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Sample records for afm force spectroscopy

  1. Interlaboratory round robin on cantilever calibration for AFM force spectroscopy.

    PubMed

    te Riet, Joost; Katan, Allard J; Rankl, Christian; Stahl, Stefan W; van Buul, Arend M; Phang, In Yee; Gomez-Casado, Alberto; Schön, Peter; Gerritsen, Jan W; Cambi, Alessandra; Rowan, Alan E; Vancso, G Julius; Jonkheijm, Pascal; Huskens, Jurriaan; Oosterkamp, Tjerk H; Gaub, Hermann; Hinterdorfer, Peter; Figdor, Carl G; Speller, Sylvia

    2011-12-01

    Single-molecule force spectroscopy studies performed by Atomic Force Microscopes (AFMs) strongly rely on accurately determined cantilever spring constants. Hence, to calibrate cantilevers, a reliable calibration protocol is essential. Although the thermal noise method and the direct Sader method are frequently used for cantilever calibration, there is no consensus on the optimal calibration of soft and V-shaped cantilevers, especially those used in force spectroscopy. Therefore, in this study we aimed at establishing a commonly accepted approach to accurately calibrate compliant and V-shaped cantilevers. In a round robin experiment involving eight different laboratories we compared the thermal noise and the Sader method on ten commercial and custom-built AFMs. We found that spring constants of both rectangular and V-shaped cantilevers can accurately be determined with both methods, although the Sader method proved to be superior. Furthermore, we observed that simultaneous application of both methods on an AFM proved an accurate consistency check of the instrument and thus provides optimal and highly reproducible calibration. To illustrate the importance of optimal calibration, we show that for biological force spectroscopy studies, an erroneously calibrated cantilever can significantly affect the derived (bio)physical parameters. Taken together, our findings demonstrated that with the pre-established protocol described reliable spring constants can be obtained for different types of cantilevers.

  2. Force and function: probing proteins with AFM-based force spectroscopy.

    PubMed

    Puchner, Elias M; Gaub, Hermann E

    2009-10-01

    Forces play a pivotal role in life, and the response of live systems to forces requires molecules and molecular interactions with adequate properties to counteract both in a passive and also, if needed, in an active, dynamic manner. However, at the level of individual molecules these forces are so minute, that the development of sophisticated experiments to measure and control them was required. With the maturation of these techniques, particularly the AFM-based single-molecule force spectroscopy into commercial instruments, the scope has widened considerably and more and more studies shed light onto the different aspects of biomolecular mechanics. Many surprises turned up and more are waiting for us.

  3. Single-Molecule Studies of Integrins by AFM-Based Force Spectroscopy on Living Cells

    NASA Astrophysics Data System (ADS)

    Eibl, Robert H.

    The characterization of cell adhesion between two living cells at the single-molecule level, i.e., between one adhesion receptor and its counter-receptor, appears to be an experimental challenge. Atomic force microscopy (AFM) can be used in its force spectroscopy mode to determine unbinding forces of a single pair of adhesion receptors, even with a living cell as a probe. This chapter provides an overview of AFM force measurements of the integrin family of cell adhesion receptors and their ligands. A focus is given to major integrins expressed on leukocytes, such as lymphocyte function-associated antigen 1 (LFA-1) and very late antigen 4 (VLA-4). These receptors are crucial for leukocyte trafficking in health and disease. LFA-1 and VLA-1 can be activated within the bloodstream from a low-affinity to a high-affinity receptor by chemokines in order to adhere strongly to the vessel wall before the receptor-bearing leukocytes extravasate. The experimental considerations needed to provide near-physiological conditions for a living cell and to be able to measure adequate forces at the single-molecule level are discussed in detail. AFM technology has been developed into a modern and extremely sensitive tool in biomedical research. It appears now that AFM force spectroscopy could enter, within a few years, medical applications in diagnosis and therapy of cancer and autoimmune diseases.

  4. Quantitating membrane bleb stiffness using AFM force spectroscopy and an optical sideview setup.

    PubMed

    Gonnermann, Carina; Huang, Chaolie; Becker, Sarah F; Stamov, Dimitar R; Wedlich, Doris; Kashef, Jubin; Franz, Clemens M

    2015-03-01

    AFM-based force spectroscopy in combination with optical microscopy is a powerful tool for investigating cell mechanics and adhesion on the single cell level. However, standard setups featuring an AFM mounted on an inverted light microscope only provide a bottom view of cell and AFM cantilever but cannot visualize vertical cell shape changes, for instance occurring during motile membrane blebbing. Here, we have integrated a mirror-based sideview system to monitor cell shape changes resulting from motile bleb behavior of Xenopus cranial neural crest (CNC) cells during AFM elasticity and adhesion measurements. Using the sideview setup, we quantitatively investigate mechanical changes associated with bleb formation and compared cell elasticity values recorded during membrane bleb and non-bleb events. Bleb protrusions displayed significantly lower stiffness compared to the non-blebbing membrane in the same cell. Bleb stiffness values were comparable to values obtained from blebbistatin-treated cells, consistent with the absence of a functional actomyosin network in bleb protrusions. Furthermore, we show that membrane blebs forming within the cell-cell contact zone have a detrimental effect on cell-cell adhesion forces, suggesting that mechanical changes associated with bleb protrusions promote cell-cell detachment or prevent adhesion reinforcement. Incorporating a sideview setup into an AFM platform therefore provides a new tool to correlate changes in cell morphology with results from force spectroscopy experiments.

  5. Combined force spectroscopy, AFM and calorimetric studies to reveal the nanostructural organization of biomimetic membranes.

    PubMed

    Suárez-Germà, C; Morros, A; Montero, M T; Hernández-Borrell, J; Domènech, Ò

    2014-10-01

    In this work we studied a binary lipid matrix of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG), a composition that mimics the inner membrane of Escherichia coli. More specifically, liposomes with varying fractions of POPG were analysed by differential scanning calorimetry (DSC) and a binary phase diagram of the system was created. Additionally, we performed atomic force microscopy (AFM) imaging of supported lipid bilayers (SLBs) of similar compositions at different temperatures, in order to create a pseudo-binary phase diagram specific to this membrane model. AFM study of SLBs is of particular interest, as it is conceived as the most adequate technique not only for studying lipid bilayer systems but also for imaging and even nanomanipulating inserted membrane proteins. The construction of the above-mentioned phase diagram enabled us to grasp better the thermodynamics of the thermal lipid transition from a gel-like POPE:POPG phase system to a more fluid phase system. Finally, AFM force spectroscopy (FS) was used to determine the nanomechanics of these two lipid phases at 27°C and at different POPG fractions. The resulting data correlated with the specific composition of each phase was calculated from the AFM phase diagram obtained. All the experiments were done in the presence of 10 mM of Ca(2+), as this ion is commonly used when performing AFM with negatively charged phospholipids.

  6. Unspecific membrane protein-lipid recognition: combination of AFM imaging, force spectroscopy, DSC and FRET measurements.

    PubMed

    Borrell, Jordi H; Montero, M Teresa; Morros, Antoni; Domènech, Òscar

    2015-11-01

    In this work, we will describe in quantitative terms the unspecific recognition between lactose permease (LacY) of Escherichia coli, a polytopic model membrane protein, and one of the main components of the inner membrane of this bacterium. Supported lipid bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) (3:1, mol/mol) in the presence of Ca(2+) display lateral phase segregation that can be distinguished by atomic force microscopy (AFM) as well as force spectroscopy. LacY shows preference for fluid (Lα) phases when it is reconstituted in POPE : POPG (3:1, mol/mol) proteoliposomes at a lipid-to-protein ratio of 40. When the lipid-to-protein ratio is decreased down to 0.5, two domains can be distinguished by AFM. While the upper domain is formed by self-segregated units of LacY, the lower domain is constituted only by phospholipids in gel (Lβ) phase. On the one hand, classical differential scanning calorimetry (DSC) measurements evidenced the segregation of a population of phospholipids and point to the existence of a boundary region at the lipid-protein interface. On the other hand, Förster Resonance Energy Transfer (FRET) measurements in solution evidenced that POPE is selectively recognized by LacY. A binary pseudophase diagram of POPE : POPG built from AFM observations enables to calculate the composition of the fluid phase where LacY is inserted. These results are consistent with a model where POPE constitutes the main component of the lipid-LacY interface segregated from the fluid bulk phase where POPG predominates.

  7. The physics of pulling polyproteins: a review of single molecule force spectroscopy using the AFM to study protein unfolding

    NASA Astrophysics Data System (ADS)

    Hughes, Megan L.; Dougan, Lorna

    2016-07-01

    One of the most exciting developments in the field of biological physics in recent years is the ability to manipulate single molecules and probe their properties and function. Since its emergence over two decades ago, single molecule force spectroscopy has become a powerful tool to explore the response of biological molecules, including proteins, DNA, RNA and their complexes, to the application of an applied force. The force versus extension response of molecules can provide valuable insight into its mechanical stability, as well as details of the underlying energy landscape. In this review we will introduce the technique of single molecule force spectroscopy using the atomic force microscope (AFM), with particular focus on its application to study proteins. We will review the models which have been developed and employed to extract information from single molecule force spectroscopy experiments. Finally, we will end with a discussion of future directions in this field.

  8. Accurate, explicit formulae for higher harmonic force spectroscopy by frequency modulation-AFM.

    PubMed

    Kuchuk, Kfir; Sivan, Uri

    2015-01-01

    The nonlinear interaction between an AFM tip and a sample gives rise to oscillations of the cantilever at integral multiples (harmonics) of the fundamental resonance frequency. The higher order harmonics have long been recognized to hold invaluable information on short range interactions but their utilization has thus far been relatively limited due to theoretical and experimental complexities. In particular, existing approximations of the interaction force in terms of higher harmonic amplitudes generally require simultaneous measurements of multiple harmonics to achieve satisfactory accuracy. In the present letter we address the mathematical challenge and derive accurate, explicit formulae for both conservative and dissipative forces in terms of an arbitrary single harmonic. Additionally, we show that in frequency modulation-AFM (FM-AFM) each harmonic carries complete information on the force, obviating the need for multi-harmonic analysis. Finally, we show that higher harmonics may indeed be used to reconstruct short range forces more accurately than the fundamental harmonic when the oscillation amplitude is small compared with the interaction range.

  9. Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample

    NASA Astrophysics Data System (ADS)

    Guo, Shifeng; Zhu, Xiaoying; Jańczewski, Dominik; Lee, Serina Siew Chen; He, Tao; Teo, Serena Lay Ming; Vancso, G. Julius

    2016-09-01

    Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force-distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7-9.8. Using this method, we show that the pI of the ‘footprint’ of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6-9.7.

  10. Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample.

    PubMed

    Guo, Shifeng; Zhu, Xiaoying; Jańczewski, Dominik; Lee, Serina Siew Chen; He, Tao; Teo, Serena Lay Ming; Vancso, G Julius

    2016-09-01

    Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force-distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7-9.8. Using this method, we show that the pI of the 'footprint' of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6-9.7.

  11. Experimental evidence of ultrathin polymer film stratification by AFM force spectroscopy.

    PubMed

    Delorme, Nicolas; Chebil, Mohamed Souheib; Vignaud, Guillaume; Le Houerou, Vincent; Bardeau, Jean-François; Busselez, Rémi; Gibaud, Alain; Grohens, Yves

    2015-06-01

    By performing Atomic Force Microscopy measurements of pull-off force as a function of the temperature, we were able to probe the dynamic of supported thin polystyrene (PS) films. Thermal transitions induce modifications in the surface energy, roughness and surface modulus that are clearly detected by AFM and related to PS chain relaxation mechanisms. We demonstrated the existence of three transition temperatures that can be associated to the relaxation of polymer chains located at different depth regions within the polymer film. Independently of the film thickness, we have confirmed the presence of a region of high mobility for the polymer chains at the free interface. The thickness of this region is estimated to be above 7nm. The detection of a transition only present for film thicker than the gyration radius Rg is linked to the dynamics of polymer chains in a bulk conformation (i.e. not in contact with the free interface). We claim here that our results demonstrate, in agreement with other techniques, the stratification of thin polymer film depth profile in terms of relaxation behavior.

  12. Mechanical properties of complex biological systems using AFM-based force spectroscopy

    NASA Astrophysics Data System (ADS)

    Graham, John Stephen

    An atomic force microscope (AFM) was designed and built to study the mechanical properties of small collagen fibrils and the plasma membrane of living cells. Collagen is a major component of bone, skin and connective tissues, and is abundant in the extracellular matrix (ECM). Because of its abundance, an understanding of how disease affects collagen mechanics is crucial in disease prevention efforts. Two levels of type I collagen structure were investigated, subfibrils (on the order of 1 mum in length) and longer fibrils. Comparisons were made between measurements of wild-type (wt) collagen and collagen from the mouse model of osteogenesis imperfecta (OI). Significant differences between OI and wt collagen were observed, primarily that intermolecular bonds in OI collagen fibrils are weaker than in wt, or not ruptured, as in the case of OI subfibrils. As cells interact with collagen in the ECM, the mechanical properties of the plasma membrane are also of great interest. Membrane tethers were extracted from living cells under varied conditions in order to assess the contributions of membrane-associated macromolecules such as the actin cytoskeleton and the glycocalyx, and intracellular signaling. Tether extraction force was found to be sensitive to all of these altered conditions, suggesting that tether extraction may be used to monitor various cellular processes.

  13. Fourier Transform Infrared (FTIR) Spectroscopy, Ultraviolet Resonance Raman (UVRR) Spectroscopy, and Atomic Force Microscopy (AFM) for Study of the Kinetics of Formation and Structural Characterization of Tau Fibrils.

    PubMed

    Ramachandran, Gayathri

    2017-01-01

    Kinetic studies of tau fibril formation in vitro most commonly employ spectroscopic probes such as thioflavinT fluorescence and laser light scattering or negative stain transmission electron microscopy. Here, I describe the use of Fourier transform infrared (FTIR) spectroscopy, ultraviolet resonance Raman (UVRR) spectroscopy, and atomic force microscopy (AFM) as complementary probes for studies of tau aggregation. The sensitivity of vibrational spectroscopic techniques (FTIR and UVRR) to secondary structure content allows for measurement of conformational changes that occur when the intrinsically disordered protein tau transforms into cross-β-core containing fibrils. AFM imaging serves as a gentle probe of structures populated over the time course of tau fibrillization. Together, these assays help further elucidate the structural and mechanistic complexity inherent in tau fibril formation.

  14. Mechanism of amyloid β-protein dimerization determined using single-molecule AFM force spectroscopy

    NASA Astrophysics Data System (ADS)

    Lv, Zhengjian; Roychaudhuri, Robin; Condron, Margaret M.; Teplow, David B.; Lyubchenko, Yuri L.

    2013-10-01

    Aβ42 and Aβ40 are the two primary alloforms of human amyloid β-protein (Aβ). The two additional C-terminal residues of Aβ42 result in elevated neurotoxicity compared with Aβ40, but the molecular mechanism underlying this effect remains unclear. Here, we used single-molecule force microscopy to characterize interpeptide interactions for Aβ42 and Aβ40 and corresponding mutants. We discovered a dramatic difference in the interaction patterns of Aβ42 and Aβ40 monomers within dimers. Although the sequence difference between the two peptides is at the C-termini, the N-terminal segment plays a key role in the peptide interaction in the dimers. This is an unexpected finding as N-terminal was considered as disordered segment with no effect on the Aβ peptide aggregation. These novel properties of Aβ proteins suggests that the stabilization of N-terminal interactions is a switch in redirecting of amyloids form the neurotoxic aggregation pathway, opening a novel avenue for the disease preventions and treatments.

  15. Nanoscale structural and mechanical effects of beta-amyloid (1-42) on polymer cushioned membranes: a combined study by neutron reflectometry and AFM Force Spectroscopy.

    PubMed

    Dante, Silvia; Hauss, Thomas; Steitz, Roland; Canale, Claudio; Dencher, Norbert A

    2011-11-01

    The interaction of beta-amyloid peptides with lipid membranes is widely studied as trigger agents in Alzheimer's disease. Their mechanism of action at the molecular level is unknown and their interaction with the neural membrane is crucial to elucidate the onset of the disease. In this study we have investigated the interaction of water soluble forms of beta-amyloid Aβ(1-42) with lipid bilayers supported by polymer cushion. A reproducible protocol for the preparation of a supported phospholipid membrane with composition mimicking the neural membrane and in physiological condition (PBS buffer, pH=7.4) was refined by neutron reflectivity. The change in structure and local mechanical properties of the membrane in the presence of Aβ(1-42) was investigated by neutron reflectivity and Atomic Force Microscopy (AFM) Force Spectroscopy. Neutron reflectivity evidenced that Aβ(1-42) interacts strongly with the supported membrane, causing a change in the scattering length density profile of the lipid bilayer, and penetrates into the membrane. Concomitantly, the local mechanical properties of the bilayer are deeply modified by the interaction with the peptide as seen by AFM Force Spectroscopy. These results may be of great importance for the onset of the Alzheimer's disease, since a simultaneous change in the structural and mechanical properties of the lipid matrix could influence all membrane based signal cascades.

  16. Phase transition behaviors of the supported DPPC bilayer investigated by sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM).

    PubMed

    Wu, Heng-Liang; Tong, Yujin; Peng, Qiling; Li, Na; Ye, Shen

    2016-01-21

    The phase transition behaviors of a supported bilayer of dipalmitoylphosphatidyl-choline (DPPC) have been systematically evaluated by in situ sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM). By using an asymmetric bilayer composed of per-deuterated and per-protonated monolayers, i.e., DPPC-d75/DPPC and a symmetric bilayer of DPPC/DPPC, we were able to probe the molecular structural changes during the phase transition process of the lipid bilayer by SFG spectroscopy. It was found that the DPPC bilayer is sequentially melted from the top (adjacent to the solution) to bottom leaflet (adjacent to the substrate) over a wide temperature range. The conformational ordering of the supported bilayer does not decrease (even slightly increases) during the phase transition process. The conformational defects in the bilayer can be removed after the complete melting process. The phase transition enthalpy for the bottom leaflet was found to be approximately three times greater than that for the top leaflet, indicating a strong interaction of the lipids with the substrate. The present SFG and AFM observations revealed similar temperature dependent profiles. Based on these results, the temperature-induced structural changes in the supported lipid bilayer during its phase transition process are discussed in comparison with previous studies.

  17. AFM force spectroscopy reveals how subtle structural differences affect the interaction strength between Candida albicans and DC-SIGN.

    PubMed

    te Riet, Joost; Reinieren-Beeren, Inge; Figdor, Carl G; Cambi, Alessandra

    2015-11-01

    The fungus Candida albicans is the most common cause of mycotic infections in immunocompromised hosts. Little is known about the initial interactions between Candida and immune cell receptors, such as the C-type lectin dendritic cell-specific intracellular cell adhesion molecule-3 (ICAM-3)-grabbing non-integrin (DC-SIGN), because a detailed characterization at the structural level is lacking. DC-SIGN recognizes specific Candida-associated molecular patterns, that is, mannan structures present in the cell wall of Candida. The molecular recognition mechanism is however poorly understood. We postulated that small differences in mannan-branching may result in considerable differences in the binding affinity. Here, we exploit atomic force microscope-based dynamic force spectroscopy with single Candida cells to gain better insight in the carbohydrate recognition capacity of DC-SIGN. We demonstrate that slight differences in the N-mannan structure of Candida, that is, the absence or presence of a phosphomannan side chain, results in differences in the recognition by DC-SIGN as follows: (i) it contributes to the compliance of the outer cell wall of Candida, and (ii) its presence results in a higher binding energy of 1.6 kB T. The single-bond affinity of tetrameric DC-SIGN for wild-type C. albicans is ~10.7 kB T and a dissociation constant kD of 23 μM, which is relatively strong compared with other carbohydrate-protein interactions described in the literature. In conclusion, this study shows that DC-SIGN specifically recognizes mannan patterns on C. albicans with high affinity. Knowledge on the binding pocket of DC-SIGN and its pathogenic ligands will lead to a better understanding of how fungal-associated carbohydrate structures are recognized by receptors of the immune system and can ultimately contribute to the development of new anti-fungal drugs.

  18. AFM-IR: Technology and Applications in Nanoscale Infrared Spectroscopy and Chemical Imaging.

    PubMed

    Dazzi, Alexandre; Prater, Craig B

    2016-12-13

    Atomic force microscopy-based infrared spectroscopy (AFM-IR) is a rapidly emerging technique that provides chemical analysis and compositional mapping with spatial resolution far below conventional optical diffraction limits. AFM-IR works by using the tip of an AFM probe to locally detect thermal expansion in a sample resulting from absorption of infrared radiation. AFM-IR thus can provide the spatial resolution of AFM in combination with the chemical analysis and compositional imaging capabilities of infrared spectroscopy. This article briefly reviews the development and underlying technology of AFM-IR, including recent advances, and then surveys a wide range of applications and investigations using AFM-IR. AFM-IR applications that will be discussed include those in polymers, life sciences, photonics, solar cells, semiconductors, pharmaceuticals, and cultural heritage. In the Supporting Information , the authors provide a theoretical section that reviews the physics underlying the AFM-IR measurement and detection mechanisms.

  19. Near-Field Spectroscopy with Nanoparticles Deposited by AFM

    NASA Technical Reports Server (NTRS)

    Anderson, Mark S.

    2008-01-01

    An alternative approach to apertureless near-field optical spectroscopy involving an atomic-force microscope (AFM) entails less complexity of equipment than does a prior approach. The alternative approach has been demonstrated to be applicable to apertureless near-field optical spectroscopy of the type using an AFM and surface enhanced Raman scattering (SERS), and is expected to be equally applicable in cases in which infrared or fluorescence spectroscopy is used. Apertureless near-field optical spectroscopy is a means of performing spatially resolved analyses of chemical compositions of surface regions of nanostructured materials. In apertureless near-field spectroscopy, it is common practice to utilize nanostructured probe tips or nanoparticles (usually of gold) having shapes and dimensions chosen to exploit plasmon resonances so as to increase spectroscopic-signal strengths. To implement the particular prior approach to which the present approach is an alternative, it is necessary to integrate a Raman spectrometer with an AFM and to utilize a special SERS-active probe tip. The resulting instrumentation system is complex, and the tasks of designing and constructing the system and using the system to acquire spectro-chemical information from nanometer-scale regions on a surface are correspondingly demanding.

  20. Tuning the instability in static mode atomic force spectroscopy as obtained in an AFM by applying an electric field between the tip and the substrate.

    PubMed

    Biswas, Soma; Raychaudhuri, A K; Sreeram, P A; Dietzel, Dirk

    2012-11-01

    We have investigated experimentally the role of cantilever instabilities in determination of the static mode force-distance curves in presence of a dc electric field. The electric field has been applied between the tip and the sample in an atomic force microscope working in ultra-high vacuum. We have shown how an electric field modifies the observed force (or cantilever deflection)-vs-distance curves, commonly referred to as the static mode force spectroscopy curves, taken using an atomic force microscope. The electric field induced instabilities shift the jump-into-contact and jump-off-contact points and also the deflection at these instability points. We explained the experimental results using a model of the tip-sample interaction and quantitatively established a relation between the observed static mode force spectroscopy curves and the applied electric field which modifies the effective tip-sample interaction in a controlled manner. The investigation establishes a way to quantitatively evaluate the electrostatic force in an atomic force microscope using the static mode force spectroscopy curves.

  1. Introduction to atomic force microscopy (AFM) in biology.

    PubMed

    Goldsbury, Claire S; Scheuring, Simon; Kreplak, Laurent

    2009-11-01

    The atomic force microscope (AFM) has the unique capability of imaging biological samples with molecular resolution in buffer solution. In addition to providing topographical images of surfaces with nanometer- to angstrom-scale resolution, forces between single molecules and mechanical properties of biological samples can be investigated from the nanoscale to the microscale. Importantly, the measurements are made in buffer solutions, allowing biological samples to "stay alive" within a physiological-like environment while temporal changes in structure are measured-e.g., before and after addition of chemical reagents. These qualities distinguish AFM from conventional imaging techniques of comparable resolution, e.g., electron microscopy (EM). This unit provides an introduction to AFM on biological systems and describes specific examples of AFM on proteins, cells, and tissues. The physical principles of the technique and methodological aspects of its practical use and applications are also described.

  2. [Application of atomic force microscopy (AFM) in ophthalmology].

    PubMed

    Milka, Michał; Mróz, Iwona; Jastrzebska, Maria; Wrzalik, Roman; Dobrowolski, Dariusz; Roszkowska, Anna M; Moćko, Lucyna; Wylegała, Edward

    2012-01-01

    Atomic force microscopy (AFM) allows to examine surface of different biological objects in the nearly physiological conditions at the nanoscale. The purpose of this work is to present the history of introduction and the potential applications of the AFM in ophthalmology research and clinical practice. In 1986 Binnig built the AFM as a next generation of the scanning tunnelling microscope (STM). The functional principle of AFM is based on the measurement of the forces between atoms on the sample surface and the probe. As a result, the three-dimensional image of the surface with the resolution on the order of nanometres can be obtained. Yamamoto used as the first the AFM on a wide scale in ophthalmology. The first investigations used the AFM method to study structure of collagen fibres of the cornea and of the sclera. Our research involves the analysis of artificial intraocular lenses (IOLs). According to earlier investigations, e.g. Lombardo et al., the AFM was used to study only native IOLs. Contrary to the earlier investigations, we focused our measurements on lenses explanted from human eyes. The surface of such lenses is exposed to the influence of the intraocular aqueous environment, and to the related impacts of biochemical processes. We hereby present the preliminary results of our work in the form of AFM images depicting IOL surface at the nanoscale. The images allowed us to observe early stages of the dye deposit formation as well as local calcinosis. We believe that AFM is a very promising tool for studying the structure of IOL surface and that further observations will make it possible to explain the pathomechanism of artificial intraocular lens opacity formation.

  3. Probing the Double Layer: Effect of Image Forces on AFM

    PubMed Central

    Sachs, Frederick

    2006-01-01

    Force probes such as AFM tips or laser trap latex beads have a dielectric constant much less than that of the water that they displace. Thus when a probe approaches a charged surface under water it will be repelled simply based upon the image forces, and these can be of nN magnitude. PMID:16714346

  4. High-speed atomic force microscopy: imaging and force spectroscopy.

    PubMed

    Eghiaian, Frédéric; Rico, Felix; Colom, Adai; Casuso, Ignacio; Scheuring, Simon

    2014-10-01

    Atomic force microscopy (AFM) is the type of scanning probe microscopy that is probably best adapted for imaging biological samples in physiological conditions with submolecular lateral and vertical resolution. In addition, AFM is a method of choice to study the mechanical unfolding of proteins or for cellular force spectroscopy. In spite of 28 years of successful use in biological sciences, AFM is far from enjoying the same popularity as electron and fluorescence microscopy. The advent of high-speed atomic force microscopy (HS-AFM), about 10 years ago, has provided unprecedented insights into the dynamics of membrane proteins and molecular machines from the single-molecule to the cellular level. HS-AFM imaging at nanometer-resolution and sub-second frame rate may open novel research fields depicting dynamic events at the single bio-molecule level. As such, HS-AFM is complementary to other structural and cellular biology techniques, and hopefully will gain acceptance from researchers from various fields. In this review we describe some of the most recent reports of dynamic bio-molecular imaging by HS-AFM, as well as the advent of high-speed force spectroscopy (HS-FS) for single protein unfolding.

  5. Athermalization in atomic force microscope based force spectroscopy using matched microstructure coupling.

    PubMed

    Torun, H; Finkler, O; Degertekin, F L

    2009-07-01

    The authors describe a method for athermalization in atomic force microscope (AFM) based force spectroscopy applications using microstructures that thermomechanically match the AFM probes. The method uses a setup where the AFM probe is coupled with the matched structure and the displacements of both structures are read out simultaneously. The matched structure displaces with the AFM probe as temperature changes, thus the force applied to the sample can be kept constant without the need for a separate feedback loop for thermal drift compensation, and the differential signal can be used to cancel the shift in zero-force level of the AFM.

  6. The importance of correcting for variable probe-sample interactions in AFM-IR spectroscopy: AFM-IR of dried bacteria on a polyurethane film.

    PubMed

    Barlow, Daniel E; Biffinger, Justin C; Cockrell-Zugell, Allison L; Lo, Michael; Kjoller, Kevin; Cook, Debra; Lee, Woo Kyung; Pehrsson, Pehr E; Crookes-Goodson, Wendy J; Hung, Chia-Suei; Nadeau, Lloyd J; Russell, John N

    2016-08-02

    AFM-IR is a combined atomic force microscopy-infrared spectroscopy method that shows promise for nanoscale chemical characterization of biological-materials interactions. In an effort to apply this method to quantitatively probe mechanisms of microbiologically induced polyurethane degradation, we have investigated monolayer clusters of ∼200 nm thick Pseudomonas protegens Pf-5 bacteria (Pf) on a 300 nm thick polyether-polyurethane (PU) film. Here, the impact of the different biological and polymer mechanical properties on the thermomechanical AFM-IR detection mechanism was first assessed without the additional complication of polymer degradation. AFM-IR spectra of Pf and PU were compared with FTIR and showed good agreement. Local AFM-IR spectra of Pf on PU (Pf-PU) exhibited bands from both constituents, showing that AFM-IR is sensitive to chemical composition both at and below the surface. One distinct difference in local AFM-IR spectra on Pf-PU was an anomalous ∼4× increase in IR peak intensities for the probe in contact with Pf versus PU. This was attributed to differences in probe-sample interactions. In particular, significantly higher cantilever damping was observed for probe contact with PU, with a ∼10× smaller Q factor. AFM-IR chemical mapping at single wavelengths was also affected. We demonstrate ratioing of mapping data for chemical analysis as a simple method to cancel the extreme effects of the variable probe-sample interactions.

  7. Study of relaxation and transport processes by means of AFM based dielectric spectroscopy

    SciTech Connect

    Miccio, Luis A.

    2014-05-15

    Since its birth a few years ago, dielectric spectroscopy studies based on atomic force microscopy (AFM) have gained a growing interest. Not only the frequency and temperature ranges have become broader since then but also the kind of processes that can be studied by means of this approach. In this work we analyze the most adequate experimental setup for the study of several dielectric processes with a spatial resolution of a few nanometers by using force mode AFM based dielectric spectroscopy. Proof of concept experiments were performed on PS/PVAc blends and PMMA homopolymer films, for temperatures ranging from 300 to 400 K. Charge transport processes were also studied by this approach. The obtained results were analyzed in terms of cantilever stray contribution, film thickness and relaxation strength. We found that the method sensitivity is strongly coupled with the film thickness and the relaxation strength, and that it is possible to control it by using an adequate experimental setup.

  8. Atomic force microscope-assisted scanning tunneling spectroscopy under ambient conditions.

    PubMed

    Vakhshouri, Amin; Hashimoto, Katsushi; Hirayama, Yoshiro

    2014-12-01

    We have developed a method of atomic force microscopy (AFM)-assisted scanning tunneling spectroscopy (STS) under ambient conditions. An AFM function is used for rapid access to a selected position prior to performing STS. The AFM feedback is further used to suppress vertical thermal drift of the tip-sample distance during spectroscopy, enabling flexible and stable spectroscopy measurements at room temperature.

  9. Searching events in AFM force-extension curves: A wavelet approach.

    PubMed

    Benítez, R; Bolós, V J

    2017-01-01

    An algorithm, based on the wavelet scalogram energy, for automatically detecting events in force-extension AFM force spectroscopy experiments is introduced. The events to be detected are characterized by a discontinuity in the signal. It is shown how the wavelet scalogram energy has different decay rates at different points depending on the degree of regularity of the signal, showing faster decay rates at regular points and slower rates at singular points (jumps). It is shown that these differences produce peaks in the scalogram energy plot at the event points. Finally, the algorithm is illustrated in a tether analysis experiment by using it for the detection of events in the AFM force-extension curves susceptible to being considered tethers. Microsc. Res. Tech. 80:153-159, 2017. © 2016 Wiley Periodicals, Inc.

  10. Optical fiber fluorescence spectroscopy for detecting AFM1 in milk

    NASA Astrophysics Data System (ADS)

    Mignani, A. G.; Cucci, C.; Ciaccheri, L.; Dall'Asta, C.; Galaverna, G.; Dossena, A.; Marchelli, R.

    2008-04-01

    Fluorescence spectroscopy carried out by means of optical fibers was used for the rapid screening of M1 aflatoxin in milk, enabling the detection of concentrations up to the legal limit, which is 50 ppt. A compact fluorometric device equipped with a LED source, a miniaturized spectrometer, and optical fibers for illumination/detection of the measuring micro-cell was tested for measuring threshold values of AFM1 in pre-treated milk samples. Multivariate processing of the spectral data made it possible to obtain a preliminary screening at the earlier stages of the industrial process, as well as to discard contaminated milk stocks before their inclusion in the production chain.

  11. Device level 3D characterization using PeakForce AFM

    NASA Astrophysics Data System (ADS)

    Timoney, Padraig; Zhang, Xiaoxiao; Vaid, Alok; Hand, Sean; Osborne, Jason; Milligan, Eric; Feinstein, Adam

    2016-03-01

    Traditional metrology solutions face a range of challenges at the 1X node such as three dimensional (3D) measurement capabilities, shrinking overlay and critical dimension (CD) error budgets driven by multi-patterning and via in trench CD measurements. With advent of advanced technology nodes and 3D processing, an increasing need is emerging for in-die metrology including across-structure and structure-to-structure characterization. A myriad of work has emerged in the past few years intending to address these challenges from various aspects; in-die OCD with reduced spot size and tilt beam on traditional critical dimension scanning electron microscopy (CDSEM) for height measurements. This paper explores the latest capability offered by PeakForceTM Tapping Atomic Force Microscopy (PFT-AFM). The use of traditional harmonic tapping mode for scanning high aspect ratio, and complex "3D" wafer structures, results in limited depth probing capability as well as excessive tip wear. These limitations arise due to the large tip-sample interaction volume in such confined spaces. PeakForce Tapping eliminates these limitations through direct real time control of the tip-sample interaction contact force. The ability of PeakForce to measure, and respond directly to tip- sample interaction forces results in more detailed feature resolution, reduced tip wear, and improved depth capability. In this work, the PFT-AFM tool was applied for multiple applications, including the 14nm fin and replacement metal gate (RMG) applications outlined below. Results from DOE wafers, detailed measurement precision studies and correlation to reference metrology are presented for validation of this methodology. With the fin application, precision of 0.3nm is demonstrated by measuring 5 dies with 10 consecutive runs. Capability to resolve within-die and localized within-macro height variation is also demonstrated. Results obtained from the fin measurements support the increasing trend that measurements

  12. Interaction imaging with amplitude-dependence force spectroscopy.

    PubMed

    Platz, Daniel; Forchheimer, Daniel; Tholén, Erik A; Haviland, David B

    2013-01-01

    Knowledge of surface forces is the key to understanding a large number of processes in fields ranging from physics to material science and biology. The most common method to study surfaces is dynamic atomic force microscopy (AFM). Dynamic AFM has been enormously successful in imaging surface topography, even to atomic resolution, but the force between the AFM tip and the surface remains unknown during imaging. Here we present a new approach that combines high-accuracy force measurements and high-resolution scanning. The method, called amplitude-dependence force spectroscopy (ADFS), is based on the amplitude dependence of the cantilever's response near resonance and allows for separate determination of both conservative and dissipative tip-surface interactions. We use ADFS to quantitatively study and map the nano-mechanical interaction between the AFM tip and heterogeneous polymer surfaces. ADFS is compatible with commercial atomic force microscopes and we anticipate its widespread use in taking AFM toward quantitative microscopy.

  13. Confocal Raman spectroscopy and AFM for evaluation of sidewalls in type II superlattice FPAs

    NASA Astrophysics Data System (ADS)

    Rotter, T. J.; Busani, T.; Rathi, P.; Jaeckel, F.; Reyes, P. A.; Malloy, K. J.; Ukhanov, A. A.; Plis, E.; Krishna, S.; Jaime-Vasquez, M.; Baril, N. F.; Benson, J. D.; Tenne, D. A.

    2015-06-01

    We propose to utilize confocal Raman spectroscopy combined with high resolution atomic force microscopy (AFM) for nondestructive characterisation of the sidewalls of etched and passivated small pixel (24 μm×24 μm) focal plane arrays (FPA) fabricated using LW/LWIR InAs/GaSb type-II strained layer superlattice (T2SL) detector material. Special high aspect ratio Si and GaAs AFM probes, with tip length of 13 μm and tip aperture less than 7°, allow characterisation of the sidewall morphology. Confocal microscopy enables imaging of the sidewall profile through optical sectioning. Raman spectra measured on etched T2SL FPA single pixels enable us to quantify the non-uniformity of the mesa delineation process.

  14. Characterization of human ovarian teratoma hair by using AFM, FT-IR, and Raman spectroscopy.

    PubMed

    Kim, Kyung Sook; Lee, Jinwoo; Jung, Min-Hyung; Choi, Young Joon; Park, Hun-Kuk

    2011-12-01

    The structural, physical, and chemical properties of hair taken from an ovarian teratoma (teratoma hair) was first examined by atomic force microscopy (AFM), Fourier transform infrared (FT-IR), and Raman spectroscopy. The similarities and differences between the teratoma hair and scalp hair were also investigated. Teratoma hair showed a similar morphology and chemical composition to scalp hair. Teratoma hair was covered with a cuticle in the same manner as scalp hair and showed the same amide bonding modes as scalp hair according to FT-IR and Raman spectroscopy. On the other hand, teratoma hair showed different physical properties and cysteic acid bands from scalp hair: the surface was rougher and the adhesive force was lower than the scalp hair. The cystine oxides modes did not change with the position unlike scalp hair. These differences can be understood by environmental effects not by the intrinsic properties of the teratoma hair.

  15. Atomic Force Microscope for Imaging and Spectroscopy

    NASA Technical Reports Server (NTRS)

    Pike, W. T.; Hecht, M. H.; Anderson, M. S.; Akiyama, T.; Gautsch, S.; deRooij, N. F.; Staufer, U.; Niedermann, Ph.; Howald, L.; Mueller, D.

    2000-01-01

    We have developed, built, and tested an atomic force microscope (AFM) for extraterrestrial applications incorporating a micromachined tip array to allow for probe replacement. It is part of a microscopy station originally intended for NASA's 2001 Mars lander to identify the size, distribution, and shape of Martian dust and soil particles. As well as imaging topographically down to nanometer resolution, this instrument can be used to reveal chemical information and perform infrared and Raman spectroscopy at unprecedented resolution.

  16. Analysis of DNA interactions using single-molecule force spectroscopy.

    PubMed

    Ritzefeld, Markus; Walhorn, Volker; Anselmetti, Dario; Sewald, Norbert

    2013-06-01

    Protein-DNA interactions are involved in many biochemical pathways and determine the fate of the corresponding cell. Qualitative and quantitative investigations on these recognition and binding processes are of key importance for an improved understanding of biochemical processes and also for systems biology. This review article focusses on atomic force microscopy (AFM)-based single-molecule force spectroscopy and its application to the quantification of forces and binding mechanisms that lead to the formation of protein-DNA complexes. AFM and dynamic force spectroscopy are exciting tools that allow for quantitative analysis of biomolecular interactions. Besides an overview on the method and the most important immobilization approaches, the physical basics of the data evaluation is described. Recent applications of AFM-based force spectroscopy to investigate DNA intercalation, complexes involving DNA aptamers and peptide- and protein-DNA interactions are given.

  17. A review of the application of atomic force microscopy (AFM) in food science and technology.

    PubMed

    Liu, Shaoyang; Wang, Yifen

    2011-01-01

    Atomic force microscopy (AFM) is a powerful nanoscale analysis technique used in food area. This versatile technique can be used to acquire high-resolution sample images and investigate local interactions in air or liquid surroundings. In this chapter, we explain the principles of AFM and review representative applications of AFM in gelatin, casein micelle, carrageenan, gellan gum, starch, and interface. We elucidate new knowledge revealed with AFM as well as ways to use AFM to obtain morphology and rheology information in different food fields.

  18. Surface-charge differentiation of streptavidin and avidin by atomic force microscopy-force spectroscopy.

    PubMed

    Almonte, Lisa; Lopez-Elvira, Elena; Baró, Arturo M

    2014-09-15

    Chemical information can be obtained by using atomic force microscopy (AFM) and force spectroscopy (FS) with atomic or molecular resolution, even in liquid media. The aim of this paper is to demonstrate that single molecules of avidin and streptavidin anchored to a biotinylated bilayer can be differentiated by using AFM, even though AFM topographical images of the two proteins are remarkably alike. At physiological pH, the basic glycoprotein avidin is positively charged, whereas streptavidin is a neutral protein. This charge difference can be determined with AFM, which can probe electrostatic double-layer forces by using FS. The force curves, owing to the electrostatic interaction, show major differences when measured on top of each protein as well as on the lipid substrate. FS data show that the two proteins are negatively charged. Nevertheless, avidin and streptavidin can be clearly distinguished, thus demonstrating the sensitivity of AFM to detect small changes in the charge state of macromolecules.

  19. A detailed guideline for the fabrication of single bacterial probes used for atomic force spectroscopy.

    PubMed

    Thewes, Nicolas; Loskill, Peter; Spengler, Christian; Hümbert, Sebastian; Bischoff, Markus; Jacobs, Karin

    2015-12-01

    The atomic force microscope (AFM) evolved as a standard device in modern microbiological research. However, its capability as a sophisticated force sensor is not used to its full capacity. The AFM turns into a unique tool for quantitative adhesion research in bacteriology by using "bacterial probes". Thereby, bacterial probes are AFM cantilevers that provide a single bacterium or a cluster of bacteria as the contact-forming object. We present a step-by-step protocol for preparing bacterial probes, performing force spectroscopy experiments and processing force spectroscopy data. Additionally, we provide a general insight into the field of bacterial cell force spectroscopy.

  20. Single molecule atomic force microscopy and force spectroscopy of chitosan.

    PubMed

    Kocun, Marta; Grandbois, Michel; Cuccia, Louis A

    2011-02-01

    Atomic force microscopy (AFM) and AFM-based force spectroscopy was used to study the desorption of individual chitosan polymer chains from substrates with varying chemical composition. AFM images of chitosan adsorbed onto a flat mica substrate show elongated single strands or aggregated bundles. The aggregated state of the polymer is consistent with the high level of flexibility and mobility expected for a highly positively charged polymer strand. Conversely, the visualization of elongated strands indicated the presence of stabilizing interactions with the substrate. Surfaces with varying chemical composition (glass, self-assembled monolayer of mercaptoundecanoic acid/decanethiol and polytetrafluoroethylene (PTFE)) were probed with chitosan modified AFM tips and the corresponding desorption energies, calculated from plateau-like features, were attributed to the desorption of individual polymer strands. Desorption energies of 2.0±0.3×10(-20)J, 1.8±0.3×10(-20)J and 3.5±0.3×10(-20)J were obtained for glass, SAM of mercaptoundecanoic/dodecanethiol and PTFE, respectively. These single molecule level results can be used as a basis for investigating chitosan and chitosan-based materials for biomaterial applications.

  1. Vibrational CD (VCD) and atomic force microscopy (AFM) study of DNA interaction with Cr3+ ions: VCD and AFM evidence of DNA condensation.

    PubMed

    Andrushchenko, V; Leonenko, Z; Cramb, D; van de Sande, H; Wieser, H

    The interaction of natural calf thymus DNA with Cr(3+) ions was studied at room temperature by means of vibrational CD (VCD) and infrared absorption (ir) spectroscopy, and atomic force microscopy (AFM). Cr(3+) ion binding mainly to N(7) (G) and to phosphate groups was demonstrated. Psi-type VCD spectra resembling electronic CD (ECD) spectra, which appear during psi-type DNA condensation, were observed. These spectra are characterized mainly by an anomalous, severalfold increase of VCD intensity. Such anomalous VCD spectra were assigned to DNA condensation with formation of large and dense particles of a size comparable to the wavelength of the probing ir beam and possessing large-scale helicity. Atomic force microscopy confirmed DNA condensation by Cr(3+) ions and the formation of tight DNA particles responsible for the psi-type VCD spectra. Upon increasing the Cr(3+) ion concentration the shape of the condensates changed from loose flower-like structures to highly packed dense spheres. No DNA denaturation was seen even at the highest concentration of Cr(3+) ions studied. The secondary structure of DNA remained in a B-form before and after the condensation. VCD and ir as well as AFM proved to be an effective combination for investigating DNA condensation. In addition to the ability of VCD to determine DNA condensation, VCD and ir can in the same experiment provide unambiguous information about the secondary structure of DNA contained in the condensed particles.

  2. Increased imaging speed and force sensitivity for bio-applications with small cantilevers using a conventional AFM setup

    PubMed Central

    Leitner, Michael; Fantner, Georg E.; Fantner, Ernest J.; Ivanova, Katerina; Ivanov, Tzvetan; Rangelow, Ivo; Ebner, Andreas; Rangl, Martina; Tang, Jilin; Hinterdorfer, Peter

    2012-01-01

    In this study, we demonstrate the increased performance in speed and sensitivity achieved by the use of small AFM cantilevers on a standard AFM system. For this, small rectangular silicon oxynitride cantilevers were utilized to arrive at faster atomic force microscopy (AFM) imaging times and more sensitive molecular recognition force spectroscopy (MRFS) experiments. The cantilevers we used had lengths between 13 and 46 μm, a width of about 11 μm, and a thickness between 150 and 600 nm. They were coated with chromium and gold on the backside for a better laser reflection. We characterized these small cantilevers through their frequency spectrum and with electron microscopy. Due to their small size and high resonance frequency we were able to increase the imaging speed by a factor of 10 without any loss in resolution for images from several μm scansize down to the nanometer scale. This was shown on bacterial surface layers (s-layer) with tapping mode under aqueous, near physiological conditions and on nuclear membranes in contact mode in ambient environment. In addition, we showed that single molecular forces can be measured with an up to 5 times higher force sensitivity in comparison to conventional cantilevers with similar spring constants. PMID:22721963

  3. Taking nanomedicine teaching into practice with atomic force microscopy and force spectroscopy.

    PubMed

    Carvalho, Filomena A; Freitas, Teresa; Santos, Nuno C

    2015-12-01

    Atomic force microscopy (AFM) is a useful and powerful tool to study molecular interactions applied to nanomedicine. The aim of the present study was to implement a hands-on atomic AFM course for graduated biosciences and medical students. The course comprises two distinct practical sessions, where students get in touch with the use of an atomic force microscope by performing AFM scanning images of human blood cells and force spectroscopy measurements of the fibrinogen-platelet interaction. Since the beginning of this course, in 2008, the overall rating by the students was 4.7 (out of 5), meaning a good to excellent evaluation. Students were very enthusiastic and produced high-quality AFM images and force spectroscopy data. The implementation of the hands-on AFM course was a success, giving to the students the opportunity of contact with a technique that has a wide variety of applications on the nanomedicine field. In the near future, nanomedicine will have remarkable implications in medicine regarding the definition, diagnosis, and treatment of different diseases. AFM enables students to observe single molecule interactions, enabling the understanding of molecular mechanisms of different physiological and pathological processes at the nanoscale level. Therefore, the introduction of nanomedicine courses in bioscience and medical school curricula is essential.

  4. FRAME (Force Review Automation Environment): MATLAB-based AFM data processor.

    PubMed

    Partola, Kostyantyn R; Lykotrafitis, George

    2016-05-03

    Data processing of force-displacement curves generated by atomic force microscopes (AFMs) for elastic moduli and unbinding event measurements is very time consuming and susceptible to user error or bias. There is an evident need for consistent, dependable, and easy-to-use AFM data processing software. We have developed an open-source software application, the force review automation environment (or FRAME), that provides users with an intuitive graphical user interface, automating data processing, and tools for expediting manual processing. We did not observe a significant difference between manually processed and automatically processed results from the same data sets.

  5. Imaging and force measurement of LDL and HDL by AFM in air and liquid

    PubMed Central

    Gan, Chaoye; Ao, Meiying; Liu, Zhanghua; Chen, Yong

    2015-01-01

    The size and biomechanical properties of lipoproteins are tightly correlated with their structures/functions. While atomic force microscopy (AFM) has been used to image lipoproteins the force measurement of these nano-sized particles is missing. We detected that the sizes of LDL and HDL in liquid are close to the commonly known values. The Young’s modulus of LDL or HDL is ∼0.4 GPa which is similar to that of some viral capsids or nanovesicles but greatly larger than that of various liposomes. The adhesive force of LDL or HDL is small (∼200 pN). The comparison of AFM detection in air and liquid was also performed which is currently lacking. Our data may provide useful information for better understanding and AFM detection of lipoproteins. PMID:25893163

  6. Imaging and force measurement of LDL and HDL by AFM in air and liquid.

    PubMed

    Gan, Chaoye; Ao, Meiying; Liu, Zhanghua; Chen, Yong

    2015-01-01

    The size and biomechanical properties of lipoproteins are tightly correlated with their structures/functions. While atomic force microscopy (AFM) has been used to image lipoproteins the force measurement of these nano-sized particles is missing. We detected that the sizes of LDL and HDL in liquid are close to the commonly known values. The Young's modulus of LDL or HDL is ∼0.4 GPa which is similar to that of some viral capsids or nanovesicles but greatly larger than that of various liposomes. The adhesive force of LDL or HDL is small (∼200 pN). The comparison of AFM detection in air and liquid was also performed which is currently lacking. Our data may provide useful information for better understanding and AFM detection of lipoproteins.

  7. Using AFM Force Curves to Explore Properties of Elastomers

    ERIC Educational Resources Information Center

    Ferguson, Megan A.; Kozlowski, Joseph J.

    2013-01-01

    polydimethylsiloxane (PDMS) elastomers. Force curves are used to quantify the stiffness of elastomers prepared with different base-to-curing agent ratios. Trends in observed spring constants of the…

  8. Atomic force microscopy and force spectroscopy on the assessment of protein folding and functionality.

    PubMed

    Carvalho, Filomena A; Martins, Ivo C; Santos, Nuno C

    2013-03-01

    Atomic force microscopy (AFM) applied to biological systems can, besides generating high-quality and well-resolved images, be employed to study protein folding via AFM-based force spectroscopy. This approach allowed remarkable advances in the measurement of inter- and intramolecular interaction forces with piconewton resolution. The detection of specific interaction forces between molecules based on the AFM sensitivity and the manipulation of individual molecules greatly advanced the understanding of intra-protein and protein-ligand interactions. Apart from the academic interest in the resolution of basic scientific questions, this technique has also key importance on the clarification of several biological questions of immediate biomedical relevance. Force spectroscopy is an especially appropriate technique for "mechanical proteins" that can provide crucial information on single protein molecules and/or domains. Importantly, it also has the potential of combining in a single experiment spatial and kinetic measurements. Here, the main principles of this methodology are described, after which the ability to measure interactions at the single-molecule level is discussed, in the context of relevant protein-folding examples. We intend to demonstrate the potential of AFM-based force spectroscopy in the study of protein folding, especially since this technique is able to circumvent some of the difficulties typically encountered in classical thermal/chemical denaturation studies.

