yield of the synthesized dots was determined using quinine sulfate as the standard. The FAM-labeled single stranded DNA, as sensing element, was adsorbed on dots by π-π interaction. The quenching of the dots fluorescence due to fluorescence resonance energy transfer (FRET) was used for mir 9-1 detection. In the presence of the complementary miRNA, the FRET did not take place and the fluorescence was recovered.

  2. A sensitive fluorescent nanosensor for chloramphenicol based on molecularly imprinted polymer-capped CdTe quantum dots.

    PubMed

    Amjadi, Mohammad; Jalili, Roghayeh; Manzoori, Jamshid L

    2016-05-01

    A novel fluorescent nanosensor using molecularly imprinted silica nanospheres embedded CdTe quantum dots (CdTe@SiO2 @MIP) was developed for detection and quantification of chloramphenicol (CAP). The imprinted sensor was prepared by synthesis of molecularly imprinting polymer (MIP) on the hydrophilic CdTe quantum dots via reverse microemulsion method using small amounts of solvents. The resulting CdTe@SiO2 @MIP nanoparticles were characterized by fluorescence, UV-vis absorption and FT-IR spectroscopy and transmission electron microscopy. They preserved 48% of fluorescence quantum yield of the parent quantum dots. CAP remarkably quenched the fluorescence of prepared CdTe@SiO2 @MIP, probably via electron transfer mechanism. Under the optimal conditions, the relative fluorescence intensity of CdTe@SiO2 @MIP decreased with increasing CAP by a Stern-Volmer type equation in the concentration range of 40-500 µg L(-1). The corresponding detection limit was 5.0 µg L(-1). The intra-day and inter-day values for the precision of the proposed method were all <4%. The developed sensor had a good selectivity and was applied to determine CAP in spiked human and bovine serum and milk samples with satisfactory results.

  3. Quantum-dot-tagged reduced graphene oxide nanocomposites for bright fluorescence bioimaging and photothermal therapy monitored in situ.

    PubMed

    Hu, Shang-Hsiu; Chen, Yu-Wei; Hung, Wen-Ting; Chen, I-Wei; Chen, San-Yuan

    2012-04-03

    Quantum-dot-tagged reduced graphene oxide (QD-rGO) nanocomposites (left) internalized into targeted tumor cells display bright fluorescence from the QDs (right); by absorbing NIR radiation incident on the rGO and converting it into heat, they also cause simultaneous cell death and fluorescence reduction (bottom). The nanocomposite is thus capable of tumor imaging, photothermal therapy and in situ monitoring of treatment in progress.

  4. Decoding of quantum dots encoded microbeads using a hyperspectral fluorescence imaging method.

    PubMed

    Liu, Yixi; Liu, Le; He, Yonghong; Zhu, Liang; Ma, Hui

    2015-05-19

    We presented a decoding method of quantum dots encoded microbeads with its fluorescence spectra using line scan hyperspectral fluorescence imaging (HFI) method. A HFI method was developed to attain both the spectra of fluorescence signal and the spatial information of the encoded microbeads. A decoding scheme was adopted to decode the spectra of multicolor microbeads acquired by the HFI system. Comparison experiments between the HFI system and the flow cytometer were conducted. The results showed that the HFI system has higher spectrum resolution; thus, more channels in spectral dimension can be used. The HFI system detection and decoding experiment with the single-stranded DNA (ssDNA) immobilized multicolor beads was done, and the result showed the efficiency of the HFI system. Surface modification of the microbeads by use of the polydopamine was characterized by the scanning electron microscopy and ssDNA immobilization was characterized by the laser confocal microscope. These results indicate that the designed HFI system can be applied to practical biological and medical applications.

  5. Fluorescently labelled multiplex lateral flow immunoassay based on cadmium-free quantum dots.

    PubMed

    Beloglazova, Natalia V; Sobolev, Aleksander M; Tessier, Mickael D; Hens, Zeger; Goryacheva, Irina Yu; De Saeger, Sarah

    2017-03-01

    A sensitive tool for simultaneous qualitative detection of two mycotoxins based on use of non-cadmium quantum dots (QDs) is presented for the first time. QDs have proven themselves as promising fluorescent labels for biolabeling and chemical analysis. With an increasing global tendency to regulate and limit the use of hazardous elements, indium phosphide (InP) QDs are highlighted as environmentally-friendly alternatives to the highly efficient and well-studied, but potentially toxic Cd- and Pb-based QDs. Here, we developed water-soluble InP QDs-based fluorescent nanostructures. They consisted of core/shell InP/ZnS QDs enrobed in a silica shell that allowed the water solubility (QD@SiO2). Then we applied the QD@SiO2 as novel, silica shell-encapsulated fluorescent labels in immunoassays for rapid multiplexed screening. Two mycotoxins, zearalenone and deoxynivalenol, were simultaneously detected in maize and wheat, since the two QD@SiO2 labelled conjugates emit at two different, individually detectable wavelengths. The cutoff values for the simultaneous determination were 50 and 500μgkg(-1) for zearalenone and deoxynivalenol, respectively, in both maize and wheat. Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was used to confirm the result.

  6. Synthesis and biological assay of GSH functionalized fluorescent quantum dots for staining Hydra vulgaris.

    PubMed

    Tortiglione, Claudia; Quarta, Alessandra; Tino, Angela; Manna, Liberato; Cingolani, Roberto; Pellegrino, Teresa

    2007-01-01

    Quantum dots (QDs) have been used extensively as fluorescent markers in several studies on living cells. Here, we report the synthesis of conjugates based on glutathione (GSH) and QDs (GSH-QDs) and we prove how these functionalized fluorescent probes can be used for staining a freshwater invertebrate called Hydra vulgaris. GSH is known to promote Hydra feeding response by inducing mouth opening. We demonstrate that GSH-QDs as well are able to elicit biological activity in such an animal, which results in the fluorescent staining of Hydra. GSH-QDs, once they reach the gastric region, are internalized by endodermal cells. The efficiency of GSH-QD internalization increases significantly when nanoparticles are coadministrated with free GSH. We also compared the behavior of bare QDs to that of GSH-QDs both in the presence and in the absence of free GSH. The conclusions from these series of experiments point to the presence of GSH binding proteins in the endodermal cell layer and uncover a novel role played by glutathione in this organism.

  7. Novel quantum criticality in CeRu2Si2 near absolute zero observed by thermal expansion and magnetostriction.

    PubMed

    Yoshida, J; Abe, S; Takahashi, D; Segawa, Y; Komai, Y; Tsujii, H; Matsumoto, K; Suzuki, H; Onuki, Y

    2008-12-19

    We report linear thermal expansion and magnetostriction measurements for CeRu2Si2 in magnetic fields up to 52.6 mT and at temperatures down to 1 mK. At high temperatures, this compound showed Landau-Fermi-liquid behavior: The linear thermal expansion coefficient and the magnetostriction coefficient were proportional to the temperature and magnetic field, respectively. In contrast, a pronounced non-Fermi-liquid effect was found below 50 mK. The negative contribution of thermal expansion and magnetostriction suggests the existence of an additional quantum critical point.

  8. Amino Nitrogen Quantum Dots-Based Nanoprobe for Fluorescence Detection and Imaging of Cysteine in Biological Samples.

    PubMed

    Tang, Zhijiao; Lin, Zhenhua; Li, Gongke; Hu, Yuling

    2017-03-20

    Fluorescent amino nitrogen quantum dots (aN-dots) were synthesized by microwave-assisted method using 2-azidoimidazole and aqueous ammonia. The aN-dots have a nitrogen component up to 40%, which exhibit high fluorescence quantum yield, good photostability, and excellent biocompatibility. We further explored the use of the aN-dots combined with AuNPs as a nanoprobe for detecting fluorescently and imaging of cysteine (Cys) in complex biological samples. In this sensing system, the fluorescence of aN-dots was quenched significantly by gold nanoparticles (AuNPs), while the addition of Cys can lead to the fluorescence signal recovery. Furthermore, we have demonstrated that this strategy can offer a rapid and selective detection of Cys with a good linear relationship in the range of 0.3-3.0 μmol/L. As expected, this assay was successfully applied to the detection of Cys in human serum and plasma samples with recoveries ranging from 90.0% to 106.7%. Especially, the nanoprobe exhibits good cell membrane permeability and excellent biocompatibility by CCK-8 assay, which is favorable for bioimaging applications. Therefore, this fluorescent probe ensemble was further used for imaging of Cys in living cells, which suggests our proposed method has strong potential for clinical diagnosis. As a novel member of the quantum-dot family, the aN-dots hold great promise to broaden applications in biological systems.

  9. Intrinsically Labeled Fluorescent Oligonucleotide Probes on Quantum Dots for Transduction of Nucleic Acid Hybridization.

    PubMed

    Shahmuradyan, Anna; Krull, Ulrich J

    2016-03-15

    Quantum dots (QDs) have been widely used in chemical and biosensing due to their unique photoelectrical properties and are well suited as donors in fluorescence resonance energy transfer (FRET). Selective hybridization interactions of oligonucleotides on QDs have been determined by FRET. Typically, the QD-FRET constructs have made use of labeled targets or have implemented labeled sandwich format assays to introduce dyes in proximity to the QDs for the FRET process. The intention of this new work is to explore a method to incorporate the acceptor dye into the probe molecule. Thiazole orange (TO) derivatives are fluorescent intercalating dyes that have been used for detection of double-stranded nucleic acids. One such dye system has been reported in which single-stranded oligonucleotide probes were doubly labeled with adjacent thiazole orange derivatives. In the absence of the fully complementary (FC) oligonucleotide target, the dyes form an H-aggregate, which results in quenching of fluorescence emission due to excitonic interactions between the dyes. The hybridization of the FC target to the probe provides for dissociation of the aggregate as the dyes intercalate into the double stranded duplex, resulting in increased fluorescence. This work reports investigation of the dependence of the ratiometric signal on the type of linkage used to conjugate the dyes to the probe, the location of the dye along the length of the probe, and the distance between adjacent dye molecules. The limit of detection for 34mer and 90mer targets was found to be identical and was 10 nM (2 pmol), similar to analogous QD-FRET using labeled oligonucleotide target. The detection system could discriminate a one base pair mismatch (1BPM) target and was functional without substantial compromise of the signal in 75% serum. The 1BPM was found to reduce background signal, indicating that the structure of the mismatch affected the environment of the intercalating dyes.

  10. Efficient fluorescence energy transfer system between fluorescein isothiocyanate and CdTe quantum dots for the detection of silver ions.

    PubMed

    Feng, Yueshu; Liu, Liwei; Hu, Siyi; Zou, Peng; Zhang, Jiaqi; Huang, Chen; Wang, Yue; Wang, Sihan; Zhang, Xihe

    2016-03-01

    We report a fluorescence resonance energy transfer (FRET) system in which the fluorescent donor is fluorescein isothiocyanate (FITC) dye and the fluorescent acceptor is CdTe quantum dot (QDs). Based on FRET quenching theory, we designed a method to detect the concentration of silver ions (Ag(+)). The results revealed a good linear trend over Ag(+) concentrations in the range 0.01-8.96 nmol/L, a range that was larger than with other methods; the quenching coefficient is 0.442. The FRET mechanism and physical mechanisms responsible for dynamic quenching are also discussed.

  11. Ratiometric fluorescent paper sensor utilizing hybrid carbon dots-quantum dots for the visual determination of copper ions

    NASA Astrophysics Data System (ADS)

    Wang, Yahui; Zhang, Cheng; Chen, Xiaochun; Yang, Bo; Yang, Liang; Jiang, Changlong; Zhang, Zhongping

    2016-03-01

    A simple and effective ratiometric fluorescence nanosensor for the selective detection of Cu2+ has been developed by covalently connecting the carboxyl-modified red fluorescent cadmium telluride (CdTe) quantum dots (QDs) to the amino-functionalized blue fluorescent carbon nanodots (CDs). The sensor exhibits the dual-emissions peaked at 437 and 654 nm, under a single excitation wavelength of 340 nm. The red fluorescence can be selectively quenched by Cu2+, while the blue fluorescence is a internal reference, resulting in a distinguishable fluorescence color change from pink to blue under a UV lamp. The detection limit of this highly sensitive ratiometric probe is as low as 0.36 nM, which is lower than the U.S. Environmental Protection Agency (EPA) defined limit (20 μM). Moreover, a paper-based sensor has been prepared by printing the hybrid carbon dots-quantum dots probe on a microporous membrane, which provides a convenient and simple approach for the visual detection of Cu2+. Therefore, the as-synthesized probe shows great potential application for the determination of Cu2+ in real samples.A simple and effective ratiometric fluorescence nanosensor for the selective detection of Cu2+ has been developed by covalently connecting the carboxyl-modified red fluorescent cadmium telluride (CdTe) quantum dots (QDs) to the amino-functionalized blue fluorescent carbon nanodots (CDs). The sensor exhibits the dual-emissions peaked at 437 and 654 nm, under a single excitation wavelength of 340 nm. The red fluorescence can be selectively quenched by Cu2+, while the blue fluorescence is a internal reference, resulting in a distinguishable fluorescence color change from pink to blue under a UV lamp. The detection limit of this highly sensitive ratiometric probe is as low as 0.36 nM, which is lower than the U.S. Environmental Protection Agency (EPA) defined limit (20 μM). Moreover, a paper-based sensor has been prepared by printing the hybrid carbon dots-quantum dots probe on a

  12. Identification of GABA A receptor modulators in Kadsura longipedunculata and assignment of absolute configurations by quantum-chemical ECD calculations

    PubMed Central

    Zaugg, Janine; Ebrahimi, Samad Nejad; Smiesko, Martin; Baburin, Igor; Hering, Steffen; Hamburger, Matthias

    2011-01-01

    A petroleum ether extract of Kadsura longipedunculata enhanced the GABA-induced chloride current (IGABA) by 122.5 ± 0.3% (n = 2) when tested at 100 μg/ml in Xenopus laevis oocytes expressing GABA A receptors (α1β2γ2S subtype) in two-microelectrode voltage clamp measurements. Thirteen compounds were subsequently identified by HPLC-based activity profiling as responsible for GABA A receptor activity and purified in preparative scale. 6-Cinnamoyl-6,7-dihydro-7-myrceneol and 5,6-dihydrocuparenic acid were thereby isolated for the first time. The determination of the absolute stereochemistry of these compounds was achieved by comparison of experimental and calculated ECD spectra. All but one of the 13 isolated compounds from K. longipedunculata potentiated IGABA through GABA A receptors composed of α1β2γ2S subunits in a concentration-dependent manner. Potencies ranged from 12.8 ± 3.1 to 135.6 ± 85.7 μM, and efficiencies ranged from 129.7 ± 36.8% to 885.8 ± 291.2%. The phytochemical profiles of petroleum ether extracts of Kadsura japonica fruits (114.1 ± 2.6% potentiation of IGABA at 100 μg/ml, n = 2), and Schisandra chinensis fruits (inactive at 100 μg/ml) were compared by HPLC-PDA-ESIMS with that of K. longipedunculata. PMID:21889177

  13. Automated four color CD4/CD8 analysis of leukocytes by scanning fluorescence microscopy using Quantum dots

    NASA Astrophysics Data System (ADS)

    Bocsi, Jozsef; Mittag, Anja; Varga, Viktor S.; Molnar, Bela; Tulassay, Zsolt; Sack, Ulrich; Lenz, Dominik; Tarnok, Attila

    2006-02-01

    Scanning Fluorescence Microscope (SFM) is a new technique for automated motorized microscopes to measure multiple fluorochrome labeled cells (Bocsi et al. Cytometry 2004, 61A:1). The ratio of CD4+/CD8+ cells is an important in immune diagnostics in immunodeficiency and HIV. Therefor a four-color staining protocol (DNA, CD3, CD4 and CD8) for automated SFM analysis of lymphocytes was developed. EDTA uncoagulated blood was stained with organic and inorganic (Quantum dots) fluorochromes in different combinations. Aliquots of samples were measured by Flow Cytometry (FCM) and SFM. By SFM specimens were scanned and digitized using four fluorescence filter sets. Automated cell detection (based on Hoechst 33342 fluorescence), CD3, CD4 and CD8 detection were performed, CD4/CD8 ratio was calculated. Fluorescence signals were well separable on SFM and FCM. Passing and Bablok regression of all CD4/CD8 ratios obtained by FCM and SFM (F(X)=0.0577+0.9378x) are in the 95% confidence interval. Cusum test did not show significant deviation from linearity (P>0.10). This comparison indicates that there is no systemic bias between the two different methods. In SFM analyses the inorganic Quantum dot staining was very stable in PBS in contrast to the organic fluorescent dyes, but bleached shortly after mounting with antioxidant and free radical scavenger mounting media. This shows the difficulty of combinations of organic dyes and Quantum dots. Slide based multi-fluorescence labeling system and automated SFM are applicable tools for the CD4/CD8 ratio determination in peripheral blood samples. Quantum Dots are stable inorganic fluorescence labels that may be used as reliable high resolution dyes for cell labeling.

  14. CdTe quantum dot-based fluorescent probes for selective detection of Hg (II): The effect of particle size

    NASA Astrophysics Data System (ADS)

    Zhu, Jian; Zhao, Zhu-Jun; Li, Jian-Jun; Zhao, Jun-Wu

    2017-04-01

    Mercury ions-induced fluorescence quenching properties of CdTe quantum dots (QDs) have been studied using the fluorescence spectroscopic techniques. By using the hydrothermal method, the CdTe QDs with different particles sizes from 1.98 to 3.68 nm have been prepared, and the corresponding fluorescence emission wavelength is changed from 518 to 620 nm. The fluorescence of QDs is enhanced after linking Bovine serum albumin (BSA) onto the surface of the QDs. Experimental results show that the fluorescence intensity of BSA-coated CdTe QDs could be effectively quenched when Hg2 + react with BSA-coated CdTe QDs. Interestingly, both the sensing sensitivity and selectivity of this fluorescence probe could be improved when the particle size of the QDs decreases. Thus the BSA-coated CdTe QDs with green fluorescence emission have better advantages than the BSA-coated CdTe QDs with red fluorescence for Hg2 + detection. Interference experiment results indicate that the influence from other metal ions could be neglected in the detection, and the Hg2 + could be specifically detected. By using this BSA-coated CdTe QDs-based fluorescence probe, the Hg2 + could be detected with an ultra-low detection limit of nanomole level, and the linear range spans a scope from 0.001 to 1 μmol/L.

  15. Using the near-field coupling of a sharp tip to tune fluorescence-emission fluctuations during quantum-dot blinking.

    PubMed

    Shafran, Eyal; Mangum, Benjamin D; Gerton, Jordan M

    2011-07-15

    We demonstrate that the cycling between internal states of quantum dots during fluorescence blinking can be used to tune the near-field coupling with a sharp tip. In particular, the fluorescence emission from states with high quantum yield is quenched due to energy transfer, while that from low-yield states is elevated due to field enhancement. Thus, as a quantum dot blinks, its emission fluctuations are progressively suppressed upon approach of a tip.

  16. Thermally activated delayed fluorescence OLEDs with fully solution processed organic layers exhibiting nearly 10% external quantum efficiency.

    PubMed

    Albrecht, Ken; Matsuoka, Kenichi; Yokoyama, Daisuke; Sakai, Yoshiya; Nakayama, Akira; Fujita, Katsuhiko; Yamamoto, Kimihisa

    2017-02-21

    New solution processable and laminatable terminally modified carbazole-triazine thermally activated delayed fluorescence (TADF) dendrimers are reported. An OLED device with fully solution processed organic layers exhibited an external quantum efficiency of up to 9.4% at 100 cd m(-2).

  17. Fabrication of fluorescent composite with ultrafast aqueous synthesized high luminescent CdTe quantum dots

    SciTech Connect

    Zhang, Lei Chen, Haibin E-mail: mejswu@ust.hk; Wu, Jingshen E-mail: mejswu@ust.hk; Bi, Xianghong

    2014-05-15

    Without precursor preparation, inert gas protection and enormous amount of additives and reductants, CdTe quantum dots (QDs) can be rapidly synthesized with high quality. A 600 nm photoluminescence peak wavelength could be obtained within 1 hour's refluxing through minimal addition of 1,2-diaminoethane (DAE). The theoretical design for the experiments are illustrated and further proved by the characterization results with different concentrations and reagents. On the other hand, generation of CdTe QDs was found even under room temperature by applying droplet quantity of DAE. This indicates that QDs can be synthesized with simply a bottle and no enormous additives required. The QDs were mixed into the epoxy matrix through solution casting method with cetyltrimethylammonium (CTA) capping for phase transfer. The acquired epoxy based nanocomposite exhibits good transparency, compatibility and fluorescence.

  18. A Fluorescence Displacement Assay for Antidepressant Drug Discovery Based on Ligand-Conjugated Quantum Dots

    SciTech Connect

    Chang, Jerry; Tomlinson, Ian; Warnement, Michael; Iwamoto, Hideki

    2011-01-01

    The serotonin (5-hydroxytryptamine, 5-HT) transporter (SERT) protein plays a central role in terminating 5-HT neurotransmission and is the most important therapeutic target for the treatment of major depression and anxiety disorders. We report an innovative, versatile, and target-selective quantum dot (QD) labeling approach for SERT in single Xenopus oocytes that can be adopted as a drug-screening platform. Our labeling approach employs a custom-made, QD-tagged indoleamine derivative ligand, IDT318, that is structurally similar to 5-HT and accesses the primary binding site with enhanced human SERT selectivity. Incubating QD-labeled oocytes with paroxetine (Paxil), a high-affinity SERT-specific inhibitor, showed a concentration- and time-dependent decrease in QD fluorescence, demonstrating the utility of our approach for the identification of SERT modulators. Furthermore, with the development of ligands aimed at other pharmacologically relevant targets, our approach may potentially form the basis for a multitarget drug discovery platform.

  19. Enhancement of squeezing in resonance fluorescence of a driven quantum dot close to a graphene sheet

    NASA Astrophysics Data System (ADS)

    Fang, Wei; Wu, Qing-lin; Wu, Shao-ping; Li, Gao-xiang

    2016-05-01

    We investigate squeezing of the resonance fluorescence of a laser-driven quantum dot (QD) close to a graphene sheet. The coupling between the QD and the surface plasmon around the graphene sheet is frequency dependent in the terahertz region, which can be adjusted by the laser intensity. Distinct decay rates in different transition channels of dressed QDs can be achieved due to the tailored photon reservoir, which can be used to improve the squeezing. It is found that increases in both the dephasing rate and the environmental temperature are harmful to the squeezing. Meanwhile, an enhancement in the QD-plasmon coupling strength may reduce the fragility of squeezing against the decoherence process. Additionally, in the strong light-matter coupling region, squeezing can be largely enhanced by tuning the strength of the pump field and its detuning from the QD.

  20. Near-IR fluorescence and reflectance confocal microscopy for imaging of quantum dots in mammalian skin

    PubMed Central

    Mortensen, Luke J.; Glazowski, Christopher E.; Zavislan, James M.; DeLouise, Lisa A.

    2011-01-01

    Understanding the skin penetration of nanoparticles (NPs) is an important concern due to the increasing presence of NPs in consumer products, including cosmetics. Technical challenges have slowed progress in evaluating skin barrier and NP factors that contribute to skin penetration risk. To limit sampling error and other problems associated with histological processing, many researchers are implementing whole tissue confocal or multiphoton microscopies. This work introduces a fluorescence and reflectance confocal microscopy system that utilizes near-IR excitation and emission to detect near-IR lead sulfide quantum dots (QDs) through ex vivo human epidermis. We provide a detailed prediction and experimental analysis of QD detection sensitivity and demonstrate detection of QD skin penetration in a barrier disrupted model. The unique properties of near-IR lead-based QDs will enable future studies that examine the impact of further barrier-disrupting agents on skin penetration of QDs and elucidate mechanistic insight into QD tissue interactions at the cellular level. PMID:21698023

  1. Fluorescent cadmium telluride quantum dots embedded chitosan nanoparticles: a stable, biocompatible preparation for bio-imaging.

    PubMed

    Ghormade, Vandana; Gholap, Haribhau; Kale, Sonia; Kulkarni, Vaishnavi; Bhat, Suresh; Paknikar, Kishore

    2015-01-01

    Fluorescent cadmium telluride quantum dots (CdTe QDs) are an optically attractive option for bioimaging, but are known to display high cytotoxicity. Nanoparticles synthesized from chitosan, a natural biopolymer of β 1-4 linked glucosamine, display good biocompatibility and cellular uptake. A facile, green synthetic strategy has been developed to embed green fluorescent cadmium telluride quantum dots (CdTe QDs) in biocompatible CNPs to obtain a safer preparation than 'as is' QDs. High-resolution transmission electron microscopy showed the crystal lattice corresponding to CdTe QDs embedded in CNPs while thermogravimetry confirmed their polymeric composition. Electrostatic interactions between thiol-capped QDs (4 nm, -57 mV) and CNPs (~300 nm, +38 mV) generated CdTe QDs-embedded CNPs that were stable up to three months. Further, viability of NIH3T3 mouse fibroblast cells in vitro increased in presence of QDs-embedded CNPs as compared to bare QDs. At the highest concentration (10 μg/ml), the former shows 34 and 39% increase in viability at 24 and 48 h, respectively, as compared to the latter. This shows that chitosan nanoparticles do not release the QDs up to 48 h and do not cause extended toxicity. Furthermore, hydrolytic enzymes such as lysozyme and chitinase did not degrade chitosan nanoparticles. Moreover, QDs-embedded CNPs show enhanced internalization in NIH3T3 cells as compared to bare QDs. This method offers ease of synthesis and handling of stable, luminescent, biocompatible CdTe QDs-embedded CNPs with a favorable toxicity profile and better cellular uptake with potential for bioimaging and targeted detection of cellular components.

  2. Measurement procedure for absolute broadband infrared up-conversion photoluminescent quantum yields: Correcting for absorption/re-emission

    SciTech Connect

    MacDougall, Sean K. W.; Ivaturi, Aruna; Marques-Hueso, Jose; Richards, Bryce S.

    2014-06-15

    The internal photoluminescent quantum yield (iPLQY) – defined as the ratio of emitted photons to those absorbed – is an important parameter in the evaluation and application of luminescent materials. The iPLQY is rarely reported due to the complexities in the calibration of such a measurement. Herein, an experimental method is proposed to correct for re-emission, which leads to an underestimation of the absorption under broadband excitation. Although traditionally the iPLQY is measured using monochromatic sources for linear materials, this advancement is necessary for nonlinear materials with wavelength dependent iPLQY, such as the application of up-conversion to solar energy harvesting. The method requires an additional measurement of the emission line shape that overlaps with the excitation and absorption spectra. Through scaling of the emission spectrum, at the long wavelength edge where an overlap of excitation does not occur, it is possible to better estimate the value of iPLQY. The method has been evaluated for a range of nonlinear material concentrations and under various irradiances to analyze the necessity and boundary conditions that favor the proposed method. Use of this refined method is important for a reliable measurement of iPLQY under a broad illumination source such as the Sun.

  3. Fluorescence of tryptophan in designed hairpin and Trp-cage miniproteins: measurements of fluorescence yields and calculations by quantum mechanical molecular dynamics simulations.

    PubMed

    McMillan, Andrew W; Kier, Brandon L; Shu, Irene; Byrne, Aimee; Andersen, Niels H; Parson, William W

    2013-02-14

    The quantum yield of tryptophan (Trp) fluorescence was measured in 30 designed miniproteins (17 β-hairpins and 13 Trp-cage peptides), each containing a single Trp residue. Measurements were made in D(2)O and H(2)O to distinguish between fluorescence quenching mechanisms involving electron and proton transfer in the hairpin peptides, and at two temperatures to check for effects of partial unfolding of the Trp-cage peptides. The extent of folding of all the peptides also was measured by NMR. The fluorescence yields ranged from 0.01 in some of the Trp-cage peptides to 0.27 in some hairpins. Fluorescence quenching was found to occur by electron transfer from the excited indole ring of the Trp to a backbone amide group or the protonated side chain of a nearby histidine, glutamate, aspartate, tyrosine, or cysteine residue. Ionized tyrosine side chains quenched strongly by resonance energy transfer or electron transfer to the excited indole ring. Hybrid classical/quantum mechanical molecular dynamics simulations were performed by a method that optimized induced electric dipoles separately for the ground and excited states in multiple π-π* and charge-transfer (CT) excitations. Twenty 0.5 ns trajectories in the tryptophan's lowest excited singlet π-π* state were run for each peptide, beginning by projections from trajectories in the ground state. Fluorescence quenching was correlated with the availability of a CT or exciton state that was strongly coupled to the π-π* state and that matched or fell below the π-π* state in energy. The fluorescence yields predicted by summing the calculated rates of charge and energy transfer are in good accord with the measured yields.

  4. Efficient stray-light suppression for resonance fluorescence in quantum dot micropillars using self-aligned metal apertures

    NASA Astrophysics Data System (ADS)

    Hopfmann, Caspar; Musiał, Anna; Maier, Sebastian; Emmerling, Monika; Schneider, Christian; Höfling, Sven; Kamp, Martin; Reitzenstein, Stephan

    2016-09-01

    Within this work we propose and demonstrate a technological approach to efficiently suppress excitation laser stray-light in resonance fluorescence experiments on quantum dot micropillars. To ensure efficient stray-light suppression, their fabrication process includes a planarization step and subsequent covering with a titanium mask to fabricate self-aligned apertures at the micropillar positions. These apertures aim to limit laser stray-light in the side-excitation vertical-detection configuration, while enabling detection of the optical signal through the top facet of the micropillars. The beneficial effects of these apertures are proven and quantitatively evaluated within a statistical study in which we determine and compare the stray-light suppression of 48 micropillars with and without metal apertures. Actual resonance fluorescence experiments on single quantum dots coupled to the cavity mode prove the relevance of the proposed approach and demonstrate that it will foster further studies on cavity quantum electrodynamics phenomena under coherent optical excitation.

  5. Manipulating quantum dot fluorescence by utilizing Brownian induced near-field interactions with plasmonic nanoparticles

    NASA Astrophysics Data System (ADS)

    Palombo, Nola

    Quantum dots (QDs) are semiconductor nanocrystals with size-dependent optical properties; thus making them supreme fluorophores. Plasmonic nanoparticles (PNPs), such as gold and silver nanoparticles, support localized surface plasmons on their surface. When the localized surface plasmons are excited, a highly concentrated electromagnetic field is formed near the particle. Therefore, if a QD is within the near-field of a PNP, the emission or excitation of the QD can be enhanced. However, due to Forster Resonance Energy Transfer (FRET), the QD fluorescence could instead be quenched by the proximity of PNPs. Whether enhancement or quenching occurs, is dependent upon the distance and geometry of the nanoparticles. Enhanced QD fluorescence would be helpful in biomedical sensing and imaging and solar energy conversion applications. In addition, quenched QD fluorescence caused by FRET could be applied to FRET-based sensing and imaging in medical diagnosis. This master's thesis first theoretically models the stochastic movement of QDs and PNPs in an aqueous solution. The simulation is based upon the Direct Simulation Monte Carlo method coupled with Langevin equations. Using this simulation, we were able to predict the percentage of QDs in the near-field region of PNPs. The percentage of QDs in the near-field region of GNPs for a concentration of 1 × 1013 QDs/mL and 5 × 108 GNPs/mL, is a very small percentage of 2 × 10-5%. Yet, the concentration of QDs in the near-field region of GNPs was calculated to be 1,510,000 QDs mL-1. In addition, this master's thesis experimentally explores the enhancement and quenching of QD emission for different concentrations and sizes of PNPs in aqueous solutions. The fluorescence spectra of two types of QD-PNP mixtures were measured. The first mixture was QDs and gold nanoparticles (GNPs) dispersed in distilled water, where the emission wavelength of the QDs matches the localized surface plasmon excitation wavelength of the GNPs. The second

  6. Ultrafast Laser Studies of Two-Photon Excited Fluorescence Intermittency in Single CdSe/ZnS Quantum Dots.

    PubMed

    Early, Kevin T; Nesbitt, David J

    2015-12-09

    Two-photon fluorescence microscopy of single quantum dots conditions has been reported by several groups, with contrasting observations regarding the kinetics and dynamics of fluorescence intermittency or "blinking". Here, we investigate the power dependence, kinetics, and statistics of two photon-excited fluorescence intermittency from single CdSe/ZnS quantum dots in a solid PMMA film as a function of sub-bandgap laser intensity at 800 nm. Fluorescence intermittency is observed at all excitation powers and a quadratic (n = 1.97(3)) dependence of the shot noise-limited fluorescence intensity on the incident laser power is verified, confirming essentially zero background contribution from one-photon excitation processes. Such analyses permit two photon absorption cross sections for single quantum dots to be extracted quantitatively from the data, which reveal good agreement with those obtained from previous two-photon FCS measurements. Strictly inverse power law-distributed off-state dwell times are observed for all excitation powers, with a mean power law exponent ⟨m(off)⟩ = 1.65(4) in excellent agreement with the behavior observed under one-photon excitation conditions. Finally, a superquadratic (n = 2.3(2)) rather than quartic (n = 4) power dependence is observed for the on-state blinking dwell times, which we kinetically analyze and interpret in terms of a novel 2 + 1 "hot" exciton ionization/blinking mechanism due to partially saturated 1-photon sub-bandgap excitation out of the two-photon single exciton state. The kinetic results are consistent with quantum dot photoionization quantum yields from "hot" exciton states (4(1) × 10(-6)) comparable with experimental estimates (10(-6)-10(-5)) of Auger ionization efficiencies out of the biexcitonic state.

  7. Quantum dot capped magnetite nanorings as high performance nanoprobe for multiphoton fluorescence and magnetic resonance imaging.

    PubMed

    Fan, Hai-Ming; Olivo, Malini; Shuter, Borys; Yi, Jia-Bao; Bhuvaneswari, Ramaswamy; Tan, Hui-Ru; Xing, Gui-Chuan; Ng, Cheng-Teng; Liu, Lei; Lucky, Sasidharan S; Bay, Boon-Huat; Ding, Jun

    2010-10-27

    In the present study, quantum dot (QD) capped magnetite nanorings (NRs) with a high luminescence and magnetic vortex core have been successfully developed as a new class of magnetic-fluorescent nanoprobe. Through electrostatic interaction, cationic polyethylenimine (PEI) capped QD have been firmly graft into negatively charged magnetite NRs modified with citric acid on the surface. The obtained biocompatible multicolor QD capped magnetite NRs exhibit a much stronger magnetic resonance (MR) T2* effect where the r2* relaxivity and r2*/r1 ratio are 4 times and 110 times respectively larger than those of a commercial superparamagnetic iron oxide. The multiphoton fluorescence imaging and cell uptake of QD capped magnetite NRs are also demonstrated using MGH bladder cancer cells. In particular, these QD capped magnetite NRs can escape from endosomes and be released into the cytoplasm. The obtained results from these exploratory experiments suggest that the cell-penetrating QD capped magnetite NRs could be an excellent dual-modality nanoprobe for intracellular imaging and therapeutic applications. This work has shown great potential of the magnetic vortex core based multifunctional nanoparticle as a high performance nanoprobe for biomedical applications.

  8. Proteolytic activity monitored by fluorescence resonance energy transfer through quantum-dot-peptide conjugates

    NASA Astrophysics Data System (ADS)

    Medintz, Igor L.; Clapp, Aaron R.; Brunel, Florence M.; Tiefenbrunn, Theresa; Tetsuo Uyeda, H.; Chang, Eddie L.; Deschamps, Jeffrey R.; Dawson, Philip E.; Mattoussi, Hedi

    2006-07-01

    Proteases are enzymes that catalyse the breaking of specific peptide bonds in proteins and polypeptides. They are heavily involved in many normal biological processes as well as in diseases, including cancer, stroke and infection. In fact, proteolytic activity is sometimes used as a marker for some cancer types. Here we present luminescent quantum dot (QD) bioconjugates designed to detect proteolytic activity by fluorescence resonance energy transfer. To achieve this, we developed a modular peptide structure which allowed us to attach dye-labelled substrates for the proteases caspase-1, thrombin, collagenase and chymotrypsin to the QD surface. The fluorescence resonance energy transfer efficiency within these nanoassemblies is easily controlled, and proteolytic assays were carried out under both excess enzyme and excess substrate conditions. These assays provide quantitative data including enzymatic velocity, Michaelis-Menten kinetic parameters, and mechanisms of enzymatic inhibition. We also screened a number of inhibitory compounds against the QD-thrombin conjugate. This technology is not limited to sensing proteases, but may be amenable to monitoring other enzymatic modifications.

  9. Synthesis and enhanced fluorescence of Ag doped CdTe semiconductor quantum dots.

    PubMed

    Ding, Si-Jing; Liang, Shan; Nan, Fan; Liu, Xiao-Li; Wang, Jia-Hong; Zhou, Li; Yu, Xue-Feng; Hao, Zhong-Hua; Wang, Qu-Quan

    2015-02-07

    Doping with intentional impurities is an intriguing way to tune the properties of semiconductor nanocrystals. However, the synthesis of some specific doped semiconductor nanocrystals remains a challenge and the doping mechanism in this strongly confined system is still not clearly understood. In this work, we report, for the first time, the synthesis of stable and water-soluble Ag-doped CdTe semiconductor quantum dots (SQDs) via a facile aqueous approach. Experimental characterization demonstrated the efficient doping of the Ag impurities into the CdTe SQDs with an appropriate reaction time. By doping 0.3% Ag impurities, the Stokes shift is decreased by 120 meV, the fluorescence intensity is enhanced more than 3 times, the radiative rate is enhanced 4.2 times, and the non-radiative rate is efficiently suppressed. These observations reveal that the fluorescence enhancement in Ag-doped CdTe SQDs is mainly attributed to the minimization of surface defects, filling of the trap states, and the enhancement of the radiative rate by the silver dopants. Our results suggest that the silver doping is an efficient method for tuning the optical properties of the CdTe SQDs.

  10. Ultrasmall near-infrared Ag2Se quantum dots with tunable fluorescence for in vivo imaging.

    PubMed

    Gu, Yi-Ping; Cui, Ran; Zhang, Zhi-Ling; Xie, Zhi-Xiong; Pang, Dai-Wen

    2012-01-11

    A strategy is presented that involes coupling Na(2)SeO(3) reduction with the binding of silver ions and alanine in a quasi-biosystem to obtain ultrasmall, near-infrared Ag(2)Se quantum dots (QDs) with tunable fluorescence at 90 °C in aqueous solution. This strategy avoids high temperatures, high pressures, and organic solvents so that water-dispersible sub-3 nm Ag(2)Se QDs can be directly obtained. The photoluminescence of the Ag(2)Se QDs was size-dependent over a wavelength range from 700 to 820 nm, corresponding to sizes from 1.5 ± 0.4 to 2.4 ± 0.5 nm, with good monodispersity. The Ag(2)Se QDs are less cytotoxic than other nanomaterials used for similar applications. Furthermore, the NIR fluorescence of the Ag(2)Se QDs could penetrate through the abdominal cavity of a living nude mouse and could be detected on its back side, demonstrating the potential applications of these less toxic NIR Ag(2)Se QDs in bioimaging.

  11. Biofunctional quantum dots as fluorescence probe for cell-specific targeting.

    PubMed

    Ag, Didem; Bongartz, Rebecca; Dogan, Leyla Eral; Seleci, Muharrem; Walter, Johanna-G; Demirkol, Dilek Odaci; Stahl, Frank; Ozcelik, Serdar; Timur, Suna; Scheper, Thomas

    2014-02-01

    We describe here the synthesis, characterization, bioconjugation, and application of water-soluble thioglycolic acid TGA-capped CdTe/CdS quantum dots (TGA-QDs) for targeted cellular imaging. Anti-human epidermal growth factor receptor 2 (HER2) antibodies were conjugated to TGA-QDs to target HER2-overexpressing cancer cells. TGA-QDs and TGA-QDs/anti-HER2 bioconjugates were characterized by fluorescence and UV-Vis spectroscopy, X-ray diffraction (XRD), hydrodynamic sizing, electron microscopy, and gel electrophoresis. TGA-QDs and TGA-QDs/anti-HER2 were incubated with cells to examine cytotoxicity, targeting efficiency, and cellular localization. The cytotoxicity of particles was measured using an MTT assay and the no observable adverse effect concentration (NOAEC), 50% inhibitory concentration (IC50), and total lethal concentration (TLC) were calculated. To evaluate localization and targeting efficiency of TGA-QDs with or without antibodies, fluorescence microscopy and flow cytometry were performed. Our results indicate that antibody-conjugated TGA-QDs are well-suited for targeted cellular imaging studies.

  12. White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis

    PubMed Central

    Meiling, Till T.; Cywiński, Piotr J.; Bald, Ilko

    2016-01-01

    In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst. PMID:27334409

  13. Fluorescence modulation of cadmium sulfide quantum dots by azobenzene photochromic switches.

    PubMed

    Javed, Hina; Fatima, Kalsoom; Akhter, Zareen; Nadeem, Muhammad Arif; Siddiq, Muhammad; Iqbal, Azhar

    2016-02-01

    We have investigated the attachment of azobenzene photochromic switches on the modified surface of cadmium sulfide (CdS) quantum dots (QDs). The modification of CdS QDs is done by varying the concentration of the capping agent (mercaptoacetic acid) and NH3 in order to control the size of the QDs. The X-ray diffraction studies revealed that the crystallite size of CdS QDs ranged from 6 to 10 nm. The azobenzene photochromic derivatives bis(4-hydroxybenzene-1-azo)4,4'(1,1' diphenylmethane) (I) and 4,4'-diazenyldibenzoic acid (II) were synthesized and attached with surface-modified CdS QDs to make fluorophore-photochrome CdS-(I) and CdS-(II) dyad assemblies. Upon UV irradiation, the photochromic compounds (I) and (II) undergo a reversible trans-cis isomerization. The photo-induced trans-cis transformation helps to transfer photo-excited electrons from the conduction band of the CdS QDs to the lowest unoccupied molecular orbital of cis isomer of photochromic compounds (I) and (II). As a result, the fluorescence of CdS-(I) and CdS-(II) dyads is suppressed approximately five times compared to bare CdS QDs. The fluorescence modulation in such systems could help to design luminescent probes for bioimaging applications.

  14. Carboxymethylcellulose/ZnCdS fluorescent quantum dot nanoconjugates for cancer cell bioimaging.

    PubMed

    Mansur, Alexandra A P; de Carvalho, Fernanda G; Mansur, Rafael L; Carvalho, Sandhra M; de Oliveira, Luiz Carlos; Mansur, Herman S

    2017-03-01

    In this study, it is reported the use of sodium carboxymethyl cellulose (CMCel) as a multifunctional biocompatible polysaccharide for the direct synthesis of fluorescent alloyed-ZnCdS quantum dot (QD) nanoconjugates via aqueous "green" process at room temperature. The nanoconjugates were extensively characterized by spectroscopical (NMR, FTIR, UV-vis, PL) and morphological techniques (DLS, TEM) for accessing their structural and physicochemical properties associated with X-ray photoelectron spectroscopy (XPS) for surface and interface analysis. The results proved the hypothesis of formation of core-shell nanostructures composed by the semiconductor ZnCdS QD core and the organic biocompatible ligand CMCel shell. Moreover, CMCel chemical functional groups played a pivotal role for controlling the size of water-soluble colloidal nanocrystals (2r=4-5nm) and hydrodynamic diameters (<15nm) evidenced by metal complexation and interactions at the nanointerfaces. Additionally, these nanoconjugates were cytocompatible and luminescent for bioimaging human osteosarcoma cancer cells. Thus, these novel polysaccharide-based fluorescent bioconjugates offer promising perspectives as nanoplatforms for cancer cell bioimaging and diagnosis purposes.

  15. Assembly and intracellular delivery of quantum dot-fluorescent protein bioconjugates

    NASA Astrophysics Data System (ADS)

    Medintz, Igor L.; Pons, Thomas; Delehanty, James B.; Susumu, Kimihiro; Dawson, Philip E.; Mattoussi, Hedi

    2008-02-01

    We have previously assembled semiconductor quantum dot (QD)-based fluorescence resonance energy transfer (FRET) sensors that can specifically detect nutrients, explosives or enzymatic activity. These sensors utilized the inherent benefits of QDs as FRET donors to optimize signal transduction. In this report we functionalize QDs with the multi-subunit multi-chromophore b-phycoerythrin (b-PE) light harvesting complex using biotin-Streptavidin binding. FRET and gel electrophoretic analyses were used to characterize and confirm the QD-b-PE self-assembly. We found that immobilizing additional cell-penetrating peptides on the nanocrystal surface along with the b-PE was the key factor allowing the mixed surface QD-cargos to undergo endocytosis and intracellular delivery. Our findings on the intracellular uptake promoted by CPP were compared to those collected using microinjection technique, where QD-assemblies were delivered directly into the cytoplasm; this strategy allows bypassing of the endocytic uptake pathway. Intracellular delivery of multifunctional QD-fluorescent protein assemblies has potential applications for use in protein tracking, sensing and diagnostics.

  16. Cytotoxicity and fluorescence studies of silica-coated CdSe quantum dots for bioimaging applications

    NASA Astrophysics Data System (ADS)

    Vibin, Muthunayagam; Vinayakan, Ramachandran; John, Annie; Raji, Vijayamma; Rejiya, Chellappan S.; Vinesh, Naresh S.; Abraham, Annie

    2011-06-01

    The toxicological effects of silica-coated CdSe quantum dots (QDs) were investigated systematically on human cervical cancer cell line. Trioctylphosphine oxide capped CdSe QDs were synthesized and rendered water soluble by overcoating with silica, using aminopropyl silane as silica precursor. The cytotoxicity studies were conducted by exposing cells to freshly synthesized QDs as a function of time (0-72 h) and concentration up to micromolar level by Lactate dehydrogenase assay, MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay, Neutral red cell viability assay, Trypan blue dye exclusion method and morphological examination of cells using phase contrast microscope. The in vitro analysis results showed that the silica-coated CdSe QDs were nontoxic even at higher loadings. Subsequently the in vivo fluorescence was also demonstrated by intravenous administration of the QDs in Swiss albino mice. The fluorescence images in the cryosections of tissues depicted strong luminescence property of silica-coated QDs under biological conditions. These results confirmed the role of these luminescent materials in biological labeling and imaging applications.

  17. Fluorescent substituted amidines of benzanthrone: Synthesis, spectroscopy and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Gonta, Svetlana; Utinans, Maris; Kirilov, Georgii; Belyakov, Sergey; Ivanova, Irena; Fleisher, Mendel; Savenkov, Valerij; Kirilova, Elena

    2013-01-01

    Several new substituted amidine derivatives of benzanthrone were synthesized by a condensation reaction from 3-aminobenzo[de]anthracen-7-one and appropriate aromatic and aliphatic amides. The obtained derivatives have a bright yellow or orange fluorescence in organic solvents and in solid state. The novel benzanthrone derivatives were characterized by TLC analysis, 1H NMR, IR, MS, UV/vis, and fluorescence spectroscopy. The solvent effect on photophysical behaviors of these dyes was investigated, and the results showed that the Stoke's shift increased, whereas quantum yield decreased with the growth of the solvent polarity. The structure of some dyes was confirmed by the X-ray single crystal structure analysis. AM1, ZINDO/S and ab initio calculations using Gaussian software were carried out to estimate the electron system of structures. The calculations show planar configurations for the aromatic core of these compounds and two possible orientations of amidine substituents. The calculation results correlate well with red-shifted absorption and emission spectra of compounds.

  18. White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis

    NASA Astrophysics Data System (ADS)

    Meiling, Till T.; Cywiński, Piotr J.; Bald, Ilko

    2016-06-01

    In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst.

  19. White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis.

    PubMed

    Meiling, Till T; Cywiński, Piotr J; Bald, Ilko

    2016-06-23

    In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst.

  20. Quantitative determination of triglyceride by photoactivated CdSe/ZnS quantum dots through fluorescence assay.

    PubMed

    Huang, Chin-Ping; Li, Yaw-Kuen; Chen, Teng-Ming

    2008-07-01

    The quantitative detection of triglycerides is an important issue for health inspection of metabolic disorders and for food and oil-refining industries. Many methods have been designed to approach this target, in which multiple reactions catalyzed by enzymes are normally coupled consecutively. In this study, we demonstrated a simple assay system containing lipase and photoactivated luminescent CdSe/ZnS quantum dots (QDs) for the quantitative detection of triglycerides. Photoactivated CdSe/ZnS QDs function as a sensitive "indicator" to reveal the minute acidity change of the assay system resulting from the enzymatic hydrolysis of triglycerides. By controlling the initial buffer condition of the assay system at 5, 10, or 20 mM phosphate buffer at pH 8.0, respectively, the quenching ratio of the QDs fluorescence intensity monitored at the maximum photoluminescence showed a linear correlation with the concentration of the examined triglyceride in the range of 0.02-6, 0.2-10, or 2-20 mM, respectively. The assay system also provides a convenient way to estimate triglyceride concentration by visualizing the color change of the QDs fluorescence. As compared to most of the existing methods, the system reported herein possessed many advantages, including simplicity, low cost, high flexibility, and high sensitivity. Furthermore, no complicated chemical modification or enzyme immobilization is needed.

  1. Quantum dots coated with molecularly imprinted polymer as fluorescence probe for detection of cyphenothrin.

    PubMed

    Ren, Xiaohui; Chen, Ligang

    2015-02-15

    A newly designed molecularly imprinted polymer (MIP) material was fabricated and successfully utilized as recognition element to develop a quantum dots (QDs) based MIP-coated composite for selective recognition of the template cyphenothrin. The MIP-coated QDs were characterized by fluorescence spectrophotometer, Fourier transform infrared spectroscopy, transmission electron microscope, dynamic light scattering and X-ray powder diffraction. The fluorescence of the coated QDs is quenched on loading the MIP with cyphenothrin, and the effect is much stronger for the MIP than for the non-imprinted polymer, which indicates the MIP could as a recognition template composite. This method can detect down to 9.0 nmol L(-1) of cyphenothrin in water, and a linear relationship has been obtained covering the concentration range of 0.1-80.0 μmol L(-1). The method has been used in the determination of cyphenothrin in water samples and gave recoveries in the range from 88.5% to 97.1% with relative standard deviations in the range of 3.1-6.2%. The present study provides a new and general strategy to fabricate inorganic-organic MIP-coated QDs with highly selective recognition ability in aqueous media and is desirable for chemical probe application.

  2. Solvent effect on the relative quantum yield and fluorescence quenching of 2DAM

    NASA Astrophysics Data System (ADS)

    Nagaraja, D.; Melavanki, R. M.; Patil, N. R.; Kusanur, R. A.

    2014-09-01

    The relative quantum yield of diethyl 2-acetamido-2-((3-oxo-3H-benzo[f]chromen-1-yl)methyl) malonate [2DAM] is estimated using single point method with quinine sulfate as standard reference. The quantum yield varies between 0.1161 and 0.3181 depending on the nature of the solvent. The rates of radiative and non radiative decay constants are also calculated. The fluorescence quenching of [2DAM] by aniline is studied at room temperature, by steady state, in five different solvents namely acetonitrile (AN), 1,4 dioxane (DX), 1,2 dichloroethane (DCE), tetrahydrofuran (THF) and toluene (TOL), in order to explore various possible quenching mechanisms. The experimental results show a positive deviation in Stern Volmer plots for all solvents. Various parameters for the quenching process are determined by ground state complex, sphere of action static quenching model and finite sink approximation model. The magnitudes of these rate parameters indicate that positive deviation in the Stern Volmer (SV) plot is due to both static and dynamic processes. Further, finite sink approximation model is used to check whether these bimolecular reactions were diffusion limited or not. The values of distance parameter R‧ and diffusion co efficient D are determined and then compared with the values of encounter distance R and diffusion coefficient D calculated using Stokes-Einstein equation.