  9. Molecular shape and binding force of Mycoplasma mobile's leg protein Gli349 revealed by an AFM study

    SciTech Connect

    Lesoil, Charles; Nonaka, Takahiro; Sekiguchi, Hiroshi; Osada, Toshiya; Miyata, Makoto; Afrin, Rehana; Ikai, Atsushi

    2010-01-15

    Recent studies of the gliding bacteria Mycoplasma mobile have identified a family of proteins called the Gli family which was considered to be involved in this novel and yet fairly unknown motility system. The 349 kDa protein called Gli349 was successfully isolated and purified from the bacteria, and electron microscopy imaging and antibody experiments led to the hypothesis that it acts as the 'leg' of M. mobile, responsible for attachment to the substrate as well as for gliding motility. However, more precise evidence of the molecular shape and function of this protein was required to asses this theory any further. In this study, an atomic force microscope (AFM) was used both as an imaging and a force measurement device to provide new information about Gli349 and its role in gliding motility. AFM images of the protein were obtained revealing a complex structure with both rigid and flexible parts, consistent with previous electron micrographs of the protein. Single-molecular force spectroscopy experiments were also performed, revealing that Gli349 is able to specifically bind to sialyllactose molecules and withstand unbinding forces around 70 pN. These findings strongly support the idea that Gli349 is the 'leg' protein of M. mobile, responsible for binding and also most probably force generation during gliding motility.

  10. AFM study of forces between silica, silicon nitride and polyurethane pads.

    PubMed

    Sokolov, Igor; Ong, Quy K; Shodiev, Hasan; Chechik, Nina; James, David; Oliver, Mike

    2006-08-15

    Interaction of silica and silicon nitride with polyurethane surfaces is rather poorly studied despite being of great interest for modern semiconductor industry, e.g., for chemical-mechanical planarization (CMP) processes. Here we show the results from the application of the atomic force microscopy (AFM) technique to study the forces between silica or silicon nitride (AFM tips) and polyurethane surfaces in aqueous solutions of different acidity. The polyurethane surface potentials are derived from the measured AFM data. The obtained potentials are in rather good agreement with measurements of zeta-potentials using the streaming-potentials method. Another important parameter, adhesion, is also measured. While the surface potentials of silica are well known, there are ambiguous results on the potentials of silicon nitride that is naturally oxidized. Deriving the surface potential of the naturally oxidized silicon nitride from our measurements, we show that it is not oxidized to silica despite some earlier published expectations.

  11. Multiparametric high-resolution imaging of native proteins by force-distance curve-based AFM.

    PubMed

    Pfreundschuh, Moritz; Martinez-Martin, David; Mulvihill, Estefania; Wegmann, Susanne; Muller, Daniel J

    2014-05-01

    A current challenge in the life sciences is to understand how the properties of individual molecular machines adjust in order to meet the functional requirements of the cell. Recent developments in force-distance (FD) curve-based atomic force microscopy (FD-based AFM) enable researchers to combine sub-nanometer imaging with quantitative mapping of physical, chemical and biological properties. Here we present a protocol to apply FD-based AFM to the multiparametric imaging of native proteins under physiological conditions. We describe procedures for experimental FD-based AFM setup, high-resolution imaging of proteins in the native unperturbed state with simultaneous quantitative mapping of multiple parameters, and data interpretation and analysis. The protocol, which can be completed in 1-3 d, enables researchers to image proteins and protein complexes in the native unperturbed state and to simultaneously map their biophysical and biochemical properties at sub-nanometer resolution.

  12. Detection of viruses: atomic force microscopy and surface enhanced raman spectroscopy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This paper demonstrated the capability of atomic force microscopy (AFM) and surface enhanced Raman spectroscopy (SERS) to function effectively as ultra-sensitive readout tools for chip-scale platforms designed for pathogen detection in complex biological media. AFM allows direct (i.e. label-free) vi...

  13. Dynamic force microscopy simulator (dForce): A tool for planning and understanding tapping and bimodal AFM experiments

    PubMed Central

    Guzman, Horacio V; Garcia, Pablo D

    2015-01-01

    Summary We present a simulation environment, dForce, which can be used for a better understanding of dynamic force microscopy experiments. The simulator presents the cantilever–tip dynamics for two dynamic AFM methods, tapping mode AFM and bimodal AFM. It can be applied for a wide variety of experimental situations in air or liquid. The code provides all the variables and parameters relevant in those modes, for example, the instantaneous deflection and tip–surface force, velocity, virial, dissipated energy, sample deformation and peak force as a function of time or distance. The simulator includes a variety of interactions and contact mechanics models to describe AFM experiments including: van der Waals, Hertz, DMT, JKR, bottom effect cone correction, linear viscoelastic forces or the standard linear solid viscoelastic model. We have compared two numerical integration methods to select the one that offers optimal accuracy and speed. The graphical user interface has been designed to facilitate the navigation of non-experts in simulations. Finally, the accuracy of dForce has been tested against numerical simulations performed during the last 18 years. PMID:25821676

  14. Minimizing pulling geometry errors in atomic force microscope single molecule force spectroscopy.

    PubMed

    Rivera, Monica; Lee, Whasil; Ke, Changhong; Marszalek, Piotr E; Cole, Daniel G; Clark, Robert L

    2008-10-01

    In atomic force microscopy-based single molecule force spectroscopy (AFM-SMFS), it is assumed that the pulling angle is negligible and that the force applied to the molecule is equivalent to the force measured by the instrument. Recent studies, however, have indicated that the pulling geometry errors can drastically alter the measured force-extension relationship of molecules. Here we describe a software-based alignment method that repositions the cantilever such that it is located directly above the molecule's substrate attachment site. By aligning the applied force with the measurement axis, the molecule is no longer undergoing combined loading, and the full force can be measured by the cantilever. Simulations and experimental results verify the ability of the alignment program to minimize pulling geometry errors in AFM-SMFS studies.

  15. Minimizing Pulling Geometry Errors in Atomic Force Microscope Single Molecule Force Spectroscopy

    PubMed Central

    Rivera, Monica; Lee, Whasil; Ke, Changhong; Marszalek, Piotr E.; Cole, Daniel G.; Clark, Robert L.

    2008-01-01

    In atomic force microscopy-based single molecule force spectroscopy (AFM-SMFS), it is assumed that the pulling angle is negligible and that the force applied to the molecule is equivalent to the force measured by the instrument. Recent studies, however, have indicated that the pulling geometry errors can drastically alter the measured force-extension relationship of molecules. Here we describe a software-based alignment method that repositions the cantilever such that it is located directly above the molecule's substrate attachment site. By aligning the applied force with the measurement axis, the molecule is no longer undergoing combined loading, and the full force can be measured by the cantilever. Simulations and experimental results verify the ability of the alignment program to minimize pulling geometry errors in AFM-SMFS studies. PMID:18641069

  16. PREFACE: NC-AFM 2004: Proceedings of the 7th International Conference on Non-contact Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Schwarz, Udo

    2005-03-01

    With the ongoing miniaturization of devices and controlled nanostructuring of materials, the importance of atomic-scale information on surfaces and surface properties is growing continuously. The astonishing progress in nanoscience and nanotechnology that took place during the last two decades was in many ways related to recent progress in high-resolution imaging techniques such as scanning tunnelling microscopy and transmission electron microscopy. Since the mid-1990s, non-contact atomic force microscopy (NC-AFM) performed in ultrahigh vacuum has evolved as an alternative technique that achieves atomic resolution, but without the restriction to conducting surfaces of the previously established techniques. Advances of the rapidly developing field of NC-AFM are discussed at annual conferences as part of a series that started in 1998 in Osaka, Japan. This special issue of Nanotechnology is a compilation of original work presented at the 7th International Conference on Non-contact Atomic Force Microscopy that took place in Seattle, USA, 12-15 September 2004. Over the years, the conference grew in size and scope. Atomic resolution imaging of oxides and semiconductors remains an issue. Noticeable new developments have been presented in this regard such as, e.g., the demonstrated ability to manipulate individual atoms. Additionally, the investigation of individual molecules, clusters, and organic materials gains more and more attention. In this context, considerable effort is undertaken to transfer the NC-AFM principle based on frequency modulation to applications in air and liquids with the goal of enabling high-resolution surface studies of biological material in native environments, as well as to reduce the experimental complexity, which so far involves the availability of (costly) vacuum systems. Force spectroscopy methods continue to be improved and are applied to topics such as the imaging of the three-dimensional force field as a function of the distance with

  17. Force Spectroscopy in Studying Infection.

    PubMed

    Zhou, Zhaokun; Leake, Mark C

    2016-01-01

    Biophysical force spectroscopy tools-for example, optical tweezers, magnetic tweezers, atomic force microscopy-have been used to study elastic, mechanical, conformational and dynamic properties of single biological specimens from single proteins to whole cells to reveal information not accessible by ensemble average methods such as X-ray crystallography, mass spectroscopy, gel electrophoresis and so on. Here, we review the application of these tools on a range of infection-related questions from antibody-inhibited protein processivity to virus-cell adhesion. In each case, we focus on how the instrumental design tailored to the biological system in question translates into the functionality suitable for that particular study. The unique insights that force spectroscopy has gained to complement knowledge learned through population averaging techniques in interrogating biomolecular details prove to be instrumental in therapeutic innovations such as those in structure-based drug design.

  18. Dynamics of a disturbed sessile drop measured by atomic force microscopy (AFM).

    PubMed

    McGuiggan, Patricia M; Grave, Daniel A; Wallace, Jay S; Cheng, Shengfeng; Prosperetti, Andrea; Robbins, Mark O

    2011-10-04

    A new method for studying the dynamics of a sessile drop by atomic force microscopy (AFM) is demonstrated. A hydrophobic microsphere (radius, r ∼ 20-30 μm) is brought into contact with a small sessile water drop resting on a polytetrafluoroethylene (PTFE) surface. When the microsphere touches the liquid surface, the meniscus rises onto it because of capillary forces. Although the microsphere volume is 6 orders of magnitude smaller than the drop, it excites the normal resonance modes of the liquid interface. The sphere is pinned at the interface, whose small (<100 nm) oscillations are readily measured with AFM. Resonance oscillation frequencies were measured for drop volumes between 5 and 200 μL. The results for the two lowest normal modes are quantitatively consistent with continuum calculations for the natural frequency of hemispherical drops with no adjustable parameters. The method may enable sensitive measurements of volume, surface tension, and viscosity of small drops.

  19. Direct Measurement of Optical Force Induced by Near-Field Plasmonic Cavity Using Dynamic Mode AFM

    PubMed Central

    Guan, Dongshi; Hang, Zhi Hong; Marcet, Zsolt; Liu, Hui; Kravchenko, I. I.; Chan, C. T.; Chan, H. B.; Tong, Penger

    2015-01-01

    Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength gold disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. The experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures. PMID:26586455

  20. Direct measurement of optical force induced by near-field plasmonic cavity using dynamic mode AFM

    DOE PAGES

    Guan, Dongshi; Hang, Zhi Hong; Marset, Zsolt; ...

    2015-11-20

    Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength goldmore » disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. Lastly, the experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures.« less

  1. Direct measurement of optical force induced by near-field plasmonic cavity using dynamic mode AFM

    SciTech Connect

    Guan, Dongshi; Hang, Zhi Hong; Marset, Zsolt; Liu, Hui; Kravchenko, Ivan I.; Chan, Ho Bun; Chan, C. T.; Tong, Penger

    2015-11-20

    Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength gold disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. Lastly, the experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures.

  2. Communication: Atomic force detection of single-molecule nonlinear optical vibrational spectroscopy

    SciTech Connect

    Saurabh, Prasoon Mukamel, Shaul

    2014-04-28

    Atomic Force Microscopy (AFM) allows for a highly sensitive detection of spectroscopic signals. This has been first demonstrated for NMR of a single molecule and recently extended to stimulated Raman in the optical regime. We theoretically investigate the use of optical forces to detect time and frequency domain nonlinear optical signals. We show that, with proper phase matching, the AFM-detected signals closely resemble coherent heterodyne-detected signals. Applications are made to AFM-detected and heterodyne-detected vibrational resonances in Coherent Anti-Stokes Raman Spectroscopy (χ{sup (3)}) and sum or difference frequency generation (χ{sup (2)})

  3. Communication: atomic force detection of single-molecule nonlinear optical vibrational spectroscopy.

    PubMed

    Saurabh, Prasoon; Mukamel, Shaul

    2014-04-28

    Atomic Force Microscopy (AFM) allows for a highly sensitive detection of spectroscopic signals. This has been first demonstrated for NMR of a single molecule and recently extended to stimulated Raman in the optical regime. We theoretically investigate the use of optical forces to detect time and frequency domain nonlinear optical signals. We show that, with proper phase matching, the AFM-detected signals closely resemble coherent heterodyne-detected signals. Applications are made to AFM-detected and heterodyne-detected vibrational resonances in Coherent Anti-Stokes Raman Spectroscopy (χ((3))) and sum or difference frequency generation (χ((2))).

  4. Molecular force spectroscopy on cells.

    PubMed

    Liu, Baoyu; Chen, Wei; Zhu, Cheng

    2015-04-01

    Molecular force spectroscopy has become a powerful tool to study how mechanics regulates biology, especially the mechanical regulation of molecular interactions and its impact on cellular functions. This force-driven methodology has uncovered a wealth of new information of the physical chemistry of molecular bonds for various biological systems. The new concepts, qualitative and quantitative measures describing bond behavior under force, and structural bases underlying these phenomena have substantially advanced our fundamental understanding of the inner workings of biological systems from the nanoscale (molecule) to the microscale (cell), elucidated basic molecular mechanisms of a wide range of important biological processes, and provided opportunities for engineering applications. Here, we review major force spectroscopic assays, conceptual developments of mechanically regulated kinetics of molecular interactions, and their biological relevance. We also present current challenges and highlight future directions.

  5. Atomic force microscopy and spectroscopy to probe single membrane proteins in lipid bilayers.

    PubMed

    Sapra, K Tanuj

    2013-01-01

    The atomic force microscope (AFM) has opened vast avenues hitherto inaccessible to the biological scientist. The high temporal (millisecond) and spatial (nanometer) resolutions of the AFM are suited for studying many biological processes in their native conditions. The AFM cantilever stylus is aptly termed as a "lab on a tip" owing to its versatility as an imaging tool as well as a handle to manipulate single bonds and proteins. Recent examples assert that the AFM can be used to study the mechanical properties and monitor processes of single proteins and single cells, thus affording insight into important mechanistic details. This chapter specifically focuses on practical and analytical protocols of single-molecule AFM methodologies related to high-resolution imaging and single-molecule force spectroscopy of membrane proteins. Both these techniques are operator oriented, and require specialized working knowledge of the instrument, theoretical, and practical skills.

  6. Interaction force measurement between E. coli cells and nanoparticles immobilized surfaces by using AFM

    SciTech Connect

    Zhang, Wen; Chen, Yongsheng

    2011-01-01

    To better understand environmental behaviors of nanoparticles (NPs), we used the atomic force microscopy (AFM) to measure interaction forces between E. coli cells and NPs immobilized on surfaces in an aqueous environment. The results showed that adhesion force strength was significantly influenced by particle size for both hematite ( -Fe2 O3 ) and corundum ( -Al2 O3 ) NPs whereas the effect on the repulsive force was not observed. The adhesion force decreased from 6.3 0.7 nN to 0.8 0.4 nN as hematite NPs increased from 26 nm to 98 nm in diameter. Corundum NPs exhibited a similar dependence of adhesion force on particle size. The Johnson Kendall Roberts (JKR) model was employed to estimate the contact area between E. coli cells and NPs, and based on the JKR model a new model that considers local effective contact area was developed. The prediction of the new model matched the size dependence of adhesion force in experimental results. Size effects on adhesion forces may originate from the difference in local effective contact areas as supported by our model. These findings provide fundamental information for interpreting the environmental behaviors and biological interactions of NPs, which barely have been addressed.

  7. Following aptamer-ricin specific binding by single molecule recognition and force spectroscopy measurements

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The atomic force microscope (AFM) recognition and dynamic force spectroscopy (DFS) experiments provide both morphology and interaction information of the aptamer and protein, which can be used for the future study on the thermodynamics and kinetics properties of ricin-aptamer/antibody interactions. ...

  8. Magnetoelectric versus thermal actuation characteristics of shear force AFM probes with piezoresistive detection

    NASA Astrophysics Data System (ADS)

    Sierakowski, Andrzej; Kopiec, Daniel; Majstrzyk, Wojciech; Kunicki, Piotr; Janus, Paweł; Dobrowolski, Rafał; Grabiec, Piotr; Rangelow, Ivo W.; Gotszalk, Teodor

    2017-03-01

    In this paper the authors compare methods used for piezoresistive microcantilevers actuation for the atomic force microscopy (AFM) imaging in the dynamic shear force mode. The piezoresistive detection is an attractive technique comparing the optical beam detection of deflection. The principal advantage is that no external alignment of optical source and detector are needed. When the microcantilever is deflected, the stress is transferred into a change of resistivity of piezoresistors. The integration of piezoresistive read-out provides a promising solution in realizing a compact non-contact AFM. Resolution of piezoresistive read-out is limited by three main noise sources: Johnson, 1/f and thermomechanical noise. In the dynamic shear force mode measurement the method used for cantilever actuation will also affect the recorded noise in the piezoresistive detection circuit. This is the result of a crosstalk between an aluminium path (current loop used for actuation) and piezoresistors located near the base of the beam. In this paper authors described an elaborated in ITE (Institute of Electron Technology) technology of fabrication cantilevers with piezoresistive detection of deflection and compared efficiency of two methods used for cantilever actuation.

  9. Medical applications of atomic force microscopy and Raman spectroscopy.

    PubMed

    Choi, Samjin; Jung, Gyeong Bok; Kim, Kyung Sook; Lee, Gi-Ja; Park, Hun-Kuk

    2014-01-01

    This paper reviews the recent research and application of atomic force microscopy (AFM) and Raman spectroscopy techniques, which are considered the multi-functional and powerful toolkits for probing the nanostructural, biomechanical and physicochemical properties of biomedical samples in medical science. We introduce briefly the basic principles of AFM and Raman spectroscopy, followed by diagnostic assessments of some selected diseases in biomedical applications using them, including mitochondria isolated from normal and ischemic hearts, hair fibers, individual cells, and human cortical bone. Finally, AFM and Raman spectroscopy applications to investigate the effects of pharmacotherapy, surgery, and medical device therapy in various medicines from cells to soft and hard tissues are discussed, including pharmacotherapy--paclitaxel on Ishikawa and HeLa cells, telmisartan on angiotensin II, mitomycin C on strabismus surgery and eye whitening surgery, and fluoride on primary teeth--and medical device therapy--collagen cross-linking treatment for the management of progressive keratoconus, radiofrequency treatment for skin rejuvenation, physical extracorporeal shockwave therapy for healing of Achilles tendinitis, orthodontic treatment, and toothbrushing time to minimize the loss of teeth after exposure to acidic drinks.

  10. Scanning electron and atomic force microscopy, and raman and x-ray photoelectron spectroscopy characterization of near-isogenic soft and hard wheat kernels and corresponding flours

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) are used to investigate vitreous (hard) and non-vitreous (soft) wheat kernels and their corresponding wheat flours. AFM data reveal two different microstructures. The vitreous kernel reveals a granular text...

  11. Piezoelectric tuning fork probe for atomic force microscopy imaging and specific recognition force spectroscopy of an enzyme and its ligand.

    PubMed

    Makky, Ali; Viel, Pascal; Chen, Shu-wen Wendy; Berthelot, Thomas; Pellequer, Jean-Luc; Polesel-Maris, Jérôme

    2013-11-01

    Piezoelectric quartz tuning fork has drawn the attention of many researchers for the development of new atomic force microscopy (AFM) self-sensing probes. However, only few works have been done for soft biological materials imaging in air or aqueous conditions. The aim of this work was to demonstrate the efficiency of the AFM tuning fork probe to perform high-resolution imaging of proteins and to study the specific interaction between a ligand and its receptor in aqueous media. Thus, a new kind of self-sensing AFM sensor was introduced to realize imaging and biochemical specific recognition spectroscopy of glucose oxidase enzyme using a new chemical functionalization procedure of the metallic tips based on the electrochemical reduction of diazonium salt. This scanning probe as well as the functionalization strategy proved to be efficient respectively for the topography and force spectroscopy of soft biological materials in buffer conditions.

  12. [Study of in-situ measurement system for porous alumina film based on AFM and reflectometric interference spectroscopy].

    PubMed

    Liu, Chao; Zhang, Dong-Xian; Zhang, Hai-Jun

    2008-07-01

    An in-situ measurement system for porous alumina (PA) film based on atomic force microscope (AFM) in liquid and reflectometric interference spectroscopy (RIFS) was developed. The present article briefly discusses the principle and structure of the system, and introduces its unique characteristic. The system consists of probe unit, XY scanner, Z-piezo feedback system, computer and software, fiber optic spectrometer, anodization control circuitry etc. When a white light beam illuminates the surface of the film, the reflective light beams at the front and back side of the layer are coherent, and lead to periodical amplifications and extinction in the reflective spectrum with the information of the optical thickness of the film. A fiber optic spectrometer was applied in the system which input the refractive spectrum into the computer by which the optical thickness of the film was calculated. Meanwhile according to the surface topography of PA films by AFM in liquid, the effective refractive index was calculated based on Maxwell-Garnett theory and coherent potential approximation (CPA). So the thickness of PA films could be gained at last. To checkout the feasibility and stability of the system, the real-time scanning and thickness measurement experiments were done during anodization of Al sheets in oxalic acid aqueous solution. In the experiment, the authors used 25 mm diameter aluminum (Al) sheets with 99.999% purity and 0.4 mm thickness as the anode, and graphite rod as the cathode. The pretreatment-cleaned Al sheets were anodized in an aqueous solution of 0.5 mol x L(-1) oxalic acid at the constant temperature (20 +/- 0.2) degrees C with 20 mA x cm(-2) anodization electronic current density. Real-time AFM images of PA film were successfully obtained during anodization. The pore-ratios of Al sheet were 7.81% and 13.83% at oxidizing time 150 min and 180 min respectively. Correspondingly, the effective indexes were calculated to be 1.62 and 1.60, respectively

  13. Investigating single molecule adhesion by atomic force spectroscopy.

    PubMed

    Stetter, Frank W S; Kienle, Sandra; Krysiak, Stefanie; Hugel, Thorsten

    2015-02-27

    Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment.

  14. Investigating Single Molecule Adhesion by Atomic Force Spectroscopy

    PubMed Central

    Stetter, Frank W. S.; Kienle, Sandra; Krysiak, Stefanie; Hugel, Thorsten

    2015-01-01

    Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment. PMID:25867282

  15. Fabrication and characterization of mesoscale protein patterns using atomic force microscopy (AFM)

    NASA Astrophysics Data System (ADS)

    Gao, Pei

    2011-07-01

    A versatile AFM local oxidation lithography was developed for fabricating clean protein patterns ranging from nanometer to sub-millimeter scale on octadecyltrichlorosilane (OTS) layer of Si (100) wafer. This protein patterning method can generate bio-active protein pattern with a clean background without the need of the anti-fouling the surface or repetitive rinsing. As a model system, lysozyme protein patterns were investigated through their binding reactions with antibodies and aptamers by AFM. Polyclonal anti-lysozyme antibodies and anti-lysozyme aptamer are found to preferentially bind to the lysozyme molecules on the edge of a protein pattern before their binding to the interior ones. It was also demonstrated that the topography of the immobilized protein pattern affects the antibody binding direction. We found that the anti-lysozyme antibodies binding to the edge lysozyme molecules on the half-buried pattern started from the top but the binding on the extruded pattern started from the side because of their different spatial accessibility. In addition, after incubating lysozyme pattern with anti-lysozyme aptamer in buffer solution for enough long time, some fractal-shaped aptamer fibers with 1-6nm high and up to tens of micrometers long were formed by the self-assembling of aptamer molecules on the surface. The aptamer fibers anchor specifically on the edge of protein patterns, which originates from the biospecific recognition between the aptamer and its target protein. Once these edge-bound fibers have formed, they can serve as scaffolds for further assembly processes. We used these aptamer fibers as templates to fabricate palladium and streptavidin nanowires, which anchored on the pattern edges and never cross over or collapse over each other. The aptamer fiber scaffold potentially can lead to an effective means to fabricate and interface nanowires to existing surface patterns. KEYWORDS: Atomic Force Microscopy (AFM), Protein Patterns, Lysozyme, Aptamer

  16. AFM study of forces between silicon oil and hydrophobic-hydrophilic surfaces in aqueous solutions.

    PubMed

    Zbik, Marek S; Frost, Ray L

    2010-09-15

    An investigation has been made of the interactions between silicone oil and various solid substrates immersed in aqueous solutions. Measurements were made using an atomic force microscope (AFM) using the colloid-probe method. The silicone oil drop is simulated by coating a small silica sphere with the oil, and measuring the force as this coated sphere is brought close to contact with a flat solid surface. It is found that the silicone oil surface is negatively charged, which causes a double-layer repulsion between the oil drop and another negatively charged surface such as mica. With hydrophilic solids, this repulsion is strong enough to prevent attachment of the drop to the solid. However, with hydrophobic surfaces there is an additional attractive force which overcomes the double-layer repulsion, and the silicone oil drop attaches to the solid. There is circumstantial evidence that linear and nonlinear effect take part in force results from compression of the silicone oil film coated on the glass sphere.

  17. Effect of enamel morphology on nanoscale adhesion forces of streptococcal bacteria : An AFM study.

    PubMed

    Wang, Chuanyong; Zhao, Yongqi; Zheng, Sainan; Xue, Jing; Zhou, Jinglin; Tang, Yi; Jiang, Li; Li, Wei

    2015-01-01

    We explore the influence of enamel surface morphology on nanoscale bacterial adhesion forces. Three dimensional morphology characteristics of enamel slices, which were treated with phosphoric acid (for 0 s, 5 s, 10 s, 20 s, and 30 s), were acquired. Adhesion forces of three initial colonizers (Streptococcus oralis, Streptococcus sanguinis, and Streptococcus mitis) and two cariogenic bacterial strains (Streptococcus mutans and Streptococcus sobrinus) with etched enamel surfaces were determined. Comparison of the forces was made by using bacterial probe method under atomic force microscope (AFM) in adhesion buffer. The results showed that enamel morphology was significantly altered by etching treatment. The roughness, peak-to-valley height, and valley-to-valley width of the depth profile, surface area, and volume increased linearly with acid exposure time, and reached the maximum at 30s, respectively. The adhesion forces of different strains increased accordingly with etching time. Adhesion forces of S. oralis, S. mitis, S. mutans, and S. sobrinus reached the maximum values of 0.81 nN, 0.84 nN, 0.73 nN, and 0.64 nN with enamel treated for 20s, respectively, whereas that of S. sanguinis at 10s (1.28nN), and dropped on coarser enamel surfaces. In conclusion, enamel micro-scale morphology may significantly alter the direct adhesion forces of bacteria. And there may be a threshold roughness for bacterial adhesion on enamel surface.

  18. Dual role of Cu²⁺ ions on the aggregation and degradation of soluble Aβ oligomers and protofibrils investigated by fluorescence spectroscopy and AFM.

    PubMed

    García, Silvia; Cuscó, Cristina; Brissos, Rosa F; Torrents, Ester; Caubet, Amparo; Gamez, Patrick

    2012-11-01

    The neuropathological character of copper(II) ions (Cu(2+)) upon interaction with soluble human amyloid-β(1-42) that subsequently generates senile plaques and/or reactive oxygen species (ROS) is considered as one of the very important features of Alzheimer's disease. The present study carried out by using fluorescence spectroscopy and atomic-force microscopy (AFM) indeed confirms the dual role played by Cu(2+), namely as mediator of protein aggregation and as generator of ROS leading to irreversible protein alteration, which most likely involve two distinct copper-binding sites. The AFM investigations clearly evidence the copper-induced aggregation of Aβ oligomers and protofibrils, while comparative fluorescence measurements with copper and zinc reveals the crucial involvement of redox-active copper in the generation of Aβ-cross-linked structures.

  19. Nanomechanical characterization of nanostructured bainitic steel: Peak Force Microscopy and Nanoindentation with AFM

    PubMed Central

    Morales-Rivas, Lucia; González-Orive, Alejandro; Garcia-Mateo, Carlos; Hernández-Creus, Alberto; Caballero, Francisca G.; Vázquez, Luis

    2015-01-01

    The full understanding of the deformation mechanisms in nanostructured bainite requires the local characterization of its mechanical properties, which are expected to change from one phase, bainitic ferrite, to another, austenite. This study becomes a challenging process due to the bainitic nanostructured nature and high Young’s modulus. In this work, we have carried out such study by means of the combination of AFM-based techniques, such as nanoindentation and Peak Force Quantitative Nanomechanical Mapping (PF-QNM) measurements. We have addressed critically the limits and advantages of these techniques and been able to measure some elastoplastic parameters of both phases. Specifically, we have analyzed by PF-QNM two nanostructured bainitic steels, with a finer and a coarser structure, and found that both phases have a similar Young’s modulus. PMID:26602631

  20. Dynamic Force Imaging and Spectroscopy of Individual Molecules

    NASA Astrophysics Data System (ADS)

    Repp, Jascha

    2014-03-01

    In atomic force microscopy (AFM) the qPlus sensor facilitates the use of metallic tips, which are typically used in scanning tunneling microscopy (STM), and thereby facilitates combined STM and AFM experiments at cryogenic temperatures. The use of CO-functionalized tips as has been introduced recently by Gross and co-workers enabled unprecedented resolution and thereby fostered the rapid recent development of the field. We made use of the complementary information that STM and AFM can provide in different contexts. When applied to STM-based single-molecule synthesis, the combination of these techniques enables a direct quantification of the interplay of geometry and electronic coupling in metal-organic complexes in real space. Further, we combined STM on semiconductors with Kelvin probe force spectroscopy (KPFS) performed simultaneously in the same setup with the very same tip. This combination of tools allows us to experimentally recover the zero point of the energy scale usually being obscured due to so-called tip-induced band bending when measuring on surfaces of semiconductors. Finally, we used KPFS with sub-molecular resolution to image the polarity of individual bonds.

  1. Single-Molecule Microscopy and Force Spectroscopy of Membrane Proteins

    NASA Astrophysics Data System (ADS)

    Engel, Andreas; Janovjak, Harald; Fotiadis, Dimtrios; Kedrov, Alexej; Cisneros, David; Müller, Daniel J.

    Single-molecule atomic force microscopy (AFM) provides novel ways to characterize the structure-function relationship of native membrane proteins. High-resolution AFM topographs allow observing the structure of single proteins at sub-nanometer resolution as well as their conformational changes, oligomeric state, molecular dynamics and assembly. We will review these feasibilities illustrating examples of membrane proteins in native and reconstituted membranes. Classification of individual topographs of single proteins allows understanding the principles of motions of their extrinsic domains, to learn about their local structural flexibilities and to find the entropy minima of certain conformations. Combined with the visualization of functionally related conformational changes these insights allow understanding why certain flexibilities are required for the protein to function and how structurally flexible regions allow certain conformational changes. Complementary to AFM imaging, single-molecule force spectroscopy (SMFS) experiments detect molecular interactions established within and between membrane proteins. The sensitivity of this method makes it possible to measure interactions that stabilize secondary structures such as transmembrane α-helices, polypeptide loops and segments within. Changes in temperature or protein-protein assembly do not change the locations of stable structural segments, but influence their stability established by collective molecular interactions. Such changes alter the probability of proteins to choose a certain unfolding pathway. Recent examples have elucidated unfolding and refolding pathways of membrane proteins as well as their energy landscapes.

  2. Dynamic force spectroscopy of parallel individual mucin1-antibody bonds

    SciTech Connect

    Sulchek, T A; Friddle, R W; Langry, K; Lau, E; Albrecht, H; Ratto, T; DeNardo, S; Colvin, M E; Noy, A

    2005-05-02

    We used atomic force microscopy (AFM) to measure the binding forces between Mucin1 (MUC1) peptide and a single chain antibody fragment (scFv) selected from a scFv library screened against MUC1. This binding interaction is central to the design of the molecules for targeted delivery of radioimmunotherapeutic agents for prostate and breast cancer treatment. Our experiments separated the specific binding interaction from non-specific interactions by tethering the antibody and MUC1 molecules to the AFM tip and sample surface with flexible polymer spacers. Rupture force magnitude and elastic characteristics of the spacers allowed identification of the bond rupture events corresponding to different number of interacting proteins. We used dynamic force spectroscopy to estimate the intermolecular potential widths and equivalent thermodynamic off rates for mono-, bi-, and tri-valent interactions. Measured interaction potential parameters agree with the results of molecular docking simulation. Our results demonstrate that an increase of the interaction valency leads to a precipitous decline in the dissociation rate. Binding forces measured for mono and multivalent interactions match the predictions of a Markovian model for the strength of multiple uncorrelated bonds in parallel configuration. Our approach is promising for comparison of the specific effects of molecular modifications as well as for determination of the best configuration of antibody-based multivalent targeting agents.

  3. PREFACE: NC-AFM 2003: Proceedings of the 6th International Conference on Non-contact Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Reichling, Michael

    2004-02-01

    Direct nanoscale and atomic resolution imaging is a key issue in nanoscience and nanotechnology. The invention of the dynamic force microscope in the early 1990s was an important step forward in this direction as this instrument provides a universal tool for measuring the topography and many other physical and chemical properties of surfaces at the nanoscale. Operation in the so-called non-contact mode now allows direct atomic resolution imaging of electrically insulating surfaces and nanostructures which has been an unsolved problem during the first decade of nanotechnology. Today, we face a most rapid development of the technique and an extension of its capabilities far beyond imaging; atomically resolved force spectroscopy provides information about local binding properties and researchers now develop sophisticated schemes of force controlled atomic manipulation with the tip of the force microscope. Progress in the field of non-contact force microscopy is discussed at the annually held NC-AFM conferences that are part of a series started in 1998 with a meeting in Osaka, Japan. The 6th International Conference on Non-contact Atomic Force Microscopy took place in Dingle, Ireland, from 31 August to 3 September 2003 and this special issue is a compilation of the original publications of work presented at this meeting. The papers published here well reflect recent achievements, current trends and some of the challenging new directions in non-contact force microscopy that have been discussed during the most stimulating conference days in Dingle. Fundamental aspects of forces and dissipation relevant in imaging and spectroscopy have been covered by experimental and theoretical contributions yielding a more detailed understanding of tip--surface interaction in force microscopy. Novel and improved imaging and spectroscopy techniques have been introduced that either improve the performance of force microscopy or pave the way towards new functionalities and applications

  4. Robust strategies for automated AFM force curve analysis--I. Non-adhesive indentation of soft, inhomogeneous materials.

    PubMed

    Lin, David C; Dimitriadis, Emilios K; Horkay, Ferenc

    2007-06-01

    The atomic force microscope (AFM) has found wide applicability as a nanoindentation tool to measure local elastic properties of soft materials. An automated approach to the processing of AFM indentation data, namely, the extraction of Young's modulus, is essential to realizing the high-throughput potential of the instrument as an elasticity probe for typical soft materials that exhibit inhomogeneity at microscopic scales. This paper focuses on Hertzian analysis techniques, which are applicable to linear elastic indentation. We compiled a series of synergistic strategies into an algorithm that overcomes many of the complications that have previously impeded efforts to automate the fitting of contact mechanics models to indentation data. AFM raster data sets containing up to 1024 individual force-displacement curves and macroscopic compression data were obtained from testing polyvinyl alcohol gels of known composition. Local elastic properties of tissue-engineered cartilage were also measured by the AFM. All AFM data sets were processed using customized software based on the algorithm, and the extracted values of Young's modulus were compared to those obtained by macroscopic testing. Accuracy of the technique was verified by the good agreement between values of Young's modulus obtained by AFM and by direct compression of the synthetic gels. Validation of robustness was achieved by successfully fitting the vastly different types of force curves generated from the indentation of tissue-engineered cartilage. For AFM indentation data that are amenable to Hertzian analysis, the method presented here minimizes subjectivity in preprocessing and allows for improved consistency and minimized user intervention. Automated, large-scale analysis of indentation data holds tremendous potential in bioengineering applications, such as high-resolution elasticity mapping of natural and artificial tissues.

  5. An AFM study of the chlorite-fluid interface. [Atomic Force Microscopy

    SciTech Connect

    Vrdoljak, G.A.; Henderson, G.S.; Fawcett, J.J. . Dept. of Geology)

    1992-01-01

    Chlorite is a ubiquitous mineral in many geologic environments and plays an important role in elemental adsorption and retention in soils. Chlorite has a 2:1 layer structure consisting of two tetrahedral sheets with an octahedral sheet between them (talc-like layer). The 2:1 layer is charge balanced and hydrogen-bonded by an interlayer of MgOH[sub 6] octahedra (brucite-like layer). The nature of chlorite's structure, its ease of imaging, and perfect 001 cleavage, make this mineral an ideal substrate for use in elemental adsorption studies in solution, with the AFM. The 001 cleavage plane of a 2b polytype with composition (Mg[sub 4.4]Fe[sub 0.6]Al[sub 1.0])[(Si[sub 2.9]Al[sub 1.1])]O[sub 10](OH)[sub g] has been imaged in air, water, and oil by atomic force microscopy. Dissolution features are observed in water, showing sub-micron features dissolving in real-time. Atomic resolution of both the talc-like and brucite-like layers has been obtained in air. However, only the tetrahedral sheet of the talc-like layer has been imaged at atomic resolution in oil and water, which may indicate a structural instability of the brucite-like surface in solution. Measurements of the unit-cell dimensions (a and b) for the talc-like layer in the three different media indicate a structural expansion of the mineral surface in solution. The a unit cell dimension expands by 7.4 [+-] 0.1% when in water; conversely, the b dimension varies greatly when in oil ([minus]10% to +20%), relative to air. The effects of these solution media on the structure of chlorite are revealed by characterization with the AFM. This information should prove useful in future studies of adsorption onto layer silicates.

  6. Spectroscopy and atomic force microscopy of biomass.

    PubMed

    Tetard, L; Passian, A; Farahi, R H; Kalluri, U C; Davison, B H; Thundat, T

    2010-05-01

    Scanning probe microscopy has emerged as a powerful approach to a broader understanding of the molecular architecture of cell walls, which may shed light on the challenge of efficient cellulosic ethanol production. We have obtained preliminary images of both Populus and switchgrass samples using atomic force microscopy (AFM). The results show distinctive features that are shared by switchgrass and Populus. These features may be attributable to the lignocellulosic cell wall composition, as the collected images exhibit the characteristic macromolecular globule structures attributable to the lignocellulosic systems. Using both AFM and a single case of mode synthesizing atomic force microscopy (MSAFM) to characterize Populus, we obtained images that clearly show the cell wall structure. The results are of importance in providing a better understanding of the characteristic features of both mature cells as well as developing plant cells. In addition, we present spectroscopic investigation of the same samples.

  7. Optical trapping force combining an optical fiber probe and an AFM metallic probe.

    PubMed

    Liu, Binghui; Yang, Lijun; Wang, Yang

    2011-02-14

    A high-resolution optical trapping and manipulating scheme combining an optical fiber probe and an AFM metallic probe is proposed. This scheme is based on the combination of evanescent illumination and light scattering at the metallic probe apex, which shapes the optical field into a localized, three-dimensional optical trap. Detailed simulations of the electromagnetic fields in composite area and the resulting forces are described the methods of Maxwell stress tensor and three-dimensional FDTD. Calculations show that the scheme is able to overcome the disturbance of other forces to trap a polystyrene particle of up to 10 nm in radius with lower laser intensity (~1040 W/mm2) than that required by conventional optical tweezers (~10(5) W/mm2). Based on the discussion of high manipulating efficiency dependent on system parameters and the implementing procedure, the scheme allowing for effective manipulation of nano-particles opens a way for research on single nano-particle area.

  8. Combined quantitative ultrasonic and time-resolved interaction force AFM imaging

    NASA Astrophysics Data System (ADS)

    Parlak, Z.; Degertekin, F. L.

    2011-01-01

    The authors describe a method where quantitative ultrasonic atomic force microscopy (UAFM) is achieved during time-resolved interaction force (TRIF) imaging in intermittent contact mode. The method uses a calibration procedure for quantitative UAFM. It improves elasticity measurements of stiff regions of surfaces while retaining the capabilities of the TRIF mode for topography, adhesion, dissipation, and elasticity measurements on soft regions of sample surfaces. This combination is especially advantageous when measuring and imaging samples with broad stiffness range in a nondestructive manner. The experiments utilize an active AFM probe with high bandwidth and the UAFM calibration is performed by measuring the magnitude of the time-resolved UAFM signal at a judiciously chosen frequency for different contact stiffness values during individual taps. Improved sensitivity to stiff surface elasticity is demonstrated on a special sample. The results show that combining UAFM with TRIF provides 2.5 GPa (5%) standard deviation on the silicon surface reduced Young's modulus, representing 5× improvement over using only TRIF mode imaging.

  9. AFM/TIRF force clamp measurements of neurosecretory vesicle tethers reveal characteristic unfolding steps

    PubMed Central

    Harris, Mark C.; Cislo, Dillon; Lenz, Joan S.; Umbach, Christopher

    2017-01-01

    Although several proteins have been implicated in secretory vesicle tethering, the identity and mechanical properties of the components forming the physical vesicle-plasma membrane link remain unknown. Here we present the first experimental measurements of nanomechanical properties of secretory vesicle-plasma membrane tethers using combined AFM force clamp and TIRF microscopy on membrane sheets from PC12 cells expressing the vesicle marker ANF-eGFP. Application of pulling forces generated tether extensions composed of multiple steps with variable length. The frequency of short (<10 nm) tether extension events was markedly higher when a fluorescent vesicle was present at the cantilever tip and increased in the presence of GTPγS, indicating that these events reflect specifically the properties of vesicle-plasma membrane tethers. The magnitude of the short tether extension events is consistent with extension lengths expected from progressive unfolding of individual helices of the exocyst complex, supporting its direct role in forming the physical vesicle-plasma membrane link. PMID:28323853

  10. Reverse engineering of an affinity-switchable molecular interaction characterized by atomic force microscopy single-molecule force spectroscopy.

    PubMed

    Anselmetti, Dario; Bartels, Frank Wilco; Becker, Anke; Decker, Björn; Eckel, Rainer; McIntosh, Matthew; Mattay, Jochen; Plattner, Patrik; Ros, Robert; Schäfer, Christian; Sewald, Norbert

    2008-02-19

    Tunable and switchable interaction between molecules is a key for regulation and control of cellular processes. The translation of the underlying physicochemical principles to synthetic and switchable functional entities and molecules that can mimic the corresponding molecular functions is called reverse molecular engineering. We quantitatively investigated autoinducer-regulated DNA-protein interaction in bacterial gene regulation processes with single atomic force microscopy (AFM) molecule force spectroscopy in vitro, and developed an artificial bistable molecular host-guest system that can be controlled and regulated by external signals (UV light exposure and thermal energy). The intermolecular binding functionality (affinity) and its reproducible and reversible switching has been proven by AFM force spectroscopy at the single-molecule level. This affinity-tunable optomechanical switch will allow novel applications with respect to molecular manipulation, nanoscale rewritable molecular memories, and/or artificial ion channels, which will serve for the controlled transport and release of ions and neutral compounds in the future.

  11. Accurate force spectroscopy in tapping mode atomic force microscopy in liquids

    NASA Astrophysics Data System (ADS)

    Xu, Xin; Melcher, John; Raman, Arvind

    2010-01-01

    Existing force spectroscopy methods in tapping mode atomic force microscopy (AFM) such as higher harmonic inversion [M. Stark, R. W. Stark, W. M. Heckl, and R. Guckenberger, Proc. Natl. Acad. Sci. U.S.A. 99, 8473 (2002)] or scanning probe acceleration microscopy [J. Legleiter, M. Park, B. Cusick, and T. Kowalewski, Proc. Natl. Acad. Sci. U.S.A. 103, 4813 (2006)] or integral relations [M. Lee and W. Jhe, Phys. Rev. Lett. 97, 036104 (2006); S. Hu and A. Raman, Nanotechnology 19, 375704 (2008); H. Hölscher, Appl. Phys. Lett. 89, 123109 (2006); A. J. Katan, Nanotechnology 20, 165703 (2009)] require and assume as an observable the tip dynamics in a single eigenmode of the oscillating microcantilever. We demonstrate that this assumption can distort significantly the extracted tip-sample interaction forces when applied to tapping mode AFM with soft cantilevers in liquid environments. This exception is due to the fact that under these conditions the second eigenmode is momentarily excited and the observed tip dynamics clearly contains contributions from the fundamental and second eigenmodes. To alleviate this problem, a simple experimental method is proposed to screen the second eigenmode contributions in the observed tip deflection signal to allow accurate tip-sample force reconstruction in liquids. The method is implemented experimentally to reconstruct interaction forces on polymer, bacteriorhodopsin membrane, and mica samples in buffer solutions.

  12. XPS, UV-vis spectroscopy and AFM studies on removal mechanisms of Si-face SiC wafer chemical mechanical polishing (CMP)

    NASA Astrophysics Data System (ADS)

    Zhou, Yan; Pan, Guoshun; Shi, Xiaolei; Xu, Li; Zou, Chunli; Gong, Hua; Luo, Guihai

    2014-10-01

    Chemical mechanical polishing (CMP) removal mechanisms of on-axis Si-face SiC wafer have been investigated through X-ray photoelectron spectroscopy (XPS), UV-visible (UV-vis) spectroscopy and atomic force microscopy (AFM). XPS results indicate that silicon oxide is formed on Si-face surface polished by the slurry including oxidant H2O2, but not that after immersing in H2O2 solution. UV-vis spectroscopy curves prove that •OH hydroxyl radical could be generated only under CMP polishing by the slurry including H2O2 and abrasive, so as to promote oxidation of Si-face to realize the effective removal; meanwhile, alkali KOH during CMP could induce the production of more radicals to improve the removal. On the other side, ultra-smooth polished surface with atomic step structure morphology and extremely low Ra of about 0.06 nm (through AFM) is obtained using the developed slurry with silica nanoparticle abrasive. Through investigating the variations of the atomic step morphology on the surface polished by different slurries, it's reveals that CMP removal mechanism involves a simultaneous process of surface chemical reaction and nanoparticle atomic scale abrasion.

  13. Intermodulation Atomic Force Microscopy and Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hutter, Carsten; Platz, Daniel; Tholen, Erik; Haviland, David; Hansson, Hans

    2009-03-01

    We present a powerful new method of dynamic AFM, which allows to gain far more information about the tip-surface interaction than standard amplitude or phase imaging, while scanning at comparable speed. Our method, called intermodulation atomic force microscopy (ImAFM), employs the manifestly nonlinear phenomenon of intermodulation to extract information about tip-surface forces. ImAFM uses one eigenmode of a mechanical resonator, the latter driven at two frequencies to produce many spectral peaks near its resonace, where sensitivity is highest [1]. We furthermore present a protocol for decoding the combined information encoded in the spectrum of intermodulation peaks. Our theoretical framework suggests methods to enhance the gained information by using a different parameter regime as compared to Ref. [1]. We also discuss strategies for solving the inverse problem, i.e., for extracting the nonlinear tip-surface interaction from the response, also naming limitations of our theoretical analysis. We will further report on latest progress to experimentally employ our new protocol.[3pt] [1] D. Platz, E. A. Tholen, D. Pesen, and D. B. Haviland, Appl. Phys. Lett. 92, 153106 (2008).

  14. AFM in mode Peak Force applied to the study of un-worn contact lenses.

    PubMed

    Torrent-Burgués, J; Sanz, F

    2014-09-01

    Contact lenses (CLs) are of common use and the biocompatibility, topography and mechanical properties of the used materials are of major importance. The objective of this contribution is to apply the AFM in mode Peak Force to obtain surface topography and mechanical characteristics of un-worn CLs of different materials. One material of hydrogel, two of siloxane-hydrogel and one of rigid gas-permeable were used in the study. The results obtained with different materials have been compared, at a nanoscopic level, and the conclusions are diverse. There is no significant influence of the two environments used to measure the characteristics of the CLs, either water or saline solution. The pHEMA hydrogel CL (Polymacon of Soflens) shows the highest values of roughness, adhesion and elastic modulus. The siloxane-hydrogel CL named Asmofilcon A of PremiO presents the lowest values of mean roughness (Ra), root-mean-square roughness (RMS or Rq), adhesion (Adh) and elastic modulus (Ym), meanwhile the siloxane-hydrogel CL named Lotrafilcon B of Air Optix presents the lowest value of skewness (Rsk) and the rigid gas-permeable CL, named RXD, presents the lowest values of kurtosis (Rku) and maximum roughness (Rmax).

  15. Understanding the TERS Effect with On-line Tunneling and Force Feedback Using Multiprobe AFM/NSOM with Raman Integration

    NASA Astrophysics Data System (ADS)

    Lewis, Aaron; Dekhter, Rimma; Hamra, Patricia; Bar-David, Yossi; Taha, Hesham

    Tip enhanced Raman scattering (TERS) has evolved in several directions over the past years. The data from this variety of methodologies has now accumulated to the point that there is a reasonable possibility of evolving an understanding of the underlying cause of the resulting effects that could be the origin of the various TERS enhancement processes. The objective of this presentation is to use the results thus far with atomic force microscopy (AFM) probes with noble metal coating, etching, transparent gold nanoparticles with and without a second nanoparticle [Wang and Schultz, ANALYST 138, 3150 (2013)] and tunneling feedback probes [R. Zhang et. al., NATURE 4 9 8, 8 2 (2013)]. We attempt at understanding this complex of results with AFM/NSOM multiprobe techniques. Results indicate that TERS is dominated by complex quantum interactions. This produces a highly confined and broadband plasmon field with all k vectors for effective excitation. Normal force tuning fork feedback with exposed tip probes provides an excellent means to investigate these effects with TERS probes that we have shown can circumvent the vexing problem of jump to contact prevalent in conventional AFM methodology and permit on-line switching between tunneling and AFM feedback modes of operation.

  16. Subpiconewton dynamic force spectroscopy using magnetic tweezers.

    PubMed

    Kruithof, M; Chien, F; de Jager, M; van Noort, J

    2008-03-15

    We introduce a simple method for dynamic force spectroscopy with magnetic tweezers. This method allows application of subpiconewton force and twist control by calibration of the applied force from the height of the magnets. Initial dynamic force spectroscopy experiments on DNA molecules revealed a large hysteresis that is caused by viscous drag on the magnetic bead and will conceal weak interactions. When smaller beads are used, this hysteresis is sufficiently reduced to reveal intramolecular interactions at subpiconewton forces. Compared with typical quasistatic force spectroscopy, a significant reduction of measurement time is achieved, allowing the real-time study of transient structures and reaction intermediates. As a proof of principle, nucleosome-nucleosome interactions on a subsaturated chromatin fiber were analyzed.

  17. Optimizing 1-μs-Resolution Single-Molecule Force Spectroscopy on a Commercial Atomic Force Microscope.

    PubMed

    Edwards, Devin T; Faulk, Jaevyn K; Sanders, Aric W; Bull, Matthew S; Walder, Robert; LeBlanc, Marc-Andre; Sousa, Marcelo C; Perkins, Thomas T

    2015-10-14

    Atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) is widely used to mechanically measure the folding and unfolding of proteins. However, the temporal resolution of a standard commercial cantilever is 50-1000 μs, masking rapid transitions and short-lived intermediates. Recently, SMFS with 0.7-μs temporal resolution was achieved using an ultrashort (L = 9 μm) cantilever on a custom-built, high-speed AFM. By micromachining such cantilevers with a focused ion beam, we optimized them for SMFS rather than tapping-mode imaging. To enhance usability and throughput, we detected the modified cantilevers on a commercial AFM retrofitted with a detection laser system featuring a 3-μm circular spot size. Moreover, individual cantilevers were reused over multiple days. The improved capabilities of the modified cantilevers for SMFS were showcased by unfolding a polyprotein, a popular biophysical assay. Specifically, these cantilevers maintained a 1-μs response time while eliminating cantilever ringing (Q ≅ 0.5). We therefore expect such cantilevers, along with the instrumentational improvements to detect them on a commercial AFM, to accelerate high-precision AFM-based SMFS studies.

  18. Leveraging Air Force Medical Service (AFMS) Senior Leadership Corps Diversity to Improve Efficiency

    DTIC Science & Technology

    2013-04-01

    commanders and AFMS senior leadership; • Set a single PME standard for AFMS officers; • Shift provider billets to patient care roles and establish...single PME standard, and by realigning human resources to increase clinical currency, medical readiness and resource efficiency. Some structural...organizational entity. Like running a surgical service or a medical service. . . . It’s much bigger than that, because you’re dealing with finance and

  19. Accelerated design and quality control of impact modifiers for plastics through atomic force microscopy (AFM) analysis

    NASA Astrophysics Data System (ADS)

    Moeller, Gunter

    2011-03-01

    Standard polymer resins are often too brittle or do not meet other mechanical property requirements for typical polymer applications. To achieve desired properties it is common to disperse so called ``impact modifiers'', which are spherical latex particles with diameters of much less than one micrometer, into the pure resin. Understanding and control of the entire process from latex particle formation to subsequent dispersion into polymer resins are necessary to accelerate the development of new materials that meet specific application requirements. In this work AFM imaging and nanoindentation techniques in combination with AFM-based spectroscopic techniques were applied to assess latex formation and dispersion. The size and size distribution of the latex particles can be measured based on AFM amplitude modulation images. AFM phase images provide information about the chemical homogeneity of individual particles. Nanoindentation may be used to estimate their elastic and viscoelastic properties. Proprietary creep and nanoscale Dynamic Mechanical Analysis (DMA) tests that we have developed were used to measure these mechanical properties. The small size of dispersed latex inclusions requires local mechanical and spectroscopic analysis techniques with high lateral and spatial resolution. We applied the CRAVE AFM method, developed at NIST, to perform mechanical analysis of individual latex inclusions and compared results with those obtained using nanoscale DMA. NanoIR, developed by Anasys Inc., and principal component confocal Raman were used for spectroscopic analysis and results from both techniques compared.

  20. Morphology of Vapor-Deposited Ice at Low Temperatures by Atomic Force Microscopy (AFM)

    NASA Astrophysics Data System (ADS)

    Fain, , Jr.; Donev, J. M. K.; Tait, B. R. Long, Jr.; Yu, Q.

    2002-03-01

    The morphology of multilayer films of ice on various substrates is measured by AFM as a function of vapor-deposition and annealing temperatures below 150K. The films are deposited in-situ in UHV from an effusive doser at 67 degrees from the surface normal. For depositions near 100K on clean Au(111), previous measurements by Donev et al. using needle-sensor AFM indicate that 3-D clustering starts near 120K for initially flat thin films of amorphous solid water (ASW). For depositions below 85K on clean Au(111), preliminary measurements using non-contact AFM (nc-AFM) indicate that clustering does not occur during annealing until bulk diffusion becomes operative at T>140K. Deposition at glancing angle at the lower temperatures is known to increase porosity and is also expected to decrease the number of crystalline nuclei in the ASW. For depositions near 100K on mica that had been annealed in UHV, preliminary measurements using ncAFM show clustering near 120K. Supported by U. W. Nanotechnology Fellowship (J.M.K.D.), Mary Gates Fellowship (B. R. L.), and M. J. Murdock Charitable Trust.

  1. Evaluating interaction forces between BSA and rabbit anti-BSA in sulphathiazole sodium, tylosin and levofloxacin solution by AFM

    NASA Astrophysics Data System (ADS)

    Wang, Congzhou; Wang, Jianhua; Deng, Linhong

    2011-11-01

    Protein-protein interactions play crucial roles in numerous biological processes. However, it is still challenging to evaluate the protein-protein interactions, such as antigen and antibody, in the presence of drug molecules in physiological liquid. In this study, the interaction between bovine serum albumin (BSA) and rabbit anti-BSA was investigated using atomic force microscopy (AFM) in the presence of various antimicrobial drugs (sulphathiazole sodium, tylosin and levofloxacin) under physiological condition. The results show that increasing the concentration of tylosin decreased the single-molecule-specific force between BSA and rabbit anti-BSA. As for sulphathiazole sodium, it dramatically decreased the specific force at a certain critical concentration, but increased the nonspecific force as its concentration increasing. In addition, the presence of levofloxacin did not greatly influence either the specific or nonspecific force. Collectively, these results suggest that these three drugs may adopt different mechanisms to affect the interaction force between BSA and rabbit anti-BSA. These findings may enhance our understanding of antigen/antibody binding processes in the presence of drug molecules, and hence indicate that AFM could be helpful in the design and screening of drugs-modulating protein-protein interaction processes.

  2. Accuracy Estimation in Force Spectroscopy Experiments

    NASA Astrophysics Data System (ADS)

    Rankl, Christian; Kienberger, Ferry; Gruber, Hermann; Blaas, Dieter; Hinterdorfer, Peter

    2007-08-01

    Force spectroscopy is a useful tool for the investigation of molecular interactions. We here present a detailed analysis of parameter estimation in force spectroscopy experiments. It provides the values of the statistical errors of the kinetic off-rate constant koff and the energy length scale xβ to be considered using the single barrier model. As a biologically relevant experimental system we used the interaction between human rhinovirus serotype 2 and a recombinant derivative of the very-low density lipoprotein receptor. The interaction forces of single virus-receptor pairs were measured at different loading rates and analysed according to the single barrier model. Accuracy estimates of koff and xβ were obtained by Monte Carlo simulation and bootstrapping. For this model of virus-receptor attachment, force spectroscopy experiments yielded xβ=(0.38± 0.07) nm and \\ln koff=(-2.3± 1.0)\\ln s-1.

  3. A measurement of the hysteresis loop in force-spectroscopy curves using a tuning-fork atomic force microscope.

    PubMed

    Lange, Manfred; van Vörden, Dennis; Möller, Rolf

    2012-01-01

    Measurements of the frequency shift versus distance in noncontact atomic force microscopy (NC-AFM) allow measurements of the force gradient between the oscillating tip and a surface (force-spectroscopy measurements). When nonconservative forces act between the tip apex and the surface the oscillation amplitude is damped. The dissipation is caused by bistabilities in the potential energy surface of the tip-sample system, and the process can be understood as a hysteresis of forces between approach and retraction of the tip. In this paper, we present the direct measurement of the whole hysteresis loop in force-spectroscopy curves at 77 K on the PTCDA/Ag/Si(111) √3 × √3 surface by means of a tuning-fork-based NC-AFM with an oscillation amplitude smaller than the distance range of the hysteresis loop. The hysteresis effect is caused by the making and breaking of a bond between PTCDA molecules on the surface and a PTCDA molecule at the tip. The corresponding energy loss was determined to be 0.57 eV by evaluation of the force-distance curves upon approach and retraction. Furthermore, a second dissipation process was identified through the damping of the oscillation while the molecule on the tip is in contact with the surface. This dissipation process occurs mainly during the retraction of the tip. It reaches a maximum value of about 0.22 eV/cycle.

  4. PREFACE: Non-contact AFM Non-contact AFM

    NASA Astrophysics Data System (ADS)

    Giessibl, Franz J.; Morita, Seizo

    2012-02-01

    This special issue is focussed on high resolution non-contact atomic force microscopy (AFM). Non-contact atomic force microscopy was established approximately 15 years ago as a tool to image conducting and insulating surfaces with atomic resolution. Since 1998, an annual international conference has taken place, and although the proceedings of these conferences are a useful source of information, several key developments warrant devoting a special issue to this subject. In the theoretic field, the possibility of supplementing established techniques such as scanning tunneling microscopy (STM) and Kelvin probe microscopy with atomically resolved force micrsoscopy poses many challenges in the calculation of contrast and contrast reversal. The surface science of insulators, self-assembled monolayers and adsorbates on insulators is a fruitful field for the application of non-contact AFM: several articles in this issue are devoted to these subjects. Atomic imaging and manipulation have been pioneered using STM, but because AFM allows the measurement of forces, AFM has had a profound impact in this field as well. Three-dimensional force spectroscopy has allowed many important insights into surface science. In this issue a combined 3D tunneling and force microscopy is introduced. Non-contact AFM typically uses frequency modulation to measure force gradients and was initially used mainly in a vacuum. As can be seen in this issue, frequency modulation is now also used in ambient conditions, allowing better spatial and force resolution. We thank all of the contributors for their time and efforts in making this special issue possible. We are also very grateful to the staff of IOP Publishing for handling the administrative aspects and for steering the refereeing process. Non-contact AFM contents Relation between the chemical force and the tunnelling current in atomic point contacts: a simple model Pavel Jelínek, Martin Ondrácek and Fernando Flores Theoretical simulation of

  5. The structure and function of cell membranes examined by atomic force microscopy and single-molecule force spectroscopy.

    PubMed

    Shan, Yuping; Wang, Hongda

    2015-06-07

    The cell membrane is one of the most complicated biological complexes, and long-term fierce debates regarding the cell membrane persist because of technical hurdles. With the rapid development of nanotechnology and single-molecule techniques, our understanding of cell membranes has substantially increased. Atomic force microscopy (AFM) has provided several unprecedented advances (e.g., high resolution, three-dimensional and in situ measurements) in the study of cell membranes and has been used to systematically dissect the membrane structure in situ from both sides of membranes; as a result, novel models of cell membranes have recently been proposed. This review summarizes the new progress regarding membrane structure using in situ AFM and single-molecule force spectroscopy (SMFS), which may shed light on the study of the structure and functions of cell membranes.

  6. Unraveling Protein-Protein Interactions in Clathrin Assemblies via Atomic Force Spectroscopy

    PubMed Central

    Jin, Albert J.; Lafer, Eileen M.; Peng, Jennifer Q.; Smith, Paul D.; Nossal, Ralph

    2013-01-01

    Atomic force microscopy (AFM), single molecule force spectroscopy (SMFS), and single particle force spectroscopy (SPFS) are used to characterize intermolecular interactions and domain structures of clathrin triskelia and clathrin-coated vesicles (CCVs). The latter are involved in receptor-mediated endocytosis (RME) and other trafficking pathways. Here, we subject individual triskelia, bovine-brain CCVs, and reconstituted clathrin-AP180 coats to AFM-SMFS and AFM-SPFS pulling experiments and apply novel analytics to extract force-extension relations from very large data sets. The spectroscopic fingerprints of these samples differ markedly, providing important new information about the mechanism of CCV uncoating. For individual triskelia, SMFS reveals a series of events associated with heavy chain alpha-helix hairpin unfolding, as well as cooperative unraveling of several hairpin domains. SPFS of clathrin assemblies exposes weaker clathrin-clathrin interactions that are indicative of inter-leg association essential for RME and intracellular trafficking. Clathrin-AP180 coats are energetically easier to unravel than the coats of CCVs, with a non-trivial dependence on force-loading rate. PMID:23270814

  7. Unraveling protein-protein interactions in clathrin assemblies via atomic force spectroscopy.

    PubMed

    Jin, Albert J; Lafer, Eileen M; Peng, Jennifer Q; Smith, Paul D; Nossal, Ralph

    2013-03-01

    Atomic force microscopy (AFM), single molecule force spectroscopy (SMFS), and single particle force spectroscopy (SPFS) are used to characterize intermolecular interactions and domain structures of clathrin triskelia and clathrin-coated vesicles (CCVs). The latter are involved in receptor-mediated endocytosis (RME) and other trafficking pathways. Here, we subject individual triskelia, bovine-brain CCVs, and reconstituted clathrin-AP180 coats to AFM-SMFS and AFM-SPFS pulling experiments and apply novel analytics to extract force-extension relations from very large data sets. The spectroscopic fingerprints of these samples differ markedly, providing important new information about the mechanism of CCV uncoating. For individual triskelia, SMFS reveals a series of events associated with heavy chain alpha-helix hairpin unfolding, as well as cooperative unraveling of several hairpin domains. SPFS of clathrin assemblies exposes weaker clathrin-clathrin interactions that are indicative of inter-leg association essential for RME and intracellular trafficking. Clathrin-AP180 coats are energetically easier to unravel than the coats of CCVs, with a non-trivial dependence on force-loading rate.

  8. Taking Nanomedicine Teaching into Practice with Atomic Force Microscopy and Force Spectroscopy

    ERIC Educational Resources Information Center

    Carvalho, Filomena A.; Freitas, Teresa; Santos, Nuno C.

    2015-01-01

    Atomic force microscopy (AFM) is a useful and powerful tool to study molecular interactions applied to nanomedicine. The aim of the present study was to implement a hands-on atomic AFM course for graduated biosciences and medical students. The course comprises two distinct practical sessions, where students get in touch with the use of an atomic…

  9. A measurement of the hysteresis loop in force-spectroscopy curves using a tuning-fork atomic force microscope

    PubMed Central

    van Vörden, Dennis; Möller, Rolf

    2012-01-01

    Summary Measurements of the frequency shift versus distance in noncontact atomic force microscopy (NC-AFM) allow measurements of the force gradient between the oscillating tip and a surface (force-spectroscopy measurements). When nonconservative forces act between the tip apex and the surface the oscillation amplitude is damped. The dissipation is caused by bistabilities in the potential energy surface of the tip–sample system, and the process can be understood as a hysteresis of forces between approach and retraction of the tip. In this paper, we present the direct measurement of the whole hysteresis loop in force-spectroscopy curves at 77 K on the PTCDA/Ag/Si(111) √3 × √3 surface by means of a tuning-fork-based NC-AFM with an oscillation amplitude smaller than the distance range of the hysteresis loop. The hysteresis effect is caused by the making and breaking of a bond between PTCDA molecules on the surface and a PTCDA molecule at the tip. The corresponding energy loss was determined to be 0.57 eV by evaluation of the force–distance curves upon approach and retraction. Furthermore, a second dissipation process was identified through the damping of the oscillation while the molecule on the tip is in contact with the surface. This dissipation process occurs mainly during the retraction of the tip. It reaches a maximum value of about 0.22 eV/cycle. PMID:22496993

  10. Atomic force microscopy for analyzing metaphase chromosomes: comparison of AFM images with fluorescence labeling images of banding patterns.

    PubMed

    Hoshi, Osamu; Ushiki, Tatsuo

    2014-01-01

    The combined use of fluorescence microscopy with atomic force microscopy (AFM) has been introduced to analyze the replication-banding patterns of human chromosomes. Human lymphocytes synchronized with excess thymidine are treated with 5-ethynyl-2'-deoxyuridine (EdU) during the late S phase. EdU-labeled DNA is detected in metaphase chromosomes using Alexa Fluor 488(®) azide, through the 1,3-dipolar cycloaddition reaction of organic azides with the terminal acetylene group of EdU. Chromosomes with EdU incorporated during the late S phase show a banding pattern similar to the G-banding pattern of normal human chromosomes. The comparison between the fluorescence and AFM image of the same chromosome indicates the presence of ridges and grooves in the chromatid arms, which correspond to G-positive and G-negative bands, respectively. This technique of EdU-labeled replication bands combined with AFM is useful to analyze the structure of chromosomes in relation to the banding pattern.

  11. Impedance Spectroscopic Investigation of Proton Conductivity in Nafion Using Transient Electrochemical Atomic Force Microscopy (AFM)

    PubMed Central

    Hink, Steffen; Wagner, Norbert; Bessler, Wolfgang G.; Roduner, Emil

    2012-01-01

    Spatially resolved impedance spectroscopy of a Nafion polyelectrolyte membrane is performed employing a conductive and Pt-coated tip of an atomic force microscope as a point-like contact and electrode. The experiment is conducted by perturbing the system by a rectangular voltage step and measuring the incurred current, followed by Fourier transformation and plotting the impedance against the frequency in a conventional Bode diagram. To test the potential and limitations of this novel method, we present a feasibility study using an identical hydrogen atmosphere at a well-defined relative humidity on both sides of the membrane. It is demonstrated that good quality impedance spectra are obtained in a frequency range of 0.2–1000 Hz. The extracted polarization curves exhibit a maximum current which cannot be explained by typical diffusion effects. Simulation based on equivalent circuits requires a Nernst element for restricted diffusion in the membrane which suggests that this effect is based on the potential dependence of the electrolyte resistance in the high overpotential region. PMID:24958175

  12. Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids.

    PubMed

    Gumí-Audenis, Berta; Costa, Luca; Carlá, Francesco; Comin, Fabio; Sanz, Fausto; Giannotti, Marina I

    2016-12-19

    Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information.

  13. Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

    PubMed Central

    Gumí-Audenis, Berta; Costa, Luca; Carlá, Francesco; Comin, Fabio; Sanz, Fausto; Giannotti, Marina I.

    2016-01-01

    Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information. PMID:27999368

  14. Spatial dependence of polycrystalline FTO’s conductance analyzed by conductive atomic force microscope (C-AFM)

    SciTech Connect

    Peixoto, Alexandre Pessoa; Costa, J. C. da

    2014-05-15

    Fluorine-doped Tin oxide (FTO) is a highly transparent, electrically conductive polycrystalline material frequently used as an electrode in organic solar cells and optical-electronic devices [1–2]. In this work a spatial analysis of the conductive behavior of FTO was carried out by Conductive-mode Atomic Force Microscopy (C-AFM). Rare highly oriented grains sample give us an opportunity to analyze the top portion of polycrystalline FTO and compare with the border one. It is shown that the current flow essentially takes place through the polycrystalline edge at grain boundaries.

  15. The Structure of Misfolded Amyloidogenic Dimers: Computational Analysis of Force Spectroscopy Data

    PubMed Central

    Zhang, Yuliang; Lyubchenko, Yuri L.

    2014-01-01

    Progress in understanding the molecular mechanism of self-assembly of amyloidogenic proteins and peptides requires knowledge about their structure in misfolded states. Structural studies of amyloid aggregates formed during the early aggregation stage are very limited. Atomic force microscopy (AFM) spectroscopy is widely used to analyze misfolded proteins and peptides, but the structural characterization of transiently formed misfolded dimers is limited by the lack of computational approaches that allow direct comparison with AFM experiments. Steered molecular dynamics (SMD) simulation is capable of modeling force spectroscopy experiments, but the modeling requires pulling rates 107 times higher than those used in AFM experiments. In this study, we describe a computational all-atom Monte Carlo pulling (MCP) approach that enables us to model results at pulling rates comparable to those used in AFM pulling experiments. We tested the approach by modeling pulling experimental data for I91 from titin I-band (PDB ID: 1TIT) and ubiquitin (PDB ID: 1UBQ). We then used MCP to analyze AFM spectroscopy experiments that probed the interaction of the peptides [Q6C] Sup35 (6–13) and [H13C] Aβ (13–23). A comparison of experimental results with the computational data for the Sup35 dimer with out-of-register and in-register arrangements of β-sheets suggests that Sup35 monomers adopt an out-of-register arrangement in the dimer. A similar analysis performed for Aβ peptide demonstrates that the out-of-register antiparallel β-sheet arrangement of monomers also occurs in this peptide. Although the rupture of hydrogen bonds is the major contributor to dimer dissociation, the aromatic-aromatic interaction also contributes to the dimer rupture process. PMID:25517155

  16. PREFACE: NC-AFM 2005: Proceedings of the 8th International Conference on Non-Contact Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Reichling, M.; Mikosch, W.

    2006-04-01

    The 8th International Conference on Non-Contact Atomic Force Microscopy, held in Bad Essen, Germany, from 15 18th August 2005, attracted a record breaking number of participants presenting excellent contributions from a variety of scientific fields. This clearly demonstrated the high level of activity and innovation present in the community of NC-AFM researchers and the continuous growth of the field. The strongest ever participation of companies for a NC-AFM meeting is a sign for the emergence of new markets for the growing NC-AFM community; and the high standard of the products presented at the exhibition, many of them brand-new developments, reflected the unbroken progress in technology. The development of novel technologies and the sophistication of known techniques in research laboratories and their subsequent commercialization is still a major driving force for progress in this area of nanoscience. The conference was a perfect demonstration of how progress in the development of enabling technologies can readily be transcribed into basic research yielding fundamental insight with an impact across disciplines. The NC-AFM 2005 scientific programme was based on five cornerstones, each representing an area of vivid research and scientific progress. Atomic resolution imaging on oxide surfaces, which has long been a vision for the catalysis community, appears to be routine in several laboratories and after a period of demonstrative experiments NC-AFM now makes unique contributions to the understanding of processes in surface chemistry. These capabilities also open up new routes for the analysis of clusters and molecules deposited on dielectric surfaces where resolution limits are pushed towards the single atom level. Atomic precision manipulation with the dynamic AFM left the cradle of its infancy and flourishes in the family of bottom-up fabrication nanotechnologies. The systematic development of established and the introduction of new concepts of contrast

  17. PREFACE: NC-AFM 2006: Proceedings of the 9th International Conference on Non-contact Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Tomitori, Masahiko; Onishi, Hiroshi

    2007-02-01

    The advent of scanning probe microscopy (SPM) in the 1980s has significantly promoted nanoscience and nanotechnology. In particular, non-contact atomic force microscopy (NC-AFM), one of the SPM family, has unique capabilities with high spatial resolution for nanoscale measurements in vacuum, air and liquids. In the last decade we have witnessed the rapid progress of NC-AFM with improved performance and increasing applications. A series of NC-AFM international conferences have greatly contributed to this field. Initiated in Osaka in 1998, the NC-AFM meeting has been followed by annual conferences at Pontresina, Hamburg, Kyoto, Montreal, Dingle, Seattle and Bad Essen. The 9th conference was held in Kobe, Japan, 16-20 July 2006. This special issue of Nanotechnology contains the outstanding contributions of the conference. During the meeting delegates learnt about a number of significant advances. Topics covered atomic resolution imaging of metals, semiconductors, insulators, ionic crystals, oxides, molecular systems, imaging of biological materials in various environments and novel instrumentation. Work also included the characterization of electronic and magnetic properties, tip and cantilever fabrication and characterization, atomic distinction based on analysis of tip-sample interaction, atomic scale manipulation, fabrication of nanostructures using NC-AFM, and related theories and simulations. We are greatly impressed by the increasing number of applications, and convinced that NC-AFM and related techniques are building a bridge to a future nano world, where quantum phenomena will dominate and nano devices will be realized. In addition, a special session on SPM road maps was held as a first trial in the field, where the future prospects of SPM were discussed enthusiastically. The overall success of the NC-AFM 2006 conference was due to the efforts of many individuals and groups with respect to scientific and technological progress, as well as the international

  18. Force profiles of protein pulling with or without cytoskeletal links studied by AFM

    SciTech Connect

    Afrin, Rehana; Ikai, Atsushi . E-mail: aikai@bio.titech.ac.jp

    2006-09-15

    To test the capability of the atomic force microscope for distinguishing membrane proteins with/without cytoskeletal associations, we studied the pull-out mechanics of lipid tethers from the red blood cell (RBC). When wheat germ agglutinin, a glycophorin A (GLA) specific lectin, was used to pull out tethers from RBC, characteristic force curves for tether elongation having a long plateau force were observed but without force peaks which are usually attributed to the forced unbinding of membrane components from the cytoskeleton. The result was in agreement with the reports that GLA is substantially free of cytoskeletal interactions. On the contrary, when the Band 3 specific lectin, concanavalin A, was used, the force peaks were indeed observed together with a plateau supporting its reported cytoskeletal association. Based on these observations, we postulate that the state of cytoskeletal association of particular membrane proteins can be identified from the force profiles of their pull-out mechanics.

  19. Nanopipette combined with quartz tuning fork-atomic force microscope for force spectroscopy/microscopy and liquid delivery-based nanofabrication

    SciTech Connect

    An, Sangmin; Lee, Kunyoung; Kim, Bongsu; Noh, Haneol; Kim, Jongwoo; Kwon, Soyoung; Lee, Manhee; Hong, Mun-Heon; Jhe, Wonho

    2014-03-15

    This paper introduces a nanopipette combined with a quartz tuning fork-atomic force microscope system (nanopipette/QTF-AFM), and describes experimental and theoretical investigations of the nanoscale materials used. The system offers several advantages over conventional cantilever-based AFM and QTF-AFM systems, including simple control of the quality factor based on the contact position of the QTF, easy variation of the effective tip diameter, electrical detection, on-demand delivery and patterning of various solutions, and in situ surface characterization after patterning. This tool enables nanoscale liquid delivery and nanofabrication processes without damaging the apex of the tip in various environments, and also offers force spectroscopy and microscopy capabilities.

  20. Nanobiosensors exploiting specific interactions between an enzyme and herbicides in atomic force spectroscopy.

    PubMed

    da Silva, Aline C N; Deda, Daiana K; Bueno, Carolina C; Moraes, Ariana S; Da Roz, Alessandra L; Yamaji, Fabio M; Prado, Rogilene A; Viviani, Vadim; Oliveira, Osvaldo N; Leite, Fábio L

    2014-09-01

    The development of sensitive methodologies for detecting agrochemicals has become important in recent years due to the increasingly indiscriminate use of these substances. In this context, nanosensors based on atomic force microscopy (AFM) tips are useful because they provide higher sensitivity with operation at the nanometer scale. In this paper we exploit specific interactions between AFM tips functionalized with the enzyme acetolactate synthase (ALS) to detect the ALS-inhibitor herbicides metsulfuron-methyl and imazaquin. Using atomic force spectroscopy (AFS) we could measure the adhesion force between tip and substrate, which was considerably higher when the ALS-functionalized tip (nanobiosensor) was employed. The increase was approximately 250% and 160% for metsulfuron-methyl and imazaquin, respectively, in comparison to unfunctionalized probes. We estimated the specific enzyme-herbicide force by assuming that the measured force comprises an adhesion force according to the Johnson-Kendall-Roberts (JKR) model, the capillary force and the specific force. We show that the specific, biorecognition force plays a crucial role in the higher sensitivity of the nanobiosensor, thus opening the way for the design of similarly engineered tips for detecting herbicides and other analytes.

  1. Force measurement enabling precise analysis by dynamic force spectroscopy.

    PubMed

    Taninaka, Atsushi; Hirano, Yuuichi; Takeuchi, Osamu; Shigekawa, Hidemi

    2012-01-01

    Dynamic force spectroscopy (DFS) makes it possible to investigate specific interactions between two molecules such as ligand-receptor pairs at the single-molecule level. In the DFS method based on the Bell-Evans model, the unbinding force applied to a molecular bond is increased at a constant rate, and the force required to rupture the molecular bond is measured. By analyzing the relationship between the modal rupture force and the logarithm of the loading rate, microscopic potential barrier landscapes and the lifetimes of bonds can be obtained. However, the results obtained, for example, in the case of streptavidin/biotin complexes, have differed among previous studies and some results have been inconsistent with theoretical predictions. In this study, using an atomic force microscopy technique that enables the precise analysis of molecular interactions on the basis of DFS, we investigated the effect of the sampling rate on DFS analysis. The shape of rupture force histograms, for example, was significantly deformed at a sampling rate of 1 kHz in comparison with that of histograms obtained at 100 kHz, indicating the fundamental importance of ensuring suitable experimental conditions for further advances in the DFS method.

  2. Comparison of the ability of quantitative parameters to differentiate surface texture of Atomic Force Microscope (AFM) images

    NASA Astrophysics Data System (ADS)

    Niedzielski, Bethany; Caragianis Broadbridge, Christine; DaPonte, John S.; Gherasimova, Maria

    2010-01-01

    The purpose of this study was to compare the ability of several texture analysis parameters to differentiate textured samples from a smooth control on images obtained with an Atomic Force Microscope (AFM). Surface roughness plays a major role in the realm of material science, especially in integrated electronic devices. As these devices become smaller and smaller, new materials with better electrical properties are needed. New materials with smoother surface morphology have been found to have superior electrical properties than their rougher counterparts. Therefore, in many cases surface texture is indicative of the electrical properties that material will have. Physical vapor deposition techniques such as Jet Vapor Deposition and Molecular Beam Epitaxy are being utilized to synthesize these materials as they have been found to create pure and uniform thin layers. For the current study, growth parameters were varied to produce a spectrum of textured samples. The focus of this study was the image processing techniques associated with quantifying surface texture. As a result of the limited sample size, there was no attempt to draw conclusions about specimen processing methods. The samples were imaged using an AFM in tapping mode. In the process of collecting images, it was discovered that roughness data was much better depicted in the microscope's "height" mode as opposed to "equal area" mode. The AFM quantified the surface texture of each image by returning RMS roughness and the first order histogram statistics of mean roughness, standard deviation, skewness, and kurtosis. Color images from the AFM were then processed on an off line computer running NIH ImageJ with an image texture plug in. This plug in produced another set of first order statistics computed from each images' histogram as well as second order statistics computed from each images' cooccurrence matrix. The second order statistics, which were originally proposed by Haralick, include contrast, angular

  3. Single molecule force spectroscopy of asphaltene aggregates.

    PubMed

    Long, Jun; Xu, Zhenghe; Masliyah, Jacob H

    2007-05-22

    Asphaltene aggregation and deposition cause severe problems in nearly all phases of petroleum processing. To resolve those problems, understanding the aggregation mechanisms is a prerequisite and has attracted the interest of a great number of investigators. However, to date, the nature and extent of asphaltene aggregation remain widely debated. In the present study, we attempt to investigate asphaltene aggregation from a completely new perspective. The technique of single molecule force spectroscopy (SMFS) was used to investigate the response of single asphaltene aggregates under an external pulling force. Force curves representing the stretching of single asphaltene aggregates were obtained in simple electrolyte solutions (KCl and calcium) and organic solvents (toluene and heptane). These force curves were well-fitted by the modified worm-like chain model, indicating that those asphaltene aggregates acted like long-chain polymers under pulling by an external force. It was found that lower solution pH values and the presence of divalent cations resulted in a lower bending rigidity of the formed aggregates. The information retrieved from the force curves suggests that asphaltene molecules with a structure featuring small aromatic clusters connected by aliphatic chains do exist and that asphaltene aggregation could occur through a linear polymerization mechanism. The current study extends the application scope of SMFS.

  4. Hydrodynamic effects of the tip movement on surface nanobubbles: a combined tapping mode, lift mode and force volume mode AFM study.

    PubMed

    Walczyk, Wiktoria; Hain, Nicole; Schönherr, Holger

    2014-08-28

    We report on an Atomic Force Microscopy (AFM) study of AFM tip-nanobubble interactions in experiments conducted on argon surface nanobubbles on HOPG (highly oriented pyrolytic graphite) in water in tapping mode, lift mode and Force Volume (FV) mode AFM. By subsequent data acquisition on the same nanobubbles in these three different AFM modes, we could directly compare the effect of different tip-sample interactions. The tip-bubble interaction strength was found to depend on the vertical and horizontal position of the tip on the bubble with respect to the bubble center. The interaction forces measured experimentally were in good agreement with the forces calculated using the dynamic interaction model. The strength of the hydrodynamic effect was also found to depend on the direction of the tip movement. It was more pronounced in the FV mode, in which the tip approaches the bubble from the top, than in the lift mode, in which the tip approaches the bubble from the side. This result suggests that the direction of tip movement influences the bubble deformation. The effect should be taken into account when nanobubbles are analysed by AFM in various scanning modes.

  5. Precision Measurement of the Casimir Force for Au Using a Dynamic Afm

    NASA Astrophysics Data System (ADS)

    Chang, C.-C.; Banishev, A. A.; Castillo-Garza, R.; Klimchitskaya, G. L.; Mostepanenko, V. M.; Mohideen, U.

    2012-07-01

    The gradient of the Casimir force between carefully cleaned Au surfaces of a sphere and a plate is measured using a dynamic atomic force microscope in the frequency modulation regime in high vacuum. The electrostatic calibration of the setup did not reveal any effect of patches or surface contaminants. The experimental data for the force gradient are found to be consistent with theory using the plasma model approach over the entire measurement range. The Drude model approach is excluded by the data at separations from 235 to 400 nm at a 67% confidence level.

  6. Recording the dynamic endocytosis of single gold nanoparticles by AFM-based force tracing

    NASA Astrophysics Data System (ADS)

    Ding, Bohua; Tian, Yongmei; Pan, Yangang; Shan, Yuping; Cai, Mingjun; Xu, Haijiao; Sun, Yingchun; Wang, Hongda

    2015-04-01

    We utilized force tracing to directly record the endocytosis of single gold nanoparticles (Au NPs) with different sizes, revealing the size-dependent endocytosis dynamics and the crucial role of membrane cholesterol. The force, duration and velocity of Au NP invagination are accurately determined at the single-particle and microsecond level unprecedentedly.We utilized force tracing to directly record the endocytosis of single gold nanoparticles (Au NPs) with different sizes, revealing the size-dependent endocytosis dynamics and the crucial role of membrane cholesterol. The force, duration and velocity of Au NP invagination are accurately determined at the single-particle and microsecond level unprecedentedly. Electronic supplementary information (ESI) available: Details of the experimental procedures and the results of the control experiments. See DOI: 10.1039/c5nr01020a

  7. Characterization of gold nanoparticle films: Rutherford backscattering spectroscopy, scanning electron microscopy with image analysis, and atomic force microscopy

    SciTech Connect

    Lansåker, Pia C. Niklasson, Gunnar A.; Granqvist, Claes G.; Hallén, Anders

    2014-10-15

    Gold nanoparticle films are of interest in several branches of science and technology, and accurate sample characterization is needed but technically demanding. We prepared such films by DC magnetron sputtering and recorded their mass thickness by Rutherford backscattering spectroscopy. The geometric thickness d{sub g}—from the substrate to the tops of the nanoparticles—was obtained by scanning electron microscopy (SEM) combined with image analysis as well as by atomic force microscopy (AFM). The various techniques yielded an internally consistent characterization of the films. In particular, very similar results for d{sub g} were obtained by SEM with image analysis and by AFM.

  8. Single Cell Wall Nonlinear Mechanics Revealed by a Multiscale Analysis of AFM Force-Indentation Curves.

    PubMed

    Digiuni, Simona; Berne-Dedieu, Annik; Martinez-Torres, Cristina; Szecsi, Judit; Bendahmane, Mohammed; Arneodo, Alain; Argoul, Françoise

    2015-05-05

    Individual plant cells are rather complex mechanical objects. Despite the fact that their wall mechanical strength may be weakened by comparison with their original tissue template, they nevertheless retain some generic properties of the mother tissue, namely the viscoelasticity and the shape of their walls, which are driven by their internal hydrostatic turgor pressure. This viscoelastic behavior, which affects the power-law response of these cells when indented by an atomic force cantilever with a pyramidal tip, is also very sensitive to the culture media. To our knowledge, we develop here an original analyzing method, based on a multiscale decomposition of force-indentation curves, that reveals and quantifies for the first time the nonlinearity of the mechanical response of living single plant cells upon mechanical deformation. Further comparing the nonlinear strain responses of these isolated cells in three different media, we reveal an alteration of their linear bending elastic regime in both hyper- and hypotonic conditions.

  9. High-resolution noncontact AFM and Kelvin probe force microscopy investigations of self-assembled photovoltaic donor–acceptor dyads

    PubMed Central

    Schwartz, Pierre-Olivier; Biniek, Laure; Brinkmann, Martin; Leclerc, Nicolas; Zaborova, Elena

    2016-01-01

    Summary Self-assembled donor–acceptor dyads are used as model nanostructured heterojunctions for local investigations by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). With the aim to probe the photo-induced charge carrier generation, thin films deposited on transparent indium tin oxide substrates are investigated in dark conditions and upon illumination. The topographic and contact potential difference (CPD) images taken under dark conditions are analysed in view of the results of complementary transmission electron microscopy (TEM) experiments. After in situ annealing, it is shown that the dyads with longer donor blocks essentially lead to standing acceptor–donor lamellae, where the acceptor and donor groups are π-stacked in an edge-on configuration. The existence of strong CPD and surface photo-voltage (SPV) contrasts shows that structural variations occur within the bulk of the edge-on stacks. SPV images with a very high lateral resolution are achieved, which allows for the resolution of local photo-charging contrasts at the scale of single edge-on lamella. This work paves the way for local investigations of the optoelectronic properties of donor–acceptor supramolecular architectures down to the elementary building block level. PMID:27335768

  10. High-resolution noncontact AFM and Kelvin probe force microscopy investigations of self-assembled photovoltaic donor-acceptor dyads.

    PubMed

    Grévin, Benjamin; Schwartz, Pierre-Olivier; Biniek, Laure; Brinkmann, Martin; Leclerc, Nicolas; Zaborova, Elena; Méry, Stéphane

    2016-01-01

    Self-assembled donor-acceptor dyads are used as model nanostructured heterojunctions for local investigations by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). With the aim to probe the photo-induced charge carrier generation, thin films deposited on transparent indium tin oxide substrates are investigated in dark conditions and upon illumination. The topographic and contact potential difference (CPD) images taken under dark conditions are analysed in view of the results of complementary transmission electron microscopy (TEM) experiments. After in situ annealing, it is shown that the dyads with longer donor blocks essentially lead to standing acceptor-donor lamellae, where the acceptor and donor groups are π-stacked in an edge-on configuration. The existence of strong CPD and surface photo-voltage (SPV) contrasts shows that structural variations occur within the bulk of the edge-on stacks. SPV images with a very high lateral resolution are achieved, which allows for the resolution of local photo-charging contrasts at the scale of single edge-on lamella. This work paves the way for local investigations of the optoelectronic properties of donor-acceptor supramolecular architectures down to the elementary building block level.

  11. Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy.

    PubMed

    Albers, Boris J; Liebmann, Marcus; Schwendemann, Todd C; Baykara, Mehmet Z; Heyde, Markus; Salmeron, Miquel; Altman, Eric I; Schwarz, Udo D

    2008-03-01

    We present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1 pm could successfully be resolved. In addition, lateral drifts rates of below 15 pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance.

  12. Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy

    SciTech Connect

    Schwarz, Udo; Albers, Boris J.; Liebmann, Marcus; Schwendemann, Todd C.; Baykara, Mehmet Z.; Heyde, Markus; Salmeron, Miquel; Altman, Eric I.; Schwarz, Udo D.

    2008-02-27

    The authors present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1 pm could successfully be resolved. In addition, lateral drifts rates of below 15 pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance.

  13. AFM in peak force mode applied to worn siloxane-hydrogel contact lenses.

    PubMed

    Abadías, Clara; Serés, Carme; Torrent-Burgués, Juan

    2015-04-01

    The objective of this work is to apply Atomic Force Microscopy in Peak Force mode to obtain topographic characteristics (mean roughness, root-mean-square roughness, skewness and kurtosis) and mechanical characteristics (adhesion, elastic modulus) of Siloxane-Hydrogel Soft Contact Lenses (CLs) of two different materials, Lotrafilcon B of Air Optix (AO) and Asmofilcon A of PremiO (P), after use (worn CLs). Thus, the results obtained with both materials will be compared, as well as the changes produced by the wear at a nanoscopic level. The results show significant changes in the topographic and mechanical characteristics of the CLs, at a nanoscopic level, due to wear. The AO CL show values of the topographic parameters lower than those of the P CL after wear, which correlates with a better comfort qualification given to the former by the wearers. A significant correlation has also been obtained between the adhesion values found after the use of the CLs with tear quality tests, both break-up-time and Schirmer.

  14. Atomic force microscopy and spectroscopy of native membrane proteins.

    PubMed

    Müller, Daniel J; Engel, Andreas

    2007-01-01

    Membrane proteins comprise 30% of the proteome of higher organisms. They mediate energy conversion, signal transduction, solute transport and secretion. Their native environment is a bilayer in a physiological buffer solution, hence their structure and function are preferably assessed in this environment. The surface structure of single membrane proteins can be determined in buffer solutions by atomic force microscopy (AFM) at a lateral resolution of less than 1 nm and a vertical resolution of 0.1-0.2 nm. Moreover, single proteins can be directly addressed, stuck to the AFM stylus and subsequently unfolded, revealing the molecular interactions of the protein studied. The examples discussed here illustrate the power of AFM in the structural analysis of membrane proteins in a native environment.

  15. Force spectroscopy of hyaluronan by atomic force microscopy: from hydrogen-bonded networks toward single-chain behavior.

    PubMed

    Giannotti, Marina I; Rinaudo, Marguerite; Vancso, G Julius

    2007-09-01

    The conformational behavior of hyaluronan (HA) polysaccharide chains in aqueous NaCl solution was characterized directly at the single-molecule level. This communication reports on one of the first single-chain atomic force microscopy (AFM) experiments performed at variable temperatures, investigating the influence of the temperature on the stability of the HA single-chain conformation. Through AFM single-molecule force spectroscopy, the temperature destabilization of a local structure was proven. This structure involved a hydrogen-bonded network along the polymeric chain, with hydrogen bonds between the polar groups of HA and possibly water, and a change from a nonrandom coil to a random coil behavior was observed when increasing the temperature from 29 +/- 1 to 46 +/- 1 degrees C. As a result of the applied force, this superstructure was found to break progressively at room temperature. The use of a hydrogen-bonding breaker solvent demonstrated the hydrogen-bonded water-bridged nature of the network structure of HA single chains in aqueous NaCl solution.

  16. Hands-on Force Spectroscopy: Weird Springs and Protein Folding

    ERIC Educational Resources Information Center

    Euler, Manfred

    2008-01-01

    A force spectroscopy model experiment is presented using a low-cost tensile apparatus described earlier. Force-extension measurements of twisted rubber bands are obtained. They exhibit a complex nonlinear elastic behaviour that resembles atomic force spectroscopy investigations of molecules of titin, a muscle protein. The model experiments open up…

  17. Single-Molecule Force Spectroscopy of DNA-Based Reversible Polymer Bridges: Surface Robustness and Homogeneity

    PubMed Central

    Serpe, Michael J.; Whitehead, Jason R.; Rivera, Monica; Clark, Robert L.; Craig, Stephen L.

    2011-01-01

    Single-molecule force spectroscopy, as implemented in an atomic force microscope, provides a rarely-used method by which to monitor dynamic processes that occur near surfaces. Here, a methodology is presented and characterized that facilitates the study of polymer bridging across nanometer-sized gaps. The model system employed is that of DNA-based reversible polymers, and an automated procedure is introduced that allows the AFM tip-surface contact point to be automatically determined, and the distance d between opposing surfaces to be actively controlled. Using this methodology, the importance of several experimental parameters was systematically studied, e.g. the frequency of repeated tip/surface contacts, the area of the substrate surface sampled by the AFM, and the use of multiple AFM tips and substrates. Experiments revealed the surfaces to be robust throughout pulling experiments, so that multiple touches and pulls could be carried out on a single spot with no measurable affect on the results. Differences in observed bridging probabilities were observed, both on different spots on the same surface and, more dramatically, from one day to another. Data normalization via a reference measurement allows data from multiple days to be directly compared. PMID:21966095

  18. Compact metal probes: a solution for atomic force microscopy based tip-enhanced Raman spectroscopy.

    PubMed

    Rodriguez, R D; Sheremet, E; Müller, S; Gordan, O D; Villabona, A; Schulze, S; Hietschold, M; Zahn, D R T

    2012-12-01

    There are many challenges in accomplishing tip-enhanced Raman spectroscopy (TERS) and obtaining a proper tip is probably the greatest one. Since tip size, composition, and geometry are the ultimate parameters that determine enhancement of intensity and lateral resolution, the tip becomes the most critical component in a TERS experiment. However, since the discovery of TERS the cantilevers used in atomic force microscopy (AFM) have remained basically the same: commercial silicon (or silicon nitride) tips covered by a metallic coating. The main issues of using metal-coated silicon cantilevers, such as wearing off of the metal layer or increased tip radius, can be completely overcome by using all-metal cantilevers. Until now in TERS experiments such probes have only been used in a scanning tunneling microscope or in a tuning fork-based shear force microscope but not in AFM. In this work for the first time, we show the use of compact silver cantilevers that are fully compatible with contact and tapping modes in AFM demonstrating their superb performance in TERS experiments.

  19. Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy

    PubMed Central

    Neuman, Keir C.; Nagy, Attila

    2012-01-01

    Single-molecule force spectroscopy has emerged as a powerful tool to investigate the forces and motions associated with biological molecules and enzymatic activity. The most common force spectroscopy techniques are optical tweezers, magnetic tweezers and atomic force microscopy. These techniques are described and illustrated with examples highlighting current capabilities and limitations. PMID:18511917

  20. Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy.

    PubMed

    Neuman, Keir C; Nagy, Attila

    2008-06-01

    Single-molecule force spectroscopy has emerged as a powerful tool to investigate the forces and motions associated with biological molecules and enzymatic activity. The most common force spectroscopy techniques are optical tweezers, magnetic tweezers and atomic force microscopy. Here we describe these techniques and illustrate them with examples highlighting current capabilities and limitations.

  1. Nano-mechanical and biochemical characterization of different subtypes of breast cells using atomic force microscopy and Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Zeng, Jinshu; Wang, Yuhua; Ruan, Qiuyong; Xu, Chaoxian; Jiang, Ningcheng; Xie, Shusen; Yang, Hongqin; Lin, Juqiang

    2016-11-01

    Combining atomic force microscopy (AFM) with Raman spectroscopy (RS), three different subtypes of breast cell lines, including metastatic cancer cells (MDA-MB-231), non-malignant cancer cells (MCF-7) and benign cells (MCF-10A), were studied to compare their differences in nano-mechanical and biochemical properties. Based on AFM measurements, two cancerous cells were found to have a close elasticity modulus, but were significantly softer than that of their benign counterparts. Raman spectral analysis revealed that the data points for two cancerous cells were distinct with completely separated clusters. The results demonstrate that combined AFM and RS techniques could obtain information about the biomechanical and biochemical properties necessary to distinguish different subtypes of breast cancer cells. This will hold great promise for cancer detection at the single cell level.

  2. Force spectroscopy of membrane hardness of SH-SY5Y neuroblastoma cells before and after differentiation

    NASA Astrophysics Data System (ADS)

    Kwon, Sangwoo; Yang, Woochul; Choi, Yun Kyong; Park, Jung Keuck

    2014-05-01

    Atomic force microscopy (AFM) is utilized in many studies for measuring the structure and the physical characteristics of soft and bio materials. In particular, the force spectroscopy function in the AFM system allows us to explore the mechanical properties of bio cells. In this study, we probe the variation in the membrane hardness of human neuroblastoma SH-SY5Y cells (SH-cells) before and after differentiation by using force spectroscopy. The SH-cell, which is usually differentiated by using a chemical treatment with retinoic acid (RA), is a neuronal cell line employed widely as an in-vitro model for neuroscience research. In force spectroscopy, the force-distance curves are obtained from both the original and the RA-treated cells while the AFM tip approaches and pushes on the cell membranes. The slope deduced from linear region in the force-distance curve is the spring constant and corresponds to the hardness of the cell membrane. The spring constant of the RA-treated cells (0.597 ± 0.010 nN/nm) was smaller than that of the original cells (0.794 ± 0.010 nN/nm), reflecting a hardness decrease in the cells differentiated with the RA treatments. The results clearly demonstrated that the differentiated cells are softer than the original cells. The change in the elasticity of the differentiated cells might be caused by morphological modification during differentiation process. We suggest that force spectroscopy can be employed as a novel method to determine the degree of differentiation of stem cells into various functional cells.

  3. Quartz tuning fork-based frequency modulation atomic force spectroscopy and microscopy with all digital phase-locked loop.

    PubMed

    An, Sangmin; Hong, Mun-heon; Kim, Jongwoo; Kwon, Soyoung; Lee, Kunyoung; Lee, Manhee; Jhe, Wonho

    2012-11-01

    We present a platform for the quartz tuning fork (QTF)-based, frequency modulation atomic force microscopy (FM-AFM) system for quantitative study of the mechanical or topographical properties of nanoscale materials, such as the nano-sized water bridge formed between the quartz tip (~100 nm curvature) and the mica substrate. A thermally stable, all digital phase-locked loop is used to detect the small frequency shift of the QTF signal resulting from the nanomaterial-mediated interactions. The proposed and demonstrated novel FM-AFM technique provides high experimental sensitivity in the measurement of the viscoelastic forces associated with the confined nano-water meniscus, short response time, and insensitivity to amplitude noise, which are essential for precision dynamic force spectroscopy and microscopy.

  4. Quartz tuning fork-based frequency modulation atomic force spectroscopy and microscopy with all digital phase-locked loop

    NASA Astrophysics Data System (ADS)

    An, Sangmin; Hong, Mun-heon; Kim, Jongwoo; Kwon, Soyoung; Lee, Kunyoung; Lee, Manhee; Jhe, Wonho

    2012-11-01

    We present a platform for the quartz tuning fork (QTF)-based, frequency modulation atomic force microscopy (FM-AFM) system for quantitative study of the mechanical or topographical properties of nanoscale materials, such as the nano-sized water bridge formed between the quartz tip (˜100 nm curvature) and the mica substrate. A thermally stable, all digital phase-locked loop is used to detect the small frequency shift of the QTF signal resulting from the nanomaterial-mediated interactions. The proposed and demonstrated novel FM-AFM technique provides high experimental sensitivity in the measurement of the viscoelastic forces associated with the confined nano-water meniscus, short response time, and insensitivity to amplitude noise, which are essential for precision dynamic force spectroscopy and microscopy.