  3. Tunable White Fluorescent Copper Gallium Sulfide Quantum Dots Enabled by Mn Doping.

    PubMed

    Jo, Dae-Yeon; Kim, Daekyoung; Kim, Jong-Hoon; Chae, Heeyeop; Seo, Hyo Jin; Do, Young Rag; Yang, Heesun

    2016-05-18

    Fluorescence of semiconductor quantum dots (QDs) can be tuned by engineering the band gap via size and composition control and further doping them with impurity ions. Targeting on highly bright white-emissive I-III-VI -type copper gallium sulfide (Cu-Ga-S, CGS) host QDs with the entire visible spectral coverage of blue to red, herein, Mn(2+) ion doping, through surface adsorption and lattice diffusion is fulfilled. Upon doping a distinct Mn emission from (4)T1-(6)A1 transition successfully appears in white photoluminescence (PL) of undoped CGS/ZnS core/shell QDs and with varying Mn concentration a systematic white spectral evolution of CGS:Mn/ZnS QDs is achievable with high PL quantum yield retained. The origins of white PL of CGS:Mn/ZnS QDs that is well decomposed into three emission bands are appropriately assigned. The resulting single-phased, doped QDs are then employed as near-UV-to-white down converters for the fabrication of white light-emitting diodes (LEDs). Electroluminescent properties of white QD-LEDs depending on Mn concentration of CGS:Mn/ZnS QDs and forward current are also discussed in detail.

  4. Absolute Zero

    NASA Astrophysics Data System (ADS)

    Donnelly, Russell J.; Sheibley, D.; Belloni, M.; Stamper-Kurn, D.; Vinen, W. F.

    2006-12-01

    Absolute Zero is a two hour PBS special attempting to bring to the general public some of the advances made in 400 years of thermodynamics. It is based on the book “Absolute Zero and the Conquest of Cold” by Tom Shachtman. Absolute Zero will call long-overdue attention to the remarkable strides that have been made in low-temperature physics, a field that has produced 27 Nobel Prizes. It will explore the ongoing interplay between science and technology through historical examples including refrigerators, ice machines, frozen foods, liquid oxygen and nitrogen as well as much colder fluids such as liquid hydrogen and liquid helium. A website has been established to promote the series: www.absolutezerocampaign.org. It contains information on the series, aimed primarily at students at the middle school level. There is a wealth of material here and we hope interested teachers will draw their student’s attention to this website and its substantial contents, which have been carefully vetted for accuracy.

  5. Quantum-dot-labeled DNA probes for fluorescence in situ hybridization (FISH) in the microorganism Escherichia coli.

    PubMed

    Wu, Sheng-Mei; Zhao, Xiang; Zhang, Zhi-Ling; Xie, Hai-Yan; Tian, Zhi-Quan; Peng, Jun; Lu, Zhe-Xue; Pang, Dai-Wen; Xie, Zhi-Xiong

    2006-05-12

    Semiconductor quantum dots (QDs) as a kind of nonisotopic biological labeling material have many unique fluorescent properties relative to conventional organic dyes and fluorescent proteins, such as composition- and size-dependent absorption and emission, a broad absorption spectrum, photostability, and single-dot sensitivity. These properties make them a promising stable and sensitive label, which can be used for long-term fluorescent tracking and subcellular location of genes and proteins. Here, a simple approach for the construction of QD-labeled DNA probes was developed by attaching thiol-ssDNA to QDs via a metal-thiol bond. The as-prepared QD-labeled DNA probes had high dispersivity, bioactivity, and specificity for hybridization. Based on such a kind of probe with a sequence complementary to multiple clone sites in plasmid pUC18, fluorescence in situ hybridization of the tiny bacterium Escherichia coli has been realized for the first time.

  6. In situ fluorescence labelling of jasmonic acid binding sites in plant tissues with cadmium-free quantum dots.

    PubMed

    Liao, Qiumei; Yu, Ying; Cao, Yujuan; Lin, Bixia; Wei, Jingjing

    2015-02-01

    The fluorescence labelling of plant hormone binding sites is an important analytical technique in research on the molecular mechanisms of plant hormone activities. The authors synthesised a jasmonic acid (JA)-conjugated ZnS:Mn quantum dot (QD) probe, with a cubic structure and average hydrodynamic sizes of about 17.0 nm. The maximum fluorescence emission of the probe was recorded at about 585 nm. The probe was used for fluorescence labelling of JA binding sites in mung bean seedling tissues. Analysis revealed that the probe exhibited high selectivity to JA binding sites and good performance in eliminating interference from background fluorescence in plant tissues. In addition, the probe did not exhibit any apparent biotoxicity, and is much more suitable than probes constructed from CdTe QDs for the analysis of biological samples.

  7. Resonance fluorescence of a site-controlled quantum dot realized by the buried-stressor growth technique

    NASA Astrophysics Data System (ADS)

    Strauß, Max; Kaganskiy, Arsenty; Voigt, Robert; Schnauber, Peter; Schulze, Jan-Hindrik; Rodt, Sven; Strittmatter, André; Reitzenstein, Stephan

    2017-03-01

    Site-controlled growth of semiconductor quantum dots (QDs) represents a major advancement to achieve scalable quantum technology platforms. One immediate benefit is the deterministic integration of quantum emitters into optical microcavities. However, site-controlled growth of QDs is usually achieved at the cost of reduced optical quality. Here, we show that the buried-stressor growth technique enables the realization of high-quality site-controlled QDs with attractive optical and quantum optical properties. This is evidenced by performing excitation power dependent resonance fluorescence experiments at cryogenic temperatures showing QD emission linewidths down to 10 μeV. Resonant excitation leads to the observation of the Mollow triplet under CW excitation and enables coherent state preparation under pulsed excitation. Under resonant π-pulse excitation we observe clean single-photon emission associated with g(2)(0) = 0.12 limited by non-ideal laser suppression.

  8. Quantum dot-fluorescence in situ hybridisation for Ectromelia virus detection based on biotin-streptavidin interactions.

    PubMed

    Wang, Ting; Zheng, Zhenhua; Zhang, Xian-En; Wang, Hanzhong

    2016-09-01

    Ectromelia virus (ECTV) is an pathogen that can lead to a lethal, acute toxic disease known as mousepox in mice. Prevention and control of ECTV infection requires the establishment of a rapid and sensitive diagnostic system for detecting the virus. In the present study, we developed a method of quantum-dot-fluorescence based in situ hybridisation for detecting ECTV genome DNA. Using biotin-dUTP to replace dTTP, biotin was incorporated into a DNA probe during polymerase chain reaction. High sensitivity and specificity of ECTV DNA detection were displayed by fluorescent quantum dots based on biotin-streptavidin interactions. ECTV DNA was then detected by streptavidin-conjugated quantum dots that bound the biotin-labelled probe. Results indicated that the established method can visualise ECTV genomic DNA in both infected cells and mouse tissues. To our knowledge, this is the first study reporting quantum-dot-fluorescence based in situ hybridisation for the detection of viral nucleic acids, providing a reference for the identification and detection of other viruses.

  9. Behaviour of fluorescence emission of cyanine dyes, cyanine based fluorescent nanoparticles and CdSe/ZnS quantum dots in water solution upon specific thermal treatments.

    PubMed

    Mortati, Leonardo; Miletto, Ivana; Alberto, Gabriele; Caputo, Giuseppe; Sassi, Maria Paola

    2011-05-01

    Fluorescence techniques are widely used as detection methods in a wide range of biological imaging and analytical applications. The purpose of this work is to determine a measurement method which leads to a comparison between different classes of fluorophores in term of stability of the fluorescence signal upon thermal treatment cycles. This kind of investigation can determine whether the fluorophore performance is affected by heating/cooling cycles and to what extent. The fluorophores considered in this work were organic fluorophores belonging to the family of indocyanine dyes (IRIS3 by Cyanine Technologies S.p.A.) in their molecular form or encapsulated within silica nanoparticles, and CdSe/ZnS carboxyl quantum dots (Qdots 565 ITK by Invitrogen). The NIST Standard Reference Material® SRM 1932 fluorescein solution was used in the certified concentration as reference material in order to evaluate the repeatability of the used spectrofluorimeter. The proposed measurement protocol allows to characterize all kind of fluorophores upon thermal treatments. This allows direct comparison of their performance under temperature changes, giving useful guidelines for the selection of the most suitable fluorophore for the envisaged application. Moreover the method appears to be a promising tool for the characterisation of reference fluorescent materials. The experimental results demonstrate that each fluorophore class shows a specific behaviour. The experimental data analysis points out an important hysteresis effect for quantum dots that was not detected for cyanine molecules and was only slightly detected for cyanine doped silica nanoparticles.

  10. Absolute Summ

    NASA Astrophysics Data System (ADS)

    Phillips, Alfred, Jr.

    Summ means the entirety of the multiverse. It seems clear, from the inflation theories of A. Guth and others, that the creation of many universes is plausible. We argue that Absolute cosmological ideas, not unlike those of I. Newton, may be consistent with dynamic multiverse creations. As suggested in W. Heisenberg's uncertainty principle, and with the Anthropic Principle defended by S. Hawking, et al., human consciousness, buttressed by findings of neuroscience, may have to be considered in our models. Predictability, as A. Einstein realized with Invariants and General Relativity, may be required for new ideas to be part of physics. We present here a two postulate model geared to an Absolute Summ. The seedbed of this work is part of Akhnaton's philosophy (see S. Freud, Moses and Monotheism). Most important, however, is that the structure of human consciousness, manifest in Kenya's Rift Valley 200,000 years ago as Homo sapiens, who were the culmination of the six million year co-creation process of Hominins and Nature in Africa, allows us to do the physics that we do. .

  11. 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.

  12. Milk-derived multi-fluorescent graphene quantum dot-based cancer theranostic system.

    PubMed

    Thakur, Mukeshchand; Mewada, Ashmi; Pandey, Sunil; Bhori, Mustansir; Singh, Kanchanlata; Sharon, Maheshwar; Sharon, Madhuri

    2016-10-01

    An economical green-chemistry approach was used for the synthesis of aqueous soluble graphene quantum dots (GQDs) from cow milk for simultaneous imaging and drug delivery in cancer. The GQDs synthesized using one-pot microwave-assisted heating were multi-fluorescent, spherical in shape having a lateral size of ca. 5nm. The role of processing parameters such as heating time and ionic strength showed a profound effect on photoluminescence properties of GQDs. The GQDs were N-doped and oxygen-rich as confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Cysteamine hydrochloride (Cys) was used to attach an anti-cancer drug berberine hydrochloride (BHC) on GQDs forming GQDs@Cys-BHC complex with c.a. 88% drug loading efficiency. In vitro drug release was studied at the acidic-basic environment and drug kinetics was studied using pharmacokinetic statistical models. The GQDs were biocompatible on L929 cells whereas theranostic GQDs@Cys-BHC complex showed a potent cytotoxic effect on different cancerous cell line models: cervical cancer cell lines such as HeLa cells and breast cancer cells such as MDA-MB-231 confirmed by Trypan blue and MTT-based cytotoxic assays. Furthermore, multi-excitation based cellular bioimaging was demonstrated using confocal laser scanning microscopy (CLSM) and fluorescence microscopy using GQDs as well as GQDs@Cys-BHC complex. Thus, drug delivery (therapeutic) and bioimaging (diagnostic) properties of GQDs@Cys-BHC complex are thought to have a potential in vitro theranostic application in cancer therapy.

  13. Identifying microbial habitats in soil using quantum dots and x-ray fluorescence microtomography

    NASA Astrophysics Data System (ADS)

    O'Brien, S. L.; Whiteside, M. D.; Sholto-Douglas, D.; Dohnalkova, A.; Durall, D. M.; Gursoy, D.; Jones, M. D.; Kovarik, L.; Lai, B.; Roehrig, C.; Sullivan, S.; Vogt, S.; Kemner, K. M.

    2015-12-01

    The metabolic activities of soil microbes are the primary drivers of biogeochemical processes controlling the terrestrial carbon cycle, nutrient availability to plants, contaminant remediation, water quality, and other ecosystem services. However, we have a limited understanding of microbial metabolic processes such as nutrient uptake rates, substrate preferences, or how microbes and microbial metabolism are distributed throughout the three-dimensional pore network of the soil. Here we use a novel combination of imaging techniques with quantum dots (QDs, engineered semiconductor nanoparticles that produce size or composition-dependent fluorescence) to locate bacteria in the three-dimensional pore network of a soil aggregate. First, we show using confocal and aberration-corrected transmission electron microscopies that bacteria (Bacillus subtilis, Pseudomonas fluorescens, and Pseudomonas protogens) actively take up and internalize CdSe/ZnS core/shell QDs conjugated to biologically relevant substrates. Next, we show that cells bearing QDs can be identified using fluorescence imaging with hard x-rays at 2ID-D at the Advanced Photon Source (APS). Finally, we demonstrate that the Se constituent to the QDs can be used to label bacteria in three-dimensional tomographic reconstructions of natural soil at 0.5 nm spatial resolution using hard x-rays at 2ID-E at the APS. This is the first time soil bacteria have been imaged in the intact soil matrix at such high resolution. These results offer a new way to experimentally investigate basic bacterial ecology in situ, revealing constraints on microbial function in soil that will help improve connections between pore-scale and ecosystem-scale processes in models.

  14. Absolute Photometry

    NASA Astrophysics Data System (ADS)

    Hartig, George

    1990-12-01

    The absolute sensitivity of the FOS will be determined in SV by observing 2 stars at 3 epochs, first in 3 apertures (1.0", 0.5", and 0.3" circular) and then in 1 aperture (1.0" circular). In cycle 1, one star, BD+28D4211 will be observed in the 1.0" aperture to establish the stability of the sensitivity and flat field characteristics and improve the accuracy obtained in SV. This star will also be observed through the paired apertures since these are not calibrated in SV. The stars will be observed in most detector/grating combinations. The data will be averaged to form the inverse sensitivity functions required by RSDP.

  15. Effects of Bleaching by Nitrogen Deficiency on the Quantum Yield of Photosystem II in Synechocystis sp. PCC 6803 Revealed by Chl Fluorescence Measurements.

    PubMed

    Ogawa, Takako; Sonoike, Kintake

    2016-03-01

    Estimation of photosynthesis by Chl fluorescence measurement of cyanobacteria is always problematic due to the interference from respiratory electron transfer and from phycocyanin fluorescence. The interference from respiratory electron transfer could be avoided by the use of DCMU or background illumination by blue light, which oxidizes the plastoquinone pool that tends to be reduced by respiration. On the other hand, the precise estimation of photosynthesis in cells with a different phycobilisome content by Chl fluorescence measurement is difficult. By subtracting the basal fluorescence due to the phycobilisome and PSI, it becomes possible to estimate the precise maximum quantum yield of PSII in cyanobacteria. Estimated basal fluorescence accounted for 60% of the minimum fluorescence, resulting in a large difference between the 'apparent' yield and 'true' yield under high phycocyanin conditions. The calculated value of the 'true' maximum quantum yield of PSII was around 0.8, which was similar to the value observed in land plants. The results suggest that the cause of the apparent low yield reported in cyanobacteria is mainly ascribed to the interference from phycocyanin fluorescence. We also found that the 'true' maximum quantum yield of PSII decreased under nitrogen-deficient conditions, suggesting the impairment of the PSII reaction center, while the 'apparent' maximum quantum yield showed a marginal change under the same conditions. Due to the high contribution of phycocyanin fluorescence in cyanobacteria, it is essential to eliminate the influence of the change in phycocyanin content on Chl fluorescence measurement and to evaluate the 'true' photosynthetic condition.

  16. Toward a hybridization assay using fluorescence resonance energy transfer and quantum dots immobilized in microfluidic channels

    NASA Astrophysics Data System (ADS)

    Tavares, Anthony J.; Petryayeva, Eleonora; Algar, W. Russ; Chen, Lu; Krull, Ulrich J.

    2010-06-01

    Quantum dots (QDs) have been widely adopted as integrated components of bioassays and biosensors. In particular, solid phase nucleic acid hybridization assays have been demonstrated to have several advantages and permit the detection of up to four DNA targets simultaneously using fluorescence resonance energy transfer (FRET). This work explores the potential for miniaturization of a solid-phase nucleic acid hybridization assay using QDs and FRET on a microfluidics platform. A method was developed for the immobilization of Streptavidin coated QDs and the preparation of QD-probe oligonucleotide conjugates within microfluidic channels using electrokinetic delivery. Proof-of-concept was demonstrated for the selective detection of target DNA using FRET-sensitized emission from a Cy3 acceptor paired with a green emitting QD donor. The microfluidic platform offered the advantages of smaller sample volumes, nearly undetectable non-specific adsorption, and hybridization within minutes. This work is an important first step toward the development of biochips that enable the multiplexed detection of nucleic acid targets.

  17. Nitrogen- Doped Graphene Quantum Dots: "Turn-off" Fluorescent Probe for Detection of Ag(+) Ions.

    PubMed

    Tabaraki, Reza; Nateghi, Ashraf

    2016-01-01

    Highly luminescent nitrogen-doped graphene quantum dots (N-GQDs) were prepared from glucose and ammonia as carbon and nitrogen sources, respectively. The N-GQDs showed a strong emission at 458 nm with excitation at 360 nm. The N-GQDs exhibited analytical potential as sensing probes for silver ions determination. Factors affecting the fluorescence sensing of Ag(+) ions such as pH, N-GQDs concentration and incubation time were studied using Box-Behnken experimental design. The optimum conditions were determined as pH 7, N-GQDs concentration 1 mg/mL and time 60 min. It suggested that N-GQDs exhibited high sensitivity and selectivity toward Ag(+). The linear range of N-GQDs and the limit of detection (LOD) were 0.2-40 μM and 168 nM, respectively. The N-GQDs-based Ag(+) ions sensor was successfully applied to the determination of Ag(+) in tap water and real river water samples.

  18. Carboxylic Carbon Quantum Dots as a Fluorescent Sensing Platform for DNA Detection.

    PubMed

    Loo, Adeline Huiling; Sofer, Zdenek; Bouša, Daniel; Ulbrich, Pavel; Bonanni, Alessandra; Pumera, Martin

    2016-01-27

    The demand for simple, sensitive, affordable, and selective DNA biosensors is ubiquitous, due to the important role that DNA detection performs in the areas of disease diagnostics, environment monitoring, and food safety. A novel application of carboxylic carbon quantum dots (cCQD) is highlighted in this study. Herein, cCQD function as a nanoquencher in the detection of nucleic acid based on a homogeneous fluorescent assay. To that purpose, the performance of two types of cCQD, namely, citric acid QD and malic acid QD, is evaluated. The principle behind the sensing of nucleic acid lies in the different propensity of single-stranded DNA and double-stranded DNA to adsorb onto the surface of cCQD. For both types of cCQD, a superior range of detection of at least 3 orders of magnitude is achieved, and the potential to distinguish single-base mismatch is also exhibited. These findings are anticipated to provide valuable insights on the employment of cCQD for the fabrication of future DNA biosensors.

  19. Measurement of the hydrodynamic radius of quantum dots by fluorescence correlation spectroscopy excluding blinking.

    PubMed

    de Thomaz, A A; Almeida, D B; Pelegati, V B; Carvalho, H F; Cesar, C L

    2015-03-19

    One of the most important properties of quantum dots (QDs) is their size. Their size will determine optical properties and in a colloidal medium their range of interaction. The most common techniques used to measure QD size are transmission electron microscopy (TEM) and X-ray diffraction. However, these techniques demand the sample to be dried and under a vacuum. This way any hydrodynamic information is excluded and the preparation process may alter even the size of the QDs. Fluorescence correlation spectroscopy (FCS) is an optical technique with single molecule sensitivity capable of extracting the hydrodynamic radius (HR) of the QDs. The main drawback of FCS is the blinking phenomenon that alters the correlation function implicating in a QD apparent size smaller than it really is. In this work, we developed a method to exclude blinking of the FCS and measured the HR of colloidal QDs. We compared our results with TEM images, and the HR obtained by FCS is higher than the radius measured by TEM. We attribute this difference to the cap layer of the QD that cannot be seen in the TEM images.

  20. Biocompatible Fluorescent Core-Shell Nanoconjugates Based on Chitosan/Bi2S3 Quantum Dots

    NASA Astrophysics Data System (ADS)

    Ramanery, Fábio P.; Mansur, Alexandra A. P.; Mansur, Herman S.; Carvalho, Sandhra M.; Fonseca, Matheus C.

    2016-04-01

    Bismuth sulfide (Bi2S3) is a narrow-bandgap semiconductor that is an interesting candidate for fluorescent biomarkers, thermoelectrics, photocatalysts, and photovoltaics. This study reports the synthesis and characterization of novel Bi2S3 quantum dots (QDs) functionalized using chitosan (CHI) as the capping ligands via aqueous "green" route at room temperature and ambient pressure. Transmission electron microscopy (TEM), UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, dynamic light scattering (DLS), and zeta potential (ZP) analysis were used to characterize the hybrids made of biopolymer-functionalized Bi2S3 semiconductor nanocrystals. The results demonstrated that the CHI ligand was effective at nucleating and controlling the growth of water-soluble colloidal Bi2S3 nanoparticles. The average sizes of the Bi2S3 nanoparticles were significantly affected by the molar ratio of the precursors but less dependent on the pH of the aqueous media, leading to the formation of nanocrystals with average diameters varying from 4.2 to 6.7 nm. These surface-modified Bi2S3 nanocrystals with CHI exhibited photoluminescence in the visible spectral region. Moreover, the results of in vitro MTT (3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide) assay with human osteosarcoma cells (SAOS) cell line demonstrated no cytotoxic response of the nanoconjugates.

  1. An improved pyrolysis route to synthesize carbon-coated CdS quantum dots with fluorescence enhancement effect

    SciTech Connect

    Zhang Kejie; Liu Xiaoheng

    2011-10-15

    Well-dispersed carbon-coated CdS (CdS-C) quantum dots were successfully prepared via the improved pyrolysis of bis(1-dodecanethiol)-cadmium(II) under nitrogen atmosphere. This simple method effectively solved the sintered problem resulted from conventional pyrolysis process. The experimental results indicated that most of the as-prepared nanoparticles displayed well-defined core-shell structures. The CdS cores with diameter of {approx}5 nm exhibited hexagonal crystal phase, the carbon shells with thickness of {approx}2 nm acted as a good dispersion medium to prevent CdS particles from aggregation, and together with CdS effectively formed a monodisperse CdS-Carbon nanocomposite. This composite presented a remarkable fluorescence enhancement effect, which indicated that the prepared nanoparticles might be a promising photoresponsive material or biosensor. This improved pyrolysis method might also offer a facile way to prepare other carbon-coated semiconductor nanostructures. - Graphical abstract: We demonstrated a facile approach to synthesize well-dispersed carbon-coated CdS quantum dots. The as-prepared nanoparticles presented remarkable fluorescence enhancement effect. Highlights: > Carbon-coated CdS quantum dots were synthesized by an one-step pyrolysis method. > Well-dispersed CdS-carbon nanoparticles were obtained by an acid treatment process. > As-prepared nanoparticles presented remarkable fluorescence enhancement effect.

  2. 13C-engineered carbon quantum dots for in vivo magnetic resonance and fluorescence dual-response.

    PubMed

    Xu, Yang; Li, Yu-Hao; Wang, Yue; Cui, Jian-Lin; Yin, Xue-Bo; He, Xi-Wen; Zhang, Yu-Kui

    2014-10-21

    (13)C-engineered carbon quantum dots ((13)C-QDs) were used as magnetic resonance (MR) and fluorescence dual-response probe. The enhanced (13)C-MR signal was observed at 171 ppm from carboxylic and carboxyl carbons in (13)C-QDs with 160-fold improvement on signal-to-noise ratio even when no hyperpolarization was applied, whereas the intrinsic fluorescence of C-QDs was still maintained. The stable MR and fluorescence dual-response was successfully used for long-term observation of zebrafish embryonic development. Cross-validation between MR and fluorescence confirmed the distribution of (13)C-QD in zebrafish. (13)C-MR provides specific information about the presence, magnitude, and progression of (13)C-QDs by defining MR intensity, whereas fluorescence reveals the location of (13)C-QDs with its high sensitivity. (13)C-MR and fluorescence was simultaneously observed within (13)C-QDs, and this work may expand the applications of isotope-engineered nanomaterials.

  3. Label-free silicon quantum dots as fluorescent probe for selective and sensitive detection of copper ions.

    PubMed

    Zhao, Jiangna; Deng, Jianhui; Yi, Yinhui; Li, Haitai; Zhang, Youyu; Yao, Shouzhuo

    2014-07-01

    In this work, label-free silicon quantum dots (SiQDs) were used as a novel fluorescence probe for the sensitive and selective detection of Cu(2+). The fluorescence of the SiQDs was effectively quenched by H2O2 from the reaction of ascorbic acid with O2, and hydroxyl radicals from Fenton reaction between H2O2 and Cu(+). The fluorescence intensity of SiQDs was quenched about 25% in 15 min after the addition of H2O2 (1mM). While the SiQDs was incubated with AA (1mM) and Cu(2+) (1 µM) under the same conditions, the fluorescence intensity of SiQDs decreased about 55%. Obviously, the recycling of Cu(2+) in the test system may lead to a dramatical decrease in the fluorescence of SiQDs. Under the optimized experimental conditions, the rate of fluorescence quenching of SiQDs was linearly dependent on the Cu(2+) concentration ranging from 25 to 600 nM with the limit of detection as low as 8 nM, which was much lower than that of existing methods. Moreover, the probe was successfully applied to the determination of Cu(2+) in different environmental water samples and human hair.

  4. Sulfur-doped graphene quantum dots as a novel fluorescent probe for highly selective and sensitive detection of Fe(3+).

    PubMed

    Li, Shuhua; Li, Yunchao; Cao, Jun; Zhu, Jia; Fan, Louzhen; Li, Xiaohong

    2014-10-21

    Sulfur-doped graphene quantum dots (S-GQDs) with stable blue-green fluorescence were synthesized by one-step electrolysis of graphite in sodium p-toluenesulfonate aqueous solution. Compared with GQDs, the S-GQDs drastically improved the electronic properties and surface chemical reactivities, which exhibited a sensitive response to Fe(3+). Therefore, the S-GQDs were used as an efficient fluorescent probe for highly selective detection of Fe(3+). Upon increasing of Fe(3+) concentration ranging from 0.01 to 0.70 μM, the fluorescence intensity of S-GQDs gradually decreased and reached a plateau at 0.90 μM. The difference in the fluorescence intensity of S-GQDs before and after adding Fe(3+) was proportional to the concentration of Fe(3+), and the calibration curve displayed linear regions over the range of 0-0.70 μM. The detection limit was 4.2 nM. Finally, this novel fluorescent probe was successfully applied to the direct analysis of Fe(3+) in human serum, which presents potential applications in clinical diagnosis and may open a new way to the design of effective fluorescence probes for other biologically related targets.

  5. Multiplexed hybridization detection of quantum dot-conjugated DNA sequences using surface plasmon enhanced fluorescence microscopy and spectrometry.

    PubMed

    Robelek, Rudolf; Niu, Lifang; Schmid, Evelyne L; Knoll, Wolfgang

    2004-10-15

    In this study, the general suitability of quantum dot (QD)-DNA conjugates for the surface plasmon enhanced fluorescence spectroscopy technique is demonstrated. Furthermore, the QD-DNA system is transferred to the platform of surface plasmon enhanced fluorescence microscopy. Using this technique together with a microarray format, in which the sensor-bound single-stranded catcher probes are organized in individual surface spots, results in a simultaneous qualitative analysis of QD-conjugated analyte DNA strands as multicolor images. A clear decomposition of different QD(x)()-DNA(y)() mixtures can be achieved for sequential, as well as mixture injections. Besides this, the study describes the successful approach of measuring spectrally resolved surface plasmon enhanced fluorescence signals derived from catcher probe hybridized QD-DNA conjugates.

  6. Conjugation and fluorescence quenching between bovine serum albumin and L-cysteine capped CdSe/CdS quantum dots.

    PubMed

    Wang, Qisui; Ye, Fangyun; Liu, Peng; Min, Xinmin; Li, Xi

    2011-04-01

    Water-soluble, biological-compatible, and excellent fluorescent CdSe/CdS quantum dots (QDs) with L-cysteine as capping agent were synthesized in aqueous medium. Fluorescence (FL) spectra, absorption spectra, and transmission electron microscopy (TEM) were employed to investigate the quality of the products. The interactions between QDs and bovine serum albumin (BSA) were studied by absorption and FL titration experiments. With addition of QDs, the FL intensity of BSA was significantly quenched which can be explained by static mechanism in nature. When BSA was added to the solution of QDs, FL intensity of QDs was faintly quenched. Fluorescent imaging suggests that QDs can be designed as a probe to label the Escherchia coli (E. coli) cells. These results indicate CdSe/CdS/L-cysteine QDs can be used as a probe for labeling biological molecule and bacteria cells.

  7. Fluorescence signals of core-shell quantum dots enhanced by single crystalline gold caps on silicon nanowires

    NASA Astrophysics Data System (ADS)

    Christiansen, S. H.; Chou, J. W.; Becker, M.; Sivakov, V.; Ehrhold, K.; Berger, A.; Chou, W. C.; Chuu, D. S.; Gösele, U.

    2009-04-01

    We use nanoscale (20-300 nm in diameter) single crystalline gold (Au)-caps on silicon nanowires (NWs) grown by the vapor-liquid-solid (VLS) growth mechanism to enhance the fluorescence photoluminescence (PL) signals of highly dilute core/shell CdSeTe/ZnS quantum dots (QDs) in aqueous solution (10-5 M). For NWs without Au-caps, as they appear, for example, after Au etching in aqua regia or buffered KI/I2-solution, essentially no fluorescence signal of the same diluted QDs could be observed. Fluorescence PL signals were measured using excitation with a laser wavelength of 633 nm. The signal enhancement by single crystalline, nanoscale Au-caps is discussed and interpreted based on finite element modeling (FEM).

  8. Correlative fluorescence and scanning transmission electron microscopy of quantum dot-labeled proteins on whole cells in liquid.

    PubMed

    Peckys, Diana B; Bandmann, Vera; de Jonge, Niels

    2014-01-01

    Correlative fluorescence microscopy combined with scanning transmission electron microscopy (STEM) of cells fully immersed in liquid is a new methodology with many application areas. Proteins, in live cells immobilized on microchips, are labeled with fluorescent quantum dot nanoparticles. In this protocol, the epidermal growth factor receptor (EGFR) is labeled. The cells are fixed after a selected labeling time, for example, 5 min as needed to form EGFR dimers. The microchip with cells is then imaged with fluorescence microscopy. Thereafter, STEM can be accomplished in two ways. The microchip with the labeled cells and one microchip with a spacer are assembled into a special microfluidic device and imaged with dedicated high-voltage STEM. Alternatively, thin edges of cells can be studied with environmental scanning electron microscopy with a STEM detector, by placing a microchip with cells in a cooled wet environment.

  9. Quantum-dot-conjugated graphene as a probe for simultaneous cancer-targeted fluorescent imaging, tracking, and monitoring drug delivery.

    PubMed

    Chen, Mei-Ling; He, Ye-Ju; Chen, Xu-Wei; Wang, Jian-Hua

    2013-03-20

    We report a novel quantum-dot-conjugated graphene, i.e., hybrid SiO2-coated quantum dots (HQDs)-conjugated graphene, for targeted cancer fluorescent imaging, tracking, and monitoring drug delivery, as well as cancer therapy. The hybrid SiO2 shells on the surface of QDs not only mitigate its toxicity, but also protect its fluorescence from being quenched by graphene. By functionalizing the surface of HQDs-conjugated graphene (graphene-HQDs) with transferrin (Trf), we developed a targeted imaging system capable of differential uptake and imaging of cancer cells that express the Trf receptor. The widely used fluorescent antineoplastic anthracycline drug, doxorubicin (DOX), is adsorbed on the surface of graphene and results in a large loading capacity of 1.4 mg mg(-1). It is advantageous that the new delivery system exhibits different fluorescence color in between graphene-HQDs and DOX in the aqueous core upon excitation at a same wavelength for the purpose of tracking and monitoring drug delivery. This simple multifunctional nanoparticle system can deliver DOX to the targeted cancer cells and enable us to localize the graphene-HQDs and monitor intracellular DOX release. The specificity and safety of the nanoparticle conjugate for cancer imaging, monitoring, and therapy has been demonstrated in vitro.

  10. Graphene quantum dots coordinated to mercaptopyridine-substituted phthalocyanines: Characterization and application as fluorescence "turn ON" nanoprobes

    NASA Astrophysics Data System (ADS)

    Achadu, Ojodomo J.; Nyokong, Tebello

    2017-03-01

    This study reports on the design of novel nanoconjugates of graphene quantum dots (GQDs) and tetra or octa-mercaptopyridine-substituted zinc and aluminium phthalocyanines (Pcs) deployed as fluorescence "turn ON" nanoprobes. The phthalocyanines were separately adsorbed onto the planar structure of graphene quantum dots (GQDs) via π-π stacking interaction to form GQDs-mercaptopyridine Pcs nanoconjugates. The quaternized Pc complexes could also interact with the GQDs through electrostatic attraction due to the positive charges on the Pcs ring substituents and the negative charges on the surface of GQDs. The fluorescence emission of the GQDs was quenched upon coordination to the respective Pcs. However, the fluorescence emission was "turned ON" in the presence of Hg2 + employed as a test analyte. The mechanism of the "turn ON" of the GQDs emission in the nanoconjugates is ascribed to the strong affinity of Hg2 + to bind with the bridging sulfur on the Pcs periphery thereby disrupting the π-π stacking interaction between the GQDs and the Pcs with a consequent "turn ON" of the coordinated GQDs' fluorescence.

  11. Color Tunable Gd-Zn-Cu-In-S/ZnS Quantum Dots for Dual Modality Magnetic Resonance and Fluorescence Imaging

    PubMed Central

    Guo, Weisheng; Yang, Weitao; Wang, Yu; Sun, Xiaolian; Liu, Zhongyun; Zhang, Bingbo

    2014-01-01

    Inorganic nanoparticles have been introduced into biological systems as useful probes for in vitro diagnosis and in vivo imaging, due to their relatively small size and exceptional physical and chemical properties. A new kind of color tunable Gd-Zn-Cu-In-S/ZnS (GZCIS/ZnS) quantum dots (QDs) with stable crystal structure was successfully synthesized and utilized for magnetic resonance (MR) and fluorescence dual modality imaging. This strategy allows successful fabrication of GZCIS/ZnS QDs by incorporating Gd into ZCIS/ZnS QDs to achieve great MR enhancement without compromising the fluorescence properties of the initial ZCIS/ZnS QDs. The as-prepared GZCIS/ZnS QDs show high T1 MR contrast as well as “color-tunable” photoluminescence (PL) in the range of 550–725 nm by adjusting the Zn/Cu feeding ratio with high PL quantum yield (QY). The GZCIS/ZnS QDs were transferred into water via a bovine serum albumin (BSA) coating strategy. The resulting Cd-free GZCIS/ZnS QDs reveal negligible cytotoxicity on both HeLa and A549 cells. Both fluorescence and MR imaging studies were successfully performed in vitro and in vivo. The results demonstrated that GZCIS/ZnS QDs could be a dual-modal contrast agent to simultaneously produce strong MR contrast enhancement as well as fluorescence emission for in vivo imaging. PMID:25485043

  12. Resonance fluorescence of a two-level quantum emitter near a plasmonic nanoparticle: role of the near-field polarization

    NASA Astrophysics Data System (ADS)

    Vladimirova, Yu V.; Chubchev, E. D.; Zadkov, V. N.

    2017-02-01

    It is demonstrated that the interaction of a two-level quantum emitter (atom, molecule, etc) with a plasmonic nanoparticle (prolate nanospheroid) in an external laser field features either an essential increase (up to a few orders of magnitude) or reduction (up to a few times) of the total decay rate of the emitter in specific areas around the nanoparticle in contrast to its decay rate in a vacuum. It is also shown that the resonance fluorescence spectrum of the emitter in close proximity to a plasmonic nanoparticle is very sensitive to both the location of the emitter around the nanoparticle and to polarization of the near-field, which depends in turn on the polarization of the incident laser field. This can be used in engineering potential quantum optics experiments with quantum emitters in the near-field, as well as for 3D nanoscopy of the near-field by registering the resonance fluorescence spectra of quantum emitters scattered in the vicinity of a plasmonic nanoparticle.

  13. Multimode Surface Functional Group Determination: Combining Steady-State and Time-Resolved Fluorescence with X-ray Photoelectron Spectroscopy and Absorption Measurements for Absolute Quantification.

    PubMed

    Fischer, Tobias; Dietrich, Paul M; Unger, Wolfgang E S; Rurack, Knut

    2016-01-19

    The quantitative determination of surface functional groups is approached in a straightforward laboratory-based method with high reliability. The application of a multimode BODIPY-type fluorescence, photometry, and X-ray photoelectron spectroscopy (XPS) label allows estimation of the labeling ratio, i.e., the ratio of functional groups carrying a label after reaction, from the elemental ratios of nitrogen and fluorine. The amount of label on the surface is quantified with UV/vis spectrophotometry based on the molar absorption coefficient as molecular property. The investigated surfaces with varying density are prepared by codeposition of 3-(aminopropyl)triethoxysilane (APTES) and cyanoethyltriethoxysilane (CETES) from vapor. These surfaces show high functional group densities that result in significant fluorescence quenching of surface-bound labels. Since alternative quantification of the label on the surface is available through XPS and photometry, a novel method to quantitatively account for fluorescence quenching based on fluorescence lifetime (τ) measurements is shown. Due to the complex distribution of τ on high-density surfaces, the stretched exponential (or Kohlrausch) function is required to determine representative mean lifetimes. The approach is extended to a commercial Rhodamine B isothiocyanate (RITC) label, clearly revealing the problems that arise from such charged labels used in conjunction with silane surfaces.

  14. Sky-Blue Organic Light Emitting Diode with 37% External Quantum Efficiency Using Thermally Activated Delayed Fluorescence from Spiroacridine-Triazine Hybrid.

    PubMed

    Lin, Ting-An; Chatterjee, Tanmay; Tsai, Wei-Lung; Lee, Wei-Kai; Wu, Meng-Jung; Jiao, Min; Pan, Kuan-Chung; Yi, Chih-Lung; Chung, Chin-Lung; Wong, Ken-Tsung; Wu, Chung-Chih

    2016-08-01

    Extremely efficient sky-blue organic electroluminescence with external quantum efficiency of ≈37% is achieved in a conventional planar device structure, using a highly efficient thermally activated delayed fluorescence emitter based on the spiroacridine-triazine hybrid and simultaneously possessing nearly unitary (100%) photoluminescence quantum yield, excellent thermal stability, and strongly horizontally oriented emitting dipoles (with a horizontal dipole ratio of 83%).

  15. Measurements of absolute concentrations of NADH in cells using the phasor FLIM method.

    PubMed

    Ma, Ning; Digman, Michelle A; Malacrida, Leonel; Gratton, Enrico

    2016-07-01

    We propose a graphical method using the phasor representation of the fluorescence decay to derive the absolute concentration of NADH in cells. The method requires the measurement of a solution of NADH at a known concentration. The phasor representation of the fluorescence decay accounts for the differences in quantum yield of the free and bound form of NADH, pixel by pixel of an image. The concentration of NADH in every pixel in a cell is obtained after adding to each pixel in the phasor plot a given amount of unmodulated light which causes a shift of the phasor towards the origin by an amount that depends on the intensity at the pixel and the fluorescence lifetime at the pixel. The absolute concentration of NADH is obtained by comparison of the shift obtained at each pixel of an image with the shift of the calibrated solution.

  16. Measurements of absolute concentrations of NADH in cells using the phasor FLIM method

    PubMed Central

    Ma, Ning; Digman, Michelle A.; Malacrida, Leonel; Gratton, Enrico

    2016-01-01

    We propose a graphical method using the phasor representation of the fluorescence decay to derive the absolute concentration of NADH in cells. The method requires the measurement of a solution of NADH at a known concentration. The phasor representation of the fluorescence decay accounts for the differences in quantum yield of the free and bound form of NADH, pixel by pixel of an image. The concentration of NADH in every pixel in a cell is obtained after adding to each pixel in the phasor plot a given amount of unmodulated light which causes a shift of the phasor towards the origin by an amount that depends on the intensity at the pixel and the fluorescence lifetime at the pixel. The absolute concentration of NADH is obtained by comparison of the shift obtained at each pixel of an image with the shift of the calibrated solution. PMID:27446681

  17. High-throughput detection of food-borne pathogenic bacteria using oligonucleotide microarray with quantum dots as fluorescent labels.

    PubMed

    Huang, Aihua; Qiu, Zhigang; Jin, Min; Shen, Zhiqiang; Chen, Zhaoli; Wang, Xinwei; Li, Jun-Wen

    2014-08-18

    Bacterial pathogens are mostly responsible for food-borne diseases, and there is still substantial room for improvement in the effective detection of these organisms. In the present study, we explored a new method to detect target pathogens easily and rapidly with high sensitivity and specificity. This method uses an oligonucleotide microarray combined with quantum dots as fluorescent labels. Oligonucleotide probes targeting the 16SrRNA gene were synthesized to create an oligonucleotide microarray. The PCR products labeled with biotin were subsequently hybridized using an oligonucleotide microarray. Following incubation with CdSe/ZnS quantum dots coated with streptavidin, fluorescent signals were detected with a PerkinElmer Gx Microarray Scanner. The results clearly showed specific hybridization profiles corresponding to the bacterial species assessed. Two hundred and sixteen strains of food-borne bacterial pathogens, including standard strains and isolated strains from food samples, were used to test the specificity, stability, and sensitivity of the microarray system. We found that the oligonucleotide microarray combined with quantum dots used as fluorescent labels can successfully discriminate the bacterial organisms at the genera or species level, with high specificity and stability as well as a sensitivity of 10 colony forming units (CFU)/mL of pure culture. We further tested 105 mock-contaminated food samples and achieved consistent results as those obtained from traditional biochemical methods. Together, these results indicate that the quantum dot-based oligonucleotide microarray has the potential to be a powerful tool in the detection and identification of pathogenic bacteria in foods.

  18. Sensitive arginine sensing based on inner filter effect of Au nanoparticles on the fluorescence of CdTe quantum dots

    NASA Astrophysics Data System (ADS)

    Liu, Haijian; Li, Ming; Jiang, Linye; Shen, Feng; Hu, Yufeng; Ren, Xueqin

    2017-02-01

    Arginine plays an important role in many biological functions, whose detection is very significant. Herein, a sensitive, simple and cost-effective fluorescent method for the detection of arginine has been developed based on the inner filter effect (IFE) of citrate-stabilized gold nanoparticles (AuNPs) on the fluorescence of thioglycolic acid-capped CdTe quantum dots (QDs). When citrate-stabilized AuNPs were mixed with thioglycolic acid-capped CdTe QDs, the fluorescence of CdTe QDs was significantly quenched by AuNPs via the IFE. With the presence of arginine, arginine could induce the aggregation and corresponding absorption spectra change of AuNPs, which then IFE-decreased fluorescence could gradually recover with increasing amounts of arginine, achieving fluorescence "turn on" sensing for arginine. The detection mechanism is clearly illustrated and various experimental conditions were also optimized. Under the optimum conditions, a decent linear relationship was obtained in the range from 16 to 121 μg L- 1 and the limit of detection was 5.6 μg L- 1. And satisfactory results were achieved in arginine analysis using arginine injection, compound amino acid injection, even blood plasma as samples. Therefore, the present assay showed various merits, such as simplicity, low cost, high sensitivity and selectivity, making it promising for sensing arginine in biological samples.

  19. Magic sized ZnS quantum dots as a highly sensitive and selective fluorescence sensor probe for Ag+ ions.

    PubMed

    Mandal, Abhijit; Dandapat, Anirban; De, Goutam

    2012-02-07

    A green and simple chemical synthesis of magic sized water soluble blue-emitting ZnS quantum dots (QDs) has been accomplished by reacting anhydrous Zn acetate, sodium sulfide and thiolactic acid (TLA) at room temperature in aqueous solution. Refluxing of this mixture in open air yielded ZnS clusters of about 3.5 nm in diameter showing very strong and narrow photoluminescence properties with long stability. Refluxing did not cause any noticeable size increment of the clusters. As a result, the QDs obtained after different refluxing conditions showed similar absorption and photoluminescence (PL) features. Use of TLA as a capping agent effectively yielded such stable and magic sized QDs. The as-synthesized and 0.5 h refluxed ZnS QDs were used as a fluorescence sensor for Ag(+) ions. It has been observed that after addition of Ag(+) ions of concentration 0.5-1 μM the strong fluorescence of ZnS QDs was almost quenched. The quenched fluorescence can be recovered by adding ethylenediamine to form a complex with Ag(+) ions. The other metal ions (K(+), Ca(2+), Au(3+), Cu(2+), Fe(3+), Mn(2+), Mg(2+), Co(2+)) showed little or no effect on the fluorescence of ZnS QDs when tested individually or as a mixture. In the presence of all these ions, Ag(+) responded well and therefore ZnS QDs reported in this work can be used as a Ag(+) ion fluorescence sensor.

  20. Fluorescence enhancement of cadmium selenide quantum dots assembled on silver nanoparticles and its application to glucose detection.

    PubMed

    Tang, Yecang; Yang, Qian; Wu, Ting; Liu, Li; Ding, Yi; Yu, Bo

    2014-06-10

    In this work, a new assembled glucose sensor based on the Ag nanoparticle (AgNP)-enhanced fluorescence of CdSe quantum dots (QDs) was developed. The mercaptoglycerol-modified AgNPs and aminophenylboronic acid-functionalized CdSe QDs are assembled into AgNP-CdSe QD complexes through the formation of a boronate ester bond. As compared to that of bare CdSe QDs, up to a 9-fold fluorescence enhancement and a clear blue shift of the emission peak for AgNP-CdSe QD complexes were observed, which is attributed to the surface plasmon resonance of AgNPs. In addition, the as-formed complexes are gradually disassembled in the presence of glucose molecules because they can replace the AgNPs by competitive binding with boronic acid groups, resulting in the weakening of fluorescence enhancement. The decrease in fluorescence intensity presents a linear relationship with glucose concentration in the range from 2 to 52 mM with a detection limit of 1.86 mM. Such a metal-enhanced QDs fluorescence system may have promising applications in chemical and biological sensors.

  1. High-throughput and rapid fluorescent visualization sensor of urinary citrate by CdTe quantum dots.

    PubMed

    Zhuo, Shujuan; Gong, Jiajia; Zhang, Ping; Zhu, Changqing

    2015-08-15

    In this paper, we have presented a novel CdTe quantum dots (QDs) based fluorescent sensor for visual and turn-on sensing of citrate in human urine samples. The europium ion (Eu(3+)) can lead to the fluorescence quenching of thioglycollic acid (TGA) modified CdTe QDs due to photoinduced electron transfer accompanied by the change of emission color from yellow to orange. Next, addition of citrate breaks the preformed assembly because citrate can replace the CdTe QDs, based on the fact that the Eu(3+) ion displays higher affinity with citrate than the CdTe QDs. Thus the photoinduced electron transfer is switched off, and the fluorescence emission of CdTe QDs is rapidly (within 5min) recovered, simultaneously, the orange emission color restores to yellow. Such proposed strategy may conveniently discriminate the patient of renal stone from normal person by naked eyes. In addition to visualization detection, the fluorescence responses can be used for well quantifying citrate in the range of 0.67-133μM. So, the present, simple, low-cost and visualized citrate fluorescence sensor has great potential in the applications for earlier screening in clinical detection.

  2. Rapid microwave-assisted synthesis of molecularly imprinted polymers on carbon quantum dots for fluorescent sensing of tetracycline in milk.

    PubMed

    Hou, Juan; Li, Huiyu; Wang, Long; Zhang, Ping; Zhou, Tianyu; Ding, Hong; Ding, Lan

    2016-01-01

    In this paper, a novel, selective and eco-friendly sensor for the detection of tetracycline was developed by grafting imprinted polymers onto the surface of carbon quantum dots. A simple microwave-assisted approach was utilized to fabricate the fluorescent imprinted composites rapidly for the first time, which could shorten the polymerization time and simplify the experimental procedure dramatically. The novel composites not only demonstrated excellent fluorescence stability and special binding sites, but also could selectively accumulate target analytes. Under optimal conditions, the relative fluorescence intensity of the composites decreased linearly with increasing the concentration of tetracycline from 20 nM to 14 µM. The detection limit of tetracycline was 5.48 nM. The precision and reproducibility of the proposed sensor were also acceptable. Significantly, the practicality of this ultrasensitive sensor for tetracycline detection in milk was further validated, revealing the advantages of simplicity, sensitivity, selectivity and low cost. This approach combines the high selective adsorption property of molecular imprinted polymers and the sensitivity of fluorescence detection. It is envisioned that the development of fluorescent molecularly imprinted composites will offer a new way of thinking for rapid analysis in complex samples.

  3. Synthesis of water-soluble CdSe quantum dots with various fluorescent properties and their application in immunoassay for determination of C-reactive protein.

    PubMed

    Gasparyan, V K

    2014-09-01

    Effects of various factors on synthesis and fluorescent properties of CdSe quantum dots were studied. It was shown that variation of pH, stabilizer and concentration of precursors brings to obtaining of quantum dots with various fluorescent properties. The nanoparticles prepared were conjugated with rabbit antibodies to C-Reactive protein and C-Reactive protein for competitive immunoassay for determination of CRP. It was shown that interaction of these dots as a result of antigen-antibody reaction brings to resonance energy transfer and these changes in fluorescence spectra correlate with concentration of CRP. This approach permits to determine CRP in range between 4-100 ng.

  4. Development of homogeneous binding assays based on fluorescence resonance energy transfer between quantum dots and Alexa Fluor fluorophores.

    PubMed

    Nikiforov, Theo T; Beechem, Joseph M

    2006-10-01

    We studied the fluorescence resonance energy transfer (FRET) between quantum dots emitting at 565, 605, and 655 nm as energy donors and Alexa Fluor fluorophores with absorbance maxima at 594, 633, 647, and 680 nm as energy acceptors. As a first step, we prepared covalent conjugates between all three types of quantum dots and each of the Alexa Fluor fluorophores that could act as an energy acceptor. All of these conjugates displayed efficient resonance energy transfer. Then we prepared covalent conjugates of these quantum dots with biotin, fluorescein, and cortisol and established that the binding of these conjugates to suitable Alexa Fluor-labeled antibodies and streptavidin (in the case of biotin) can be efficiently detected by measuring the resonance energy transfer in homogeneous solutions. Finally, based on these observations, competitive binding assays for these three small analytes were developed. The performance of these assays as a function of the degree of labeling of the quantum dots was evaluated. It was found that decreasing the degree of loading of the quantum dots leads to decreases of the limits of detection. The results show the great potential of this FRET system for the development of new homogeneous binding assays.

  5. Hydrothermal synthetic mercaptopropionic acid stabled CdTe quantum dots as fluorescent probes for detection of Ag⁺.

    PubMed

    Gan, Ting-Ting; Zhang, Yu-Jun; Zhao, Nan-Jing; Xiao, Xue; Yin, Gao-Fang; Yu, Shao-Hui; Wang, Huan-Bo; Duan, Jing-Bo; Shi, Chao-Yi; Liu, Wen-Qing

    2012-12-01

    Mercaptopropionic acid (MPA) capped CdTe quantum dots (QDs) with particle size 3 nm have been successfully synthesized in aqueous medium by hydrothermal synthesis method. And the effects of different metal ions on MPA capped CdTe QDs fluorescence were studied using fluorescence spectrometry. The results demonstrated that at the same concentration level, Ag(+) could strongly quench CdTe QDs fluorescence, and the other metal ions had little effect on CdTe QDs fluorescence except Cu(2+). On the basis of this fact, a rapid, simple, highly sensitive and selective method based on fluorescence quenching principle for Ag(+) detection in aqueous solution was proposed. Under optimal conditions, the quenched fluorescence intensity (F(0)-F) increased linearly with the concentration of Ag(+) ranging from 4 × 10(-7) to 32 × 10(-7)mol L(-1). The limit of detection for Ag(+) was 4.106 × 10(-8)mol L(-1). The obtained plot of F(0)/F versus [Ag(+)] was an upward curvature, concave towards the y-axis, rather than a straight line. The modified form of the Stern-Volmer equation was third order in Ag(+) concentration. According to the modified Stern-Volmer equation, it can be inferred that dynamic quenching and static quenching simultaneously occurred when Ag(+) interacted with MPA capped CdTe QDs. At the same time other factors might also influence the quenching process. Based on this study, hydrothermal synthesized MPA capped CdTe QDs with particle size 3 nm may be used as a novel fluorescence probe to quantificationally and selectively detect Ag(+).

  6. Fluorescent properties of DNA base analogue tC upon incorporation into DNA — negligible influence of neighbouring bases on fluorescence quantum yield

    PubMed Central

    Sandin, Peter; Wilhelmsson, L. Marcus; Lincoln, Per; Powers, Vicki E. C.; Brown, Tom; Albinsson, Bo

    2005-01-01

    The quantum yield of the fluorescent tricyclic cytosine analogue, 1,3-diaza-2-oxophenothiazine, tC, is high and virtually unaffected by incorporation into both single- and double-stranded DNA irrespective of neighbouring bases (0.17–0.24 and 0.16–0.21, respectively) and the corresponding fluorescence decay curves are all mono-exponential, properties that are unmatched by any base analogue so far. The fluorescence lifetimes increase when going from tC free in solution (3.2 ns) to single- and double-stranded DNA (on average 5.7 and 6.3 ns, respectively). The mono-exponential decays further support previous NMR results where it was found that tC has a well-defined position and geometry within the DNA helix. Furthermore, we find that the oxidation potential of tC is 0.4 V lower than for deoxyguanosine, the natural base with the lowest oxidation potential. This suggests that tC may be of interest in charge transfer studies in DNA as an electron hole acceptor. We also present a novel synthetic route to the phosphoramidite form of tC. The results presented here together with previous work show that tC is a very good C-analogue that induces minimal perturbation to the native structure of DNA. This makes tC unique as a fluorescent base analogue and is thus highly interesting in a range of applications for studying e.g. structure, dynamics and kinetics in nucleic acid systems. PMID:16147985

  7. CdSe/CdS-quantum rods: fluorescent probes for in vivo two-photon laser scanning microscopy

    NASA Astrophysics Data System (ADS)

    Dimitrijevic, Jelena; Krapf, Lisa; Wolter, Christopher; Schmidtke, Christian; Merkl, Jan-Philip; Jochum, Tobias; Kornowski, Andreas; Schüth, Anna; Gebert, Andreas; Hüttmann, Gereon; Vossmeyer, Tobias; Weller, Horst

    2014-08-01

    CdSe/CdS-Quantum-dots-quantum-rods (QDQRs) with an aspect ratio of ~6 are prepared via the seeded growth method, encapsulated within a shell of crosslinked poly(isoprene)-block-poly(ethylene glycol) (PI-b-PEG) diblock copolymer, and transferred from the organic phase into aqueous media. Their photoluminescence quantum yield (PLQY) of 78% is not compromised by the phase transfer. Within a period of two months the PLQY of QDQRs in aqueous solution at neutral pH decreases only slightly (to ~65%). The two-photon (TP) action cross sections of QDQRs (~105 GM) are two orders of magnitude higher than those of CdSe/CdS/ZnS-core/shell/shell quantum dots (QDs, ~103 GM) with comparable diameter (~5 nm). After applying PI-b-PEG encapsulated QDQRs onto the small intestinal mucosa of mice in vivo, their strong red fluorescence can easily be observed by two-photon laser scanning microscopy (TPLSM) and clearly distinguished from autofluorescent background. Our results demonstrate that PI-b-PEG encapsulated CdSe/CdS-QDQRs are excellent probes for studying the uptake and fate of nanoparticles by two-photon imaging techniques in vivo.CdSe/CdS-Quantum-dots-quantum-rods (QDQRs) with an aspect ratio of ~6 are prepared via the seeded growth method, encapsulated within a shell of crosslinked poly(isoprene)-block-poly(ethylene glycol) (PI-b-PEG) diblock copolymer, and transferred from the organic phase into aqueous media. Their photoluminescence quantum yield (PLQY) of 78% is not compromised by the phase transfer. Within a period of two months the PLQY of QDQRs in aqueous solution at neutral pH decreases only slightly (to ~65%). The two-photon (TP) action cross sections of QDQRs (~105 GM) are two orders of magnitude higher than those of CdSe/CdS/ZnS-core/shell/shell quantum dots (QDs, ~103 GM) with comparable diameter (~5 nm). After applying PI-b-PEG encapsulated QDQRs onto the small intestinal mucosa of mice in vivo, their strong red fluorescence can easily be observed by two-photon laser

  8. Magnetically engineered Cd-free quantum dots as dual-modality probes for fluorescence/magnetic resonance imaging of tumors.

    PubMed

    Ding, Ke; Jing, Lihong; Liu, Chunyan; Hou, Yi; Gao, Mingyuan

    2014-02-01

    Magnetically engineered Cd-free CuInS2@ZnS:Mn quantum dots (QDs) were designed, synthesized, and evaluated as potential dual-modality probes for fluorescence and magnetic resonance imaging (MRI) of tumors in vivo. The synthesis of Mn-doped core-shell structured CuInS2@ZnS mainly comprised three steps, i.e., the preparation of fluorescent CuInS2 seeds, the particle surface coating of ZnS, and the Mn-doping of the ZnS shells. Systematic spectroscopy studies were carried out to illustrate the impacts of ZnS coating and the following Mn-doping on the optical properties of the QDs. In combination with conventional fluorescence, fluorescence excitation, and time-resolved fluorescence measurements, the structure of CuInS2@ZnS:Mn QDs prepared under optimized conditions presented a Zn gradient CuInS2 core and a ZnS outer shell, while Mn ions were mainly located in the ZnS shell, which well balanced the optical and magnetic properties of the resultant QDs. For the following in vivo imaging experiments, the hydrophobic CuInS2@ZnS:Mn QDs were transferred into water upon ligand exchange reactions by replacing the 1-dodecanethiol ligand with dihydrolipoic acid-poly(ethylene glycol) (DHLA-PEG) ligand. The MTT assays based on HeLa cells were carried out to evaluate the cytotoxicity of the current Cd-free CuInS2@ZnS:Mn QDs for comparing with that of water soluble CdTe QDs. Further in vivo fluorescence and MR imaging experiments suggested that the PEGylated CuInS2@ZnS:Mn QDs could well target both subcutaneous and intraperitoneal tumors in vivo.

  9. A dual-channel fluorescent chemosensor for discriminative detection of glutathione based on functionalized carbon quantum dots.

    PubMed

    Huang, Yuanyuan; Zhou, Jin; Feng, Hui; Zheng, Jieyu; Ma, Hui-Min; Liu, Weidong; Tang, Cong; Ao, Hang; Zhao, Meizhi; Qian, Zhaosheng

    2016-12-15

    A convenient, fluorescent dual-channel chemosensor on the basis of bis(3-pyridylmethyl)amine-functionalized carbon quantum dots (BPMA-CQDs) nanoprobe was constructed, and it can discriminatively detect glutathione from its analogues cysteine and homocysteine based on two distinctive strategies. Two distinct fluorescence responses of BPMA-CQDs probe to Cu(II) and Ag(I) were identified and further employed to achieve selective detection of Cu(II) and Ag(I) respectively. Based on the BPMA-CQDs/Cu(II) conjugate, discriminative detection of GSH was achieved in terms of correlation between the amounts of GSH and fluorescence recovery. The addition of GSH into BPMA-CQDs/Cu(II) system induces the reduction of Cu(II) to Cu(I), which could efficiently block PET process resulting in the following fluorescence recovery. Based on the BPMA-CQDs/Ag(I) conjugate, GSH assay could also be established on the basis of fluorescence response to GSH. The introduction of GSH into the preceding system triggers the competitive coordination to Ag(I) between BPMA and GSH, and silver ions are finally taken away by GSH from the probe, where the fluorescence is restored to its original weak state. Both of the detection strategies can achieve discriminative detection of GSH from Cys and Hcy. The assays showed good stability and repeatability, and covered a broad linear range of up to 13.3μM with a lowest detection limit of 42.0nM. Moreover, both of them were utilized to monitor GSH level in live cells.

  10. Paramagnetic lipid-coated silica nanoparticles with a fluorescent quantum dot core: a new contrast agent platform for multimodality imaging.

    PubMed

    Koole, Rolf; van Schooneveld, Matti M; Hilhorst, Jan; Castermans, Karolien; Cormode, David P; Strijkers, Gustav J; de Mello Donegá, Celso; Vanmaekelbergh, Daniel; Griffioen, Arjan W; Nicolay, Klaas; Fayad, Zahi A; Meijerink, Andries; Mulder, Willem J M

    2008-12-01

    Silica particles as a nanoparticulate carrier material for contrast agents have received considerable attention the past few years, since the material holds great promise for biomedical applications. A key feature for successful application of this material in vivo is biocompatibility, which may be significantly improved by appropriate surface modification. In this study, we report a novel strategy to coat silica particles with a dense monolayer of paramagnetic and PEGylated lipids. The silica nanoparticles carry a quantum dot in their center and are made target-specific by the conjugation of multiple alphavbeta3-integrin-specific RGD-peptides. We demonstrate their specific uptake by endothelial cells in vitro using fluorescence microscopy, quantitative fluorescence imaging, and magnetic resonance imaging. The lipid-coated silica particles introduced here represent a new platform for nanoparticulate multimodality contrast agents.

  11. In situ preparation of fluorescent CdTe quantum dots with small thiols and hyperbranched polymers as co-stabilizers

    PubMed Central

    2014-01-01

    A new strategy for in situ preparation of highly fluorescent CdTe quantum dots (QDs) with 3-mercaptopropionic acid (MPA) and hyperbranched poly(amidoamine)s (HPAMAM) as co-stabilizers was proposed in this paper. MPA and HPAMAM were added in turn to coordinate Cd2+. After adding NaHTe and further microwave irradiation, fluorescent CdTe QDs stabilized by MPA and HPAMAM were obtained. Such a strategy avoids the aftertreatment of thiol-stabilized QDs in their bioapplication and provides an opportunity for direct biomedical use of QDs due to the existence of biocompatible HPAMAM. The resulting CdTe QDs combine the mechanical, biocompatibility properties of HPAMAM and the optical, electrical properties of CdTe QDs together. PMID:24636234

  12. Decorating multi-walled carbon nanotubes with quantum dots for construction of multi-color fluorescent nanoprobes

    NASA Astrophysics Data System (ADS)

    Jia, Nengqin; Lian, Qiong; Tian, Zhong; Duan, Xin; Yin, Min; Jing, Lihong; Chen, Shouhui; Shen, Hebai; Gao, Mingyuan

    2010-01-01

    Novel multi-color fluorescent nanoprobes were prepared by electrostatically assembling differently sized CdTe quantum dots on polyethylenimine (PEI) functionalized multi-walled carbon nanotubes (MWNTs). The structural and optical properties of the nano-assemblies (MWNTs-PEI-CdTe) were characterized by transmission electron microscopy (TEM), electron diffraction spectra (EDS), Raman spectroscopy, confocal microscopy and photoluminescence spectroscopy (PL), respectively. Electrochemical impedance spectroscopy (EIS) was also applied to investigate the electrostatic assembling among oxidized MWNTs, PEI and CdTe. Furthermore, confocal fluorescence microscopy was used to monitor the nano-assemblies' delivery into tumor cells. It was found that the nano-assemblies exhibit efficient intracellular transporting and strong intracellular tracking. These properties would make this luminescent nano-assembly an excellent building block for the construction of intracellular nanoprobes, which could hold great promise for biomedical applications.

  13. Absorption and fluorescence of PRODAN in phospholipid bilayers: a combined quantum mechanics and classical molecular dynamics study.

    PubMed

    Cwiklik, Lukasz; Aquino, Adelia J A; Vazdar, Mario; Jurkiewicz, Piotr; Pittner, Jiří; Hof, Martin; Lischka, Hans

    2011-10-20

    Absorption and fluorescence spectra of PRODAN (6-propionyl-2-dimethylaminonaphthalene) were studied by means of the time-dependent density functional theory and the algebraic diagrammatic construction method. The influence of environment, a phosphatidylcholine lipid bilayer and water, was taken into account employing a combination of quantum chemical calculations with empirical force-field molecular dynamics simulations. Additionally, experimental absorption and emission spectra of PRODAN were measured in cyclohexane, water, and lipid vesicles. Both planar and twisted configurations of the first excited state of PRODAN were taken into account. The twisted structure is stabilized in both water and a lipid bilayer, and should be considered as an emitting state in polar environments. Orientation of the excited dye in the lipid bilayer significantly depends on configuration. In the bilayer, the fluorescence spectrum can be regarded as a combination of emission from both planar and twisted structures.

  14. Paramagnetic lipid-coated silica nanoparticles with a fluorescent quantum dot core: a new contrast agent platform for multimodality imaging

    PubMed Central

    Koole, Rolf; van Schooneveld, Matti M.; Hilhorst, Jan; Castermans, Karolien; Cormode, David P.; Strijkers, Gustav J.; de Mello Donegá, Celso; Vanmaekelbergh, Daniel; Griffioen, Arjan W.; Nicolay, Klaas; Fayad, Zahi A.; Meijerink, Andries; Mulder, Willem J. M.

    2012-01-01

    Silica particles as a nanoparticulate carrier material for contrast agents have received considerable attention the past few years, since the material holds great promise for biomedical applications. A key feature for successful application of this material in vivo is biocompatibility, which may be significantly improved by appropriate surface modification. In this study we report a novel strategy to coat silica particles with a dense monolayer of paramagnetic and PEGylated lipids. The silica nanoparticles carry a quantum dot in their centre and are made target-specific by the conjugation of multiple αvβ3-integrin-specifc RGD-peptides. We demonstrate their specific uptake by endothelial cells in vitro using fluorescence microscopy, quantitative fluorescence imaging and magnetic resonance imaging. The lipid coated silica particles introduced here represent a new platform for nanoparticulate multimodality contrast agents. PMID:19035793

  15. Crystallization of fluorescent quantum dots within a three-dimensional bio-organic template of actin filaments and lipid membranes.

    PubMed

    Henry, Etienne; Dif, Aurélien; Schmutz, Marc; Legoff, Loic; Amblard, François; Marchi-Artzner, Valérie; Artzner, Franck

    2011-12-14

    Biological molecules and molecular self-assemblies are promising templates to organize well-defined inorganic nanostructures. We demonstrate the ability of a self-assembled three-dimensional crystal template of helical actin protein filaments and lipids bilayers to generate a hierarchical self-assembly of quantum dots. Functionnalized tricystein peptidic quantum dots (QDs) are incorporated during the dynamical self-assembly of this actin/lipid template resulting in the formation of crystalline fibers. The crystal parameters, 26.5×18.9×35.5 nm3, are imposed by the membrane thickness, the diameter, and the pitch of the actin self-assembly. This process ensures the high quality of the crystal and results in unexpected fluorescence properties. This method of preparation offers opportunities to generate crystals with new symmetries and a large range of distance parameters.

  16. Boronic acid functionalized N-doped carbon quantum dots as fluorescent probe for selective and sensitive glucose determination

    NASA Astrophysics Data System (ADS)

    Jiang, Guohua; Jiang, Tengteng; Li, Xia; Wei, Zheng; Du, Xiangxiang; Wang, Xiaohong

    2014-04-01

    Nitrogen doped carbon quantum dots (NCQDs) of about 10 nm in diameter have been obtained by hydrothermal reaction from collagen. Because of the superiority of water dispersion, low toxicity and ease of functionlization, the NCQDs were designed as a glucose sensor after covalent grafting by 3-aminophenylboronic (APBA) (APBA-NCQDs). The as-prepared APBA-NCQDs were imparted with glucose sensitivity and selectivity from other saccharides via fluorescence (FL) quenching effect at physiological pH and at room temperature, which show high sensitivity and specificity for glucose determination with a wide range from 1 mM to 14 mM. FL quenching mechanism of APBA-NCQDs was also investigated by adding an external quencher. The APBA-NCQDs-based platform is an environmentally friendly way to substitute inorganic quantum dots containing heavy metals which offer a facile and low cost detection method.

  17. Synthesis and characterization of DNA-quantum dot conjugates for the fluorescence ratiometric detection of unlabelled DNA.

    PubMed

    Page, Leah Elizabeth; Zhang, Xi; Tyrakowski, Christina Marie; Ho, Chiun-Teh; Snee, Preston Todd

    2016-11-21

    A quantum dot-based ratiometrically responsive fluorescent sensor for unlabeled single-stranded DNA (ssDNA) is reported. Several technical issues concerning the development of high yield ssDNA-QD conjugation chemistry were addressed. The DNA sensor was synthesized by conjugating methacrylic phosphoramidite-functional oligonucleotides to water-soluble cadmium zinc sulfide core/zinc sulfide shell quantum dots (CdZnS/ZnS QDs). Duplex DNA was formed when the QD-bound ssDNA was incubated with its complement. Next, titration with PicoGreen resulted in FRET energy transfer from the dot to the dsDNA intercalating dye. The resulting ratio of the dye to QD integrated emissions is a calibratable metric for label-free DNA detection with a LOD of 3.8 nmol.

  18. Correlative fluorescence microscopy and scanning transmission electron microscopy of quantum-dot-labeled proteins in whole cells in liquid.

    PubMed

    Dukes, Madeline J; Peckys, Diana B; de Jonge, Niels

    2010-07-27

    Correlative fluorescence microscopy and transmission electron microscopy (TEM) is a state-of-the-art microscopy methodology to study cellular function, combining the functionality of light microscopy with the high resolution of electron microscopy. However, this technique involves complex sample preparation procedures due to its need for either thin sections or frozen samples for TEM imaging. Here, we introduce a novel correlative approach capable of imaging whole eukaryotic cells in liquid with fluorescence microscopy and with scanning transmission electron microscopy (STEM); there is no additional sample preparation necessary for the electron microscopy. Quantum dots (QDs) were bound to epidermal growth factor (EGF) receptors of COS7 fibroblast cells. Fixed whole cells in saline water were imaged with fluorescence microscopy and subsequently with STEM. The STEM images were correlated with fluorescence images of the same cellular regions. QDs of dimensions 7x12 nm were visible in a 5 microm thick layer of saline water, consistent with calculations. A spatial resolution of 3 nm was achieved on the QDs.

  19. Correlative Fluorescence Microscopy and Scanning Transmission Electron Microscopy of Quantum Dot Labeled Proteins in Whole Cells in Liquid

    PubMed Central

    Dukes, Madeline J.; Peckys, Diana B.; de Jonge, Niels

    2010-01-01

    Correlative fluorescence microscopy and transmission electron microscopy (TEM) is a state-of-the-art microscopy methodology to study cellular function, combining the functionality of light microscopy with the high resolution of electron microscopy. However, this technique involves complex sample preparation procedures due to its need for either thin sections or frozen samples for TEM imaging. Here, we introduce a novel correlative approach capable of imaging whole eukaryotic cells in liquid with fluorescence microscopy and with scanning transmission electron microscopy (STEM); there is no additional sample preparation necessary for the electron microscopy. Quantum dots (QDs) were bound to epidermal growth factor (EGF) receptors of COS7 fibroblast cells. Fixed whole cells in saline water were imaged with fluorescence microscopy and subsequently with STEM. The STEM images were correlated with fluorescence images of the same cellular regions. QDs of dimensions 7 × 12 nm were visible in a 5 μm thick layer of saline water, consistent with calculations. A spatial resolution of 3 nm was achieved on the QDs. PMID:20550177

  20. Carbon quantum dots-based recyclable real-time fluorescence assay for alkaline phosphatase with adenosine triphosphate as substrate.

    PubMed

    Qian, Zhaosheng; Chai, Lujing; Tang, Cong; Huang, Yuanyuan; Chen, Jianrong; Feng, Hui

    2015-03-03

    A convenient, reliable, and highly sensitive real-time assay for alkaline phosphatase (ALP) activity in the continuous and recyclable way is established on the basis of aggregation and disaggregation of carbon quantum dots (CQDs) through the competitive assay approach. CQDs and adenosine triphosphate (ATP) were used as the fluorescent indicator and substrate for ALP activity assessment, respectively. Richness of carboxyl groups on the surface of CQDs enables their severe aggregation triggered by cerium ions, which results in effective fluorescence quenching. Under the catalytic hydrolysis of ALP, ATP can be rapidly transformed to phosphate ions. Stronger affinity of phosphate ions to cerium ions than carboxyl groups is taken advantage of to achieve fluorescence recovery induced by redispersion of CQDs in the presence of ALP and ATP. Quantitative evaluation of ALP activity in a broad range from 4.6 to 383.3 U/L with the detection limit of 1.4 U/L can be realized in this way, which endows the assay with high enough sensitivity for practical detection in human serum. The assay can be used in a recyclable way for more than three times since the generated product CePO4 as a precipitate can be easily removed from the standard assay system. This strategy broadens the sensing application of fluorescent CQDs with excellent biocompatibility and provides an example based on disaggregation in optical probe development.

  1. l-Tryptophan-capped carbon quantum dots for the sensitive and selective fluorescence detection of mercury ion in aqueous solution

    NASA Astrophysics Data System (ADS)

    Wan, Xuejuan; Li, Shifeng; Zhuang, Lulu; Tang, Jiaoning

    2016-07-01

    l-Tryptophan-capped carbon quantum dots ( l-CQDs) were facilely synthesized through "green" methodology, and the obtained material was utilized as a sensitive and selective fluorescence sensor for mercury ion (Hg2+) in pure aqueous solutions. Carboxyl-functionalized CQDs were first green synthesized by a one-step hydrothermal route, and l-tryptophan was then attached to CQDs via direct surface condensation reaction in aqueous solution at room temperature. The as-synthesized l-CQDs had an average size of ca. 5 nm with a good dispersity in water, and exhibited a favorable selectivity for Hg2+ ions over a range of other common metal cations in aqueous solution (10 mM PBS buffer, pH 6.0). Upon the addition of Hg2+, a complete fluorescence quenching (ON-OFF switching) of l-CQDs was evident from the fluorescence titration experiment, and the fluorescence detection limit of Hg2+ was calculated to be 11 nM, which indicated that the obtained environmentally friendly l-CQDs had sensitive detection capacity for Hg2+ in aqueous solution.

  2. Monte Carlo study of PbSe quantum dots as the fluorescent material in luminescent solar concentrators.

    PubMed

    Wilton, S R; Fetterman, M R; Low, J J; You, Guanjun; Jiang, Zhenyu; Xu, Jian

    2014-01-13

    In this paper, Monte Carlo simulations were performed to determine the potential efficiencies of luminescent solar concentrator (LSC) systems using PbSe quantum dots (QDs) as the active fluorescent material. The simulation results suggest that PbSe QD LSCs display good absorption characteristics, but yield limited LSC power conversion efficiency due to self-absorption and down-conversion loss. It is proposed that the self-absorption loss can be reduced by utilizing Förster resonance energy transfer between two different sizes of PbSe QDs, yielding pronounced improvement in the optical efficiency of LSCs.

  3. In vivo fluorescence imaging with Ag2S quantum dots in the second near-infrared region.

    PubMed

    Hong, Guosong; Robinson, Joshua T; Zhang, Yejun; Diao, Shuo; Antaris, Alexander L; Wang, Qiangbin; Dai, Hongjie

    2012-09-24

    Hits the dot: Ag(2)S quantum dots (QDs) with bright near-infrared-II fluorescence emission (around 1200 nm) and six-arm branched PEG surface coating were synthesized for in vivo small-animal imaging. The 6PEG-Ag(2)S QDs afforded a tumor uptake of approximately 10 % injected dose/gram, owing to a long circulation half-life of approximately 4 h. Clearance of the injected 6PEG-Ag(2)S QDs occurs mainly through the biliary pathway in mice.

  4. Charge-controlled assembling of bacteriorhodopsin and semiconductor quantum dots for fluorescence resonance energy transfer-based nanophotonic applications

    NASA Astrophysics Data System (ADS)

    Bouchonville, Nicolas; Molinari, Michael; Sukhanova, Alyona; Artemyev, Mikhail; Oleinikov, Vladimir A.; Troyon, Michel; Nabiev, Igor

    2011-01-01

    The fluorescence resonance energy transfer (FRET) between quantum dots (QDs) and photochromic protein bacteriorhodopsin within its natural purple membrane (PM) is explored to monitor their assembling. It is shown that the efficiency of FRET may be controlled by variation of the surface charge and thickness of QD organic coating. Atomic force microscopy imaging revealed correlation between the surface charge of QDs and degree of their ordering on the surface of PM. The most FRET-efficient QD-PM complexes have the highest level of QDs ordering, and their assembling design may be further optimized to engineer hybrid materials with advanced biophotonic and photovoltaic properties.

  5. Photophysical investigation of (D-π-A) DMHP dye: Dipole moments, photochemical quantum yield and fluorescence quantum yield, by solvatochromic shift methods and DFT studies

    NASA Astrophysics Data System (ADS)

    Asiri, Abdullah M.; Sobahi, Tariq R.; Osman, Osman I.; Khan, Salman A.

    2017-01-01

    (2E)-3-(3,4-dimethoxyphenyl)-1-(2-hydroxyphenyl)prop-2-en-1-one (DMHP) was synthesized by the reaction of 3,4-dimethoxy benzaldehyde with 1-(2-hydroxyphenyl) ethanone under microwave irradiation. The structure of DMHP was established experimentally by EI-MS, FT-IR, 1H and 13C NMR spectral studies and elemental analysis and theoretically. Electronic absorption and emission spectra of DMHP were studied in different solvents on the basis of polarities, and the obtain data were used to determine the solvatochromic properties such as extinction coefficient, oscillator strength, transition dipole moment, stokes shift, fluorescence quantum yield and photochemical quantum yield. The absorption and emission maxima were red-shifted when the polarity of the solvent was increased from dioxan to DMSO; in excellent agreement the DFT findings. The DMHP experimental intramolecular charge transfer (ICT) was complemented by a natural bond orbital (NBO) analysis. Fluorescence intensities of DMHP were increase and decrease in presence of CTAB and SDS, so DMHP was used to find out the critical micelle concentration (CMC) of CTAB and SDS.

  6. In-capillary probing of quantum dots and fluorescent protein self-assembly and displacement using Förster resonance energy transfer.

    PubMed

    Wang, Jianhao; Fan, Jie; Li, Jinchen; Liu, Li; Wang, Jianpeng; Jiang, Pengju; Liu, Xiaoqian; Qiu, Lin

    2017-02-01

    Herein, a Förster resonance energy transfer system was designed, which consisted of CdSe/ZnS quantum dots donor and mCherry fluorescent protein acceptor. The quantum dots and the mCherry proteins were conjugated to permit Förster resonance energy transfer. Capillary electrophoresis with fluorescence detection was used for the analyses for the described system. The quantum dots and mCherry were sequentially injected into the capillary, while the real-time fluorescence signal of donor and acceptor was simultaneously monitored by two channels with fixed wavelength detectors. An effective separation of complexes from free donor and acceptor was achieved. Results showed quantum dots and hexahistidine tagged mCherry had high affinity and the assembly was affected by His6 -mCherry/quantum dot molar ratio. The kinetics of the self-assembly was calculated using the Hill equation. The microscopic dissociation constant values for out of- and in-capillary assays were 10.49 and 23.39 μM, respectively. The capillary electrophoresis with fluorescence detection that monitored ligands competition assay further delineated the different binding capacities of histidine containing peptide ligands for binding sites on quantum dots. This work demonstrated a novel approach for the improvement of Förster resonance energy transfer for higher efficiency, increased sensitivity, intuitionistic observation, and low sample requirements of the in-capillary probing system.

  7. Cooperative effects and slow dynamics of fluorescence intensity from quantum emitters in a dielectric

    NASA Astrophysics Data System (ADS)

    Lozing, N. A.; Gladush, M. G.

    2016-12-01

    We study theoretically the possibility of spontaneous switching between dim and bright fluorescence modes from a cooperative ensemble of two-level atoms driven by a cw-laser. A numerical analysis of transient regimes and transformations of the fluorescence spectrum are reported.

  8. Absolute nitrogen atom density measurements by two-photon laser-induced fluorescence spectroscopy in atmospheric pressure dielectric barrier discharges of pure nitrogen

    SciTech Connect

    Es-Sebbar, Et-Touhami; Sarra-Bournet, Christian; Naude, Nicolas; Gherardi, Nicolas; Massines, Francoise

    2009-10-01

    In this paper, two-photon absorption laser induced fluorescence spectroscopy is used to follow the nitrogen atom density in flowing dielectric barrier discharges fed with pure nitrogen and operating at atmospheric pressure. Two different dielectric barrier discharge regimes are investigated: the Townsend regime, which is homogeneous although operating at atmospheric pressure, and the more common filamentary regime. In both regimes, densities as high as 3x10{sup 14}/cm{sup 3} are detected. However, the N atoms kinetic formation depends on the discharge regime. The saturation level is reached more rapidly with a filamentary discharge. For a given discharge regime, the N atom density depends strongly on the energy dissipated in the plasma between the gas inlet and the measurement position, whether the energy is varied by varying the position of the measurements, the gas flow, or the dissipated power. Experiments performed in the postdischarge show that the N atom decay cannot be simply attributed to three-body recombination of atomic nitrogen with nitrogen molecules, meaning that other mechanisms such as surface recombination or gas impurities play a role.

  9. Development of defined microbial population standards using fluorescence activated cell sorting for the absolute quantification of S. aureus using real-time PCR.

    PubMed

    Martinon, Alice; Cronin, Ultan P; Wilkinson, Martin G

    2012-01-01

    In this article, four types of standards were assessed in a SYBR Green-based real-time PCR procedure for the quantification of Staphylococcus aureus (S. aureus) in DNA samples. The standards were purified S. aureus genomic DNA (type A), circular plasmid DNA containing a thermonuclease (nuc) gene fragment (type B), DNA extracted from defined populations of S. aureus cells generated by Fluorescence Activated Cell Sorting (FACS) technology with (type C) or without purification of DNA by boiling (type D). The optimal efficiency of 2.016 was obtained on Roche LightCycler(®) 4.1. software for type C standards, whereas the lowest efficiency (1.682) corresponded to type D standards. Type C standards appeared to be more suitable for quantitative real-time PCR because of the use of defined populations for construction of standard curves. Overall, Fieller Confidence Interval algorithm may be improved for replicates having a low standard deviation in Cycle Threshold values such as found for type B and C standards. Stabilities of diluted PCR standards stored at -20°C were compared after 0, 7, 14 and 30 days and were lower for type A or C standards compared with type B standards. However, FACS generated standards may be useful for bacterial quantification in real-time PCR assays once optimal storage and temperature conditions are defined.

  10. A brilliant sandwich type fluorescent nanostructure incorporating a compact quantum dot layer and versatile silica substrates.

    PubMed

    Huang, Liang; Wu, Qiong; Wang, Jing; Foda, Mohamed; Liu, Jiawei; Cai, Kai; Han, Heyou

    2014-03-18

    A "hydrophobic layer in silica" structure was designed to integrate a compact quantum dot (QD) layer with high quantum yield into scalable silica hosts containing desired functionality. This was based on metal affinity driven assembly of hydrophobic QDs with versatile silica substrates and homogeneous encapsulation of organosilica/silica layers.

  11. A sensitive quantum dots-based "OFF-ON" fluorescent sensor for ruthenium anticancer drugs and ctDNA.

    PubMed

    Huang, Shan; Zhu, Fawei; Qiu, Hangna; Xiao, Qi; Zhou, Quan; Su, Wei; Hu, Baoqing

    2014-05-01

    In this contribution, a simple and sensitive fluorescent sensor for the determination of both the three ruthenium anticancer drugs (1 to 3) and calf thymus DNA (ctDNA) was established based on the CdTe quantum dots (QDs) fluorescence "OFF-ON" mode. Under the experimental conditions, the fluorescence of CdTe QDs can be effectively quenched by ruthenium anticancer drugs because of the surface binding of these drugs on CdTe QDs and the subsequent photoinduced electron transfer (PET) process from CdTe QDs to ruthenium anticancer drugs, which render the system into fluorescence "OFF" status. The system can then be "ON" after the addition of ctDNA which brought the restoration of CdTe QDs fluorescence intensity, since ruthenium anticancer drugs broke away from the surface of CdTe QDs and inserted into double helix structure of ctDNA. The fluorescence quenching effect of the CdTe QDs-ruthenium anticancer drugs systems was mainly concentration dependent, which could be used to detect three ruthenium anticancer drugs. The limits of detection were 5.5 × 10(-8) M for ruthenium anticancer drug 1, 7.0 × 10(-8) M for ruthenium anticancer drug 2, and 7.9× 10(-8) M for ruthenium anticancer drug 3, respectively. The relative restored fluorescence intensity was directly proportional to the concentration of ctDNA in the range of 1.0 × 10(-8) M ∼ 3.0 × 10(-7) M, with a correlation coefficient (R) of 0.9983 and a limit of detection of 1.1 × 10(-9) M. The relative standard deviation (RSD) for 1.5 × 10(-7) M ctDNA was 1.5% (n = 5). There was almost no interference to some common chemical compounds, nucleotides, amino acids, and proteins. The proposed method was applied to the determination of ctDNA in three synthetic samples with satisfactory results. The possible reaction mechanism of CdTe QDs fluorescence "OFF-ON" was further investigated. This simple and sensitive approach possessed some potential applications in the investigation of interaction between drug molecules and DNA.

  12. Electrolyzing synthesis of boron-doped graphene quantum dots for fluorescence determination of Fe(3+) ions in water samples.

    PubMed

    Chen, Li; Wu, Chuanli; Du, Pan; Feng, Xiaowei; Wu, Ping; Cai, Chenxin

    2017-03-01

    This work reports a facile electrolyzing method to synthesize boron-doped graphene quantum dots (BGQDs) and uses the BGQDs as a fluorescent probe to determine Fe(3+) ion levels in water samples. The BGQDs were produced by oxidizing graphite in an aqueous borax solution at pH 7; then, the borate solution was filtered with BGQDs, and the borate was dialyzed from the filtrate, leaving a solution of BGQDs in water. The amount of the B in the BGQDs can be adjusted by changing the concentration of borax used for the electrolyte. The excitation wavelength- and B amount-dependent fluorescence characteristics of BQGDs were studied. The fluorescence intensity of the BGQDs is measurable in real time, and its quenching is very sensitive to the concentration of Fe(3+) ions in the system but not to other possible coexisting metal ions. The fluorescence quenching mechanism of Fe(3+) ions to BGQDs is studied and explained based on electrochemical voltammetry and DFT simulations. The analytical signal, which is defined as F0/F, where F0 and F are the fluorescence intensities of the BGQDs before and after interaction with Fe(3+) ions, respectively, displays a good linear relationship in the Fe(3+) ion concentration range of 0.01-100µm with a correlation coefficient of 0.999 and a limit of detection (LOD) of ~(0.005±0.001) μM. The LOD value is much lower than the water quality standards for Fe(3+) ions (0.3ppm, ~5.36µm) in drinking water suggested by the WHO (World Health Organization) and EPA (U.S. Environmental Protection Agency), implying that this method has great potential for applications in real sample assays. For example, the determination of the Fe(3+) ion levels in three water samples (tap water, groundwater, and lake water) gives approximately the same results as those determined by the EPA-recommended AAS (atomic adsorption spectroscopy) method.

  13. One-Pot Synthesis of Biocompatible CdSe/CdS Quantum Dots and Their Applications as Fluorescent Biological Labels.

    PubMed

    Zhai, Chuanxin; Zhang, Hui; Du, Ning; Chen, Bingdi; Huang, Hai; Wu, Yulian; Yang, Deren

    2011-12-01

    We developed a novel one-pot polyol approach for the synthesis of biocompatible CdSe quantum dots (QDs) using poly(acrylic acid) (PAA) as a capping ligand at 240°C. The morphological and structural characterization confirmed the formation of biocompatible and monodisperse CdSe QDs with several nanometers in size. The encapsulation of CdS thin layers on the surface of CdSe QDs (CdSe/CdS core-shell QDs) was used for passivating the defect emission (650 nm) and enhancing the fluorescent quantum yields up to 30% of band-to-band emission (530-600 nm). Moreover, the PL emission peak of CdSe/CdS core-shell QDs could be tuned from 530 to 600 nm by the size of CdSe core. The as-prepared CdSe/CdS core-shell QDs with small size, well water solubility, good monodispersity, and bright PL emission showed high performance as fluorescent cell labels in vitro. The viability of QDs-labeled 293T cells was evaluated using a 3-(4,5-dimethylthiazol)-2-diphenyltertrazolium bromide (MTT) assay. The results showed the satisfactory (>80%) biocompatibility of as-synthesized PAA-capped QDs at the Cd concentration of 15 μg/ml.

  14. Water-soluble Ag(2)S quantum dots for near-infrared fluorescence imaging in vivo.

    PubMed

    Jiang, Peng; Zhu, Chun-Nan; Zhang, Zhi-Ling; Tian, Zhi-Quan; Pang, Dai-Wen

    2012-07-01

    A one-step method for synthesizing water-soluble Ag(2)S quantum dots terminated with carboxylic acid group has been reported. The crystal structure and surface of the prepared Ag(2)S quantum dots were characterized. The prepared Ag(2)S quantum dots exhibited bright photoluminescence and excellent photostabilities. The photoluminescence emissions could be tuned from visible region to near-infrared (NIR) region (from 510 nm to 1221 nm). Ultra-small sized Ag(2)S nanoclusters were synthesized with high initial monomer concentration in the current system. The in vivo imaging experiments of nude mice showed that the NIR photoluminescence of the prepared Ag(2)S quantum dots could penetrate the body of mice. Compared to the conventional NIR quantum dots, the Ag(2)S quantum dots don't contain toxic elements to body (such as Cd and Pb), thus, the prepared Ag(2)S quantum dots could serve as excellent NIR optical imaging probes and would open the opportunity to study nanodiagnostics and imaging in vivo.

  15. A fusion-spliced near-field optical fiber probe using photonic crystal fiber for nanoscale thermometry based on fluorescence-lifetime measurement of quantum dots.

    PubMed

    Fujii, Takuro; Taguchi, Yoshihiro; Saiki, Toshiharu; Nagasaka, Yuji

    2011-01-01

    We have developed a novel nanoscale temperature-measurement method using fluorescence in the near-field called fluorescence near-field optics thermal nanoscopy (Fluor-NOTN). Fluor-NOTN enables the temperature distributions of nanoscale materials to be measured in vivo/in situ. The proposed method measures temperature by detecting the temperature dependent fluorescence lifetimes of Cd/Se quantum dots (QDs). For a high-sensitivity temperature measurement, the auto-fluorescence generated from a fiber probe should be reduced. In order to decrease the noise, we have fabricated a novel near-field optical-fiber probe by fusion-splicing a photonic crystal fiber (PCF) and a conventional single-mode fiber (SMF). The validity of the novel fiber probe was assessed experimentally by evaluating the auto-fluorescence spectra of the PCF. Due to the decrease of auto-fluorescence, a six- to ten-fold increase of S/N in the near-field fluorescence lifetime detection was achieved with the newly fabricated fusion-spliced near-field optical fiber probe. Additionally, the near-field fluorescence lifetime of the quantum dots was successfully measured by the fabricated fusion-spliced near-field optical fiber probe at room temperature, and was estimated to be 10.0 ns.

  16. On-Resonance Fluorescence, Resonance Rayleigh Scattering, and Ratiometric Resonance Synchronous Spectroscopy of Molecular- and Quantum Dot-Fluorophores.

    PubMed

    Siriwardana, Kumudu; Nettles, Charles B; Vithanage, Buddhini C N; Zhou, Yadong; Zou, Shengli; Zhang, Dongmao

    2016-09-20

    Existing studies on molecular fluorescence have almost exclusively been focused on Stokes-shifted fluorescence spectroscopy (SSF) in which the emitted photon is detected at the wavelengths longer than that for the excitation photons. Information on fluorophore on-resonance fluorescence (ORF) and resonance Rayleigh scattering (RRS) is limited and often problematic due to the complex interplay of the fluorophore photon absorption, ORF emission, RRS, and solvent Rayleigh scattering. Reported herein is a relatively large-scale systematic study on fluorophore ORF and RRS using the conventional UV-vis extinction and SSF measurements in combination with the recently reported ratiometric resonance synchronous spectroscopic (R2S2, pronounced as "R-Two-S-Two") method. A series of fundamental parameters including fluorophore ORF cross sections and quantum yields have been quantified for the first time for a total of 12 molecular and 6 semiconductor quantum dot (QD) fluorophores. All fluorophore spectra comprise a well-defined Gaussian peak with a full width at half-maximum ranging from 4 to 30 nm. However, the RRS features of fluorophores differ drastically. The effect of fluorophore aggregation on its RRS, UV-vis, R2S2, and SSF spectra was also discussed. This work highlights the critical importance of the combined UV-vis extinction, SSF, and R2S2 spectroscopic measurements for material characterizations. The method and insights described in this work can be directly used for improving the reliability of RRS spectroscopic methods in chemical analysis. In addition, it should pave the way for developing novel R2S2-based analytical applications.

  17. CdSe/ZnS quantum dot fluorescence spectra shape-based thermometry via neural network reconstruction

    NASA Astrophysics Data System (ADS)

    Munro, Troy; Liu, Liwang; Glorieux, Christ; Ban, Heng

    2016-06-01

    As a system of interest gets small, due to the influence of the sensor mass and heat leaks through the sensor contacts, thermal characterization by means of contact temperature measurements becomes cumbersome. Non-contact temperature measurement offers a suitable alternative, provided a reliable relationship between the temperature and the detected signal is available. In this work, exploiting the temperature dependence of their fluorescence spectrum, the use of quantum dots as thermomarkers on the surface of a fiber of interest is demonstrated. The performance is assessed of a series of neural networks that use different spectral shape characteristics as inputs (peak-based—peak intensity, peak wavelength; shape-based—integrated intensity, their ratio, full-width half maximum, peak normalized intensity at certain wavelengths, and summation of intensity over several spectral bands) and that yield at their output the fiber temperature in the optically probed area on a spider silk fiber. Starting from neural networks trained on fluorescence spectra acquired in steady state temperature conditions, numerical simulations are performed to assess the quality of the reconstruction of dynamical temperature changes that are photothermally induced by illuminating the fiber with periodically intensity-modulated light. Comparison of the five neural networks investigated to multiple types of curve fits showed that using neural networks trained on a combination of the spectral characteristics improves the accuracy over use of a single independent input, with the greatest accuracy observed for inputs that included both intensity-based measurements (peak intensity) and shape-based measurements (normalized intensity at multiple wavelengths), with an ultimate accuracy of 0.29 K via numerical simulation based on experimental observations. The implications are that quantum dots can be used as a more stable and accurate fluorescence thermometer for solid materials and that use of

  18. Fluorescent sensor for selective determination of copper ion based on N-acetyl-L-cysteine capped CdHgSe quantum dots.

    PubMed

    Wang, Qingqing; Yu, Xiangyang; Zhan, Guoqing; Li, Chunya

    2014-04-15

    Using N-acetyl-L-cysteine as a stabilizer, well water-dispersed, high-quality and stable CdHgSe quantum dots were facilely synthesized via a simple aqueous phase method. The as-prepared N-acetyl-L-cysteine capped CdHgSe quantum dots were thoroughly characterized by transmission electron microscopy, X-ray diffraction spectroscopy and FTIR. A fluorescent sensor for selective determination of copper ions was developed using N-acetyl-L-cysteine capped CdHgSe quantum dots as fluorescent probe. The fluorescence intensity of N-acetyl-L-cysteine capped CdHgSe quantum dots decreased when interacted with copper ions due to the formation of coordination complex and aggregates. The method possesses high selectivity and is not influenced by some potential interferences such as Ag(+), Zn(2+), Co(2+) and Ni(2+). Under the optimal conditions, the change of fluorescence intensity (ΔI) was linearly proportional to the concentration of copper ions in the range of 1.0×10(-9)-4.0×10(-7) mol L(-1), with a detection limit as low as 2.0×10(-10) mol L(-1) (S/N=3). The developed method had been successfully employed to determine Cu(2+) in shrimp and South-lake water samples, and the results were verified by atomic absorption spectroscopy. The fluorescent sensor was demonstrated to be selective, sensitive and simple for copper ion determination, and promise for practical applications.

  19. A dark-field microscope for background-free detection of resonance fluorescence from single semiconductor quantum dots operating in a set-and-forget mode

    SciTech Connect

    Kuhlmann, Andreas V.; Houel, Julien; Warburton, Richard J.; Brunner, Daniel; Ludwig, Arne; Reuter, Dirk; Wieck, Andreas D.

    2013-07-15

    Optically active quantum dots, for instance self-assembled InGaAs quantum dots, are potentially excellent single photon sources. The fidelity of the single photons is much improved using resonant rather than non-resonant excitation. With resonant excitation, the challenge is to distinguish between resonance fluorescence and scattered laser light. We have met this challenge by creating a polarization-based dark-field microscope to measure the resonance fluorescence from a single quantum dot at low temperature. We achieve a suppression of the scattered laser exceeding a factor of 10{sup 7} and background-free detection of resonance fluorescence. The same optical setup operates over the entire quantum dot emission range (920–980 nm) and also in high magnetic fields. The major development is the outstanding long-term stability: once the dark-field point has been established, the microscope operates for days without alignment. The mechanical and optical designs of the microscope are presented, as well as exemplary resonance fluorescence spectroscopy results on individual quantum dots to underline the microscope's excellent performance.

  20. A dark-field microscope for background-free detection of resonance fluorescence from single semiconductor quantum dots operating in a set-and-forget mode.

    PubMed

    Kuhlmann, Andreas V; Houel, Julien; Brunner, Daniel; Ludwig, Arne; Reuter, Dirk; Wieck, Andreas D; Warburton, Richard J

    2013-07-01

    Optically active quantum dots, for instance self-assembled InGaAs quantum dots, are potentially excellent single photon sources. The fidelity of the single photons is much improved using resonant rather than non-resonant excitation. With resonant excitation, the challenge is to distinguish between resonance fluorescence and scattered laser light. We have met this challenge by creating a polarization-based dark-field microscope to measure the resonance fluorescence from a single quantum dot at low temperature. We achieve a suppression of the scattered laser exceeding a factor of 10(7) and background-free detection of resonance fluorescence. The same optical setup operates over the entire quantum dot emission range (920-980 nm) and also in high magnetic fields. The major development is the outstanding long-term stability: once the dark-field point has been established, the microscope operates for days without alignment. The mechanical and optical designs of the microscope are presented, as well as exemplary resonance fluorescence spectroscopy results on individual quantum dots to underline the microscope's excellent performance.

  1. A Novel Sensor for Sensitive and Selective Detection of Iodide Using Turn-on Fluorescence Graphene Quantum Dots/Ag Nanocomposite.

    PubMed

    Xu, Xianghong; Wang, Yanhui

    2015-01-01

    Based on the principle of fluorescence enhancing, by the strong and specific interreaction between iodide (I(-)) ions and nanoAg on the surface of graphene quantum dots/Ag (GQDs/Ag) nanocomposite, we propose a simple label-free and turn-on method for the detection of I(-) ions with high selectivity and sensitivity by using fluorescent GQDs/Ag nanocomposite in aqueous media.

  2. Fabrication of highly fluorescent graphene quantum dots using L-glutamic acid for in vitro/in vivo imaging and sensing.

    PubMed

    Wu, Xu; Tian, Fei; Wang, Wenxue; Chen, Jiao; Wu, Min; Zhao, Julia Xiaojun

    2013-08-21

    A facile bottom-up method for the synthesis of highly fluorescent graphene quantum dots (GQDs) has been developed using a one-step pyrolysis of a natural amino acid, L-glutamic acid, with the assistance of a simple heating mantle device. The developed GQDs showed strong blue, green and red luminescence under the irradiation of ultra-violet, blue and green light, respectively. Moreover, the GQDs emitted near-infrared (NIR) fluorescence in the range of 800-850 nm with the excitation-dependent manner. This NIR fluorescence has a large Stokes shift of 455 nm, providing significant advantage for sensitive determination and imaging of biological targets. The fluorescence properties of the GQDs, such as quantum yields, fluorescence life time, and photostability, were measured and the fluorescence quantum yield was as high as 54.5 %. The morphology and composites of the GQDs were characterized using TEM, SEM, EDS, and FT-IR. The feasibility of using the GQDs as a fluorescent biomarker was investigated through in vitro and in vivo fluorescence imaging. The results showed that the GQDs could be a promising candidate for bioimaging. Most importantly, compared to the traditional quantum dots (QDs), the GQDs is chemically inert. Thus, the potential toxicity of the intrinsic heavy metal in the traditional QDs would not be a concern for GQDs. In addition, the GQDs possessed an intrinsic peroxidase-like catalytic activity that was similar to the graphene sheets and carbon nanotubes. Coupled with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), the GQDs can be used for the sensitive detection of hydrogen peroxide with a limit of detection of 20 μM.

  3. Exciton energy transfer-based quantum dot fluorescence sensing array: "chemical noses" for discrimination of different nucleobases.

    PubMed

    Liu, Jianbo; Li, Gui; Yang, Xiaohai; Wang, Kemin; Li, Li; Liu, Wei; Shi, Xing; Guo, Yali

    2015-01-20

    A novel exciton energy transfer-based fluorescence sensing array for the discrimination of different nucleobases was developed through target nucleobase-triggered self-assembly of quantum dots (QDs). Four QD nanoprobes with different ligand receptors, including mercaptoethylamine, N-acetyl-l-cysteine, 2-dimethyl-aminethanethiol, and thioglycolic acid, were created to detect and identify nucleobase targets. These QDs served as both selective recognition scaffolds and signal transduction elements for a biomolecule target. The extent of particle assembly, induced by the analyte-triggered self-assembly of QDs, led to an exciton energy transfer effect between interparticles that gave a readily detectable fluorescence quenching and distinct fluorescence response patterns. These patterns are characteristic for each nucleobase and can be quantitatively differentiated by linear discriminate analysis. Furthermore, a fingerprint-based barcode was established to conveniently discriminate the nucleobases. This pattern sensing was successfully used to identify nucleobase samples at unknown concentrations and five rare bases. In this "chemical noses" strategy, the robust characteristics of QD nanoprobes, coupled with the diversity of surface functionality that can be readily obtained using nanoparticles, provides a simple and label-free biosensing approach that shows great promise for biomedical applications.

  4. Toward a multiplexed solid-phase nucleic acid hybridization assay using quantum dots as donors in fluorescence resonance energy transfer.

    PubMed

    Algar, W Russ; Krull, Ulrich J

    2009-05-15

    Solid-phase assays using immobilized quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) have been developed for the selective detection of nucleic acids. QDs were immobilized on optical fibers and conjugated with probe oligonucleotides. Hybridization with acceptor labeled target oligonucleotides generated FRET-sensitized acceptor fluorescence that was used as the analytical signal. A sandwich assay was also introduced and avoided the need for target labeling. Green and red emitting CdSe/ZnS QDs were used as donors with Cy3 and Alexa Fluor 647 acceptors, respectively. Quantitative measurements were made via spectrofluorimetry or fluorescence microscopy. Detection limits as low as 1 nM were obtained, and the discrimination of single nucleotide polymorphisms (SNPs) with contrast ratios as high as 31:1 was possible. The assays retained their selectivity and at least 50% of their signal when tested in bovine serum and against a large background of noncomplementary genomic DNA. Mixed films of the two colors of QD and two probe oligonucleotide sequences were prepared for multiplexed solid-phase hybridization assays. It was possible to simultaneously detect two target sequences with retention of selectivity, including SNP discrimination. This research provides an important precedent and framework for the future development of QD-based bioassays and biosensors.

  5. Efficient ratiometric fluorescence probe based on dual-emission quantum dots hybrid for on-site determination of copper ions.