  5. 3D simulation of AFM non-uniform piezoelectric micro-cantilever with various geometries subjected to the tip-sample forces

    NASA Astrophysics Data System (ADS)

    Korayem, Alireza Habibnejad; Abdi, Moein

    2017-03-01

    Atomic force microscope (AFM) is a powerful instrument for investigation of surface topography at different workspaces. It is important to understand the dynamic behavior of AFM to improve its performance. 3D numerical method is suitable in order to simulate experimental conditions. This paper has investigated modeling and dynamic simulation of rectangular, Dagger and V-shaped geometries of AFM piezoelectric micro-cantilever (MC) with two electrode layers in the air environment. For a better understanding of the system dynamic, multi-layer MC dynamic equation has been derived. Euler-Bernoulli beam theory has been used for modeling the AFM cantilever. Hamilton's principle has been used for the MC modeling and the finite element method (FEM) has been applied for its discretization. In 3D, with respect to the tip-sample forces piezoelectric MC has been simulated via the COMSOL software. The frequency and time responses have been also investigated. The topographies have been performed on different surfaces with various roughness's types in the tapping and non-contact mode. The results of these two methods have been compared with experimental results. Moreover, the effects of MC geometrical parameters on surfaces topography and frequency responses have been studied and optimal dimensions of topographies have been obtained for each of the beam geometries. Simulations of various tip geometries have been performed in order to examine the effects of tip dimensions on the frequency and time responses. Furthermore, the effect of tip displacement on the frequency response has been investigated for different MC lengths.

  6. AFM Force measurements of the gp120-sCD4 and gp120 or CD4 antigen-antibody interactions

    PubMed Central

    Chen, Yong; Zeng, Gucheng; Chen, Sherry Shiyi; Feng, Qian; Chen, Zheng Wei

    2011-01-01

    Soluble CD4 (sCD4), anti-CD4 antibody, and anti-gp120 antibody have long been regarded as entry inhibitors in human immunodeficiency virus (HIV) therapy. However, the interactions between these HIV entry inhibitors and corresponding target molecules are still poorly understood. In this study, atomic force microscopy (AFM) was utilized to investigate the interaction forces among them. We found that the unbinding forces of sCD4-gp120 interaction, CD4 antigen-antibody interaction, and gp120 antigen-antibody interaction were 25.45 ± 20.46 pN, 51.22 ± 34.64 pN, and 89.87 ± 44.63 pN, respectively, which may provide important mechanical information for understanding the effects of viral entry inhibitors on HIV infection. Moreover, we found that the functionalization of an interaction pair on AFM tip or substrate significantly influenced the results, implying that we must perform AFM force measurement and analyze the data with more caution. PMID:21382342

  7. Single Cell Force Spectroscopy for Quantification of Cellular Adhesion on Surfaces

    NASA Astrophysics Data System (ADS)

    Christenson, Wayne B.

    Cell adhesion is an important aspect of many biological processes. The atomic force microscope (AFM) has made it possible to quantify the forces involved in cellular adhesion using a technique called single cell force spectroscopy (SCFS). AFM based SCFS offers versatile control over experimental conditions for probing directly the interaction between specific cell types and specific proteins, surfaces, or other cells. Transmembrane integrins are the primary proteins involved in cellular adhesion to the extra cellular matix (ECM). One of the chief integrins involved in the adhesion of leukocyte cells is alpha Mbeta2 (Mac-1). The experiments in this dissertation quantify the adhesion of Mac-1 expressing human embryonic kidney (HEK Mac-1), platelets, and neutrophils cells on substrates with different concentrations of fibrinogen and on fibrin gels and multi-layered fibrinogen coated fibrin gels. It was shown that multi-layered fibrinogen reduces the adhesion force of these cells considerably. A novel method was developed as part of this research combining total internal reflection microscopy (TIRFM) with SCFS allowing for optical microscopy of HEK Mac-1 cells interacting with bovine serum albumin (BSA) coated glass after interacting with multi-layered fibrinogen. HEK Mac-1 cells are able to remove fibrinogen molecules from the multi-layered fibrinogen matrix. An analysis methodology for quantifying the kinetic parameters of integrin-ligand interactions from SCFS experiments is proposed, and the kinetic parameters of the Mac-1 fibrinogen bond are quantified. Additional SCFS experiments quantify the adhesion of macrophages and HEK Mac-1 cells on functionalized glass surfaces and normal glass surfaces. Both cell types show highest adhesion on a novel functionalized glass surface that was prepared to induce macrophage fusion. These experiments demonstrate the versatility of AFM based SCFS, and how it can be applied to address many questions in cellular biology offering

  8. Investigation of biopolymer networks by means of AFM

    NASA Astrophysics Data System (ADS)

    Keresztes, Z.; Rigó, T.; Telegdi, J.; Kálmán, E.

    Natural hydrogel alginate was investigated by means of atomic force microscopy (AFM) to gain microscale information on the morphological and rheological properties of the biopolymer network cross-linked by various cations. Local rheological properties of the gels measured by force spectroscopy gave correlation between increasing ion selectivity and increasing polymer elasticity. Adhesive forces acting between the surface of the gel and the probe, and also the intrinsic rheological properties of bulk polymers affect the microscopical image formation.

  9. Application of Electron Backscattered Diffraction (EBSD) and Atomic Force Microscopy (AFM) to Determine Texture, Microtexture, and Grain Boundary Energies in Ceramics

    SciTech Connect

    Glass, S.J.; Rohrer, G.S.; Saylor, D.M.; Vedula, V.R.

    1999-05-19

    Crystallographic orientations in alumina (Al203) and magnesium aluminate spinel (MgAl204) were obtained using electron backscattered diffraction (EBSD) patterns. The texture and mesotexture (grain boundary misorientations) were random and no special boundaries were observed. The relative grain boundary energies were determined by thermal groove geometries using atomic force microscopy (AFM) to identify relationships between the grain boundary energies and misorientations.

  10. Comparison of the bias voltage effect and the force effect during the nanoscale AFM electric lithography on the copper thin film surface.

    PubMed

    Yang, Ye; Lin, Jun

    2016-09-01

    As one of the tip-based nanoscale machining methods, AFM-based nanolithography has been proved to be capable of fabricating nanostructures and devices on a wide range of materials by means of mechanical force, bias voltage, chemical reaction, etc. In this paper, we have compared the influences of the bias voltage effect and the force effect during the nanoscale AFM electric lithography on the metallic copper film surface respectively through the bias voltage dominating scheme and the contact force dominating scheme. The geometric sizes of the line structures and the area patterns fabricated under the two schemes with different parameter settings were compared to obtain the machining characteristics and mechanisms of the two distinct effects separately. The ratios of debris amount to the total material removal amount under the two schemes were quantitatively evaluated. Furthermore, both the arbitrary line structure with high aspect ratio and the area pattern with small surface roughness were fabricated under the appropriate scheme and parameter settings. This study is of great help to effectively achieve the desired nanoscale patterns by AFM electric lithography for their promising applications in the fabrication of various MEMS or NEMS devices. SCANNING 38:412-420, 2016. © 2015 Wiley Periodicals, Inc.

  11. Atomic force microscopy imaging and single molecule recognition force spectroscopy of coat proteins on the surface of Bacillus subtilis spore.

    PubMed

    Tang, Jilin; Krajcikova, Daniela; Zhu, Rong; Ebner, Andreas; Cutting, Simon; Gruber, Hermann J; Barak, Imrich; Hinterdorfer, Peter

    2007-01-01

    Coat assembly in Bacillus subtilis serves as a tractable model for the study of the self-assembly process of biological structures and has a significant potential for use in nano-biotechnological applications. In the present study, the morphology of B. subtilis spores was investigated by magnetically driven dynamic force microscopy (MAC mode atomic force microscopy) under physiological conditions. B. subtilis spores appeared as prolate structures, with a length of 0.6-3 microm and a width of about 0.5-2 microm. The spore surface was mainly covered with bump-like structures with diameters ranging from 8 to 70 nm. Besides topographical explorations, single molecule recognition force spectroscopy (SMRFS) was used to characterize the spore coat protein CotA. This protein was specifically recognized by a polyclonal antibody directed against CotA (anti-CotA), the antibody being covalently tethered to the AFM tip via a polyethylene glycol linker. The unbinding force between CotA and anti-CotA was determined as 55 +/- 2 pN. From the high-binding probability of more than 20% in force-distance cycles it is concluded that CotA locates in the outer surface of B. subtilis spores.

  12. Analysis the effect of different geometries of AFM's cantilever on the dynamic behavior and the critical forces of three-dimensional manipulation.

    PubMed

    Korayem, Moharam Habibnejad; Saraie, Maniya B; Saraee, Mahdieh B

    2017-01-13

    An important challenge when using an atomic force microscope (AFM) is to be able to control the force exerted by the AFM for performing various tasks. Nevertheless, the exerted force is proportional to the deflection of the AFM cantilever, which itself is affected by a cantilever's stiffness coefficient. Many papers have been published so far on the methods of obtaining the stiffness coefficients of AFM cantilevers in 2D; however, a comprehensive model is yet to be presented on 3D cantilever motion. The discrepancies between the equations of the 2D and 3D analysis are due to the number and direction of forces and moments that are applied to a cantilever. Moreover, in the 3D analysis, contrary to the 2D analysis, due to the interaction between the forces and moments applied on a cantilever, its stiffness values cannot be separately expressed for each direction; and instead, a stiffness matrix should be used to correctly derive the relevant equations. In this paper, 3D stiffness coefficient matrices have been obtained for three common cantilever geometries including the rectangular, V-shape and dagger-shape cantilevers. The obtained equations are validated by two methods. In the first approach, the Finite Element Method is combined with the cantilever deflection values computed by using the obtained stiffness matrices. In the second approach, by reducing the problem's parameters, the forces applied on a cantilever along different directions are compared with each other in 2D and 3D cases. Then the 3D manipulation of a stiff nanoparticle is modeled and simulated by using the stiffness matrices obtained for the three cantilever geometries. The obtained results indicate that during the manipulation process, the dagger-shaped and rectangular cantilevers exert the maximum and minimum amounts of forces on the stiff nanoparticle, respectively. Also, by examining the effects of different probe tip geometries, it is realized that a probe tip of cylindrical geometry exerts the

  13. Review insights into the interactions of amino acids and peptides with inorganic materials using single molecule force spectroscopy.

    PubMed

    Das, Priyadip; Reches, Meital

    2015-09-01

    Understanding the interactions between proteins and inorganic surfaces is important for the development of new biomaterials and implants as they interface with the immune response by proteins. In addition, the adsorption of proteins to inorganic surfaces leads to the formation of a conditioning layer that facilitates bacterial attachments and biofilm formation. As biofilm provides bacterial resistance to antibiotics, biofilm formation is an undesirable process that could be prevented by resisting protein interactions with the substrate. Moreover, the interaction between proteins and inorganic materials is the basis for the formation of composite materials in nature. Understanding the underlying forces that governs these interactions would lead to the design of new and unique composite materials in vitro. This review focuses on the insights gained using single-molecule force spectroscopy by AFM on these interactions. This tool provides molecular information, at the single molecule level, on the interaction between a molecule on the AFM tip and a substrate.

  14. Quadrature phase interferometer for high resolution force spectroscopy

    SciTech Connect

    Paolino, Pierdomenico; Aguilar Sandoval, Felipe A.; Bellon, Ludovic

    2013-09-15

    In this article, we present a deflection measurement setup for Atomic Force Microscopy (AFM). It is based on a quadrature phase differential interferometer: we measure the optical path difference between a laser beam reflecting above the cantilever tip and a reference beam reflecting on the static base of the sensor. A design with very low environmental susceptibility and another allowing calibrated measurements on a wide spectral range are described. Both enable a very high resolution (down to 2.5×10{sup −15} m/√(Hz)), illustrated by thermal noise measurements on AFM cantilevers. They present an excellent long-term stability and a constant sensitivity independent of the optical phase of the interferometer. A quick review shows that our precision is equaling or out-performing the best results reported in the literature, but for a much larger deflection range, up to a few μm.

  15. Analyzing the vibrational response of an AFM cantilever in liquid with the consideration of tip mass by comparing the hydrodynamic and contact repulsive force models in higher modes

    NASA Astrophysics Data System (ADS)

    Korayem, Moharam Habibnejad; Nahavandi, Amir

    2017-04-01

    This paper investigates the vibration of a tapping-mode Atomic Force Microscope (AFM) cantilever covered with two whole piezoelectric layers in a liquid medium. The authors of this article have already modeled the vibration of a cantilever immersed in liquid over rough surfaces. Five new ideas have been considered for improving the results of the previous work. Mass and damping of a cantilever probe tip have been considered. Since the probe tip of an AFM cantilever has a mass, which can itself affect the natural frequency of vibration, the significance of this mass has been explored. Also, two hydrodynamic force models for analyzing the mass and damping added to a cantilever in liquid medium have been evaluated. In modeling the vibration of a cantilever in liquid, simplifications are made to the theoretical equations used in the modeling, which may make the obtained results different from those in the real case. So, two hydrodynamic force models are introduced and compared with each other. In addition to the already introduced DMT model, the JKR model has been proposed. The forces acting on a probe tip have attractive and repulsive effects. The attractive Van der Waals force can vary depending on the surface smoothness or roughness, and the repulsive contact force, which is independent of the type of surface roughness and usually varies with the hardness or softness of a surface. When the first mode is used in the vibration of an AFM cantilever, the changes of the existing physical parameters in the simulation do not usually produce a significant difference in the response. Thus, three cantilever vibration modes have been investigated. Finally, an analytical approach for obtaining the response of equations is presented which solves the resulting motion equation by the Laplace method and, thus, a time function is obtained for cantilever deflection is determined. Also, using the COMSOL software to model a cantilever in a liquid medium, the computed natural

  16. Versatile method for AFM-tip functionalization with biomolecules: fishing a ligand by means of an in situ click reaction.

    PubMed

    Kumar, Rakesh; Ramakrishna, Shivaprakash N; Naik, Vikrant V; Chu, Zonglin; Drew, Michael E; Spencer, Nicholas D; Yamakoshi, Yoko

    2015-04-21

    A facile and universal method for the functionalization of an AFM tip has been developed for chemical force spectroscopy (CFS) studies of intermolecular interactions of biomolecules. A click reaction between tripod-acetylene and an azide-linker-ligand molecule was successfully carried out on the AFM tip surface and used for the CFS study of ligand-receptor interactions.

  17. Capillary and van der Waals interactions on CaF2 crystals from amplitude modulation AFM force reconstruction profiles under ambient conditions

    PubMed Central

    Calò, Annalisa; Robles, Oriol Vidal; Santos, Sergio

    2015-01-01

    Summary There has been much interest in the past two decades to produce experimental force profiles characteristic of the interaction between nanoscale objects or a nanoscale object and a plane. Arguably, the advent of the atomic force microscope AFM was instrumental in driving such efforts because, in principle, force profiles could be recovered directly. Nevertheless, it has taken years before techniques have developed enough as to recover the attractive part of the force with relatively low noise and without missing information on critical ranges, particularly under ambient conditions where capillary interactions are believed to dominate. Thus a systematic study of the different profiles that may arise in such situations is still lacking. Here we employ the surfaces of CaF2, on which nanoscale water films form, to report on the range and force profiles that might originate by dynamic capillary interactions occurring between an AFM tip and nanoscale water patches. Three types of force profiles were observed under ambient conditions. One in which the force decay resembles the well-known inverse-square law typical of van der Waals interactions during the first 0.5–1 nm of decay, a second one in which the force decays almost linearly, in relatively good agreement with capillary force predicted by the constant chemical potential approximation, and a third one in which the attractive force is almost constant, i.e., forms a plateau, up to 3–4 nm above the surface when the formation of a capillary neck dominates the tip–sample interaction. PMID:25977852

  18. A biophysical investigation on the binding of proflavine with human hemoglobin: Insights from spectroscopy, thermodynamics and AFM studies.

    PubMed

    Basu, Anirban; Kumar, Gopinatha Suresh

    2016-12-01

    Interaction of proflavine with hemoglobin (Hgb) was studied employing spectroscopy, calorimetry, and atomic force microscopy. The equilibrium constant was found to be of the order 10(4)M(-1). The quenching of Hgb fluorescence by proflavine was due to the complex formation. Calculation of the molecular distance (r) between the donor (β-Trp37 of Hgb) and acceptor (proflavine) suggested that energy can be efficiently transferred from the β-Trp37 residue at the α1β2 interface of the protein to the dye. Proflavine induced significant secondary structural changes in Hgb. Synchronous fluorescence studies showed that proflavine altered the microenvironment around the tryptophan residues to a greater extent than the tyrosine residues. Circular dichroism spectral studies showed that proflavine caused significant reduction in the α-helical content of Hgb. The esterase activity assay further complemented the circular dichroism data. The Soret band intensity of Hgb decreased upon complexation. Differential scanning calorimetry and circular dichroism melting results revealed that proflavine induced destabilization of Hgb. The binding was driven by both positive entropy and negative enthalpy. Atomic force microscopy studies revealed that the essential morphological features of hemoglobin were retained in the presence of proflavine. Overall, insights on the photophysical aspects and energetics of the binding of proflavine with Hgb are presented.

  19. The ReactorAFM: Non-contact atomic force microscope operating under high-pressure and high-temperature catalytic conditions

    SciTech Connect

    Roobol, S. B.; Cañas-Ventura, M. E.; Bergman, M.; Spronsen, M. A. van; Onderwaater, W. G.; Tuijn, P. C. van der; Koehler, R.; Frenken, J. W. M.; Ofitserov, A.; Baarle, G. J. C. van

    2015-03-15

    An Atomic Force Microscope (AFM) has been integrated in a miniature high-pressure flow reactor for in-situ observations of heterogeneous catalytic reactions under conditions similar to those of industrial processes. The AFM can image model catalysts such as those consisting of metal nanoparticles on flat oxide supports in a gas atmosphere up to 6 bar and at a temperature up to 600 K, while the catalytic activity can be measured using mass spectrometry. The high-pressure reactor is placed inside an Ultrahigh Vacuum (UHV) system to supplement it with standard UHV sample preparation and characterization techniques. To demonstrate that this instrument successfully bridges both the pressure gap and the materials gap, images have been recorded of supported palladium nanoparticles catalyzing the oxidation of carbon monoxide under high-pressure, high-temperature conditions.

  20. Insights into the Interactions of Amino Acids and Peptides with Inorganic Materials Using Single-Molecule Force Spectroscopy.

    PubMed

    Das, Priyadip; Duanias-Assaf, Tal; Reches, Meital

    2017-03-06

    The interactions between proteins or peptides and inorganic materials lead to several interesting processes. For example, combining proteins with minerals leads to the formation of composite materials with unique properties. In addition, the undesirable process of biofouling is initiated by the adsorption of biomolecules, mainly proteins, on surfaces. This organic layer is an adhesion layer for bacteria and allows them to interact with the surface. Understanding the fundamental forces that govern the interactions at the organic-inorganic interface is therefore important for many areas of research and could lead to the design of new materials for optical, mechanical and biomedical applications. This paper demonstrates a single-molecule force spectroscopy technique that utilizes an AFM to measure the adhesion force between either peptides or amino acids and well-defined inorganic surfaces. This technique involves a protocol for attaching the biomolecule to the AFM tip through a covalent flexible linker and single-molecule force spectroscopy measurements by atomic force microscope. In addition, an analysis of these measurements is included.

  1. Analytical solutions of the first three frequency shifts of AFM non-uniform probe subjected to the Lennard-Jones force.

    PubMed

    Lin, Shueei-Muh; Liauh, Chihng-Tsung; Wang, Wen-Rong; Ho, Shing-Huei

    2006-04-01

    The role of higher cantilever modes is important to obtain some material contrast. The analysis of AFM subjected to a short-range force can improve greatly the studies of surface topography and interaction energies and interaction forces, especially for chemical and biological materials. When the tip-sample distance is in the order of inter-atomic spacing, the short-range tip-sample force is usually simulated by the Lennard-Jones model. In this study, the analytical method to determine the frequency shift of AFM subjected to the Lennard-Jones force is proposed. The closed-form solution of the partial differential equation with a nonlinear boundary condition is derived and then the corresponding frequency shifts of higher modes can be determined easily. Moreover, the conventional perturbation method is usually used to determine the frequency shift, but only for the first mode. This is because the original continuous beam system is transformed into a discrete lumped-masses model. Although the above disadvantages exist, the lumped-masses model is simple and intuitive. Using the principle of dynamic strain energy, the conventional perturbation method is revised successfully to determine the frequency shifts of higher modes. The assessment of the generalized perturbation method and the proposed method is made. Finally, the effects of several parameters on the first three frequency shifts are investigated.

  2. X-ray photoelectron spectroscopy and atomic force microscopy characterization of the effects of etching Zn xCd 1- xTe surfaces

    NASA Astrophysics Data System (ADS)

    George, M. A.; Azoulay, M.; Jayatirtha, H. N.; Burger, A.; Collins, W. E.; Silberman, E.

    1993-10-01

    X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) was used for the first time to characterize the chemical composition of modified surfaces of Zn xCd 1- xTe single crystals. These surface treatments were selected for their relevance to device preparation procedures. The XPS peaks indicated an increase of the tellurium and a depletion of the cadmium concentrations upon etching in bromine methanol solution. AFM revealed the formation of pronounced Te inclusions. Higher x values correlated with a decrease in residual bromine left on the surface, while cut and polished samples had higher oxide concentrations and increased bromination of the surface than cleaved samples.

  3. The nature of the force-induced conformation transition of dsDNA studied by using single molecule force spectroscopy.

    PubMed

    Liu, Ningning; Bu, Tianjia; Song, Yu; Zhang, Wei; Li, Jinjing; Zhang, Wenke; Shen, Jiacong; Li, Hongbin

    2010-06-15

    Single-stranded DNA binding proteins (SSB) interact with single-stranded DNA (ssDNA) specifically. Taking advantage of this character, we have employed Bacillus subtilis SSB protein to investigate the nature of force-induced conformation transition of double-stranded DNA (dsDNA) by using AFM-based single molecule force spectroscopy (SMFS) technique. Our results show that, when a dsDNA is stretched beyond its contour length, the dsDNA is partially melted, producing some ssDNA segments which can be captured by SSB proteins. We have also systematically investigated the effects of stretching length, waiting time, and salt concentration on the conformation transition of dsDNA and SSB-ssDNA interactions, respectively. Furthermore, the effect of proflavine, a DNA intercalator, on the SSB-DNA interactions has been investigated, and the results indicate that the proflavine-saturated dsDNA can be stabilized to the extent that the dsDNA will no longer melt into ssDNA under the mechanical force even up to 150 pN, and no SSB-DNA interactions are detectable.

  4. Charge injection in thin dielectric layers by atomic force microscopy: influence of geometry and material work function of the AFM tip on the injection process

    NASA Astrophysics Data System (ADS)

    Villeneuve-Faure, C.; Makasheva, K.; Boudou, L.; Teyssedre, G.

    2016-06-01

    Charge injection and retention in thin dielectric layers remain critical issues for the reliability of many electronic devices because of their association with a large number of failure mechanisms. To overcome this drawback, a deep understanding of the mechanisms leading to charge injection close to the injection area is needed. Even though the charge injection is extensively studied and reported in the literature to characterize the charge storage capability of dielectric materials, questions about charge injection mechanisms when using atomic force microscopy (AFM) remain open. In this paper, a thorough study of charge injection by using AFM in thin plasma-processed amorphous silicon oxynitride layers with properties close to that of thermal silica layers is presented. The study considers the impact of applied voltage polarity, work function of the AFM tip coating and tip curvature radius. A simple theoretical model was developed and used to analyze the obtained experimental results. The electric field distribution is computed as a function of tip geometry. The obtained experimental results highlight that after injection in the dielectric layer the charge lateral spreading is mainly controlled by the radial electric field component independently of the carrier polarity. The injected charge density is influenced by the nature of electrode metal coating (work function) and its geometry (tip curvature radius). The electron injection is mainly ruled by the Schottky injection barrier through the field electron emission mechanism enhanced by thermionic electron emission. The hole injection mechanism seems to differ from the electron one depending on the work function of the metal coating. Based on the performed analysis, it is suggested that for hole injection by AFM, pinning of the metal Fermi level with the metal-induced gap states in the studied silicon oxynitride layers starts playing a role in the injection mechanisms.

  5. 2011 AFMS Medical Research Symposium Held in National Harbor, Maryland on August 2-4, 2011. Volume 3: Force Health Protection Track

    DTIC Science & Technology

    2011-08-01

    hearing loss indicating JP-8 only potentiates NIHL. A fourth 28-day study consisted of exposures at 102 dB for 15 min per hr for 6 hrs per day, 1000 mg...frequencies "f1" and "f2" p Sound energy generated by cochlea consists of different frequencies than the "primary tones" so they are "distortion products...Noite95d6 ..,_, :t~ i ;.~ I i·j .. .,... ·- ··~ 14 16 Proceedings of the 2011 AFMS Medical Research Symposium Volume 3 Force Health Protection 21

  6. Nanomechanics of Yeast Surfaces Revealed by AFM

    NASA Astrophysics Data System (ADS)

    Dague, Etienne; Beaussart, Audrey; Alsteens, David

    Despite the large and well-documented characterization of the microbial cell wall in terms of chemical composition, the determination of the mechanical properties of surface molecules in relation to their function remains a key challenge in cell biology.The emergence of powerful tools allowing molecular manipulations has already revolutionized our understanding of the surface properties of fungal cells. At the frontier between nanophysics and molecular biology, atomic force microscopy (AFM), and more specifically single-molecule force spectroscopy (SMFS), has strongly contributed to our current knowledge of the cell wall organization and nanomechanical properties. However, due to the complexity of the technique, measurements on live cells are still at their infancy.In this chapter, we describe the cell wall composition and recapitulate the principles of AFM as well as the main current methodologies used to perform AFM measurements on live cells, including sample immobilization and tip functionalization.The current status of the progress in probing nanomechanics of the yeast surface is illustrated through three recent breakthrough studies. Determination of the cell wall nanostructure and elasticity is presented through two examples: the mechanical response of mannoproteins from brewing yeasts and elasticity measurements on lacking polysaccharide mutant strains. Additionally, an elegant study on force-induced unfolding and clustering of adhesion proteins located at the cell surface is also presented.

  7. Point of zero charge of a corundum-water interface probed with optical second harmonic generation (SHG) and atomic force microscopy (AFM): New approaches to oxide surface charge

    NASA Astrophysics Data System (ADS)

    Stack, Andrew G.; Higgins, Steven R.; Eggleston, Carrick M.

    2001-09-01

    The pH and ionic strength dependence of light generated at a corundum-solution interface by the nonlinear optical process of second harmonic generation (SHG) is reported. A point of zero salt effect occurs in the pH range 5 to 6. The pH and ionic strength dependence of the SHG is qualitatively consistent with a model describing SHG from a charged mineral/water interface from Ong et al. (1992) and Zhao et al. (1993a, 1993b), but certain aspects of the model appear inadequate to describe the full range of our data. Atomic force microscopy (AFM) force-distance measurements, though imprecise, were consistent with a point of zero charge (p.z.c.) for the interface also in the pH range 5 to 6. The SHG (and AFM) results are different from expectation; the observed p.z.s.e. (and presumably also the p.z.c.) is considerably lower than the accepted point of zero charge of clean alumina powders ( pH 8-9.4; Parks, 1965; Sverjenksy and Sahai, 1996). Although the reasons for this are unclear, SHG holds promise as a probe of oxide-water interfaces that is independent of interpretation of acid-base titration stoichiometry.

  8. Absorption Spectroscopy and Imaging from the Visible through Mid-IR with 20 nm Resolution Using AFM probes

    NASA Astrophysics Data System (ADS)

    Centrone, Andrea

    2015-03-01

    Correlated nanoscale composition and optical property maps are important to engineer nanomaterials in applications ranging from photovoltaics to sensing and therapeutics. Wavelengths (λs) from the visible to near-IR probe electronic transitions in materials, providing information regarding band gap and defects while light in mid-IR probes vibrational transitions and provide chemical composition. However, light diffraction limits the lateral resolution of conventional micro-spectroscopic techniques to approximately λ/2, which is insufficient to image nanomaterials. Additionally, the λ-dependent resolution impedes direct comparison of spectral maps from different spectral ranges. Photo Thermal Induced Resonance (PTIR) is a novel technique that circumvents light diffraction by employing an AFM tip as a local detector for measuring light absorption with λ-independent nanoscale resolution. Our PTIR setup combines an AFM microscope with three lasers providing λ-tunability from 500 nm to 16000 nm continuously. The AFM tip transduces locally the sample thermal expansion induced by light absorption into large cantilever oscillations. Local absorption spectra (electronic or vibrational) and maps are obtained recording the amplitude of the tip deflection as a function of λ and position, respectively. The working principles of the PTIR technique will be described first, and nano-patterned polymer samples will be used to evaluate its lateral resolution, sensitivity and linearity. Results show that the PTIR signal intensity is proportional to the local absorbed energy suggesting applicability of this technique for quantitative chemical analysis at nanoscale, at least for thin (less than 1000 nm thick) samples. Additionally, a λ-independent resolution as high as 20 nm is demonstrated across the whole spectral range. In the second part of the talk, PTIR will be applied to image the dark plasmonic resonance of gold Asymmetric Split Ring Resonators (A-SRRs) in the mid

  9. Origin of the nonadhesive properties of fibrinogen matrices probed by force spectroscopy.

    PubMed

    Yermolenko, Ivan S; Fuhrmann, Alexander; Magonov, Sergei N; Lishko, Valeryi K; Oshkadyerov, Stanislav P; Ros, Robert; Ugarova, Tatiana P

    2010-11-16

    The deposition of a multilayered fibrinogen matrix on various surfaces results in a dramatic reduction of integrin-mediated cell adhesion and outside-in signaling in platelets and leukocytes. The conversion of a highly adhesive, low-density fibrinogen substrate to the nonadhesive high-density fibrinogen matrix occurs within a very narrow range of fibrinogen coating concentrations. The molecular events responsible for this transition are not well understood. Herein, single-cell and molecular force spectroscopy were used to determine the early steps in the formation of nonadhesive fibrinogen substrates. We show that the adsorption of fibrinogen in the form of a molecular bilayer coincides with a several-fold reduction in the adhesion forces generated between the AFM tip and the substrate as well as between a cell and the substrate. The subsequent deposition of new layers at higher coating concentrations of fibrinogen results in a small additional decrease in adhesion forces. The poorly adhesive fibrinogen bilayer is more extensible under an applied tensile force than is the surface-bound fibrinogen monolayer. Following chemical cross-linking, the stabilized bilayer displays the mechanical and adhesive properties characteristic of a more adhesive fibrinogen monolayer. We propose that a greater compliance of the bi- and multilayer fibrinogen matrices has its origin in the interaction between the molecules forming the adjacent layers. Understanding the mechanical properties of nonadhesive fibrinogen matrices should be of importance in the therapeutic control of pathological thrombosis and in biomaterials science.

  10. Single-cell force spectroscopy as a technique to quantify human red blood cell adhesion to subendothelial laminin.

    PubMed

    Maciaszek, Jamie L; Partola, Kostyantyn; Zhang, Jing; Andemariam, Biree; Lykotrafitis, George

    2014-12-18

    Single-cell force spectroscopy (SCFS), an atomic force microscopy (AFM)-based assay, enables quantitative study of cell adhesion while maintaining the native state of surface receptors in physiological conditions. Human healthy and pathological red blood cells (RBCs) express a large number of surface proteins which mediate cell-cell interactions, or cell adhesion to the extracellular matrix. In particular, RBCs adhere with high affinity to subendothelial matrix laminin via the basal cell adhesion molecule and Lutheran protein (BCAM/Lu). Here, we established SCFS as an in vitro technique to study human RBC adhesion at baseline and following biochemical treatment. Using blood obtained from healthy human subjects, we recorded adhesion forces from single RBCs attached to AFM cantilevers as the cell was pulled-off of substrates coated with laminin protein. We found that an increase in the overall cell adhesion measured via SCFS is correlated with an increase in the resultant total force measured on 1 µm(2) areas of the RBC membrane. Further, we showed that SCFS can detect significant changes in the adhesive response of RBCs to modulation of the cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) pathway. Lastly, we identified variability in the RBC adhesion force to laminin amongst the human subjects, suggesting that RBCs maintain diverse levels of active BCAM/Lu adhesion receptors. By using single-cell measurements, we established a powerful new method for the quantitative measurement of single RBC adhesion with specific receptor-mediated binding.

  11. The interaction of 2-mercaptobenzimidazole with human serum albumin as determined by spectroscopy, atomic force microscopy and molecular modeling.

    PubMed

    Li, Yuqin; Jia, Baoxiu; Wang, Hao; Li, Nana; Chen, Gaopan; Lin, Yuejuan; Gao, Wenhua

    2013-04-01

    The interaction of 2-mercaptobenzimidazole (MBI) with human serum albumin (HSA) was studied in vitro by equilibrium dialysis under normal physiological conditions. This study used fluorescence, ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared (FT-IR), circular dichroism (CD) and Raman spectroscopy, atomic force microscopy (AFM) and molecular modeling techniques. Association constants, the number of binding sites and basic thermodynamic parameters were used to investigate the quenching mechanism. Based on the fluorescence resonance energy transfer, the distance between the HSA and MBI was 2.495 nm. The ΔG(0), ΔH(0), and ΔS(0) values across temperature indicated that the hydrophobic interaction was the predominant binding Force. The UV, FT-IR, CD and Raman spectra confirmed that the HSA secondary structure was altered in the presence of MBI. In addition, the molecular modeling showed that the MBI-HSA complex was stabilized by hydrophobic forces, which resulted from amino acid residues. The AFM results revealed that the individual HSA molecule dimensions were larger after interaction with MBI. Overall, this study suggested a method for characterizing the weak intermolecular interaction. In addition, this method is potentially useful for elucidating the toxigenicity of MBI when it is combined with the biomolecular function effect, transmembrane transport, toxicological testing and other experiments.

  12. Probing local bias-induced transitions using photothermal excitation contact resonance atomic force microscopy and voltage spectroscopy

    SciTech Connect

    Li, Qian; Jesse, Stephen; Tselev, Alexander; Collins, Liam; Yu, Pu; Kravchenko, Ivan; Kalinin, Sergei V.; Balke, Nina

    2015-01-05

    In this paper, nanomechanical properties are closely related to the states of matter, including chemical composition, crystal structure, mesoscopic domain configuration, etc. Investigation of these properties at the nanoscale requires not only static imaging methods, e.g., contact resonance atomic force microscopy (CR-AFM), but also spectroscopic methods capable of revealing their dependence on various external stimuli. Here we demonstrate the voltage spectroscopy of CR-AFM, which was realized by combining photothermal excitation (as opposed to the conventional piezoacoustic excitation method) with the band excitation technique. We applied this spectroscopy to explore local bias-induced phenomena ranging from purely physical to surface electromechanical and electrochemical processes. Our measurements show that the changes in the surface properties associated with these bias-induced transitions can be accurately assessed in a fast and dynamic manner, using resonance frequency as a signature. Finally, with many of the advantages offered by photothermal excitation, contact resonance voltage spectroscopy not only is expected to find applications in a broader field of nanoscience but also will provide a basis for future development of other nanoscale elastic spectroscopies.

  13. Probing local bias-induced transitions using photothermal excitation contact resonance atomic force microscopy and voltage spectroscopy

    DOE PAGES

    Li, Qian; Jesse, Stephen; Tselev, Alexander; ...

    2015-01-05

    In this paper, nanomechanical properties are closely related to the states of matter, including chemical composition, crystal structure, mesoscopic domain configuration, etc. Investigation of these properties at the nanoscale requires not only static imaging methods, e.g., contact resonance atomic force microscopy (CR-AFM), but also spectroscopic methods capable of revealing their dependence on various external stimuli. Here we demonstrate the voltage spectroscopy of CR-AFM, which was realized by combining photothermal excitation (as opposed to the conventional piezoacoustic excitation method) with the band excitation technique. We applied this spectroscopy to explore local bias-induced phenomena ranging from purely physical to surface electromechanical andmore » electrochemical processes. Our measurements show that the changes in the surface properties associated with these bias-induced transitions can be accurately assessed in a fast and dynamic manner, using resonance frequency as a signature. Finally, with many of the advantages offered by photothermal excitation, contact resonance voltage spectroscopy not only is expected to find applications in a broader field of nanoscience but also will provide a basis for future development of other nanoscale elastic spectroscopies.« less

  14. Probing Cytoskeletal Structures by Coupling Optical Superresolution and AFM Techniques for a Correlative Approach

    PubMed Central

    Chacko, Jenu Varghese; Zanacchi, Francesca Cella; Diaspro, Alberto

    2013-01-01

    In this article, we describe and show the application of some of the most advanced fluorescence superresolution techniques, STED AFM and STORM AFM microscopy towards imaging of cytoskeletal structures, such as microtubule filaments. Mechanical and structural properties can play a relevant role in the investigation of cytoskeletal structures of interest, such as microtubules, that provide support to the cell structure. In fact, the mechanical properties, such as the local stiffness and the elasticity, can be investigated by AFM force spectroscopy with tens of nanometers resolution. Force curves can be analyzed in order to obtain the local elasticity (and the Young's modulus calculation by fitting the force curves from every pixel of interest), and the combination with STED/STORM microscopy integrates the measurement with high specificity and yields superresolution structural information. This hybrid modality of superresolution-AFM working is a clear example of correlative multimodal microscopy. PMID:24027190

  15. Optimized free energies from bidirectional single-molecule force spectroscopy.

    PubMed

    Minh, David D L; Adib, Artur B

    2008-05-09

    An optimized method for estimating path-ensemble averages using data from processes driven in opposite directions is presented. Based on this estimator, bidirectional expressions for reconstructing free energies and potentials of mean force from single-molecule force spectroscopy-valid for biasing potentials of arbitrary stiffness-are developed. Numerical simulations on a model potential indicate that these methods perform better than unidirectional strategies.

  16. Resolving dual binding conformations of cellulosome cohesin-dockerin complexes using single-molecule force spectroscopy.

    PubMed

    Jobst, Markus A; Milles, Lukas F; Schoeler, Constantin; Ott, Wolfgang; Fried, Daniel B; Bayer, Edward A; Gaub, Hermann E; Nash, Michael A

    2015-10-31

    Receptor-ligand pairs are ordinarily thought to interact through a lock and key mechanism, where a unique molecular conformation is formed upon binding. Contrary to this paradigm, cellulosomal cohesin-dockerin (Coh-Doc) pairs are believed to interact through redundant dual binding modes consisting of two distinct conformations. Here, we combined site-directed mutagenesis and single-molecule force spectroscopy (SMFS) to study the unbinding of Coh:Doc complexes under force. We designed Doc mutations to knock out each binding mode, and compared their single-molecule unfolding patterns as they were dissociated from Coh using an atomic force microscope (AFM) cantilever. Although average bulk measurements were unable to resolve the differences in Doc binding modes due to the similarity of the interactions, with a single-molecule method we were able to discriminate the two modes based on distinct differences in their mechanical properties. We conclude that under native conditions wild-type Doc from Clostridium thermocellum exocellulase Cel48S populates both binding modes with similar probabilities. Given the vast number of Doc domains with predicted dual binding modes across multiple bacterial species, our approach opens up new possibilities for understanding assembly and catalytic properties of a broad range of multi-enzyme complexes.

  17. Study of the interactions between endolysin and bacterial peptidoglycan on S. aureus by dynamic force spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Jianli; Zhang, Xuejie; Yang, Hang; Yuan, Jinghe; Wei, Hongping; Yu, Junping; Fang, Xiaohong

    2015-09-01

    The cell wall binding domain (CBD) of bacteriophage lysins can recognize target bacteria with extraordinary specificity through binding to bacterial peptidoglycan, thus it is a promising new probe to identify the corresponding bacterial pathogen. In this work, we used atomic force microscopy (AFM) based single-molecule force spectroscopy to investigate the interaction between the CBD of lysin PlyV12 (PlyV12C) and pathogenic bacterium Staphylococcus aureus (S. aureus). The binding forces of PlyV12C with S. aureus have been measured, and the dissociation process of their binding complex has been characterized. Furthermore, we compared the interactions of PlyV12C-S. aureus and antibody-S. aureus. It is revealed that PlyV12C has a comparable affinity to bacterial peptidoglycans as that of the S. aureus antibody. The results provide new information on the binding properties of lysin CBD with bacterium, and the application of lysin CBD in bacterium detection.

  18. Study of the interactions between endolysin and bacterial peptidoglycan on S. aureus by dynamic force spectroscopy.

    PubMed

    Liu, Jianli; Zhang, Xuejie; Yang, Hang; Yuan, Jinghe; Wei, Hongping; Yu, Junping; Fang, Xiaohong

    2015-10-07

    The cell wall binding domain (CBD) of bacteriophage lysins can recognize target bacteria with extraordinary specificity through binding to bacterial peptidoglycan, thus it is a promising new probe to identify the corresponding bacterial pathogen. In this work, we used atomic force microscopy (AFM) based single-molecule force spectroscopy to investigate the interaction between the CBD of lysin PlyV12 (PlyV12C) and pathogenic bacterium Staphylococcus aureus (S. aureus). The binding forces of PlyV12C with S. aureus have been measured, and the dissociation process of their binding complex has been characterized. Furthermore, we compared the interactions of PlyV12C-S. aureus and antibody-S. aureus. It is revealed that PlyV12C has a comparable affinity to bacterial peptidoglycans as that of the S. aureus antibody. The results provide new information on the binding properties of lysin CBD with bacterium, and the application of lysin CBD in bacterium detection.

  19. Local tunneling decay length and Kelvin probe force spectroscopy

    NASA Astrophysics Data System (ADS)

    Albrecht, Florian; Fleischmann, Martin; Scheer, Manfred; Gross, Leo; Repp, Jascha

    2015-12-01

    In the past, current-distance spectroscopy has been widely applied to determine variations of the work function at surfaces. While for homogeneous sample areas this technique is commonly accepted to yield at least qualitative results, its applicability to atomic-scale variations has not been proven neither right nor wrong. Here we benchmark measurements of the current-distance decay constant against the well established Kelvin probe force spectroscopy for four distinctly different cases with atomic-scale variations of the local contact potential. The two techniques yield quite different results. Whereas the maps of the current-distance decay constant are consistent with being topographical artifacts, the Kelvin probe force spectroscopy maps show variations of the local contact potential difference in agreement with expected surface dipoles. This comparison clarifies that maps of the current-distance decay constant are not suited to directly characterize contact potential variations at surfaces on atomic length scales.

  20. Nanostructure and force spectroscopy analysis of human peripheral blood CD4+ T cells using atomic force microscopy.

    PubMed

    Hu, Mingqian; Wang, Jiongkun; Cai, Jiye; Wu, Yangzhe; Wang, Xiaoping

    2008-09-12

    To date, nanoscale imaging of the morphological changes and adhesion force of CD4(+) T cells during in vitro activation remains largely unreported. In this study, we used atomic force microscopy (AFM) to study the morphological changes and specific binding forces in resting and activated human peripheral blood CD4(+) T cells. The AFM images revealed that the volume of activated CD4(+) T cells increased and the ultrastructure of these cells also became complex. Using a functionalized AFM tip, the strength of the specific binding force of the CD4 antigen-antibody interaction was found to be approximately three times that of the unspecific force. The adhesion forces were not randomly distributed over the surface of a single activated CD4(+) T cell, indicated that the CD4 molecules concentrated into nanodomains. The magnitude of the adhesion force of the CD4 antigen-antibody interaction did not change markedly with the activation time. Multiple bonds involved in the CD4 antigen-antibody interaction were measured at different activation times. These results suggest that the adhesion force involved in the CD4 antigen-antibody interaction is highly selective and of high affinity.

  1. Single-molecule force spectroscopy approach to enzyme catalysis.

    PubMed

    Alegre-Cebollada, Jorge; Perez-Jimenez, Raul; Kosuri, Pallav; Fernandez, Julio M

    2010-06-18

    Enzyme catalysis has been traditionally studied using a diverse set of techniques such as bulk biochemistry, x-ray crystallography, and NMR. Recently, single-molecule force spectroscopy by atomic force microscopy has been used as a new tool to study the catalytic properties of an enzyme. In this approach, a mechanical force ranging up to hundreds of piconewtons is applied to the substrate of an enzymatic reaction, altering the conformational energy of the substrate-enzyme interactions during catalysis. From these measurements, the force dependence of an enzymatic reaction can be determined. The force dependence provides valuable new information about the dynamics of enzyme catalysis with sub-angstrom resolution, a feat unmatched by any other current technique. To date, single-molecule force spectroscopy has been applied to gain insight into the reduction of disulfide bonds by different enzymes of the thioredoxin family. This minireview aims to present a perspective on this new approach to study enzyme catalysis and to summarize the results that have already been obtained from it. Finally, the specific requirements that must be fulfilled to apply this new methodology to any other enzyme will be discussed.

  2. Quantitative Measurements of Elastic Properties with Ultrasonic-Based AFM and Conventional Techniques

    NASA Astrophysics Data System (ADS)

    Hurley, D. C.

    A prime motivation for the original development of ultrasonic-based AFM methods was to enable measurements of elastic properties with nanoscale spatial resolution. In this chapter, we discuss the quantitative measurement of elastic modulus with ultrasonic-based AFM methods and compare it to measurement by more conventional or established techniques. First, we present the basic principles of modulus measurement with methods that involve contact resonance spectroscopy, such as atomic force acoustic microscopy (AFAM) and ultrasonic AFM (U-AFM). Fundamental concepts of modulus measurement with more established approaches, especially instrumented (nano-) indentation (NI) and surface acoustic wave spectroscopy (SAWS), are then discussed. We consider the relative strengths and limitations of various approaches, for example measurement accuracy, spatial resolution, and applicability to different materials. Example results for specific material systems are given with an emphasis on studies involving direct intercomparison of different techniques. Finally, current research in this area and opportunities for future work are described.

  3. The effect of surface properties on the strength of attachment of fungal spores using AFM perpendicular force measurements.

    PubMed

    Whitehead, Kathryn A; Deisenroth, Ted; Preuss, Andrea; Liauw, Christopher M; Verran, Joanna

    2011-02-01

    Polymeric substrata may be biodegraded by fungal species resulting in damaged, weakened and unsightly materials. This process typically begins with fungal spore attachment to the surface. In order to better understand the processes that precedes a biofouling event, fungal spore attachment to a range of surfaces, was determined using perpendicular force measurements. This was carried out using atomic force microscope cantilevers modified with fungal spores from Aspergillus niger 1957 (5μm diameter, non-wettable, spherical), Aspergillus niger 1988 (5μm diameter non-wettable, spikey) or Aureobasidium pullulans (5μm-10μm sized, wettable, ellipsoidal). The strength of attachment of the spores was determined in combination with seven surfaces (nitric acid cleaned glass, cast poly(methylmethacrylate) sheet [c-PMMA], polytetrafluoroethylene [PTFE], silicon wafers spin coated with poly(3-methacryloxypropyltrimethoxy silane (γ-MPS)-co-methylmethacrylate (MMA)) [p(γ-MPS-co-MMA)], poly (γ-MPS-co-lauryl methacrylate) [p(γ-MPS-co-LMA)] [both in a ratio of 10-90], PMMA dissolved in a solvent [PMMAsc] and silicon wafers). Perpendicular force measurements could not be related to the R(a) values of the surfaces, but surface wettability was shown to have an effect. All three spore types interacted comparably with the surfaces. All spores attached strongly to c-PMMA and glass (wettable surfaces), and weakly to PTFE, (p(γ- MPS-co-LMA)) (non-wettable) and (p(γ-MPS-co-MMA)). Spore shape also affected the strength of attachment. Aureobasidium pullulans spores attached with the widest range of forces whilst A. niger 1957 attached with the smallest. Findings will inform the selection of surfaces for use in environments where biofouling is an important consideration.

  4. Vibrational analysis of single-layered piezoelectric AFM microcantilever in amplitude mode by considering the capillary force

    NASA Astrophysics Data System (ADS)

    Habibnejad Korayem, Alireza; Habibnejad Korayem, Moharam; Ghaderi, Reza

    2014-12-01

    In this article, the vibrational behavior of a microcantilever (MC) with an extended piezoelectric layer in the air ambient undergoes examination. To model the vibrational motion of this type of cantilever, the Hamilton's principle has been used. For this purpose, the MC vibrational equation has been derived by the assumption of the continuous beam based on the Euler-Bernoulli beam theory. By adopting the finite element method (FEM), the MC differential equation has been solved. In the present simulation not only van der Waals and contact forces but also the capillary forces resulting from the condensation of the water vapors in air on MC tip have been considered. The results illustrate that the force between the sample surface and the probe affects the MC amplitude; furthermore, it causes the reduction in the resonance frequency. In addition, to reduce the time delay during topography from the surface roughness, it is better to select MCs with larger width and length and smaller thickness. Furthermore, the results indicate that the best imaging takes place when the vibration is in its second vibrational mode. Finally, the effects of MC geometric parameters on the time delay between the starting moment of surface roughness and the moment of variation in the MC amplitude (surface roughness topography) have been analyzed.

  5. Single-cell force spectroscopy of pili-mediated adhesion

    NASA Astrophysics Data System (ADS)

    Sullan, Ruby May A.; Beaussart, Audrey; Tripathi, Prachi; Derclaye, Sylvie; El-Kirat-Chatel, Sofiane; Li, James K.; Schneider, Yves-Jacques; Vanderleyden, Jos; Lebeer, Sarah; Dufrêne, Yves F.

    2013-12-01

    Although bacterial pili are known to mediate cell adhesion to a variety of substrates, the molecular interactions behind this process are poorly understood. We report the direct measurement of the forces guiding pili-mediated adhesion, focusing on the medically important probiotic bacterium Lactobacillus rhamnosus GG (LGG). Using non-invasive single-cell force spectroscopy (SCFS), we quantify the adhesion forces between individual bacteria and biotic (mucin, intestinal cells) or abiotic (hydrophobic monolayers) surfaces. On hydrophobic surfaces, bacterial pili strengthen adhesion through remarkable nanospring properties, which - presumably - enable the bacteria to resist high shear forces under physiological conditions. On mucin, nanosprings are more frequent and adhesion forces larger, reflecting the influence of specific pili-mucin bonds. Interestingly, these mechanical responses are no longer observed on human intestinal Caco-2 cells. Rather, force curves exhibit constant force plateaus with extended ruptures reflecting the extraction of membrane nanotethers. These single-cell analyses provide novel insights into the molecular mechanisms by which piliated bacteria colonize surfaces (nanosprings, nanotethers), and offer exciting avenues in nanomedicine for understanding and controlling the adhesion of microbial cells (probiotics, pathogens).