    PubMed

    Yao, Jianlei; Zhang, Kui; Zhu, Houjuan; Ma, Fang; Sun, Mingtai; Yu, Huan; Sun, Jian; Wang, Suhua

    2013-07-02

    Of various chemosensory protocols, the color change observed by the naked eye is considered to be a conceivable and on-site way to indicate the presence of an analyte. We herein designed a ratiometric fluorescence probe by hybridizing dual-emission quantum dots (QDs) and demonstrated its efficiency for on-site visual determination of copper ions. The hybrid probe comprises two sizes of cadmium telluride QDs emitting red and green fluorescence, respectively, in which the red-emitting ones are embedded in silica nanoparticles and the green-emitting ones are covalently linked onto the surface. The fluorescence of the embedded QDs is insensitive to the analyte, whereas the green emissive QDs are functionalized to be selectively quenched by the analyte. Upon exposure to different amounts of copper ions, the variations of the dual emission intensity ratios display continuous color changes from green to red, which can be clearly observed by the naked eye. The limit of detection for copper is estimated to be 1.1 nM, much lower than the allowable level of copper (~20 μM) in drinking water set by U.S. Environmental Protection Agency. The probe is demonstrated for the determination of copper ions in lake water and mineral water samples, especially for visually monitoring copper residues on herb leaves. This prototype ratiometric probe is simple, fully self-contained, and thus potentially attractive for visual identification without the need for elaborate equipment.

  6. The inhibition of fluorescence resonance energy transfer between multicolor quantum dots for rapid and sensitive detection of Staphylococcus aureus

    NASA Astrophysics Data System (ADS)

    Wang, Beibei; Wang, Qi; Ma, Meihu; Cai, Zhaoxia

    2015-01-01

    In this paper, we constructed the fluorescence resonance energy transfer (FRET) system between two multi-color quantum dots (QDs) of two sizes for rapid and sensitive detection of Staphylococcus aureus. In this system, green-emitting QDs conjugated with rabbit anti-S. aureus antibodies were used as energy donors while orange-emitting QDs conjugated with goat-anti-rabbit IgG were used as energy acceptors to form FRET system. Pre-binding of Staphylococcus aureus (S. aureus) on the donor occupied the binding sites and thus blocked resonance energy transfer between two colors QDs, leading to the quenching fluorescence of the acceptor. The fluorescence of acceptor has a linear calibration graph with the concentrations of S. aureus from 52 to 2.6 × 105 CFU mL-1. The low detection limit was 10 CFU/mL. It was worth mentioning that the detection method of S. aureus had been applied to the analysis of apple juice and milk samples, which could potentially be developed into a sensor in the further study.

  7. Silica-coated ZnS quantum dots as fluorescent probes for the sensitive detection of Pb2+ ions

    NASA Astrophysics Data System (ADS)

    Qu, Hua; Cao, Lixin; Su, Ge; Liu, Wei; Gao, Rongjie; Xia, Chenghui; Qin, Junjie

    2014-12-01

    The silica-coated ZnS quantum dots (ZnS@SiO2 QDs) were prepared via a simple and environmentally friendly process. The oil-soluble ZnS cores were successfully transferred to water by the coating of SiO2 shells. The QDs exhibited satisfying dispersion and luminescent properties in water. The ZnS@SiO2 QDs were directly used as fluorescent probes for heavy metal ions without the addition of any buffer solution. The luminescence of QDs was extremely sensitive to Pb2+ ions, and the fluorescence quenching was well described by the Stern-Volmer equation, with an even quenching constant for the Pb2+ ions samples concentration ranging from 10-9 to 2.6 × 10-4 M. An extended hypothesis based on the traditional cation exchange mechanism is proposed to analyze the most significant fluorescence quenching effect by Pb2+ ions. Studies show that ZnS@SiO2 QDs have great potentials to be a sensor for Pb2+ analysis at low to high concentrations.

  8. Chemical redox modulated fluorescence of nitrogen-doped graphene quantum dots for probing the activity of alkaline phosphatase.

    PubMed

    Liu, JingJing; Tang, Duosi; Chen, Zhitao; Yan, Xiaomei; Zhong, Zhou; Kang, Longtian; Yao, Jiannian

    2017-03-08

    Alkaline phosphatase (ALP) as an essential enzyme plays an important role in clinical diagnoses and biomedical researches. Hence, the development of convenient and sensitivity assay for monitoring ALP is extremely important. In this work, on the basis of chemical redox strategy to modulate the fluorescence of nitrogen-doped graphene quantum dots (NGQDs), a novel label-free fluorescent sensing system for the detection of alkaline phosphatase (ALP) activity has been developed. The fluorescence of NGQDs is firstly quenched by ultrathin cobalt oxyhydroxide (CoOOH) nanosheets, and then restored by ascorbic acid (AA), which can reduce CoOOH to Co(2+), thus the ALP can be monitored based on the enzymatic hydrolysis of L-ascorbic acid-2-phosphate (AAP) by ALP to generate AA. Quantitative evaluation of ALP activity in a range from 0.1 to 5U/L with the detection limit of 0.07U/L can be realized in this sensing system. Endowed with high sensitivity and selectivity, the proposed assay is capable of detecting ALP in biological system with satisfactory results. Meanwhile, this sensing system can be easily extended to the detection of various AA-involved analytes.

  9. Fluorescence-Lifetime Imaging Microscopy for Visualization of Quantum Dots’ Endocytic Pathway

    PubMed Central

    Damalakiene, Leona; Karabanovas, Vitalijus; Bagdonas, Saulius; Rotomskis, Ricardas

    2016-01-01

    Accumulation of carboxylated polyethylene glycol (PEG) CdSe/ZnSquantum dots (QDs) has been monitored in living fibroblasts using confocal microscopy for fluorescence intensity and fluorescence-lifetime imaging (FLIM). The wide range of mean photoluminescence (PL) lifetime values was observed for the intracellular QDs in different intracellular microenvironment, which revealed structural heterogeneity of endosomes and enabled the distinguishing among endosomes of different maturity.

  10. Direct Detection of Time-Resolved Rabi Oscillationsin a Single Quantum Dot via Resonance Fluorescence

    DTIC Science & Technology

    2013-03-19

    spin based QD network mediated by a spin - photon interface .18,24 In many scalable quantum computing architectures, the ability to...required in quantum information protocols that rely on coherent mapping between a single elec- tron spin qubit confined to a QD and a photonic qubit .24...This coherent spin - photon interface can be used to deterministically entangle spin qubits through an appropriately designed optical

  11. Near-Infrared Fluorescent Probe with High Quantum Yield and Its Application in the Selective Detection of Glutathione in Living Cells and Tissues.

    PubMed

    Xie, Jun-Ying; Li, Chun-Yan; Li, Yong-Fei; Fei, Junjie; Xu, Fen; Ou-Yang, Juan; Liu, Juan

    2016-10-04

    Glutathione (GSH), cysteine (Cys), and homocysteine (Hcy) are small-molecular biothiols that play key roles in various biological systems. Among these biothiols, GSH is the most abundant intracellular thiol. Until now, a small number of the near-infrared (NIR) fluorescent probes have been designed for the detection of GSH. Unfortunately, most of these NIR probes are based on cyanine dyes, which generally suffer low fluorescence quantum yield (Φ < 0.25), which are not suitable for bioimaging. In addition, some probes are difficult to effectively distinguish GSH from Cys and Hcy. In this work, an NIR fluorescent probe with high fluorescence quantum yield is developed by introducing a rigid coplanar structure such as rhodamine dyes, and the NIR probe (CyR) with spirolactam structure is first synthesized and used to recognize GSH. The characteristics of this NIR probe are as follows: (1) probe CyR exhibits high fluorescence quantum yield (Φ = 0.43) after the addition of GSH and high sensitivity toward GSH with 75-fold fluorescence enhancement. (2) The probe is highly selective, which will not interfere with the other biological thiols (Cys, Hcy) and amino acids. (3) A possible reaction mechanism of the NIR probe CyR and GSH (Cys, Hcy) can be proposed and proved by (1)H NMR, (13)C NMR, and MS (mass spectra). (4) The NIR probe displays selective detection of GSH in biological samples such as living cells and tissues.

  12. Advantages of time-resolved fluorescent nanobeads compared with fluorescent submicrospheres, quantum dots, and colloidal gold as label in lateral flow assays for detection of ractopamine.

    PubMed

    Hu, Li-Ming; Luo, Kai; Xia, Jun; Xu, Guo-Mao; Wu, Cheng-Hui; Han, Jiao-Jiao; Zhang, Gang-Gang; Liu, Miao; Lai, Wei-Hua

    2017-05-15

    Label selection is a critical factor for improving the sensitivity of lateral flow assay. Time-resolved fluorescent nanobeads, fluorescent submicrospheres, quantum dots, and colloidal gold-based lateral flow assay (TRFN-LFA, FM-LFA, QD-LFA, and CG-LFA) were first systematically compared for the quantitative detection of ractopamine in swine urine based on competitive format. The limits of detection (LOD) of TRFN-LFA, FM-LFA, QD-LFA, and CG-LFA were 7.2, 14.7, 23.6, and 40.1pg/mL in swine urine samples, respectively. The sensitivity of TRFN-LFA was highest. In the quantitative determination of ractopamine (RAC) in swine urine samples, TRFN-LFA exhibited a wide linear range of 5pg/mL to 2500pg/mL with a reliable coefficient of correlation (R(2)=0.9803). Relatively narrow linear ranges of 10-500pg/mL (FM-LFA) and 25-2500pg/mL (QD-LFA and CG-LFA) were acquired. Approximately 0.005µg of anti-RAC poly antibody (pAb) was used in each TRFN-LFA test strip, whereas 0.02, 0.054, and 0.15µg of pAb were used in each of the FM-LFA, QD-LFA, and CG-LFA test strips, respectively. In addition, TRFN-LFA required the least RAC-BSA antigens and exhibited the shortest detection time compared with the other lateral flow assays. Analysis of the RAC in swine urine samples showed that the result of TRFN-LFA was consistent with that of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and a commercial enzyme-linked immunosorbent assay (ELISA) kit.

  13. "Turn-off" fluorescent sensor for highly sensitive and specific simultaneous recognition of 29 famous green teas based on quantum dots combined with chemometrics.

    PubMed

    Liu, Li; Fan, Yao; Fu, Haiyan; Chen, Feng; Ni, Chuang; Wang, Jinxing; Yin, Qiaobo; Mu, Qingling; Yang, Tianming; She, Yuanbin

    2017-04-22

    Fluorescent "turn-off" sensors based on water-soluble quantum dots (QDs) have drawn increasing attention owing to their unique properties such as high fluorescence quantum yields, chemical stability and low toxicity. In this work, a novel method based on the fluorescence "turn-off" model with water-soluble CdTe QDs as the fluorescent probes for differentiation of 29 different famous green teas is established. The fluorescence of the QDs can be quenched in different degrees in light of positions and intensities of the fluorescent peaks for the green teas. Subsequently, with aid of classic partial least square discriminant analysis (PLSDA), all the green teas can be discriminated with high sensitivity, specificity and a satisfactory recognition rate of 100% for training set and 98.3% for prediction set, respectively. Especially, the "turn-off" fluorescence PLSDA model based on second-order derivatives (2nd der) with reduced least complexity (LVs = 3) was the most effective one for modeling. Most importantly, we further demonstrated the established "turn-off" fluorescent sensor mode has several significant advantages and appealing properties over the conventional fluorescent method for large-class-number classification (LCNC) of green teas. This work is, to the best of our knowledge, the first report on the rapid and effective identification of so many kinds of famous green teas based on the "turn-off" model of QDs combined with chemometrics, which also implies other potential applications on complex LCNC classification system with weak fluorescence or even without fluorescence to achieve higher detective response and specificity.

  14. Teaching Absolute Value Meaningfully

    ERIC Educational Resources Information Center

    Wade, Angela

    2012-01-01

    What is the meaning of absolute value? And why do teachers teach students how to solve absolute value equations? Absolute value is a concept introduced in first-year algebra and then reinforced in later courses. Various authors have suggested instructional methods for teaching absolute value to high school students (Wei 2005; Stallings-Roberts…

  15. The enhancement of fluorescence quantum yields of anilino naphthalene sulfonic acids by inclusion of various cyclodextrins and cucurbit[7]uril.

    PubMed

    Sueishi, Yoshimi; Fujita, Tomonori; Nakatani, Shinichiro; Inazumi, Naoya; Osawa, Yoshihiro

    2013-10-01

    The association constants (K) for the inclusion complexation of four kinds of cyclodextrins (CDs (β- and γ-), 2,6-di-O-methylated β-CD, and 2,3,6-tri-O-methylated β-CD) and cucurbit[7]uril (CB[7]) with 1,8- and 2,6-anilinonaphthalene sulfonic acids (ANSs) were determined from fluorescence spectra enhanced by inclusion. Various CDs and CB[7] form stable 1:1 inclusion complexes with 1,8- and 2,6-ANSs: K=80-11700 M(-1) for 2,6-ANS and 50-195 M(-1) for 1,8-ANS. The high stability of the inclusion complexes of 2,6-ANS with CB[7] and 2,6-di-O-methylated β-CD is shown. Further, we determined the fluorescence quantum yields (Φ values) for the inclusion complexes of ANSs by using a fluorescence spectrophotometer equipped with a half-moon unit. The Φ values of 1,8- and 2,6-ANSs were largely enhanced by the inclusion of methylated β-CDs and did not correlate with the degree of stability (K) of the inclusion complexes. We characterized the structures of the inclusion complexes by 2D ROESY-NMR measurements. In addition, the microenvironmental polarity inside the hydrophobic CD and CB[7] cavities was evaluated using the fluorescence probe 2,6-ANS. Based on the emission mechanism and the aspect of inclusion in a hydrophobic cavity, we have suggested that the microenvironmental polarity and viscosity for the excited state of ANS plays an important role for the Φ values of inclusion complexes.

  16. An Analytical Quantum Model to Calculate Fluorescence Enhancement of a Molecule in Vicinity of a Sub-10 nm Metal Nanoparticle.

    PubMed

    Bagheri, Zahra; Massudi, Reza

    2016-11-16

    An analytical quantum model is used to calculate electrical permittivity of a metal nanoparticle located in an adjacent molecule. Different parameters, such as radiative and non-radiative decay rates, quantum yield, electrical field enhancement factor, and fluorescence enhancement are calculated by such a model and they are compared with those obtained by using the classical Drude model. It is observed that using an analytical quantum model presents a higher enhancement factor, up to 30%, as compared to classical model for nanoparticles smaller than 10 nm. Furthermore, the results are in better agreement with those experimentally realized.

  17. Efficient assembly of multi-walled carbon nanotube-CdSe/ZnS quantum dot hybrids with high biocompatibility and fluorescence property.

    PubMed

    Zhang, Yingying; Qin, Weiling; Tang, Hao; Yan, Feng; Tan, Liang; Xie, Qingji; Ma, Ming; Zhang, Youyu; Yao, Shouzhuo

    2011-10-15

    CdSe/ZnS core-shell quantum dots (QDs) were efficiently tethered onto polyamidoamine dendrimer-modified multi-walled carbon nanotubes (MWCNTs) by covalent linkage and mercapto-mediated assembly. The obtained MWCNT-QD hybrids were both photophysically and morphologically characterized. The QDs are well-distributed on single nanotube surface in high density and the assembly of QDs onto MWCNTs does not change the fluorescence emission wavelength of QDs but significantly decreases the emission density. Cytotoxicity of MWCNT-QD hybrids to HeLa cells and their fluorescence property in living cell system were evaluated in detail. The hybrids show a little effect on cell viability even at very high concentration (100 μg mL(-1)). Moreover, they possess intense red fluorescence signal under optical fluorescence microscopy and good fluorescence stability over 72-h exposure in living cell system.

  18. CdSe/AsS core-shell quantum dots: preparation and two-photon fluorescence.

    PubMed

    Wang, Junzhong; Lin, Ming; Yan, Yongli; Wang, Zhe; Ho, Paul C; Loh, Kian Ping

    2009-08-19

    Arsenic(II) sulfide (AsS)-coated CdSe core-shell nanocrystals can be prepared by a cluster-complex deposition approach under mild conditions. At 60 degrees C, growth of an AsS shell onto a CdSe nanocrystal can be realized through the crystallization of a cluster complex of AsS/butylamine in a mixed solvent of isopropanol/chloroform. The new, type I core-shell nanocrystal exhibits markedly enhanced one-photon fluorescence as well two-photon upconversion fluorescence. The nanocrystals can be used for infrared-excited upconversion cellular labeling.

  19. Detection of 15 dB Squeezed States of Light and their Application for the Absolute Calibration of Photoelectric Quantum Efficiency

    NASA Astrophysics Data System (ADS)

    Vahlbruch, Henning; Mehmet, Moritz; Danzmann, Karsten; Schnabel, Roman

    2016-09-01

    Squeezed states of light belong to the most prominent nonclassical resources. They have compelling applications in metrology, which has been demonstrated by their routine exploitation for improving the sensitivity of a gravitational-wave detector since 2010. Here, we report on the direct measurement of 15 dB squeezed vacuum states of light and their application to calibrate the quantum efficiency of photoelectric detection. The object of calibration is a customized InGaAs positive intrinsic negative (p-i-n) photodiode optimized for high external quantum efficiency. The calibration yields a value of 99.5% with a 0.5% (k =2 ) uncertainty for a photon flux of the order 1 017 s-1 at a wavelength of 1064 nm. The calibration neither requires any standard nor knowledge of the incident light power and thus represents a valuable application of squeezed states of light in quantum metrology.

  20. Fluorescence biosensor based on CdTe quantum dots for specific detection of H5N1 avian influenza virus

    NASA Astrophysics Data System (ADS)

    Hoa Nguyen, Thi; Dieu Thuy Ung, Thi; Hien Vu, Thi; Tran, Thi Kim Chi; Quyen Dong, Van; Khang Dinh, Duy; Liem Nguyen, Quang

    2012-09-01

    This report highlights the fabrication of fluorescence biosensors based on CdTe quantum dots (QDs) for specific detection of H5N1 avian influenza virus. The core biosensor was composed of (i) the highly luminescent CdTe/CdS QDs, (ii) chromatophores extracted from bacteria Rhodospirillum rubrum, and (iii) the antibody of β-subunit. This core part was linked to the peripheral part of the biosensor via a biotin-streptavidin-biotin bridge and finally connected to the H5N1 antibody to make it ready for detecting H5N1 avian influenza virus. Detailed studies of each constituent were performed showing the image of QDs-labeled chromatophores under optical microscope, proper photoluminescence (PL) spectra of CdTe/CdS QDs, chromatophores and the H5N1 avian influenza viruses.

  1. Optical Properties of Fluorescent Mixtures: Comparing Quantum Dots to Organic Dyes

    ERIC Educational Resources Information Center

    Hutchins, Benjamin M.; Morgan, Thomas T.; Ucak-Astarlioglu, Mine G.; Wlilliams, Mary Elizabeth

    2007-01-01

    The study describes and compares the size-dependent optical properties of organic dyes with those of semiconductor nanocrystals or quantum dots (QDs). The analysis shows that mixtures of QDs contain emission colors that are sum of the individual QD components.

  2. Physical and biophysical assessment of highly fluorescent, magnetic quantum dots of a wurtzite-phase manganese selenide system

    NASA Astrophysics Data System (ADS)

    Sarma, Runjun; Das, Queen; Hussain, Anowar; Ramteke, Anand; Choudhury, Amarjyoti; Mohanta, Dambarudhar

    2014-07-01

    Combining fluorescence and magnetic features in a non-iron based, select type of quantum dots (QDs) can have immense value in cellular imaging, tagging and other nano-bio interface applications, including targeted drug delivery. Herein, we report on the colloidal synthesis and physical and biophysical assessment of wurtzite-type manganese selenide (MnSe) QDs in cell culture media. Aiming to provide a suitable colloidal system of biological relevance, different concentrations of reactants and ligands (e.g., thioglycolic acid, TGA) have been considered. The average size of the QDs is ˜7 nm, which exhibited a quantum yield of ˜75% as compared to rhodamine 6 G dye®. As revealed from time-resolved photoluminescence (TR-PL) response, the near band edge emission followed a bi-exponential decay feature with characteristic times of ˜0.64 ns and 3.04 ns. At room temperature, the QDs were found to exhibit paramagnetic features with coercivity and remanence impelled by TGA concentrations. With BSA as a dispersing agent, the QDs showed an improved optical stability in Dulbecco’s Modified Eagle Media® (DMEM) and Minimum Essential Media® (MEM), as compared to the Roswell Park Memorial Institute® (RPMI-1640) media. Finally, the cell viability of lymphocytes was found to be strongly influenced by the concentration of MnSe QDs, and had a safe limit upto 0.5 μM. With BSA inclusion in cell media, the cellular uptake of MnSe QDs was observed to be more prominent, as revealed from fluorescence imaging. The fabrication of water soluble, nontoxic MnSe QDs would open up an alternative strategy in nanobiotechnology, while preserving their luminescent and magnetic properties intact.

  3. Physical and biophysical assessment of highly fluorescent, magnetic quantum dots of a wurtzite-phase manganese selenide system.

    PubMed

    Sarma, Runjun; Das, Queen; Hussain, Anowar; Ramteke, Anand; Choudhury, Amarjyoti; Mohanta, Dambarudhar

    2014-07-11

    Combining fluorescence and magnetic features in a non-iron based, select type of quantum dots (QDs) can have immense value in cellular imaging, tagging and other nano-bio interface applications, including targeted drug delivery. Herein, we report on the colloidal synthesis and physical and biophysical assessment of wurtzite-type manganese selenide (MnSe) QDs in cell culture media. Aiming to provide a suitable colloidal system of biological relevance, different concentrations of reactants and ligands (e.g., thioglycolic acid, TGA) have been considered. The average size of the QDs is ∼7 nm, which exhibited a quantum yield of ∼75% as compared to rhodamine 6 G dye(®). As revealed from time-resolved photoluminescence (TR-PL) response, the near band edge emission followed a bi-exponential decay feature with characteristic times of ∼0.64 ns and 3.04 ns. At room temperature, the QDs were found to exhibit paramagnetic features with coercivity and remanence impelled by TGA concentrations. With BSA as a dispersing agent, the QDs showed an improved optical stability in Dulbecco's Modified Eagle Media(®) (DMEM) and Minimum Essential Media(®) (MEM), as compared to the Roswell Park Memorial Institute(®) (RPMI-1640) media. Finally, the cell viability of lymphocytes was found to be strongly influenced by the concentration of MnSe QDs, and had a safe limit upto 0.5 μM. With BSA inclusion in cell media, the cellular uptake of MnSe QDs was observed to be more prominent, as revealed from fluorescence imaging. The fabrication of water soluble, nontoxic MnSe QDs would open up an alternative strategy in nanobiotechnology, while preserving their luminescent and magnetic properties intact.

  4. A fluorescent nanosensor based on graphene quantum dots-aptamer probe and graphene oxide platform for detection of lead (II) ion.

    PubMed

    Qian, Zhao Sheng; Shan, Xiao Yue; Chai, Lu Jing; Chen, Jian Rong; Feng, Hui

    2015-06-15

    The sensitive detection of heavy metal ions in the organism and aquatic ecosystem using nanosensors based on environment friendly and biocompatible materials still remains a challenge. A fluorescent turn-on nanosensor for lead (II) detection based on biocompatible graphene quantum dots and graphene oxide by employment of Pb(2+)-induced G-quadruplex formation was reported. Graphene quantum dots with high quantum yield, good biocompatibility were prepared and served as the fluorophore of Pb(2+) probe. Fluorescence turn-off of graphene quantum dots is easily achieved through efficient photoinduced electron transfer between graphene quantum dots and graphene oxide, and subsequent fluorescence turn-on process is due to the formation of G-quadraplex aptamer-Pb(2+) complex triggered by the addition of Pb(2+). This nanosensor can distinguish Pb(2+) ion from other ions with high sensitivity and good reproducibility. The detection method based on this nanosensor possesses a fast response time of one minute, a broad linear span of up to 400.0 nM and ultralow detection limit of 0.6 nM.

  5. Study of gold nanostar@SiO2@CdTeS quantum dots@SiO2 with enhanced-fluorescence and photothermal therapy multifunctional cell nanoprobe

    NASA Astrophysics Data System (ADS)

    Yin, Naiqiang; Jiang, Tongtong; Yu, Jing; He, Jiawei; Li, Xu; Huang, Qianpeng; Liu, Ling; Xu, Xiaoliang; Zhu, Lixin

    2014-03-01

    A novel class of cell probe structured as gold nanostar@SiO2@CdTeS quantum dots@SiO2 nanoprobes with multifunctional (MFNPs) fluorescent and photothermal properties were demonstrated. The MFNPs with good homogeneity (129 ± 10 nm) and dispersity were synthesized by a liquid phase method. The fluorescence signal of quantum dots was enhanced in the MFNPs, compared with the pure quantum dots. The vitro study showed that the MFNPs can realize the targeted labeling after functionalized with anti-body. Furthermore, the nanoprobe displays strong surface plasmonic resonance absorbance in the near-infrared region, thus exhibiting an NIR (808 nm)-induced temperature elevation. When cancer cells were cultured with the anti-body linked MFNPs and irradiated by laser, the MFNPs were demonstrated as good candidates for curing cancer cells. Therefore, such a multifunctional probe can be developed as a promising nanosystem that integrates multiple capabilities for effective cancer diagnosis and therapy.

  6. Sensitive detection of sodium cromoglycate with glutathione-capped CdTe quantum dots as a novel fluorescence probe.

    PubMed

    Hao, Chenxia; Liu, Shaopu; Li, Dan; Yang, Jidong; He, Youqiu

    2015-11-01

    A sensitive and simple analytical strategy for the detection of sodium cromoglycate (SCG) has been established based on a readily detectable fluorescence quenching effect of SCG for glutathione-capped (GSH-capped) CdTe quantum dots (QDs). The fluorescence of GSH-capped CdTe QDs could be efficiently quenched by SCG through electron transfer from GSH-capped CdTe QDs to SCG. Under optimum conditions, the response was linearly proportional to the concentration of SCG between 0.6419 and 100 µg/mL, with a correlation coefficient (R) of 0.9964; the detection limit (3δ/K) was 0.1926 µg/mL. The optimum conditions and the influence of coexisting foreign substances on the reaction were also investigated. The very effective and simple method reported here has been successfully applied to the determination of SCG in synthetic and real samples. It is believed that the established approach could have good prospects for application in the fields of clinical diseases diagnosis and treatment.

  7. Using fluorescence immunochromatographic test strips based on quantum dots for the rapid and sensitive determination of microcystin-LR.

    PubMed

    Sun, Jiadi; Li, Ying; Pi, Fuwei; Ji, Jian; Zhang, Yinzhi; Sun, Xiulan

    2017-03-01

    A novel immunosensor for the detection of microcystin-LR (MC-LR) was constructed with use of immunochromatographic test strips (ICTS). Quantum dots were chosen to be the fluorescent labels for the immune sensor in ICTS because of their excellent optical and electronic properties with a relatively narrow emission spectrum. The detection sensitivity of the ICTS was related to the concentration of the fluorescent probe and the amount of the MC-LR standards. Under optimal conditions, with MC-LR as the target, the ICTS sensor had a linear range from 0.25 to 5 μg/L, with a correlation coefficient of 0.9901 and a detection limit of 0.1 μg/L. Furthermore, the repeatability of the ICTS was good, and the coefficient of variation was 10%. The ICTS immunosensor allows the reliable detection of MC-LR in water, and has potential in simple, sensitive detection applications. Graphical Abstract A novel method was developed to detect MC-LR using QDs based immunochromatographic test strip.

  8. Dopamine functionalized-CdTe quantum dots as fluorescence probes for l-histidine detection in biological fluids.

    PubMed

    Shi, Fanping; Liu, Siyu; Su, Xingguang

    2014-07-01

    In this paper, we developed dopamine functionalized-CdTe quantum dots as fluorescence probes for the determination of l-histidine. Firstly, CdTe was covalently linked to dopamine to form a kind of fluorescence sensor with pyrocatechol structure on the surface. The photoluminescence intensity of CdTe-dopamine (QDs-DA) could be quenched by Ni(2+) due to the strong coordination interaction between the pyrocatechol structure of QDs-DA and Ni(2+). In the presence of l-histidine, Ni(2+) preferred to bind with l-histidine due to high affinity of Ni(2+) to l-histidine and the photoluminescence intensity of QDs-DA was recovered. The recovered photoluminescence intensity of QDs-DA was proportional to the concentration of l-histidine in the ranges of 1.0×10(-6)-1.0×10(-4)mol L(-1) and the detection limit was 5.0×10(-7)mol L(-1) respectively. The established method showed a good selectivity for l-histidine among other common amino acids, and it was applied for determination of l-histidine in human serum sample with satisfactory results.

  9. Effects of multi-walled carbon nanotubes on the electrogenerated chemiluminescence and fluorescence of CdTe quantum dots.

    PubMed

    Wusimanjiang, Yiliyasi; Meyer, Alexander; Lu, Liping; Miao, Wujian

    2016-10-01

    Effects of multi-walled carbon nanotubes (CNTs) that were immobilized on glassy carbon electrode (GCE) on the electrogenerated chemiluminescence (ECL) of CdTe quantum dots (QDs) using tri-n-propylamine (TPrA) and 2-(dibutylamino)ethanol (DBAE) as the anodic coreactant are reported. Depending on the solution concentration of coreactant and QDs, the surface-confined CNTs could either quench or enhance the ECL intensity. Lowering the solution concentration of QDs was found to be beneficial for enhancing ECL. A V-shaped profile of ECL intensity ratio (at CNTs over bare GCE) versus coreactant concentration suggested that either low or high concentrations of coreactant were needed for effective ECL generation. The ECL quenching by CNTs was believed to follow the typical dynamic quenching mechanism, which was confirmed by fluorescent data that provided a Stern-Volmer and an estimated quenching constant of 11.7 g/L and 1.2 × 10(9) L/g•s, respectively, for the excited state CdTe* quenching by CNTs in solution. Furthermore, the ECL performance at CNTs was also affected by the type of the coreactant used, where up to 30 times enhancement in ECL was observed from the CdTe/DBAE system under the given experimental conditions. Graphical Abstract Illustration of anodic quantum dots ECL enhancement and quenching by multi-walled carbon nanotubes.

  10. Silica-on-silicon waveguide integrated polydimethylsiloxane lab-on-a-chip for quantum dot fluorescence bio-detection

    NASA Astrophysics Data System (ADS)

    Ozhikandathil, Jayan; Packirisamy, Muthukumaran

    2012-01-01

    Integration of microfluidics and optical components is an essential requirement for the realization of optical detection in lab-on-a-chip (LOC). In this work, a novel hybrid integration of silica-on-silicon (SOS) waveguide and polydymethylsiloxane (PDMS) microfluidics for realizing optical detection based biochip is demonstrated. SOS is a commonly used platform for integrated photonic circuits due to its lower absorption coefficient of silica and the availability of advanced microfabrication technologies for fabricating complicated optical components. However, the fabrication of complex microfluidics circuits on SOS is an expensive process. On the other hand, any complex 3D and high-aspect-ratio microstructures for the microfluidic applications can be easily patterned on PDMS using soft lithography. By exploring the advantages of these two materials, the proposed hybrid integration method greatly simplifies the fabrication of optical LOC. Two simple technologies--namely, diamond machining and soft lithography--were employed for the integration of an optical microfluidic system. Use of PDMS for the fabrication of any complex 3D microfluidics structures, together with the integration of low loss silica-on-silicon photonic waveguides with a straight microfluidic channel, opens up new possibilities to produce low-cost biochips. The performance of SOS-PDMS-integrated hybrid biochip is demonstrated with the detection of laser induced fluorescence of quantum dots. As quantum dots have immense application potential for biodetection, they are used for the demonstration of biodetection.

  11. Permethylated-β-Cyclodextrin Capped CdTe Quantum Dot and its Sensitive Fluorescence Analysis of Malachite Green.

    PubMed

    Cao, Yujuan; Wei, Jiongling; Wu, Wei; Wang, Song; Hu, Xiaogang; Yu, Ying

    2015-09-01

    In the present work, the CdTe quantum dots were covalently conjugated with permethylated-β-cyclodextrin (OMe-β-CD) using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride as cross-linking reagent. The obtained functional quantum dots (OMe-β-CD/QDs) showed highly luminescent, water solubility and photostability as well as good inclusion ability to malachite green. A sensitive fluorescence method was developed for the analysis of malachite green in different samples. The good linearity was 2.0 × 10(-7)-1.0 × 10(-5) mol/L and the limit of detect was 1.7 × 10(-8) mol/L. The recoveries for three environmental water samples were 92.0-108.2 % with relative standard deviation (RSD) of 0.24-1.87 %, while the recovery for the fish sample was 94.3 % with RSD of 1.04 %. The results showed that the present method was sensitive and convenient to determine malachite green in complex samples. Graphical Abstract The analytical mechanism of OMe-β-CD/QDs and its linear response to MG.

  12. Silica-on-silicon waveguide integrated polydimethylsiloxane lab-on-a-chip for quantum dot fluorescence bio-detection.

    PubMed

    Ozhikandathil, Jayan; Packirisamy, Muthukumaran

    2012-01-01

    Integration of microfluidics and optical components is an essential requirement for the realization of optical detection in lab-on-a-chip (LOC). In this work, a novel hybrid integration of silica-on-silicon (SOS) waveguide and polydymethylsiloxane (PDMS) microfluidics for realizing optical detection based biochip is demonstrated. SOS is a commonly used platform for integrated photonic circuits due to its lower absorption coefficient of silica and the availability of advanced microfabrication technologies for fabricating complicated optical components. However, the fabrication of complex microfluidics circuits on SOS is an expensive process. On the other hand, any complex 3D and high-aspect-ratio microstructures for the microfluidic applications can be easily patterned on PDMS using soft lithography. By exploring the advantages of these two materials, the proposed hybrid integration method greatly simplifies the fabrication of optical LOC. Two simple technologies--namely, diamond machining and soft lithography--were employed for the integration of an optical microfluidic system. Use of PDMS for the fabrication of any complex 3D microfluidics structures, together with the integration of low loss silica-on-silicon photonic waveguides with a straight microfluidic channel, opens up new possibilities to produce low-cost biochips. The performance of SOS-PDMS-integrated hybrid biochip is demonstrated with the detection of laser induced fluorescence of quantum dots. As quantum dots have immense application potential for biodetection, they are used for the demonstration of biodetection.

  13. CdTe quantum dots conjugated to concanavalin A as potential fluorescent molecular probes for saccharides detection in Candida albicans.

    PubMed

    Tenório, Denise P L A; Andrade, Camila G; Cabral Filho, Paulo E; Sabino, Caetano P; Kato, Ilka T; Carvalho, Luiz B; Alves, Severino; Ribeiro, Martha S; Fontes, Adriana; Santos, Beate S

    2015-01-01

    Semiconductor colloidal quantum dots (QDs) have been applied in biological analysis due to their unique optical properties and their versatility to be conjugated to biomolecules, such as lectins and antibodies, acquiring specificity to label a variety of targets. Concanavalin A (Con A) lectin binds specifically to α-d-mannose and α-d-glucose regions of saccharides that are usually expressed on membranes of mammalian cells and on cell walls of microbials. Candida albicans is the most common fungal opportunistic pathogen present in humans. Therefore, in this work, this fungus was chosen as a model for understanding cells and biofilm-forming organisms. Here, we report an efficient bioconjugation process to bind CdTe (Cadmium Telluride) QDs to Con A, and applied the bioconjugates to label saccharide structures on the cellular surface of C. albicans suspensions and biofilms. By accomplishing hemagglutination experiments and circular dichroism, we observed that the Con A structure and biochemical properties were preserved after the bioconjugation. Fluorescence microscopy images of yeasts and hyphae cells, as well as biofilms, incubated with QDs-(Con A) showed a bright orange fluorescence profile, indicating that the cell walls were specifically labeled. Furthermore, flow cytometry measurements confirmed that over 93% of the yeast cells were successfully labeled by QD-(Con A) complex. In contrast, non-conjugated QDs or QDs-(inhibited Con A) do not label any kind of biological system tested, indicating that the bioconjugation was specific and efficient. The staining pattern of the cells and biofilms demonstrate that QDs were effectively bioconjugated to Con A with specific labeling of saccharide-rich structures on C. albicans. Consequently, this work opens new possibilities to monitor glucose and mannose molecules through fluorescence techniques, which can help to optimize phototherapy protocols for this kind of fungus.

  14. Ionic liquid-capped graphene quantum dots as label-free fluorescent probe for direct detection of ferricyanide.

    PubMed

    Sun, Xue; Qian, Yuting; Jiao, Yajie; Liu, Jiyang; Xi, Fengna; Dong, Xiaoping

    2017-04-01

    Despite complex molecular and atomic doping, efficient post-functionalization strategies for graphene quantum dots (GQDs) are of key importance to control the physicochemical properties and broaden the practical applications. With ionic liquid as specific modification agents, herein, the preparation of ionic liquid-capped GQDs (IL-GQDs) and its application as label-free fluorescent probe for direct detection of anion were reported. Hydroxyl-functionalized GQDs that could be easily gram-scale synthesized and possessed single-crystalline were chosen as the model GQDs. Also, the most commonly used ionic liquids, water-soluble 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIMBF4) was chosen as the model IL. Under the ultrasonic treatment, BMIMBF4 easily composited with GQDs to form IL-GQDs. The synthesized IL-GQDs were characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and fluorescence (FL) spectrum. After successful combination with IL, the excitation-independent photoluminescence behavior of GQDs presented almost no change, whereas, the anion responsiveness of IL-GQDs drastically improved, which afforded the IL-GQDs a sensitive response to Fe(CN)6(3-). Based on the strong fluorescence quench, a facile and sensitive detection of Fe(CN)6(3-) was achieved. A wide linear range of 1.0×10(-7) to 2.5×10(-3)moll(-1) with a low detection limit of 40 nmol l(-1) was obtained. As the composition and properties of IL and GQDs could be easily tuned by varying the structure, ionic liquids-capped GQDs might present promising potential for their applications in sensing and catalysis.

  15. Quantum dot-based multiphoton fluorescent pipettes for targeted neuronal electrophysiology

    PubMed Central

    Huber, Daniel; Barbic, Mladen; Macklin, John J.; Susumu, Kimihiro; Delehanty, James B.; Huston, Alan L.; Makara, Judit K.; Medintz, Igor L.

    2014-01-01

    Targeting visually-identified neurons for electrophysiological recording is a fundamental neuroscience technique; however, its potential is hampered by poor visualization of pipette tips in deep brain tissue. We describe a technique whereby quantum dots coat glass pipettes providing strong two-photon contrast at deeper penetration depths than current methods. We demonstrate utility in targeted patch-clamp recording experiments and single cell electroporation from identified rat and mouse neurons in vitro and in vivo. PMID:25326662

  16. In cellulo evaluation of phototransformation quantum yields in fluorescent proteins used as markers for single-molecule localization microscopy.

    PubMed

    Avilov, Sergiy; Berardozzi, Romain; Gunewardene, Mudalige S; Adam, Virgile; Hess, Samuel T; Bourgeois, Dominique

    2014-01-01

    Single-molecule localization microscopy of biological samples requires a precise knowledge of the employed fluorescent labels. Photoactivation, photoblinking and photobleaching of phototransformable fluorescent proteins influence the data acquisition and data processing strategies to be used in (Fluorescence) Photoactivation Localization Microscopy ((F)-PALM), notably for reliable molecular counting. As these parameters might depend on the local environment, they should be measured in cellulo in biologically relevant experimental conditions. Here, we measured phototransformation quantum yields for Dendra2 fused to actin in fixed mammalian cells in typical (F)-PALM experiments. To this aim, we developed a data processing strategy based on the clustering optimization procedure proposed by Lee et al (PNAS 109, 17436-17441, 2012). Using simulations, we estimated the range of experimental parameters (molecular density, molecular orientation, background level, laser power, frametime) adequate for an accurate determination of the phototransformation yields. Under illumination at 561 nm in PBS buffer at pH 7.4, the photobleaching yield of Dendra2 fused to actin was measured to be (2.5 ± 0.4) × 10(-5), whereas the blinking-off yield and thermally-activated blinking-on rate were measured to be (2.3 ± 0.2) × 10(-5) and 11.7 ± 0.5 s-1, respectively. These phototransformation yields differed from those measured in poly-vinyl alcohol (PVA) and were strongly affected by addition of the antifading agent 1,4-diazabicyclo[2.2.2]octane (DABCO). In the presence of DABCO, the photobleaching yield was reduced 2-fold, the blinking-off yield was decreased more than 3-fold, and the blinking-on rate was increased 2-fold. Therefore, DABCO largely improved Dendra2 photostability in fixed mammalian cells. These findings are consistent with redox-based bleaching and blinking mechanisms under (F)-PALM experimental conditions. Finally, the green-to-red photoconversion quantum yield of Dendra

  17. In cellulo Evaluation of Phototransformation Quantum Yields in Fluorescent Proteins Used As Markers for Single-Molecule Localization Microscopy

    PubMed Central

    Avilov, Sergiy; Berardozzi, Romain; Gunewardene, Mudalige S.; Adam, Virgile; Hess, Samuel T.; Bourgeois, Dominique

    2014-01-01

    Single-molecule localization microscopy of biological samples requires a precise knowledge of the employed fluorescent labels. Photoactivation, photoblinking and photobleaching of phototransformable fluorescent proteins influence the data acquisition and data processing strategies to be used in (Fluorescence) Photoactivation Localization Microscopy ((F)-PALM), notably for reliable molecular counting. As these parameters might depend on the local environment, they should be measured in cellulo in biologically relevant experimental conditions. Here, we measured phototransformation quantum yields for Dendra2 fused to actin in fixed mammalian cells in typical (F)-PALM experiments. To this aim, we developed a data processing strategy based on the clustering optimization procedure proposed by Lee et al (PNAS 109, 17436–17441, 2012). Using simulations, we estimated the range of experimental parameters (molecular density, molecular orientation, background level, laser power, frametime) adequate for an accurate determination of the phototransformation yields. Under illumination at 561 nm in PBS buffer at pH 7.4, the photobleaching yield of Dendra2 fused to actin was measured to be (2.5±0.4)×10−5, whereas the blinking-off yield and thermally-activated blinking-on rate were measured to be (2.3±0.2)×10−5 and 11.7±0.5 s−1, respectively. These phototransformation yields differed from those measured in poly-vinyl alcohol (PVA) and were strongly affected by addition of the antifading agent 1,4-diazabicyclo[2.2.2]octane (DABCO). In the presence of DABCO, the photobleaching yield was reduced 2-fold, the blinking-off yield was decreased more than 3-fold, and the blinking-on rate was increased 2-fold. Therefore, DABCO largely improved Dendra2 photostability in fixed mammalian cells. These findings are consistent with redox-based bleaching and blinking mechanisms under (F)-PALM experimental conditions. Finally, the green-to-red photoconversion quantum yield of Dendra2 was

  18. Using quantum mechanics to investigate the photophysical properties of the DNA and RNA bases and their fluorescent analogs

    NASA Astrophysics Data System (ADS)

    Kistler, Kurt A.

    The ability of the nucleic acids to absorb ultraviolet light and remain relatively photostable is a property upon which life depends. The nucleobases, which are the primary chromophores, when irradiated display rapid radiationless decay back to the ground state, in general faster than is needed for photoreaction. Fluorescent analogs of these bases have structures similar to the nucleic acid bases, but display much longer excited state lifetimes. Theoretical investigations using quantum mechanical methods can provide insight into the precise mechanisms of these decay processes, and to the molecular specifics that contribute to them. The results of multi-reference configuration interaction (MRCI) ab initio investigations into these mechanisms are presented, with emphasis on cytosine and its fluorescent analog 5-methyl-2-pyrimidinone (5M2P). A comprehensive picture of the potential energy surfaces of these two bases is given, including stationary points and conical intersections, where radiationless transisitons are promoted, between up to three state surfaces, as well as pathways connecting these points for each base. Cytosine is shown to have two different energetically accessible radiationless decay channels. The fluorescence of 5M2P is also demonstrated theoretically, with mechanism proposed. The potential energy surfaces of the two bases have many close similarities, with the different photophysical properties being attributed to subtle energetic differences between the two bases. Nonadiabatic coupling and the geometric phase effect are analyzed in detail near conical intersections in cytosine, including in a region close to a three-state conical intersection. A substituent effect study on the 2-pyrimidinone ring system shows that the presence, position and orientation of the amino group in cytosine is central to its photophysical properties, particulary its high absorption energy, and can be explained with a simple Frontier Molecular Orbital model. The effects

  19. Fluorescence Quenching of CdSe/ZnS Quantum Dots by Using Black Hole Quencher Molecules Intermediated With Peptide for Biosensing Application.

    PubMed

    Pillai, Sreenadh Sasidharan; Yukawa, Hiroshi; Onoshima, Daisuke; Biju, Vasudevanpillai; Baba, Yoshinobu

    2015-12-17

    Quantum dots (QDs) have recently been investigated as fluorescent probes for detecting a very small number of biomolecules and live cells; however, the establishment of molecular imaging technology with on-off control of QD fluorescence remains to be established. Here we have achieved the fluorescence off state of QDs with the conjugation of black hole quencher (BHQ) molecules intermediated with peptide by using streptavidin-QDs585 and biotin-pep-BHQ-1. The fluorescence of streptavidin-QDs585 was decreased by the addition of biotin-pep-BHQ-1 in a dose-dependent manner. It has been suggested that the decrease in QDs585 fluorescence occurred through a Förster resonance energy transfer (FRET) mechanism from the analysis of fluorescence intensity and lifetime of streptavidin-QDs585 and QDs585-pep-BHQ-1. QDs585 fluorescence could be quenched by more than 60% efficiency in this system. The sequence of intermediate peptide (pep) was GPLGVRGK, which can be cleaved by matrix metalloproteinases (MMPs) produced by cancer cells. QDs585-pep-BHQ-1 is thus expected to detect the MMP production by the recovery of QDs585 fluorescence as a new bioanalytical agent for molecular imaging.

  20. Fluorescence Quenching of CdSe/ZnS Quantum Dots by Using Black Hole Quencher Molecules Intermediated With Peptide for Biosensing Application

    PubMed Central

    Pillai, Sreenadh Sasidharan; Yukawa, Hiroshi; Onoshima, Daisuke; Biju, Vasudevanpillai; Baba, Yoshinobu

    2015-01-01

    Quantum dots (QDs) have recently been investigated as fluorescent probes for detecting a very small number of biomolecules and live cells; however, the establishment of molecular imaging technology with on–off control of QD fluorescence remains to be established. Here we have achieved the fluorescence off state of QDs with the conjugation of black hole quencher (BHQ) molecules intermediated with peptide by using streptavidin-QDs585 and biotin-pep-BHQ-1. The fluorescence of streptavidin-QDs585 was decreased by the addition of biotin-pep-BHQ-1 in a dose-dependent manner. It has been suggested that the decrease in QDs585 fluorescence occurred through a Förster resonance energy transfer (FRET) mechanism from the analysis of fluorescence intensity and lifetime of streptavidin-QDs585 and QDs585-pep-BHQ-1. QDs585 fluorescence could be quenched by more than 60% efficiency in this system. The sequence of intermediate peptide (pep) was GPLGVRGK, which can be cleaved by matrix metalloproteinases (MMPs) produced by cancer cells. QDs585-pep-BHQ-1 is thus expected to detect the MMP production by the recovery of QDs585 fluorescence as a new bioanalytical agent for molecular imaging. PMID:26858909

  1. Reaction analysis on Yb(3+) and DNA based on quantum dots: The design of a fluorescent reversible off-on mode.

    PubMed

    Wang, Linlin; Song, Jing; Liu, Shaopu; Hao, Chenxia; Kuang, Nianxi; He, Youqiu

    2015-11-01

    Even though various strategies have reported for DNA detection, development of a simple, time-saving and specific fluorescent sensing platform still remains a desired goal. In this work, a quantum dots (QDs) based fluorescent reversible "off-on" mode was developed for sensitively recognition of herring sperm DNA (hsDNA). Firstly, in the "turn off" stage, the fluorescence of glutathione (GSH) capped CdTe QDs could be effectively quenched by ytterbium ion (Yb(3+)) was due to the occurrence of the electron transfer between Yb(3+) and the photoexcited QDs. And then, in the following "turn on" stage, with the effective binding reaction of Yb(3+) to hsDNA, the fluorescence intensity of GSH-capped CdTe QDs enhanced. Under the optimal conditions, the linear range of fluorescence versus the concentration of hsDNA was 0.010-12 μg/mL, and the detection limit was 3.033 ng/mL. In addition, the reaction mechanism among GSH-capped CdTe QDs, Yb(3+) and hsDNA were investigated by fluorescence spectroscopy, UV-vis spectrophotometry, fluorescence lifetime measurement and viscosity measurements. This analytical fluorescent reversible "off-on" pattern offered a way with good sensitivity and selectivity for the detection of hsDNA.

  2. Near-Infrared Emitting PbS Quantum Dots for in Vivo Fluorescence Imaging of the Thrombotic State in Septic Mouse Brain.

    PubMed

    Imamura, Yukio; Yamada, Sayumi; Tsuboi, Setsuko; Nakane, Yuko; Tsukasaki, Yoshikazu; Komatsuzaki, Akihito; Jin, Takashi

    2016-08-18

    Near-infrared (NIR) fluorescent imaging is a powerful tool for the non-invasive visualization of the inner structure of living organisms. Recently, NIR fluorescence imaging at 1000-1400 nm (second optical window) has been shown to offer better spatial resolution compared with conventional NIR fluorescence imaging at 700-900 nm (first optical window). Here we report lead sulfide (PbS) quantum dots (QDs) and their use for in vivo NIR fluorescence imaging of cerebral venous thrombosis in septic mice. Highly fluorescent PbS QDs with a 1100 nm emission peak (QD1100) were prepared from lead acetate and hexamethyldisilathiane, and the surface of QD1100 was coated with mercaptoundecanoic acid so as to be soluble in water. NIR fluorescence imaging of the cerebral vessels of living mice was performed after intravascular injection (200-300 μL) of QD1100 (3 μM) from a caudal vein. By detecting the NIR fluorescence of QD1100, we achieved non-invasive NIR fluorescence imaging of cerebral blood vessels through the scalp and skull. We also achieved NIR fluorescence imaging of cerebral venous thrombosis in septic mice induced by the administration of lipopolysaccharide (LPS). From the NIR fluorescence imaging, we found that the number of thrombi in septic mice was significantly increased by the administration of LPS. The formation of thrombi in cerebral blood vessels in septic mice was confirmed by enzyme-linked immunosorbent assay (ELISA). We also found that the number of thrombi significantly decreased after the administration of heparin, an inhibitor of blood coagulation. These results show that NIR fluorescence imaging with QD1100 is useful for the evaluation of the pathological state of cerebral blood vessels in septic mice.

  3. Highly Enhanced Fluorescence of CdSeTe Quantum Dots Coated with Polyanilines via In-Situ Polymerization and Cell Imaging Application.

    PubMed

    Xue, Jingjing; Chen, Xinyi; Liu, Shanglin; Zheng, Fenfen; He, Li; Li, Lingling; Zhu, Jun-Jie

    2015-09-02

    The polyaniline (PAN)-coated CdSeTe quantum dots (QDs) were prepared by in situ polymerization of aniline on the surface of CdSeTe QDs. The PAN-coated CdSeTe QDs has a tremendously enhanced fluorescence (∼40 times) and improved biocompatibility compared to the uncoated CdSeTe QDs. The fluorescence intensity of the PAN-coated CdSeTe QDs can be adjusted by controlling the construction parameters of the PAN shell. The kinetics of the in situ controllable polymerization process was studied by varying the temperature, and the apparent activation energy of polymerization was estimated. With the same method, a series of the PAN derivatives were also tested to coat the CdSeTe QDs in this study. All the QDs showed a significant enhancement of the fluorescence intensity and better biocompatibility. The significantly enhanced fluorescence can provide highly amplified signal for luminescence-based cell imaging.