  6. Investigation of Cell-Substrate Adhesion Properties of Living Chondrocyte by Measuring Adhesive Shear Force and Detachment Using AFM and Inverse FEA

    PubMed Central

    Nguyen, Trung Dung; Gu, YuanTong

    2016-01-01

    It is well-known that cell adhesion is important in many biological processes such as cell migration and proliferation. A better understanding of the cell adhesion process will shed insight into these cellular biological responses as well as cell adhesion-related diseases treatment. However, there is little research which has attempted to investigate the process of cell adhesion and its mechanism. Thus, this paper aims to study the time-dependent adhesion properties of single living chondrocytes using an advanced coupled experimental-numerical approach. Atomic Force Microscopy (AFM) tips will be used to apply lateral forces to detach chondrocytes that are seeded for three different periods. An advanced Finite Element Analysis (FEA) model combining porohyperelastic (PHE) constitutive model and cohesive zone formulation is developed to explore the mechanism of adhesion. The results revealed that the cells can resist normal traction better than tangential traction in the beginning of adhesion. This is when the cell adhesion molecules establish early attachment to the substrates. After that when the cells are spreading, stress fiber bundles generate tangential traction on the substrate to form strong adhesion. Both simulation and experimental results agree well with each other, providing a powerful tool to study the cellular adhesion process. PMID:27892536

  7. Probing the nanoscale interaction forces and elastic properties of organic and inorganic materials using force-distance (F-D) spectroscopy

    NASA Astrophysics Data System (ADS)

    Vincent, Abhilash

    Due to their therapeutic applications such as radical scavenging, MRI contrast imaging, Photoluminescence imaging, drug delivery, etc., nanoparticles (NPs) have a significant importance in bio-nanotechnology. The reason that prevents the utilizing NPs for drug delivery in medical field is mostly due to their biocompatibility issues (incompatibility can lead to toxicity and cell death). Changes in the surface conditions of NPs often lead to NP cytotoxicity. Investigating the role of NP surface properties (surface charges and surface chemistry) on their interactions with biomolecules (Cells, protein and DNA) could enhance the current understanding of NP cytotoxicity. Hence, it is highly beneficial to the nanotechnology community to bring more attention towards the enhancement of surface properties of NPs to make them more biocompatible and less toxic to biological systems. Surface functionalization of NPs using specific ligand biomolecules have shown to enhance the protein adsorption and cellular uptake through more favorable interaction pathways. Cerium oxide NPs (CNPs also known as nanoceria) are potential antioxidants in cell culture models and understanding the nature of interaction between cerium oxide NPs and biological proteins and cells are important due to their therapeutic application (especially in site specific drug delivery systems). The surface charges and surface chemistry of CNPs play a major role in protein adsorption and cellular uptake. Hence, by tuning the surface charges and by selecting proper functional molecules on the surface, CNPs exhibiting strong adhesion to biological materials can be prepared. By probing the nanoscale interaction forces acting between CNPs and protein molecules using Atomic Force Microscopy (AFM) based force-distance (F-D) spectroscopy, the mechanism of CNP-protein adsorption and CNP cellular uptake can be understood more quantitatively. The work presented in this dissertation is based on the application of AFM in

  8. Effects of nonlinear forces on dynamic mode atomic force microscopy and spectroscopy.

    PubMed

    Das, Soma; Sreeram, P A; Raychaudhuri, A K

    2007-06-01

    In this paper, we describe the effects of nonlinear tip-sample forces on dynamic mode atomic force microscopy and spectroscopy. The jumps and hysteresis observed in the vibration amplitude (A) versus tip-sample distance (h) curves have been traced to bistability in the resonance curve. A numerical analysis of the basic dynamic equation was used to explain the hysteresis in the experimental curve. It has been found that the location of the hysteresis in the A-h curve depends on the frequency of the forced oscillation relative to the natural frequency of the cantilever.

  9. Using High Resolution Force Spectroscopy to Study Haemocompatibility

    NASA Astrophysics Data System (ADS)

    Rixman, Monica; Macias, Celia; Dean, Delphine; Ortiz, Christine

    2003-03-01

    A critical determinant of the biocompatibility of implanted blood-contacting devices is the initial noncovalent adsorption of blood plasma proteins onto the biomaterial surface. Using high resolution force spectroscopy, we have measured the intermolecular interaction forces between a probe tip covalently bound with human serum albumin (HSA), the most abundant blood plasma protein in the human body, and various chemically modified surfaces that either already are, or may potentially be, used as biomaterial surface coatings. Statistical analysis and theoretical modeling enable us to interpret our experimental results in terms of electrostatic interactions, hydrogen bonding, and steric forces. We have expanded our initial studies on surfaces of poly(ethylene oxide) to explore a variety of experimental conditions, and then utilized our results in identifying and studying various oligosaccharides, which we hope may be useful in the discovery of novel materials for future biomaterial applications.

  10. Effects of Intermediate Bound States in Dynamic Force Spectroscopy

    PubMed Central

    Derényi, Imre; Bartolo, Denis; Ajdari, Armand

    2004-01-01

    We revisit some aspects of the interpretation of dynamic force spectroscopy experiments. The standard theory predicts that the typical unbinding force f* is linearly proportional to the logarithm of the loading rate r when a single energy barrier controls the unbinding process. For a more complex situation of N barriers, it predicts at most N linear segments for the f* vs. log(r) curve, each segment characterizing a different barrier. Here we extend this existing picture using a refined approximation, provide a more general analytical formula, and show that in principle up to N(N + 1) / 2 segments can show up experimentally. As a consequence, the determination of the positions and even the number of the energy barriers from the experimental data can be ambiguous. A further possible consequence of a multiple-barrier landscape is a bimodal or multimodal distribution of the unbinding force at certain loading rates, a feature recently observed experimentally. PMID:14990459

  11. Force spectroscopy of biomolecular folding and binding: theory meets experiment

    NASA Astrophysics Data System (ADS)

    Dudko, Olga

    2015-03-01

    Conformational transitions in biological macromolecules usually serve as the mechanism that brings biomolecules into their working shape and enables their biological function. Single-molecule force spectroscopy probes conformational transitions by applying force to individual macromolecules and recording their response, or ``mechanical fingerprints,'' in the form of force-extension curves. However, how can we decode these fingerprints so that they reveal the kinetic barriers and the associated timescales of a biological process? I will present an analytical theory of the mechanical fingerprints of macromolecules. The theory is suitable for decoding such fingerprints to extract the barriers and timescales. The application of the theory will be illustrated through recent studies on protein-DNA interactions and the receptor-ligand complexes involved in blood clot formation.

  12. Dielectrophoresis force spectroscopy for colloidal nanoparticles (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Ou-Yang, H. Daniel; Huang, Hao

    2016-09-01

    Dielectrophoresis (DEP) is the motion of colloidal particles in an inhomogeneous electric field. Accurate determination of dielectrophoresis (DEP) force is important for lab-on-a-chip applications. However current DEP force spectroscopy methods are not suitable for accurately measuring the DEP force for sub-micron particles. A new and facile method is developed to measure the DEP force as a function of the frequency of the electric field for nanoparticles by an ensemble analysis approach. Using the principle of Boltzmann distribution of the concentration of non-interacting particles in a DEP potential field, the new method determines the DEP potential field from the measured time-averaged concentration distribution of fluorescently labeled nanoparticle in the DEP field by confocal fluorescence microscopy. Frequency dependent DEP force is determined by the negative gradient of the DEP potential created by the electric field across gold-film electrodes in a microfluidic setting. This approach is capable of measuring forces at the level of one femto Newton for particles with diameters in the range of 63 nm to 410 nm.

  13. Linear and Nonlinear Optical Spectroscopy at the Nanoscale with Photoinduced Force Microscopy.

    PubMed

    Jahng, Junghoon; Fishman, Dmitry A; Park, Sung; Nowak, Derek B; Morrison, Will A; Wickramasinghe, H Kumar; Potma, Eric O

    2015-10-20

    The enormous advances made in nanotechnology have also intensified the need for tools that can characterize newly synthesized nanoaterials with high sensitivity and with high spatial resolution. Many existing tools with nanoscopic resolution or better, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning tunneling microscopy (STM) methods, can generate highly detailed maps of nanoscopic structures. However, while these approaches provide great views of the morphological properties of nanomaterials, it has proven more challenging to derive chemical information from the corresponding images. To address this issue, attempts have been made to dress existing nanoscopy methods with spectroscopic sensitivity. A powerful approach in this direction is the combination of scan probe techniques with optical illumination, which aims to marry the nanoscopic resolution provided by a sharp tip with the chemical selectivity provided by optical spectroscopy. Examples of this approach include existing techniques such as scattering-type scanning near-field optical microscopy and tip-enhanced Raman spectroscopy. A new and emerging technique in this direction is photoinduced force microscopy (PiFM), which enables spectroscopic probing of materials with a spatial resolution well under 10 nm. In PiFM, the sample is optically excited and the response of the material is probed directly in the near-field by reading out the time-integrated force between the tip and the sample. Because the magnitude of the force is dependent on the photoinduced polarization in the sample, PiFM exhibits spectroscopic sensitivity. The photoinduced forces measured in PiFM are spatially confined on the nanometer scale, which translates into a very high spatial resolution even under ambient conditions. The PiFM approach is compatible with a wide range optical excitation frequencies, from the visible to the mid-infrared, enabling nanoscale imaging contrast based on either

  14. Role of trimer-trimer interaction of bacteriorhodopsin studied by optical spectroscopy and high-speed atomic force microscopy.

    PubMed

    Yamashita, Hayato; Inoue, Keiichi; Shibata, Mikihiro; Uchihashi, Takayuki; Sasaki, Jun; Kandori, Hideki; Ando, Toshio

    2013-10-01

    Bacteriorhodopsin (bR) trimers form a two-dimensional hexagonal lattice in the purple membrane of Halobacterium salinarum. However, the physiological significance of forming the lattice has long been elusive. Here, we study this issue by comparing properties of assembled and non-assembled bR trimers using directed mutagenesis, high-speed atomic force microscopy (HS-AFM), optical spectroscopy, and a proton pumping assay. First, we show that the bonds formed between W12 and F135 amino acid residues are responsible for trimer-trimer association that leads to lattice assembly; the lattice is completely disrupted in both W12I and F135I mutants. HS-AFM imaging reveals that both crystallized D96N and non-crystallized D96N/W12I mutants undergo a large conformational change (i.e., outward E-F loop displacement) upon light-activation. However, lattice disruption significantly reduces the rate of conformational change under continuous light illumination. Nevertheless, the quantum yield of M-state formation, measured by low-temperature UV-visible spectroscopy, and proton pumping efficiency are unaffected by lattice disruption. From these results, we conclude that trimer-trimer association plays essential roles in providing bound retinal with an appropriate environment to maintain its full photo-reactivity and in maintaining the natural photo-reaction pathway.

  15. Nanoscale investigation of the interaction of colistin with model phospholipid membranes by Langmuir technique, and combined infrared and force spectroscopies.

    PubMed

    Freudenthal, Oona; Quilès, Fabienne; Francius, Grégory; Wojszko, Kamila; Gorczyca, Marcelina; Korchowiec, Beata; Rogalska, Ewa

    2016-11-01

    Colistin (Polymyxin E), an antimicrobial peptide, is increasingly put forward as salvage for severe multidrug-resistant infections. Unfortunately, colistin is potentially toxic to mammalian cells. A better understanding of the interaction with specific components of the cell membranes may be helpful in controlling the factors that may enhance toxicity. Here, we report a physico-chemical study of model phospholipid (PL) mono- and bilayers exposed to colistin at different concentrations by Langmuir technique, atomic force microscopy (AFM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The effect of colistin on chosen PL monolayers was examined. Insights into the topographical and elastic changes in the PL bilayers within time after peptide injection are presented via AFM imaging and force spectra. Finally, changes in the PL bilayers' ATR-FTIR spectra as a function of time within three bilayer compositions, and the influence of colistin on their spectral fingerprint are examined together with the time-evolution of the Amide II and νCO band integrated intensity ratios. Our study reveals a great importance in the role of the PL composition as well as the peptide concentration on the action of colistin on PL model membranes.

  16. An integrated instrumental setup for the combination of atomic force microscopy with optical spectroscopy.

    PubMed

    Owen, R J; Heyes, C D; Knebel, D; Röcker, C; Nienhaus, G U

    2006-07-01

    In recent years, the study of single biomolecules using fluorescence microscopy and atomic force microscopy (AFM) techniques has resulted in a plethora of new information regarding the physics underlying these complex biological systems. It is especially advantageous to be able to measure the optical, topographical, and mechanical properties of single molecules simultaneously. Here an AFM is used that is especially designed for integration with an inverted optical microscope and that has a near-infrared light source (850 nm) to eliminate interference between the optical experiment and the AFM operation. The Tip Assisted Optics (TAO) system consists of an additional 100 x 100-microm(2) X-Y scanner for the sample, which can be independently and simultaneously used with the AFM scanner. This allows the offset to be removed between the confocal optical image obtained with the sample scanner and the simultaneously acquired AFM topography image. The tip can be positioned exactly into the optical focus while the user can still navigate within the AFM image for imaging or manipulation of the sample. Thus the tip-enhancement effect can be maximized and it becomes possible to perform single molecule manipulation experiments within the focus of a confocal optical image. Here this is applied to simultaneous measurement of single quantum dot fluorescence and topography with high spatial resolution.

  17. High-resolution high-speed dynamic mechanical spectroscopy of cells and other soft materials with the help of atomic force microscopy.

    PubMed

    Dokukin, M; Sokolov, I

    2015-07-28

    Dynamic mechanical spectroscopy (DMS), which allows measuring frequency-dependent viscoelastic properties, is important to study soft materials, tissues, biomaterials, polymers. However, the existing DMS techniques (nanoindentation) have limited resolution when used on soft materials, preventing them from being used to study mechanics at the nanoscale. The nanoindenters are not capable of measuring cells, nanointerfaces of composite materials. Here we present a highly accurate DMS modality, which is a combination of three different methods: quantitative nanoindentation (nanoDMA), gentle force and fast response of atomic force microscopy (AFM), and Fourier transform (FT) spectroscopy. This new spectroscopy (which we suggest to call FT-nanoDMA) is fast and sensitive enough to allow DMS imaging of nanointerfaces, single cells, while attaining about 100x improvements on polymers in both spatial (to 10-70 nm) and temporal resolution (to 0.7 s/pixel) compared to the current art. Multiple frequencies are measured simultaneously. The use of 10 frequencies are demonstrated here (up to 300 Hz which is a rather relevant range for biological materials and polymers, in both ambient conditions and liquid). The method is quantitatively verified on known polymers and demonstrated on cells and polymers blends. Analysis shows that FT-nanoDMA is highly quantitative. The FT-nanoDMA spectroscopy can easily be implemented in the existing AFMs.

  18. High-resolution high-speed dynamic mechanical spectroscopy of cells and other soft materials with the help of atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Dokukin, M.; Sokolov, I.

    2015-07-01

    Dynamic mechanical spectroscopy (DMS), which allows measuring frequency-dependent viscoelastic properties, is important to study soft materials, tissues, biomaterials, polymers. However, the existing DMS techniques (nanoindentation) have limited resolution when used on soft materials, preventing them from being used to study mechanics at the nanoscale. The nanoindenters are not capable of measuring cells, nanointerfaces of composite materials. Here we present a highly accurate DMS modality, which is a combination of three different methods: quantitative nanoindentation (nanoDMA), gentle force and fast response of atomic force microscopy (AFM), and Fourier transform (FT) spectroscopy. This new spectroscopy (which we suggest to call FT-nanoDMA) is fast and sensitive enough to allow DMS imaging of nanointerfaces, single cells, while attaining about 100x improvements on polymers in both spatial (to 10-70 nm) and temporal resolution (to 0.7s/pixel) compared to the current art. Multiple frequencies are measured simultaneously. The use of 10 frequencies are demonstrated here (up to 300 Hz which is a rather relevant range for biological materials and polymers, in both ambient conditions and liquid). The method is quantitatively verified on known polymers and demonstrated on cells and polymers blends. Analysis shows that FT-nanoDMA is highly quantitative. The FT-nanoDMA spectroscopy can easily be implemented in the existing AFMs.

  19. High-resolution high-speed dynamic mechanical spectroscopy of cells and other soft materials with the help of atomic force microscopy

    PubMed Central

    Dokukin, M.; Sokolov, I.

    2015-01-01

    Dynamic mechanical spectroscopy (DMS), which allows measuring frequency-dependent viscoelastic properties, is important to study soft materials, tissues, biomaterials, polymers. However, the existing DMS techniques (nanoindentation) have limited resolution when used on soft materials, preventing them from being used to study mechanics at the nanoscale. The nanoindenters are not capable of measuring cells, nanointerfaces of composite materials. Here we present a highly accurate DMS modality, which is a combination of three different methods: quantitative nanoindentation (nanoDMA), gentle force and fast response of atomic force microscopy (AFM), and Fourier transform (FT) spectroscopy. This new spectroscopy (which we suggest to call FT-nanoDMA) is fast and sensitive enough to allow DMS imaging of nanointerfaces, single cells, while attaining about 100x improvements on polymers in both spatial (to 10–70 nm) and temporal resolution (to 0.7s/pixel) compared to the current art. Multiple frequencies are measured simultaneously. The use of 10 frequencies are demonstrated here (up to 300 Hz which is a rather relevant range for biological materials and polymers, in both ambient conditions and liquid). The method is quantitatively verified on known polymers and demonstrated on cells and polymers blends. Analysis shows that FT-nanoDMA is highly quantitative. The FT-nanoDMA spectroscopy can easily be implemented in the existing AFMs. PMID:26218346

  20. Characterization of novel sufraces by FTIR spectroscopy and atomic force microscopy for food pathogen detection

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Single molecular detection of pathogens and toxins of interest to food safety is within grasp using technology such as Atomic Force Microscopy. Using antibodies or specific aptamers connected to the AFM tip make it possible to detect a pathogen molecule on a surface. However, it also becomes necess...

  1. Force spectroscopy on single passive biomolecules and single biomolecular bonds

    NASA Astrophysics Data System (ADS)

    Merkel, Rudolf

    2001-06-01

    This article describes the recent development of the rapidly expanding field of single molecule force spectroscopy. As the advancement of this field was dictated by technical progress, a large part of this review is focussed on methodological aspects. Moreover, several instructive experiments will be presented. However, it is already impossible to cover the whole field in one review article. Experiments on stretching of single polymers, on force induced dissociation of single bonds, and on unfolding of multidomain proteins are covered whereas active molecules (molecular motors) will be excluded. The physical interpretation of the selected experiments is addressed. The connection between the experimental results and the underlying microscopic properties of the molecules and their respective bonds will be discussed. Especially kinetic effects are of high importance for the interpretation of these experiments.

  2. Mechanical Properties of Single Collagen Fibrils Revealed by Force Spectroscopy

    NASA Astrophysics Data System (ADS)

    Graham, John; Phillips, Charlotte; Grandbois, Michel

    2004-03-01

    In the field of biomechanics, collagen fibrils are believed to be robust mechanical structures characterized by a low extensibility. Until very recently, information on the mechanical properties of collagen fibrils could only be derived from ensemble measurements performed on complete tissues such as bone, skin and tendon. Here we measure force-elongation/relaxation profiles of single collagen fibrils using atomic force microscopy-based force spectroscopy. The elongation profiles indicate that in vitro assembled heterotrimeric type I collagen fibrils are characterized by a large extensibility. Numerous discontinuities and a plateau in the force profile indicate major reorganization occurs within the fibrils in the 1.5 -- 4.5 nN range. Our study demonstrates that newly assembled collagen fibrils are robust structures with a significant reserve of elasticity that could play a determinant role in cellular motion in the context of tissue growth and morphogenesis. In contrast, homotrimeric collagen fibrils corresponding to osteogenesis imperfecta pathology exhibit a marked difference in their elasticity profile.

  3. Improving single molecule force spectroscopy through automated real-time data collection and quantification of experimental conditions

    PubMed Central

    Scholl, Zackary N.; Marszalek, Piotr E.

    2013-01-01

    The benefits of single molecule force spectroscopy (SMFS) clearly outweigh the challenges which include small sample sizes, tedious data collection and introduction of human bias during the subjective data selection. These difficulties can be partially eliminated through automation of the experimental data collection process for atomic force microscopy (AFM). Automation can be accomplished using an algorithm that triages usable force-extension recordings quickly with positive and negative selection. We implemented an algorithm based on the windowed fast Fourier transform of force-extension traces that identifies peaks using force-extension regimes to correctly identify usable recordings from proteins composed of repeated domains. This algorithm excels as a real-time diagnostic because it involves <30 ms computational time, has high sensitivity and specificity, and efficiently detects weak unfolding events. We used the statistics provided by the automated procedure to clearly demonstrate the properties of molecular adhesion and how these properties change with differences in the cantilever tip and protein functional groups and protein age. PMID:24001740

  4. Fundamental High-Speed Limits in Single-Molecule, Single-Cell, and Nanoscale Force Spectroscopies.

    PubMed

    Amo, Carlos A; Garcia, Ricardo

    2016-07-26

    Force spectroscopy is enhancing our understanding of single-biomolecule, single-cell, and nanoscale mechanics. Force spectroscopy postulates the proportionality between the interaction force and the instantaneous probe deflection. By studying the probe dynamics, we demonstrate that the total force acting on the probe has three different components: the interaction, the hydrodynamic, and the inertial. The amplitudes of those components depend on the ratio between the resonant frequency and the frequency at which the data are measured. A force-distance curve provides a faithful measurement of the interaction force between two molecules when the inertial and hydrodynamic components are negligible. Otherwise, force spectroscopy measurements will underestimate the value of unbinding forces. Neglecting the above force components requires the use of frequency ratios in the 50-500 range. These ratios will limit the use of high-speed methods in force spectroscopy. The theory is supported by numerical simulations.

  5. Towards force spectroscopy of single tip-link bonds

    NASA Astrophysics Data System (ADS)

    Koussa, Mounir A.; Sotomayor, Marcos; Wong, Wesley P.; Corey, David P.

    2015-12-01

    Inner-ear mechanotransduction relies on tip links, fine protein filaments made of cadherin-23 and protocadherin-15 that convey tension to mechanosensitive channels at the tips of hair-cell stereocilia. The tip-link cadherins are thought to form a heterotetrameric complex, with two cadherin-23 molecules forming the upper part of the filament and two protocadherin-15 molecules forming the lower end. The interaction between cadherin-23 and protocadherin-15 is mediated by their N-terminal tips. Missense mutations that modify the interaction interface impair binding and lead to deafness. Molecular dynamics simulations predict that the tip-link bond is mechanically strong enough to withstand forces in hair cells, but its experimentally determined strength is unknown. We have developed molecular tools to facilitate single-molecule force spectroscopy on the tip link bond. Self-assembling DNA nanoswitches are functionalized with the interacting tips of cadherin-23 and protocadherin-15 using the enzyme sortase under conditions that preserve protein function. These tip link nanoswitches are designed to provide a signature force-extension profile. This molecular signature should allow us to identify single-molecule rupture events in pulling experiments.

  6. Probing of Amyloid Aβ (14–23) Trimers by Single-Molecule Force Spectroscopy

    PubMed Central

    Maity, Sibaprasad; Lyubchenko, Yuri L.

    2016-01-01

    Self-assembly and aggregation of amyloid peptides, such as Aβ(1–40) and Aβ(1–42), lead to the development of Alzheimer disease and similar neurodegenerative disorders associated with protein aggregation. The structures of large aggregates, specifically fibrils, are well characterized. However, our understanding about the structure of oligomeric forms of amyloids is incomplete and needs to be expanded, particularly given the finding that oligomeric rather than fibrillar amyloid morphologies are neurotoxic. This lack of knowledge is primarily due to the existence of transient oligomeric forms that require the use of non-traditional approaches capable of probing transiently existing amyloid forms. We have recently developed the Single-Molecule Force Spectroscopy (SMFS) approach enabling us to probe dimeric forms of amyloids. These studies suggest that the assembly of amyloid proteins into dimers leads to extremely stabilized amyloids in non-native, misfolded states [1]. Herein, we applied the SMFS approach to probe amyloid trimers. We used the Aβ(14–23) segment of Aβ42 protein that is responsible for full-size protein aggregation. The dimerization of this peptide was recently characterized [2]. The dimeric form of Aβ (14–23) was assembled by the use of a tandem Aβ(14–23)-YNGK-Aβ(14–23), in which the YNGK motif between the two Aβ(14–23) monomers makes a β turn to form a hairpin loop with an antiparallel arrangement of Aβ(14–23) monomers[3]. The Aβ(14–23) monomer was tethered to the AFM tip, and trimers were formed by approaching the tip to the mica surface on which the Aβ(14–23)-YNGK-Aβ(14–23) dimer was immobilized via a polyethylene glycol tether. We identified trimers by rupture forces that were considerably larger than those for dimers. Models for the trimer assembly process are discussed.

  7. Molecular basis of lateral force spectroscopy nano-diagnostics: computational unbinding of autism related chemokine MCP-1 from IgG antibody.

    PubMed

    Gogolinska, Anna; Nowak, Wieslaw

    2013-11-01

    Monocyte-chemoattractant protein-1 (MCP-1), also known as CCL2, is a potent chemoattractant of T cells and monocytes, involved in inflammatory and angio-proliferative brain and retinal diseases. Higher expression of MCP-1 is observed in metastatic tumors. Unusual levels of MCP-1 in the brain may be correlated with autism. Immunochemistry where atomic force microscope (AFM) tips functionalized with appropriate antibodies against MCP-1 are used could in principle support medical diagnostics. Useful signals from single molecule experiments may be generated if interaction forces are large enough. The chemokine-antibody unbinding force depends on a relative motion of the interacting fragments of the complex. In this paper the stability of the medically important MCP-1- immunoglobulin G antibody Fab fragment complex has been studied using steered molecular dynamics (SMD) computer simulations with the aim to model possible arrangements of nano-diagnostics experiments. Using SMD we confirm that molecular recognition in MCP1-IgG is based mainly on six pairs of residues: Glu39A - Arg98H, Lys56A - Asp52H, Asp65A - Arg32L, Asp68A - Arg32L, Thr32A - Glu55L, Gln61A - Tyr33H. The minimum external force required for mechanical dissociation of the complex depends on a direction of the force. The pulling of the MCP-1 antigen in the directions parallel to the antigen-antibody contact plane requires forces about 20 %-40 % lower than in the perpendicular one. Fortunately, these values are large enough that the fast lateral force spectroscopy may be used for effective nano-diagnostics purposes. We show that molecular modeling is a useful tool in planning AFM force spectroscopy experiments.

  8. Cryogenic AFM-STM for mesoscopic physics

    NASA Astrophysics Data System (ADS)

    Le Sueur, H.

    Electronic spectroscopy based on electron tunneling gives access to the electronic density of states (DOS) in conductive materials, and thus provides detailed information about their electronic properties. During this thesis work, we have developed a microscope in order to perform spatially resolved (10 nm) tunneling spectroscopy, with an unprecedented energy resolution (10 μeV), on individual nanocircuits. This machine combines an Atomic Force Microscope (AFM mode) together with a Scanning Tunneling Spectroscope (STS mode) and functions at very low temperatures (30 mK). In the AFM mode, the sample topography is recorded using a piezoelectric quartz tuning fork, which allows us to locate and image nanocircuits. Tunneling can then be performed on conductive areas of the circuit. With this microscope, we have measured the local DOS in a hybrid Superconductor-Normal metal-Superconductor (S-N-S) structure. In such circuit, the electronic properties of N and S are modified by the superconducting proximity effect. In particular, for short N wires, we have observed a minigap independent of position in the DOS of the N wire, as was previously predicted. Moreover, when varying the superconducting phase difference between the S electrodes, we have measured the modification of the minigap and its disappearance when the phase difference equals π. Our experimental results for the DOS, and its dependences (on phase, position, N length), are quantitatively accounted for by the quasiclassical theory of superconductivity. Some predictions of this theory are observed for the first time. La spectroscopie électronique basée sur l'effet tunnel donne accès à la densité d'états des électrons (DOS) dans les matériaux conducteurs, et renseigne ainsi en détail sur leurs propriétés électroniques. Au cours de cette thèse, nous avons développé un microscope permettant d'effectuer la spectroscopie tunnel résolue spatialement (10 nm) de nanocircuits individuels, avec une r

  9. Fundamental High-Speed Limits in Single-Molecule, Single-Cell, and Nanoscale Force Spectroscopies

    PubMed Central

    2016-01-01

    Force spectroscopy is enhancing our understanding of single-biomolecule, single-cell, and nanoscale mechanics. Force spectroscopy postulates the proportionality between the interaction force and the instantaneous probe deflection. By studying the probe dynamics, we demonstrate that the total force acting on the probe has three different components: the interaction, the hydrodynamic, and the inertial. The amplitudes of those components depend on the ratio between the resonant frequency and the frequency at which the data are measured. A force–distance curve provides a faithful measurement of the interaction force between two molecules when the inertial and hydrodynamic components are negligible. Otherwise, force spectroscopy measurements will underestimate the value of unbinding forces. Neglecting the above force components requires the use of frequency ratios in the 50–500 range. These ratios will limit the use of high-speed methods in force spectroscopy. The theory is supported by numerical simulations. PMID:27359243

  10. Characterization of chemically and enzymatically treated hemp fibres using atomic force microscopy and spectroscopy

    NASA Astrophysics Data System (ADS)

    George, Michael; Mussone, Paolo G.; Abboud, Zeinab; Bressler, David C.

    2014-09-01

    The mechanical and moisture resistance properties of natural fibre reinforced composites are dependent on the adhesion between the matrix of choice and the fibre. The main goal of this study was to investigate the effect of NaOH swelling of hemp fibres prior to enzymatic treatment and a novel chemical sulfonic acid method on the physical properties of hemp fibres. The colloidal properties of treated hemp fibres were studied exclusively using an atomic force microscope. AFM imaging in tapping mode revealed that each treatment rendered the surface topography of the hemp fibres clean and exposed the individual fibre bundles. Hemp fibres treated with laccase had no effect on the surface adhesion forces measured. Interestingly, mercerization prior to xylanase + cellulase and laccase treatments resulted in greater enzyme access evident in the increased adhesion force measurements. Hemp fibres treated with sulfonic acid showed an increase in surface de-fibrillation and smoothness. A decrease in adhesion forces for 4-aminotoulene-3-sulfonic acid (AT3S) treated fibres suggested a reduction in surface polarity. This work demonstrated that AFM can be used as a tool to estimate the surface forces and roughness for modified fibres and that enzymatic coupled with chemical methods can be used to improve the surface properties of natural fibres for composite applications. Further, this work is one of the first that offers some insight into the effect of mercerization prior to enzymes and the effect on the surface topography. AFM will be used to selectively screen treated fibres for composite applications based on the adhesion forces associated with the colloidal interface between the AFM tip and the fibre surfaces.

  11. Pulling angle-dependent force microscopy

    NASA Astrophysics Data System (ADS)

    Grebíková, L.; Gojzewski, H.; Kieviet, B. D.; Klein Gunnewiek, M.; Vancso, G. J.

    2017-03-01

    In this paper, we describe a method allowing one to perform three-dimensional displacement control in force spectroscopy by atomic force microscopy (AFM). Traditionally, AFM force curves are measured in the normal direction of the contacted surface. The method described can be employed to address not only the magnitude of the measured force but also its direction. We demonstrate the technique using a case study of angle-dependent desorption of a single poly(2-hydroxyethyl methacrylate) (PHEMA) chain from a planar silica surface in an aqueous solution. The chains were end-grafted from the AFM tip in high dilution, enabling single macromolecule pull experiments. Our experiments give evidence of angular dependence of the desorption force of single polymer chains and illustrate the added value of introducing force direction control in AFM.

  12. Subnanometre enzyme mechanics probed by single-molecule force spectroscopy

    PubMed Central

    Pelz, Benjamin; Žoldák, Gabriel; Zeller, Fabian; Zacharias, Martin; Rief, Matthias

    2016-01-01

    Enzymes are molecular machines that bind substrates specifically, provide an adequate chemical environment for catalysis and exchange products rapidly, to ensure fast turnover rates. Direct information about the energetics that drive conformational changes is difficult to obtain. We used subnanometre single-molecule force spectroscopy to study the energetic drive of substrate-dependent lid closing in the enzyme adenylate kinase. Here we show that in the presence of the bisubstrate inhibitor diadenosine pentaphosphate (AP5A), closing and opening of both lids is cooperative and tightly coupled to inhibitor binding. Surprisingly, binding of the substrates ADP and ATP exhibits a much smaller energetic drive towards the fully closed state. Instead, we observe a new dominant energetic minimum with both lids half closed. Our results, combining experiment and molecular dynamics simulations, give detailed mechanical insights into how an enzyme can cope with the seemingly contradictory requirements of rapid substrate exchange and tight closing, to ensure efficient catalysis. PMID:26906294

  13. Subnanometre enzyme mechanics probed by single-molecule force spectroscopy

    NASA Astrophysics Data System (ADS)

    Pelz, Benjamin; Žoldák, Gabriel; Zeller, Fabian; Zacharias, Martin; Rief, Matthias

    2016-02-01

    Enzymes are molecular machines that bind substrates specifically, provide an adequate chemical environment for catalysis and exchange products rapidly, to ensure fast turnover rates. Direct information about the energetics that drive conformational changes is difficult to obtain. We used subnanometre single-molecule force spectroscopy to study the energetic drive of substrate-dependent lid closing in the enzyme adenylate kinase. Here we show that in the presence of the bisubstrate inhibitor diadenosine pentaphosphate (AP5A), closing and opening of both lids is cooperative and tightly coupled to inhibitor binding. Surprisingly, binding of the substrates ADP and ATP exhibits a much smaller energetic drive towards the fully closed state. Instead, we observe a new dominant energetic minimum with both lids half closed. Our results, combining experiment and molecular dynamics simulations, give detailed mechanical insights into how an enzyme can cope with the seemingly contradictory requirements of rapid substrate exchange and tight closing, to ensure efficient catalysis.

  14. Custom AFM for X-ray beamlines: in situ biological investigations under physiological conditions

    PubMed Central

    Gumí-Audenis, B.; Carlà, F.; Vitorino, M. V.; Panzarella, A.; Porcar, L.; Boilot, M.; Guerber, S.; Bernard, P.; Rodrigues, M. S.; Sanz, F.; Giannotti, M. I.; Costa, L.

    2015-01-01

    A fast atomic force microscope (AFM) has been developed that can be installed as a sample holder for grazing-incidence X-ray experiments at solid/gas or solid/liquid interfaces. It allows a wide range of possible investigations, including soft and biological samples under physiological conditions (hydrated specimens). The structural information obtained using the X-rays is combined with the data gathered with the AFM (morphology and mechanical properties), providing a unique characterization of the specimen and its dynamics in situ during an experiment. In this work, lipid monolayers and bilayers in air or liquid environment have been investigated by means of AFM, both with imaging and force spectroscopy, and X-ray reflectivity. In addition, this combination allows the radiation damage induced by the beam on the sample to be studied, as has been observed on DOPC and DPPC supported lipid bilayers under physiological conditions. PMID:26524300

  15. Mapping mechanical force propagation through biomolecular complexes

    SciTech Connect

    Schoeler, Constantin; Bernardi, Rafael C.; Malinowska, Klara H.; Durner, Ellis; Ott, Wolfgang; Bayer, Edward A.; Schulten, Klaus; Nash, Michael A.; Gaub, Hermann E.

    2015-08-11

    In this paper, we employ single-molecule force spectroscopy with an atomic force microscope (AFM) and steered molecular dynamics (SMD) simulations to reveal force propagation pathways through a mechanically ultrastable multidomain cellulosome protein complex. We demonstrate a new combination of network-based correlation analysis supported by AFM directional pulling experiments, which allowed us to visualize stiff paths through the protein complex along which force is transmitted. Finally, the results implicate specific force-propagation routes nonparallel to the pulling axis that are advantageous for achieving high dissociation forces.

  16. An open source/real-time atomic force microscope architecture to perform customizable force spectroscopy experiments.

    PubMed

    Materassi, Donatello; Baschieri, Paolo; Tiribilli, Bruno; Zuccheri, Giampaolo; Samorì, Bruno

    2009-08-01

    We describe the realization of an atomic force microscope architecture designed to perform customizable experiments in a flexible and automatic way. Novel technological contributions are given by the software implementation platform (RTAI-LINUX), which is free and open source, and from a functional point of view, by the implementation of hard real-time control algorithms. Some other technical solutions such as a new way to estimate the optical lever constant are described as well. The adoption of this architecture provides many degrees of freedom in the device behavior and, furthermore, allows one to obtain a flexible experimental instrument at a relatively low cost. In particular, we show how such a system has been employed to obtain measures in sophisticated single-molecule force spectroscopy experiments [Fernandez and Li, Science 303, 1674 (2004)]. Experimental results on proteins already studied using the same methodologies are provided in order to show the reliability of the measure system.

  17. Forced translocation of DNA hairpins through a tight molecular nanopore studied by atomic force microscopy in force-spectroscopy mode

    NASA Astrophysics Data System (ADS)

    Ashcroft, Brian Alan

    The transit of Deoxyribonucleic acid (DNA) through a molecular nanopore has been studied by pulling a beta-cyclodextrin ring over single stranded DNA using an atomic force microscope. After an exhaustive search, it was determined that n-propyl silane surface provides the most reliable background surface for performing force spectroscopy of DNA. A versatile rotaxane complex was formed between a hydrophobic molecule and cyclodextrin. DNA was then added to this complex to form a DNA rotaxane. The cyclodextrin is covalently linked by a molecular tether to the force probe, which both pulls on the cyclodextrin and reads off the forces required for passage of the DNA. The bases do not provide an obstacle to the passage of the cyclodextrin, but hairpins represent large barriers to transit, and analysis of the pulling kinetics show the opening rates of the hairpins. The utility of the system was determined by investigating the kinetics of the analogous biological system with two unusual hairpins: Unusually stable hairpins (consisting of the bases CTTG in the loop) and sequences with CTG repeats motifs. CTTG hairpins prove to be completely impassable both to reverse transcriptase and the cyclodextrin, while CTG repeats pass with an ease appropriate to their bulk measurements, but still enough force to stall a polymerase enzyme proving that the kinetic analysis is alone responsible for the stalling.

  18. Single ricin detection by atomic force microscopy chemomechanical mapping

    NASA Astrophysics Data System (ADS)

    Chen, Guojun; Zhou, Jianfeng; Park, Bosoon; Xu, Bingqian

    2009-07-01

    The authors report on a study of detecting ricin molecules immobilized on chemically modified Au (111) surface by chemomechanically mapping the molecular interactions with a chemically modified atomic force microscopy (AFM) tip. AFM images resolved the different fold-up conformations of single ricin molecule as well as their intramolecule structure of A- and B-chains. AFM force spectroscopy study of the interaction indicates that the unbinding force has a linear relation with the logarithmic force loading rate, which agrees well with calculations using one-barrier bond dissociation model.

  19. Segmented nanofibers of spider dragline silk: Atomic force microscopy and single-molecule force spectroscopy

    PubMed Central

    Oroudjev, E.; Soares, J.; Arcidiacono, S.; Thompson, J. B.; Fossey, S. A.; Hansma, H. G.

    2002-01-01

    Despite its remarkable materials properties, the structure of spider dragline silk has remained unsolved. Results from two probe microscopy techniques provide new insights into the structure of spider dragline silk. A soluble synthetic protein from dragline silk spontaneously forms nanofibers, as observed by atomic force microscopy. These nanofibers have a segmented substructure. The segment length and amino acid sequence are consistent with a slab-like shape for individual silk protein molecules. The height and width of nanofiber segments suggest a stacking pattern of slab-like molecules in each nanofiber segment. This stacking pattern produces nano-crystals in an amorphous matrix, as observed previously by NMR and x-ray diffraction of spider dragline silk. The possible importance of nanofiber formation to native silk production is discussed. Force spectra for single molecules of the silk protein demonstrate that this protein unfolds through a number of rupture events, indicating a modular substructure within single silk protein molecules. A minimal unfolding module size is estimated to be around 14 nm, which corresponds to the extended length of a single repeated module, 38 amino acids long. The structure of this spider silk protein is distinctly different from the structures of other proteins that have been analyzed by single-molecule force spectroscopy, and the force spectra show correspondingly novel features. PMID:11959907

  20. Resonant Optical Gradient Force Interaction for Nano-Imaging and-Spectroscopy

    DTIC Science & Technology

    2016-07-19

    New J. Phys. 18 (2016) 053042 doi:10.1088/1367-2630/18/5/053042 PAPER Resonant optical gradient force interaction for nano-imaging and -spectroscopy...honghua.yang@colorado.edu andmarkus.raschke@colorado.edu Keywords:nano spectroscopy, optical force , near-field optics Abstract The optical gradient force ...theoretical basis in terms of spectral behavior, resonant enhancement, and distance dependence of the optical gradient force fromnumerical simulations

  1. Versatile method for AFM-tip functionalization with biomolecules: fishing a ligand by means of an in situ click reaction

    NASA Astrophysics Data System (ADS)

    Kumar, Rakesh; Ramakrishna, Shivaprakash N.; Naik, Vikrant V.; Chu, Zonglin; Drew, Michael E.; Spencer, Nicholas D.; Yamakoshi, Yoko

    2015-04-01

    A facile and universal method for the functionalization of an AFM tip has been developed for chemical force spectroscopy (CFS) studies of intermolecular interactions of biomolecules. A click reaction between tripod-acetylene and an azide-linker-ligand molecule was successfully carried out on the AFM tip surface and used for the CFS study of ligand-receptor interactions.A facile and universal method for the functionalization of an AFM tip has been developed for chemical force spectroscopy (CFS) studies of intermolecular interactions of biomolecules. A click reaction between tripod-acetylene and an azide-linker-ligand molecule was successfully carried out on the AFM tip surface and used for the CFS study of ligand-receptor interactions. Electronic supplementary information (ESI) available: Experimental details with synthesis and characterization of compounds. Procedures for modifications of Au surfaces and AFM tips. AFM images and full PM-IRRAS spectra of modified surfaces. Detailed procedure for QCM measurement. A table showing ligand-receptor interaction probability. NMR, IR and MS charts. See DOI: 10.1039/c5nr01495f

  2. The Study of Biomolecule-Substrate Interactions by Single Molecule Force Spectroscopy and Brownian Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Cook, Sara Iliafar

    Hybrids of biomolecules and nanomaterials have been identified as promising candidates in the development of novel therapeutics and electronic devices. Single stranded DNA (ssDNA)-bound Single-walled carbon nanotubes (SWCNTs) are of particular interest as they may be the key to solving the challenges that face the carbon nanotube separation technology and because of their potential application in bio-nanomedicine. The ability of ssDNA to form a stable hybrid with CNTs has been attributed to the structure and amphiphilic nature of this macromolecule, enabling the dispersion, sorting and patterned placement of nanotubes. Considering the significant role of ssDNA-CNTs in future technologies and the potential toxicity of such nanomaterials in biological systems, it is essential to gain a quantitative and fundamental understanding on the interactions that allow, weaken or prevent the formation of these hybrids. In this dissertation, we use both experimental and theoretical methods to systematically investigate the major characteristics of these interactions. The free energy of binding of ssDNA homopolymers to solvated carbon nanotubes is one of the key characteristics that determine the stability of such dispersions. We used single molecule force spectroscopy (SMFS), first on graphite and next on single walled carbon nanotubes, to probe and directly quantify the binding strength of ssDNA homopolymer oligomers to these substrates. The force resisting removal of DNA molecules from these surfaces shows characteristic steady-state force plateaus which were distinguishable for each DNA sequence. The free energy of binding per nucleotide for these oligomers on graphite were ranked as T >= A > G >= C (11.3 +/- 0.8 kT, 9.9 +/- 0.4 kT, 8.3 +/- 0.2 kT, and 7.5 +/- 0.8 kT, respectively). On SWCNTs, these interactions decreased in the following order: A > G > T > C, and their magnitude was much larger than on graphite (38.1 +/- 0.2; 33.9 +/- 0.1; 23.3 +/- 0.1; 17.1 +/- 0.1 k

  3. Understanding the plasmonics of nanostructured atomic force microscopy tips

    NASA Astrophysics Data System (ADS)

    Sanders, A.; Bowman, R. W.; Zhang, L.; Turek, V.; Sigle, D. O.; Lombardi, A.; Weller, L.; Baumberg, J. J.

    2016-10-01

    Structured metallic tips are increasingly important for optical spectroscopies such as tip-enhanced Raman spectroscopy, with plasmonic resonances frequently cited as a mechanism for electric field enhancement. We probe the local optical response of sharp and spherical-tipped atomic force microscopy (AFM) tips using a scanning hyperspectral imaging technique to identify the plasmonic behaviour. Localised surface plasmon resonances which radiatively couple with far-field light are found only for spherical AFM tips, with little response for sharp AFM tips, in agreement with numerical simulations of the near-field response. The precise tip geometry is thus crucial for plasmon-enhanced spectroscopies, and the typical sharp cones are not preferred.

  4. The Emergence of AFM Applications to Cell Biology: How new technologies are facilitating investigation of human cells in health and disease at the nanoscale.

    PubMed

    Yang, Ruiguo; Xi, Ning; Fung, Carmen Kar Man; Seiffert-Sinha, Kristina; Lai, King Wai Chiu; Sinha, Animesh A

    2011-01-01

    Atomic Force Microscopy (AFM) based nanorobotics has been used for building nano devices in semiconductors for almost a decade. Leveraging the unparallel precision localization capabilities of this technology, high resolution imaging and mechanical property characterization is now increasingly being performed in biological settings. AFM also offers the prospect for handling and manipulating biological materials at nanometer scale. It has unique advantages over other methods, permitting experiments in the liquid phase where physiological conditions can be maintained. Taking advantage of these properties, our group has visualized membrane and cytoskeletal structures of live cells by controlling the interaction force of the AFM tip with cellular components at the nN or sub-nN range. Cell stiffness changes were observed by statistically analyzing the Young's modulus values of human keratinocytes before and after specific antibody treatment. Furthermore, we used the AFM cantilever as a robotic arm for mechanical pushing, pulling and cutting to perform nanoscale manipulations of cell-associated structures. AFM guided nano-dissection, or nanosurgery was enacted on the cell in order to sever intermediate filaments connecting neighboring keratinocytes via sub 100 nm resolution cuts. Finally, we have used a functionalized AFM tip to probe cell surface receptors to obtain binding force measurements. This technique formed the basis for Single Molecule Force Spectroscopy (SMFS). In addition to enhancing our basic understanding of dynamic signaling events in cell biology, these advancements in AFM based biomedical investigations can be expected to facilitate the search for biomarkers related to disease diagnosis progress and treatment.

  5. Atomic force microscopy on liquid crystals

    NASA Astrophysics Data System (ADS)

    Bahr, Christian; Schulz, Benjamin

    This chapter provides an introduction to the atomic force microscopy (AFM) on thermotropic liquid crystals. We first give a general introduction to the technique of AFM and then describe the special requirements that have to be met for the imaging of liquid-crystalline surfaces. We also discuss the relation between the quality or reliability of the imaging results and various parameters of the scanning conditions. We briey review the existing work on AFM on liquid crystals and finally describe applications beyond the imaging, such as molecular force spectroscopy or manipulation of surface structures.

  6. Polynomial force approximations and multifrequency atomic force microscopy.

    PubMed

    Platz, Daniel; Forchheimer, Daniel; Tholén, Erik A; Haviland, David B

    2013-01-01

    We present polynomial force reconstruction from experimental intermodulation atomic force microscopy (ImAFM) data. We study the tip-surface force during a slow surface approach and compare the results with amplitude-dependence force spectroscopy (ADFS). Based on polynomial force reconstruction we generate high-resolution surface-property maps of polymer blend samples. The polynomial method is described as a special example of a more general approximative force reconstruction, where the aim is to determine model parameters that best approximate the measured force spectrum. This approximative approach is not limited to spectral data, and we demonstrate how it can be adapted to a force quadrature picture.

  7. Noise in NC-AFM measurements with significant tip–sample interaction

    PubMed Central

    Lübbe, Jannis; Temmen, Matthias

    2016-01-01

    The frequency shift noise in non-contact atomic force microscopy (NC-AFM) imaging and spectroscopy consists of thermal noise and detection system noise with an additional contribution from amplitude noise if there are significant tip–sample interactions. The total noise power spectral density D Δ f(f m) is, however, not just the sum of these noise contributions. Instead its magnitude and spectral characteristics are determined by the strongly non-linear tip–sample interaction, by the coupling between the amplitude and tip–sample distance control loops of the NC-AFM system as well as by the characteristics of the phase locked loop (PLL) detector used for frequency demodulation. Here, we measure D Δ f(f m) for various NC-AFM parameter settings representing realistic measurement conditions and compare experimental data to simulations based on a model of the NC-AFM system that includes the tip–sample interaction. The good agreement between predicted and measured noise spectra confirms that the model covers the relevant noise contributions and interactions. Results yield a general understanding of noise generation and propagation in the NC-AFM and provide a quantitative prediction of noise for given experimental parameters. We derive strategies for noise-optimised imaging and spectroscopy and outline a full optimisation procedure for the instrumentation and control loops. PMID:28144538

  8. AFM-Based Mechanical Nanomanipulation

    NASA Astrophysics Data System (ADS)

    Landolsi, Fakhreddine

    2011-12-01

    Advances in several research areas increase the need for more sophisticated fabrication techniques and better performing materials. Tackling this problem from a bottom-up perspective is currently an active field of research. The bottom-up fabrication procedure offers sub-nanometer accurate manipulation. At this time, candidates to achieve nanomanipulation include chemical (self-assembly), biotechnology methods (DNA-based), or using controllable physical forces (e.g. electrokinetic forces, mechanical forces). In this thesis, new methods and techniques for mechanical nanomanipulation using probe force interaction are developed. The considered probes are commonly used in Atomic Force Microscopes (AFMs) for high resolution imaging. AFM-based mechanical nanomanipulation will enable arranging nanoscale entities such as nanotubes and molecules in a precise and controlled manner to assemble and produce novel devices and systems at the nanoscale. The novelty of this research stems from the development of new modeling of the physics and mechanics of the tip interaction with nanoscale entities, coupled with the development of new smart cantilevers with multiple degrees of freedom. The gained knowledge from the conducted simulations and analysis is expected to enable true precision and repeatability of nanomanipulation tasks which is not feasible with existing methods and technologies.

  9. Interaction between Pheromone and Its Receptor of the Fission Yeast Schizosaccharomyces pombe Examined by a Force Spectroscopy Study

    PubMed Central

    Sasuga, Shintaro; Abe, Ryohei; Nikaido, Osamu; Kiyosaki, Shoichi; Sekiguchi, Hiroshi; Ikai, Atsushi; Osada, Toshiya

    2012-01-01

    Interaction between P-factor, a peptide pheromone composed of 23 amino acid residues, and its pheromone receptor, Mam2, on the cell surface of the fission yeast Schizosaccharomyces pombe was examined by an atomic force microscope (AFM). An AFM tip was modified with P-factor derivatives to perform force curve measurements. The specific interaction force between P-factor and Mam2 was calculated to be around 120 pN at a probe speed of 1.74 μm/s. When the AFM tip was modified with truncated P-factor derivative lacking C-terminal Leu, the specific interaction between the tip and the cell surface was not observed. These results were also confirmed with an assay system using a green fluorescent protein (GFP) reporter gene to monitor the activation level of signal transduction following the interaction of Mam2 with P-factor. PMID:22500108

  10. Interaction between pheromone and its receptor of the fission yeast Schizosaccharomyces pombe examined by a force spectroscopy study.