  4. Enhanced fluorescence properties of type-I and type-II CdTe/CdS quantum dots using porous silver membrane

    NASA Astrophysics Data System (ADS)

    Thuy, Ung Thi Dieu; Chae, Weon-Sik; Yang, Won-Geun; Liem, Nguyen Quang

    2017-04-01

    This paper reports the metal-induced fluorescence property on the CdTe/CdS core/shell quantum dots (QDs), which exhibit the systematic band-gap transition from type-I to type-II with increasing shell thickness, near porous silver membrane by using time-resolved fluorescence lifetime imaging microscopy (FLIM). The results revealed that notable fluorescence enhancement came from the closed location to the cavity of the porous silver metal due to an increase in the local electromagnetic fields at the cavity. In the cases of the type-II CdTe/CdS QDs, interestingly, multiple exciton generation can be an additional factor for the lifetime reduction and fluorescence amplification compared to the type-I QDs. Without CdS shell, the strong interaction between the bare core CdTe QDs and silver caused emission quenching.

  5. Effect of Controlled Deposition of ZnS Shell on the Photostability of CdTe Quantum Dots as Studied by Conventional Fluorescence and FCS Techniques.

    PubMed

    Patra, Satyajit; Seth, Sudipta; Samanta, Anunay

    2015-12-21

    The effect of one and two monolayers of ZnS shells on the photostability of CdTe quantum dots (QDs) in aqueous and nonaqueous media has been studied by monitoring the fluorescence behavior of the QDs under ensemble and single-molecule conditions. ZnS capping of the CdTe QDs leads to significant enhancement of the fluorescence brightness of these QDs. Considerable enhancement of the photostability of the shell-protected QDs, including the suppression of photoactivation, is also observed. Fluorescence correlation spectroscopy measurements reveal an increase in the number of particles undergoing reversible fluorescent on-off transitions in the volume under observation with increasing excitation power; this effect is found to be more pronounced in the case of core-only QDs than for core-shell QDs.

  6. CsPbBr3 Perovskite Quantum Dots-Based Monolithic Electrospun Fiber Membrane as an Ultrastable and Ultrasensitive Fluorescent Sensor in Aqueous Medium.

    PubMed

    Wang, Yuanwei; Zhu, Yihua; Huang, Jianfei; Cai, Jin; Zhu, Jingrun; Yang, Xiaoling; Shen, Jianhua; Jiang, Hao; Li, Chunzhong

    2016-11-03

    Perovskite quantum dots with excellent optical properties and robust durability stand as an appealing and desirable candidate for fluorescence resonance energy transfer (FRET) based fluorescence detection, a powerful technique featuring excellent accuracy and convenience. In this work, a monolithic superhydrophobic polystyrene fiber membrane with CsPbBr3 perovskite quantum dots encapsulated within (CPBQDs/PS FM) was prepared via one-step electrospinning. Coupling CPBQDs with PS matrix, this CPBQDs/PS FM composite exhibits high quantum yields (∼91%), narrow half-peak width (∼16 nm), nearly 100% fluorescence retention after being exposed to water for 10 days and 79.80% fluorescence retention after 365 nm UV-light (1 mW/cm(2)) illumination for 60 h. Thanks to the outstanding optical property of CPBQDs, an ultralow detection limit of 0.01 ppm was obtained for Rhodamine 6G (R6G) detection, with the FRET efficiency calculated to be 18.80% in 1 ppm R6G aqueous solution. Electrospun as well-designed fiber membranes, CPBQDs/PS FM composite also possesses good tailorability and recyclability, showing exciting potential for future implementation into practical applications.

  7. Rapid and Sensitive Detection of Protein Biomarker Using a Portable Fluorescence Biosensor based on Quantum Dots and a Lateral Flow Test Strip

    SciTech Connect

    Li, Zhaohui; Wang, Ying; Wang, Jun; Tang, Zhiwen; Pounds, Joel G.; Lin, Yuehe

    2010-08-15

    A portable fluorescence biosensor with rapid and ultrasensitive response for trace protein has been built up with quantum dots and lateral flow test strip. The superior signal brightness and high photostability of quantum dots are combined with the promising advantages of lateral flow test strip and resulted in high sensitivity, selectivity and speedy for protein detection. Nitrated ceruloplasmin, a significant biomarker for cardiovascular disease, lung cancer and stress response to smoking, was used as model protein to demonstrate the good performances of this proposed Qdot-based lateral flow test strip. Quantitative detection of nitrated ceruloplasmin was realized by recording the fluorescence intensity of quantum dots captured on the test line. Under optimal conditions, this portable fluorescence biosensor displays rapid responses for nitrated ceruloplasmin in wide dynamic range with a detection limit of 0.1ng/mL (S/N=3). Furthermore, the biosensor was successfully utilized for spiked human plasma sample detection with the concentration as low as 1ng/mL. The results demonstrate that the quantum dot-based lateral flow test strip is capable for rapid, sensitive, and quantitative detection of nitrated ceruloplasmin and hold a great promise for point-of-care and in field analysis of other protein biomarkers.

  8. Quantitative photoabsorption and fluorescence spectroscopy of benzene, naphthalene, and some derivatives at 106-295 nm

    NASA Technical Reports Server (NTRS)

    Suto, Masako; Wang, Xiuyan; Shan, Jun; Lee, L. C.

    1992-01-01

    Photoabsorption and fluorescence cross sections of benzene, (o-, m-, p-) xylenes, naphthalene, 1-methylnaphthalene, and 2-ethylnaphthalene in the gas phase are measured at 106-295 nm using synchrotron radiation as a light source. Fluorescences are observed from the photoexcitation of benzene and xylenes at 230-280 nm and from naphthalene and its derivatives at 190-295 nm. The absolute fluorescence cross section is determined by calibration with respect to the emission intensity of the NO(A-X) system, for which the fluorescence quantum yield is equal to 1. To cross-check the current calibration method, the quantum yield of the SO2(C-X) system at 220-230 nm was measured since it is about equal to 1. The current quantum-yield data are compared with previously published values measured by different methods.

  9. Tuning the Aggregation/Disaggregation Behavior of Graphene Quantum Dots by Structure-Switching Aptamer for High-Sensitivity Fluorescent Ochratoxin A Sensor.

    PubMed

    Wang, Song; Zhang, Yajun; Pang, Guangsheng; Zhang, Yingwei; Guo, Shaojun

    2017-02-07

    The design of graphene quantum dots (GQDs)-aptamer bioconjugates as the new sensing platform is very important for developing high-sensitivity fluorescent biosensors; however, achieving new bioconjugates is still a great challenge. Herein, we report the development of a new high-sensitivity fluorescent aptasensor for the detection of ochratoxin A (OTA) based on tuning aggregation/disaggregation behavior of GQDs by structure-switching aptamers. The fluorescence sensing process for OTA detection involved two key steps: (1) cDNA-aptamer (cDNA, complementary to part of the OTA aptamer) hybridization induced the aggregation of GQD (fluorescence quenching) after cDNA was added into the GQDs-aptamer bioconjugate solution, and (2) the target of OTA triggered disaggregation of GQD aggregates (fluorescence recovery). Such new fluorescent sensing platform can be used to monitor OTA with a linear range of 0 to 1 ng/mL and very low detection limit of 13 pg/mL, which is among the best in all the developed fluorescent nanoparticles-based sensors. Such sensing strategy is also successful in analyzing OTA in practical red wine sample with 94.4-102.7% of recoveries and relative standard deviation in the range of 2.9-5.8%. The present works open a new way for signaling the target-aptamer binding event by tuning aggregation/disaggregation behavior of GQDs-bioconjugates.

  10. Fluorescence quenching of CdS quantum dots by 4-azetidinyl-7-nitrobenz-2-oxa-1,3-diazole: a mechanistic study.

    PubMed

    Santhosh, Kotni; Patra, Satyajit; Soumya, S; Khara, Dinesh Chandra; Samanta, Anunay

    2011-10-24

    Fluorescence quenching of CdS quantum dots (QDs) by 4-azetidinyl-7-nitrobenz-2-oxa-1,3-diazole (NBD), where the two quenching partners satisfy the spectral overlap criterion necessary for Förster resonance energy transfer (FRET), is studied by steady-state and time-resolved fluorescence techniques. The fluorescence quenching of the QDs is accompanied by an enhancement of the acceptor fluorescence and a reduction of the average fluorescence lifetime of the donor. Even though these observations are suggestive of a dynamic energy transfer process, it is shown that the quenching actually proceeds through a static interaction between the quenching partners and is probably mediated by charge-transfer interactions. The bimolecular quenching rate constant estimated from the Stern-Volmer plot of the fluorescence intensities, is found to be exceptionally high and unrealistic for the dynamic quenching process. Hence, a kinetic model is employed for the estimation of actual quencher/QD ratio dependent exciton quenching rate constants of the fluorescence quenching of CdS by NBD. The present results point to the need for a deeper analysis of the experimental quenching data to avoid erroneous conclusions.

  11. "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.

  12. Synthesis and formation mechanistic investigation of nitrogen-doped carbon dots with high quantum yields and yellowish-green fluorescence

    NASA Astrophysics Data System (ADS)

    Hou, Juan; Wang, Wei; Zhou, Tianyu; Wang, Bo; Li, Huiyu; Ding, Lan

    2016-05-01

    Heteroatom doped carbon dots (CDs) have received increasing attention due to their unique properties and related applications. However, previously reported CDs generally show strong emission only in the blue-light region, thus restricting their further applications. And the fundamental investigation on the preparation process is always neglected. Herein, we have developed a simple and solvent-free synthetic strategy to fabricate nitrogen-doped CDs (N-CDs) from citric acid and dicyandiamide. The as-prepared N-CDs exhibited a uniform size distribution, strong yellowish-green fluorescence emission and a high quantum yield of 73.2%. The products obtained at different formation stages were detailedly characterized by transmission electron microscopy, X-ray diffraction spectrometer, X-ray photoelectron spectroscopy and UV absorbance spectroscopy. A possible formation mechanism has thus been proposed including dehydration, polymerization and carbonization. Furthermore, the N-CDs could serve as a facile and label-free probe for the detection of iron and fluorine ions with detection limits of 50 nmol L-1 and 75 nmol L-1, respectively.Heteroatom doped carbon dots (CDs) have received increasing attention due to their unique properties and related applications. However, previously reported CDs generally show strong emission only in the blue-light region, thus restricting their further applications. And the fundamental investigation on the preparation process is always neglected. Herein, we have developed a simple and solvent-free synthetic strategy to fabricate nitrogen-doped CDs (N-CDs) from citric acid and dicyandiamide. The as-prepared N-CDs exhibited a uniform size distribution, strong yellowish-green fluorescence emission and a high quantum yield of 73.2%. The products obtained at different formation stages were detailedly characterized by transmission electron microscopy, X-ray diffraction spectrometer, X-ray photoelectron spectroscopy and UV absorbance spectroscopy. A

  13. Interfacial transduction of nucleic acid hybridization using immobilized quantum dots as donors in fluorescence resonance energy transfer.

    PubMed

    Algar, W Russ; Krull, Ulrich J

    2009-01-06

    Fluorescence resonance energy transfer (FRET) using immobilized quantum dots (QDs) as energy donors was explored as a transduction method for the detection of nucleic acid hybridization at an interface. This research was motivated by the success of the QD-FRET-based transduction of nucleic acid hybridization in solution-phase assays. This new work represents a fundamental step toward the assembly of a biosensor, where immobilization of the selective chemistry on a surface is desired. After immobilizing QD-probe oligonucleotide conjugates on optical fibers, a demonstration of the retention of selectivity was achieved by the introduction of acceptor (Cy3)-labeled single-stranded target oligonucleotides. Hybridization generated the proximity required for FRET, and the resulting fluorescence spectra provided an analytical signal proportional to the amount of target. This research provides an important framework for the future development of nucleic acid biosensors based on QDs and FRET. The most important findings of this work are that (1) a QD-FRET solid-phase hybridization assay is viable and (2) a passivating layer of denatured bovine serum albumin alleviates nonspecific adsorption, ultimately resulting in (3) the potential for a reusable assay format and mismatch discrimination. In this, the first incarnation of a solid-phase QD-FRET hybridization assay, the limit of detection was found to be 5 nM, and the dynamic range was almost 2 orders of magnitude. Selective discrimination of the target was shown using a three-base-pairs mismatch from a fully complementary sequence. Despite a gradual loss of signal, reuse of the optical fibers over multiple cycles of hybridization and dehybridization was possible. Directions for further improvement of the analytical performance by optimizing the design of the QD-probe oligonucleotide interface are identified.

  14. Interference-free determination of ischemia-modified albumin using quantum dot coupled X-ray fluorescence spectroscopy.

    PubMed

    Luo, Yang; Wang, Chaoming; Jiang, Tianlun; Zhang, Bo; Huang, Junfu; Liao, Pu; Fu, Weiling

    2014-01-15

    Ischemia-modified protein (IMA) is the most sensitive diagnostic biomarker of ischemic heart disease, but differentiation of IMA from human serum albumin (HSA), a ubiquitous serum protein, is still challenging owing to the shared antigenicity. In this investigation, we developed a rapid and interference-free approach for IMA determination using quantum dots-coupled X-ray Fluorescence Spectroscopy (Q-XRF). In a typical Q-XRF assay, serum total HSA is quantified using quantum dot-coupled sandwich immunoassay, and intact HSA (iHSA) is determined using a XRF spectroscopy, by measuring XRF intensity of Co (II) bonded to iHSA. IMA concentration is automatically determined within 30 min by calculating the difference between total HSA and iHSA. This strategy can effectively eliminate the interference from native HSA level. Results show that no significant influences have been observed from hemolysis or high levels of cholesterol (7 mg/L), triglyceride (5.2 mg/L), IgG (10 g/L), and fibrinogen (4 g/L). A linearity of 1-100mg/mL is obtained in iHSA determination using XRF (r(2)=0.979). The proposed Q-XRF assay demonstrates a lowest detection limit of 0.05 U/mL. Receiver-operating characteristic (ROC) curves reveal that Q-XRF assay provide an improved sensitivity than ACB assay (95.9% vs. 82.9%) in differentiating ischemic patients from health individuals, at an optimal cutoff point of 79.2U/mL. The proposed approach provides a new strategy for interference-free, simple and rapid evaluation of IMA concentration by combining sandwich immunoassay and XRF spectroscopy.

  15. Absolute determination of charge-coupled device quantum detection efficiency using Si K-edge x-ray absorption fine structure

    SciTech Connect

    Dunn, J; Steel, A B

    2012-05-06

    We report a method to determine the quantum detection efficiency and the absorbing layers on a front-illuminated charge-coupled device (CCD). The CCD under study, as part of a crystal spectrometer, measures intense continuum x-ray emission from a picosecond laser-produced plasma and spectrally resolves the Si K-edge x-ray absorption fine structure features due to the electrode gate structure of the device. The CCD response across the Si K-edge shows a large discontinuity as well as a number of oscillations that are identified individually and uniquely from Si, SiO{sub 2}, and Si{sub 3}N{sub 4} layers. From the spectral analysis of the structure and K-edge discontinuity, the active layer thickness and the different absorbing layers thickness can be determined precisely. A precise CCD detection model from 0.2-10 keV can be deduced from this highly sensitive technique.

  16. CdSe/ZnS Quantum Dots-Labeled Mesenchymal Stem Cells for Targeted Fluorescence Imaging of Pancreas Tissues and Therapy of Type 1 Diabetic Rats.

    PubMed

    Liu, Haoqi; Tang, Wei; Li, Chao; Lv, Pinlei; Wang, Zheng; Liu, Yanlei; Zhang, Cunlei; Bao, Yi; Chen, Haiyan; Meng, Xiangying; Song, Yan; Xia, Xiaoling; Pan, Fei; Cui, Daxiang; Shi, Yongquan

    2015-12-01

    Mesenchymal stem cells (MSCs) have been used for therapy of type 1 diabetes mellitus. However, the in vivo distribution and therapeutic effects of transplanted MSCs are not clarified well. Herein, we reported that CdSe/ZnS quantum dots-labeled MSCs were prepared for targeted fluorescence imaging and therapy of pancreas tissues in rat models with type 1 diabetes. CdSe/ZnS quantum dots were synthesized, their biocompatibility was evaluated, and then, the appropriate concentration of quantum dots was selected to label MSCs. CdSe/ZnS quantum dots-labeled MSCs were injected into mouse models with type 1 diabetes via tail vessel and then were observed by using the Bruker In-Vivo F PRO system, and the blood glucose levels were monitored for 8 weeks. Results showed that prepared CdSe/ZnS quantum dots owned good biocompatibility. Significant differences existed in distribution of quantum dots-labeled MSCs between normal control rats and diabetic rats (p < 0.05). The ratios of the fluorescence intensity (RFI) analysis showed an accumulation rate of MSCs in the pancreas of rats in the diabetes group which was about 32 %, while that in the normal control group rats was about 18 %. The blood glucose levels were also monitored for 8 weeks after quantum dots-labeled MSC injection. Statistical differences existed between the blood glucose levels of the diabetic rat control group and MSC-injected diabetic rat group (p < 0.01), and the MSC-injected diabetic rat group displayed lower blood glucose levels. In conclusion, CdSe/ZnS-labeled MSCs can target in vivo pancreas tissues in diabetic rats, and significantly reduce the blood glucose levels in diabetic rats, and own potential application in therapy of diabetic patients in the near future.

  17. CdSe/ZnS Quantum Dots-Labeled Mesenchymal Stem Cells for Targeted Fluorescence Imaging of Pancreas Tissues and Therapy of Type 1 Diabetic Rats

    NASA Astrophysics Data System (ADS)

    Liu, Haoqi; Tang, Wei; Li, Chao; Lv, Pinlei; Wang, Zheng; Liu, Yanlei; Zhang, Cunlei; Bao, Yi; Chen, Haiyan; Meng, Xiangying; Song, Yan; Xia, Xiaoling; Pan, Fei; Cui, Daxiang; Shi, Yongquan

    2015-06-01

    Mesenchymal stem cells (MSCs) have been used for therapy of type 1 diabetes mellitus. However, the in vivo distribution and therapeutic effects of transplanted MSCs are not clarified well. Herein, we reported that CdSe/ZnS quantum dots-labeled MSCs were prepared for targeted fluorescence imaging and therapy of pancreas tissues in rat models with type 1 diabetes. CdSe/ZnS quantum dots were synthesized, their biocompatibility was evaluated, and then, the appropriate concentration of quantum dots was selected to label MSCs. CdSe/ZnS quantum dots-labeled MSCs were injected into mouse models with type 1 diabetes via tail vessel and then were observed by using the Bruker In-Vivo F PRO system, and the blood glucose levels were monitored for 8 weeks. Results showed that prepared CdSe/ZnS quantum dots owned good biocompatibility. Significant differences existed in distribution of quantum dots-labeled MSCs between normal control rats and diabetic rats ( p < 0.05). The ratios of the fluorescence intensity (RFI) analysis showed an accumulation rate of MSCs in the pancreas of rats in the diabetes group, and was about 32 %, while that in the normal control group rats was about 18 %. The blood glucose levels were also monitored for 8 weeks after quantum dots-labeled MSC injection. Statistical differences existed between the blood glucose levels of the diabetic rat control group and MSC-injected diabetic rat group ( p < 0.01), and the MSC-injected diabetic rat group displayed lower blood glucose levels. In conclusion, CdSe/ZnS-labeled MSCs can target in vivo pancreas tissues in diabetic rats, and significantly reduce the blood glucose levels in diabetic rats, and own potential application in therapy of diabetic patients in the near future.

  18. Fluorescent refrigeration

    DOEpatents

    Epstein, Richard I.; Edwards, Bradley C.; Buchwald, Melvin I.; Gosnell, Timothy R.

    1995-01-01

    Fluorescent refrigeration is based on selective radiative pumping, using substantially monochromatic radiation, of quantum excitations which are then endothermically redistributed to higher energies. Ultimately, the populated energy levels radiatively deexcite emitting, on the average, more radiant energy than was initially absorbed. The material utilized to accomplish the cooling must have dimensions such that the exciting radiation is strongly absorbed, but the fluorescence may exit the material through a significantly smaller optical pathlength. Optical fibers and mirrored glasses and crystals provide this requirement.

  19. Absolute nuclear material assay

    DOEpatents

    Prasad, Manoj K [Pleasanton, CA; Snyderman, Neal J [Berkeley, CA; Rowland, Mark S [Alamo, CA

    2012-05-15

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  20. Absolute nuclear material assay

    DOEpatents

    Prasad, Manoj K.; Snyderman, Neal J.; Rowland, Mark S.

    2010-07-13

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  1. Evaluation of quantum dot-based concentric FRET configurations with a fluorescent dye and dark quencher for multiplexed bioanalyses

    NASA Astrophysics Data System (ADS)

    Conroy, Erin M.; Algar, W. Russ

    2014-03-01

    Semiconductor quantum dots (QDs) continue to emerge as a highly advantageous platform for bioanalysis. Their unique physical and optical properties are especially well suited for Förster resonance energy transfer (FRET)-based bioprobes. Concentric FRET configurations are a recent development in this area of research and are best described as QD bioconjugates where multiple energy transfer pathways have been assembled around the central QD. Concentric FRET configurations permit multiplexed bioanalysis using one type of QD vector, but require more sophisticated analyses than conventional FRET pairs. In this paper, we describe the design and characterization of a new concentric FRET configuration that assembles both a fluorescent dye, Alexa Fluor 555 or Alexa Fluor 647, and a dark quencher, QSY9, at different ratios around a central CdSeS/ZnS QD. It was found that the magnitudes of the total photoluminescence (PL) intensity and either the A555/QD or A647/QD PL ratio can be related to the number of QSY9 and A555 or A647 per QD. The trends in these parameters with changes in the number of each dye molecule per QD have both similarities and differences between configurations with A555 and A647. In each case, a system of equations can be defined to permit calculation of the number of each dye molecule per QD from PL measurements. Both of these dark quencher-based concentric FRET configurations are therefore good candidates for quantitative, multiplexed bioanalysis.

  2. Enhancement of the Upconversion Emission by Visible-to-Near-Infrared Fluorescent Graphene Quantum Dots for miRNA Detection

    PubMed Central

    2016-01-01

    We developed a sensor for the detection of specific microRNA (miRNA) sequences that was based on graphene quantum dots (GQDs) and ssDNA-UCNP@SiO2. The proposed sensor exploits the interaction between the sp2 carbon atoms of the GQD, mainly π–π stacking, and the DNA nucleobases anchored on the upconversion nanoparticles (UCNPs). This interaction brings the GQD to the surface of the ssDNA-UCNP@SiO2 system, enhancing the upconversion emission. On the other hand, hybridization of the single-stranded DNA (ssDNA) chains anchored on the nanoparticles with their complementary miRNA sequences blocks the capacity of the UCNPs to interact with the GQD through π–π stacking. That gives as result a reduction of the fluorescent enhancement, which is dependent on the concentration of miRNA sequences. This effect was used to create a sensor for miRNA sequences with a detection limit of 10 fM. PMID:27153453

  3. Nucleic acid sandwich hybridization assay with quantum dot-induced fluorescence resonance energy transfer for pathogen detection.

    PubMed

    Chou, Cheng-Chung; Huang, Yi-Han

    2012-12-04

    This paper reports a nucleic acid sandwich hybridization assay with a quantum dot (QD)-induced fluorescence resonance energy transfer (FRET) reporter system. Two label-free hemagglutinin H5 sequences (60-mer DNA and 630-nt cDNA fragment) of avian influenza viruses were used as the targets in this work. Two oligonucleotides (16 mers and 18 mers) that specifically recognize two separate but neighboring regions of the H5 sequences were served as the capturing and reporter probes, respectively. The capturing probe was conjugated to QD655 (donor) in a molar ratio of 10:1 (probe-to-QD), and the reporter probe was labeled with Alexa Fluor 660 dye (acceptor) during synthesis. The sandwich hybridization assay was done in a 20 μL transparent, adhesive frame-confined microchamber on a disposable, temperature-adjustable indium tin oxide (ITO) glass slide. The FRET signal in response to the sandwich hybridization was monitored by a homemade optical sensor comprising a single 400 nm UV light-emitting diode (LED), optical fibers, and a miniature 16-bit spectrophotometer. The target with a concentration ranging from 0.5 nM to 1 μM was successfully correlated with both QD emission decrease at 653 nm and dye emission increase at 690 nm. To sum up, this work is beneficial for developing a portable QD-based nucleic acid sensor for on-site pathogen detection.

  4. Blue organic light-emitting diodes realizing external quantum efficiency over 25% using thermally activated delayed fluorescence emitters.

    PubMed

    Miwa, Takuya; Kubo, Shosei; Shizu, Katsuyuki; Komino, Takeshi; Adachi, Chihaya; Kaji, Hironori

    2017-03-21

    Improving the performance of blue organic light-emitting diodes (OLEDs) is needed for full-colour flat-panel displays and solid-state lighting sources. The use of thermally activated delayed fluorescence (TADF) is a promising approach to efficient blue electroluminescence. However, the difficulty of developing efficient blue TADF emitters lies in finding a molecular structure that simultaneously incorporates (i) a small energy difference between the lowest excited singlet state (S1) and the lowest triplet state (T1), ΔE ST, (ii) a large oscillator strength, f, between S1 and the ground state (S0), and (iii) S1 energy sufficiently high for blue emission. In this study, we develop TADF emitters named CCX-I and CCX-II satisfying the above requirements. They show blue photoluminescence and high triplet-to-singlet up-conversion yield. In addition, their transition dipole moments are horizontally oriented, resulting in further increase of their electroluminescence efficiency. Using CCX-II as an emitting dopant, we achieve a blue OLED showing a high external quantum efficiency of 25.9%, which is one of the highest EQEs in blue OLEDs reported previously.

  5. Ultrasensitive quantum dot fluorescence quenching assay for selective detection of mercury ions in drinking water.

    PubMed

    Ke, Jun; Li, Xinyong; Zhao, Qidong; Hou, Yang; Chen, Junhong

    2014-07-09

    Mercury is one of the most acutely toxic substances at trace level to human health and living thing. Developing a rapid, cheap and water soluble metal sensor for detecting mercury ions at ppb level remains a challenge. Herein, a metal sensor consisting of MPA coated Mn doped ZnSe/ZnS colloidal nanoparticles was utilized to ultrasensitively and selectively detect Hg(2+) ions with a low detection limit (0.1 nM) over a dynamic range from 0 to 20 nM. According to strong interaction between thiol(s) and mercury ions, mercaptopropionic acid (MPA) was used as a highly unique acceptor for mercury ions in the as-obtained ultrasensitive sensor. In the presence of mercury ions, colloidal nanoparticles rapidly agglomerated due to changes of surface chemical properties, which results in severe quenching of fluorescent intensity. Meanwhile, we find that the original ligands are separated from the surface of colloidal nanoparticles involving strongly chelation between mercury ion and thiol(s) proved by controlled IR analysis. The result shows that the QD-based metal ions sensor possesses satisfactory precision, high sensitivity and selectivity, and could be applied for the quantification analysis of real samples.

  6. Ultrasensitive Quantum Dot Fluorescence quenching Assay for Selective Detection of Mercury Ions in Drinking Water

    PubMed Central

    Ke, Jun; Li, Xinyong; Zhao, Qidong; Hou, Yang; Chen, Junhong

    2014-01-01

    Mercury is one of the most acutely toxic substances at trace level to human health and living thing. Developing a rapid, cheap and water soluble metal sensor for detecting mercury ions at ppb level remains a challenge. Herein, a metal sensor consisting of MPA coated Mn doped ZnSe/ZnS colloidal nanoparticles was utilized to ultrasensitively and selectively detect Hg2+ ions with a low detection limit (0.1 nM) over a dynamic range from 0 to 20 nM. According to strong interaction between thiol(s) and mercury ions, mercaptopropionic acid (MPA) was used as a highly unique acceptor for mercury ions in the as-obtained ultrasensitive sensor. In the presence of mercury ions, colloidal nanoparticles rapidly agglomerated due to changes of surface chemical properties, which results in severe quenching of fluorescent intensity. Meanwhile, we find that the original ligands are separated from the surface of colloidal nanoparticles involving strongly chelation between mercury ion and thiol(s) proved by controlled IR analysis. The result shows that the QD-based metal ions sensor possesses satisfactory precision, high sensitivity and selectivity, and could be applied for the quantification analysis of real samples. PMID:25005836

  7. Ultrasensitive Quantum Dot Fluorescence quenching Assay for Selective Detection of Mercury Ions in Drinking Water

    NASA Astrophysics Data System (ADS)

    Ke, Jun; Li, Xinyong; Zhao, Qidong; Hou, Yang; Chen, Junhong

    2014-07-01

    Mercury is one of the most acutely toxic substances at trace level to human health and living thing. Developing a rapid, cheap and water soluble metal sensor for detecting mercury ions at ppb level remains a challenge. Herein, a metal sensor consisting of MPA coated Mn doped ZnSe/ZnS colloidal nanoparticles was utilized to ultrasensitively and selectively detect Hg2+ ions with a low detection limit (0.1 nM) over a dynamic range from 0 to 20 nM. According to strong interaction between thiol(s) and mercury ions, mercaptopropionic acid (MPA) was used as a highly unique acceptor for mercury ions in the as-obtained ultrasensitive sensor. In the presence of mercury ions, colloidal nanoparticles rapidly agglomerated due to changes of surface chemical properties, which results in severe quenching of fluorescent intensity. Meanwhile, we find that the original ligands are separated from the surface of colloidal nanoparticles involving strongly chelation between mercury ion and thiol(s) proved by controlled IR analysis. The result shows that the QD-based metal ions sensor possesses satisfactory precision, high sensitivity and selectivity, and could be applied for the quantification analysis of real samples.

  8. Modulation of quantum dot photoemission based on fluorescence resonance energy transfer to a photochromic dye acceptor

    NASA Astrophysics Data System (ADS)

    Medintz, Igor L.; Clapp, Aaron R.; Trammel, Scott A.; Mattoussi, Hedi M.

    2004-12-01

    We demonstrate the use of a photochromic dye to achieve fluorescence resonance energy transfer (FRET) modulation between a QD donor and the dye acceptor brought in close proximity in a selfassembled QD-protein-dye conjugate. The E. coli maltose binding protein (MBP) appended on its C-terminal with an oligohistidine attachment domain, immobilized onto CdSe-ZnS core-shell QDs was labeled with a sulfo-N-hydroxysuccinimide activated photochromic BIPS molecule (1',3-dihydro-1'-(2-carboxyethyl)-3,3-dimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indoline]). Two different dye-to-MBP-protein ratios of 1:1 and 5:1 were used. The ability of MBP-BIPS to modulate QD photoluminescence was tested by switching BIPS from the colorless spiropyran (SP) to the colored merocyanine (MC) using irradiation with white light (>500 nm) or with UV light (~365 nm), respectively. QDs surrounded by ~20 MBP-BIPS with a dye to protein ratio of 1 showed ~25% loss in their photoemission with consecutive repeated switches, while QDs surrounded by ~20 MBP-BIPS with BIPS to MBP ratio of 5 produced a substantially more pronounced rate of FRET where the QD emission was quenched by ~60%. This result suggests the possibility of using QD-protein conjugates to assemble reversible FRET nanoassemblies where the QD emission can be controlled by changing the properties of the acceptors dyes bound to the protein.

  9. Investigation of multivalent interactions between conjugate of quantum dots with c-Myc peptide tag and the anti-c-Myc antibody by capillary electrophoresis with fluorescence detection.

    PubMed

    Wang, Jianhao; Yang, Li; Liu, Li; Wu, Hao; Wang, Jianpeng; Jiang, Pengju; Jiang, Xiyuan; Qiu, Lin

    2016-12-01

    Herein, we report an assay for detecting the binding of a multivalent peptide and antibody within a capillary with the use of fluorescence coupled capillary electrophoresis. Quantum dots and a c-Myc tag containing peptide EQKLISEEDLG4 H6 were injected sequentially and formed a multivalent quantum dot-EQKLISEEDLG4 H6 assembly within the capillary. The efficiency of the quantum dot-peptide self-assembly was affected by the peptide/quantum dot molar ratio, sampling time, and interval time. Finally, the binding of the monoclonal anti-c-Myc antibody and the multivalent quantum dot-EQKLISEEDLG4 H6 ligand was studied using an in-capillary assay. The microscopic dissociation constant for the self-assembly of monoclonal anti-c-Myc antibody and quantum dot-EQKLISEEDLG4 H6 was determined to be 14.1 μM with a stoichiometry of the peptide-antibody complex of 1.7 determined after fitting this to the Hill equation. This method can be further extended to detect a wide range of biomolecule-biomolecule binding interactions.

  10. PEG-phospholipid-encapsulated bismuth sulfide and CdSe/ZnS quantum dot core-shell nanoparticle and its computed tomography/fluorescence performance

    NASA Astrophysics Data System (ADS)

    Chen, Jun; Yang, Xiao-Quan; Qin, Meng-Yao; Zhang, Xiao-Shuai; Xuan, Yang; Zhao, Yuan-Di

    2015-11-01

    In this paper, polyethylene glycol-phospholipid structure is used to synthesize hybrid cluster of 40-50 nm diameter that contains hydrophobic bismuth sulfide nanoparticles and CdSe/ZnS quantum dots. The composite probe's toxicity, CT imaging, and fluorescence imaging performance are also studied. Experimental results show that the nanocomposite hybrid cluster has obvious CT contrast enhancement and fluorescence imaging capability in vitro even after cellular uptake. It gives a CT number of 700 (Hounsfield units) at 15 mg/mL, higher than that of the current iobitridol CT contrast agent. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide experiment reveals that it has low cytotoxicity at concentration up to of 3.14 mg/mL of Bi, indicating the composite probe has potential ability for CT and fluorescence bimodal imaging.

  11. A fluorescent probe based on nitrogen doped graphene quantum dots for turn off sensing of explosive and detrimental water pollutant, TNP in aqueous medium.

    PubMed

    Kaur, Manjot; Mehta, Surinder K; Kansal, Sushil Kumar

    2017-06-05

    This paper reports the carbonization assisted green approach for the fabrication of nitrogen doped graphene quantum dots (N-GQDs). The obtained N-GQDs displayed good water dispersibility and stability in the wide pH range. The as synthesized N-GQDs were used as a fluorescent probe for the sensing of explosive 2,4,6-trinitrophenol (TNP) in aqueous medium based on fluorescence resonance energy transfer (FRET), molecular interactions and charge transfer mechanism. The quenching efficiency was found to be linear in proportion to the TNP concentration within the range of 0-16μM with detection limit (LOD) of 0.92μM. The presented method was successfully applied to the sensing of TNP in tap and lake water samples with satisfactory results. Thus, N-GQDs were used as a selective, sensitive and turn off fluorescent sensor for the detection of perilous water contaminant i.e. TNP.

  12. A novel method for fabricating hybrid biobased nanocomposites film with stable fluorescence containing CdTe quantum dots and montmorillonite-chitosan nanosheets.

    PubMed

    Guo, Yawen; Ge, Xuesong; Guan, Jing; Wu, Lin; Zhao, Fuhua; Li, Hui; Mu, Xindong; Jiang, Yijun; Chen, Aibing

    2016-07-10

    A method was presented for fabricating the fluorescent nanocomposites containing CdTe quantum dots (QDs) and montmorillonite (MMT)-chitosan (CS). MMT-CS/CdTe QDs nanocomposites were prepared via a simple, versatile and robust approach combination of covalent and electrostatic assembly methods (Scheme 1). The negatively charged MMT was initially modified with positively charged CS through electrostatic assembly, followed by incorporation of CdTe-QDs into the MMT-CS nanosheets by covalent connections between the amino groups of CS and the carboxylic acid groups of thioglycollic acid (TGA). The X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and the FTIR were used to prove the QDs have intercalated into the MMT-CS matrix. The fluorescence emission spectra showed that the MMT-CS/CdTe QDs nanocomposites had the best fluorescence intensity compared with the bare CdTe QDs and CS-QDs.

  13. Study on the Ultrahigh Quantum Yield of Fluorescent P,O-g-C3 N4 Nanodots and its Application in Cell Imaging.

    PubMed

    Rong, Mingcong; Cai, Zhixiong; Xie, Lei; Lin, Chunshui; Song, Xinhong; Luo, Feng; Wang, Yiru; Chen, Xi

    2016-06-27

    Graphitic carbon nitride nanodots (g-C3 N4 nanodots), as a new kind of heavy-metal-free quantum dots, have attracted considerable attention because of their unique physical and chemical properties. Although various methods to obtain g-C3 N4 nanodots have been reported, it is still a challenge to synthesize g-C3 N4 nanodots with ultrahigh fluorescence quantum yield (QY). In this study, highly fluorescent phosphorus/oxygen-doped graphitic carbon nitride (P,O-g-C3 N4 ) nanodots were prepared by chemical oxidation and hydrothermal etching of bulk P-g-C3 N4 derived from the pyrolysis of phytic acid and melamine. The as-prepared P,O-g-C3 N4 nanodots showed strong blue fluorescence and a relatively high QY of up to 90.2 %, which can be ascribed to intrinsic phosphorus/oxygen-containing groups, and surface-oxidation-related fluorescence enhancement. In addition, the P,O-g-C3 N4 nanodots were explored for cell imaging with excellent stability and biocompatibility, which suggest that they have great potential in biological applications.

  14. Microwave assisted one-pot synthesis of graphene quantum dots as highly sensitive fluorescent probes for detection of iron ions and pH value.

    PubMed

    Zhang, Chunfang; Cui, Yanyan; Song, Li; Liu, Xiangfeng; Hu, Zhongbo

    2016-04-01

    Recently, carbon nanomaterials have received considerable attention as fluorescent probes owing to their low toxicity, water solubility and stable photochemical properties. However, the development of graphene quantum dots (GQDs) is still on its early stage. In this work, GQDs were successfully synthesized by one-step microwave assisted pyrolysis of aspartic acid (Asp) and NH4HCO3 mixture. The as-prepared GQDs exhibited strongly blue fluorescence with high quantum yield up to 14%. Strong fluorescence quenching effect of Fe(3+) on GQDs can be used for its high selectivity detection among of general metal ions. The probe exhibited a wide linear response concentration range (0-50 μM) to Fe(3+) and the limit of detection (LOD) was calculated to be 0.26 μM. In addition, GQDs are also sensitive to the pH value in the range from 2 to 12 indicating a great potential as optical pH sensors. More importantly, the GQDs possess lower cellular toxicity and high photostability and can be directly used as fluorescent probes for cell imaging.

  15. Visual and fluorescent assays for selective detection of beta-amyloid oligomers based on the inner filter effect of gold nanoparticles on the fluorescence of CdTe quantum dots.

    PubMed

    Xia, Ning; Zhou, Binbin; Huang, Nanbing; Jiang, Mengsha; Zhang, Jiebing; Liu, Lin

    2016-11-15

    Beta-amyloid (Aβ) peptides are the major constituents of senile plaques in the brains of Alzheimer's disease (AD) patients. Aβ monomers (AβMs) can coalesce to form small, soluble oligomers (AβOs), followed by reorganization and assembly into long, thread-like fibrils (AβFs). Recently, soluble AβOs have been regarded as reliable molecular biomarkers for the diagnosis of AD because of their high toxicity for neuronal synapse and high concentration levels in the brains of AD patients. In this work, we reported a label-free, sensitive and selective method for visual and fluorescent detection of AβOs based on the inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (QDs). Specifically, the fluorescence of CdTe QDs was quenched significantly by AuNPs through the IFE. PrP(95-110), an AβOs-specific binding peptide from cellular prion protein, triggered the aggregation and color change of AuNPs suspension; thus, the IFE of AuNPs on the fluorescence of CdTe QDs was weakened and the fluorescence intensity was recovered. However, in the presence of AβOs, the specific interaction of AβOs and PrP(95-110) prevented the absorption of PrP(95-110) onto the surface of AuNPs. As a result, the aggregation of AuNPs was inhibited and the fluorescence intensity of CdTe QDs was quenched again. This label-free method is specific for detection of AβOs but not for AβMs and AβFs. The detection limits were found to be 0.5nM for the visual assay and 0.2nM for the fluorescent detection. We believe that this work would be valuable for many investigations related to AD diagnosis and drug discovery.

  16. Synthesis and Characterization of Anti-HER2 Antibody Conjugated CdSe/CdZnS Quantum Dots for Fluorescence Imaging of Breast Cancer Cells.

    PubMed

    Tiwari, Dhermendra K; Tanaka, Shin-Ichi; Inouye, Yasushi; Yoshizawa, Keiko; Watanabe, Tomonobu M; Jin, Takashi

    2009-01-01

    The early detection of HER2 (human epidermal growth factor receptor 2) status in breast cancer patients is very important for the effective implementation of anti-HER2 antibody therapy. Recently, HER2 detections using antibody conjugated quantum dots (QDs) have attracted much attention. QDs are a new class of fluorescent materials that have superior properties such as high brightness, high resistance to photo-bleaching, and multi-colored emission by a single-light source excitation. In this study, we synthesized three types of anti-HER2 antibody conjugated QDs (HER2Ab-QDs) using different coupling agents (EDC/sulfo-NHS, iminothiolane/sulfo-SMCC, and sulfo-SMCC). As water-soluble QDs for the conjugation of antibody, we used glutathione coated CdSe/CdZnS QDs (GSH-QDs) with fluorescence quantum yields of 0.23∼0.39 in aqueous solution. Dispersibility, hydrodynamic size, and apparent molecular weights of the GSH-QDs and HER2Ab-QDs were characterized by using dynamic light scattering, fluorescence correlation spectroscopy, atomic force microscope, and size-exclusion HPLC. Fluorescence imaging of HER2 overexpressing cells (KPL-4 human breast cancer cell line) was performed by using HER2Ab-QDs as fluorescent probes. We found that the HER2Ab-QD prepared by using SMCC coupling with partially reduced antibody is a most effective probe for the detection of HER2 expression in KPL-4 cells. We have also studied the size dependency of HER2Ab-QDs (with green, orange, and red emission) on the fluorescence image of KPL-4 cells.

  17. Synthesis and Characterization of Anti-HER2 Antibody Conjugated CdSe/CdZnS Quantum Dots for Fluorescence Imaging of Breast Cancer Cells

    PubMed Central

    Tiwari, Dhermendra K.; Tanaka, Shin-Ichi; Inouye, Yasushi; Yoshizawa, Keiko; Watanabe, Tomonobu M.; Jin, Takashi

    2009-01-01

    The early detection of HER2 (human epidermal growth factor receptor 2) status in breast cancer patients is very important for the effective implementation of anti-HER2 antibody therapy. Recently, HER2 detections using antibody conjugated quantum dots (QDs) have attracted much attention. QDs are a new class of fluorescent materials that have superior properties such as high brightness, high resistance to photo-bleaching, and multi-colored emission by a single-light source excitation. In this study, we synthesized three types of anti-HER2 antibody conjugated QDs (HER2Ab-QDs) using different coupling agents (EDC/sulfo-NHS, iminothiolane/sulfo-SMCC, and sulfo-SMCC). As water-soluble QDs for the conjugation of antibody, we used glutathione coated CdSe/CdZnS QDs (GSH-QDs) with fluorescence quantum yields of 0.23∼0.39 in aqueous solution. Dispersibility, hydrodynamic size, and apparent molecular weights of the GSH-QDs and HER2Ab-QDs were characterized by using dynamic light scattering, fluorescence correlation spectroscopy, atomic force microscope, and size-exclusion HPLC. Fluorescence imaging of HER2 overexpressing cells (KPL-4 human breast cancer cell line) was performed by using HER2Ab-QDs as fluorescent probes. We found that the HER2Ab-QD prepared by using SMCC coupling with partially reduced antibody is a most effective probe for the detection of HER2 expression in KPL-4 cells. We have also studied the size dependency of HER2Ab-QDs (with green, orange, and red emission) on the fluorescence image of KPL-4 cells. PMID:22291567

  18. Evaluation of the absolute photoluminescence quantum yields of molecularly doped organic composite films and the electroluminescence efficiencies of molecular light-emitting devices containing oligoheterocycles as efficient emission centers

    NASA Astrophysics Data System (ADS)

    Kushto, Gary P.; Hill, Ian G.; Mitschke, Ullrich; Baeuerle, Peter; Kafafi, Zakya H.

    2001-02-01

    The absolute photoluminescence quantum yields ((Phi) PL) of three end-capped oligothiophene derivatives dispersed in N,N'-((alpha) -naphthyl)-N,N'-diphenyl-1,1'-biphenyl ((alpha) -NPD) have been evaluated and the most efficient of the emitters was used as a dopant in molecular organic LEDs. Composite films of 2,5-bis [5-(4,5,6,7- tetrahydrobenzo[b]thien-2-yl) thien-2-yl]-furan (EC5FUR); 2,5-bis [5-(4,5,6,7- tetrahydrobenzo[b]thien-2-yl) thien-2-yl]-oxazole (EC5OXZ) and 2,5-bis [5-(4,5,6,7- tetrahydrobenzo[b]thien-2-yl)thien-2-yl]-1,3,4- oxadiazole (EC5OXD) doped into (alpha) -NPD were found to have (Phi) PL values of 78, 62 and 28%, respectively. MOLED devices were fabricated using an EC5FUR/(alpha) -NPD composite as the emitting layer and the external quantum efficiencies ((eta) EL) of these devices were evaluated. The results of the device characterization show that the inclusion of EC5FUR in the NPD hole transport layer increases the device (eta) EL to 1.45% at a current density of 10 mA/cm2. In addition, the concentration dependence of the (eta) EL on the EC5FUR dopant in certain device structures when considered in conjunction with the current results of ultraviolet photoemission spectroscopic experiments suggests that this dopant species may be acting as both a hole and electron trap in the (alpha) -NPD host.

  19. Synthesis, solubilization, and surface functionalization of highly fluorescent quantum dots for cellular targeting through a small molecule

    NASA Astrophysics Data System (ADS)

    Galloway, Justin F.

    To achieve long-term fluorescence imaging with quantum dots (QDs), a CdSe core/shell must first be synthesized. The synthesis of bright CdSe QDs is not trivial and as a consequence, the role of surfactant in nucleation and growth was investigated. It was found that the type of surfactant used, either phosphonic or fatty acid, played a pivotal role in the size of the CdSe core. The study of surfactant on CdSe synthesis, ultimately led to an electrical passivation method that utilized a short-chained phosphonic acid and highly reactive organometallic precursors to achieve high quantum yield (QY) as has been previously described. The synthesis of QDs using organometallic precursors and a phosphonic acid for passivation resulted in 4 out of 9 batches of QDs achieving QYs greater than 50% and 8 out of 9 batches with QYs greater than 35%. The synthesis of CdSe QDs was done in organic solutions rendering the surface of the particle hydrophobic. To perform cell-targeting experiments, QDs must be transferred to water. The transfer of QDs to water was successfully accomplished by using single acyl chain lipids. A systematic study of different lipid combinations and coatings demonstrated that 20-40 mol% single acyl chained lipids were able to transfer QDs to water resulting in monodispersed, stable QDs without adversely affecting the QY. The advantage to water solubilization using single acyl chain lipids is that the QD have a hydrodynamic radius less than 15 nm, QYs that can exceed 50% and additional surface functionalization can be down using the reactive sites incorporated into the lipid bilayer. QDs that are bright and stable in water were studied for the purpose of targeting G protein-coupled Receptors (GPCR). GPCRs are transmembrane receptors that internalize extracellular cues, and thus mediate signal transduction. The cyclic Adenosine Monophosphate Receptor 1 of the model organism Dictyostelium disodium was the receptor of interest. The Halo protein, a genetically

  20. Fluorescence properties of SrAl12O19 : Pr3+ quantum cutting phosphor

    NASA Astrophysics Data System (ADS)

    Ikeda, Y.; Masada, K.; Kurokawa, H.; Motomura, H.; Jinno, M.; Tachibana, K.

    2013-02-01

    A phosphor, SrAl12O19 doped with Pr (SA : Pr), is investigated in this research in order to improve the luminous efficacy of a mercury-free Xe discharge fluorescent lamp (FL). The obtained sample works as a quantum cutting phosphor which converts an absorbed photon of Xe emission at 172 nm into two visible photons, one at 401.8 nm and the other at 486.3, 526.3, 623.7 or 644.6 nm. The concentration of Pr is optimized and the visible emission of the phosphor becomes maximum at 5 mol%. The photoluminescence measurements show that the relative quantum efficiency of SA : Pr (Pr: 5 mol%) is 38.4% of BaMgAl10O17 : Eu2+ (BAM : Eu). The luminance of a Xe dielectric-barrier-discharge (DBD) FL coated with SA : Pr (Pr: 5 mol%) achieves 28.8% of the same lamp with BAM : Eu. The CIE colour coordinate of the SA : Pr (Pr: 5 mol%) excited by the Xe-DBD lamp is x = 0.307 and y = 0.292. The SA : Pr phosphor has an excitation band peaking at 468 nm corresponding to the 1I6 state and a low intensity excitation band lying from 250 to 420 nm. The latter is attributed to the self-trapped exciton (STE) band. This STE band causes an energy path due to non-radiative transition from 1S0 to 3P0 in the excitation at 172 nm. The former excitation band around 468 nm coincides with an ordinary blue LED's emission. When the phosphor is excited at this wavelength, the emission spectra are observed at 486.3, 526.3, 623.7 and 644.6 nm. Therefore, the SA : Pr may alternatively be useful for white LEDs excited by blue light.

  1. Integrated miniature fluorescent probe to leverage the sensing potential of ZnO quantum dots for the detection of copper (II) ions.

    PubMed

    Ng, Sing Muk; Wong, Derrick Sing Nguong; Phung, Jane Hui Chiun; Chin, Suk Fun; Chua, Hong Siang

    2013-11-15

    Quantum dots are fluorescent semiconductor nanoparticles that can be utilised for sensing applications. This paper evaluates the ability to leverage their analytical potential using an integrated fluorescent sensing probe that is portable, cost effective and simple to handle. ZnO quantum dots were prepared using the simple sol-gel hydrolysis method at ambient conditions and found to be significantly and specifically quenched by copper (II) ions. This ZnO quantum dots system has been incorporated into an in-house developed miniature fluorescent probe for the detection of copper (II) ions in aqueous medium. The probe was developed using a low power handheld black light as excitation source and three photo-detectors as sensor. The sensing chamber placed between the light source and detectors was made of 4-sided clear quartz windows. The chamber was housed within a dark compartment to avoid stray light interference. The probe was operated using a microcontroller (Arduino Uno Revision 3) that has been programmed with the analytical response and the working algorithm of the electronics. The probe was sourced with a 12 V rechargeable battery pack and the analytical readouts were given directly using a LCD display panel. Analytical optimisations of the ZnO quantum dots system and the probe have been performed and further described. The probe was found to have a linear response range up to 0.45 mM (R(2)=0.9930) towards copper (II) ion with a limit of detection of 7.68×10(-7) M. The probe has high repeatable and reliable performance.

  2. Development of Fluorescence Sensing Material Based on CdSe/ZnS Quantum Dots and Molecularly Imprinted Polymer for the Detection of Carbaryl in Rice and Chinese Cabbage.

    PubMed

    Zhang, Can; Cui, Hanyu; Cai, Jianrong; Duan, Yuqing; Liu, Yuan

    2015-05-27

    A fluorescence sensing material based on quantum dots with excellent optical properties and molecularly imprinted polymer (QDs@MIP) with specific recognition has been developed. First the surface of CdSe/ZnS QDs was modified with ionic liquids (ILs) by electrostatic interaction. The fluorescence sensing material was constructed from anchoring the MIP layer on IL modified CdSe/ZnS QDs by copolymerization, which had been developed for the detection of carbaryl in rice and Chinese cabbage. The MIP fluorescence was more strongly quenched by carbaryl than the non-imprinted polymer (NIP) fluorescence, which indicated that the QDs@MIP could selectively recognize the corresponding carbaryl. Furthermore, the developed QDs@MIP method was validated by HPLC and ELISA respectively, and the results of these methods were well correlated (R(2) = 0.98). The fluorescence sensing material had obvious advantages, such as being easily prepared and having specific recognition and photostability. The developed method was simple and effective for the detection of carbaryl. And, it could also provide the technical support for the rapid detection in food safety fields.