    PubMed

    Sasuga, Shintaro; Abe, Ryohei; Nikaido, Osamu; Kiyosaki, Shoichi; Sekiguchi, Hiroshi; Ikai, Atsushi; Osada, Toshiya

    2012-01-01

    Interaction between P-factor, a peptide pheromone composed of 23 amino acid residues, and its pheromone receptor, Mam2, on the cell surface of the fission yeast Schizosaccharomyces pombe was examined by an atomic force microscope (AFM). An AFM tip was modified with P-factor derivatives to perform force curve measurements. The specific interaction force between P-factor and Mam2 was calculated to be around 120 pN at a probe speed of 1.74 μm/s. When the AFM tip was modified with truncated P-factor derivative lacking C-terminal Leu, the specific interaction between the tip and the cell surface was not observed. These results were also confirmed with an assay system using a green fluorescent protein (GFP) reporter gene to monitor the activation level of signal transduction following the interaction of Mam2 with P-factor.

  11. Discrimination of bladder cancer cells from normal urothelial cells with high specificity and sensitivity: combined application of atomic force microscopy and modulated Raman spectroscopy.

    PubMed

    Canetta, Elisabetta; Riches, Andrew; Borger, Eva; Herrington, Simon; Dholakia, Kishan; Adya, Ashok K

    2014-05-01

    Atomic force microscopy (AFM) and modulated Raman spectroscopy (MRS) were used to discriminate between living normal human urothelial cells (SV-HUC-1) and bladder tumour cells (MGH-U1) with high specificity and sensitivity. MGH-U1 cells were 1.5-fold smaller, 1.7-fold thicker and 1.4-fold rougher than normal SV-HUC-1 cells. The adhesion energy was 2.6-fold higher in the MGH-U1 cells compared to normal SV-HUC-1 cells, which possibly indicates that bladder tumour cells are more deformable than normal cells. The elastic modulus of MGH-U1 cells was 12-fold lower than SV-HUC-1 cells, suggesting a higher elasticity of the bladder cancer cell membranes. The biochemical fingerprints of cancer cells displayed a higher DNA and lipid content, probably due to an increase in the nuclear to cytoplasm ratio. Normal cells were characterized by higher protein contents. AFM studies revealed a decrease in the lateral dimensions and an increase in thickness of cancer cells compared to normal cells; these studies authenticate the observations from MRS. Nanostructural, nanomechanical and biochemical profiles of bladder cells provide qualitative and quantitative markers to differentiate between normal and cancerous cells at the single cellular level. AFM and MRS allow discrimination between adhesion energy, elasticity and Raman spectra of SV-HUC-1 and MGH-U1 cells with high specificity (83, 98 and 95%) and sensitivity (97, 93 and 98%). Such single-cell-level studies could have a pivotal impact on the development of AFM-Raman combined methodologies for cancer profiling and screening with translational significance.

  12. APOBEC3G Interacts with ssDNA by Two Modes: AFM Studies

    NASA Astrophysics Data System (ADS)

    Shlyakhtenko, Luda S.; Dutta, Samrat; Banga, Jaspreet; Li, Ming; Harris, Reuben S.; Lyubchenko, Yuri L.

    2015-10-01

    APOBEC3G (A3G) protein has antiviral activity against HIV and other pathogenic retroviruses. A3G has two domains: a catalytic C-terminal domain (CTD) that deaminates cytidine, and a N-terminal domain (NTD) that binds to ssDNA. Although abundant information exists about the biological activities of A3G protein, the interplay between sequence specific deaminase activity and A3G binding to ssDNA remains controversial. We used the topographic imaging and force spectroscopy modalities of Atomic Force Spectroscopy (AFM) to characterize the interaction of A3G protein with deaminase specific and nonspecific ssDNA substrates. AFM imaging demonstrated that A3G has elevated affinity for deaminase specific ssDNA than for nonspecific ssDNA. AFM force spectroscopy revealed two distinct binding modes by which A3G interacts with ssDNA. One mode requires sequence specificity, as demonstrated by stronger and more stable complexes with deaminase specific ssDNA than with nonspecific ssDNA. Overall these observations enforce prior studies suggesting that both domains of A3G contribute to the sequence specific binding of ssDNA.

  13. Nano Mechanical Machining Using AFM Probe

    NASA Astrophysics Data System (ADS)

    Mostofa, Md. Golam

    Complex miniaturized components with high form accuracy will play key roles in the future development of many products, as they provide portability, disposability, lower material consumption in production, low power consumption during operation, lower sample requirements for testing, and higher heat transfer due to their very high surface-to-volume ratio. Given the high market demand for such micro and nano featured components, different manufacturing methods have been developed for their fabrication. Some of the common technologies in micro/nano fabrication are photolithography, electron beam lithography, X-ray lithography and other semiconductor processing techniques. Although these methods are capable of fabricating micro/nano structures with a resolution of less than a few nanometers, some of the shortcomings associated with these methods, such as high production costs for customized products, limited material choices, necessitate the development of other fabricating techniques. Micro/nano mechanical machining, such an atomic force microscope (AFM) probe based nano fabrication, has, therefore, been used to overcome some the major restrictions of the traditional processes. This technique removes material from the workpiece by engaging micro/nano size cutting tool (i.e. AFM probe) and is applicable on a wider range of materials compared to the photolithographic process. In spite of the unique benefits of nano mechanical machining, there are also some challenges with this technique, since the scale is reduced, such as size effects, burr formations, chip adhesions, fragility of tools and tool wear. Moreover, AFM based machining does not have any rotational movement, which makes fabrication of 3D features more difficult. Thus, vibration-assisted machining is introduced into AFM probe based nano mechanical machining to overcome the limitations associated with the conventional AFM probe based scratching method. Vibration-assisted machining reduced the cutting forces

  14. Microfluidics, Chromatography, and Atomic-Force Microscopy

    NASA Technical Reports Server (NTRS)

    Anderson, Mark

    2008-01-01

    A Raman-and-atomic-force microscope (RAFM) has been shown to be capable of performing several liquid-transfer and sensory functions essential for the operation of a microfluidic laboratory on a chip that would be used to perform rapid, sensitive chromatographic and spectro-chemical analyses of unprecedentedly small quantities of liquids. The most novel aspect of this development lies in the exploitation of capillary and shear effects at the atomic-force-microscope (AFM) tip to produce shear-driven flow of liquids along open microchannels of a microfluidic device. The RAFM can also be used to perform such functions as imaging liquids in microchannels; removing liquid samples from channels for very sensitive, tip-localized spectrochemical analyses; measuring a quantity of liquid adhering to the tip; and dip-pen deposition from a chromatographic device. A commercial Raman-spectroscopy system and a commercial AFM were integrated to make the RAFM so as to be able to perform simultaneous topographical AFM imaging and surface-enhanced Raman spectroscopy (SERS) at the AFM tip. The Raman-spectroscopy system includes a Raman microprobe attached to an optical microscope, the translation stage of which is modified to accommodate the AFM head. The Raman laser excitation beam, which is aimed at the AFM tip, has a wavelength of 785 nm and a diameter of about 5 m, and its power is adjustable up to 10 mW. The AFM is coated with gold to enable tip-localized SERS.

  15. SU-8 hollow cantilevers for AFM cell adhesion studies

    NASA Astrophysics Data System (ADS)

    Martinez, Vincent; Behr, Pascal; Drechsler, Ute; Polesel-Maris, Jérôme; Potthoff, Eva; Vörös, Janos; Zambelli, Tomaso

    2016-05-01

    A novel fabrication method was established to produce flexible, transparent, and robust tipless hollow atomic force microscopy (AFM) cantilevers made entirely from SU-8. Channels of 3 μm thickness and several millimeters length were integrated into 12 μm thick and 40 μm wide cantilevers. Connected to a pressure controller, the devices showed high sealing performance with no leakage up to 6 bars. Changing the cantilever lengths from 100 μm to 500 μm among the same wafer allowed the targeting of various spring constants ranging from 0.5 to 80 N m-1 within a single fabrication run. These hollow polymeric AFM cantilevers were operated in the optical beam deflection configuration. To demonstrate the performance of the device, single-cell force spectroscopy experiments were performed with a single probe detaching in a serial protocol more than 100 Saccharomyces cerevisiae yeast cells from plain glass and glass coated with polydopamine while measuring adhesion forces in the sub-nanoNewton range. SU-8 now offers a new alternative to conventional silicon-based hollow cantilevers with more flexibility in terms of complex geometric design and surface chemistry modification.

  16. Savinase action on bovine serum albumin (BSA) monolayers demonstrated with measurements at the air-water interface and liquid Atomic Force Microscopy (AFM) imaging.

    PubMed

    Balashev, Konstantin; Callisen, Thomas H; Svendsen, Allan; Bjørnholm, Thomas

    2011-12-01

    We studied the enzymatic action of Savinase on bovine serum albumin (BSA) organized in a monolayer spread at the air/water interface or adsorbed at the mica surface. We carried out two types of experiments. In the first one we followed the degradation of the protein monolayer by measuring the surface pressure and surface area decrease versus time. In the second approach we applied AFM imaging of the supported BSA monolayers adsorbed on mica solid supports and extracted information for the enzyme action by analyzing the obtained images of the surface topography in the course of enzyme action. In both cases we obtained an estimate for the turnover number (TON) of the enzyme reaction.

  17. Multiplexed single-molecule force spectroscopy using a centrifuge

    PubMed Central

    Yang, Darren; Ward, Andrew; Halvorsen, Ken; Wong, Wesley P.

    2016-01-01

    We present a miniature centrifuge force microscope (CFM) that repurposes a benchtop centrifuge for high-throughput single-molecule experiments with high-resolution particle tracking, a large force range, temperature control and simple push-button operation. Incorporating DNA nanoswitches to enable repeated interrogation by force of single molecular pairs, we demonstrate increased throughput, reliability and the ability to characterize population heterogeneity. We perform spatiotemporally multiplexed experiments to collect 1,863 bond rupture statistics from 538 traceable molecular pairs in a single experiment, and show that 2 populations of DNA zippers can be distinguished using per-molecule statistics to reduce noise. PMID:26984516

  18. Electron work functions of ferrite and austenite phases in a duplex stainless steel and their adhesive forces with AFM silicon probe.

    PubMed

    Guo, Liqiu; Hua, Guomin; Yang, Binjie; Lu, Hao; Qiao, Lijie; Yan, Xianguo; Li, Dongyang

    2016-02-12

    Local electron work function, adhesive force, modulus and deformation of ferrite and austenite phases in a duplex stainless steel were analyzed by scanning force microscopy. It is demonstrated that the austenite has a higher electron work function than the ferrite, corresponding to higher modulus, smaller deformation and larger adhesive force. Relevant first-principles calculations were conducted to elucidate the mechanism behind. It is demonstrated that the difference in the properties between austenite and ferrite is intrinsically related to their electron work functions.

  19. Stable, non-destructive immobilization of native nuclear membranes to micro-structured PDMS for single-molecule force spectroscopy.

    PubMed

    Rangl, Martina; Nevo, Reinat; Liashkovich, Ivan; Shahin, Victor; Reich, Ziv; Ebner, Andreas; Hinterdorfer, Peter

    2009-07-13

    In eukaryotic cells the nucleus is separated from the cytoplasm by a double-membraned nuclear envelope (NE). Exchange of molecules between the two compartments is mediated by nuclear pore complexes (NPCs) that are embedded in the NE membranes. The translocation of molecules such as proteins and RNAs through the nuclear membrane is executed by transport shuttling factors (karyopherines). They thereby dock to particular binding sites located all over the NPC, the so-called phenylalanine-glycin nucleoporines (FG Nups). Molecular recognition force spectroscopy (MRFS) allows investigations of the binding at the single-molecule level. Therefore the AFM tip carries a ligand for example, a particular karyopherin whereas the nuclear membrane with its receptors is mounted on a surface. Hence, one of the first requirements to study the nucleocytoplasmatic transport mechanism using MRFS is the development of an optimized membrane preparation that preserves structure and function of the NPCs. In this study we present a stable non-destructive preparation method of Xenopus laevis nuclear envelopes. We use micro-structured polydimethylsiloxane (PDMS) that provides an ideal platform for immobilization and biological integrity due to its elastic, chemical and mechanical properties. It is a solid basis for studying molecular recognition, transport interactions, and translocation processes through the NPC. As a first recognition system we investigate the interaction between an important transport shuttling factor, importin beta, and its binding sites on the NPC, the FG-domains.

  20. [Atomic force microscopy: a tool to analyze the viral cycle].

    PubMed

    Bernaud, Julien; Castelnovo, Martin; Muriaux, Delphine; Faivre-Moskalenko, Cendrine

    2015-05-01

    Each step of the HIV-1 life cycle frequently involves a change in the morphology and/or mechanical properties of the viral particle or core. The atomic force microscope (AFM) constitutes a powerful tool for characterizing these physical changes at the scale of a single virus. Indeed, AFM enables the visualization of viral capsids in a controlled physiological environment and to probe their mechanical properties by nano-indentation. Finally, AFM force spectroscopy allows to characterize the affinities between viral envelope proteins and cell receptors at the single molecule level.

  1. Progressing single biomolecule force spectroscopy measurements for the screening of DNA binding agents

    NASA Astrophysics Data System (ADS)

    Zhang, Wenke; Barbagallo, Romina; Madden, Claire; Roberts, Clive J.; Woolford, Alison; Allen, Stephanie

    2005-10-01

    Recent studies have indicated that the force-extension properties of single molecules of double stranded (ds) DNA are sensitive to the presence of small molecule DNA binding agents, and also to their mode of binding. These observations raise the possibility of using this approach as a highly sensitive tool for the screening of such agents. However, particularly for studies employing the atomic force microscope (AFM), several non-trivial barriers hinder the progress of this approach to the non-specialist arena and hence also the full realization of this possibility. In this paper, we therefore address a series of key reproducibility and metrological issues associated with this type of measurement. Specifically, we present an improved immobilization method that covalently anchors one end (5' end) of a dual labelled (5'-thiol, 3'-biotin) p53 DNA molecule onto a gold substrate via gold-thiol chemistry, whilst the biotinylated 3' end is available for 'pick-up' using a streptavidin modified AFM tip. We also show that co-surface immobilization of DNA with 6-mercapto-1-hexanol (MCH) can also lead to a further increase the measured contour length. We demonstrate the impact of these improved protocols through the observation of the cooperative transition plateau in a DNA fragment of approximately 118 bp, a significantly smaller fragment than previously investigated. The results of a comparative study of the effects of a model minor groove binder (Hoechst 33258) and an intercalating drug (proflavine), alone, as a mixture and under different buffer conditions, are also presented.

  2. Mechanism of high-resolution STM, AFM and IETS-STM imaging with functionalized tips

    NASA Astrophysics Data System (ADS)

    Temirov, R.; Hapala, P.; Tautz, F. S.; Jelinek, P.

    2015-03-01

    High-resolution AFM and STM with functionalized tips is well established, but a detailed understanding of the image mechanism is still missing. Moreover, recently this family of imaging techniques has been complemented by a method based on inelastic electron tunneling spectroscopy. Here we present a comprehensive mechanical and transport simulation model that explains essentially all image features in functionalized tip STM, AFM and IETS-STM. Important aspects of the mechanism are: (i) Images are dominantly determined by Pauli repulsion, (ii) in STM and IETS STM this force signal is transduced into an elastic or inelastic conductance signal, (iii) probe particle relaxation leads to image sharpening, (iv) the apparent imaging of hydrogen bonds can be explained by a relaxation effect, and (v) electrostatic forces may also influence the image contrast.

  3. Conductance of AFM Deformed Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexei; Maiti, Amitesh; Anatram, M. P.; Biegel, Bryan (Technical Monitor)

    2002-01-01

    This viewgraph presentation provides information on the electrical conductivity of carbon nanotubes upon deformation by atomic force microscopy (AFM). The density of states and conductance were computed using four orbital tight-binding method with various parameterizations. Different chiralities develop bandgap that varies with chirality.

  4. Investigation of Molecular Interactions between AFM-Tip and Thiol Films

    NASA Astrophysics Data System (ADS)

    Touhami, Ahmed; Moore, Justin; Lee, T. Randall

    Among various self-assembly processes, the formation of a self-assembled monolayer (SAM) is one of the most elegant ways for making an organic film with specific surface properties. Recently, much effort has been devoted in using AFM-based single-molecule force spectroscopy (SMFS) to understanding the formation of alkanethiol SAMs on gold surfaces. Investigating the factors that affect the AFM tip-SAMs interactions is necessary to clarify the controversial results of these studies. Here, we investigated the interactions between bare AFM-tips and several SAMs thiols-gold surfaces under controlled humidity conditions. Our results demonstrate that the Tip-SAM interactions can be used to precisely determine the length of the thiol chains, the adhesion force between thiols head groups and the AFM tip, and the strength of the thiol-gold contact. Our findings on the dynamics and the structure of the SAMs of alkanethiols on gold are useful for detail understanding of the thermodynamics, kinetics and mechanisms of SAM technology assembly. NSF.

  5. Nanometer-Sized Water Bridge and Pull-Off Force in AFM at Different Relative Humidities: Reproducibility Measurement and Model Based on Surface Tension Change.

    PubMed

    Bartošík, Miroslav; Kormoš, Lukáš; Flajšman, Lukáš; Kalousek, Radek; Mach, Jindřich; Lišková, Zuzana; Nezval, David; Švarc, Vojtěch; Šamořil, Tomáš; Šikola, Tomáš

    2017-01-26

    This article deals with the analysis of the relationship between the pull-off force measured by atomic force microscopy and the dimensions of water bridge condensed between a hydrophilic silicon oxide tip and a silicon oxide surface under ambient conditions. Our experiments have shown that the pull-off force increases linearly with the radius of the tip and nonmonotonically with the relative humidity (RH). The latter dependence generally consists of an initial constant part changing to a convex-concave-like increase of the pull-off force and finally followed by a concave-like decrease of this force. The reproducibility tests have demonstrated that the precision limits have to be taken into account for comparing these measurements carried out under atmospheric conditions. The results were fitted by a classical thermodynamic model based on water-bridge envelope calculations using the numerical solution of the Kelvin equation in the form of axisymmetric differential equations and consequent calculation of adhesive forces. To describe the measured data more precisely, a decrease of the water surface tension for low RH was incorporated into the calculation. Such a decrease can be expected as a consequence of the high surface curvature in the nanometer-sized water bridge between the tip and the surface.

  6. Unbinding forces and energies between a siRNA molecule and a dendrimer measured by force spectroscopy

    NASA Astrophysics Data System (ADS)

    Dumitru, Andra C.; Herruzo, Elena T.; Rausell, Estrella; Ceña, Valentin; Garcia, Ricardo

    2015-11-01

    We have measured the intermolecular forces between small interference RNA (siRNA) and polyamidoamine dendrimers at the single molecular level. A single molecule force spectroscopy approach has been developed to measure the unbinding forces and energies between a siRNA molecule and polyamidoamine dendrimers deposited on a mica surface in a buffer solution. We report three types of unbinding events which are characterized by forces and free unbinding energies, respectively, of 28 pN, 0.709 eV; 38 pN, 0.722 eV; and 50 pN, 0.724 eV. These events reflect different possible electrostatic interactions between the positive charges of one or two dendrimers and the negatively charged phosphate groups of a single siRNA. We have evidence of a high binding affinity of siRNA towards polyamidoamine dendrimers that leads to a 45% probability of measuring specific unbinding events.

  7. Unbinding forces and energies between a siRNA molecule and a dendrimer measured by force spectroscopy.

    PubMed

    Dumitru, Andra C; Herruzo, Elena T; Rausell, Estrella; Ceña, Valentin; Garcia, Ricardo

    2015-12-21

    We have measured the intermolecular forces between small interference RNA (siRNA) and polyamidoamine dendrimers at the single molecular level. A single molecule force spectroscopy approach has been developed to measure the unbinding forces and energies between a siRNA molecule and polyamidoamine dendrimers deposited on a mica surface in a buffer solution. We report three types of unbinding events which are characterized by forces and free unbinding energies, respectively, of 28 pN, 0.709 eV; 38 pN, 0.722 eV; and 50 pN, 0.724 eV. These events reflect different possible electrostatic interactions between the positive charges of one or two dendrimers and the negatively charged phosphate groups of a single siRNA. We have evidence of a high binding affinity of siRNA towards polyamidoamine dendrimers that leads to a 45% probability of measuring specific unbinding events.

  8. Spatial spectrograms of vibrating atomic force microscopy cantilevers coupled to sample surfaces

    SciTech Connect

    Wagner, Ryan; Raman, Arvind; Proksch, Roger

    2013-12-23

    Many advanced dynamic Atomic Force Microscopy (AFM) techniques such as contact resonance, force modulation, piezoresponse force microscopy, electrochemical strain microscopy, and AFM infrared spectroscopy exploit the dynamic response of a cantilever in contact with a sample to extract local material properties. Achieving quantitative results in these techniques usually requires the assumption of a certain shape of cantilever vibration. We present a technique that allows in-situ measurements of the vibrational shape of AFM cantilevers coupled to surfaces. This technique opens up unique approaches to nanoscale material property mapping, which are not possible with single point measurements alone.

  9. Corrosive effects of fluoride on titanium: investigation by X-ray photoelectron spectroscopy, atomic force microscopy, and human epithelial cell culturing.

    PubMed

    Stájer, Anette; Ungvári, Krisztina; Pelsoczi, István K; Polyánka, Hilda; Oszkó, Albert; Mihalik, Erzsébet; Rakonczay, Zoltán; Radnai, Márta; Kemény, Lajos; Fazekas, András; Turzó, Kinga

    2008-11-01

    High fluoride (F(-)) concentrations and acidic pH impair the corrosion resistance of titanium (Ti). Effects of F(-)-containing caries-preventive prophylactic rinses, and gels on Ti were investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Human epithelial cell attachment and proliferation were investigated by dimethylthiazol-diphenyl tetrazolium bromide (MTT) and protein content assays. Aqueous 1% NaF solution (3800 ppm F(-), pH 4.5) or high (12,500 ppm) F(-) content gel (pH 4.8) strongly corroded the surface and modified its composition. XPS revealed formation of a strongly bound F(-)-containing complex (Na(2)TiF(6)). AFM indicated an increase in roughness (R(a)) of the surfaces: 10-fold for the NaF solution and smaller for the gel or a mouthwash (250 ppm F(-), pH 4.4). MTT revealed that cell attachment was significantly increased by the gel, but was not disturbed by either the mouthwash or the NaF. Cell proliferation determined by MTT decreased significantly only for the NaF-treated samples; protein content assay experiments showed no such effect. This study indicates that epithelial cell culturing results can depend on the method used, and the adverse effects of a high F(-) concentration and low pH should be considered when prophylactic gels are applied by patients with Ti implants or other dental devices.

  10. PLA-PEG nanocapsules radiolabeled with 99mTechnetium-HMPAO: release properties and physicochemical characterization by atomic force microscopy and photon correlation spectroscopy.

    PubMed

    Pereira, Maira Alves; Mosqueira, Vanessa Carla Furtado; Vilela, José Mário Carneiro; Andrade, Margareth Spangler; Ramaldes, Gilson Andrade; Cardoso, Valbert Nascimento

    2008-01-01

    The present work describes the preparation, characterization and labelling of conventional and surface-modified nanocapsules (NC) with 99m Tc-HMPAO. The size, size distribution and homogeneity were determined by photon correlation spectroscopy (PCS) and zeta potential by laser doppler anemometry. The morphology and the structural organization were evaluated by atomic force microscopy (AFM). The stability and release profile of the NC were determined in vitro in plasma. The results showed that the use of methylene blue induces significant increase in the encapsulation efficiency of 99m Tc-HMPAO, from 24.4 to 49.8% in PLA NC and 22.37 to 52.93% in the case of PLA-PEG NC (P<0.05) by improving the complex stabilization. The average diameter of NC calculated by PCS varied from 216 to 323 nm, while the average diameter determined by AFM varied from 238 to 426 nm. The AFM analysis of diameter/height ratios suggested a greater homogeneity of the surface-modified PLA-PEG nanocapsules compared to PLA NC concerning their flattening properties. The in vitro release of the 99m Tc-HMPAO in plasma medium was faster for the conventional PLA NC than for the surface-modified NC. For the latter, 60% of the radioactivity remained associated with NC, even after 12h of incubation. The results suggest that the surface-modified 99m Tc-HMPAO-PLA-PEG NC was more stable against label leakage in the presence of proteins and could present better performance as radiotracer in vivo.

  11. Interaction of human plasma fibrinogen with commercially pure titanium as studied with atomic force microscopy and X-ray photoelectron spectroscopy.

    PubMed

    Keere, Isabel Van De; Willaert, Ronnie; Hubin, Annick; Vereecken, Jean

    2008-03-04

    The surface of a biomaterial interacts with the body fluid upon implantation in the human body. The biocompatibility of a material is strongly influenced by the adsorption of proteins onto the surface. Titanium is frequently used as a biomaterial for implants in orthopedics and cardiovascular devices. Understanding the biocompatibility is very important to improve implants. The surface chemistry of an implant material and its influence on the interaction with body fluid is crucial in that perspective. The main goal of this study was to investigate the conformation of human plasma fibrinogen (HPF) adsorbed on commercially pure titanium (CP Ti) on a molecular level by means of ex situ atomic force microscopy (AFM). With X-ray photoelectron spectroscopy combined with argon ion beam depth profiling, it was shown that the oxide layer present at the surface was mainly composed of TiO2, with a small percentage of Ti2O3. Ex situ AFM imaging showed the conformation of HPF on CP Ti. Single molecules and aggregates of fibrinogen were observed. The trinodular structure of single HPF molecules (two spherical D domains at the distal ends of the extended molecule and the central spherical E domain) adsorbed onto CP Ti was visualized. Aggregate formation through the connection of the D domains of the HPF molecules was observed on CP Ti. The alphaC domains of HPF were not visible on CP Ti. The ex situ AFM images indicated conformational changes of HPF upon adsorption onto CP Ti. The conformation of the adsorbed HPF molecules was different on mica and titanium. The difference in wettability between both substrates caused a larger spread of the protein on the CP Ti surface and thus resulted in a larger perturbation to the native structure of HPF as compared to mica.

  12. Stiffness, resilience, compressibility. Atomic scale force spectroscopy of biomolecules

    NASA Astrophysics Data System (ADS)

    Leu, Bogdan M.; Sage, J. Timothy

    2016-12-01

    The flexibility of a protein is an important component of its functionality. We use nuclear resonance vibrational spectroscopy (NRVS) to quantify the flexibility of the heme iron environment in the electron-carrying protein cytochrome c by measuring the stiffness and the resilience. These quantities are sensitive to structural differences between the active sites of different proteins, as illustrated by a comparative analysis with myoglobin. The elasticity of the entire protein, on the other hand, can be probed quantitatively from NRVS and high energy-resolution inelastic X-ray scattering (IXS) measurements, an approach that we used to extract the bulk modulus of cytochrome c.

  13. Measurement of the interaction forces at various pH levels by using AFM for the interpretation of DNA adsorption on silanized surfaces

    NASA Astrophysics Data System (ADS)

    Han, Seung Pil; Suga, Kosaku; Fujihara, Masamichi; Park, Byung-Eun

    2014-09-01

    Various surfaces have been used for deoxyribonucleic acid (DNA) immobilization, one example being a silanized surface. This is useful for determining DNA lengths and, thus, locating specific gene sequences in DNA by using fluorescence microscopy and scanning probe microscopy. In this study, we deposited DNA by using the molecular combing method and, we used fluorescence microscopy to study how the chain lengths of n-alkylsilanes affected the surface density of DNA deposited on the silanized surfaces in a tris-ethylenediaminetetraacetic acid (TE) buffer. The forces between a cleaned silicon-nitride (Si3N4) tip and each substrate surface in aqueous buffers at various pH levels (1.0 ~ 9.0) were also studied by using atomic force microscopy to measure the force-distance curves. We explain why the density of lambda bacteriophage DNA (λ-DNA) deposited by using the molecular combing method at pH 8 was lower on the silanized surface with the shorter alkyl chain than it was on the silanized surface with the longer alkyl chain in terms of the electrical double layer (EDL) and the adhesive force.

  14. Microfluidic multifunctional probe array dielectrophoretic force spectroscopy with wide loading rates.

    PubMed

    Park, In Soo; Eom, Kilho; Son, Jongsang; Chang, Woo-Jin; Park, Kidong; Kwon, Taeyun; Yoon, Dae Sung; Bashir, Rashid; Lee, Sang Woo

    2012-10-23

    The simultaneous investigation of a large number of events with different types of intermolecular interactions, from nonequilibrium high-force pulling assays to quasi-equilibrium unbinding events in the same environment, can be very important for fully understanding intermolecular bond-rupture mechanisms. Here, we describe a novel dielectrophoretic force spectroscopy technique that utilizes microsized beads as multifunctional probes for parallel measurement of intermolecular forces with an extremely wide range of force rate (10(-4) to 10(4) pN/s) inside a microfluidic device. In our experiments, various forces, which broadly form the basis of all molecular interactions, were measured across a range of force loading rates by multifunctional probes of various diameters with a throughput of over 600 events per mm(2), simultaneously and in the same environment. Furthermore, the individual bond-rupture forces, the parameters for the characterization of entire energy landscapes, and the effective stiffness of the force spectroscopy were determined on the basis of the measured results. This method of determining intermolecular forces could be very useful for the precise and simultaneous examination of various molecular interactions, as it can be easily and cost-effectively implemented within a microfluidic device for a range of applications including immunoassays, molecular mechanics, chemical and biological screening, and mechanobiology.

  15. Directly measuring single-molecule heterogeneity using force spectroscopy

    PubMed Central

    Hinczewski, Michael; Thirumalai, D.

    2016-01-01

    One of the most intriguing results of single-molecule experiments on proteins and nucleic acids is the discovery of functional heterogeneity: the observation that complex cellular machines exhibit multiple, biologically active conformations. The structural differences between these conformations may be subtle, but each distinct state can be remarkably long-lived, with interconversions between states occurring only at macroscopic timescales, fractions of a second or longer. Although we now have proof of functional heterogeneity in a handful of systems—enzymes, motors, adhesion complexes—identifying and measuring it remains a formidable challenge. Here, we show that evidence of this phenomenon is more widespread than previously known, encoded in data collected from some of the most well-established single-molecule techniques: atomic force microscopy or optical tweezer pulling experiments. We present a theoretical procedure for analyzing distributions of rupture/unfolding forces recorded at different pulling speeds. This results in a single parameter, quantifying the degree of heterogeneity, and also leads to bounds on the equilibration and conformational interconversion timescales. Surveying 10 published datasets, we find heterogeneity in 5 of them, all with interconversion rates slower than 10 s−1. Moreover, we identify two systems where additional data at realizable pulling velocities is likely to find a theoretically predicted, but so far unobserved crossover regime between heterogeneous and nonheterogeneous behavior. The significance of this regime is that it will allow far more precise estimates of the slow conformational switching times, one of the least understood aspects of functional heterogeneity. PMID:27317744

  16. Molecular force spectroscopy of homophilic nectin-1 interactions

    SciTech Connect

    Vedula, Sri Ram Krishna; Lim, T.S.; Hui Shi; Kausalya, P. Jaya; Lane, E. Birgitte; Rajagopal, Gunaretnam; Hunziker, Walter; Lim, C.T.

    2007-11-03

    Nectins are Ca{sup 2+} independent cell adhesion molecules localizing at the cadherin based adherens junctions. In this study, we have used atomic force microscopy to study interaction of a chimera of extra cellular fragment of nectin-1 and Fc of human IgG (nef-1) with wild type L-fibroblasts that express endogenous nectin-1 to elucidate the biophysical characteristics of homophilic nectin-1 trans-interactions at the level of single molecule. Bond strength distribution revealed three distinct bound states (or configurations) of trans-interactions between paired nectins, where each bound state has a unique unstressed off-rate and reactive compliance. Kinetic analysis of force-dependent off-rate of the bound state involving trans-interacting V-V domains between paired nectin-1 (unstressed off-rate {approx}1.465 {+-} 0.779 s{sup -1}, reactive compliance {approx}0.143 {+-} 0.072 nm) was found to be closest to E-cadherin, indicating that V-V domain trans-interactions are probably necessary to initiate and promote adhesions of E-cadherin at adherens junctions (AJs)

  17. Atomic-scale mechanical properties of orientated C60 molecules revealed by noncontact atomic force microscopy.

    PubMed

    Pawlak, Rémy; Kawai, Shigeki; Fremy, Sweetlana; Glatzel, Thilo; Meyer, Ernst

    2011-08-23

    In this work, the mechanical properties of C(60) molecules adsorbed on Cu(111) are measured by tuning-fork-based noncontact atomic force microscopy (nc-AFM) and spectroscopy at cryogenic conditions. Site-specific tip-sample force variations are detected above the buckyball structure. Moreover, high-resolution images obtained by nc-AFM show the chemical structure of this molecule and describes unambiguously its orientations on the surface.

  18. Anomalies in nanostructure size measurements by AFM

    NASA Astrophysics Data System (ADS)

    Mechler, Ádám; Kopniczky, Judit; Kokavecz, János; Hoel, Anders; Granqvist, Claes-Göran; Heszler, Peter

    2005-09-01

    Anomalies in atomic force microscopy (AFM) based size determination of nanoparticles were studied via comparative analysis of experiments and numerical calculations. Single tungsten oxide nanoparticles with a mean diameter of 3nm were deposited on mica and graphite substrates and were characterised by AFM. The size (height) of the nanoparticles, measured by tapping mode AFM, was found to be sensitive to the free amplitude of the oscillating tip, thus indicating that the images were not purely topographical. By comparing the experimental results to model calculations, we demonstrate that the dependence of the nanoparticle size on the oscillation amplitude of the tip is an inherent characteristic of the tapping mode AFM; it is also a function of physical properties such as elasticity and surface energy of the nanoparticle and the sample surface, and it depends on the radius of curvature of the tip. We show that good approximation of the real size can easily be obtained from plots of particle height vs free amplitude of the oscillating tip, although errors might persist for individual experiments. The results are valid for size (height) determination of any nanometer-sized objects imaged by tapping mode AFM.

  19. Release profiles and morphological characterization by atomic force microscopy and photon correlation spectroscopy of 99mTechnetium-fluconazole nanocapsules.

    PubMed

    de Assis, Danielle Nogueira; Mosqueira, Vanessa Carla Furtado; Vilela, José Mário Carneiro; Andrade, Margareth Spangler; Cardoso, Valbert Nascimento

    2008-02-12

    Several classes of antifungal have been employed in candidiasis treatment, but patients with advanced immunodeficiency can present unsatisfactory results after therapy. In these cases, high doses of drugs or the use of multiple agents are sometimes used, and hence increasing the risk of serious side effects. Considering theses difficulties, the encapsulation of antifungal agents in nanoparticulate carriers has been used with the objective of modifying the pharmacokinetic of drugs resulting in more efficient treatments with less side effects. The purpose of this work was the preparation, characterization and the investigation of the release profiles of radiolabeled fluconazole nanocapsules. The size, homogeneity and zeta potential of NC preparations were determined with a Zetasizer 3000HS. The morphology and the structural organization were evaluated by atomic force microscopy (AFM). The release study in vitro of NC was evaluated in physiologic solution with or without 70% mouse plasma. The labeling yield of fluconazole with 99mTc was 94% and the radiolabeled drug was stable within 24h period. The encapsulation percentage of 99mTc-fluconazole in PLA-POLOX NC and PLA-PEG NC was approximately of 30%. The average diameter calculated by photon correlation spectroscopy (PCS) varied from 236 to 356 nm, while the average diameter determined by AFM varied from 238 to 411 nm. The diameter/height relation decreased significantly when 25% glutaraldehyde was used for NC fixation on mica. The zeta potential varied from -55 to -69 nm and surface-modified NC showed lower absolute values than conventional NC. The in vitro release of 99mTc-fluconazole in plasma medium of the conventional and surface-modified NC was greater than in saline. The drug release in plasma medium from conventional NC was faster than for surface-modified NC. The results obtained in this work suggest that the nanocapsules containing fluconazole could be used to identify infectious foci, due to the properties

  20. Vibrational spectroscopy and the development of new force fields for biological molecules.

    PubMed

    Gerber, R B; Chaban, G M; Gregurick, S K; Brauer, B

    2003-03-01

    The role of vibrational spectroscopy in the testing of force fields of biological molecules and in the determination of improved force fields is discussed. Analysis shows that quantitative testing of potential energy surfaces by comparison with spectroscopic data generally requires calculations that include anharmonic couplings between different vibrational modes. Applications of the vibrational self-consistent field (VSCF) method to calculations of spectroscopy of biological molecules are presented, and comparison with experiment is used to determine the merits and flaws of various types of force fields. The main conclusions include the following: (1) Potential surfaces from ab initio methods at the level of MP2 yield very satisfactory agreement with spectroscopic experimental data. (2) By the test of spectroscopy, ab initio force fields are considerably superior to the standard versions of force fields such as AMBER or OPLS. (3) Much of the spectroscopic weakness of AMBER and OPLS is due to incorrect description of anharmonic coupling between different vibrational modes. (4) Potential surfaces of the QM/MM (Quantum Mechanics/Molecular Mechanics) type, and potentials based on improved versions of semi-empirical electronic structure theory, which are feasible for large biological molecules, yield encouraging results by the test of vibrational spectroscopy.

  1. NMR Spectroscopy for Thin Films by Magnetic Resonance Force Microscopy

    PubMed Central

    Won, Soonho; Saun, Seung-Bo; Lee, Soonchil; Lee, SangGap; Kim, Kiwoong; Han, Yunseok

    2013-01-01

    Nuclear magnetic resonance (NMR) is a fundamental research tool that is widely used in many fields. Despite its powerful applications, unfortunately the low sensitivity of conventional NMR makes it difficult to study thin film or nano-sized samples. In this work, we report the first NMR spectrum obtained from general thin films by using magnetic resonance force microscopy (MRFM). To minimize the amount of imaging information inevitably mixed into the signal when a gradient field is used, we adopted a large magnet with a flat end with a diameter of 336 μm that generates a homogeneous field on the sample plane and a field gradient in a direction perpendicular to the plane. Cyclic adiabatic inversion was used in conjunction with periodic phase inversion of the frequency shift to maximize the SNR. In this way, we obtained the 19F NMR spectrum for a 34 nm-thick CaF2 thin film. PMID:24217000

  2. Single-molecule bonds characterized by solid-state nanopore force spectroscopy.

    PubMed

    Tabard-Cossa, Vincent; Wiggin, Matthew; Trivedi, Dhruti; Jetha, Nahid N; Dwyer, Jason R; Marziali, Andre

    2009-10-27

    Weak molecular interactions drive processes at the core of living systems, such as enzyme-substrate interactions, receptor-ligand binding, and nucleic acid replication. Single-molecule force spectroscopy is a remarkable tool for revealing molecular scale energy landscapes of noncovalent bonds, by exerting a mechanical force directly on an individual molecular complex and tracking its survival as a function of time and applied force. In principle, force spectroscopy methods can also be used for highly specific molecular recognition assays, by directly characterizing the strength of bonds between probe and target molecules. However, complexity and low throughput of conventional force spectroscopy techniques render such biosensing applications impractical. Here we demonstrate a straightforward single-molecule approach, suitable for both biophysical studies and molecular recognition assays, in which a approximately 3 nm silicon nitride nanopore is used to determine the bond lifetime spectrum of the biotin-neutravidin complex. Thousands of individual molecular complexes are captured and dissociated in the solid-state nanopore under constant applied forces, ranging from 400 to 900 mV, allowing us to extract the location of the energy barrier that governs the interaction, mapped at Deltax approximately 0.5 nm. These results highlight the capacity of a solid-state nanopore to detect and characterize intermolecular interactions and demonstrate how this could be applied to rapid, highly specific molecular detection assays.

  3. Energy landscape investigation by wavelet transform analysis of atomic force spectroscopy data in a biorecognition experiment.

    PubMed

    Bizzarri, Anna Rita

    2016-01-01

    Force fluctuations recorded in an atomic force spectroscopy experiment, during the approach of a tip functionalized with biotin towards a substrate charged with avidin, have been analyzed by a wavelet transform. The observation of strong transient changes only when a specific biorecognition process between the partners takes place suggests a drastic modulation of the force fluctuations when biomolecules recognize each other. Such an analysis allows to investigate the peculiar features of a biorecognition process. These results are discussed in connection with the possible role of energy minima explored by biomolecules during the biorecognition process.

  4. Molecular force spectroscopy with a DNA origami-based nanoscopic force clamp.

    PubMed

    Nickels, Philipp C; Wünsch, Bettina; Holzmeister, Phil; Bae, Wooli; Kneer, Luisa M; Grohmann, Dina; Tinnefeld, Philip; Liedl, Tim

    2016-10-21

    Forces in biological systems are typically investigated at the single-molecule level with atomic force microscopy or optical and magnetic tweezers, but these techniques suffer from limited data throughput and their requirement for a physical connection to the macroscopic world. We introduce a self-assembled nanoscopic force clamp built from DNA that operates autonomously and allows massive parallelization. Single-stranded DNA sections of an origami structure acted as entropic springs and exerted controlled tension in the low piconewton range on a molecular system, whose conformational transitions were monitored by single-molecule Förster resonance energy transfer. We used the conformer switching of a Holliday junction as a benchmark and studied the TATA-binding protein-induced bending of a DNA duplex under tension. The observed suppression of bending above 10 piconewtons provides further evidence of mechanosensitivity in gene regulation.

  5. Dielectrophoretic positioning of single nanoparticles on atomic force microscope tips for tip-enhanced Raman spectroscopy.

    PubMed

    Leiterer, Christian; Deckert-Gaudig, Tanja; Singh, Prabha; Wirth, Janina; Deckert, Volker; Fritzsche, Wolfgang

    2015-05-01

    Tip-enhanced Raman spectroscopy, a combination of Raman spectroscopy and scanning probe microscopy, is a powerful technique to detect the vibrational fingerprint of molecules at the nanometer scale. A metal nanoparticle at the apex of an atomic force microscope tip leads to a large enhancement of the electromagnetic field when illuminated with an appropriate wavelength, resulting in an increased Raman signal. A controlled positioning of individual nanoparticles at the tip would improve the reproducibility of the probes and is quite demanding due to usually serial and labor-intensive approaches. In contrast to commonly used submicron manipulation techniques, dielectrophoresis allows a parallel and scalable production, and provides a novel approach toward reproducible and at the same time affordable tip-enhanced Raman spectroscopy tips. We demonstrate the successful positioning of an individual plasmonic nanoparticle on a commercial atomic force microscope tip by dielectrophoresis followed by experimental proof of the Raman signal enhancing capabilities of such tips.

  6. Assembly of live micro-organisms on microstructured PDMS stamps by convective/capillary deposition for AFM bio-experiments.

    PubMed

    Dague, E; Jauvert, E; Laplatine, L; Viallet, B; Thibault, C; Ressier, L

    2011-09-30

    Immobilization of live micro-organisms on solid substrates is an important prerequisite for atomic force microscopy (AFM) bio-experiments. The method employed must immobilize the cells firmly enough to enable them to withstand the lateral friction forces exerted by the tip during scanning but without denaturing the cell interface. In this work, a generic method for the assembly of living cells on specific areas of substrates is proposed. It consists in assembling the living cells within the patterns of microstructured, functionalized poly-dimethylsiloxane (PDMS) stamps using convective/capillary deposition. This versatile approach is validated by applying it to two systems of foremost importance in biotechnology and medicine: Saccharomyces cerevisiae yeasts and Aspergillus fumigatus fungal spores. We show that this method allows multiplexing AFM nanomechanical measurements by force spectroscopy on S. cerevisiae yeasts and high-resolution AFM imaging of germinated Aspergillus conidia in buffer medium. These two examples clearly demonstrate the immense potential of micro-organism assembly on functionalized, microstructured PDMS stamps by convective/capillary deposition for performing rigorous AFM bio-experiments on living cells.

  7. Assembly of live micro-organisms on microstructured PDMS stamps by convective/capillary deposition for AFM bio-experiments

    NASA Astrophysics Data System (ADS)

    Dague, E.; Jauvert, E.; Laplatine, L.; Viallet, B.; Thibault, C.; Ressier, L.

    2011-09-01

    Immobilization of live micro-organisms on solid substrates is an important prerequisite for atomic force microscopy (AFM) bio-experiments. The method employed must immobilize the cells firmly enough to enable them to withstand the lateral friction forces exerted by the tip during scanning but without denaturing the cell interface. In this work, a generic method for the assembly of living cells on specific areas of substrates is proposed. It consists in assembling the living cells within the patterns of microstructured, functionalized poly-dimethylsiloxane (PDMS) stamps using convective/capillary deposition. This versatile approach is validated by applying it to two systems of foremost importance in biotechnology and medicine: Saccharomyces cerevisiae yeasts and Aspergillus fumigatus fungal spores. We show that this method allows multiplexing AFM nanomechanical measurements by force spectroscopy on S. cerevisiae yeasts and high-resolution AFM imaging of germinated Aspergillus conidia in buffer medium. These two examples clearly demonstrate the immense potential of micro-organism assembly on functionalized, microstructured PDMS stamps by convective/capillary deposition for performing rigorous AFM bio-experiments on living cells.

  8. Numerical analysis of dynamic force spectroscopy using the torsional harmonic cantilever

    NASA Astrophysics Data System (ADS)

    Solares, Santiago D.; Hölscher, Hendrik

    2010-02-01

    A spectral analysis method has been recently introduced by Stark et al (2002 Proc. Natl Acad. Sci. USA 99 8473-8) and implemented by Sahin et al (2007 Nat. Nanotechnol. 2 507-14) using a T-shaped cantilever design, the torsional harmonic cantilever (THC), which is capable of performing simultaneous tapping-mode atomic force microscopy imaging and force spectroscopy. Here we report on numerical simulations of the THC system using a simple dual-mass flexural-torsional model, which is applied in combination with Fourier data processing software to illustrate the spectroscopy process for quality factors corresponding to liquid, air and vacuum environments. We also illustrate the acquisition of enhanced topographical images and deformed surface contours under the application of uniform forces, and compare the results to those obtained with a previously reported linear dual-spring-mass model.

  9. The Emergence of AFM Applications to Cell Biology: How new technologies are facilitating investigation of human cells in health and disease at the nanoscale

    PubMed Central

    Yang, Ruiguo; Xi, Ning; Fung, Carmen Kar Man; Seiffert-Sinha, Kristina; Lai, King Wai Chiu; Sinha, Animesh A.

    2013-01-01

    Atomic Force Microscopy (AFM) based nanorobotics has been used for building nano devices in semiconductors for almost a decade. Leveraging the unparallel precision localization capabilities of this technology, high resolution imaging and mechanical property characterization is now increasingly being performed in biological settings. AFM also offers the prospect for handling and manipulating biological materials at nanometer scale. It has unique advantages over other methods, permitting experiments in the liquid phase where physiological conditions can be maintained. Taking advantage of these properties, our group has visualized membrane and cytoskeletal structures of live cells by controlling the interaction force of the AFM tip with cellular components at the nN or sub-nN range. Cell stiffness changes were observed by statistically analyzing the Young’s modulus values of human keratinocytes before and after specific antibody treatment. Furthermore, we used the AFM cantilever as a robotic arm for mechanical pushing, pulling and cutting to perform nanoscale manipulations of cell-associated structures. AFM guided nano-dissection, or nanosurgery was enacted on the cell in order to sever intermediate filaments connecting neighboring keratinocytes via sub 100 nm resolution cuts. Finally, we have used a functionalized AFM tip to probe cell surface receptors to obtain binding force measurements. This technique formed the basis for Single Molecule Force Spectroscopy (SMFS). In addition to enhancing our basic understanding of dynamic signaling events in cell biology, these advancements in AFM based biomedical investigations can be expected to facilitate the search for biomarkers related to disease diagnosis progress and treatment. PMID:24416719

  10. Single-molecule force spectroscopy studies of fibrin 'A-a' polymerization interactions via the atomic force microscope

    NASA Astrophysics Data System (ADS)

    Averett, Laurel E.

    Fibrin, the polymerized form of the soluble plasma protein fibrinogen, plays a critical role in hemostasis as the structural scaffold of blood clots. The primary functions of fibrin are to withstand the shear forces of blood flow and provide mechanical stability to the clot, protecting the wound. While studies have investigated the mechanical properties of fibrin constructs, the response to force of critical polymerization interactions such as the 'A--a' knob--hole interaction remains unclear. Herein, the response of the 'A--a' bond to force was examined at the single-molecule level using the atomic force microscope. Force spectroscopy methodology was developed to examine the 'A--a' interaction while reducing the incidence of both nonspecific and multiple molecule interactions. The rupture of this interaction resulted in a previously unreported characteristic force profile comprised of up to four events. We hypothesized that the first event represented reorientation of the fibrinogen molecule, the second and third represented unfolding of structures in the D region of fibrinogen, and the last event was the rupture of the 'A--a' bond weakened by prior structural unfolding. The configuration, molecular extension, and kinetic parameters of each event in the characteristic pattern were examined to compare the unfolding of fibrin to other proteins unfolded by force. Fitting the pattern with polymer models showed that the D region of fibrinogen could lengthen by ˜50% of the length of a fibrin monomer before rupture of the 'A--a' bond. Analysis showed that the second and third events had kinetic parameters similar to other protein structures unfolded by force. Studies of the dependence of the characteristic pattern on calcium, concentration of sodium chloride, pH, and temperature demonstrated that the incidence of the last event was affected by solution conditions. However, only low pH and high temperatures reduced the probability that an interaction was characteristic

  11. Contact nanomechanical measurements with the AFM

    NASA Astrophysics Data System (ADS)

    Geisse, Nicholas

    2013-03-01

    The atomic force microscope (AFM) has found broad use in the biological sciences largely due to its ability to make measurements on unfixed and unstained samples under liquid. In addition to imaging at multiple spatial scales ranging from micro- to nanometer, AFMs are commonly used as nanomechanical probes. This is pertinent for cell biology, as it has been demonstrated that the geometrical and mechanical properties of the extracellular microenvironment are important in such processes as cancer, cardiovascular disease, muscular dystrophy, and even the control of cell life and death. Indeed, the ability to control and quantify these external geometrical and mechanical parameters arises as a key issue in the field. Because AFM can quantitatively measure the mechanical properties of various biological samples, novel insights to cell function and to cell-substrate interactions are now possible. As the application of AFM to these types of problems is widened, it is important to understand the performance envelope of the technique and its associated data analyses. This talk will discuss the important issues that must be considered when mechanical models are applied to real-world data. Examples of the effect of different model assumptions on our understanding of the measured material properties will be shown. Furthermore, specific examples of the importance of mechanical stimuli and the micromechanical environment to the structure and function of biological materials will be presented.

  12. Tip in-light on: Advantages, challenges, and applications of combining AFM and Raman microscopy on biological samples.