  3. Selective turn-on fluorescence sensor for Ag+ using cysteamine capped CdS quantum dots: determination of free Ag+ in silver nanoparticles solution.

    PubMed

    Khantaw, Thitima; Boonmee, Chanida; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2013-10-15

    Cadmium sulfide quantum dots capped with cysteamine (Cys-CdS QDs) were demonstrated as a selective fluorescence probe for sensing of free trace silver ions. The fluorescence intensity of the Cys-CdS QDs can be enhanced only in the presence of free Ag(+) and the fluorescence spectrum was slightly red shift from the original spectra. In addition, the fluorescence intensities were linearly increased upon increasing Ag(+) concentration. At the optimized condition for Ag(+) detection, when adding other metal ions to the Cys-CdS QDs solution, fluorescence spectra of Cys-CdS QDs did not change significantly revealing good selectivity of the sensors towards Ag(+). The working linear concentration range was found to be 0.1-1.5 µM with LOD of 68 nM. The proposed sensor was then applied to detect free Ag(+) in the silver nanoparticles solution. The results showed that the proposed sensor can be efficiently used with good accuracy and precision providing the simple method for detection of free Ag(+) in silver nanoparticles of quality control products.

  4. Fluorescence quenching studies on the interaction of catechin-quinone with CdTe quantum dots. Mechanism elucidation and feasibility studies.

    PubMed

    Dwiecki, Krzysztof; Neunert, Grażyna; Nogala-Kałucka, Małgorzata; Polewski, Krzysztof

    2015-01-01

    Changes of the photoluminescent properties of QD in the presence of oxidized catechin (CQ) were investigated by absorption, steady-state fluorescence, fluorescence lifetime and dynamic light scattering measurements. Photoluminescence intensity and fluorescence lifetime was decreasing with increasing CQ concentration. Dynamic light scattering technique found the hydrodynamic diameter of QD suspension in water is in range of 45 nm, whereas in presence of CQ increased to mean values of 67 nm. Calculated from absorption peak position of excition band indicated on average QD size of 3.2 nm. Emission spectroscopy and time-resolved emission studies confirmed preservation of electronic band structure in QD-CQ aggregates. On basis of the presented results, the elucidated mechanism of QD fluorescence quenching is a result of the interaction between QD and CQ due to electron transfer and electrostatic attraction. The results of fluorescence quenching of water-soluble CdTe quantum dot (QD) capped with thiocarboxylic acid were used to implement a simple and fast method to determine the presence of native antioxidant quinones in aqueous solutions. Feasibility studies on this method carried out with oxidized catechin showed a linear relation between the QD emission and quencher concentration, in range from 1 up to 200 μM. The wide linear range of concentration dependence makes it possible to apply this method for the fast and sensitive detection of quinones in solutions.

  5. Fluorescence enhancement of glutathione capped CdTe/ZnS quantum dots by embedding into cationic starch for sensitive detection of rifampicin

    NASA Astrophysics Data System (ADS)

    Hooshyar, Zari; Bardajee, Ghasem Rezanejade

    2017-02-01

    In this study, we describe the synthesis of a new quantum dots (QDs) by embedding glutathione capped CdTe/ZnS QDs into cationic starch biopolymer (CS-GSH-CdTe/ZnS QDs). The fluorescence intensity of prepared QDs was significantly enhanced. When QDs interacted with rifampicin, the fluorescence intensity of the CS-GSH-CdTe/ZnS QDs was highly quenched compared with GSH-CdTe/ZnS QDs. Based on the above, a new fluorescent nanosensor for simple, sensitive and selective detection of rifampicin was developed. The fluorescence quenching was well described by the typical Stern-Volmer equation. After optimization, the linear range of the as-prepared QDs fluorescence intensity versus the concentration of rifampicin was F0/F = 0.0422Q + 1.109 (R2 = 0.99). The detection limit was 0.06 × 10- 6 mol/L. The proposed method with satisfactory results was used to detect rifampicin in commercial capsules and tablets.

  6. Studies on multivalent interactions of quantum dots-protein self-assemble using fluorescence coupled capillary electrophoresis

    NASA Astrophysics Data System (ADS)

    Wang, Jianhao; Li, Jingyan; Teng, Yiwan; Hu, Wei; Chai, Hong; Li, Jinchen; Wang, Cheli; Qiu, Lin; Jiang, Pengju

    2014-07-01

    Nanoparticle-biomolecules self-assembly is the key to the understanding of biomolecular coating of nanoparticle. However, the self-assembly of biomolecules with nanoparticles is still under-exploited because of the lack of an efficient method to detect the subtle changes in the surface of nanoparticles. In this study, we utilized fluorescence coupled capillary electrophoresis (CE-FL) to probe the binding interaction between a multivalent ligand (dBSA, denatured bovine serum albumin which contains multiple thiol groups) and CdSe/ZnS quantum dots (QDs, 5 nm in diameter). The yield of QDs-dBSA complex increased with increasing molar ratio of dBSA to QDs, which plateaued at a ratio of 8:1. Besides, QDs-dBSA complex showed good stability due to the multivalent interaction, revealing that dBSA is a superior ligand for QDs. The self-assembly kinetics of QDs with dBSA manifested a bi-phasic kinetics with a linear initial stage followed by a saturating stage. This work revealed for the first time that there exist two types of binding sites on the surface of QDs for dBSA: one type termed "high priority" binding sites, which preferentially bind to the protein, whereas the "low priority" sites are occupied only after the first-type binding sites are fully bound. Our work thereby represents the first example of systematic investigation on the details of the metal-affinity driven self-assembly between QDs and dBSA utilizing the high-resolution CE-FL. It also expanded the application of CE-FL in the study of nanoparticle-biomolecule interaction and kinetics analysis.

  7. High resolution spectroscopy of silane with an external-cavity quantum cascade laser: Absolute line strengths of the ν3 fundamental band at 4.6 μm

    NASA Astrophysics Data System (ADS)

    van Helden, J. H.; Lopatik, D.; Nave, A.; Lang, N.; Davies, P. B.; Röpcke, J.

    2015-01-01

    The introduction of room temperature continuous wave external-cavity quantum cascade lasers (EC-QCLs) with narrow linewidths has greatly facilitated high resolution spectroscopy over wide spectral ranges in the mid-infrared (MIR) region. Using the wide tuning range of an EC-QCL we have measured the absolute line strengths of many P-branch transitions of the stretching dyad of the ν3 fundamental band of 28SiH4 between 2096 and 2178 cm-1. Furthermore, the high spectral resolution available has enabled us to resolve and measure representative examples of the tetrahedral splittings associated with each component of the P-branch. The positions of these components are in excellent agreement with spherical top data system (STDS) predictions and theoretical transitions from the TDS spectroscopic database for spherical top molecules. These are the first measurements of these line strengths of 28SiH4 and are an example of the applicability of high-powered, widely tunable EC-QCLs to high resolution spectroscopy.

  8. "Turn-off-on" fluorescent sensor for (N-methyl-4-pyridyl) porphyrin -DNA and G-quadruplex interactions based on ZnCdSe quantum dots.

    PubMed

    Zhao, Dan; Fan, Yao; Gao, Fang; Yang, Tian-ming

    2015-08-12

    As a new detection model, the reversible fluorescence "turn-off-on" sensor based on quantum dots (QDs) has already been successfully employed in the detections of many biochemical materials, especially in the researches on the interactions between anticancer drugs. The previous studies, however, mainly focused on simple-structured oligonucleotides and Calf thymus DNA. G-quadruplex, an important target for anti-cancer drug with special secondary structure, has been stimulating increasing research interests. In this paper, we report a new detection method based on the fluorescence "turn-off-on" model with water-soluble ZnCdSe QDs as the fluorescent probe, to analyze the interactions between anticancer drug (N-methyl-4-pyridyl) porphyrin (TMPyP) and nucleic acid, especially the G-quadruplex. The fluorescence of QDs can be quenched by TMPyP via photo-induced electron transfer and fluorescence resonance energy transfer, while on the other hand, the combination between TMPyP and G-quadruplex releases QDs from their quenchers and thus recovers the fluorescence. Most importantly, the fluorescence "turn-off-on" model has been employed, for the first time, to analyze the impacts of special factors on the interaction between TMPyP and G-quadruplex. The excellent selectivity of the system has been verified in the studies of the interactions between TMPyP and different DNAs (double-stranded DNA, single-stranded G-quadruplex, and different types of G-quadruplexes) in Na(+) or K(+)-containing buffer.

  9. An ultrasensitive quantum dots fluorescent polarization immunoassay based on the antibody modified Au nanoparticles amplifying for the detection of adenosine triphosphate.

    PubMed

    He, Yanlong; Tian, Jianniao; Hu, Kun; Zhang, Juanni; Chen, Sheng; Jiang, Yixuan; Zhao, Yanchun; Zhao, Shulin

    2013-11-13

    In this work, an ultrasensitive fluorescent polarization immunoassay (FPIA) method based on the quantum dot/aptamer/antibody/gold nanoparticles ensemble has been developed for the detection of adenosine triphosphate (ATP). DNA hybridization is formed when ATP is present in the PBS solution containing the DNA-conjugated quantum dots (QDs) and antibody-AuNPs. The substantial sensitivity improvement of the antibody-AuNPs-enhanced method is mainly attributed to the slower rotation of fluorescent unit when QDs-labeled oligonucleotides hybridize with antibody modified the gold nanoparticle. As a result, the fluorescent polarization (FP) values of the system increase significantly. Under the optimal conditions, a linear response with ATP concentration is ranged from 8×10(-12) M to 2.40×10(-4) M. The detection limit reached as low as 1.8 pM. The developed work provides a sensitive and selective immunoassay protocol for ATP detection, which could be applied in more bioanalytical systems.

  10. Adding Fluorescence Lifetime Spectroscopy to the Tool Kit used to Study the Formation and Degradation of Luminescent Quantum Dots in Solution.

    PubMed

    Lyons, Taeyjuana Y; Williams, Denise N; Rosenzweig, Zeev

    2017-02-28

    The increasing commercialization of consumer electronic products that make use of II-VI semiconductor quantum dots (QD) has raised significant concerns about their impact on natural systems and human health once released to the environment at the end of their product's lifetime. In this paper, we demonstrate the addition of fluorescence lifetime spectroscopy to the existing tool kit of spectroscopic techniques to quantitatively monitor changes in QD properties as they form and degrade in solution. Our study reveals that due to its rich information content, fluorescence lifetime spectroscopy has a limited utility as a stand-alone technique in studying QD formation and degradation. However, combining fluorescence lifetime spectroscopy with commonly used emission quantum yield, and peak width measurements along with other analytical methods - including UV-VIS, TEM, and ICP-MS measurements significantly enhances the existing analytical tool kit and provides the capability to monitor in real time, the formation and degradation of luminescent QD in organic and aqueous solutions under environmentally relevant conditions.

  11. CdTe/CdS-MPA quantum dots as fluorescent probes to label yeast cells: synthesis, characterization and conjugation with Concanavalin A

    NASA Astrophysics Data System (ADS)

    Kato, Ilka T.; Santos, Camila C.; Benetti, Endi; Tenório, Denise P. L. A.; Cabral Filho, Paulo E.; Sabino, Caetano P.; Fontes, Adriana; Santos, Beate S.; Prates, Renato A.; Ribeiro, Martha S.

    2012-03-01

    Candida albicans is the most frequent human opportunistic pathogenic fungus and one of the most important causes of nosocomial infections. In fact, diagnosis of invasive candidiasis presents unique problems. The aim of this work was to evaluate, by fluorescence image analysis, cellular labeling of C. albicans with CdTe/CdS quantum dots conjugated or not to concanavalin A (ConA). Yeast cells were incubated with CdTe/CdS quantum dots (QD) stabilized with mercaptopropionic acid (MPA) (emission peak at 530 nm) for 1 hour. In the overall study we observed no morphological alterations. The fluorescence microscopic analysis of the yeast cells showed that the non-functionalized QDs do not label C. albicans cells, while for the QD conjugated to ConA the cells showed a fluorescence profile indicating that the membrane was preferentially marked. This profile was expected since Concanavalin A is a protein that binds specifically to terminal carbohydrate residues at the membrane cell surface. The results suggest that the QD-labeled Candida cells represent a promising tool to open new possibilities for a precise evaluation of fungal infections in pathological conditions.

  12. Hybrid nanostructures of well-organized arrays of colloidal quantum dots and a self-assembled monolayer of gold nanoparticles for enhanced fluorescence

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoying; McBride, Sean P.; Jaeger, Heinrich M.; Nealey, Paul F.

    2016-07-01

    Hybrid nanomaterials comprised of well-organized arrays of colloidal semiconductor quantum dots (QDs) in close proximity to metal nanoparticles (NPs) represent an appealing system for high-performance, spectrum-tunable photon sources with controlled photoluminescence. Experimental realization of such materials requires well-defined QD arrays and precisely controlled QD-metal interspacing. This long-standing challenge is tackled through a strategy that synergistically combines lateral confinement and vertical stacking. Lithographically generated nanoscale patterns with tailored surface chemistry confine the QDs into well-organized arrays with high selectivity through chemical pattern directed assembly, while subsequent coating with a monolayer of close-packed Au NPs introduces the plasmonic component for fluorescence enhancement. The results show uniform fluorescence emission in large-area ordered arrays for the fabricated QD structures and demonstrate five-fold fluorescence amplification for red, yellow, and green QDs in the presence of the Au NP monolayer. Encapsulation of QDs with a silica shell is shown to extend the design space for reliable QD/metal coupling with stronger enhancement of 11 times through the tuning of QD-metal spatial separation. This approach provides new opportunities for designing hybrid nanomaterials with tailored array structures and multiple functionalities for applications such as multiplexed optical coding, color display, and quantum transduction.

  13. Cosmology with negative absolute temperatures

    NASA Astrophysics Data System (ADS)

    Vieira, J. P. P.; Byrnes, Christian T.; Lewis, Antony

    2016-08-01

    Negative absolute temperatures (NAT) are an exotic thermodynamical consequence of quantum physics which has been known since the 1950's (having been achieved in the lab on a number of occasions). Recently, the work of Braun et al. [1] has rekindled interest in negative temperatures and hinted at a possibility of using NAT systems in the lab as dark energy analogues. This paper goes one step further, looking into the cosmological consequences of the existence of a NAT component in the Universe. NAT-dominated expanding Universes experience a borderline phantom expansion (w < -1) with no Big Rip, and their contracting counterparts are forced to bounce after the energy density becomes sufficiently large. Both scenarios might be used to solve horizon and flatness problems analogously to standard inflation and bouncing cosmologies. We discuss the difficulties in obtaining and ending a NAT-dominated epoch, and possible ways of obtaining density perturbations with an acceptable spectrum.

  14. Design and study of activatable ("OFF/ON") quantum dots (Qdots): ligand selection for Qdot surface modification for controlling Qdot fluorescence quenching and restoration

    NASA Astrophysics Data System (ADS)

    Teblum, Andrew; Basumallick, Srijita; Shah, Rikhav; Mitra, Rajendra N.; Banerjee, Subhash; Santra, Swadeshmukul

    2012-03-01

    We report design and synthesis of a series of activatable "OFF/ON" CdS:Mn/ZnS quantum dot (Qdot) based sensing probes. The Qdot "OFF" state represent the "quenched state" where the Qdot fluorescence is quenched by ligands attached to Qdot surface. Fluorescence quenching is likely due to ligand assisted electron transfer process. Qdot fluorescence is restored when the electron transfer process is stopped. Using this activatable Qdots, we have successfully demonstrated usefulness of these Qdot probes for reliable detection of toxic cadmium ions in solution, selective detection of glutathione and sensitive detection of intracellular cancer drug release event. In this paper, we will discuss a simple but robust method of making water-soluble CdS:Mn/ZnS Qdots at the room-temperature. Two different water-soluble biomolecules, the N-acetyl cysteine (NAC) and the glutathione (GSH) were used as surface coating ligands. This is a singlestep, one-pot synthesis where the Qdot nanocrystals were grown in the presence of the biomolecules. These Qdots were characterized by fluorescence spectroscopy. Stability of the GSH coated Qdots and the NAC coated Qdots were studied by treating with ethylenediaminetetraacetic acid (EDTA, a strong chelating agent for Zn and Cd ions). Our results show that fluorescence properties of Qdots are affected by the type of surface coated ligands. In comparison to the GSH coated Qdots, the NAC coated Qdots show broad but strong emission towards near infra-red region. When treated with EDTA, fluorescence property of the GSH coated Qdot was affected less than the NAC coated Qdots. This preliminary study shows that NAC coated Qdots could potentially be used to develop activatable ("OFF/ON") probes for potential deep-tissue imaging applications. Similarly, the GSH coated Qdots could be applied for probing desired analytes or for bioimaging purposes in environmentally harsh conditions.

  15. Absolute nonlocality via distributed computing without communication

    NASA Astrophysics Data System (ADS)

    Czekaj, Ł.; Pawłowski, M.; Vértesi, T.; Grudka, A.; Horodecki, M.; Horodecki, R.

    2015-09-01

    Understanding the role that quantum entanglement plays as a resource in various information processing tasks is one of the crucial goals of quantum information theory. Here we propose an alternative perspective for studying quantum entanglement: distributed computation of functions without communication between nodes. To formalize this approach, we propose identity games. Surprisingly, despite no signaling, we obtain that nonlocal quantum strategies beat classical ones in terms of winning probability for identity games originating from certain bipartite and multipartite functions. Moreover we show that, for a majority of functions, access to general nonsignaling resources boosts success probability two times in comparison to classical ones for a number of large enough outputs. Because there are no constraints on the inputs and no processing of the outputs in the identity games, they detect very strong types of correlations: absolute nonlocality.

  16. Two-photon-excited fluorescence resonance energy transfer in an aqueous system of CdTe quantum dots and Rhodamine B

    SciTech Connect

    Li, Muye; Lu, Peixiang; Li, Fang He, Zhicong; Zhang, Junpei; Han, Junbo

    2014-12-21

    Two-photon excited fluorescence resonance energy transfer (FRET) between CdTe quantum dots with different emission peaks and Rhodamine B in aqueous solution are investigated both experimentally and theoretically. The photoluminescence and lifetime are measured using a time-resolved fluorescence test system. The two-photon excited FRET efficiency is found to increase as the degree of spectral overlap of the emission spectrum of CdTe and the absorption spectrum of Rhodamine B increases, which is due to the increase of Forster radius of the sample. Moreover, FRET efficiency increases when the ratio of acceptor/donor concentration increases. The two-photon excited FRET efficiency was found to reach 40%.

  17. Biodistribution of intact fluorescent CdSe/CdS/ZnS quantum dots coated by mercaptopropionic acid after intravenous injection into mice.

    PubMed

    Loginova, Yana F; Kazachkina, Natalia I; Zherdeva, Victoria V; Rusanov, Alexander L; Shirmanova, Marina V; Zagaynova, Elena V; Sergeeva, Ekaterina A; Dezhurov, Sergey V; Wakstein, Maxim S; Savitsky, Alexander P

    2012-11-01

    Semiconductor quantum dots (QD) have been widely used for fluorescent bioimaging. However their biosafety has attracted increasing attention, since the data about their in vivo behavior in biological systems are still limited. In this paper we have investigated the short- and long-term biodistribution of intact fluorescent CdSe/CdS/ZnS QD coated by 3-mercaptopropionic acid in mice. The results showed that intravenously injected QD accumulated mainly in the lungs, liver and spleen and were retained in these tissues for over 22 days. QD caused signs of acute toxicity in mice including death. The investigated QD possibly caused vascular thrombosis. The results of a toxicological assay indicated that some histopathological changes occurred in the lung tissue after the injection of QD. Our study highlights the need for careful evaluation of QD safety before their use in biological applications.

  18. Aqueous synthesis of type-II CdTe/CdSe core-shell quantum dots for fluorescent probe labeling tumor cells.

    PubMed

    Zeng, Ruosheng; Zhang, Tingting; Liu, Jincheng; Hu, Song; Wan, Qiang; Liu, Xuanming; Peng, Zhiwei; Zou, Bingsuo

    2009-03-04

    In this paper, we report a two-step aqueous synthesis of highly luminescent CdTe/CdSe core/shell quantum dots (QDs) via a simple method. The emission range of the CdTe/CdSe QDs can be tuned from 510 to 640 nm by controlling the thickness of the CdSe shell. Accordingly, the photoluminescence quantum yield (PL QY) of CdTe/CdSe QDs with an optimized thickness of the CdSe shell can reach up to 40%. The structures and compositions of the core/shell QDs were characterized by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy experiments, and their formation mechanism is discussed. Furthermore, folate conjugated CdTe/CdSe QDs in Hela cells were assessed with a fluorescence microscope. The results show that folate conjugated CdTe/CdSe QDs could enter tumor cells efficiently.

  19. Anorganic fluorescence reference materials for decay time of fluorescence emission

    NASA Astrophysics Data System (ADS)

    Engel, A.; Ottermann, C.; Klahn, J.; Korb, T.; Resch-Genger, U.; Hoffmann, K.; Kynast, U.; Rupertus, V.

    2008-02-01

    Fluorescence techniques are known for their high sensitivity and are widely used as analytical tools, detection methods and imaging applications for product and process control, material sciences, environmental and bio-technical analysis, molecular genetics, cell biology, medical diagnostics, and drug screening. According to DIN/ISO 17025 certified standards are used for steady state fluorescence diagnostics, a method having the drawback of giving relative values for fluorescence intensities only. Therefore reference materials for a quantitative characterization have to be related directly to the materials under investigation. In order to evaluate these figures it is necessary to calculate absolute numbers such as absorption/excitation cross sections and quantum yield. This has been done for different types of dopands in different materials such as glass, glass ceramics, crystals or nano crystalline material embedded in polymer matrices. Samples doped with several fluophores of different emission wavelengths and decay times are required for fluorescent multiplexing applications. Decay times shorter than 100 ns are of special interest. In addition, a proper knowledge is necessary of quantum efficiency in highly scattering media. Recently, quantum efficiency in YAG:Ce glass ceramics has been successfully investigated. Glass and glass ceramics doped with threefold charged rare earth elements are available. However, these samples have the disadvantage of emission decay times much longer than 1 microsecond, due to the excitation and emission of their optical forbidden electronic transitions. Therefore first attempts have been made to produce decay-time standards based on organic and inorganic fluophores. Stable LUMOGEN RED pigments and YAG:Ce phosphors are diluted simultaneously in silicone matrices using a wide range of concentrations between 0.0001 and 2 wt%. Organic LUMOGEN RED has decay times in the lower nanosecond range with a slight dependency on concentration

  20. Mercaptopropionic acid-capped CdTe quantum dots as fluorescence probe for the determination of salicylic acid in pharmaceutical products.

    PubMed

    Bunkoed, Opas; Kanatharana, Proespichaya

    2015-11-01

    Mercaptopropionic acid (MPA)-capped cadmium telluride (CdTe) quantum dot (QDs) fluorescent probes were synthesized in aqueous solution and used for the determination of salicylic acid. The interaction between the MPA-capped CdTe QDs and salicylic acid was studied using fluorescence spectroscopy and some parameters that could modify the fluorescence were investigated to optimize the measurements. Under optimum conditions, the quenched fluorescence intensity of MPA-capped CdTe QDs was linearly proportional to the concentration of salicylic acid in the range of 0.5-40 µg mL(-1) with a coefficient of determination of 0.998, and the limit of detection was 0.15 µg mL(-1). The method was successfully applied to the determination of salicylic acid in pharmaceutical products, and satisfactory results were obtained that were in agreement with both the high pressure liquid chromatography (HPLC) method and the claimed values. The recovery of the method was in the range 99 ± 3% to 105 ± 9%. The proposed method is simple, rapid, cost effective, highly sensitivity and eminently suitable for the quality control of pharmaceutical preparation. The possible mechanisms for the observed quenching reaction was also discussed.

  1. An efficient ratiometric fluorescence sensor based on metal-organic frameworks and quantum dots for highly selective detection of 6-mercaptopurine.

    PubMed

    Jin, Meng; Mou, Zhao-Li; Zhang, Rui-Ling; Liang, Si-Si; Zhang, Zhi-Qi

    2017-05-15

    The development of a simple and accurate quantitative method for the determination of 6-mercaptopurine (6-MP) is of great importance because of its serious side effects. Ratiometric fluorescence (RF) sensors are not subject to interference from environmental factors, and exhibit enhanced precision and accuracy. Therefore, a novel RF sensor for the selective detection of 6-MP was developed based on a dual-emission nanosensor. The nanosensor was fabricated by combining a blue-emission metal-organic framework (MOF) NH2-MIL-53(Al) (λem=425nm) with green-emission 3-mercaptopropionic acid-capped CdTe quantum dots (MPA-CdTe QDs) (λem=528nm) under a single excitation wavelength (335nm). Upon addition of 6-MP, the fluorescence of NH2-MIL-53(Al) in the nanohybrid was selectively quenched due to strong inner filter effects, while the fluorescence of the MPA-CdTe QDs was enhanced. The novel RF sensor exhibited higher selectivity towards 6-MP than CdTe QDs alone, and higher sensitivity than MOFs alone. 6-MP could be detected in the range of 0-50μM with a detection limit of 0.15μM (S/N=3). The developed sensor was applied for the determination of 6-MP in human urine samples and satisfactory results were obtained. Overall, a novel and efficient fluorescence-based method was developed for the detection of 6-MP in biosamples.

  2. In vivo cancer targeting and fluorescence-CT dual-mode imaging with nanoprobes based on silver sulfide quantum dots and iodinated oil.

    PubMed

    Qin, Meng-Yao; Yang, Xiao-Quan; Wang, Kan; Zhang, Xiao-Shuai; Song, Ji-Tao; Yao, Ming-Hao; Yan, Dong-Mei; Liu, Bo; Zhao, Yuan-Di

    2015-12-14

    In this article, a fluorescence-CT dual-mode nanoprobe is successfully synthesized by making use of distearoylphosphatidylethanolamine-poly(ethylene glycol)-folate (DSPE-PEG2000-FA) and other amphiphilic molecules to coat silver sulfide (Ag2S) quantum dots (QDs) and iodinated oil simultaneously. In vitro experiments show that the fluorescence wavelength of the nanoprobe is 1170 nm in the near infrared-II region. Its size is 139.6 nm, it has good dispersibility, and it has low cellular toxicity at concentrations up to 25 μg mL(-1) Ag. In vivo experiments revealed that the probe has a rather long circulation time (blood half-life of 5.7 hours), and the tissue histopathological tests show that it is not obviously harmful to major organs' normal function. Biochemical analysis (glutamic pyruvic transaminase and glutamic oxaloacetic transaminase levels) and blood analysis (white blood cell, red blood cell, hemoglobin and blood platelet counts) reveal that it has little influence on blood within 15 days of administration. When injected into HeLa xenograft nude mice by the tail vein, the probe elicited intensely enhanced fluorescence and X-ray computed tomography (CT) signals in the tumors after 24 hours, and the structure, size and position of tumor tissue were shown clearly. In a word, the probe has good tumor targeting capabilities, and it has significant value in fluorescence-CT dual-mode imaging in vivo.

  3. Graphene oxide quantum dots@silver core-shell nanocrystals as turn-on fluorescent nanoprobe for ultrasensitive detection of prostate specific antigen.

    PubMed

    Pei, Haimeng; Zhu, Shuyun; Yang, Minghui; Kong, Rongmei; Zheng, Yiqun; Qu, Fengli

    2015-12-15

    We report a fluorescent turn-on nanoprobe for ultrasensitive detection of prostate specific antigen (PSA) based on graphene oxide quantum dots@silver (GQDs@Ag) core-shell nanocrystals. The success of this work relies on the assembly of quantities of GQDs in one GQDs@Ag probe, which makes the ratio of probe to target significantly increased and thus enables the fluorescent signal enhancement. When the silver shell was removed via oxidative etching using hydrogen peroxide (H2O2), the incorporated GQDs could be readily released and the whole process caused little change to their fluorescence performance. We tested the probe for the ultrasensitive detection of PSA based on the sandwich protocol of immunosensors. In particular, magnetic beads (MBs) were employed to immobilize anti-PSA antibody (Ab1) and acted as a separable capture probe, while GQDs@Ag was used as detection probe by linking antibody (Ab2). The developed immunosensor showed a good linear relationship between the fluorescence intensity and the concentration of PSA in the range from 1 pg/mL to 20 ng/mL with a detection limit of 0.3 pg/mL. The immunosensor used for the analysis of clinical serum samples exhibited satisfactory results, which demonstrated its potential for practical diagnostic applications. This method provides a possible solution to the application of GQDs in immunosensing and could be potentially extended to other similar systems.

  4. 3-Aminophenylboronic acid-functionalized CuInS2 quantum dots as a near-infrared fluorescence probe for the detection of dicyandiamide.

    PubMed

    Liu, Siyu; Pang, Shu; Huang, Hui; Su, Xingguang

    2014-11-21

    In this paper, a simple and highly selective method for the determination of dicyandiamide (DCD) was developed based on the fluorescence quenching of functionalized CuInS2 quantum dots (QDs). Water-soluble CuInS2 QDs, capped by mercaptopropionic acid, were directly synthesized in aqueous solution and then covalently linked to 3-aminophenylboronic acid molecules to form the 3-aminophenylboronic acid-functionalized CuInS2 QDs (F-CuInS2 QDs) that had a fairly symmetric fluorescence emission centered at 736 nm. Based on the cyclization of the guanidine group of DCD with 2,3-butanedione and 3-aminophenylboronic acid, the fluorescence of the F-CuInS2 QDs is quenched by DCD in the presence of 2,3-butanedione. This method effectively distinguishes DCD from other amino acids and nitrogen pollutants, such as melamine, in real milk samples. Under optimum conditions, there was a good linear relationship between the fluorescence intensity of F-CuInS2 QDs and the concentration of DCD in the range of 2.0 × 10(-6) to 2.0 × 10(-3) mol L(-1), with a detection limit of 0.6 μmol L(-1).

  5. "Use of acidophilic bacteria of the genus Acidithiobacillus to biosynthesize CdS fluorescent nanoparticles (quantum dots) with high tolerance to acidic pH".

    PubMed

    Ulloa, G; Collao, B; Araneda, M; Escobar, B; Álvarez, S; Bravo, D; Pérez-Donoso, J M

    2016-12-01

    The use of bacterial cells to produce fluorescent semiconductor nanoparticles (quantum dots, QDs) represents a green alternative with promising economic potential. In the present work, we report for the first time the biosynthesis of CdS QDs by acidophilic bacteria of the Acidithiobacillus genus. CdS QDs were obtained by exposing A. ferrooxidans, A. thiooxidans and A. caldus cells to sublethal Cd(2+) concentrations in the presence of cysteine and glutathione. The fluorescence of cadmium-exposed cells moves from green to red with incubation time, a characteristic property of QDs associated with nanocrystals growth. Biosynthesized nanoparticles (NPs) display an absorption peak at 360nm and a broad emission spectra between 450 and 650nm when excited at 370nm, both characteristic of CdS QDs. Average sizes of 6 and 10nm were determined for green and red NPs, respectively. The importance of cysteine and glutathione on QDs biosynthesis in Acidithiobacillus was related with the generation of H2S. Interestingly, QDs produced by acidophilic bacteria display high tolerance to acidic pH. Absorbance and fluorescence properties of QDs was not affected at pH 2.0, a condition that totally inhibits the fluorescence of QDs produced chemically or biosynthesized by mesophilic bacteria (stable until pH 4.5-5.0). Results presented here constitute the first report of the generation of QDs with improved properties by using extremophile microorganisms.

  6. Detection of lead (II) with a "turn-on" fluorescent biosensor based on energy transfer from CdSe/ZnS quantum dots to graphene oxide.

    PubMed

    Li, Ming; Zhou, Xuejiao; Guo, Shouwu; Wu, Nianqiang

    2013-05-15

    Graphene oxide (GO) sheets are mixed with the aptamer-functionalized CdSe/ZnS quantum dots (QDs). Consequently, the aptamer-conjugated QDs bind to the GO sheets to form a GO/aptamer-QD ensemble, which enables the energy transfer from the QDs to the GO sheets, quenching the fluorescence of QDs. The GO/aptamer-QD ensemble assay acts as a "turn-on" fluorescent sensor for Pb(2+) detection. When Pb(2+) ions are present in the assay, the interaction of Pb(2+) with the aptamer induces a conformational change in the aptamer, leading to the formation of a G-quadruplex/Pb(2+) complex. As a result, the QDs that are linked to the G-quadruplex/Pb(2+) complex are detached from the GO sheet, which "turns on" the fluorescence of the QDs. This sensor exhibits a limit of detection of 90pM and excellent selectivity toward Pb(2+) over a wide range of metal ions. The experiments have provided direct evidence that the fluorescence of QDs is quenched by GO via the nano-metal surface energy transfer (NSET) mechanism rather than the conventional Förster resonance energy transfer (FRET) process.

  7. Absolute and relative blindsight.

    PubMed

    Balsdon, Tarryn; Azzopardi, Paul

    2015-03-01

    The concept of relative blindsight, referring to a difference in conscious awareness between conditions otherwise matched for performance, was introduced by Lau and Passingham (2006) as a way of identifying the neural correlates of consciousness (NCC) in fMRI experiments. By analogy, absolute blindsight refers to a difference between performance and awareness regardless of whether it is possible to match performance across conditions. Here, we address the question of whether relative and absolute blindsight in normal observers can be accounted for by response bias. In our replication of Lau and Passingham's experiment, the relative blindsight effect was abolished when performance was assessed by means of a bias-free 2AFC task or when the criterion for awareness was varied. Furthermore, there was no evidence of either relative or absolute blindsight when both performance and awareness were assessed with bias-free measures derived from confidence ratings using signal detection theory. This suggests that both relative and absolute blindsight in normal observers amount to no more than variations in response bias in the assessment of performance and awareness. Consideration of the properties of psychometric functions reveals a number of ways in which relative and absolute blindsight could arise trivially and elucidates a basis for the distinction between Type 1 and Type 2 blindsight.

  8. A water-soluble ESIPT fluorescent probe with high quantum yield and red emission for ratiometric detection of inorganic and organic palladium.

    PubMed

    Gao, Tang; Xu, Pengfei; Liu, Meihui; Bi, Anyao; Hu, Pengzhi; Ye, Bin; Wang, Wei; Zeng, Wenbin

    2015-05-01

    A novel fluorescent probe with a high quantum yield (0.41), large Stokes shifts (255 nm), and red emission (635 nm) was designed to detect all typical oxidation states of palladium species (0, +2, +4) by palladium-mediated terminal propargyl ethers cleavage reaction in water solution without any organic media. The probe showed a high selectivity and excellent sensitivity for palladium species, with a detection as low as 57 nM (6.2 μg L(-1)).

  9. A general sensing strategy for detection of Fe3+ by using amino acid-modified graphene quantum dots as fluorescent probe

    NASA Astrophysics Data System (ADS)

    Ma, Qi; Song, Jinping; Wang, Shangzhi; Yang, Jie; Guo, Yong; Dong, Chuan

    2016-12-01

    Amino acid-modified graphene quantum dots (GQDs) were synthesized through acylation and amination reactions. The as-synthesized GQDs were characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV-vis absorption and fluorescence spectroscopy. A general sensing strategy for detection of Fe3+ was successfully developed. The detection limit can reach as low as 50 nM. Moreover, the proposed sensing system was successfully employed to detect Fe3+ in real water sample, and satisfactory results were obtained. This work will open up new avenues to develop potential applications of GQDs materials in environmental monitoring.

  10. Above 20% external quantum efficiency in novel hybrid white organic light-emitting diodes having green thermally activated delayed fluorescent emitter

    PubMed Central

    Kim, Bo Seong; Yook, Kyoung Soo; Lee, Jun Yeob

    2014-01-01

    High efficiency hybrid type white organic light-emitting diodes (WOLEDs) combining a green thermally activated delayed fluorescent (TADF) emitting material with red/blue phosphorescent emitting materials were developed by manipulating the device architecture of WOLEDs. Energy transfer between a blue phosphorescent emitting material and a green TADF emitter was efficient and could be managed by controlling the doping concentration of emitters. A high quantum efficiency above 20% was achieved in the hybrid WOLEDs by optimizing the device structure of the hybrid type WOLEDs for the first time and the device performances of the hybrid WOLEDs were comparable to those of all phosphorescent WOLEDs. PMID:25317855

  11. Above 20% external quantum efficiency in novel hybrid white organic light-emitting diodes having green thermally activated delayed fluorescent emitter

    NASA Astrophysics Data System (ADS)

    Kim, Bo Seong; Yook, Kyoung Soo; Lee, Jun Yeob

    2014-08-01

    High efficiency hybrid type white organic light-emitting diodes (WOLEDs) combining a green thermally activated delayed fluorescent (TADF) emitting material with red/blue phosphorescent emitting materials were developed by manipulating the device architecture of WOLEDs. Energy transfer between a blue phosphorescent emitting material and a green TADF emitter was efficient and could be managed by controlling the doping concentration of emitters. A high quantum efficiency above 20% was achieved in the hybrid WOLEDs by optimizing the device structure of the hybrid type WOLEDs for the first time and the device performances of the hybrid WOLEDs were comparable to those of all phosphorescent WOLEDs.

  12. Gold Nanoparticle-Quantum Dot Fluorescent Nanohybrid: Application for Localized Surface Plasmon Resonance-induced Molecular Beacon Ultrasensitive DNA Detection

    NASA Astrophysics Data System (ADS)

    Adegoke, Oluwasesan; Park, Enoch Y.

    2016-11-01

    In biosensor design, localized surface plasmon resonance (LSPR)-induced signal from gold nanoparticle (AuNP)-conjugated reporter can produce highly sensitive nanohybrid systems. In order to retain the physicochemical properties of AuNPs upon conjugation, high colloidal stability in aqueous solution is needed. In this work, the colloidal stability with respect to the zeta potential (ZP) of four negatively charged thiol-functionalized AuNPs, thioglycolic (TGA)-AuNPs, 3-mercaptopropionic acid (MPA)-AuNPs, l-cysteine-AuNPs and l-glutathione (GSH)-AuNPs, and a cationic cyteamine-capped AuNPs was studied at various pHs, ionic strength, and NP concentration. A strong dependence of the ZP charge on the nanoparticle (NP) concentration was observed. High colloidal stability was exhibited between pH 3 and 9 for the negatively charged AuNPs and between pH 3 and 7 for the cationic AuNPs. With respect to the ionic strength, high colloidal stability was exhibited at ≤104 μM for TGA-AuNPs, l-cysteine-AuNPs, and GSH-AuNPs, whereas ≤103 μM is recommended for MPA-AuNPs. For the cationic AuNPs, very low ionic strength of ≤10 μM is recommended due to deprotonation at higher concentration. GSH-AuNPs were thereafter bonded to SiO2-functionalized alloyed CdZnSeS/ZnSe1.0S1.3 quantum dots (SiO2-Qdots) to form a plasmon-enhanced AuNP-SiO2-Qdots fluorescent nanohybrid. The AuNP-SiO2-Qdots conjugate was afterward conjugated to a molecular beacon (MB), thus forming an ultrasensitive LSPR-induced SiO2-Qdots-MB biosensor probe that detected a perfect nucleotide DNA sequence at a concentration as low as 10 fg/mL. The limit of detection was 11 fg/mL (1.4 fM) while the biosensor probe efficiently distinguished between single-base mismatch and noncomplementary sequence target.

  13. Europium-decorated graphene quantum dots as a fluorescent probe for label-free, rapid and sensitive detection of Cu(2+) and L-cysteine.

    PubMed

    Lin, Liping; Song, Xinhong; Chen, Yiying; Rong, Mingcong; Wang, Yiru; Zhao, Li; Zhao, Tingting; Chen, Xi

    2015-09-03

    In this work, europium-decorated graphene quantum dots (Eu-GQDs) were prepared by treating three-dimensional Eu-decorated graphene (3D Eu-graphene) via a strong acid treatment. Various characterizations revealed that Eu atoms were successfully complexed with the oxygen functional groups on the surface of graphene quantum dots (GQDs) with the atomic ratio of 2.54%. Compared with Eu free GQDs, the introduction of Eu atoms enhanced the electron density and improved the surface chemical activities of Eu-GQDs. Therefore, the obtained Eu-GQDs were used as a novel "off-on" fluorescent probe for the label-free determination of Cu(2+) and l-cysteine (L-Cys) with high sensitivity and selectivity. The fluorescence intensity of Eu-GQDs was quenched in the presence of Cu(2+) owing to the coordination reaction between Cu(2+) and carboxyl groups on the surface of the Eu-GQDs. The fluorescence intensity of Eu-GQDs recovered with the subsequent addition of L-Cys because of the strong affinity of Cu(2+) to L-Cys via the Cu-S bond. The experimental results showed that the fluorescence variation of the proposed approach had a good linear relationship in the range of 0.1-10 μM for Cu(2+) and 0.5-50 μM for L-Cys with corresponding detection limits of 0.056 μM for Cu(2+) and 0.31 μM for L-Cys. The current approach also displayed a special response to Cu(2+) and L-Cys over the other co-existing metal ions and amino acids, and the results obtained from buffer-diluted serum samples suggested its applicability in biological samples.

  14. Absolute neutrino mass scale

    NASA Astrophysics Data System (ADS)

    Capelli, Silvia; Di Bari, Pasquale

    2013-04-01

    Neutrino oscillation experiments firmly established non-vanishing neutrino masses, a result that can be regarded as a strong motivation to extend the Standard Model. In spite of being the lightest massive particles, neutrinos likely represent an important bridge to new physics at very high energies and offer new opportunities to address some of the current cosmological puzzles, such as the matter-antimatter asymmetry of the Universe and Dark Matter. In this context, the determination of the absolute neutrino mass scale is a key issue within modern High Energy Physics. The talks in this parallel session well describe the current exciting experimental activity aiming to determining the absolute neutrino mass scale and offer an overview of a few models beyond the Standard Model that have been proposed in order to explain the neutrino masses giving a prediction for the absolute neutrino mass scale and solving the cosmological puzzles.

  15. Consistent thermostatistics forbids negative absolute temperatures

    NASA Astrophysics Data System (ADS)

    Dunkel, Jörn; Hilbert, Stefan

    2014-01-01

    Over the past 60 years, a considerable number of theories and experiments have claimed the existence of negative absolute temperature in spin systems and ultracold quantum gases. This has led to speculation that ultracold gases may be dark-energy analogues and also suggests the feasibility of heat engines with efficiencies larger than one. Here, we prove that all previous negative temperature claims and their implications are invalid as they arise from the use of an entropy definition that is inconsistent both mathematically and thermodynamically. We show that the underlying conceptual deficiencies can be overcome if one adopts a microcanonical entropy functional originally derived by Gibbs. The resulting thermodynamic framework is self-consistent and implies that absolute temperature remains positive even for systems with a bounded spectrum. In addition, we propose a minimal quantum thermometer that can be implemented with available experimental techniques.

  16. The absolute path command

    SciTech Connect

    Moody, A.

    2012-05-11

    The ap command traveres all symlinks in a given file, directory, or executable name to identify the final absolute path. It can print just the final path, each intermediate link along with the symlink chan, and the permissions and ownership of each directory component in the final path. It has functionality similar to "which", except that it shows the final path instead of the first path. It is also similar to "pwd", but it can provide the absolute path to a relative directory from the current working directory.

  17. Simultaneous multicolor detection system of the single-molecular microbial antigen by total internal reflection fluorescence microscopy with fluorescent nanocrystal quantum dots

    NASA Astrophysics Data System (ADS)

    Hoshino, Akiyoshi; Fujioka, Kouki; Yamamoto, Mayu; Manabe, Noriyoshi; Yasuhara, Masato; Suzuki, Kazuo; Yamamoto, Kenji

    2005-11-01

    Immunological diagnostic methods have been widely performed and showed high performance in molecular and cellular biology, molecular imaging, and medical diagnostics. We have developed novel methods for the fluorescent labeling of several antibodies coupled with fluorescent nanocrystals QDs. In this study we demonstrated that two bacterial toxins, diphtheria toxin and tetanus toxin, were detected simultaneously in the same view field of a cover slip by using directly QD-conjugated antibodies. We have succeeded in detecting bacterial toxins by counting luminescent spots on the evanescent field with using primary antibody conjugated to QDs. In addition, each bacterial toxin in the mixture can be separately detected by single excitation laser with emission band pass filters, and simultaneously in situ pathogen quantification was performed by calculating the luminescent density on the surface of the cover slip. Our results demonstrate that total internal reflection fluorescence microscopy (TIRFM) enables us to distinguish each antigen from mixed samples and can simultaneously quantitate multiple antigens by QD-conjugated antibodies. Bioconjugated QDs could have great potentialities for in practical biomedical applications to develop various high-sensitivity detection systems.

  18. Fluorescent refrigeration

    DOEpatents

    Epstein, R.I.; Edwards, B.C.; Buchwald, M.I.; Gosnell, T.R.

    1995-09-05

    Fluorescent refrigeration is based on selective radiative pumping, using substantially monochromatic radiation, of quantum excitations which are then endothermically redistributed to higher energies. Ultimately, the populated energy levels radiatively deexcite emitting, on the average, more radiant energy than was initially absorbed. The material utilized to accomplish the cooling must have dimensions such that the exciting radiation is strongly absorbed, but the fluorescence may exit the material through a significantly smaller optical pathlength. Optical fibers and mirrored glasses and crystals provide this requirement. 6 figs.

  19. Dual role of blue luminescent MoS2 quantum dots in fluorescence resonance energy transfer phenomenon.

    PubMed

    Ha, Hyun Dong; Han, Dong Ju; Choi, Jong Seob; Park, Minsu; Seo, Tae Seok

    2014-10-15

    Homogeneous blue luminescent MoS2 quantum dots are fabricated by using a lithium intercalation method from MoS2 nanoparticles, and the unique blue photoluminescence property is utilized in the Alexa Fluor 430-dsDNA-MoS2 FRET system, demonstrating the dual function of MoS2 quantum dots as a donor and an acceptor.

  20. Fluorescence Microscopy of Single Molecules

    ERIC Educational Resources Information Center

    Zimmermann, Jan; van Dorp, Arthur; Renn, Alois

    2004-01-01

    The investigation of photochemistry and photophysics of individual quantum systems is described with the help of a wide-field fluorescence microscopy approach. The fluorescence single molecules are observed in real time.

  1. Aqueous synthesis of nontoxic Ag2Se/ZnSe quantum dots designing as fluorescence sensors for detection of Ag(I) and Cu(II) ions.

    PubMed

    Wang, Chunlei; Xu, Shuhong; Zhao, Zengxia; Wang, Zhuyuan; Cui, Yiping

    2015-01-01

    We reported the synthesis of water-soluble and nontoxic Ag(2)Se/ZnSe Quantum Dots (QDs) using for fluorescence sensors. The influences of various experimental conditions including the synthesis pH, types of ligand, feed ratios, and the refluxed time on the growth process and fluorescence of QDs were investigated in detail. Under optimal conditions, Ag(2)Se/ZnSe QDs show a single emission peak around 490 nm with the maximal photoluminescence (PL) quantum yield (QYs) of 13.7 %. As-prepared Ag(2)Se/ZnSe QDs can be used for detection of Ag(II) and Cu(II). The detection limits are 1 × 10(-6) mol/L to 5 × 10(-5) mol/L for Ag (I), and 2 × 10(-6) mol/L to 1.10 × 10(-4) mol/L for Cu(II).

  2. Determination of five quinolone antibiotic residues in foods by micellar electrokinetic capillary chromatography with quantum dot indirect laser-induced fluorescence.

    PubMed

    Meng, Hong-Lian; Chen, Guan-Hua; Guo, Xin; Chen, Ping; Cai, Qing-Hong; Tian, Yi-Fang

    2014-05-01

    A new assay was developed for the determination of five quinolone antibiotic residues in foods, loxacin, enrofloxacin, ciprofloxacin, lomefloxacin, and norfloxacin, by micellar electrokinetic capillary chromatography with indirect laser-induced fluorescence, in which cadmium telluride quantum dots were used as a fluorescent background substance. Some factors that affected the peak height and the resolution were examined. The optimized running buffer was composed of 20 mM SDS, 7.2 mg/L quantum dots, and 10 mM borate at pH 8.8. The separation voltage was 20 kV. Under these conditions, five quinolone antibiotic residues were separated successfully within 8 min. The detection limits ranged from 0.003 to 0.008 mg/kg; the linear dynamic ranges were all 0.01 ∼ 10 mg/kg; and the average recoveries of the spiked samples were 81.4 ∼ 94.6 %. The assay can meet the requirement of maximum residue limits to these five quinolone antibiotics in the regulations of the European Union and Japan and has been applied for determining their residues in animal-derived food.

  3. Selective recognition of cis-trans-isomers of platinum drugs and the detection of triplex DNA based on fluorescence reversible model of quantum dots.

    PubMed

    Xu, Xiaoling; Gao, Fang; Xiao, Xincai; Hu, Yan; Zhu, Chaozhen; Zhao, Dan

    2017-02-05

    The identification of spatial structures of drugs and the researches on their interaction mechanism with DNA are always attractive to the researchers. However, their realization is lack of simple and fast method. This paper reports the establishment of multiple-functional detection platform based on the "turn off-on" model of ZnCdSe quantum dots. In this system, ZnCdSe quantum dots work as the fluorescent probe, platinum anti-cancer drugs as the quencher and triplex DNA as the trapping agent. The seemingly similar cisplatin and transplatin exhibited different fluorescent recovery behaviors due to their difference in structure, and thus realized the selective detection of cisplatin and transplatin with the reaction time set at 10min as well as the quantitation of cisplatin over the range of 2.5×10(-8)-100×10(-8)M. Based on this, the interactions between platinum anti-cancer drugs and ctDNA as well as polymorphic DNA were further studied, and realized the recognition of triplex DNA. The multiple-functional detection platform integrates the functions of the filtration of high-efficient platinum anti-cancer drugs, the researches on interaction mechanism of drugs, and the recognition of polymorphic DNA, meaningful to the future treatment of viral and cancers based on antisense gene strategy.

  4. A versatile ratiometric nanosensing approach for sensitive and accurate detection of Hg(2+) and biological thiols based on new fluorescent carbon quantum dots.

    PubMed

    Fu, Huili; Ji, Zhongyin; Chen, Xuejie; Cheng, Anwei; Liu, Shucheng; Gong, Peiwei; Li, Guoliang; Chen, Guang; Sun, Zhiwei; Zhao, Xianen; Cheng, Feng; You, Jinmao

    2017-03-01

    Herein, we first reported a facile synthesis method for fabrication of highly photoluminescent carbon quantum dots (CQDs) using sodium alginate as the carbon source and histidine as both the nitrogen source and functional monomer by one-pot hydrothermal synthesis. The as-prepared CQDs gave a high quantum yield of 32%. By employing the new CQDs and rhodamine B (RhB), we demonstrated a simple, facile, sensitive, and accurate ratiometric sensor for detection of Hg(2+) and biological thiols. The photoluminescence of CQDs in the ratiometric sensor can be selectively and intensively suppressed by Hg(2+) due to strong electrostatic interaction between the surface functional groups of the CQDs and Hg(2+). When glutathione (GSH) was introduced into the "Turn Off" CQDs-RhB-Hg(2+) sensing system, the fluorescence of the CQDs can be recovered rapidly due to the stronger affinity between thiol and Hg(2+), while the fluorescence of the RhB remained constant in this sensing process. Based on the above principle, the ratiometric strategy for detecting Hg(2+) and GSH can be achieved readily, and gives satisfactory limit of detections (LODs) of 30 and 20 nM for Hg(2+) and GSH, respectively. The dual-emission fluorescent CQDs-RhB sensor does not need the complicated molecular design and the synthesis of dual-emission fluorophores. Meanwhile, the feasibility of the proposed method for analysis of water samples, food samples, and biological samples (plasma from mice oxidative stress study) was investigated. The developed ratiometric nanosensor is proven to be facile, with less sample consumption, rapid, lost cost, highly sensitive, and very selective for Hg(2+) and biological thiol detection, which offers a new approach for environmental, food, and biological analysis. Graphical abstract Ratiometric nanosensing approach detection of Hg(2+) and biological thiols.