    PubMed

    Prats-Mateu, Batirtze; Gierlinger, Notburga

    2017-01-01

    Scanning probe microscopies and spectroscopies, especially AFM and Confocal Raman microscopy are powerful tools to characterize biological materials. They are both non-destructive methods and reveal mechanical and chemical properties on the micro and nano-scale. In the last years the interest for increasing the lateral resolution of optical and spectral images has driven the development of new technologies that overcome the diffraction limit of light. The combination of AFM and Raman reaches resolutions of about 50-150 nm in near-field Raman and 1.7-50 nm in tip enhanced Raman spectroscopy (TERS) and both give a molecular information of the sample and the topography of the scanned surface. In this review, the mentioned approaches are introduced, the main advantages and problems for application on biological samples discussed and some examples for successful experiments given. Finally the potential of colocated AFM and Raman measurements is shown on a case study of cellulose-lignin films: the topography structures revealed by AFM can be related to a certain chemistry by the colocated Raman scan and additionally the mechanical properties be revealed by using the digital pulsed force mode. Microsc. Res. Tech. 80:30-40, 2017. © 2016 Wiley Periodicals, Inc.

  13. Tip in–light on: Advantages, challenges, and applications of combining AFM and Raman microscopy on biological samples

    PubMed Central

    Gierlinger, Notburga

    2016-01-01

    Abstract Scanning probe microscopies and spectroscopies, especially AFM and Confocal Raman microscopy are powerful tools to characterize biological materials. They are both non‐destructive methods and reveal mechanical and chemical properties on the micro and nano‐scale. In the last years the interest for increasing the lateral resolution of optical and spectral images has driven the development of new technologies that overcome the diffraction limit of light. The combination of AFM and Raman reaches resolutions of about 50–150 nm in near‐field Raman and 1.7–50 nm in tip enhanced Raman spectroscopy (TERS) and both give a molecular information of the sample and the topography of the scanned surface. In this review, the mentioned approaches are introduced, the main advantages and problems for application on biological samples discussed and some examples for successful experiments given. Finally the potential of colocated AFM and Raman measurements is shown on a case study of cellulose‐lignin films: the topography structures revealed by AFM can be related to a certain chemistry by the colocated Raman scan and additionally the mechanical properties be revealed by using the digital pulsed force mode. Microsc. Res. Tech. 80:30–40, 2017. © 2016 Wiley Periodicals, Inc. PMID:27514318

  14. Detecting cell-adhesive sites in extracellular matrix using force spectroscopy mapping

    PubMed Central

    Chirasatitsin, Somyot; Engler, Adam J

    2010-01-01

    The cell microenvironment is composed of extracellular matrix (ECM), which contains specific binding sites that allow the cell to adhere to its surroundings. Cells employ focal adhesion proteins, which must be able to resist a variety of forces to bind to ECM. Current techniques for detecting the spatial arrangement of these adhesions, however, have limited resolution and those that detect adhesive forces lack sufficient spatial characterization or resolution. Using a unique application of force spectroscopy, we demonstrate here the ability to determine local changes in the adhesive property of a fibronectin substrate down to the resolution of the fibronectin antibody-functionalized tip diameter, ~20 nm. To verify the detection capabilities of force spectroscopy mapping (FSM), changes in loading rate and temperature were used to alter the bond dynamics and change the adhesion force. Microcontact printing was also used to pattern fluorescein isothiocyanate-conjugated fibronectin in order to mimic the discontinuous adhesion domains of native ECM. Fluorescent detection was used to identify the pattern while FSM was used to map cell adhesion sites in registry with the initial fluorescent image. The results show that FSM can be used to detect the adhesion domains at high resolution and may subsequently be applied to native ECM with randomly distributed cell adhesion sites. PMID:21152375

  15. Nanomechanical characterization of phospholipid bilayer islands on flat and porous substrates: a force spectroscopy study.

    PubMed

    Nussio, Matthew R; Oncins, Gerard; Ridelis, Ingrid; Szili, Endre; Shapter, Joseph G; Sanz, Fausto; Voelcker, Nicolas H

    2009-07-30

    In this study, we compare for the first time the nanomechanical properties of lipid bilayer islands on flat and porous surfaces. 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) bilayers were deposited on flat (silicon and mica) and porous silicon (pSi) substrate surfaces and examined using atomic force spectroscopy and force volume imaging. Force spectroscopy measurements revealed the effects of the underlying substrate and of the lipid phase on the nanomechanical properties of bilayers islands. For mica and silicon, significant differences in breakthrough force between the center and the edges of bilayer islands were observed for both phospolipids. These differences were more pronounced for DMPC than for DPPC, presumably due to melting effects at the edges of DMPC bilayers. In contrast, bilayer islands deposited on pSi yielded similar breakthrough forces in the central region and along the perimeter of the islands, and those values in turn were similar to those measured along the perimeter of bilayer islands deposited on the flat substrates. The study also demonstrates that pSi is suitable solid support for the formation of pore-spanning phospholipid bilayers with potential applications in transmembrane protein studies, drug delivery, and biosensing.

  16. A low temperature scanning tunneling microscope for electronic and force spectroscopy.

    PubMed

    Smit, R H M; Grande, R; Lasanta, B; Riquelme, J J; Rubio-Bollinger, G; Agraït, N

    2007-11-01

    In this article, we describe and test a novel way to extend a low temperature scanning tunneling microscope with the capability to measure forces. The tuning fork that we use for this is optimized to have a high quality factor and frequency resolution. Moreover, as this technique is fully compatible with the use of bulk tips, it is possible to combine the force measurements with the use of superconductive or magnetic tips, advantageous for electronic spectroscopy. It also allows us to calibrate both the amplitude and the spring constant of the tuning fork easily, in situ and with high precision.

  17. Crystallographic order and decomposition of [MnIII6CrIII]3+ single-molecule magnets deposited in submonolayers and monolayers on HOPG studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin probe force microscopy in UHV

    PubMed Central

    2014-01-01

    Monolayers and submonolayers of [Mn III 6 Cr III ] 3+ single-molecule magnets (SMMs) adsorbed on highly oriented pyrolytic graphite (HOPG) using the droplet technique characterized by non-contact atomic force microscopy (nc-AFM) as well as by Kelvin probe force microscopy (KPFM) show island-like structures with heights resembling the height of the molecule. Furthermore, islands were found which revealed ordered 1D as well as 2D structures with periods close to the width of the SMMs. Along this, islands which show half the heights of intact SMMs were observed which are evidences for a decomposing process of the molecules during the preparation. Finally, models for the structure of the ordered SMM adsorbates are proposed to explain the observations. PMID:24495692

  18. Maximum likelihood estimation of protein kinetic parameters under weak assumptions from unfolding force spectroscopy experiments

    NASA Astrophysics Data System (ADS)

    Aioanei, Daniel; Samorì, Bruno; Brucale, Marco

    2009-12-01

    Single molecule force spectroscopy (SMFS) is extensively used to characterize the mechanical unfolding behavior of individual protein domains under applied force by pulling chimeric polyproteins consisting of identical tandem repeats. Constant velocity unfolding SMFS data can be employed to reconstruct the protein unfolding energy landscape and kinetics. The methods applied so far require the specification of a single stretching force increase function, either theoretically derived or experimentally inferred, which must then be assumed to accurately describe the entirety of the experimental data. The very existence of a suitable optimal force model, even in the context of a single experimental data set, is still questioned. Herein, we propose a maximum likelihood (ML) framework for the estimation of protein kinetic parameters which can accommodate all the established theoretical force increase models. Our framework does not presuppose the existence of a single force characteristic function. Rather, it can be used with a heterogeneous set of functions, each describing the protein behavior in the stretching time range leading to one rupture event. We propose a simple way of constructing such a set of functions via piecewise linear approximation of the SMFS force vs time data and we prove the suitability of the approach both with synthetic data and experimentally. Additionally, when the spontaneous unfolding rate is the only unknown parameter, we find a correction factor that eliminates the bias of the ML estimator while also reducing its variance. Finally, we investigate which of several time-constrained experiment designs leads to better estimators.

  19. High-speed AFM of human chromosomes in liquid

    NASA Astrophysics Data System (ADS)

    Picco, L. M.; Dunton, P. G.; Ulcinas, A.; Engledew, D. J.; Hoshi, O.; Ushiki, T.; Miles, M. J.

    2008-09-01

    Further developments of the previously reported high-speed contact-mode AFM are described. The technique is applied to the imaging of human chromosomes at video rate both in air and in water. These are the largest structures to have been imaged with high-speed AFM and the first imaging in liquid to be reported. A possible mechanism that allows such high-speed contact-mode imaging without significant damage to the sample is discussed in the context of the velocity dependence of the measured lateral force on the AFM tip.

  20. Raman and AFM study of gamma irradiated plastic bottle sheets

    NASA Astrophysics Data System (ADS)

    Ali, Yasir; Kumar, Vijay; Sonkawade, R. G.; Dhaliwal, A. S.

    2013-02-01

    In this investigation, the effects of gamma irradiation on the structural properties of plastic bottle sheet are studied. The Plastic sheets were exposed with 1.25MeV 60Co gamma rays source at various dose levels within the range from 0-670 kGy. The induced modifications were followed by micro-Raman and atomic force microscopy (AFM). The Raman spectrum shows the decrease in Raman intensity and formation of unsaturated bonds with an increase in the gamma dose. AFM image displays rough surface morphology after irradiation. The detailed Raman analysis of plastic bottle sheets is presented here, and the results are correlated with the AFM observations.

  1. Evaluating the Optoelectronic Quality of Hybrid Perovskites by Conductive Atomic Force Microscopy with Noise Spectroscopy.

    PubMed

    Lee, Byungho; Lee, Sangheon; Cho, Duckhyung; Kim, Jinhyun; Hwang, Taehyun; Kim, Kyung Hwan; Hong, Seunghun; Moon, Taeho; Park, Byungwoo

    2016-11-16

    Organic-inorganic hybrid perovskite solar cells have emerged as promising candidates for next-generation solar cells. To attain high photovoltaic efficiency, reducing the defects in perovskites is crucial along with a uniform coating of the films. Also, evaluating the quality of synthesized perovskites via facile and adequate methods is important as well. Herein, CH3NH3PbI3 perovskites were synthesized by applying second solvent dripping to nonstoichiometric precursors containing excess CH3NH3I. The resulting perovskite films exhibited a larger average grain size with a better crystallinity compared to that from stoichiometric precursors. As a result, the performance of planar perovskite solar cells was significantly improved, achieving an efficiency of 14.3%. Furthermore, perovskite films were effectively analyzed using a conductive AFM and noise spectroscopy, which have been uncommon in the field of perovskite solar cells. Comparing the topography and photocurrent maps, the variation of photocurrents in nanoscale was systematically investigated, and a linear relationship between the grain size and photocurrent was revealed. Also, noise analyses with a conductive probe enabled examination of the defect density of perovskites at specific grain interiors by excluding the grain-boundary effect, and reduced defects were clearly observed for the perovskites using CH3NH3I-rich precursors.

  2. Investigation of free fatty acid associated recombinant membrane receptor protein expression in HEK293 cells using Raman spectroscopy, calcium imaging, and atomic force microscopy.

    PubMed

    Lin, Juqiang; Xu, Han; Wu, Yangzhe; Tang, Mingjie; McEwen, Gerald D; Liu, Pin; Hansen, Dane R; Gilbertson, Timothy A; Zhou, Anhong

    2013-02-05

    G-protein-coupled receptor 120 (GPR120) is a previously orphaned G-protein-coupled receptor that apparently functions as a sensor for dietary fat in the gustatory and digestive systems. In this study, a cDNA sequence encoding a doxycycline (Dox)-inducible mature peptide of GPR120 was inserted into an expression vector and transfected in HEK293 cells. We measured Raman spectra of single HEK293 cells as well as GPR120-expressing HEK293-GPR120 cells at a 48 h period following the additions of Dox at several concentrations. We found that the spectral intensity of HEK293-GPR120 cells is dependent upon the dose of Dox, which correlates with the accumulation of GPR120 protein in the cells. However, the amount of the fatty acid activated changes in intracellular calcium (Ca(2+)) as measured by ratiometric calcium imaging was not correlated with Dox concentration. Principal components analysis (PCA) of Raman spectra reveals that the spectra from different treatments of HEK293-GPR120 cells form distinct, completely separated clusters with the receiver operating characteristic (ROC) area of 1, while those spectra for the HEK293 cells form small overlap clusters with the ROC area of 0.836. It was also found that expression of GPR120 altered the physiochemical and biomechanical properties of the parental cell membrane surface, which was quantitated by atomic force microscopy (AFM). These findings demonstrate that the combination of Raman spectroscopy, calcium imaging, and AFM may provide new tools in noninvasive and quantitative monitoring of membrane receptor expression induced alterations in the biophysical and signaling properties of single living cells.

  3. Specific binding of the regulatory protein ExpG to promoter regions of the galactoglucan biosynthesis gene cluster of Sinorhizobium meliloti--a combined molecular biology and force spectroscopy investigation.

    PubMed

    Bartels, Frank Wilco; Baumgarth, Birgit; Anselmetti, Dario; Ros, Robert; Becker, Anke

    2003-08-01

    Specific protein-DNA interaction is fundamental for all aspects of gene transcription. We focus on a regulatory DNA-binding protein in the Gram-negative soil bacterium Sinorhizobium meliloti 2011, which is capable of fixing molecular nitrogen in a symbiotic interaction with alfalfa plants. The ExpG protein plays a central role in regulation of the biosynthesis of the exopolysaccharide galactoglucan, which promotes the establishment of symbiosis. ExpG is a transcriptional activator of exp gene expression. We investigated the molecular mechanism of binding of ExpG to three associated target sequences in the exp gene cluster with standard biochemical methods and single molecule force spectroscopy based on the atomic force microscope (AFM). Binding of ExpG to expA1, expG-expD1, and expE1 promoter fragments in a sequence specific manner was demonstrated, and a 28 bp conserved region was found. AFM force spectroscopy experiments confirmed the specific binding of ExpG to the promoter regions, with unbinding forces ranging from 50 to 165 pN in a logarithmic dependence from the loading rates of 70-79000 pN/s. Two different regimes of loading rate-dependent behaviour were identified. Thermal off-rates in the range of k(off)=(1.2+/-1.0) x 10(-3)s(-1) were derived from the lower loading rate regime for all promoter regions. In the upper loading rate regime, however, these fragments exhibited distinct differences which are attributed to the molecular binding mechanism.

  4. Force spectroscopy studies on protein-ligand interactions: a single protein mechanics perspective.

    PubMed

    Hu, Xiaotang; Li, Hongbin

    2014-10-01

    Protein-ligand interactions are ubiquitous and play important roles in almost every biological process. The direct elucidation of the thermodynamic, structural and functional consequences of protein-ligand interactions is thus of critical importance to decipher the mechanism underlying these biological processes. A toolbox containing a variety of powerful techniques has been developed to quantitatively study protein-ligand interactions in vitro as well as in living systems. The development of atomic force microscopy-based single molecule force spectroscopy techniques has expanded this toolbox and made it possible to directly probe the mechanical consequence of ligand binding on proteins. Many recent experiments have revealed how ligand binding affects the mechanical stability and mechanical unfolding dynamics of proteins, and provided mechanistic understanding on these effects. The enhancement effect of mechanical stability by ligand binding has been used to help tune the mechanical stability of proteins in a rational manner and develop novel functional binding assays for protein-ligand interactions. Single molecule force spectroscopy studies have started to shed new lights on the structural and functional consequence of ligand binding on proteins that bear force under their biological settings.

  5. Detection of Pathogens Using AFM and SPR

    NASA Astrophysics Data System (ADS)

    Vaseashta, Ashok

    2005-03-01

    A priori detection of pathogens in food and water has become a subject of paramount importance. Several recent incidents have resulted in the government passing stringent regulations for tolerable amounts of contamination of food products. Identification and/or monitoring of bacterial contamination in food are critical. The conventional methods of pathogen detection require time-consuming steps to arrive disembark at meaningful measurement in a timely manner as the detection time exceeds the time in which perishable food recycles through the food chain distribution. The aim of this presentation is to outline surface plasmon resonance (SPR) and atomic force microscopy (AFM) as two methods for fast detect6ion of pathogens. Theoretical basis of SPR and experimental results of SPR and AFM on E. coli O157:H7 and prion are presented.

  6. Acquisition of a Modular, Multi-laser, Raman-AFM Instrument for Multdisciplinary Research

    DTIC Science & Technology

    2015-04-28

    vapor deposition on copper foils. The four lasers range from the blue to 785 nm and provides a unique handle to determine excitation dependence of...Acquisition of a Modular, Multi- laser , Raman- AFM Instrument for Multdisciplinary Research A four- laser , confocal Raman/Atomic Force Scanning... laser , Raman-AFM Instrument for Multdisciplinary Research Report Title A four- laser , confocal Raman/Atomic Force Scanning microscope (Raman-AFM

  7. Harmonic force spectroscopy reveals a force-velocity curve from a single human beta cardiac myosin motor

    NASA Astrophysics Data System (ADS)

    Sung, Jongmin; Nag, Suman; Vestergaard, Christian; Mortensen, Kim; Flyvbjerg, Henrik; Spudich, James

    2014-03-01

    A muscle contracts rapidly under low load, but slowly under high load. Its molecular mechanisms remain to be elucidated, however. During contraction, myosins in thick filaments interact with actin in thin filaments in the sarcomere, cycling between a strongly bound (force producing) state and a weakly bound (relaxed) state. Huxley et al. have previously proposed that the transition from the strong to the weak interaction can be modulated by a load. We use a new method we call ``harmonic force spectroscopy'' to extract a load-velocity curve from a single human beta cardiac myosin II motor. With a dual-beam optical trap, we hold an actin dumbbell over a myosin molecule anchored to the microscope stage that oscillates sinusoidally. Upon binding, the motor experiences an oscillatory load with a mean that is directed forward or backward, depending on binding location We find that the bound time at saturating [ATP] is exponentially correlated with the mean load, which is explained by Arrhenius transition theory. With a stroke size measurement, we obtained a load-velocity curve from a single myosin. We compare the curves for wild-type motors with mutants that cause hypertrophic cardiomyopathies, to understand the effects on the contractile cycle

  8. Investigating the binding behaviour of two avidin-based testosterone binders using molecular recognition force spectroscopy.

    PubMed

    Rangl, Martina; Leitner, Michael; Riihimäki, Tiina; Lehtonen, Soili; Hytönen, Vesa P; Gruber, Hermann J; Kulomaa, Markku; Hinterdorfer, Peter; Ebner, Andreas

    2014-02-01

    Molecular recognition force spectroscopy, a biosensing atomic force microscopy technique allows to characterise the dissociation of ligand-receptor complexes at the molecular level. Here, we used molecular recognition force spectroscopy to study the binding capability of recently developed testosterone binders. The two avidin-based proteins called sbAvd-1 and sbAvd-2 are expected to bind both testosterone and biotin but differ in their binding behaviour towards these ligands. To explore the ligand binding and dissociation energy landscape of these proteins, we tethered biotin or testosterone to the atomic force microscopy probe while the testosterone-binding protein was immobilized on the surface. Repeated formation and rupture of the ligand-receptor complex at different pulling velocities allowed determination of the loading rate dependence of the complex-rupturing force. In this way, we obtained the molecular dissociation rate (k(off)) and energy landscape distances (x(β)) of the four possible complexes: sbAvd-1-biotin, sbAvd-1-testosterone, sbAvd-2-biotin and sbAvd-2-testosterone. It was found that the kinetic off-rates for both proteins and both ligands are similar. In contrast, the x(β) values, as well as the probability of complex formations, varied considerably. In addition, competitive binding experiments with biotin and testosterone in solution differ significantly for the two testosterone-binding proteins, implying a decreased cross-reactivity of sbAvd-2. Unravelling the binding behaviour of the investigated testosterone-binding proteins is expected to improve their usability for possible sensing applications.

  9. Force spectroscopy of DNA: there is still a lot to learn

    NASA Astrophysics Data System (ADS)

    Paik, D. H.; Perkins, Thomas T.

    2012-10-01

    Single-molecule studies of the mechanical properties of individual double-stranded DNA have excited interest across many scientific disciplines because of DNA's fundamental role in biology and DNA's remarkable overstretching transition at higher forces. Here, we discuss a recent result on the overstretching transition of DNA and on the dynamics of dye molecules intercalating into DNA under tension. Overstretching DNA is mechanical transition whereby DNA's extension increases by 70% at 65 pN. Notwithstanding more than a decade of experimental and theoretical studies, there remains significant debate on the nature of overstretched DNA. We developed a topologically closed but torsionally unconstrained DNA assay that contains no nicks or free ends. DNA in this assay exhibited the canonical overstretching transition at 65 pN but without hysteresis upon retraction. Controlled introduction of a nick led to hysteresis in the force extension curve. Moreover, the degree of hysteresis increased with the number of nicks. In the second study, we isolated the effects of binding and intercalation of a DNA staining dye, by combining single molecule force spectroscopy with simple buffer exchange. We showed that force-enhanced intercalation can occur from a reservoir of bound dye that was not bis-intercalated, yet remained out of equilibrium with free dye for long periods (<5 min for YOPRO and <2 hr for YOYO). Our work highlights that binding/unbinding and intercalation/de-intercalation are distinct processes that can occur on very different time scales. Taken together, these works highlight ongoing discoveries based on a twenty year old technique, force spectroscopy of single DNA molecules.

  10. Single-cell force spectroscopy of the medically important Staphylococcus epidermidis-Candida albicans interaction

    NASA Astrophysics Data System (ADS)

    Beaussart, Audrey; Herman, Philippe; El-Kirat-Chatel, Sofiane; Lipke, Peter N.; Kucharíková, Soňa; van Dijck, Patrick; Dufrêne, Yves F.

    2013-10-01

    Despite the clinical importance of bacterial-fungal interactions, their molecular details are poorly understood. A hallmark of such medically important interspecies associations is the interaction between the two nosocomial pathogens Staphylococcus aureus and Candida albicans, which can lead to mixed biofilm-associated infections with enhanced antibiotic resistance. Here, we use single-cell force spectroscopy (SCFS) to quantify the forces engaged in bacterial-fungal co-adhesion, focusing on the poorly investigated S. epidermidis-C. albicans interaction. Force curves recorded between single bacterial and fungal germ tubes showed large adhesion forces (~5 nN) with extended rupture lengths (up to 500 nm). By contrast, bacteria poorly adhered to yeast cells, emphasizing the important role of the yeast-to-hyphae transition in mediating adhesion to bacterial cells. Analysis of mutant strains altered in cell wall composition allowed us to distinguish the main fungal components involved in adhesion, i.e. Als proteins and O-mannosylations. We suggest that the measured co-adhesion forces are involved in the formation of mixed biofilms, thus possibly as well in promoting polymicrobial infections. In the future, we anticipate that this SCFS platform will be used in nanomedicine to decipher the molecular mechanisms of a wide variety of pathogen-pathogen interactions and may help in designing novel anti-adhesion agents.

  11. Dwell-time distribution analysis of polyprotein unfolding using force-clamp spectroscopy.

    PubMed

    Brujic, Jasna; Hermans, Rodolfo I Z; Garcia-Manyes, Sergi; Walther, Kirstin A; Fernandez, Julio M

    2007-04-15

    Using the recently developed single molecule force-clamp technique we quantitatively measure the kinetics of conformational changes of polyprotein molecules at a constant force. In response to an applied force of 110 pN, we measure the dwell times of 1647 unfolding events of individual ubiquitin modules within each protein chain. We then establish a rigorous method for analyzing force-clamp data using order statistics. This allows us to test the success of a history-independent, two-state model in describing the kinetics of the unfolding process. We find that the average unfolding trajectory is independent of the number of protein modules N in each trajectory, which varies between 3 and 12 (the engineered protein length), suggesting that the unfolding events in each chain are uncorrelated. We then derive a binomial distribution of dwell times to describe the stochastic dynamics of protein unfolding. This distribution successfully describes 81% of the data with a single rate constant of alpha = 0.6 s(-1) for all N. The remainder of the data that cannot be accounted for suggests alternative unfolding barriers in the energy landscape of the protein. This method investigates the statistical features of unfolding beyond the average measurement of a single rate constant, thus providing an attractive alternative for measuring kinetics by force-clamp spectroscopy.

  12. Dielectrophoretic Tweezers as a Platform for Single Molecular Force Spectroscopy in a Highly Parallel Format

    NASA Astrophysics Data System (ADS)

    Cheng, Peng; Barrett, Michael; Oliver, Piercen; Vezenov, Dmitri

    2012-02-01

    Miniaturization has driven down the cost of tools used in bioanalysis and diagnostics, with single molecules becoming the ultimate detection limit. I will describe how one can exploit mechanical properties of individual biomolecules to determine changes in their state or structure. Our aim is to build a force-spectroscopy-on-a-chip device that can detect and manipulate many (millions) single molecules in parallel. A critical element of this approach is the design of materials properties of molecular handles or probes. By tuning interactions of these probes with electric fields which generate by a simple electrode geometry, we are able to apply piconewton forces to individual DNA molecules and record their response with a single base sensitivity. I will present how we determined the approximate crossover frequency between negative and positive DEP using plain electrodes instead of conventional micro-structures. The technique is attractive not only for conducting single molecule force spectroscopy but also for label-free single cell detection. I will discuss potential applications of this approach to high throughput analyses such as genome sequencing and HIV detection.

  13. Investigating biomolecular recognition at the cell surface using atomic force microscopy.

    PubMed

    Wang, Congzhou; Yadavalli, Vamsi K

    2014-05-01

    Probing the interaction forces that drive biomolecular recognition on cell surfaces is essential for understanding diverse biological processes. Force spectroscopy has been a widely used dynamic analytical technique, allowing measurement of such interactions at the molecular and cellular level. The capabilities of working under near physiological environments, combined with excellent force and lateral resolution make atomic force microscopy (AFM)-based force spectroscopy a powerful approach to measure biomolecular interaction forces not only on non-biological substrates, but also on soft, dynamic cell surfaces. Over the last few years, AFM-based force spectroscopy has provided biophysical insight into how biomolecules on cell surfaces interact with each other and induce relevant biological processes. In this review, we focus on describing the technique of force spectroscopy using the AFM, specifically in the context of probing cell surfaces. We summarize recent progress in understanding the recognition and interactions between macromolecules that may be found at cell surfaces from a force spectroscopy perspective. We further discuss the challenges and future prospects of the application of this versatile technique.

  14. Optimization of phase contrast in bimodal amplitude modulation AFM

    PubMed Central

    Damircheli, Mehrnoosh; Payam, Amir F

    2015-01-01

    Summary Bimodal force microscopy has expanded the capabilities of atomic force microscopy (AFM) by providing high spatial resolution images, compositional contrast and quantitative mapping of material properties without compromising the data acquisition speed. In the first bimodal AFM configuration, an amplitude feedback loop keeps constant the amplitude of the first mode while the observables of the second mode have not feedback restrictions (bimodal AM). Here we study the conditions to enhance the compositional contrast in bimodal AM while imaging heterogeneous materials. The contrast has a maximum by decreasing the amplitude of the second mode. We demonstrate that the roles of the excited modes are asymmetric. The operational range of bimodal AM is maximized when the second mode is free to follow changes in the force. We also study the contrast in trimodal AFM by analyzing the kinetic energy ratios. The phase contrast improves by decreasing the energy of second mode relative to those of the first and third modes. PMID:26114079

  15. Multilayer silicon rich oxy-nitride films characterization by SIMS, VASE and AFM

    NASA Astrophysics Data System (ADS)

    Barozzi, M.; Vanzetti, L.; Iacob, E.; Bersani, M.; Anderle, M.; Pucker, G.; Kompocholis, C.; Ghulinyan, M.; Bellutti, P.

    2008-03-01

    In this work secondary ion mass spectrometry (SIMS), variable angle spectroscopy ellipsometry (VASE) and atomic force microscopy (AFM) are used to investigate the structure, composition and morphology of multilayer SRON films. Three/four SRON sequential layers were deposited on silicon wafers by PECVD and silicon, nitrogen and oxygen content was varied by changing the N2O/SiH4 ratio. The total thickness of the resulting SRON stack is about 50nm. SIMS analyses of NCs+, OCs+, SiCs+, in MCs+ methodology are performed by a Cameca SC-ultra instrument. Depth profiles are obtained at 500eV of primary beam impact energy with sample rotation. An approximate method to obtain silicon concentration is used. Total layer thickness are obtained from both SIMS and VASE measurements. In addition, we compare the thickness of the single layers obtained from VASE with the SIMS depth profiles. A detailed analysis of films morphology is obtained by AFM. The SRON stack is sputtered by SIMS until a certain layer is exposed, which is then analyzed by AFM. The sputtered layers are then etched in HF solution to better resolve the exposed nano-crystals.

  16. Characterizing Cell Mechanics with AFM and Microfluidics

    NASA Astrophysics Data System (ADS)

    Walter, N.; Micoulet, A.; Suresh, S.; Spatz, J. P.

    2007-03-01

    Cell mechanical properties and functionality are mainly determined by the cytoskeleton, besides the cell membrane, the nucleus and the cytosol, and depend on various parameters e.g. surface chemistry and rigidity, surface area and time available for cell spreading, nutrients and drugs provided in the culture medium. Human epithelial pancreatic and mammary cancer cells and their keratin intermediate filaments are the main focus of our work. We use Atomic Force Microscopy (AFM) to study cells adhering to substrates and Microfluidic Channels to probe cells in suspension, respectively. Local and global properties are extracted by varying AFM probe tip size and the available adhesion area for cells. Depth-sensing, instrumented indentation tests with AFM show a clear difference in contact stiffness for cells that are spread of controlled substrates and those that are loosely attached. Microfluidic Channels are utilized in parallel to evaluate cell deformation and ``flow resistance'', which are dependent on channel cross section, flow rate, cell nucleus size and the mechanical properties of cytoskeleton and membrane. The results from the study are used to provide some broad and quantitative assessments of the connections between cellular/subcellular mechanics and biochemical origins of disease states.

  17. Vibration signature analysis of AFM images

    SciTech Connect

    Joshi, G.A.; Fu, J.; Pandit, S.M.

    1995-12-31

    Vibration signature analysis has been commonly used for the machine condition monitoring and the control of errors. However, it has been rarely employed for the analysis of the precision instruments such as an atomic force microscope (AFM). In this work, an AFM was used to collect vibration data from a sample positioning stage under different suspension and support conditions. Certain structural characteristics of the sample positioning stage show up as a result of the vibration signature analysis of the surface height images measured using an AFM. It is important to understand these vibration characteristics in order to reduce vibrational uncertainty, improve the damping and structural design, and to eliminate the imaging imperfections. The choice of method applied for vibration analysis may affect the results. Two methods, the data dependent systems (DDS) analysis and the Welch`s periodogram averaging method were investigated for application to this problem. Both techniques provide smooth spectrum plots from the data. Welch`s periodogram provides a coarse resolution as limited by the number of samples and requires a choice of window to be decided subjectively by the user. The DDS analysis provides sharper spectral peaks at a much higher resolution and a much lower noise floor. A decomposition of the signal variance in terms of the frequencies is provided as well. The technique is based on an objective model adequacy criterion.

  18. Interactions of Histone Acetyltransferase p300 with the Nuclear Proteins Histone and HMGB1, As Revealed by Single Molecule Atomic Force Spectroscopy.

    PubMed

    Banerjee, S; Rakshit, T; Sett, S; Mukhopadhyay, R

    2015-10-22

    One of the important properties of the transcriptional coactivator p300 is histone acetyltransferase (HAT) activity that enables p300 to influence chromatin action via histone modulation. p300 can exert its HAT action upon the other nuclear proteins too--one notable example being the transcription-factor-like protein HMGB1, which functions also as a cytokine, and whose accumulation in the cytoplasm, as a response to tissue damage, is triggered by its acetylation. Hitherto, no information on the structure and stability of the complexes between full-length p300 (p300FL) (300 kDa) and the histone/HMGB1 proteins are available, probably due to the presence of unstructured regions within p300FL that makes it difficult to be crystallized. Herein, we have adopted the high-resolution atomic force microscopy (AFM) approach, which allows molecularly resolved three-dimensional contour mapping of a protein molecule of any size and structure. From the off-rate and activation barrier values, obtained using single molecule dynamic force spectroscopy, the biochemical proposition of preferential binding of p300FL to histone H3, compared to the octameric histone, can be validated. Importantly, from the energy landscape of the dissociation events, a model for the p300-histone and the p300-HMGB1 dynamic complexes that HAT forms, can be proposed. The lower unbinding forces of the complexes observed in acetylating conditions, compared to those observed in non-acetylating conditions, indicate that upon acetylation, p300 tends to weakly associate, probably as an outcome of charge alterations on the histone/HMGB1 surface and/or acetylation-induced conformational changes. To our knowledge, for the first time, a single molecule level treatment of the interactions of HAT, where the full-length protein is considered, is being reported.

  19. AFM single-cell force spectroscopy links altered nuclear and cytoskeletal mechanics to defective cell adhesion in cardiac myocytes with a nuclear lamin mutation

    PubMed Central

    Lanzicher, Thomas; Martinelli, Valentina; Long, Carlin S; Del Favero, Giorgia; Puzzi, Luca; Borelli, Massimo; Mestroni, Luisa; Taylor, Matthew R G; Sbaizero, Orfeo

    2015-01-01

    Previous investigations suggested that lamin A/C gene (LMNA) mutations, which cause a variety of human diseases including muscular dystrophies and cardiomyopathies, alter the nuclear mechanical properties. We hypothesized that biomechanical changes may extend beyond the nucleus. PMID:26309016

  20. Elastic Properties of Nucleic Acids by Single-Molecule Force Spectroscopy.

    PubMed

    Camunas-Soler, Joan; Ribezzi-Crivellari, Marco; Ritort, Felix

    2016-07-05

    We review the current knowledge on the use of single-molecule force spectroscopy techniques to extrapolate the elastic properties of nucleic acids. We emphasize the lesser-known elastic properties of single-stranded DNA. We discuss the importance of accurately determining the elastic response in pulling experiments, and we review the simplest models used to rationalize the experimental data as well as the experimental approaches used to pull single-stranded DNA. Applications used to investigate DNA conformational transitions and secondary structure formation are also highlighted. Finally, we provide an overview of the effects of salt and temperature and briefly discuss the effects of contour length and sequence dependence.

  1. Domain Dynamics in Piezoresponse Force Spectroscopy: Quantitative Deconvolution and Hysteresis Loop Fine Structure

    SciTech Connect

    Bdikin, Igor; Kholkin, Andrei; Morozovska, A. N.; Svechnikov, S. V.; Kim, S.-H.; Kalinin, Sergei V

    2008-01-01

    Domain dynamics in the Piezoresponse Force Spectroscopy (PFS) experiment is studied using the combination of local hysteresis loop acquisition with simultaneous domain imaging. The analytical theory for PFS signal from domain of arbitrary cross-section and length is developed for the analysis of experimental data on Pb(Zr,Ti)O3 polycrystalline films. The results suggest formation of oblate domain at early stage of the nucleation and growth, consistent with efficient screening of depolarization field. The fine structure of the hysteresis loop is shown to be related to the observed jumps in the domain geometry during domain wall propagation (nanoscale Barkhausen jumps), indicative of strong domain-defect interactions.

  2. Harmonic force spectroscopy measures load-dependent kinetics of individual human β-cardiac myosin molecules

    NASA Astrophysics Data System (ADS)

    Sung, Jongmin; Nag, Suman; Mortensen, Kim I.; Vestergaard, Christian L.; Sutton, Shirley; Ruppel, Kathleen; Flyvbjerg, Henrik; Spudich, James A.

    2015-08-01

    Molecular motors are responsible for numerous cellular processes from cargo transport to heart contraction. Their interactions with other cellular components are often transient and exhibit kinetics that depend on load. Here, we measure such interactions using `harmonic force spectroscopy'. In this method, harmonic oscillation of the sample stage of a laser trap immediately, automatically and randomly applies sinusoidally varying loads to a single motor molecule interacting with a single track along which it moves. The experimental protocol and the data analysis are simple, fast and efficient. The protocol accumulates statistics fast enough to deliver single-molecule results from single-molecule experiments. We demonstrate the method's performance by measuring the force-dependent kinetics of individual human β-cardiac myosin molecules interacting with an actin filament at physiological ATP concentration. We show that a molecule's ADP release rate depends exponentially on the applied load, in qualitative agreement with cardiac muscle, which contracts with a velocity inversely proportional to external load.

  3. Harmonic force spectroscopy measures load-dependent kinetics of individual human β-cardiac myosin molecules.

    PubMed

    Sung, Jongmin; Nag, Suman; Mortensen, Kim I; Vestergaard, Christian L; Sutton, Shirley; Ruppel, Kathleen; Flyvbjerg, Henrik; Spudich, James A

    2015-08-04

    Molecular motors are responsible for numerous cellular processes from cargo transport to heart contraction. Their interactions with other cellular components are often transient and exhibit kinetics that depend on load. Here, we measure such interactions using 'harmonic force spectroscopy'. In this method, harmonic oscillation of the sample stage of a laser trap immediately, automatically and randomly applies sinusoidally varying loads to a single motor molecule interacting with a single track along which it moves. The experimental protocol and the data analysis are simple, fast and efficient. The protocol accumulates statistics fast enough to deliver single-molecule results from single-molecule experiments. We demonstrate the method's performance by measuring the force-dependent kinetics of individual human β-cardiac myosin molecules interacting with an actin filament at physiological ATP concentration. We show that a molecule's ADP release rate depends exponentially on the applied load, in qualitative agreement with cardiac muscle, which contracts with a velocity inversely proportional to external load.

  4. AFM imaging of fenestrated liver sinusoidal endothelial cells.

    PubMed

    Braet, F; Wisse, E

    2012-12-01

    Each microscope with its dedicated sample preparation technique provides the investigator with a specific set of data giving an instrument-determined (or restricted) insight into the structure and function of a tissue, a cell or parts thereof. Stepwise improvements in existing techniques, both instrumental and preparative, can sometimes cross barriers in resolution and image quality. Of course, investigators get really excited when completely new principles of microscopy and imaging are offered in promising new instruments, such as the AFM. The present paper summarizes a first phase of studies on the thin endothelial cells of the liver. It describes the preparation-dependent differences in AFM imaging of these cells after isolation. Special point of interest concerned the dynamics of the fenestrae, thought to filter lipid-carrying particles during their transport from the blood to the liver cells. It also describes the attempts to image the details of these cells when alive in cell cultures. It explains what physical conditions, mainly contributed to the scanning stylus, are thought to play a part in the limitations in imaging these cells. The AFM also offers promising specifications to those interested in cell surface details, such as membrane-associated structures, receptors, coated pits, cellular junctions and molecular aggregations or domains. The AFM also offers nano-manipulation possibilities, strengths and elasticity measurements, force interactions, affinity measurements, stiffness and other physical aspects of membranes and cytoskeleton. The potential for molecular approaches is there. New developments in cantilever construction and computer software promise to bring real time video imaging to the AFM. Home made accessories for the first generation of AFM are now commodities in commercial instruments and make the life of the AFM microscopist easier. Also, the combination of different microscopies, such as AFM and TEM, or AFM and SEM find their way to the

  5. AFM AND XPS Characterization of Zinc-Aluminum Alloy Coatings with Attention to Surface Dross and Flow Lines

    NASA Astrophysics Data System (ADS)

    Harding, Felipe A.; Alarcon, Nelson A.; Toledo, Pedro G.

    Surfaces of various zinc-aluminum alloy (Zn-Al) coated steel samples are studied with attention to foreign surface dross by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS/ESCA). AFM topographic maps of zinc-aluminum alloy surfaces free of dross reveal the perfect nanoscale details of two kinds of dendrites: branched and globular. In all magnifications the dendrites appear smooth and, in general, very clean. XPS analysis of the extreme surface of a Zn-Al sample reveals Al, Zn, Si and O as the main components. The XPS results show no segregation or separation of phases other than those indicated by the ternary Al-Zn-Si diagram. For surfaces of Zn-Al plagued with impurities, high resolution AFM topographic maps reveal three situations: (1) areas with well-defined dendrites, relatively free of dross; (2) areas with small, millimeter-sized black spots known as dross; and (3) areas with large black stains, known as flow lines. Dendrite deformation and dross accumulation increase notably in the neighborhood, apparently clean to the naked eye, of dross or flow lines. XPS results of areas with dross and flow lines indicate unacceptable high concentration of Si and important Si phase separation. These results, in the light of AFM work, reveal that dross and flow lines are a consequence of a high local concentration of Si from high melting point silica and silicate impurities in the Zn-Al alloy source.

  6. A broadband x-ray imaging spectroscopy with high-angular resolution: the FORCE mission

    NASA Astrophysics Data System (ADS)

    Mori, Koji; Tsuru, Takeshi Go; Nakazawa, Kazuhiro; Ueda, Yoshihiro; Okajima, Takashi; Murakami, Hiroshi; Awaki, Hisamitsu; Matsumoto, Hironori; Fukazawa, Yasushi; Tsunemi, Hiroshi; Takahashi, Tadayuki; Zhang, William W.

    2016-07-01

    We are proposing FORCE (Focusing On Relativistic universe and Cosmic Evolution) as a future Japan-lead Xray observatory to be launched in the mid 2020s. Hitomi (ASTRO-H) possesses a suite of sensitive instruments enabling the highest energy-resolution spectroscopy in soft X-ray band, a broadband X-ray imaging spectroscopy in soft and hard X-ray bands, and further high energy coverage up to soft gamma-ray band. FORCE is the direct successor to the broadband X-ray imaging spectroscopy aspect of Hitomi (ASTRO-H) with significantly higher angular resolution. The current design of FORCE defines energy band pass of 1-80 keV with angular resolution of < 15 in half-power diameter, achieving a 10 times higher sensitivity above 10 keV compared to any previous missions with simultaneous soft X-ray coverage. Our primary scientific objective is to trace the cosmic formation history by searching for "missing black holes" in various mass-scales: "buried supermassive black holes (SMBHs)" (> 104 M⊙) residing in the center of galaxies in a cosmological distance, "intermediate-mass black holes" (102-104 M⊙) acting as the possible seeds from which SMBHs grow, and "orphan stellar-mass black holes" (< 102 M⊙) without companion in our Galaxy. In addition to these missing BHs, hunting for the nature of relativistic particles at various astrophysical shocks is also in our scope, utilizing the broadband X-ray coverage with high angular-resolution. FORCE are going to open a new era in these fields. The satellite is proposed to be launched with the Epsilon vehicle that is a Japanese current solid-fuel rocket. FORCE carries three identical pairs of Super-mirror and wide-band X-ray detector. The focal length is currently planned to be 10 m. The silicon mirror with multi-layer coating is our primary choice to achieve lightweight, good angular optics. The detector is a descendant of hard X-ray imager onboard Hitomi (ASTRO-H) replacing its silicon strip detector with SOI-CMOS silicon pixel

  7. Quantifying the effect of electric current on cell adhesion studied by single-cell force spectroscopy.

    PubMed

    Jaatinen, Leena; Young, Eleanore; Hyttinen, Jari; Vörös, János; Zambelli, Tomaso; Demkó, László

    2016-03-20

    This study presents the effect of external electric current on the cell adhesive and mechanical properties of the C2C12 mouse myoblast cell line. Changes in cell morphology, viability, cytoskeleton, and focal adhesion structure were studied by standard staining protocols, while single-cell force spectroscopy based on the fluidic force microscopy technology provided a rapid, serial quantification and detailed analysis of cell adhesion and its dynamics. The setup allowed measurements of adhesion forces up to the μN range, and total detachment distances over 40 μm. Force-distance curves have been fitted with a simple elastic model including a cell detachment protocol in order to estimate the Young's modulus of the cells, as well as to reveal changes in the dynamic properties as functions of the applied current dose. While the cell spreading area decreased monotonously with increasing current doses, small current doses resulted only in differences related to cell elasticity. Current doses above 11 As/m(2), however, initiated more drastic changes in cell morphology, viability, cellular structure, as well as in properties related to cell adhesion. The observed differences, eventually leading to cell death toward higher doses, might originate from both the decrease in pH and the generation of reactive oxygen species.

  8. Antigen-antibody biorecognition events as discriminated by noise analysis of force spectroscopy curves

    NASA Astrophysics Data System (ADS)

    Bizzarri, Anna Rita; Cannistraro, Salvatore

    2014-08-01

    Atomic force spectroscopy is able to extract kinetic and thermodynamic parameters of biomolecular complexes provided that the registered unbinding force curves could be reliably attributed to the rupture of the specific complex interactions. To this aim, a commonly used strategy is based on the analysis of the stretching features of polymeric linkers which are suitably introduced in the biomolecule-substrate immobilization procedure. Alternatively, we present a method to select force curves corresponding to specific biorecognition events, which relies on a careful analysis of the force fluctuations of the biomolecule-functionalized cantilever tip during its approach to the partner molecules immobilized on a substrate. In the low frequency region, a characteristic 1/f α noise with α equal to one (flickering noise) is found to replace white noise in the cantilever fluctuation power spectrum when, and only when, a specific biorecognition process between the partners occurs. The method, which has been validated on a well-characterized antigen-antibody complex, represents a fast, yet reliable alternative to the use of linkers which may involve additional surface chemistry and reproducibility concerns.

  9. Antigen-antibody biorecognition events as discriminated by noise analysis of force spectroscopy curves.

    PubMed

    Bizzarri, Anna Rita; Cannistraro, Salvatore

    2014-08-22

    Atomic force spectroscopy is able to extract kinetic and thermodynamic parameters of biomolecular complexes provided that the registered unbinding force curves could be reliably attributed to the rupture of the specific complex interactions. To this aim, a commonly used strategy is based on the analysis of the stretching features of polymeric linkers which are suitably introduced in the biomolecule-substrate immobilization procedure. Alternatively, we present a method to select force curves corresponding to specific biorecognition events, which relies on a careful analysis of the force fluctuations of the biomolecule-functionalized cantilever tip during its approach to the partner molecules immobilized on a substrate. In the low frequency region, a characteristic 1/f (α) noise with α equal to one (flickering noise) is found to replace white noise in the cantilever fluctuation power spectrum when, and only when, a specific biorecognition process between the partners occurs. The method, which has been validated on a well-characterized antigen-antibody complex, represents a fast, yet reliable alternative to the use of linkers which may involve additional surface chemistry and reproducibility concerns.

  10. Mechanical stability of bivalent transition metal complexes analyzed by single-molecule force spectroscopy

    PubMed Central

    Gensler, Manuel; Eidamshaus, Christian; Taszarek, Maurice; Reissig, Hans-Ulrich

    2015-01-01

    Summary Multivalent biomolecular interactions allow for a balanced interplay of mechanical stability and malleability, and nature makes widely use of it. For instance, systems of similar thermal stability may have very different rupture forces. Thus it is of paramount interest to study and understand the mechanical properties of multivalent systems through well-characterized model systems. We analyzed the rupture behavior of three different bivalent pyridine coordination complexes with Cu2+ in aqueous environment by single-molecule force spectroscopy. Those complexes share the same supramolecular interaction leading to similar thermal off-rates in the range of 0.09 and 0.36 s−1, compared to 1.7 s−1 for the monovalent complex. On the other hand, the backbones exhibit different flexibility, and we determined a broad range of rupture lengths between 0.3 and 1.1 nm, with higher most-probable rupture forces for the stiffer backbones. Interestingly, the medium-flexible connection has the highest rupture forces, whereas the ligands with highest and lowest rigidity seem to be prone to consecutive bond rupture. The presented approach allows separating bond and backbone effects in multivalent model systems. PMID:26124883

  11. Single-molecule force-conductance spectroscopy of hydrogen-bonded complexes

    NASA Astrophysics Data System (ADS)

    Pirrotta, Alessandro; De Vico, Luca; Solomon, Gemma C.; Franco, Ignacio

    2017-03-01

    The emerging ability to study physical properties at the single-molecule limit highlights the disparity between what is observable in an ensemble of molecules and the heterogeneous contributions of its constituent parts. A particularly convenient platform for single-molecule studies are molecular junctions where forces and voltages can be applied to individual molecules, giving access to a series of electromechanical observables that can form the basis of highly discriminating multidimensional single-molecule spectroscopies. Here, we computationally examine the ability of force and conductance to inform about molecular recognition events at the single-molecule limit. For this, we consider the force-conductance characteristics of a prototypical class of hydrogen bonded bimolecular complexes sandwiched between gold electrodes. The complexes consist of derivatives of a barbituric acid and a Hamilton receptor that can form up to six simultaneous hydrogen bonds. The simulations combine classical molecular dynamics of the mechanical deformation of the junction with non-equilibrium Green's function computations of the electronic transport. As shown, in these complexes hydrogen bonds mediate transport either by directly participating as a possible transport pathway or by stabilizing molecular conformations with enhanced conductance properties. Further, we observe that force-conductance correlations can be very sensitive to small changes in the chemical structure of the complexes and provide detailed information about the behavior of single molecules that cannot be gleaned from either measurement alone. In fact, there are regions during the elongation that are only mechanically active, others that are only conductance active, and regions where both force and conductance changes as the complex is mechanically manipulated. The implication is that force and conductance provide complementary information about the evolution of molecules in junctions that can be used to

  12. Nanomechanics of new materials — AFM and computer modelling studies of trichoptera silk

    NASA Astrophysics Data System (ADS)

    Strzelecki, Janusz; Strzelecka, Joanna; Mikulska, Karolina; Tszydel, Mariusz; Balter, Aleksander; Nowak, Wiesław

    2011-04-01

    Caddisfly (Trichopera) can glue diverse material underwater with a silk fiber. This makes it a particularly interesting subject for biomimetcs. Better understanding of silk composition and structure could lead to an adhesive capable to close bleeding wounds or to new biomaterials. However, while spiderweb or silkworm secretion is well researched, caddisfly silk is still poorly understood. Here we report a first nanomechanical analysis of H. Angustipennis caddisfly silk fiber. An Atomic Force Microscope (AFM) imaging shows dense 150 nm bumps on silk surface, which can be identified as one of features responsible for its outstanding adhesive properties. AFM force spectroscopy at the fiber surface showed, among others, characteristic saw like pattern. This pattern is attributed to sacrificial bond stretching and enhances energy dissipation in mechanical deformation. Similarities of some force curves observed on Tegenaria domestica spiderweb and caddisfly silk are also discussed. Steered Molecular Dynamics simulations revealed that the strength of short components of Fib-H HA species molecules, abundant in Trichoptera silk is critically dependent on calcium presence.

  13. Supramolecular self-assembly of linear oligosilsesquioxanes on mica--AFM surface imaging and hydrophilicity studies.

    PubMed

    Kowalewska, Anna; Nowacka, Maria; Tracz, Adam; Makowski, Tomasz

    2015-06-28

    Linear oligomeric [2-(carboxymethylthio)ethylsilsesquioxanes] (LPSQ-COOH) adsorb spontaneously on muscovite mica and form smooth, well-ordered lamellar structures at the liquid-solid interface. Side carboxylic groups, having donor-acceptor character with regard to hydrogen bonds, are engaged both in multipoint molecule-to-substrate interactions and intermolecular cross-linking. The unique arrangement of silsesquioxane macromolecules, with COOH groups situated at the interface with air, produces highly hydrophilic surfaces of good thermal and solvolytic stability. Supramolecular assemblies of LPSQ-COOH were studied using atomic force microscopy (AFM), angle-resolved X-ray photoelectron spectroscopy (ARXPS) and attenuated total reflectance (ATR) FTIR spectroscopy. Comparative height profile analysis combined with ATR-FTIR studies of the spectral regions characteristic of carboxylic groups and C1s core level envelope by XPS confirmed specific interactions between LPSQ-COOH and mica.