  5. A homogeneous and "off-on" fluorescence aptamer-based assay for chloramphenicol using vesicle quantum dot-gold colloid composite probes.

    PubMed

    Miao, Yang-Bao; Ren, Hong-Xia; Gan, Ning; Zhou, You; Cao, Yuting; Li, Tianhua; Chen, Yinji

    2016-07-27

    In this work, a novel homogeneous and signal "off-on" aptamer based fluorescence assay was successfully developed to detect chloramphenicol (CAP) residues in food based on the fluorescence resonance energy transfer (FRET). The vesicle nanotracer was prepared through labeling single stranded DNA binding protein (SSB) on limposome-CdSe/ZnS quantum dot (SSB/L-QD) complexes. It was worth mentioning that the signal tracer (SSB/L-QD) with vesicle shape, which was fabricated being encapsulated with a number of quantum dots and SSB. The nanotracer has excellent signal amplification effects. The vesicle composite probe was formed by combining aptamer labeled nano-gold (Au-Apt) and SSB/L-QD. Which based on SSB's specific affinity towards aptamer. This probe can't emit fluoresce which is in "off" state because the signal from SSB/L-QD as donor can be quenched by the Au-aptas acceptor. When CAP was added in the composite probe solution, the aptamer on the Au-Apt can be preferentially bounded with CAP then release from the composite probe, which can turn the "off" signal of SSB/L-QD tracer into "on" state. The assay indicates excellent linear response to CAP from 0.001 nM to 10 nM and detection limit down to 0.3 pM. The vesicle probes with size of 88 nm have strong signal amplification. Because a larger number of QDs can be labeled inside the double phosphorus lipid membrane. Besides, it was employed to detect CAP residues in the milk samples with results being agreed well with those from ELISA, verifying its accuracy and reliability.

  6. NeutrAvidin Functionalization of CdSe/CdS Quantum Nanorods and Quantification of Biotin Binding Sites using Biotin-4-Fluorescein Fluorescence Quenching.

    PubMed

    Lippert, Lisa G; Hallock, Jeffrey T; Dadosh, Tali; Diroll, Benjamin T; Murray, Christopher B; Goldman, Yale E

    2016-03-16

    We developed methods to solubilize, coat, and functionalize with NeutrAvidin elongated semiconductor nanocrystals (quantum nanorods, QRs) for use in single molecule polarized fluorescence microscopy. Three different ligands were compared with regard to efficacy for attaching NeutrAvidin using the "zero-length cross-linker" 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC). Biotin-4-fluorescene (B4F), a fluorophore that is quenched when bound to avidin proteins, was used to quantify biotin binding activity of the NeutrAvidin coated QRs and biotin binding activity of commercially available streptavidin coated quantum dots (QDs). All three coating methods produced QRs with NeutrAvidin coating density comparable to the streptavidin coating density of the commercially available quantum dots (QDs) in the B4F assay. One type of QD available from the supplier (ITK QDs) exhibited ∼5-fold higher streptavidin surface density compared to our QRs, whereas the other type of QD (PEG QDs) had 5-fold lower density. The number of streptavidins per QD increased from ∼7 streptavidin tetramers for the smallest QDs emitting fluorescence at 525 nm (QD525) to ∼20 tetramers for larger, longer wavelength QDs (QD655, QD705, and QD800). QRs coated with NeutrAvidin using mercaptoundecanoicacid (MUA) and QDs coated with streptavidin bound to biotinylated cytoplasmic dynein in single molecule TIRF microscopy assays, whereas Poly(maleic anhydride-alt-1-ocatdecene) (PMAOD) or glutathione (GSH) QRs did not bind cytoplasmic dynein. The coating methods require optimization of conditions and concentrations to balance between substantial NeutrAvidin binding vs tendency of QRs to aggregate and degrade over time.

  7. Recombinant protein (EGFP-Protein G)-coated PbS quantum dots for in vitro and in vivo dual fluorescence (visible and second-NIR) imaging of breast tumors

    NASA Astrophysics Data System (ADS)

    Sasaki, Akira; Tsukasaki, Yoshikazu; Komatsuzaki, Akihito; Sakata, Takao; Yasuda, Hidehiro; Jin, Takashi

    2015-03-01

    We report a one-step synthetic strategy for the preparation of recombinant protein (EGFP-Protein G)-coated PbS quantum dots for dual (visible and second-NIR) fluorescence imaging of breast tumors at the cellular and whole-body level.We report a one-step synthetic strategy for the preparation of recombinant protein (EGFP-Protein G)-coated PbS quantum dots for dual (visible and second-NIR) fluorescence imaging of breast tumors at the cellular and whole-body level. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr06480a

  8. Significant metal enhanced fluorescence of Ag2S quantum dots in the second near-infrared window

    NASA Astrophysics Data System (ADS)

    Theodorou, I. G.; Jawad, Z. A. R.; Qin, H.; Aboagye, E. O.; Porter, A. E.; Ryan, M. P.; Xie, F.

    2016-06-01

    The amplification of light in NIR-II from Ag2S QDs via metal enhanced fluorescence (MEF) is reported for the first time. Significant fluorescence enhancement of over 100 times for Ag2S QDs deposited on Au-nanostructured arrays, paves the way for novel sensing and imaging applications based on Ag2S QDs, with improved detection sensitivity and contrast enhancement.The amplification of light in NIR-II from Ag2S QDs via metal enhanced fluorescence (MEF) is reported for the first time. Significant fluorescence enhancement of over 100 times for Ag2S QDs deposited on Au-nanostructured arrays, paves the way for novel sensing and imaging applications based on Ag2S QDs, with improved detection sensitivity and contrast enhancement. Electronic supplementary information (ESI) available: Detailed description of experimental methods. See DOI: 10.1039/c6nr03220f

  9. An ultrasensitive and selective method for the determination of Ceftriaxone using cysteine capped cadmium sulfide fluorescence quenched quantum dots as fluorescence probes

    NASA Astrophysics Data System (ADS)

    Samadi, Naser; Narimani, Saeedeh

    2016-06-01

    In this paper, L-cysteine (Cys) coated CdS quantum dots (QDs) have been prepared, which have excellent water-solubility and are highly stable in aqueous solution. These QDs is proposed as sensitizers for the determination of Ceftriaxone. The quantum dot nanoparticles were structurally and optically characterized by Ultra Violet-Visible absorption Spectroscopy (UV-vis absorption spectroscopy), Fourier transform infrared spectroscopy (FT-IR spectra) and photoluminescence (PL) emission spectroscopy. High resolution transmission electron microscopy (HRTEM) confirms that the Cys-CdS QDs have a spherical structure with good crystallinity. Therefore, a new simple and selective PL analysis system was developed for the determination of Ceftriaxone (CFX). Under the optimum conditions, The response of L-Cys capped CdS QDs as the probe was linearly proportional to the concentration of Ceftriaxone ions in the range of 1.6 × 10- 9-1.1 × 10- 3 M with a correlation coefficient (R2) of 0.9902. The limit of detection of this system was found to be 1.3 nM. This method is simple, sensitive and low cost.

  10. Highly Fluorescent Ribonuclease-A-Encapsulated Lead Sulfide Quantum Dots for Ultrasensitive Fluorescence in Vivo Imaging in the Second Near-Infrared Window.

    PubMed

    Kong, Yifei; Chen, Jun; Fang, Hongwei; Heath, George; Wo, Yan; Wang, Weili; Li, Yunxia; Guo, Yuan; Evans, Stephen D; Chen, Shiyi; Zhou, Dejian

    2016-05-10

    Ribonuclease-A (RNase-A) encapsulated PbS quantum dots (RNase-A@PbS Qdots) which emit in the second near-infrared biological window (NIR-II, ca. 1000-1400 nm) are rapidly synthesized under microwave heating. Photoluminescence (PL) spectra of the Qdots can be tuned across the entire NIR-II range by simply controlling synthesis temperature. The size and morphology of the Qdots are examined by transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS). Quantum yield (Φf) measurement confirms that the prepared Qdots are one of the brightest water-soluble NIR-II emitters for in vivo imaging. Their high Φf (∼17.3%) and peak emission at ∼1300 nm ensure deep optical penetration to muscle tissues (up to 1.5 cm) and excellent imaging contrast at an extremely low threshold dose of ∼5.2 pmol (∼1 μg) per mouse. Importantly, this protein coated Qdot displays no signs of toxicity toward model neuron, normal, and cancer cells in vitro. In addition, the animal's metabolism results in thorough elimination of intravenously injected Qdots from the body within several days via the reticuloendothelial system (RES), which minimizes potential long-term toxicity in vivo from possible release of lead content. With a combination of attractive properties of high brightness, robust photostability, and excellent biocompatibility, this new NIR-II emitting Qdot is highly promising in accurate disease screening and diagnostic applications.

  11. An ultrasensitive and selective method for the determination of Ceftriaxone using cysteine capped cadmium sulfide fluorescence quenched quantum dots as fluorescence probes.

    PubMed

    Samadi, Naser; Narimani, Saeedeh

    2016-06-15

    In this paper, l-cysteine (Cys) coated CdS quantum dots (QDs) have been prepared, which have excellent water-solubility and are highly stable in aqueous solution. These QDs is proposed as sensitizers for the determination of Ceftriaxone. The quantum dot nanoparticles were structurally and optically characterized by Ultra Violet-Visible absorption Spectroscopy (UV-vis absorption spectroscopy), Fourier transform infrared spectroscopy (FT-IR spectra) and photoluminescence (PL) emission spectroscopy. High resolution transmission electron microscopy (HRTEM) confirms that the Cys-CdS QDs have a spherical structure with good crystallinity. Therefore, a new simple and selective PL analysis system was developed for the determination of Ceftriaxone (CFX). Under the optimum conditions, The response of l-Cys capped CdS QDs as the probe was linearly proportional to the concentration of Ceftriaxone ions in the range of 1.6×10(-9)-1.1×10(-3)M with a correlation coefficient (R2) of 0.9902. The limit of detection of this system was found to be 1.3nM. This method is simple, sensitive and low cost.

  12. Multimodal Mn-doped I-III-VI quantum dots for near infrared fluorescence and magnetic resonance imaging: from synthesis to in vivo application

    NASA Astrophysics Data System (ADS)

    Sitbon, Gary; Bouccara, Sophie; Tasso, Mariana; Francois, Aurélie; Bezdetnaya, Lina; Marchal, Frédéric; Beaumont, Marine; Pons, Thomas

    2014-07-01

    The development of sensitive multimodal contrast agents is a key issue to provide better global, multi-scale images for diagnostic or therapeutic purposes. Here we present the synthesis of Zn-Cu-In-(S, Se)/Zn1-xMnxS core-shell quantum dots (QDs) that can be used as markers for both near-infrared fluorescence imaging and magnetic resonance imaging (MRI). We first present the synthesis of Zn-Cu-In-(S, Se) cores coated with a thick ZnS shell doped with various proportions of Mn. Their emission wavelengths can be tuned over the NIR optical window suitable for deep tissue imaging. The incorporation of manganese ions (up to a few thousand ions per QD) confers them a paramagnetic character, as demonstrated by structural analysis and electron paramagnetic resonance spectroscopy. These QDs maintain their optical properties after transfer to water using ligand exchange. They exhibit T1-relaxivities up to 1400 mM-1 [QD] s-1 at 7 T and 300 K. We finally show that these QDs are suitable multimodal in vivo probes and demonstrate MRI and NIR fluorescence detection of regional lymph nodes in mice.The development of sensitive multimodal contrast agents is a key issue to provide better global, multi-scale images for diagnostic or therapeutic purposes. Here we present the synthesis of Zn-Cu-In-(S, Se)/Zn1-xMnxS core-shell quantum dots (QDs) that can be used as markers for both near-infrared fluorescence imaging and magnetic resonance imaging (MRI). We first present the synthesis of Zn-Cu-In-(S, Se) cores coated with a thick ZnS shell doped with various proportions of Mn. Their emission wavelengths can be tuned over the NIR optical window suitable for deep tissue imaging. The incorporation of manganese ions (up to a few thousand ions per QD) confers them a paramagnetic character, as demonstrated by structural analysis and electron paramagnetic resonance spectroscopy. These QDs maintain their optical properties after transfer to water using ligand exchange. They exhibit T1-relaxivities

  13. Epitope imprinted polymer coating CdTe quantum dots for specific recognition and direct fluorescent quantification of the target protein bovine serum albumin.

    PubMed

    Yang, Ya-Qiong; He, Xi-Wen; Wang, Yi-Zhi; Li, Wen-You; Zhang, Yu-Kui

    2014-04-15

    A novel epitope molecularly imprinted polymer (EMIP) for specific recognition and direct fluorescent quantification of the target protein bovine serum albumin (BSA) was demonstrated where polymerization was performed on the surface of silica nanospheres embedded CdTe quantum dots (QDs). The synthetic peptide derived from the surface-exposed C-terminus of bovine serum albumin (BSA, residues 599-607) was selected as the template molecule. The resulting EMIP film was able to selectively capture the template peptide and the corresponding target protein BSA via the recognition cavities. Based on the fluorescence quenching, the EMIP-coated QDs (molecular imprinted polymer coating CdTe QDs using epitope as the template) nanospheres were successfully applied to the direct fluorescence quantification of BSA. Compared with BMIP-coated QDs (molecular imprinted polymer coating CdTe QDs using BSA as the template), the imprinting factor and adsorption capacity of EMIP-coated QDs were greatly increased. The prepared EMIP-coated QDs can also discriminate even one mismatched sequences from the original sequences of the epitope of the BSA. The practical analytical performance of the EMIP-coated QDs was examined by evaluating the detection of BSA in the bovine calf serum sample with satisfactory results. In addition, the resulting EMIP-coated QDs nanospheres were also successfully applied to separating BSA from the bovine blood sample.

  14. As-prepared MoS2 quantum dot as a facile fluorescent probe for long-term tracing of live cells

    NASA Astrophysics Data System (ADS)

    Zhou, Kai; Zhang, Yue; Xia, Zhining; Wei, Weili

    2016-07-01

    Recently, the newly emerged two-dimensional nanomaterials, layered transition metal dichalcogenide (e.g. MoS2) nanosheets, have drawn tremendous attentions due to their extraordinary electronic and optical properties, and MoS2 quantum dots (MoS2 QDs) with lateral sizes less than 10 nm have been found to be highly luminescent. In the present study, a facile approach for large-scale preparation of MoS2 QDs by Na intercalation reaction without using any toxic organic reagents is proposed. MoS2 QDs were carefully characterized by various techniques including transmission electron microscopy, atomic force microscopy, dynamic light scattering, spectroscopy, in vitro cytotoxicology, and capillary electrophoresis. The as-prepared MoS2 QDs were strongly fluorescent, highly photo-stable, low in cytotoxicity, and readily reactive to thiols. These inherent properties of MoS2 QDs make them excellent fluorescent probes for long-term live cell tracing. The results of live cells imaging indicated that MoS2 QD stained cells remained highly fluorescent after long-term culture, and could be easily traced from other co-cultured cell lines.

  15. 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.

  16. Detection of acrylamide in potato chips using a fluorescent sensing method based on acrylamide polymerization-induced distance increase between quantum dots.

    PubMed

    Hu, Qinqin; Xu, Xiahong; Li, Zhanming; Zhang, Ying; Wang, Jianping; Fu, Yingchun; Li, Yanbin

    2014-04-15

    Acrylamide is a neurotoxin and potential carcinogen, but is found in various thermally processed foods such as potato chips, biscuits, and coffee. Simple and sensitive methods for on-line detection of acrylamide are needed to ensure food safety. In this paper, a novel fluorescent sensing method based on acrylamide polymerization-induced distance increase between quantum dots (QDs) was proposed for detecting acrylamide in potato chips. The functional QDs were prepared by their binding with N-acryloxysuccinimide (NAS), which was characterized by Fourier transform infrared (FR-IR) spectra. The carbon-carbon double bonds of NAS modified QDs polymerized with assistance of photo initiator under UV irradiation, leading to QDs getting closer along with fluorescence intensity decreasing. Acrylamide in the sample participated in the polymerization and induced an increase of fluorescence intensity. This method possessed a linear range from 3.5×10(-5) to 3.5 g L(-1) (r(2)=0.94) and a limit of detection of 3.5×10(-5) g L(-1). Although the sensitivity and specificity cannot be compared with standard LC-MS/MS analysis, this new method requires much less time and cost, which is promising for on-line rapid detection of acrylamide in food processing.

  17. Preparation of graphene quantum dots based core-satellite hybrid spheres and their use as the ratiometric fluorescence probe for visual determination of mercury(II) ions.

    PubMed

    Hua, Mengjuan; Wang, Chengquan; Qian, Jing; Wang, Kan; Yang, Zhenting; Liu, Qian; Mao, Hanping; Wang, Kun

    2015-08-12

    We herein proposed a simple and effective strategy for preparing graphene quantum dots (GQDs)-based core-satellite hybrid spheres and further explored the feasibility of using such spheres as the ratiometric fluorescence probe for the visual determination of Hg(2+). The red-emitting CdTe QDs were firstly entrapped in the silica nanosphere to reduce their toxicity and improve their photo and chemical stabilities, thus providing a built-in correction for environmental effects, while the GQDs possessing good biocompatibility and low toxicity were electrostatic self-assembly on the silica surface acting as reaction sites. Upon exposure to the increasing contents of Hg(2+), the blue fluorescence of GQDs can be gradually quenched presumably due to facilitating nonradiative electron/hole recombination annihilation. With the embedded CdTe QDs as the internal standard, the variations of the tested solution display continuous fluorescence color changes from blue to red, which can be easily observed by the naked eye without any sophisticated instrumentations and specially equipped laboratories. This sensor exhibits high sensitivity and selectivity toward Hg(2+) in a broad linear range of 10 nM-22 μM with a low detection limit of 3.3 nM (S/N = 3), much lower than the allowable Hg(2+) contents in drinking water set by U.S. Environmental Protection Agency. This prototype ratiometric probe is of good simplicity, low toxicity, excellent stabilities, and thus potentially attractive for Hg(2+) quantification related biological systems.

  18. Design of weak-donor alkyl-functionalized push-pull pyrene dyes exhibiting enhanced fluorescence quantum yields and unique on/off switching properties.

    PubMed

    Niko, Yosuke; Sasaki, Shunsuke; Kawauchi, Susumu; Tokumaru, Katsumi; Konishi, Gen-Ichi

    2014-07-01

    We designed, synthesized, and evaluated environmentally responsive solvatochromic fluorescent dyes by incorporating weak push-pull moieties. The quantum yields of the push (alkyl)-pull (formyl) pyrene dyes were dramatically enhanced by the introduction of alkyl groups into formylpyrene (1-formylpyrene: Φ(F) =0.10; 3,6,8-tri-n-butyl-1-formylpyrene: Φ(F) =0.90; in MeOH). The new dyes exhibited unique sensitivity to solvent polarity and hydrogen-bond donor ability, and specific fluorescence turn-on/off properties (e.g., 3,6,8-tri-n-butyl-1-formylpyrene: Φ(F) =0.004, 0.80, 0.37, and 0.90 in hexane, chloroform, DMSO, and MeOH, respectively). Here, the alkyl groups act as weak donors to suppress intersystem crossing by destabilizing the HOMOs of 1-formylpyrene while maintaining weak intramolecular charge-transfer properties. By using alkyl groups as weak donors, environmentally responsive, and in particular, pH-responsive fluorescent materials may be developed in the future.

  19. Surface Molecular Imprinting on Silica-Coated CdTe Quantum Dots for Selective and Sensitive Fluorescence Detection of p-aminophenol in Water.

    PubMed

    Lu, Xialin; Wei, Fangdi; Xu, Guanhong; Wu, Yanzi; Yang, Jing; Hu, Qin

    2017-01-01

    In this paper, a selective and sensitive sensor for the determination of p-aminophenol (PAP) was developed by grafting molecularly imprinted polymers (MIPs) on the surface of silica-coated CdTe quantum dots (CdTe@SiO2@MIPs). The obtained CdTe@SiO2@MIPs were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and fluorescence spectroscopy. The fluorescence intensity of CdTe@SiO2@MIPs was more strongly quenched by PAP than that of the structural analogues of PAP. Under the optimal conditions, the fluorescence intensity of the CdTe@SiO2@MIPs decreased sensitively with the increase of PAP concentration in the range of 0.05-50 μM. The limit of detection was 0.02 μM (3σ/K sv). The sensor was successfully used to determine PAP in tap and lake water samples, and the average recoveries of PAP at various spiking levels ranged from 97.33 % to 103.3 % with relative standard deviations below 20 %.

  20. Intensity calibration and flat-field correction for fluorescence microscopes.

    PubMed

    Model, Michael

    2014-04-01

    Standardization in fluorescence microscopy involves calibration of intensity in reproducible units and correction for spatial nonuniformity of illumination (flat-field or shading correction). Both goals can be achieved using concentrated solutions of fluorescent dyes. When a drop of a highly concentrated fluorescent dye is placed between a slide and a coverslip it produces a spatially uniform field, resistant to photobleaching and with reproducible quantum yield; it can be used as a brightness standard for wide-field and confocal microscopes. For wide-field microscopes, calibration can be further extended to absolute molecular units. This can be done by imaging a solution of known concentration and known depth; the latter can be prepared by placing a small spherical lens in a diluted solution of the same fluorophore that is used in the biological specimen.

  1. Highly Fluorescent Ribonuclease-A-Encapsulated Lead Sulfide Quantum Dots for Ultrasensitive Fluorescence in Vivo Imaging in the Second Near-Infrared Window

    PubMed Central

    2016-01-01

    Ribonuclease-A (RNase-A) encapsulated PbS quantum dots (RNase-A@PbS Qdots) which emit in the second near-infrared biological window (NIR-II, ca. 1000–1400 nm) are rapidly synthesized under microwave heating. Photoluminescence (PL) spectra of the Qdots can be tuned across the entire NIR-II range by simply controlling synthesis temperature. The size and morphology of the Qdots are examined by transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS). Quantum yield (Φf) measurement confirms that the prepared Qdots are one of the brightest water-soluble NIR-II emitters for in vivo imaging. Their high Φf (∼17.3%) and peak emission at ∼1300 nm ensure deep optical penetration to muscle tissues (up to 1.5 cm) and excellent imaging contrast at an extremely low threshold dose of ∼5.2 pmol (∼1 μg) per mouse. Importantly, this protein coated Qdot displays no signs of toxicity toward model neuron, normal, and cancer cells in vitro. In addition, the animal’s metabolism results in thorough elimination of intravenously injected Qdots from the body within several days via the reticuloendothelial system (RES), which minimizes potential long-term toxicity in vivo from possible release of lead content. With a combination of attractive properties of high brightness, robust photostability, and excellent biocompatibility, this new NIR-II emitting Qdot is highly promising in accurate disease screening and diagnostic applications. PMID:27212793

  2. In vivo cancer targeting and fluorescence-CT dual-mode imaging with nanoprobes based on silver sulfide quantum dots and iodinated oil

    NASA Astrophysics Data System (ADS)

    Qin, Meng-Yao; Yang, Xiao-Quan; Wang, Kan; Zhang, Xiao-Shuai; Song, Ji-Tao; Yao, Ming-Hao; Yan, Dong-Mei; Liu, Bo; Zhao, Yuan-Di

    2015-11-01

    In this article, a fluorescence-CT dual-mode nanoprobe is successfully synthesized by making use of distearoylphosphatidylethanolamine-poly(ethylene glycol)-folate (DSPE-PEG2000-FA) and other amphiphilic molecules to coat silver sulfide (Ag2S) quantum dots (QDs) and iodinated oil simultaneously. In vitro experiments show that the fluorescence wavelength of the nanoprobe is 1170 nm in the near infrared-II region. Its size is 139.6 nm, it has good dispersibility, and it has low cellular toxicity at concentrations up to 25 μg mL-1 Ag. In vivo experiments revealed that the probe has a rather long circulation time (blood half-life of 5.7 hours), and the tissue histopathological tests show that it is not obviously harmful to major organs' normal function. Biochemical analysis (glutamic pyruvic transaminase and glutamic oxaloacetic transaminase levels) and blood analysis (white blood cell, red blood cell, hemoglobin and blood platelet counts) reveal that it has little influence on blood within 15 days of administration. When injected into HeLa xenograft nude mice by the tail vein, the probe elicited intensely enhanced fluorescence and X-ray computed tomography (CT) signals in the tumors after 24 hours, and the structure, size and position of tumor tissue were shown clearly. In a word, the probe has good tumor targeting capabilities, and it has significant value in fluorescence-CT dual-mode imaging in vivo.In this article, a fluorescence-CT dual-mode nanoprobe is successfully synthesized by making use of distearoylphosphatidylethanolamine-poly(ethylene glycol)-folate (DSPE-PEG2000-FA) and other amphiphilic molecules to coat silver sulfide (Ag2S) quantum dots (QDs) and iodinated oil simultaneously. In vitro experiments show that the fluorescence wavelength of the nanoprobe is 1170 nm in the near infrared-II region. Its size is 139.6 nm, it has good dispersibility, and it has low cellular toxicity at concentrations up to 25 μg mL-1 Ag. In vivo experiments revealed that the

  3. Self consistent, absolute calibration technique for photon number resolving detectors.

    PubMed

    Avella, A; Brida, G; Degiovanni, I P; Genovese, M; Gramegna, M; Lolli, L; Monticone, E; Portesi, C; Rajteri, M; Rastello, M L; Taralli, E; Traina, P; White, M

    2011-11-07

    Well characterized photon number resolving detectors are a requirement for many applications ranging from quantum information and quantum metrology to the foundations of quantum mechanics. This prompts the necessity for reliable calibration techniques at the single photon level. In this paper we propose an innovative absolute calibration technique for photon number resolving detectors, using a pulsed heralded photon source based on parametric down conversion. The technique, being absolute, does not require reference standards and is independent upon the performances of the heralding detector. The method provides the results of quantum efficiency for the heralded detector as a function of detected photon numbers. Furthermore, we prove its validity by performing the calibration of a Transition Edge Sensor based detector, a real photon number resolving detector that has recently demonstrated its effectiveness in various quantum information protocols.

  4. 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.

  5. Design and Synthesis of New Circularly Polarized Thermally Activated Delayed Fluorescence Emitters.

    PubMed

    Feuillastre, Sophie; Pauton, Mathilde; Gao, Longhui; Desmarchelier, Alaric; Riives, Adrian J; Prim, Damien; Tondelier, Denis; Geffroy, Bernard; Muller, Gilles; Clavier, Gilles; Pieters, Grégory

    2016-03-30

    This work describes the first thermally activated delayed fluorescence material enabling circularly polarized light emission through chiral perturbation. These new molecular architectures obtained through a scalable one-pot sequential synthetic procedure at room temperature (83% yield) display high quantum yield (up to 74%) and circularly polarized luminescence with an absolute luminescence dissymmetry factor, |glum|, of 1.3 × 10(-3). These chiral molecules have been used as an emissive dopant in an organic light emitting diode exhibiting external quantum efficiency as high as 9.1%.

  6. Design and simulation of perturbed onion-like quantum-dot-quantum-well (CdSe/ZnS/CdSe/ZnS) and its influence on fluorescence resonance energy transfer mechanism.

    PubMed

    SalmanOgli, Ahmad; Rostami, Ali

    2013-12-01

    In this study, the authors investigate one of the biological sensory applications (fluorescence resonance energy transfer (FRET)) that has astonishing influence on implementation of the bio-medical assays. For the first time, in this study, the new inorganic modified nanoparticle structure (quantum-dot quantum-well (QDQW) heteronanocrystal) is used as donor particle. By considering the mentioned structure, the authors can easily manipulate the donor emission spectrum and all parameters of FRET, such as overlapping between the donor emission and acceptor absorption. In this procedure, the Förster radius can be completely controlled. Moreover, the quantum confinement effects, including the strong-confinement and the weak-confinement regime, are investigated for FRET essential variables. As a main goal of this study, the authors will mathematically explore the influences of perturbation on the intrinsic parameters of nanoparticles (lifetime and bandwidth of emission spectrum) and on the sensitivity of FRET. It can be revealed that the presence of perturbation in nanoparticle has a devastating influence on biological assay characteristics, which will be probe in presented simulations. Furthermore, the physically analysing of QDQW heteronanocrystal structure is performed by the accurate eight-band K.P theory and finite-element method.

  7. Encapsulation of novel fluorescent nanocrystals (quantum dots) with a nanocomposite polymer and their assessment by in-vitro and in-vivo studies

    NASA Astrophysics Data System (ADS)

    Iga, Arthur M.

    Advance in nanotechnology has led to the development of novel fluorescent probes called quantum dots which are being exploited for potential new methods of early cancer detection spread and therapeutic management. Concerns regarding the release of potentially toxic inorganic core atoms into their surrounding environment and possession of hydrophobic surfaces are hindering the development of quantum dots. In order to abrogate their toxicity and solubilise the nanocrystals in aqueous solution a novel polyhedral oligomeric silsesquioxanes (POSS) poly(carbonate-urea)urethane (PCU), a silica nanocomposite (NC) polymer has been used to coat them. Physical and chemical analysis of the coated quantum dots with UV-Visible spectrometry, Photoluminescence, transmission electron microscopy, X-ray microanalysis and diffraction. Atomic force microscope and FTIR Spectrophotometry has enabled us ascertain the characteristics of these unique nanocrystals. The biocompatibility of the nanocomposite coated quantum dots (NCCQD) was assessed by using Alamar blue metabolic assay, Pico green assay and by measuring lactate dehydrogenase release on endothelial cell damage. Potential interference of NCCQD with a rat's normal physiology and systemic tissue distribution were assessed in an in-vivo animal model. Results demonstrated that the nanocrystals retained their unique optical properties, had a mean hydrodynamic diameter of 10.5 nm, excellent monodispersivity, large absorption spectrum with a narrow emission band at 790 nm and were highly photostable after polymer coating. NCCQD were compatible with endothelial cells as viable cells were demonstrated to be present after 14 days of growing cells in cell culture medium exposed to NCCQD at concentrations of 2.25 X 10"2 nM. There was no significant disturbance in the physiological parameters on injecting the NCCQD in an in-vivo rat model over a 2 hour period. NCCQD were seen to be deposited in the spleen and thymus as they are

  8. Quantum Yield Measurements of Fluorophores in Lipid Bilayers Using a Plasmonic Nanocavity.

    PubMed

    Schneider, Falk; Ruhlandt, Daja; Gregor, Ingo; Enderlein, Jörg; Chizhik, Alexey I

    2017-03-20

    Precise knowledge of the quantum yield is important for many fluorescence-spectroscopic techniques, for example, for Förster resonance energy transfer. However, to measure it for emitters in a complex environment and at low concentrations is far from being trivial. Using a plasmonic nanocavity, we measure the absolute quantum yield value of lipid-conjugated dyes incorporated into a supported lipid bilayer. We show that for both hydrophobic and hydrophilic molecules the quantum yield of dyes inside the lipid bilayer strongly differs from its value in aqueous solution. This finding is of particular importance for all fluorescence-spectroscopic studies involving lipid bilayers, such as protein-protein or protein-lipid interactions in membranes or direct fluorescence-spectroscopic measurements of membrane physical properties.

  9. Localized surface plasmon resonance-mediated fluorescence signals in plasmonic nanoparticle-quantum dot hybrids for ultrasensitive Zika virus RNA detection via hairpin hybridization assays.

    PubMed

    Adegoke, Oluwasesan; Morita, Masahiro; Kato, Tatsuya; Ito, Masahito; Suzuki, Tetsuro; Park, Enoch Y

    2017-03-22

    The current epidemic caused by the Zika virus (ZIKV) and the devastating effects of this virus on fetal development, which result in an increased incidence of congenital microcephaly symptoms, have prompted the World Health Organization (WHO) to declare the ZIKV a public health issue of global concern. Efficient probes that offer high detection sensitivity and specificity are urgently required to aid in the point-of-care treatment of the virus. In this study, we show that localized surface plasmon resonance (LSPR) signals from plasmonic nanoparticles (NPs) can be used to mediate the fluorescence signal from semiconductor quantum dot (Qdot) nanocrystals in a molecular beacon (MB) biosensor probe for ZIKV RNA detection. Four different plasmonic NPs functionalized with 3-mercaptopropionic acid (MPA), namely MPA-AgNPs, MPA-AuNPs, core/shell (CS) Au/AgNPs, and alloyed AuAgNPs, were synthesized and conjugated to L-glutathione-capped CdSeS alloyed Qdots to form the respective LSPR-mediated fluorescence nanohybrid. The concept of the plasmonic NP-Qdot-MB biosensor involves using LSPR from the plasmonic NPs to mediate a fluorescence signal to the Qdots, triggered by the hybridization of the target ZIKV RNA with the DNA loop sequence of the MB. The extent of the fluorescence enhancement based on ZIKV RNA detection was proportional to the LSPR-mediated fluorescence signal. The limits of detection (LODs) of the nanohybrids were as follows: alloyed AuAgNP-Qdot646-MB (1.7 copies/mL)) > CS Au/AgNP-Qdot646-MB (LOD =2.4 copies/mL) > AuNP-Qdot646-MB (LOD =2.9 copies/mL) > AgNP-Qdot646-MB (LOD =7.6 copies/mL). The LSPR-mediated fluorescence signal was stronger for the bimetallic plasmonic NP-Qdots than the single metallic plasmonic NP-Qdots. The plasmonic NP-Qdot-MB biosensor probes exhibited excellent selectivity toward ZIKV RNA and could serve as potential diagnostic probes for the point-of care detection of the virus.

  10. A general solid-state synthesis of chemically-doped fluorescent graphene quantum dots for bioimaging and optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Ma, Chong-Bo; Zhu, Zhen-Tong; Wang, Hang-Xing; Huang, Xiao; Zhang, Xiao; Qi, Xiaoying; Zhang, Hao-Li; Zhu, Yihan; Deng, Xia; Peng, Yong; Han, Yu; Zhang, Hua

    2015-05-01

    Graphene quantum dots (GQDs) have attracted increasing interest because of their excellent properties such as strong photoluminescence, excellent biocompatibility and low cost. Herein, we develop a general method for the synthesis of doped and undoped GQDs, which relies on direct carbonization of organic precursors in the solid state.Graphene quantum dots (GQDs) have attracted increasing interest because of their excellent properties such as strong photoluminescence, excellent biocompatibility and low cost. Herein, we develop a general method for the synthesis of doped and undoped GQDs, which relies on direct carbonization of organic precursors in the solid state. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr01757b

  11. Electronic Absolute Cartesian Autocollimator

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B.

    2006-01-01

    An electronic absolute Cartesian autocollimator performs the same basic optical function as does a conventional all-optical or a conventional electronic autocollimator but differs in the nature of its optical target and the manner in which the position of the image of the target is measured. The term absolute in the name of this apparatus reflects the nature of the position measurement, which, unlike in a conventional electronic autocollimator, is based absolutely on the position of the image rather than on an assumed proportionality between the position and the levels of processed analog electronic signals. The term Cartesian in the name of this apparatus reflects the nature of its optical target. Figure 1 depicts the electronic functional blocks of an electronic absolute Cartesian autocollimator along with its basic optical layout, which is the same as that of a conventional autocollimator. Referring first to the optical layout and functions only, this or any autocollimator is used to measure the compound angular deviation of a flat datum mirror with respect to the optical axis of the autocollimator itself. The optical components include an illuminated target, a beam splitter, an objective or collimating lens, and a viewer or detector (described in more detail below) at a viewing plane. The target and the viewing planes are focal planes of the lens. Target light reflected by the datum mirror is imaged on the viewing plane at unit magnification by the collimating lens. If the normal to the datum mirror is parallel to the optical axis of the autocollimator, then the target image is centered on the viewing plane. Any angular deviation of the normal from the optical axis manifests itself as a lateral displacement of the target image from the center. The magnitude of the displacement is proportional to the focal length and to the magnitude (assumed to be small) of the angular deviation. The direction of the displacement is perpendicular to the axis about which the

  12. Absolute airborne gravimetry

    NASA Astrophysics Data System (ADS)

    Baumann, Henri

    This work consists of a feasibility study of a first stage prototype airborne absolute gravimeter system. In contrast to relative systems, which are using spring gravimeters, the measurements acquired by absolute systems are uncorrelated and the instrument is not suffering from problems like instrumental drift, frequency response of the spring and possible variation of the calibration factor. The major problem we had to resolve were to reduce the influence of the non-gravitational accelerations included in the measurements. We studied two different approaches to resolve it: direct mechanical filtering, and post-processing digital compensation. The first part of the work describes in detail the different mechanical passive filters of vibrations, which were studied and tested in the laboratory and later in a small truck in movement. For these tests as well as for the airborne measurements an absolute gravimeter FG5-L from Micro-G Ltd was used together with an Inertial navigation system Litton-200, a vertical accelerometer EpiSensor, and GPS receivers for positioning. These tests showed that only the use of an optical table gives acceptable results. However, it is unable to compensate for the effects of the accelerations of the drag free chamber. The second part describes the strategy of the data processing. It is based on modeling the perturbing accelerations by means of GPS, EpiSensor and INS data. In the third part the airborne experiment is described in detail, from the mounting in the aircraft and data processing to the different problems encountered during the evaluation of the quality and accuracy of the results. In the part of data processing the different steps conducted from the raw apparent gravity data and the trajectories to the estimation of the true gravity are explained. A comparison between the estimated airborne data and those obtained by ground upward continuation at flight altitude allows to state that airborne absolute gravimetry is feasible and

  13. 2,5-disubstituted oxazole research: fluorescence quantum yields and laser conversion efficiencies of 2-(p-italic-biphenyl)-5-phenyl oxazole and its 5-p-italic-substituted derivatives

    SciTech Connect

    Yu Peifeng

    1986-03-01

    The fluorescence quantum yield and laser conversion efficiency of 2-(p-italic-biphenyl)-5-phenyl-oxazole and thirteen 5-substituted phenyl derivatives are measured. A brief discussion is also given on the relation between the subtituent effects and spectral properties of the compounds.

  14. Dopamine-functionalized InP/ZnS quantum dots as fluorescence probes for the detection of adenosine in microfluidic chip

    PubMed Central

    Ankireddy, Seshadri Reddy; Kim, Jongsung

    2015-01-01

    Microbeads are frequently used as solid supports for biomolecules such as proteins and nucleic acids in heterogeneous microfluidic assays. Chip-based, quantum dot (QD)-bead-biomolecule probes have been used for the detection of various types of DNA. In this study, we developed dopamine (DA)-functionalized InP/ZnS QDs (QDs-DA) as fluorescence probes for the detection of adenosine in microfluidic chips. The photoluminescence (PL) intensity of the QDs-DA is quenched by Zn2+ because of the strong coordination interactions. In the presence of adenosine, Zn2+ cations preferentially bind to adenosine, and the PL intensity of the QDs-DA is recovered. A polydimethylsiloxane-based microfluidic chip was fabricated, and adenosine detection was confirmed using QDs-DA probes. PMID:26347351

  15. Slow-Injection Growth of Seeded CdSe/CdS Nanorods with Unity Fluorescence Quantum Yield and Complete Shell to Core Energy Transfer.

    PubMed

    Coropceanu, Igor; Rossinelli, Aurelio; Caram, Justin R; Freyria, Francesca S; Bawendi, Moungi G

    2016-03-22

    A two-step process has been developed for growing the shell of CdSe/CdS core/shell nanorods. The method combines an established fast-injection-based step to create the initial elongated shell with a second slow-injection growth that allows for a systematic variation of the shell thickness while maintaining a high degree of monodispersity at the batch level and enhancing the uniformity at the single-nanorod level. The second growth step resulted in nanorods exhibiting a fluorescence quantum yield up to 100% as well as effectively complete energy transfer from the shell to the core. This improvement suggests that the second step is associated with a strong suppression of the nonradiative channels operating both before and after the thermalization of the exciton. This hypothesis is supported by the suppression of a defect band, ubiquitous to CdSe-based nanocrystals after the second growth.

  16. Cysteamine CdS quantum dots decorated with Fe3+ as a fluorescence sensor for the detection of PPi

    NASA Astrophysics Data System (ADS)

    Noipa, Tuanjai; Ngamdee, Kessarin; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2014-01-01

    A new sensitive and selective fluorescence sensor for the detection of pyrophosphate (PPi) in aqueous media based on the Fe3+ decorated cysteamine CdS QDs ([Cys-CdS QDs]-Fe3+) was proposed. The presence of PPi can induce the fluorescence quenching of [Cys-CdS QDs]-Fe3+ due to the high formation constants between the phosphate group and Fe3+. Because the complex between Fe3+ and PPi acts as an efficient quencher, the concentration of PPi can be evaluated by tracking the degree of fluorescence quenching. The fabricated sensor was optimized to obtain the best sensor selectivity and sensitivity. Under optimal conditions, a linear relationship between the fluorescence response and the concentration of PPi was established in the range of 0.5-10 μM. The limits of detection and quantitation for PPi were found to be 0.11 and 2.78 μM, respectively. Furthermore, the proposed sensor exhibited high selectivity toward PPi relative to other common anions. The proposed sensor was successfully applied to the detection of PPi in urine samples with satisfactory results.

  17. A general solid-state synthesis of chemically-doped fluorescent graphene quantum dots for bioimaging and optoelectronic applications.

    PubMed

    Ma, Chong-Bo; Zhu, Zhen-Tong; Wang, Hang-Xing; Huang, Xiao; Zhang, Xiao; Qi, Xiaoying; Zhang, Hao-Li; Zhu, Yihan; Deng, Xia; Peng, Yong; Han, Yu; Zhang, Hua

    2015-06-14

    Graphene quantum dots (GQDs) have attracted increasing interest because of their excellent properties such as strong photoluminescence, excellent biocompatibility and low cost. Herein, we develop a general method for the synthesis of doped and undoped GQDs, which relies on direct carbonization of organic precursors in the solid state.

  18. Absolute-structure reports.

    PubMed

    Flack, Howard D

    2013-08-01

    All the 139 noncentrosymmetric crystal structures published in Acta Crystallographica Section C between January 2011 and November 2012 inclusive have been used as the basis of a detailed study of the reporting of absolute structure. These structure determinations cover a wide range of space groups, chemical composition and resonant-scattering contribution. Defining A and D as the average and difference of the intensities of Friedel opposites, their level of fit has been examined using 2AD and selected-D plots. It was found, regardless of the expected resonant-scattering contribution to Friedel opposites, that the Friedel-difference intensities are often dominated by random uncertainty and systematic error. An analysis of data collection strategy is provided. It is found that crystal-structure determinations resulting in a Flack parameter close to 0.5 may not necessarily be from crystals twinned by inversion. Friedifstat is shown to be a robust estimator of the resonant-scattering contribution to Friedel opposites, very little affected by the particular space group of a structure nor by the occupation of special positions. There is considerable confusion in the text of papers presenting achiral noncentrosymmetric crystal structures. Recommendations are provided for the optimal way of treating noncentrosymmetric crystal structures for which the experimenter has no interest in determining the absolute structure.

  19. Fluorescence properties of alloyed ZnSeS quantum dots overcoated with ZnTe and ZnTe/ZnS shells

    NASA Astrophysics Data System (ADS)

    Adegoke, Oluwasesan; Mashazi, Philani; Nyokong, Tebello; Forbes, Patricia B. C.

    2016-04-01

    Fluorescent alloyed ternary ZnSeS quantum dots (QDs) have been synthesized via the pyrolysis of organometallic precursors. The effects of passivation of ZnTe and ZnTe/ZnS shells on the optical properties of the ternary alloyed ZnSeS core have been studied. A ligand exchange reaction using L-cysteine as a capping ligand was used to obtain water-soluble nanocrystals. The nanocrystals were each characterized by UV/vis absorption and fluorescence spectroscopy, transmission electron microscopy, X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The photoluminescence (PL) quantum yield (QY) of alloyed ZnSeS QDs was 14% and this value increased to 27% when ZnTe was overcoated around the surface but further coating with a ZnS shell decreased the PL QY slightly to 24%. This implies that ZnTe shell suppressed non-radiative recombination exciton states in the alloyed core while further layering with a ZnS shell offered no further improvement in suppressing the defect states. XPS analysis confirmed the presence of the first shell layering but showed a weakened intensity signal of S (2p) and Se (3d) for the ZnSeS/ZnTe/ZnS QDs. Our work demonstrates for the first time that shell passivation of alloyed Zn-based QDs can offer improved optical properties. We hope the optical information presented in this work will be useful in the selection of alloyed Zn-based QDs appropriate for the intended application.

  20. Synthesis and characterization of novel molecularly imprinted polymer - coated Mn-doped ZnS quantum dots for specific fluorescent recognition of cocaine.

    PubMed

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

    2016-01-15

    Mn-doped ZnS quantum dots (QDs) coated with a molecularly imprinted polymer (MIP) material selective toward cocaine and its metabolites have been prepared and applied to cocaine (COC) and metabolites assessment by spectrofluorimetry. Ultrasound irradiation (37kHz) was novelty used for performing the Mn-doped ZnS QDs synthesis as well as for preparing the QD based MIP-coated composite by precipitation polymerization (imprinting process). This fact allowed the synthesis to be accomplished in four hours. In addition, the use of ultrasound irradiation during MIP-QDs synthesis increased the homogeneity of the QDs size, and reduced nanoparticles agglomeration. MIP was synthesized using COC as a template molecule, ethylene dimethacrylate (EDMA) as a functional monomer, divinylbenzene (DVB) as a cross-linker, and 2,2'-azobisisobutyronitrile (AIBN) as an initiator. The fluorescence of MIP-coated QDs was quenched by the template (COC) and also by metabolites from COC such as benzoylecgonine (BZE), and ecgonine methyl ester (EME). Quenching was not observed when performing experiments with non-imprinted polymer (NIP)-coated QDs; and also, fluorescence quenching of MIP-coated QDs was not observed by other drugs of abuse and metabolites (heroin and cannabis abuse). This fact indicates that the prepared material recognize only COC (template) and metabolites.

  1. Vibronic coupling in molecular crystals: A Franck-Condon Herzberg-Teller model of H-aggregate fluorescence based on quantum chemical cluster calculations

    SciTech Connect

    Wykes, M. Parambil, R.; Gierschner, J.; Beljonne, D.

    2015-09-21

    Here, we present a general approach to treating vibronic coupling in molecular crystals based on atomistic simulations of large clusters. Such clusters comprise model aggregates treated at the quantum chemical level embedded within a realistic environment treated at the molecular mechanics level. As we calculate ground and excited state equilibrium geometries and vibrational modes of model aggregates, our approach is able to capture effects arising from coupling to intermolecular degrees of freedom, absent from existing models relying on geometries and normal modes of single molecules. Using the geometries and vibrational modes of clusters, we are able to simulate the fluorescence spectra of aggregates for which the lowest excited state bears negligible oscillator strength (as is the case, e.g., ideal H-aggregates) by including both Franck-Condon (FC) and Herzberg-Teller (HT) vibronic transitions. The latter terms allow the adiabatic excited state of the cluster to couple with vibrations in a perturbative fashion via derivatives of the transition dipole moment along nuclear coordinates. While vibronic coupling simulations employing FC and HT terms are well established for single-molecules, to our knowledge this is the first time they are applied to molecular aggregates. Here, we apply this approach to the simulation of the low-temperature fluorescence spectrum of para-distyrylbenzene single-crystal H-aggregates and draw comparisons with coarse-grained Frenkel-Holstein approaches previously extensively applied to such systems.

  2. A selective determination of copper ions in water samples based on the fluorescence quenching of thiol-capped CdTe quantum dots.

    PubMed

    Nurerk, Piyaluk; Kanatharana, Proespichaya; Bunkoed, Opas

    2016-03-01

    CdTe quantum dots (QDs) capped with different stabilizers, i.e. thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA) and glutathione (GSH) were investigated as fluorescent probes for the determination of Cu(2+). The stabilizer was shown to play an important role in both the sensitivity and selectivity for the determination of Cu(2+). TGA-capped CdTe QDs showed the highest sensitivity, followed by the MPA and GSH-capped CdTe QDs, respectively. The TGA- and MPA-capped CdTe QDs were not selective for Cu(2+) that was affected by Ag(+). The GSH-capped CdTe QDs were insensitive to Ag(+) and were used to determine Cu(2+) in water samples. Under optimal conditions, quenching of the fluorescence intensity (F0/F) increased linearly with the concentration of Cu(2+) over a range of 0.10-4.0 µg/mL and the detection limit was 0.06 µg/mL. The developed method was successfully applied to the determination of Cu(2+) in water samples. Good recoveries of 93-104%, with a relative standard deviation of < 6% demonstrated that the developed simple method was accurate and reliable. The quenching mechanisms were also described.

  3. Fluorescence reports intact quantum dot uptake into roots and translocation to leaves of Arabidopsis thaliana and subsequent ingestion by insect herbivores.

    PubMed

    Koo, Yeonjong; Wang, Jing; Zhang, Qingbo; Zhu, Huiguang; Chehab, E Wassim; Colvin, Vicki L; Alvarez, Pedro J J; Braam, Janet

    2015-01-06

    We explored the impact of quantum dot (QD) coat characteristics on NP stability, uptake, and translocation in Arabidopsis thaliana, and subsequent transfer to primary consumers, Trichoplusia ni (T. ni). Arabidopsis was exposed to CdSe/CdZnS QDs with three different coatings: Poly(acrylic acid-ethylene glycol) (PAA-EG), polyethylenimine (PEI) and poly(maleic anhydride-alt-1-octadecene)-poly(ethylene glycol) (PMAO-PEG), which are anionic, cationic, and relatively neutral, respectively. PAA-EG-coated QDs were relatively stable and taken up from a hydroponic medium through both Arabidopsis leaf petioles and roots, without apparent aggregation, and showed generally uniform distribution in leaves. In contrast, PEI- and PMAO-PEG-coated QDs displayed destabilization in the hydroponic medium, and generated particulate fluorescence plant tissues, suggesting aggregation. PAA-EG QDs moved faster than PEI QDs through leaf petioles; however, 8-fold more cadmium accumulated in PEI QD-treated leaves than in those exposed to PAA-EG QDs, possibly due to PEI QD dissolution and direct metal uptake. T. ni caterpillars that fed on Arabidopsis exposed to QDs had reduced performance, and QD fluorescence was detected in both T. ni bodies and frass, demonstrating trophic transfer of intact QDs from plants to insects. Overall, this paper demonstrates that QD coat properties influence plant nanoparticle uptake and translocation and can impact transfer to herbivores.

  4. Water soluble and efficient amino acid Schiff base receptor for reversible fluorescence turn-on detection of Zn2+ ions: Quantum chemical calculations and detection of bacteria

    NASA Astrophysics Data System (ADS)

    Subha, L.; Balakrishnan, C.; Natarajan, Satheesh; Theetharappan, M.; Subramanian, Balanehru; Neelakantan, M. A.

    2016-01-01

    An amino acid Schiff base (R) capable of recognizing Zn2+ ions selectively and sensitively in an aqueous medium was prepared and characterized. Upon addition of Zn2+ ions, the receptor exhibits fluorescence intensity enhancements ( 40 fold) at 460 nm (quantum yield, Φ = 0.05 for R and Φ = 0.18 for R-Zn2+) and can be detected by naked eye under UV light. The receptor can recognize the Zn2+ (1.04 × 10- 8 M) selectively for other metal ions in the pH range of 7.5-11. The Zn2+ chelation with R decreases the loss of energy through non-radiative transition and leads to fluorescence enhancement. The binding mode of the receptor with Zn2+ was investigated by 1H NMR titration and further validated by ESI-MS. The elemental color mapping and SEM/EDS analysis were also used to study the binding of R with Zn2+. Density functional theory calculations were carried out to understand the binding mechanism. The receptor was applied as a microbial sensor for Escherichia coli and Staphylococcus aureus.

  5. Fluorescent/magnetic micro/nano-spheres based on quantum dots and/or magnetic nanoparticles: preparation, properties, and their applications in cancer studies.

    PubMed

    Wen, Cong-Ying; Xie, Hai-Yan; Zhang, Zhi-Ling; Wu, Ling-Ling; Hu, Jiao; Tang, Man; Wu, Min; Pang, Dai-Wen

    2016-07-07

    The study of cancer is of great significance to human survival and development, due to the fact that cancer has become one of the greatest threats to human health. In recent years, the rapid progress of nanoscience and nanotechnology has brought new and bright opportunities to this field. In particular, the applications of quantum dots (QDs) and magnetic nanoparticles (MNPs) have greatly promoted early diagnosis and effective therapy of cancer. In this review, we focus on fluorescent/magnetic micro/nano-spheres based on QDs and/or MNPs (we may call them "nanoparticle-sphere (NP-sphere) composites") from their preparation to their bio-application in cancer research. Firstly, we outline and compare the main four kinds of methods for fabricating NP-sphere composites, including their design principles, operation processes, and characteristics (merits and limitations). The NP-sphere composites successfully inherit the unique fluorescence or magnetic properties of QDs or MNPs. Moreover, compared with the nanoparticles (NPs) alone, the NP-sphere composites show superior properties, which are also discussed in this review. Then, we summarize their recent applications in cancer research from three aspects, that is: separation and enrichment of target tumor cells or biomarkers; cancer diagnosis mainly through medical imaging or tumor biomarker detection; and cancer therapy via targeted drug delivery systems. Finally, we provide some perspectives on the future challenges and development trends of the NP-sphere composites.

  6. Vibronic coupling in molecular crystals: A Franck-Condon Herzberg-Teller model of H-aggregate fluorescence based on quantum chemical cluster calculations.

    PubMed

    Wykes, M; Parambil, R; Beljonne, D; Gierschner, J

    2015-09-21

    Here, we present a general approach to treating vibronic coupling in molecular crystals based on atomistic simulations of large clusters. Such clusters comprise model aggregates treated at the quantum chemical level embedded within a realistic environment treated at the molecular mechanics level. As we calculate ground and excited state equilibrium geometries and vibrational modes of model aggregates, our approach is able to capture effects arising from coupling to intermolecular degrees of freedom, absent from existing models relying on geometries and normal modes of single molecules. Using the geometries and vibrational modes of clusters, we are able to simulate the fluorescence spectra of aggregates for which the lowest excited state bears negligible oscillator strength (as is the case, e.g., ideal H-aggregates) by including both Franck-Condon (FC) and Herzberg-Teller (HT) vibronic transitions. The latter terms allow the adiabatic excited state of the cluster to couple with vibrations in a perturbative fashion via derivatives of the transition dipole moment along nuclear coordinates. While vibronic coupling simulations employing FC and HT terms are well established for single-molecules, to our knowledge this is the first time they are applied to molecular aggregates. Here, we apply this approach to the simulation of the low-temperature fluorescence spectrum of para-distyrylbenzene single-crystal H-aggregates and draw comparisons with coarse-grained Frenkel-Holstein approaches previously extensively applied to such systems.

  7. Vibronic coupling in molecular crystals: A Franck-Condon Herzberg-Teller model of H-aggregate fluorescence based on quantum chemical cluster calculations

    NASA Astrophysics Data System (ADS)

    Wykes, M.; Parambil, R.; Beljonne, D.; Gierschner, J.

    2015-09-01

    Here, we present a general approach to treating vibronic coupling in molecular crystals based on atomistic simulations of large clusters. Such clusters comprise model aggregates treated at the quantum chemical level embedded within a realistic environment treated at the molecular mechanics level. As we calculate ground and excited state equilibrium geometries and vibrational modes of model aggregates, our approach is able to capture effects arising from coupling to intermolecular degrees of freedom, absent from existing models relying on geometries and normal modes of single molecules. Using the geometries and vibrational modes of clusters, we are able to simulate the fluorescence spectra of aggregates for which the lowest excited state bears negligible oscillator strength (as is the case, e.g., ideal H-aggregates) by including both Franck-Condon (FC) and Herzberg-Teller (HT) vibronic transitions. The latter terms allow the adiabatic excited state of the cluster to couple with vibrations in a perturbative fashion via derivatives of the transition dipole moment along nuclear coordinates. While vibronic coupling simulations employing FC and HT terms are well established for single-molecules, to our knowledge this is the first time they are applied to molecular aggregates. Here, we apply this approach to the simulation of the low-temperature fluorescence spectrum of para-distyrylbenzene single-crystal H-aggregates and draw comparisons with coarse-grained Frenkel-Holstein approaches previously extensively applied to such systems.

  8. A highly selective and simple fluorescent sensor for mercury (II) ion detection based on cysteamine-capped CdTe quantum dots synthesized by the reflux method.

    PubMed

    Ding, Xiaojie; Qu, Lingbo; Yang, Ran; Zhou, Yuchen; Li, Jianjun

    2015-06-01

    Cysteamine (CA)-capped CdTe quantum dots (QDs) (CA-CdTe QDs) were prepared by the reflux method and utilized as an efficient nano-sized fluorescent sensor to detect mercury (II) ions (Hg(2+) ). Under optimum conditions, the fluorescence quenching effect of CA-CdTe QDs was linear at Hg(2+) concentrations in the range of 6.0-450 nmol/L. The detection limit was calculated to be 4.0 nmol/L according to the 3σ IUPAC criteria. The influence of 10-fold Pb(2+) , Cu(2+) and Ag(+) on the determination of Hg(2+) was < 7% (superior to other reports based on crude QDs). Furthermore, the detection sensitivity and selectivity were much improved relative to a sensor based on the CA-CdTe QDs probe, which was prepared using a one-pot synthetic method. This CA-CdTe QDs sensor system represents a new feasibility to improve the detection performance of a QDs sensor by changing the synthesis method.

  9. Fluorescent/magnetic micro/nano-spheres based on quantum dots and/or magnetic nanoparticles: preparation, properties, and their applications in cancer studies

    NASA Astrophysics Data System (ADS)

    Wen, Cong-Ying; Xie, Hai-Yan; Zhang, Zhi-Ling; Wu, Ling-Ling; Hu, Jiao; Tang, Man; Wu, Min; Pang, Dai-Wen

    2016-06-01

    The study of cancer is of great significance to human survival and development, due to the fact that cancer has become one of the greatest threats to human health. In recent years, the rapid progress of nanoscience and nanotechnology has brought new and bright opportunities to this field. In particular, the applications of quantum dots (QDs) and magnetic nanoparticles (MNPs) have greatly promoted early diagnosis and effective therapy of cancer. In this review, we focus on fluorescent/magnetic micro/nano-spheres based on QDs and/or MNPs (we may call them ``nanoparticle-sphere (NP-sphere) composites'') from their preparation to their bio-application in cancer research. Firstly, we outline and compare the main four kinds of methods for fabricating NP-sphere composites, including their design principles, operation processes, and characteristics (merits and limitations). The NP-sphere composites successfully inherit the unique fluorescence or magnetic properties of QDs or MNPs. Moreover, compared with the nanoparticles (NPs) alone, the NP-sphere composites show superior properties, which are also discussed in this review. Then, we summarize their recent applications in cancer research from three aspects, that is: separation and enrichment of target tumor cells or biomarkers; cancer diagnosis mainly through medical imaging or tumor biomarker detection; and cancer therapy via targeted drug delivery systems. Finally, we provide some perspectives on the future challenges and development trends of the NP-sphere composites.

  10. Quantum dot immunoassays in renewable surface column and 96-well plate formats for the fluorescence detection of Botulinum neurotoxin using high-affinity antibodies

    SciTech Connect

    Warner, Marvin G.; Grate, Jay W.; Tyler, Abby J.; Ozanich, Richard M.; Miller, Keith D.; Lou, Jianlong; Marks, James D.; Bruckner-Lea, Cindy J.

    2009-09-01

    A fluorescence sandwich immunoassay using high affinity antibodies and quantum dot (QD) reporters has been developed for detection of botulinum toxin serotype A (BoNT/A). For the development of the assay, a nontoxic recombinant fragment of the holotoxin (BoNT/A-HC-fragment) has been used as a structurally valid simulant for the full toxin molecule. The antibodies used, AR4 and RAZ1, bind to nonoverlapping epitopes present on both the full toxin and on the recombinant fragment. In one format, the immunoassay is carried out in a 96-well plate with detection in a standard plate reader. Detection down to 31 pM of the BoNT/Hc-fragment was demonstrated with a total incubation time of 3 hours, using AR4 as the capture antibody and QD-coupled RAZ1 as the reporter. In a second format, the AR4 capture antibody was coupled to Sepharose beads, and the immunochemical reactions were carried out in microcentrifuge tubes with an incubation time of 1 hour. These beads were subsequently captured and concentrated in a rotating rod “renewable surface” flow cell as part of a sequential injection fluidic system. This flow cell was equipped with a fiber optic system for fluorescence measurements. In PBS buffer solution matrix, the BoNT/A-HC-fragment was detected to concentrations as low as 5 pM using the fluidic measurement approach.

  11. A novel fluorescent probe for copper ions based on polymer-modified CdSe/CdS core/shell quantum dots.

    PubMed

    Cao, Zhong; Gu, Zheng; Zeng, Ju-Lan; Liu, Jin-Hua; Deng, Qin; Fan, Jun-Bing; Xiang, Jian-Nan

    2011-01-01

    Quantum dots (QDs) have become one of the most attractive fields of current research because of their unique optical properties. Novel copper-sensitive fluorescent fluoroionophores based on CdSe/CdS core/shell QDs modified with a polymer of MAO-mPEG were synthesized and characterized in the present work. A pH of 6.47 was optimally selected for measurements. By modifying QDs with MAO-mPEG, significant aqueous fluorescence quenching was observed upon binding with copper ions involving both reduced and oxidized environments, indicating great sensitivity and specificity for copper-ion sensing. No significant interfering effects from other metal ions, such as Ag(+), Al(3+), Ba(2+), Ca(2+), Cd(2+), Co(2+), Cr(3+), Fe(2+), Fe(3+), Hg(2+), K(+), Mg(2+), Mn(2+), Na(+), Ni(2+), Pb(2+), Sn(2+), and Zn(2+), were observed. The linear response range for Cu(2+) was found to be 0.01-0.50 µM, and the limit of detection was evaluated to be 16 nM. The proposed method demonstrated improved sensitivity and selectivity characteristics for Cu(II) determinations based on CdSe/CdS core/shell QDs modified with MAO-mPEG by using a typical liquid-phase quenching assay, showing its potential application to multiplex sensing of different analytes through distinct ligand conjugation and functionalization of individual fluorophores.

  12. Strong two-photon-induced fluorescence from photostable, biocompatible nitrogen-doped graphene quantum dots for cellular and deep-tissue imaging.

    PubMed

    Liu, Qian; Guo, Beidou; Rao, Ziyu; Zhang, Baohong; Gong, Jian Ru

    2013-06-12

    Bright two-photon fluorescent probes are highly desirable to be able to optically probe biological activities deep inside living organisms with larger imaging depth, minor autofluorescence background, and less photodamage. In this study, we report the biocompatible nitrogen-doped graphene quantum dots (N-GQDs) as efficient two-photon fluorescent probes for cellular and deep-tissue imaging. The N-GQD was prepared by a facile solvothermal method using dimethylformamide as a solvent and nitrogen source. The two-photon absorption cross-section of N-GQD reaches 48,000 Göppert-Mayer units, which far surpasses that of the organic dyes and is comparable to that of the high performance semiconductor QDs, achieving the highest value ever reported for carbon-based nanomaterials. More importantly, a study of penetration depth in tissue phantom demonstrates that the N-GQD can achieve a large imaging depth of 1800 μm, significantly extending the fundamental two-photon imaging depth limit. In addition, the N-GQD is nontoxic to living cells and exhibits super photostability under repeated laser irradiation. The high two-photon absorption cross-section, large imaging depth, good biocompatibility, and extraordinary photostability render the N-GQD an attractive alternative probe for efficient two-photon imaging in biological and biomedical applications.

  13. Hydrothermal synthesis of high-quality type-II CdTe/CdSe quantum dots with near-infrared fluorescence.

    PubMed

    Wang, Jing; Han, Heyou

    2010-11-01

    A simple hydrothermal method is developed for the synthesis of high-quality, water-soluble, and near-infrared (NIR)-emitting type-II core/shell CdTe/CdSe quantum dots (QDs) by employing thiol-capped CdTe QDs as core templates and CdCl(2) and Na(2)SeO(3) as shell precursors. Compared with the original CdTe core QDs, the core/shell CdTe/CdSe QDs exhibit an obvious red-shifted emission, whose color can be tuned between visible and NIR regions (620-740 nm) by controlling the thickness of the CdSe shell. The photoluminescence quantum yield (PL QY) of CdTe/CdSe QDs with an optimized thickness of the CdSe shell can reach up to 44.2% without any post-preparative treatment. Through a thorough study of the core/shell structure by high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible (UV-vis) absorption spectra, fluorescence spectra, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the as-prepared CdTe/CdSe QDs demonstrate good monodispersity, hardened lattice structure and excellent photostability, offering a great potential for biological application.

  14. Facile preparation of Gd3+ doped carbon quantum dots: Photoluminescence materials with magnetic resonance response as magnetic resonance/fluorescence bimodal probes

    NASA Astrophysics Data System (ADS)

    Ren, X. Y.; Yuan, X. X.; Wang, Y. P.; Liu, C. L.; Qin, Y.; Guo, L. P.; Liu, L. H.

    2016-07-01

    There are a few bimodal molecular imaging probes constructed by gadolinium (3+) ions in combination with carbon quantum dots (CQDs), and the reported ones show such obvious drawbacks as low luminous efficiency and weak MRI contrast. In the paper, a kind of CQDs photoluminescence materials with magnetic resonance response was prepared by hydrothermal method and employing gadopentetate monomeglumine (GdPM) as a precusor. Here, the GdPM plays a role of not only carbon source, but also gadolinium (3+) sources. When the GdPM aqueous solution with a concentration of 4 mg mL-1 was pyrolyzed under 220 °C and 2.0 MPa for 8 h, an optimal CQDs was obtained which are doped with gadolinium (3+) ions in both chelates and Gd2O3 (named as Gd3+-CQDs). The average diameter of the Gd3+-CQDs is about 1.6 nm, which show a high photoluminescence quantum yield of 7.1%, as well as high longitudinal relaxivity (r1) of 9.87 mM-1 s-1. And owing to the unconspicuous cell toxicity, the Gd3+-CQDs show big possibility for clinical application in magnetic resonance/fluorescence bimodal molecular imaging.

  15. Folic acid-conjugated core/shell ZnS:Mn/ZnS quantum dots as targeted probes for two photon fluorescence imaging of cancer cells.

    PubMed

    Geszke, Malgorzata; Murias, Marek; Balan, Lavinia; Medjahdi, Ghouti; Korczynski, Jaroslaw; Moritz, Michal; Lulek, Janina; Schneider, Raphaël

    2011-03-01

    This work presents a novel approach to producing water soluble manganese-doped core/shell ZnS/ZnS quantum dots (ZnS:Mn/ZnS). The Mn-doped ZnS core was prepared through a nucleation doping strategy and a ZnS shell was grown on ZnS:Mn d-dots by decomposition of Zn(2+)-3-mercaptopropionic acid (MPA) complexes at 100 °C. It was found that the Mn2+(4)T1→6A1 fluorescence emission at ∼590 nm significantly increased after growth of the shell when the Mn2+ doping content was 4.0 at.%. A photoluminescence quantum yield of ∼22% was obtained for core/shell nanocrystals. The nanoparticles were structurally and compositionally characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and dynamic light scattering. The surface MPA molecules favor the dispersion of ZnS:Mn/ZnS QDs in aqueous media and make possible conjugation with targeting folic acid molecules. The folate receptor-mediated delivery of folic acid-conjugated ZnS:Mn/ZnS QDs was demonstrated using confocal microscopy with biphotonic excitation. Bare and folate-conjugated QDs exhibit only weak cytotoxicity towards folate receptor-positive T47D cancer cells and MCF-7 cells, used as a reference, at high concentrations (mmolar range) after 72h incubation.

  16. Cancer Cell Targeting Using Folic Acid/Anti-HER2 Antibody Conjugated Fluorescent CdSe/CdS/ZnS-MPA and CdTe-MSA Quantum Dots.

    PubMed

    Singh, Gurpal; Kumar, Manoj; Soni, Udit; Arora, Vikas; Bansal, Vivek; Gupta, Dikshi; Bhat, Madhusudan; Dinda, Amit K; Sapra, Sameer; Singh, Harpal

    2015-12-01

    CdSe/CdS/ZnS and CdTe quantum dots (QDs) were synthesized by successive ion layer adsorption and reaction (SILAR) technique and direct aqueous synthesis respectively using thiol stabilizers. Synthesized CdSe/CdS/ZnS and CdTe QDs stabilized with 3-mercaptopropionic acid (MPA) and mercaptosuccinic acid (MSA) were used as fluorescent labels after conjugation with folic acid (FA) and anti-HER2 antibodies. Photoluminescence quantum yield of folated CdSe/CdS/ZnS-MPA and CdTe-MSA QDs was 59% and 77% than that of non-folated hydrophilic QDs. The folate receptor-mediated delivery of folic acid-conjugated CdTe-MSA and CdSe/CdS/ZnS-MPA QDs showed higher cellular internalization as observed by confocal laser scanning microscopic studies. Folated and non-folated CdTe-MSA QDs were highly toxic and exhibited only 10% cell viability as compared to > 80% cell viability with CdSe/CdS/ZnS-MPA QDs over the concentration ranging from 3.38 to 50 pmoles. Immunohistochemistry (IHC) results of human breast cancer tissue samples showed positive results with anti-HER2 antibody conjugated CdSe/CdS/ZnS-MPA QDs with better sensitivity and specificity as compared to conventional IHC analysis using diaminobenzedene staining.

  17. Bioresponsive Release System for Visual Fluorescence Detection of Carcinoembryonic Antigen from Mesoporous Silica Nanocontainers Mediated Optical Color on Quantum Dot-Enzyme-Impregnated Paper.

    PubMed

    Qiu, Zhenli; Shu, Jian; Tang, Dianping

    2017-04-12

    An all-in-one paper-based analytical device (PAD) was successfully developed for visual fluorescence detection of carcinoembryonic antigen (CEA) on CdTe/CdSe quantum dot (QD)-enzyme-impregnated paper by coupling with a bioresponsive controlled-release system from DNA-gated mesoporous silica nanocontainers (MSNs). The assay was carried out in a centrifuge tube by using glucose-loaded MSNs with a CEA aptamer and a QD-enzyme-paper attached on the lid. Initially, single-strand complementary DNA to a CEA aptamer was covalently conjugated to the aminated MSN, and then glucose (enzyme substrate) molecules were gated into the pore with the help of the aptamer. Glucose oxidase (GOD) and CdTe/CdSe QDs were coimmobilized on paper for the visual fluorescence signal output. Upon target CEA introduction in the detection cell, the analyte specifically reacted with the immobilized aptamer on the MSN to open the pore, thereby resulting in the glucose release. The released glucose was oxidized by the immobilized GOD on paper to produce gluconic acid and hydrogen peroxide, and the latter quenched the fluorescence of CdTe/CdSe QDs, which could be determined by the naked eye on a portable smartphone and a commercial fluorospectrometer. Under optimal conditions, the PAD-based sensing system enabled sensitive discrimination of target CEA against other biomarkers or proteins in a linear range of 0.05-20 ng mL(-1) with a limit of detection of 6.7 pg mL(-1) (ppt). In addition, our strategy displayed high specificity, good reproducibility, and acceptable accuracy for analyzing human serum specimens with a commercial human CEA ELISA kit. Importantly, this methodology offers promise for simple analysis of biological samples and is suitable for use in the mass production of miniaturized devices, thus opening new opportunities for protein diagnostics and biosecurity.

  18. Investigating the intersystem crossing rate and triplet quantum yield of Protoporphyrin IX by means of pulse train fluorescence technique

    NASA Astrophysics Data System (ADS)

    Gotardo, Fernando; Cocca, Leandro H. Z.; Acunha, Thiago V.; Longoni, Ana; Toldo, Josene; Gonçalves, Paulo F. B.; Iglesias, Bernardo A.; De Boni, Leonardo

    2017-04-01

    Photophysical investigations of PPIX were described in order to determine the triplet conversion efficiency. Time resolved fluorescence and pulse train fluorescence were employed to characterize the main mechanism responsible for deactivation of the first singlet excited state (excited singlet and triplet states). Single pulse and Z-Scan analysis were employed to measure the singlet excited state absorption cross-sections. Theoretical calculations were performed in order to get some properties of PPIX in ground state, first singlet and triplet excited state. A TD-DFT result shows a great possibility of ISC associated to out-of-plane distortions in porphyrinic ring. Furthermore, the B and Q bands in the calculated spectrum are assigned to the four frontier molecular orbitals as proposed by Gouterman for free-based porphyrins.

  19. Absolute Equilibrium Entropy

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    1997-01-01

    The entropy associated with absolute equilibrium ensemble theories of ideal, homogeneous, fluid and magneto-fluid turbulence is discussed and the three-dimensional fluid case is examined in detail. A sigma-function is defined, whose minimum value with respect to global parameters is the entropy. A comparison is made between the use of global functions sigma and phase functions H (associated with the development of various H-theorems of ideal turbulence). It is shown that the two approaches are complimentary though conceptually different: H-theorems show that an isolated system tends to equilibrium while sigma-functions allow the demonstration that entropy never decreases when two previously isolated systems are combined. This provides a more complete picture of entropy in the statistical mechanics of ideal fluids.

  20. Absolute multilateration between spheres

    NASA Astrophysics Data System (ADS)

    Muelaner, Jody; Wadsworth, William; Azini, Maria; Mullineux, Glen; Hughes, Ben; Reichold, Armin

    2017-04-01

    Environmental effects typically limit the accuracy of large scale coordinate measurements in applications such as aircraft production and particle accelerator alignment. This paper presents an initial design for a novel measurement technique with analysis and simulation showing that that it could overcome the environmental limitations to provide a step change in large scale coordinate measurement accuracy. Referred to as absolute multilateration between spheres (AMS), it involves using absolute distance interferometry to directly measure the distances between pairs of plain steel spheres. A large portion of each sphere remains accessible as a reference datum, while the laser path can be shielded from environmental disturbances. As a single scale bar this can provide accurate scale information to be used for instrument verification or network measurement scaling. Since spheres can be simultaneously measured from multiple directions, it also allows highly accurate multilateration-based coordinate measurements to act as a large scale datum structure for localized measurements, or to be integrated within assembly tooling, coordinate measurement machines or robotic machinery. Analysis and simulation show that AMS can be self-aligned to achieve a theoretical combined standard uncertainty for the independent uncertainties of an individual 1 m scale bar of approximately 0.49 µm. It is also shown that combined with a 1 µm m‑1 standard uncertainty in the central reference system this could result in coordinate standard uncertainty magnitudes of 42 µm over a slender 1 m by 20 m network. This would be a sufficient step change in accuracy to enable next generation aerospace structures with natural laminar flow and part-to-part interchangeability.

  1. Challenge to the Charging Model of Semiconductor-Nanocrystal Fluorescence Intermittency from Off-State Quantum Yields and Multiexciton Blinking

    NASA Astrophysics Data System (ADS)

    Zhao, Jing; Nair, Gautham; Fisher, Brent R.; Bawendi, Moungi G.

    2010-04-01

    Semiconductor nanocrystals emit light intermittently; i.e., they “blink,” under steady illumination. The dark periods have been widely assumed to be due to photoluminescence (PL) quenching by an Auger-like process involving a single additional charge present in the nanocrystal. Our results challenge this long-standing assumption. Close examination of exciton PL intensity time traces of single CdSe(CdZnS) core(shell) nanocrystals reveals that the dark state PL quantum yield can be 10 times less than the biexciton PL quantum yield. In addition, we observe spectrally resolved multiexciton emission and find that it also blinks with an on/off ratio greater than 10∶1. These results directly contradict the predictions of the charging model.

  2. Challenge to the Charging Model of Semiconductor-Nanocrystal Fluorescence Intermittency from Off-State Quantum Yields and Multiexciton Blinking

    PubMed Central

    Zhao, Jing; Nair, Gautham; Fisher, Brent R.; Bawendi, Moungi G.

    2012-01-01

    Semiconductor nanocrystals emit light intermittently; i.e., they “blink,” under steady illumination. The dark periods have been widely assumed to be due to photoluminescence (PL) quenching by an Auger-like process involving a single additional charge present in the nanocrystal. Our results challenge this long-standing assumption. Close examination of exciton PL intensity time traces of single CdSe(CdZnS) core (shell) nanocrystals reveals that the dark state PL quantum yield can be 10 times less than the biexciton PL quantum yield. In addition, we observe spectrally resolved multiexciton emission and find that it also blinks with an on/off ratio greater than 10:1. These results directly contradict the predictions of the charging model. PMID:20482016

  3. Challenge to the charging model of semiconductor-nanocrystal fluorescence intermittency from off-state quantum yields and multiexciton blinking.

    PubMed

    Zhao, Jing; Nair, Gautham; Fisher, Brent R; Bawendi, Moungi G

    2010-04-16

    Semiconductor nanocrystals emit light intermittently; i.e., they "blink," under steady illumination. The dark periods have been widely assumed to be due to photoluminescence (PL) quenching by an Auger-like process involving a single additional charge present in the nanocrystal. Our results challenge this long-standing assumption. Close examination of exciton PL intensity time traces of single CdSe(CdZnS) core(shell) nanocrystals reveals that the dark state PL quantum yield can be 10 times less than the biexciton PL quantum yield. In addition, we observe spectrally resolved multiexciton emission and find that it also blinks with an on/off ratio greater than 10:1. These results directly contradict the predictions of the charging model.

  4. Development of steady-state electrical-heating fluorescence-sensing (SEF) technique for thermal characterization of one dimensional (1D) structures by employing graphene quantum dots (GQDs) as temperature sensors

    NASA Astrophysics Data System (ADS)

    Wan, Xiang; Li, Changzheng; Yue, Yanan; Xie, Danmei; Xue, Meixin; Hu, Niansu

    2016-11-01

    A fluorescence signal has been demonstrated as an effective implement for micro/nanoscale temperature measurement which can be realized by either direct fluorescence excitation from materials or by employing nanoparticles as sensors. In this work, a steady-state electrical-heating fluorescence-sensing (SEF) technique is developed for the thermal characterization of one-dimensional (1D) materials. In this method, the sample is suspended between two electrodes and applied with steady-state Joule heating. The temperature response of the sample is monitored by collecting a simultaneous fluorescence signal from the sample itself or nanoparticles uniformly attached on it. According to the 1D heat conduction model, a linear temperature dependence of heating powers is obtained, thus the thermal conductivity of the sample can be readily determined. In this work, a standard platinum wire is selected to measure its thermal conductivity to validate this technique. Graphene quantum dots (GQDs) are employed as the fluorescence agent for temperature sensing. Parallel measurement by using the transient electro-thermal (TET) technique demonstrates that a small dose of GQDs has negligible influence on the intrinsic thermal property of platinum wire. This SEF technique can be applied in two ways: for samples with a fluorescence excitation capability, this method can be implemented directly; for others with weak or no fluorescence excitation, a very small portion of nanoparticles with excellent fluorescence excitation can be used for temperature probing and thermophysical property measurement.

  5. Developing mixed films of immobilized oligonucleotides and quantum dots for the multiplexed detection of nucleic acid hybridization using a combination of fluorescence resonance energy transfer and direct excitation of fluorescence.

    PubMed

    Algar, W Russ; Krull, Ulrich J

    2010-04-20

    Methods have been developed for the simultaneous and selective detection of three target nucleic acid sequences based on mixed films of immobilized quantum dots (QDs) and oligonucleotide probes. CdSe/ZnS QDs were immobilized on optical fibers and conjugated with mixtures of different probe oligonucleotides. Hybridization events were detected using a combination of fluorescence from direct excitation and fluorescence sensitized by resonance energy transfer (FRET). A sandwich assay format was used to associate dye labeled reporter oligonucleotides with probe-target hybrids formed at the surface of the optical fiber. One detection channel utilized direct excitation of Pacific Blue and the two other detection channels were based on FRET. In one strategy, green emitting QDs were used as donors with Cy3 and Rhodamine Red-X acceptors. In a second strategy, green and red emitting QDs were coimmobilized and used as donors with Cy3 and Alexa Fluor 647 acceptors, respectively. Selective three-plex detection was demonstrated with both strategies. Several key design criteria that were explored to optimize the relative signal magnitude between channels included: the ratio of probe associated with direct excitation versus probes associated with FRET; the relative amounts of each FRET probe and corresponding spectral overlap; and the photoluminescence ratio between immobilized green and red emitting QDs (where applicable). Careful selection of probe sequences and lengths were important for the discrimination of single nucleotide polymorphisms in one channel without suppressing binding of target in the other two channels. This work provides a basis for the development of multiplexed biosensors that are ensemble compatible and do not require discrete sensor elements, spatial registration, sorting technology, or single molecule spectroscopy.

  6. Optimizing methods to recover absolute FRET efficiency from immobilized single molecules.

    PubMed

    McCann, James J; Choi, Ucheor B; Zheng, Liqiang; Weninger, Keith; Bowen, Mark E

    2010-08-04

    Microscopy-based fluorescence resonance energy transfer (FRET) experiments measure donor and acceptor intensities by isolating these signals with a series of optical elements. Because this filtering discards portions of the spectrum, the observed FRET efficiency is dependent on the set of filters in use. Similarly, observed FRET efficiency is also affected by differences in fluorophore quantum yield. Recovering the absolute FRET efficiency requires normalization for these effects to account for differences between the donor and acceptor fluorophores in their quantum yield and detection efficiency. Without this correction, FRET is consistent across multiple experiments only if the photophysical and instrument properties remain unchanged. Here we present what is, to our knowledge, the first systematic study of methods to recover the true FRET efficiency using DNA rulers with known fluorophore separations. We varied optical elements to purposefully alter observed FRET and examined protein samples to achieve quantum yields distinct from those in the DNA samples. Correction for calculated instrument transmission reduced FRET deviations, which can facilitate comparison of results from different instruments. Empirical normalization was more effective but required significant effort. Normalization based on single-molecule photobleaching was the most effective depending on how it is applied. Surprisingly, per-molecule gamma-normalization reduced the peak width in the DNA FRET distribution because anomalous gamma-values correspond to FRET outliers. Thus, molecule-to-molecule variation in gamma has an unrecognized effect on the FRET distribution that must be considered to extract information on sample dynamics from the distribution width.

  7. Synthesis of a quantum nanocrystal-gold nanoshell complex for near-infrared generated fluorescence and photothermal decay of luminescence.

    PubMed

    Lin, Adam Y; Young, Joseph K; Nixon, Ariel V; Drezek, Rebekah A

    2014-09-21

    Multifunction nanoparticle complexes have previously been developed to aid physicians in both diagnosis and treatment of cancerous tissue. Here, we designed a nanoparticle complex structure that consists of a plasmonically active hollow gold nanoshell core surrounded by photoluminescent quantum nanocrystals (QNs) in the form of PbS encapsulated by a silica layer. There are three main design variables including HGN synthesis and optical tuning, formation of the silica layer on the hollow gold nanoshell surface, and fabrication and photoluminescence tuning of PbS quantum nanocrystals. The hollow gold nanoshells were deliberately designed to function in the optical regimes that maximize tissue transmissivity (800 nm) and minimize tissue absorption (1100 nm). Secondly, several chemical ligands were tested such as (3-mercaptopropyl)trimethoxysilane and mercaptoundecanoic acid for controlled growth of the silica layer. Last, PbS QNs were synthesized and optimized with various capping agents, where the nanocrystals excited at the same wavelength were used to activate the photothermal properties of the hollow gold nanoshells. Upon irradiation of the complex with a lower power 800 nm laser, the nanocrystals luminesce at 1100 nm. At ablative temperatures the intrinsic luminescent properties of the QNs are altered and the luminescent output is significantly reduced (>70%). While this paper focuses on synthesis and optimization of the QN-HGN complex, in the future we believe that this novel particle complex design may have the potential to serve as a triple theranostic agent, which will aid satellite tumor localization, photothermal treatment, and ablative confirmation.

  8. Lyman alpha SMM/UVSP absolute calibration and geocoronal correction

    NASA Technical Reports Server (NTRS)

    Fontenla, Juan M.; Reichmann, Edwin J.

    1987-01-01

    Lyman alpha observations from the Ultraviolet Spectrometer Polarimeter (UVSP) instrument of the Solar Maximum Mission (SMM) spacecraft were analyzed and provide instrumental calibration details. Specific values of the instrument quantum efficiency, Lyman alpha absolute intensity, and correction for geocoronal absorption are presented.

  9. Estimating Absolute Site Effects

    SciTech Connect

    Malagnini, L; Mayeda, K M; Akinci, A; Bragato, P L

    2004-07-15

    The authors use previously determined direct-wave attenuation functions as well as stable, coda-derived source excitation spectra to isolate the absolute S-wave site effect for the horizontal and vertical components of weak ground motion. They used selected stations in the seismic network of the eastern Alps, and find the following: (1) all ''hard rock'' sites exhibited deamplification phenomena due to absorption at frequencies ranging between 0.5 and 12 Hz (the available bandwidth), on both the horizontal and vertical components; (2) ''hard rock'' site transfer functions showed large variability at high-frequency; (3) vertical-motion site transfer functions show strong frequency-dependence, and (4) H/V spectral ratios do not reproduce the characteristics of the true horizontal site transfer functions; (5) traditional, relative site terms obtained by using reference ''rock sites'' can be misleading in inferring the behaviors of true site transfer functions, since most rock sites have non-flat responses due to shallow heterogeneities resulting from varying degrees of weathering. They also use their stable source spectra to estimate total radiated seismic energy and compare against previous results. they find that the earthquakes in this region exhibit non-constant dynamic stress drop scaling which gives further support for a fundamental difference in rupture dynamics between small and large earthquakes. To correct the vertical and horizontal S-wave spectra for attenuation, they used detailed regional attenuation functions derived by Malagnini et al. (2002) who determined frequency-dependent geometrical spreading and Q for the region. These corrections account for the gross path effects (i.e., all distance-dependent effects), although the source and site effects are still present in the distance-corrected spectra. The main goal of this study is to isolate the absolute site effect (as a function of frequency) by removing the source spectrum (moment-rate spectrum) from

  10. Selective nanomanipulation of fluorescent polystyrene nano-beads and single quantum dots at gold nanostructures based on the AC-dielectrophoretic force

    NASA Astrophysics Data System (ADS)

    Kim, Jinsik; Hwang, Kyo Seon; Lee, Sangyoup; Park, Jung Ho; Shin, Hyun-Joon

    2015-11-01

    We introduced the selective manipulation of polystyrene (PS) nano-beads and single quantum dots (QDs) at a gold nanostructure by using the AC-dielectrophoretic (DEP) force. Manipulation in three degrees of freedom (end-facet, side, and position-selective manipulation) was accomplished in gold nanostructures between microelectrodes. A 10 μm gap between the microelectrodes, which has a 100 nm-wide nanowire and 200 nm-wide vortex nanostructures at the inside of the gap, was fabricated, and nanostructures were not connected with the electrodes. We also performed theoretical calculations to verify the selective manipulation through the floating AC-DEP force. A sufficiently high gradient of the square of the electric field (∇|E|2, ~1019 V2 m-3) was accomplished and controlled for achieving a strong attaching force of nanoparticles using the gap between microelectrodes and nanostructures as well as the rotation of structures. Fluorescent PS nano-beads and QDs were attached at the designed end facet, side, and position of nanostructures with high selectivity. A single QD attachment was also realized at gold nanostructures, and the attached QDs were verified as single using optical ``blinking'' measurements.We introduced the selective manipulation of polystyrene (PS) nano-beads and single quantum dots (QDs) at a gold nanostructure by using the AC-dielectrophoretic (DEP) force. Manipulation in three degrees of freedom (end-facet, side, and position-selective manipulation) was accomplished in gold nanostructures between microelectrodes. A 10 μm gap between the microelectrodes, which has a 100 nm-wide nanowire and 200 nm-wide vortex nanostructures at the inside of the gap, was fabricated, and nanostructures were not connected with the electrodes. We also performed theoretical calculations to verify the selective manipulation through the floating AC-DEP force. A sufficiently high gradient of the square of the electric field (∇|E|2, ~1019 V2 m-3) was accomplished and

  11. A novel sensitive colorimetric sensor for Cu(2+) based on in situ formation of fluorescent quantum dots with photocatalytic activity.

    PubMed

    Tang, Shurong; Wang, Meili; Li, Zhijun; Tong, Ping; Chen, Qiang; Li, Guangwen; Chen, Jinghua; Zhang, Lan

    2017-03-15

    This work demonstrates the use of quantum dots (QDs) with photocatalytic activity as a sensitive, inexpensive and rapid colorimetric platform for Cu(2+) sensing. Based on the simple thiol compound mediated QDs growing method, CdS QDs can be quickly formed in situ, which possess excellent photocatalytic ability for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce a colored product under light irradiation. Cu(2+) can catalyze the oxidation of sulfhydryl groups in glutathione (GSH) which act as a stabilizer for CdS QDs. In the presence of Cu(2+), GSH is oxidized and loss the stabilization ability for the growth of CdS QDs, thus resulting in the decrease of the absorbance. Under optimum conditions, as low as 5.3nM Cu(2+) can be detected. This sensing system is simple, reliable and holds great potential to provide a new general platform for ultrasensitive monitoring of a variety of analytes.

  12. Fluorescent MoS2 Quantum Dots: Ultrasonic Preparation, Up-Conversion and Down-Conversion Bioimaging, and Photodynamic Therapy.

    PubMed

    Dong, Haifeng; Tang, Songsong; Hao, Yansong; Yu, Haizhu; Dai, Wenhao; Zhao, Guifeng; Cao, Yu; Lu, Huiting; Zhang, Xueji; Ju, Huangxian

    2016-02-10

    Small size molybdenum disulfide (MoS2) quantum dots (QDs) with desired optical properties were controllably synthesized by using tetrabutylammonium-assisted ultrasonication of multilayered MoS2 powder via OH-mediated chain-like Mo-S bond cleavage mode. The tunable up-bottom approach of precise fabrication of MoS2 QDs finally enables detailed experimental investigations of their optical properties. The synthesized MoS2 QDs present good down-conversion photoluminescence behaviors and exhibit remarkable up-conversion photoluminescence for bioimaging. The mechanism of the emerging photoluminescence was investigated. Furthermore, superior (1)O2 production ability of MoS2 QDs to commercial photosensitizer PpIX was demonstrated, which has great potential application for photodynamic therapy. These early affording results of tunable synthesis of MoS2 QDs with desired photo properties can lead to application in fields of biomedical and optoelectronics.

  13. Synthesis of a quantum nanocrystal-gold nanoshell complex for near-infrared generated fluorescence and photothermal decay of luminescence

    NASA Astrophysics Data System (ADS)

    Lin, Adam Y.; Young, Joseph K.; Nixon, Ariel V.; Drezek, Rebekah A.

    2014-08-01

    Multifunction nanoparticle complexes have previously been developed to aid physicians in both diagnosis and treatment of cancerous tissue. Here, we designed a nanoparticle complex structure that consists of a plasmonically active hollow gold nanoshell core surrounded by photoluminescent quantum nanocrystals (QNs) in the form of PbS encapsulated by a silica layer. There are three main design variables including HGN synthesis and optical tuning, formation of the silica layer on the hollow gold nanoshell surface, and fabrication and photoluminescence tuning of PbS quantum nanocrystals. The hollow gold nanoshells were deliberately designed to function in the optical regimes that maximize tissue transmissivity (800 nm) and minimize tissue absorption (1100 nm). Secondly, several chemical ligands were tested such as (3-mercaptopropyl)trimethoxysilane and mercaptoundecanoic acid for controlled growth of the silica layer. Last, PbS QNs were synthesized and optimized with various capping agents, where the nanocrystals excited at the same wavelength were used to activate the photothermal properties of the hollow gold nanoshells. Upon irradiation of the complex with a lower power 800 nm laser, the nanocrystals luminesce at 1100 nm. At ablative temperatures the intrinsic luminescent properties of the QNs are altered and the luminescent output is significantly reduced (>70%). While this paper focuses on synthesis and optimization of the QN-HGN complex, in the future we believe that this novel particle complex design may have the potential to serve as a triple theranostic agent, which will aid satellite tumor localization, photothermal treatment, and ablative confirmation.Multifunction nanoparticle complexes have previously been developed to aid physicians in both diagnosis and treatment of cancerous tissue. Here, we designed a nanoparticle complex structure that consists of a plasmonically active hollow gold nanoshell core surrounded by photoluminescent quantum nanocrystals (QNs

  14. Rapid screening and identification of dominant B cell epitopes of HBV surface antigen by quantum dot-based fluorescence polarization assay

    NASA Astrophysics Data System (ADS)

    Meng, Zhongji; Song, Ruihua; Chen, Yue; Zhu, Yang; Tian, Yanhui; Li, Ding; Cui, Daxiang

    2013-03-01

    A method for quickly screening and identifying dominant B cell epitopes was developed using hepatitis B virus (HBV) surface antigen as a target. Eleven amino acid fragments from HBV surface antigen were synthesized by 9-fluorenylmethoxy carbonyl solid-phase peptide synthesis strategy, and then CdTe quantum dots were used to label the N-terminals of all peptides. After optimizing the factors for fluorescence polarization (FP) immunoassay, the antigenicities of synthetic peptides were determined by analyzing the recognition and combination of peptides and standard antibody samples. The results of FP assays confirmed that 10 of 11 synthetic peptides have distinct antigenicities. In order to screen dominant antigenic peptides, the FP assays were carried out to investigate the antibodies against the 10 synthetic peptides of HBV surface antigen respectively in 159 samples of anti-HBV surface antigen-positive antiserum. The results showed that 3 of the 10 antigenic peptides may be immunodominant because the antibodies against them existed more widely among the samples and their antibody titers were higher than those of other peptides. Using three dominant antigenic peptides, 293 serum samples were detected for HBV infection by FP assays; the results showed that the antibody-positive ratio was 51.9% and the sensitivity and specificity were 84.3% and 98.2%, respectively. In conclusion, a quantum dot-based FP assay is a very simple, rapid, and convenient method for determining immunodominant antigenic peptides and has great potential in applications such as epitope mapping, vaccine designing, or clinical disease diagnosis in the future.

  15. Enhanced Emission from Single Isolated Gold Quantum Dots Investigated Using Two-Photon-Excited Fluorescence Near-Field Scanning Optical Microscopy.

    PubMed

    Abeyasinghe, Neranga; Kumar, Santosh; Sun, Kai; Mansfield, John F; Jin, Rongchao; Goodson, Theodore

    2016-12-21

    New approaches in molecular nanoscopy are greatly desired for interrogation of biological, organic, and inorganic objects with sizes below the diffraction limit. Our current work investigates emergent monolayer-protected gold quantum dots (nanoclusters, NCs) composed of 25 Au atoms by utilizing two-photon-excited fluorescence (TPEF) near-field scanning optical microscopy (NSOM) at single NC concentrations. Here, we demonstrate an approach to synthesize and isolate single NCs on solid glass substrates. Subsequent investigation of the NCs using TPEF NSOM reveals that, even when they are separated by distances of several tens of nanometers, we can excite and interrogate single NCs individually. Interestingly, we observe an enhanced two-photon absorption (TPA) cross section for single Au25 NCs that can be attributed to few-atom local field effects and to local field-induced microscopic cascading, indicating their potential for use in ultrasensitive sensing, disease diagnostics, cancer cell therapy, and molecular computers. Finally, we report room-temperature aperture-based TPEF NSOM imaging of these NCs for the first time at 30 nm point resolution, which is a ∼5-fold improvement compared to the previous best result for the same technique. This report unveils the unique combination of an unusually large TPA cross section and the high photostability of Au NCs to (non-destructively) investigate stable isolated single NCs using TPEF NSOM. This is the first reported optical study of monolayer-protected single quantum clusters, opening some very promising opportunities in spectroscopy of nanosized objects, bioimaging, ultrasensitive sensing, molecular computers, and high-density data storage.

  16. Decay kinetics and quantum yields of fluorescence in photosystem I from Synechococcus elongatus with P700 in the reduced and oxidized state: are the kinetics of excited state decay trap-limited or transfer-limited?

    PubMed Central

    Byrdin, M; Rimke, I; Schlodder, E; Stehlik, D; Roelofs, T A

    2000-01-01

    Transfer and trapping of excitation energy in photosystem I (PS I) trimers isolated from Synechococcus elongatus have been studied by an approach combining fluorescence induction experiments with picosecond time-resolved fluorescence measurements, both at room temperature (RT) and at low temperature (5 K). Special attention was paid to the influence of the oxidation state of the primary electron donor P700. A fluorescence induction effect has been observed, showing a approximately 12% increase in fluorescence quantum yield upon P700 oxidation at RT, whereas at temperatures below 160 K oxidation of P700 leads to a decrease in fluorescence quantum yield ( approximately 50% at 5 K). The fluorescence quantum yield for open PS I (with P700 reduced) at 5 K is increased by approximately 20-fold and that for closed PS I (with P700 oxidized) is increased by approximately 10-fold, as compared to RT. Picosecond fluorescence decay kinetics at RT reveal a difference in lifetime of the main decay component: 34 +/- 1 ps for open PS I and 37 +/- 1 ps for closed PS I. At 5 K the fluorescence yield is mainly associated with long-lived components (lifetimes of 401 ps and 1.5 ns in closed PS I and of 377 ps, 1.3 ns, and 4.1 ns in samples containing approximately 50% open and 50% closed PS I). The spectra associated with energy transfer and the steady-state emission spectra suggest that the excitation energy is not completely thermally equilibrated over the core-antenna-RC complex before being trapped. Structure-based modeling indicates that the so-called red antenna pigments (A708 and A720, i.e., those with absorption maxima at 708 nm and 720 nm, respectively) play a decisive role in the observed fluorescence kinetics. The A720 are preferentially located at the periphery of the PS I core-antenna-RC complex; the A708 must essentially connect the A720 to the reaction center. The excited-state decay kinetics turn out to be neither purely trap limited nor purely transfer (to the trap

  17. Multiplexed interfacial transduction of nucleic acid hybridization using a single color of immobilized quantum dot donor and two acceptors in fluorescence resonance energy transfer.

    PubMed

    Algar, W Russ; Krull, Ulrich J

    2010-01-01

    A multiplexed solid-phase assay for the detection of nucleic acid hybridization was developed on the basis of a single color of immobilized CdSe/ZnS quantum dot (QD) as a donor in fluorescence resonance energy transfer (FRET). This work demonstrated that two channels of detection did not necessitate two different QD donors. Two probe oligonucleotides were coimmobilized on optical fibers modified with QDs, and a sandwich assay was used to associate the acceptor dyes with interfacial hybridization events without target labeling. FRET-sensitized acceptor emission provided an analytical signal that was concentration dependent down to 10 nM. Changes in the ratio of coimmobilized probe oligonucleotides were found to yield linear changes in the relative amounts of acceptor emission. These changes were compared to previous studies that used mixed films of two QD donors for two detection channels. The analysis indicated that probe dilution effects were primarily driven by changes in acceptor number density and that QD dilution effects or changes in mean donor-acceptor distance were secondary. Hybridization kinetics were found to be consistent between different ratios of coimmobilized probes, suggesting that hybridization in this type of system occurred via the accepted model for solid-phase hybridization, where adsorption and then diffusion at the solid interface drove hybridization.

  18. Immobilization of CdSe/ZnS quantum dots on glass beads for the detection of nucleic acid hybridization using fluorescence resonance energy transfer

    NASA Astrophysics Data System (ADS)

    Algar, W. Russ; Krull, Ulrich J.

    2011-03-01

    The photoluminescence (PL) properties of quantum dots (QD) are of significant interest in the development of new methods for bioanalysis. Multiplexed solid-phase nucleic acid hybridization assays that use immobilized QDs as donors in fluorescence resonance energy transfer (FRET) are one such example, and offer several unique advantages over other methods. In this work, new interfacial chemistry is described for the immobilization of red-emitting CdSe/ZnS QDs on glass beads for use in hybridization assays. The beads were chemically modified with a dithiolate surface ligand and the QDs immobilized via self-assembly. Further derivatization of the QDs with dithiolate-terminated probe oligonucleotides enabled a hybridization assay that could detect unlabeled target down to nanomolar levels with discrimination of single base-pair mismatches. The use of beads as an immobilization platform afforded shorter analysis times and superior reusability compared to previous studies using optical fibers. Hybridization between probe, target, and Alexa Fluor 647 (A647) labeled reporter oligonucleotides in a sandwich format generated a spectroscopic signal by introducing the proximity needed for FRET between the QDs and A647. The results indicate clear directions for the optimization of solid-phase hybridization assays, and are important for the future development of true multiplexed biosensors based on QDs and FRET.

  19. Near-Infrared Emission CuInS/ZnS Quantum Dots: All-in-One Theranostic Nanomedicines with Intrinsic Fluorescence/Photoacoustic Imaging for Tumor Phototherapy.

    PubMed

    Lv, Guoxian; Guo, Weisheng; Zhang, Wei; Zhang, Tingbin; Li, Shuyi; Chen, Shizhu; Eltahan, Ahmed Shaker; Wang, Dongliang; Wang, Yuqing; Zhang, Jinchao; Wang, Paul C; Chang, Jin; Liang, Xing-Jie

    2016-09-20

    Many theranostic nanomedicines (NMs) have been fabricated by packaging imaging and therapeutic moieties together. However, concerns about their potential architecture instability and pharmacokinetic complexity remain major obstacles to their clinical translation. Herein, we demonstrated the use of CuInS/ZnS quantum dots (ZCIS QDs) as "all-in-one" theranostic nanomedicines that possess intrinsic imaging and therapeutic capabilities within a well-defined nanostructure. ZCIS QDs were exploited for multispectral optical tomography (MSOT) imaging and synergistic PTT/PDT therapy. Due to the intrinsic fluorescence/MSOT imaging ability of the ZCIS QDs, their size-dependent distribution profiles were successfully visualized at tumor sites in vivo. Our results showed that the smaller nanomedicines (ZCIS NMs-25) have longer tumor retention times, higher tumor uptake, and deeper tumor penetration than the larger nanomedicines (ZCIS NMs-80). The ability of ZCIS QDs to mediate photoinduced tumor ablation was also explored. Our results verified that under a single 660 nm laser irradiation, the ZCIS NMs had simultaneous inherent photothermal and photodynamic effects, resulting in high therapy efficacy against tumors. In summary, the ZCIS QDs as "all-in-one" versatile nanomedicines allow high therapeutic efficacy as well as noninvasively monitoring tumor site localization profiles by imaging techniques and thus hold great potential as precision theranostic nanomedicines.

  20. Interfacial chemistry and the design of solid-phase nucleic acid hybridization assays using immobilized quantum dots as donors in fluorescence resonance energy transfer.

    PubMed

    Algar, W Russ; Krull, Ulrich J

    2011-01-01

    The use of quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) offer several advantages for the development of multiplexed solid-phase QD-FRET nucleic acid hybridization assays. Designs for multiplexing have been demonstrated, but important challenges remain in the optimization of these systems. In this work, we identify several strategies based on the design of interfacial chemistry for improving sensitivity, obtaining lower limits of detection (LOD) and enabling the regeneration and reuse of solid-phase QD-FRET hybridization assays. FRET-sensitized emission from acceptor dyes associated with hybridization events at immobilized QD donors provides the analytical signal in these assays. The minimization of active sensing area reduces background from QD donor PL and allows the resolution of smaller amounts of acceptor emission, thus lowering the LOD. The association of multiple acceptor dyes with each hybridization event can enhance FRET efficiency, thereby improving sensitivity. Many previous studies have used interfacial protein layers to generate selectivity; however, transient destabilization of these layers is shown to prevent efficient regeneration. To this end, we report a protein-free interfacial chemistry and demonstrate the specific detection of as little as 2 pmol of target, as well as an improved capacity for regeneration.