  14. Investigations of the intermolecular forces between RDX and polyethylene by force-distance spectroscopy and molecular dynamics simulations.

    PubMed

    Taylor, D E; Strawhecker, K E; Shanholtz, E R; Sorescu, D C; Sausa, R C

    2014-07-10

    The development of novel nanoenergetic materials with enhanced bulk properties requires an understanding of the intermolecular interactions occurring between molecular components. We investigate the surface interactions between 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and polyethylene (PE) crystals on the basis of combined use of molecular dynamics (MD) simulations and force-distance spectroscopy, in conjunction with Lifshitz macroscopic theory of van der Waals forces between continuous materials. The binding energy in the RDX-PE system depends both on the degree of PE crystallinity and on the RDX crystal face. Our MD simulations yield binding energies of approximately 132 and 120 mJ/m(2) for 100% amorphous and 100% crystalline PE on RDX (210), respectively. The average value is about 36% greater than our experimental value of 81 ± 15 mJ/m(2) for PE (∼48% amorphous) on RDX (210). By comparison, Liftshitz theory predicts a value of about 79 mJ/m(2) for PE interacting with RDX. Our MD simulations also predict larger binding energies for both amorphous and crystalline PE on RDX (210) compared to the RDX (001) surface. Analysis of the interaction potential indicates that about 60% of the binding energy in the PE-RDX system is due to attractive interactions between HPE-ORDX and CPE-NRDX pairs of atoms. Further, amorphous PE shows a much longer interaction distance than crystalline PE with the (210) and (001) RDX surfaces due to the possibility of larger polymer elongations in the case of amorphous PE as strain is applied. Also, we report estimates of the binding energies of energetic materials RDX and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) with PE, propylene, polystyrene, and several fluorine-containing polymers using Lifshitz theory and compare these with reported MD calculations.

  15. Investigation of adhesion and mechanical properties of human glioma cells by single cell force spectroscopy and atomic force microscopy.

    PubMed

    Andolfi, Laura; Bourkoula, Eugenia; Migliorini, Elisa; Palma, Anita; Pucer, Anja; Skrap, Miran; Scoles, Giacinto; Beltrami, Antonio Paolo; Cesselli, Daniela; Lazzarino, Marco

    2014-01-01

    Active cell migration and invasion is a peculiar feature of glioma that makes this tumor able to rapidly infiltrate into the surrounding brain tissue. In our recent work, we identified a novel class of glioma-associated-stem cells (defined as GASC for high-grade glioma--HG--and Gasc for low-grade glioma--LG) that, although not tumorigenic, act supporting the biological aggressiveness of glioma-initiating stem cells (defined as GSC for HG and Gsc for LG) favoring also their motility. Migrating cancer cells undergo considerable molecular and cellular changes by remodeling their cytoskeleton and cell interactions with surrounding environment. To get a better understanding about the role of the glioma-associated-stem cells in tumor progression, cell deformability and interactions between glioma-initiating stem cells and glioma-associated-stem cells were investigated. Adhesion of HG/LG-cancer cells on HG/LG-glioma-associated stem cells was studied by time-lapse microscopy, while cell deformability and cell-cell adhesion strengths were quantified by indentation measurements by atomic force microscopy and single cell force spectroscopy. Our results demonstrate that for both HG and LG glioma, cancer-initiating-stem cells are softer than glioma-associated-stem cells, in agreement with their neoplastic features. The adhesion strength of GSC on GASC appears to be significantly lower than that observed for Gsc on Gasc. Whereas, GSC spread and firmly adhere on Gasc with an adhesion strength increased as compared to that obtained on GASC. These findings highlight that the grade of glioma-associated-stem cells plays an important role in modulating cancer cell adhesion, which could affect glioma cell migration, invasion and thus cancer aggressiveness. Moreover this work provides evidence about the importance of investigating cell adhesion and elasticity for new developments in disease diagnostics and therapeutics.

  16. Investigation of Adhesion and Mechanical Properties of Human Glioma Cells by Single Cell Force Spectroscopy and Atomic Force Microscopy

    PubMed Central

    Andolfi, Laura; Bourkoula, Eugenia; Migliorini, Elisa; Palma, Anita; Pucer, Anja; Skrap, Miran; Scoles, Giacinto; Beltrami, Antonio Paolo; Cesselli, Daniela; Lazzarino, Marco

    2014-01-01

    Active cell migration and invasion is a peculiar feature of glioma that makes this tumor able to rapidly infiltrate into the surrounding brain tissue. In our recent work, we identified a novel class of glioma-associated-stem cells (defined as GASC for high-grade glioma -HG- and Gasc for low-grade glioma -LG-) that, although not tumorigenic, act supporting the biological aggressiveness of glioma-initiating stem cells (defined as GSC for HG and Gsc for LG) favoring also their motility. Migrating cancer cells undergo considerable molecular and cellular changes by remodeling their cytoskeleton and cell interactions with surrounding environment. To get a better understanding about the role of the glioma-associated-stem cells in tumor progression, cell deformability and interactions between glioma-initiating stem cells and glioma-associated-stem cells were investigated. Adhesion of HG/LG-cancer cells on HG/LG-glioma-associated stem cells was studied by time-lapse microscopy, while cell deformability and cell-cell adhesion strengths were quantified by indentation measurements by atomic force microscopy and single cell force spectroscopy. Our results demonstrate that for both HG and LG glioma, cancer-initiating-stem cells are softer than glioma-associated-stem cells, in agreement with their neoplastic features. The adhesion strength of GSC on GASC appears to be significantly lower than that observed for Gsc on Gasc. Whereas, GSC spread and firmly adhere on Gasc with an adhesion strength increased as compared to that obtained on GASC. These findings highlight that the grade of glioma-associated-stem cells plays an important role in modulating cancer cell adhesion, which could affect glioma cell migration, invasion and thus cancer aggressiveness. Moreover this work provides evidence about the importance of investigating cell adhesion and elasticity for new developments in disease diagnostics and therapeutics. PMID:25390644

  17. Amyloid beta oligomers induce neuronal elasticity changes in age-dependent manner: a force spectroscopy study on living hippocampal neurons

    PubMed Central

    Ungureanu, Andreea-Alexandra; Benilova, Iryna; Krylychkina, Olga; Braeken, Dries; De Strooper, Bart; Van Haesendonck, Chris; Dotti, Carlos G.; Bartic, Carmen

    2016-01-01

    Small soluble species of amyloid-beta (Aβ) formed during early peptide aggregation stages are responsible for several neurotoxic mechanisms relevant to the pathology of Alzheimer’s disease (AD), although their interaction with the neuronal membrane is not completely understood. This study quantifies the changes in the neuronal membrane elasticity induced by treatment with the two most common Aβ isoforms found in AD brains: Aβ40 and Aβ42. Using quantitative atomic force microscopy (AFM), we measured for the first time the static elastic modulus of living primary hippocampal neurons treated with pre-aggregated Aβ40 and Aβ42 soluble species. Our AFM results demonstrate changes in the elasticity of young, mature and aged neurons treated for a short time with the two Aβ species pre-aggregated for 2 hours. Neurons aging under stress conditions, showing aging hallmarks, are the most susceptible to amyloid binding and show the largest decrease in membrane stiffness upon Aβ treatment. Membrane stiffness defines the way in which cells respond to mechanical forces in their environment and has been shown to be important for processes such as gene expression, ion-channel gating and neurotransmitter vesicle transport. Thus, one can expect that changes in neuronal membrane elasticity might directly induce functional changes related to neurodegeneration. PMID:27173984

  18. Force spectroscopy predicts thermal stability of immobilized proteins by measuring microbead mechanics.

    PubMed

    Gregurec, Danijela; Velasco-Lozano, Susana; Moya, Sergio E; Vázquez, Luis; López-Gallego, Fernando

    2016-10-26

    Optimal immobilization of enzymes on porous microbeads enables the fabrication of highly active and stable heterogeneous biocatalysts to implement biocatalysis in synthetic and analytical chemistry. However, empirical procedures for enzyme immobilization still prevail over rational ones because there is an unmet need for more comprehensive characterization techniques that aid to understand and trace the immobilization process. Here, we present the use of atomic force spectroscopy (AFS) as an innovative solution to indirectly characterize immobilized proteins on porous materials and monitor the immobilization process in real time. We investigate the mechanical properties of porous agarose microbeads immobilizing proteins by indenting a colloidal probe (silica microparticle) into a single bead. AFS demonstrates that the binding of proteins to the solid matrix of an agarose microbead alters its stiffness. Interestingly, we discovered that irreversible and multivalent immobilizations that make microbeads stiffer also stabilize the immobilized proteins against the temperature. Hence, we propose atomic force spectroscopy as a useful technique to indirectly unravel the stability of the immobilized enzymes investigating the mechanics of the heterogenous biocatalysts as a solid biomaterial beyond the intrinsic mechanics of the proteins.

  19. Probing Single Membrane Proteins by Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Scheuring, S.; Sapra, K. Tanuj; Müller, Daniel J.

    In this book chapter, we describe the working principle of the atomic force microscope (AFM), followed by the applications of AFM in high-resolution imaging and single-molecule force spectroscopy of membrane proteins. In the imaging mode, AFM allows observing the assembly of membrane proteins directly in native membranes approaching a resolution of ~0.5 nm with an outstanding signal-to-noise ratio. Conformational deviations of individual membrane proteins can be observed and their functional states directly imaged. Time-lapse AFM can image membrane proteins at work. In conjunction with high- resolution imaging, the use of the AFM as a single-molecule force spectroscope (SMFS) has gained tremendous importance in recent years. This combination allows to locate the inter- and intramolecular interactions of single membrane proteins. SMFS allows characterization of interactions that guide the folding of proteins and describe the parameters that lead to their destabilization, malfunction and misfolding. Moreover, it enables to measure the interactions established by ligand- and inhibitor-binding and in membrane protein assemblies. Because of its practical use in characterizing various parameters of membrane proteins in their native environment, AFM can be aptly described as a `lab on a tip' device.

  20. The thermal near-field: Coherence, spectroscopy, heat-transfer, and optical forces

    NASA Astrophysics Data System (ADS)

    Jones, Andrew C.; O'Callahan, Brian T.; Yang, Honghua U.; Raschke, Markus B.

    2013-12-01

    One of the most universal physical processes shared by all matter at finite temperature is the emission of thermal radiation. The experimental characterization and theoretical description of far-field black-body radiation was a cornerstone in the development of modern physics with the groundbreaking contributions from Gustav Kirchhoff and Max Planck. With its origin in thermally driven fluctuations of the charge carriers, thermal radiation reflects the resonant and non-resonant dielectric properties of media, which is the basis for far-field thermal emission spectroscopy. However, associated with the underlying fluctuating optical source polarization are fundamentally distinct spectral, spatial, resonant, and coherence properties of the evanescent thermal near-field. These properties have been recently predicted theoretically and characterized experimentally for systems with thermally excited molecular, surface plasmon polariton (SPP), and surface phonon polariton (SPhP) resonances. We review, starting with the early historical developments, the emergence of theoretical models, and the description of the thermal near-field based on the fluctuation-dissipation theory and in terms of the electromagnetic local density of states (EM-LDOS). We discuss the optical and spectroscopic characterization of distance dependence, magnitude, spectral distribution, and coherence of evanescent thermal fields. Scattering scanning near-field microscopy proved instrumental as an enabling technique for the investigations of several of these fundamental thermal near-field properties. We then discuss the role of thermal fields in nano-scale heat transfer and optical forces, and the correlation to the van der Waals, Casimir, and Casimir-Polder forces. We conclude with an outlook on the possibility of intrinsic and extrinsic resonant manipulation of optical forces, control of nano-scale radiative heat transfer with optical antennas and metamaterials, and the use of thermal infrared near

  1. Method and system for near-field spectroscopy using targeted deposition of nanoparticles

    NASA Technical Reports Server (NTRS)

    Anderson, Mark S. (Inventor)

    2012-01-01

    There is provided in one embodiment of the invention a method for analyzing a sample material using surface enhanced spectroscopy. The method comprises the steps of imaging the sample material with an atomic force microscope (AFM) to select an area of interest for analysis, depositing nanoparticles onto the area of interest with an AFM tip, illuminating the deposited nanoparticles with a spectrometer excitation beam, and disengaging the AFM tip and acquiring a localized surface enhanced spectrum. The method may further comprise the step of using the AFM tip to modulate the spectrometer excitation beam above the deposited nanoparticles to obtain improved sensitivity data and higher spatial resolution data from the sample material. The invention further comprises in one embodiment a system for analyzing a sample material using surface enhanced spectroscopy.

  2. Fractal properties of macrophage membrane studied by AFM.

    PubMed

    Bitler, A; Dover, R; Shai, Y

    2012-12-01

    Complexity of cell membrane poses difficulties to quantify corresponding morphology changes during cell proliferation and damage. We suggest using fractal dimension of the cell membrane to quantify its complexity and track changes produced by various treatments. Glutaraldehyde fixed mouse RAW 264.7 macrophage membranes were chosen as model system and imaged in PeakForce QNM (quantitative nanomechanics) mode of AFM (atomic force microscope). The morphology of the membranes was characterized by fractal dimension. The parameter was calculated for set of AFM images by three different methods. The same calculations were done for the AFM images of macrophages treated with colchicine, an inhibitor of the microtubule polymerization, and microtubule stabilizing agent taxol. We conclude that fractal dimension can be additional and useful parameter to characterize the cell membrane complexity and track the morphology changes produced by different treatments.

  3. Reconsideration of dynamic force spectroscopy analysis of streptavidin-biotin interactions.

    PubMed

    Taninaka, Atsushi; Takeuchi, Osamu; Shigekawa, Hidemi

    2010-05-13

    To understand and design molecular functions on the basis of molecular recognition processes, the microscopic probing of the energy landscapes of individual interactions in a molecular complex and their dependence on the surrounding conditions is of great importance. Dynamic force spectroscopy (DFS) is a technique that enables us to study the interaction between molecules at the single-molecule level. However, the obtained results differ among previous studies, which is considered to be caused by the differences in the measurement conditions. We have developed an atomic force microscopy technique that enables the precise analysis of molecular interactions on the basis of DFS. After verifying the performance of this technique, we carried out measurements to determine the landscapes of streptavidin-biotin interactions. The obtained results showed good agreement with theoretical predictions. Lifetimes were also well analyzed. Using a combination of cross-linkers and the atomic force microscope that we developed, site-selective measurement was carried out, and the steps involved in bonding due to microscopic interactions are discussed using the results obtained by site-selective analysis.

  4. In Situ Adsorption Studies at the Solid/Liquid Interface:Characterization of Biological Surfaces and Interfaces Using SumFrequency Generation Vibrational Spectroscopy, Atomic Force Microscopy,and Quartz Crystal Microbalance

    SciTech Connect

    Phillips, Diana Christine

    2006-01-01

    Sum frequency generation (SFG) vibrational spectroscopy, atomic force microscopy (AFM), and quartz crystal microbalance (QCM) have been used to study the molecular surface structure, surface topography and mechanical properties, and quantitative adsorbed amount of biological molecules at the solid-liquid interface. The molecular-level behavior of designed peptides adsorbed on hydrophobic polystyrene and hydrophilic silica substrates has been examined as a model of protein adsorption on polymeric biomaterial surfaces. Proteins are such large and complex molecules that it is difficult to identify the features in their structure that lead to adsorption and interaction with solid surfaces. Designed peptides which possess secondary structure provide simple model systems for understanding protein adsorption. Depending on the amino acid sequence of a peptide, different secondary structures (α-helix and β-sheet) can be induced at apolar (air/liquid or air/solid) interfaces. Having a well-defined secondary structure allows experiments to be carried out under controlled conditions, where it is possible to investigate the affects of peptide amino acid sequence and chain length, concentration, buffering effects, etc. on adsorbed peptide structure. The experiments presented in this dissertation demonstrate that SFG vibrational spectroscopy can be used to directly probe the interaction of adsorbing biomolecules with a surface or interface. The use of well designed model systems aided in isolation of the SFG signal of the adsorbing species, and showed that surface functional groups of the substrate are sensitive to surface adsorbates. The complementary techniques of AFM and QCM allowed for deconvolution of the effects of surface topography and coverage from the observed SFG spectra. Initial studies of biologically relevant surfaces are also presented: SFG spectroscopy was used to study the surface composition of common soil bacteria for use in bioremediation of nuclear waste.

  5. Dispersion and Fixation of Adeno-Associated Virus with Glutaraldehyde for Afm Studies

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Wang, Xinyan; Yang, Haijun; Lü, Junhong

    Sample preparation is an important procedure for atomic force microscope (AFM) studies. However, flexible virus particles have a tendency to aggregate together and are easily compressed during sample preparation or by AFM tip that subsequently hamper studying of virus by AFM. Herein, low concentration chemical reagent of glutaraldehyde (2%, v/v) is pre-mixed in virus suspension that facilitates the dispersion and observation of recombinant serotype 2 adeno-associated virus particles deposited on mica surface with little deformation.

  6. AFM Structural Characterization of Drinking Water Biofilm ...

    EPA Pesticide Factsheets

    Due to the complexity of mixed culture drinking water biofilm, direct visual observation under in situ conditions has been challenging. In this study, atomic force microscopy (AFM) revealed the three dimensional morphology and arrangement of drinking water relevant biofilm in air and aqueous solution. Operating parameters were optimized to improve imaging of structural details for a mature biofilm in liquid. By using a soft cantilever (0.03 N/m) and slow scan rate (0.5 Hz), biofilm and individual bacterial cell’s structural topography were resolved and continuously imaged in liquid without loss of spatial resolution or sample damage. The developed methodology will allow future in situ investigations to temporally monitor mixed culture drinking water biofilm structural changes during disinfection treatments. Due to the complexity of mixed culture drinking water biofilm, direct visual observation under in situ conditions has been challenging. In this study, atomic force microscopy (AFM) revealed the three dimensional morphology and arrangement of drinking water relevant biofilm in air and aqueous solution. Operating parameters were optimized to improve imaging of structural details for a mature biofilm in liquid. By using a soft cantilever (0.03 N/m) and slow scan rate (0.5 Hz), biofilm and individual bacterial cell’s structural topography were resolved and continuously imaged in liquid without loss of spatial resolution or sample damage. The developed methodo

  7. Nano-Wilhelmy investigation of dynamic wetting properties of AFM tips through tip-nanobubble interaction.

    PubMed

    Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin

    2016-07-25

    The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation.

  8. Nano-Wilhelmy investigation of dynamic wetting properties of AFM tips through tip-nanobubble interaction

    NASA Astrophysics Data System (ADS)

    Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin

    2016-07-01

    The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation.

  9. Nano-Wilhelmy investigation of dynamic wetting properties of AFM tips through tip-nanobubble interaction

    PubMed Central

    Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin

    2016-01-01

    The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation. PMID:27452115

  10. Observation of electronic states on Si(111)-(7 x 7) through short-range attractive force with noncontact atomic force spectroscopy.

    PubMed

    Arai, T; Tomitori, M

    2004-12-17

    We experimentally reveal that the short-range attractive force between a Si tip and a Si(111)-(7 x 7) surface is enhanced at specified bias voltages; we conduct force spectroscopy based on noncontact atomic force microscopy with changing bias voltage at a fixed separation. The spectra exhibit prominent peaks and a broad peak, which are attributed to quantum mechanical resonance as the energy levels of sample surface states are tuned to those of the tip states by shifting the Fermi level through changing bias voltage, and to the resonating states over a lowered tunneling barrier, respectively.

  11. Direct Force Measurements of Receptor-Ligand Interactions on Living Cells

    NASA Astrophysics Data System (ADS)

    Eibl, Robert H.

    The characterization of cell adhesion between two living cells at the level of single receptor-ligand bonds is an experimental challenge. This chapter describes how the extremely sensitive method of atomic force microscopy (AFM) based force spectroscopy can be applied to living cells in order to probe for cell-to-cell or cell-to-substrate interactions mediated by single pairs of adhesion receptors. In addition, it is outlined how single-molecule AFM force spectroscopy can be used to detect physiologic changes of an adhesion receptor in a living cell. This force spectroscopy allows us to detect in living cells rapidly changing, chemokine SDF-1 triggered activation states of single VLA-4 receptors. This recently developed AFM application will allow for the detailed investigation of the integrin-chemokine crosstalk of integrin activation mechanisms and on how other adhesion receptors are modulated in health and disease. As adhesion molecules, living cells and even bacteria can be studied by single-molecule AFM force spectroscopy, this method is set to become a powerful tool that can not only be used in biophysics, but in cell biology as well as in immunology and cancer research.

  12. Effect of contact force on breast tissue optical property measurements using a broadband diffuse optical spectroscopy handheld probe

    PubMed Central

    Cerussi, Albert; Siavoshi, Sarah; Durkin, Amanda; Chen, Cynthia; Tanamai, Wendy; Hsiang, David; Tromberg, Bruce J.

    2010-01-01

    We investigated the effects of operator-applied force on diffuse optical spectroscopy (DOS) by integrating a force transducer into the handheld probe. Over the typical range of contact forces measured in the breasts of eight patients, absorption and reduced scattering coefficients (650 to 1000 nm) variance was 3.1 ± 1.0% and 1.0 ± 0.4%. For trained operators, we observed <5% variation in hemoglobin and <2% variation in water and lipids. Contact force is not a significant source of variation, most likely because of a relatively wide probe surface area and the stability of the DOS method for calculating tissue optical properties. PMID:19623242

  13. Atomic Force Microscope Mediated Chromatography

    NASA Technical Reports Server (NTRS)

    Anderson, Mark S.

    2013-01-01

    The atomic force microscope (AFM) is used to inject a sample, provide shear-driven liquid flow over a functionalized substrate, and detect separated components. This is demonstrated using lipophilic dyes and normal phase chromatography. A significant reduction in both size and separation time scales is achieved with a 25-micron-length column scale, and one-second separation times. The approach has general applications to trace chemical and microfluidic analysis. The AFM is now a common tool for ultra-microscopy and nanotechnology. It has also been demonstrated to provide a number of microfluidic functions necessary for miniaturized chromatography. These include injection of sub-femtoliter samples, fluidic switching, and sheardriven pumping. The AFM probe tip can be used to selectively remove surface layers for subsequent microchemical analysis using infrared and tip-enhanced Raman spectroscopy. With its ability to image individual atoms, the AFM is a remarkably sensitive detector that can be used to detect separated components. These diverse functional components of microfluidic manipulation have been combined in this work to demonstrate AFM mediated chromatography. AFM mediated chromatography uses channel-less, shear-driven pumping. This is demonstrated with a thin, aluminum oxide substrate and a non-polar solvent system to separate a mixture of lipophilic dyes. In conventional chromatographic terms, this is analogous to thin-layer chromatography using normal phase alumina substrate with sheardriven pumping provided by the AFM tip-cantilever mechanism. The AFM detection of separated components is accomplished by exploiting the variation in the localized friction of the separated components. The AFM tip-cantilever provides the mechanism for producing shear-induced flows and rapid pumping. Shear-driven chromatography (SDC) is a relatively new concept that overcomes the speed and miniaturization limitations of conventional liquid chromatography. SDC is based on a

  14. Optical tweezers for single molecule force spectroscopy on bacterial adhesion organelles

    NASA Astrophysics Data System (ADS)

    Andersson, Magnus; Axner, Ove; Uhlin, Bernt Eric; Fällman, Erik

    2006-08-01

    Instrumentation and methodologies for single molecule force spectroscopy on bacterial adhesion organelles by the use of force measuring optical tweezers have been developed. A thorough study of the biomechanical properties of fimbrial adhesion organelles expressed by uropathogenic E. coli, so-called pili, is presented. Steady-state as well as dynamic force measurements on P pili, expressed by E. coli causing pyelonephritis, have revealed, among other things, various unfolding and refolding properties of the helical structure of P pili, the PapA rod. Based on these properties an energy landscape model has been constructed by which specific biophysical properties of the PapA rod have been extracted, e.g. the number of subunits, the length of a single pilus, bond lengths and activation energies for bond opening and closure. Moreover, long time repetitive measurements have shown that the rod can be unfolded and refolded repetitive times without losing its intrinsic properties. These properties are believed to be of importance for the bacteria's ability to maintain close contact with host cells during initial infections. The results presented are considered to be of importance for the field of biopolymers in general and the development of new pharmaceuticals towards urinary tract infections in particular. The results show furthermore that the methodology can be used to gain knowledge of the intrinsic biomechanical function of adhesion organelles. The instrumentation is currently used for characterization of type 1 pili, expressed by E. coli causing cystitis, i.e. infections in the bladder. The first force spectrometry investigations of these pili will be presented.

  15. Characterization of the molecular structure and mechanical properties of polymer surfaces and protein/polymer interfaces by sum frequency generation vibrational spectroscopy and atomic force microscopy

    SciTech Connect

    Koffas, Telly Stelianos

    2004-01-01

    Sum frequency generation (SFG) vibrational spectroscopy, atomic force microscopy (AFM), and other complementary surface-sensitive techniques have been used to study the surface molecular structure and surface mechanical behavior of biologically-relevant polymer systems. SFG and AFM have emerged as powerful analytical tools to deduce structure/property relationships, in situ, for polymers at air, liquid and solid interfaces. The experiments described in this dissertation have been performed to understand how polymer surface properties are linked to polymer bulk composition, substrate hydrophobicity, changes in the ambient environment (e.g., humidity and temperature), or the adsorption of macromolecules. The correlation of spectroscopic and mechanical data by SFG and AFM can become a powerful methodology to study and engineer materials with tailored surface properties. The overarching theme of this research is the interrogation of systems of increasing structural complexity, which allows us to extend conclusions made on simpler model systems. We begin by systematically describing the surface molecular composition and mechanical properties of polymers, copolymers, and blends having simple linear architectures. Subsequent chapters focus on networked hydrogel materials used as soft contact lenses and the adsorption of protein and surfactant at the polymer/liquid interface. The power of SFG is immediately demonstrated in experiments which identify the chemical parameters that influence the molecular composition and ordering of a polymer chain's side groups at the polymer/air and polymer/liquid interfaces. In general, side groups with increasingly greater hydrophobic character will be more surface active in air. Larger side groups impose steric restrictions, thus they will tend to be more randomly ordered than smaller hydrophobic groups. If exposed to a hydrophilic environment, such as water, the polymer chain will attempt to orient more of its hydrophilic groups to the

  16. Multi-scale modeling of biophysical phenomena: ionic transport, biomineralization, and force spectroscopy

    NASA Astrophysics Data System (ADS)

    Kelly, Mark A.

    2011-07-01

    Biophysics is the study of the complex physical processes occurring in biological systems that are responsible for life. This dissertation addresses three important topics in biophysics: ionic transport, biomineralization, and force spectroscopy. Ionic transport involves the passage of ions through a special class of hollow, transmembrane proteins called ion channels which regulate the movement of charged species across nearly all biological membranes with varying degrees of specificity. Despite the fundamental importance of these channels to many physiological processes little is known about how channel structure and composition couple to determine its function. Deriving inspiration from these systems, a simple computational platform is developed to study the salient features of these channels in order to better understand the fundamental physics of these systems. The results of this work indicate that a converging-diverging region formed within the pore to create a single constriction is the most effective method to regulate the passage of ions through the pore. By controlling the geometry of the constriction the local potential and chemical gradients can be manipulated to tailor the channel for specific applications. The process of selective extraction and incorporation of local elements from the surrounding environment into functional structures under strict biological control is known as biomineralization. As an initial step to gain a more fundamental understanding of directed crystallization of zinc oxide molecular dynamics simulations were performed to study the conformational behavior of two experimentally derived biomimetic peptides in a precursor solution. Substantial differences in the conformational properties and affinity for zinc and hydroxide ions in solution were observed. These findings are in qualitative agreement with experimental observations. The mechanical response of biopolymers such as RNA and DNA to externally applied forces is a topic that

  17. AFM Structural Characterization of Drinking Water Biofilm under Physiological Conditions

    EPA Science Inventory

    Due to the complexity of mixed culture drinking water biofilm, direct visual observation under in situ conditions has been challenging. In this study, atomic force microscopy (AFM) revealed the three dimensional morphology and arrangement of drinking water relevant biofilm in air...

  18. Cantilever's behavior in the AC mode of an AFM

    SciTech Connect

    Nunes, V.B.; Zanette, S.I.; Caride, A.O.; Prioli, R.; Rivas, A.M.F

    2003-03-15

    In this paper, a model with a small number of parameters is used to simulate the motion of a cantilever in the AC mode of an atomic force microscope (AFM). The results elucidate the transition dependence-from noncontact to tapping operating mode-on the height of the contamination layer and on the stiffness of the sample.

  19. Decoupling indirect topographic cross-talk in band excitation piezoresponse force microscopy imaging and spectroscopy

    DOE PAGES

    Mazet, Lucie; Jesse, Stephen; Niu, Gang; ...

    2016-06-20

    Here, all scanning probe microscopies are subjected to topographic cross-talk, meaning the topography-related contrast in functional images. Here, we investigate the signatures of indirect topographic cross-talk in piezoresponse force microscopy (PFM) imaging and spectroscopy and its decoupling using band excitation (BE) method in ferroelectric BaTiO3 deposited on the Si substrates with free standing nanopillars of diameter 50 nm. Comparison between the single-frequency PFM and BE-PFM results shows that the measured signal can be significantly distorted by topography-induced shifts in the contact resonance frequency and cantilever transfer function. However, with proper correction, such shifts do not affect PFM imaging and hysteresismore » loop measurements. This suggests the necessity of an advanced approach, such as BE-PFM, for detection of intrinsic sample piezoresponse on the topographically non-uniform surfaces.« less

  20. Excited-state spectroscopy on an individual quantum dot using atomic force microscopy.

    PubMed

    Cockins, Lynda; Miyahara, Yoichi; Bennett, Steven D; Clerk, Aashish A; Grutter, Peter

    2012-02-08

    We present a new charge sensing technique for the excited-state spectroscopy of individual quantum dots, which requires no patterned electrodes. An oscillating atomic force microscope cantilever is used as a movable charge sensor as well as gate to measure the single-electron tunneling between an individual self-assembled InAs quantum dot and back electrode. A set of cantilever dissipation versus bias voltage curves measured at different cantilever oscillation amplitudes forms a diagram analogous to the Coulomb diamond usually measured with transport measurements. The excited-state levels as well as the electron addition spectrum can be obtained from the diagram. In addition, a signature which can result from inelastic tunneling by phonon emission or a peak in the density of states of the electrode is also observed, which demonstrates the versatility of the technique.

  1. Decoupling indirect topographic cross-talk in band excitation piezoresponse force microscopy imaging and spectroscopy

    SciTech Connect

    Mazet, Lucie; Jesse, Stephen; Niu, Gang; Schroeder, Thomas; Schamm-Chardon, Sylvie; Dubourdieu, Catherine; Baddorf, Arthur P.; Kalinin, Sergei V.; Yang, Sang Mo; Okatan, M. Baris

    2016-06-20

    Here, all scanning probe microscopies are subjected to topographic cross-talk, meaning the topography-related contrast in functional images. Here, we investigate the signatures of indirect topographic cross-talk in piezoresponse force microscopy (PFM) imaging and spectroscopy and its decoupling using band excitation (BE) method in ferroelectric BaTiO3 deposited on the Si substrates with free standing nanopillars of diameter 50 nm. Comparison between the single-frequency PFM and BE-PFM results shows that the measured signal can be significantly distorted by topography-induced shifts in the contact resonance frequency and cantilever transfer function. However, with proper correction, such shifts do not affect PFM imaging and hysteresis loop measurements. This suggests the necessity of an advanced approach, such as BE-PFM, for detection of intrinsic sample piezoresponse on the topographically non-uniform surfaces.

  2. Structure, cell wall elasticity and polysaccharide properties of living yeast cells, as probed by AFM

    NASA Astrophysics Data System (ADS)

    Alsteens, David; Dupres, Vincent; McEvoy, Kevin; Wildling, Linda; Gruber, Hermann J.; Dufrêne, Yves F.

    2008-09-01

    Although the chemical composition of yeast cell walls is known, the organization, assembly, and interactions of the various macromolecules remain poorly understood. Here, we used in situ atomic force microscopy (AFM) in three different modes to probe the ultrastructure, cell wall elasticity and polymer properties of two brewing yeast strains, i.e. Saccharomyces carlsbergensis and S. cerevisiae. Topographic images of the two strains revealed smooth and homogeneous cell surfaces, and the presence of circular bud scars on dividing cells. Nanomechanical measurements demonstrated that the cell wall elasticity of S. carlsbergensis is homogeneous. By contrast, the bud scar of S. cerevisiae was found to be stiffer than the cell wall, presumably due to the accumulation of chitin. Notably, single molecule force spectroscopy with lectin-modified tips revealed major differences in polysaccharide properties of the two strains. Polysaccharides were clearly more extended on S. cerevisiae, suggesting that not only oligosaccharides, but also polypeptide chains of the mannoproteins were stretched. Consistent with earlier cell surface analyses, these findings may explain the very different aggregation properties of the two organisms. This study demonstrates the power of using multiple complementary AFM modalities for probing the organization and interactions of the various macromolecules of microbial cell walls.

  3. Measuring cell wall elasticity on enteroaggregative Escherichia coli wild type and dispersin mutant by AFM

    SciTech Connect

    Beckmann, Melissa; Venkataraman, Sankar; Doktycz, Mitchel John; Nataro, James P; Sullivan, Claretta J; Morrell-Falvey, Jennifer L; Allison, David P

    2006-07-01

    Enteroaggregative Escherichia coli (EAEC) is pathogenic and produces severe diarrhea in humans. A mutant of EAEC that does not produce dispersin, a cell surface protein, is not pathogenic. It has been proposed that dispersin imparts a positive charge to the bacterial cell surface allowing the bacteria to colonize on the negatively charged intestinal mucosa. However, physical properties of the bacterial cell surface, such as rigidity, may be influenced by the presence of dispersin and may contribute to pathogenicity. Using the system developed in our laboratory for mounting and imaging bacterial cells by atomic force microscopy (AFM), in liquid, on gelatin coated mica surfaces, studies were initiated to measure cell surface elasticity. This was carried out in both wild type EAEC, that produces dispersin, and the mutant that does not produce dispersin. This was accomplished using AFM force-distance (FD) spectroscopy on the wild type and mutant grown in liquid or on solid medium. Images in liquid and in air of both the wild-type and mutant grown in liquid and on solid media are presented. This work represents an initial step in efforts to understand the pathogenic role of the dispersin protein in the wild-type bacteria.

  4. Atomic force microscopy of Precambrian microscopic fossils.

    PubMed

    Kempe, André; Schopf, J William; Altermann, Wladyslaw; Kudryavtsev, Anatoliy B; Heckl, Wolfgang M

    2002-07-09

    Atomic force microscopy (AFM) is a technique used routinely in material science to image substances at a submicron (including nm) scale. We apply this technique to analysis of the fine structure of organic-walled Precambrian fossils, microscopic sphaeromorph acritarchs (cysts of planktonic unicellular protists) permineralized in approximately 650-million-year-old cherts of the Chichkan Formation of southern Kazakhstan. AFM images, backed by laser-Raman spectroscopic analysis of individual specimens, demonstrate that the walls of these petrified fossils are composed of stacked arrays of approximately 200-nm-sized angular platelets of polycyclic aromatic kerogen. Together, AFM and laser-Raman spectroscopy provide means by which to elucidate the submicron-scale structure of individual microscopic fossils, investigate the geochemical maturation of ancient organic matter, and, potentially, distinguish true fossils from pseudofossils and probe the mechanisms of fossil preservation by silica permineralization.

  5. Atomic force microscopy of Precambrian microscopic fossils

    PubMed Central

    Kempe, André; Schopf, J. William; Altermann, Wladyslaw; Kudryavtsev, Anatoliy B.; Heckl, Wolfgang M.

    2002-01-01

    Atomic force microscopy (AFM) is a technique used routinely in material science to image substances at a submicron (including nm) scale. We apply this technique to analysis of the fine structure of organic-walled Precambrian fossils, microscopic sphaeromorph acritarchs (cysts of planktonic unicellular protists) permineralized in ≈650-million-year-old cherts of the Chichkan Formation of southern Kazakhstan. AFM images, backed by laser-Raman spectroscopic analysis of individual specimens, demonstrate that the walls of these petrified fossils are composed of stacked arrays of ≈200-nm-sized angular platelets of polycyclic aromatic kerogen. Together, AFM and laser-Raman spectroscopy provide means by which to elucidate the submicron-scale structure of individual microscopic fossils, investigate the geochemical maturation of ancient organic matter, and, potentially, distinguish true fossils from pseudofossils and probe the mechanisms of fossil preservation by silica permineralization. PMID:12089337

  6. The formation of liquid bridge in different operating modes of AFM

    NASA Astrophysics Data System (ADS)

    Wei, Zheng; Sun, Yan; Ding, WenXuan; Wang, ZaiRan

    2016-09-01

    The liquid bridge is one of the principal factors that cause artifacts in ambient-pressure atomic force microscope (AFM) images. Additionally, it is the main component of the adhesion force in ambient conditions. To understand the AFM imaging mechanism and the sample characteristics, it is essential to study the liquid bridge. This study interprets the physical mechanism involved in liquid bridge formation, which is composed of three different physical processes: the squeezing process, capillary condensation, and liquid film flow. We discuss the contributions of these three mechanisms to the volume and the capillary force of the liquid bridge in different AFM operation modes.

  7. Wetting properties of AFM probes by means of contact angle measurement

    NASA Astrophysics Data System (ADS)

    Tao, Zhenhua; Bhushan, Bharat

    2006-09-01

    An atomic force microscopy (AFM) based technique was developed to measure the wetting properties of probe tips. By advancing and receding the AFM tip across the water surface, the meniscus force between the tip and the liquid was measured at the tip-water separation. The water contact angle was determined from the meniscus force. The obtained contact angle results were compared with that by the sessile drop method. It was found that the AFM based technique provided higher contact angle values than the sessile drop method. The mechanisms responsible for the difference are discussed.

  8. Single-molecule force spectroscopy of the Aplysia cell adhesion molecule reveals two homophilic bonds.

    PubMed

    Martines, E; Zhong, J; Muzard, J; Lee, A C; Akhremitchev, B B; Suter, D M; Lee, G U

    2012-08-22

    Aplysia californica neurons comprise a powerful model system for quantitative analysis of cellular and biophysical properties that are essential for neuronal development and function. The Aplysia cell adhesion molecule (apCAM), a member of the immunoglobulin superfamily of cell adhesion molecules, is present in the growth cone plasma membrane and involved in neurite growth, synapse formation, and synaptic plasticity. apCAM has been considered to be the Aplysia homolog of the vertebrate neural cell adhesion molecule (NCAM); however, whether apCAM exhibits similar binding properties and neuronal functions has not been fully established because of the lack of detailed binding data for the extracellular portion of apCAM. In this work, we used the atomic force microscope to perform single-molecule force spectroscopy of the extracellular region of apCAM and show for the first time (to our knowledge) that apCAM, like NCAM, is indeed a homophilic cell adhesion molecule. Furthermore, like NCAM, apCAM exhibits two distinct bonds in the trans configuration, although the kinetic and structural parameters of the apCAM bonds are quite different from those of NCAM. In summary, these single-molecule analyses further indicate that apCAM and NCAM are species homologs likely performing similar functions.

  9. Characterization of Monobody Scaffold Interactions with Ligand via Force Spectroscopy and Steered Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Cheung, Luthur Siu-Lun; Shea, Daniel J.; Nicholes, Nathan; Date, Amol; Ostermeier, Marc; Konstantopoulos, Konstantinos

    2015-02-01

    Monobodies are antibody alternatives derived from fibronectin that are thermodynamically stable, small in size, and can be produced in bacterial systems. Monobodies have been engineered to bind a wide variety of target proteins with high affinity and specificity. Using alanine-scanning mutagenesis simulations, we identified two scaffold residues that are critical to the binding interaction between the monobody YS1 and its ligand, maltose-binding protein (MBP). Steered molecular dynamics (SMD) simulations predicted that the E47A and R33A mutations in the YS1 scaffold substantially destabilize the YS1-MBP interface by reducing the bond rupture force and the lifetime of single hydrogen bonds. SMD simulations further indicated that the R33A mutation weakens the hydrogen binding between all scaffold residues and MBP and not just between R33 and MBP. We validated the simulation data and characterized the effects of mutations on YS1-MBP binding by using single-molecule force spectroscopy and surface plasmon resonance. We propose that interfacial stability resulting from R33 of YS1 stacking with R344 of MBP synergistically stabilizes both its own bond and the interacting scaffold residues of YS1. Our integrated approach improves our understanding of the monobody scaffold interactions with a target, thus providing guidance for the improved engineering of monobodies.

  10. Harmonic force spectroscopy measures load-dependent kinetics of individual human β-cardiac myosin molecules

    PubMed Central

    Sung, Jongmin; Nag, Suman; Mortensen, Kim I.; Vestergaard, Christian L.; Sutton, Shirley; Ruppel, Kathleen; Flyvbjerg, Henrik; Spudich, James A.

    2015-01-01

    Molecular motors are responsible for numerous cellular processes from cargo transport to heart contraction. Their interactions with other cellular components are often transient and exhibit kinetics that depend on load. Here, we measure such interactions using ‘harmonic force spectroscopy'. In this method, harmonic oscillation of the sample stage of a laser trap immediately, automatically and randomly applies sinusoidally varying loads to a single motor molecule interacting with a single track along which it moves. The experimental protocol and the data analysis are simple, fast and efficient. The protocol accumulates statistics fast enough to deliver single-molecule results from single-molecule experiments. We demonstrate the method's performance by measuring the force-dependent kinetics of individual human β-cardiac myosin molecules interacting with an actin filament at physiological ATP concentration. We show that a molecule's ADP release rate depends exponentially on the applied load, in qualitative agreement with cardiac muscle, which contracts with a velocity inversely proportional to external load. PMID:26239258

  11. Unraveling the complexity of the interactions of DNA nucleotides with gold by single molecule force spectroscopy

    NASA Astrophysics Data System (ADS)

    Bano, Fouzia; Sluysmans, Damien; Wislez, Arnaud; Duwez, Anne-Sophie

    2015-11-01

    Addressing the effect of different environmental factors on the adsorption of DNA to solid supports is critical for the development of robust miniaturized devices for applications ranging from biosensors to next generation molecular technology. Most of the time, thiol-based chemistry is used to anchor DNA on gold - a substrate commonly used in nanotechnology - and little is known about the direct interaction between DNA and gold. So far there have been no systematic studies on the direct adsorption behavior of the deoxyribonucleotides (i.e., a nitrogenous base, a deoxyribose sugar, and a phosphate group) and on the factors that govern the DNA-gold bond strength. Here, using single molecule force spectroscopy, we investigated the interaction of the four individual nucleotides, adenine, guanine, cytosine, and thymine, with gold. Experiments were performed in three salinity conditions and two surface dwell times to reveal the factors that influence nucleotide-Au bond strength. Force data show that, at physiological ionic strength, adenine-Au interactions are stronger, asymmetrical and independent of surface dwell time as compared to cytosine-Au and guanine-Au interactions. We suggest that in these conditions only adenine is able to chemisorb on gold. A decrease of the ionic strength significantly increases the bond strength for all nucleotides. We show that moderate ionic strength along with longer surface dwell period suggest weak chemisorption also for cytosine and guanine.Addressing the effect of different environmental factors on the adsorption of DNA to solid supports is critical for the development of robust miniaturized devices for applications ranging from biosensors to next generation molecular technology. Most of the time, thiol-based chemistry is used to anchor DNA on gold - a substrate commonly used in nanotechnology - and little is known about the direct interaction between DNA and gold. So far there have been no systematic studies on the direct

  12. Biophysical properties of cardiomyocyte surface explored by multiparametric AFM.

    PubMed

    Smolyakov, Georges; Cauquil, Marie; Severac, Childerick; Lachaize, Véronique; Guilbeau-Frugier, Céline; Sénard, Jean-Michel; Galés, Céline; Dague, Etienne

    2017-03-02

    PeakForce Quantitative Nanomechanical Mapping (PeakForce QNM) multiparametric AFM mode was adapted to qualitative and quantitative study of the lateral membrane of cardiomyocytes (CMs), extending this powerful mode to the study of soft cells. On living CM, PeakForce QNM depicted the crests and hollows periodic alternation of cell surface architecture previously described using AFM Force Volume (FV) mode. PeakForce QNM analysis provided better resolution in terms of pixel number compared to FV mode and reduced acquisition time, thus limiting the consequences of spontaneous living adult CM dedifferentiation once isolated from the cardiac tissue. PeakForce QNM mode on fixed CMs clearly visualized subsarcolemmal mitochondria (SSM) and their loss following formamide treatment, concomitant with the interfibrillar mitochondria climbing up and forming heaps at the cell surface. Interestingly, formamide-promoted SSM loss allowed visualization of the sarcomeric apparatus ultrastructure below the plasma membrane. High PeakForce QNM resolution led to better contrasted mechanical maps than FV mode and provided correlation between adhesion, dissipation, mechanical and topographical maps. Modified hydrophobic AFM tip enhanced contrast on adhesion and dissipation maps and suggested that CM surface crests and hollows exhibit distinct chemical properties. Finally, two-dimensional Fast Fourier Transform to objectively quantify AFM maps allowed characterization of periodicity of both sarcomeric Z-line and M-band. Overall, this study validated PeakForce QNM as a valuable and innovative mode for the exploration of living and fixed CMs. In the future, it could be applied to depict cell membrane architectural, mechanical and chemical defects as well as sarcomeric abnormalities associated with cardiac diseases.

  13. Mapping individual cosmid DNAs by direct AFM imaging.

    PubMed

    Allison, D P; Kerper, P S; Doktycz, M J; Thundat, T; Modrich, P; Larimer, F W; Johnson, D K; Hoyt, P R; Mucenski, M L; Warmack, R J

    1997-05-01

    Individual cosmid clones have been restriction mapped by directly imaging, with the atomic force microscope (AFM), a mutant EcoRI endonuclease site-specifically bound to DNA. Images and data are presented that locate six restriction sites, predicted from gel electrophoresis, on a 35-kb cosmid isolated from mouse chromosome 7. Measured distances between endonuclease molecules bound to lambda DNA, when compared to known values, demonstrate the accuracy of AFM mapping to better than 1%. These results may be extended to identify other important site-specific protein-DNA interactions, such as transcription factor and mismatch repair enzyme binding, difficult to resolve by current techniques.

  14. Determining surface properties with bimodal and multimodal AFM.

    PubMed

    Forchheimer, D; Borysov, Stanislav S; Platz, D; Haviland, David B

    2014-12-05

    Conventional dynamic atomic force microscopy (AFM) can be extended to bimodal and multimodal AFM in which the cantilever is simultaneously excited at two or more resonance frequencies. Such excitation schemes result in one additional amplitude and phase images for each driven resonance, and potentially convey more information about the surface under investigation. Here we present a theoretical basis for using this information to approximate the parameters of a tip-surface interaction model. The theory is verified by simulations with added noise corresponding to room-temperature measurements.

  15. Can Dissipative Properties of Single Molecules Be Extracted from a Force Spectroscopy Experiment?

    PubMed

    Benedetti, Fabrizio; Gazizova, Yulia; Kulik, Andrzej J; Marszalek, Piotr E; Klinov, Dmitry V; Dietler, Giovanni; Sekatskii, Sergey K

    2016-09-20

    We performed dynamic force spectroscopy of single dextran and titin I27 molecules using small-amplitude and low-frequency (40-240 Hz) dithering of an atomic force microscope tip excited by a sine wave voltage fed onto the tip-carrying piezo. We show that for such low-frequency dithering experiments, recorded phase information can be unambiguously interpreted within the framework of a transparent theoretical model that starts from a well-known partial differential equation to describe the dithering of an atomic force microscope cantilever and a single molecule attached to its end system, uses an appropriate set of initial and boundary conditions, and does not exploit any implicit suggestions. We conclude that the observed phase (dissipation) signal is due completely to the dissipation related to the dithering of the cantilever itself (i.e., to the change of boundary conditions in the course of stretching). For both cases, only the upper bound of the dissipation of a single molecule has been established as not exceeding 3⋅10(-7)kg/s. We compare our results with previously reported measurements of the viscoelastic properties of single molecules, and we emphasize that extreme caution must be taken in distinguishing between the dissipation related to the stretched molecule and the dissipation that originates from the viscous damping of the dithered cantilever. We also present the results of an amplitude channel data analysis, which reveal that the typical values of the spring constant of a I27 molecule at the moment of module unfolding are equal to 4±1.5mN/m, and the typical values of the spring constant of dextran at the moment of chair-boat transition are equal to 30-50mN/m.

  16. Force Spectroscopy of the Plasmodium falciparum Vaccine Candidate Circumsporozoite Protein Suggests a Mechanically Pliable Repeat Region.

    PubMed

    Patra, Aditya Prasad; Sharma, Shobhona; Ainavarapu, Sri Rama Koti

    2017-02-10

    The most effective vaccine candidate of malaria is based on the Plasmodium falciparum circumsporozoite protein (CSP), a major surface protein implicated in the structural strength, motility, and immune evasion properties of the infective sporozoites. It is suspected that reversible conformational changes of CSP are required for infection of the mammalian host, but the detailed structure and dynamic properties of CSP remain incompletely understood, limiting our understanding of its function in the infection. Here, we report the structural and mechanical properties of the CSP studied using single-molecule force spectroscopy on several constructs, one including the central region of CSP, which is rich in NANP amino acid repeats (CSPrep), and a second consisting of a near full-length sequence without the signal and anchor hydrophobic domains (CSPΔHP). Our results show that the CSPrep is heterogeneous, with 40% of molecules requiring virtually no mechanical force to unfold (<10 piconewtons (pN)), suggesting that these molecules are mechanically compliant and perhaps act as entropic springs, whereas the remaining 60% are partially structured with low mechanical resistance (∼70 pN). CSPΔHP having multiple force peaks suggests specifically folded domains, with two major populations possibly indicating the open and collapsed forms. Our findings suggest that the overall low mechanical resistance of the repeat region, exposed on the outer surface of the sporozoites, combined with the flexible full-length conformations of CSP, may provide the sporozoites not only with immune evasion properties, but also with lubricating capacity required during its navigation through the mosquito and vertebrate host tissues. We anticipate that these findings would further assist in the design and development of future malarial vaccines.

  17. Formation of sensor array on the AFM chip surface by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Shumov, I. D.; Kanashenko, S. L.; Ziborov, V. S.; Ivanov, Yu D.; Archakov, A. I.; Pleshakova, T. O.

    2017-01-01

    Development of atomic force microscopy (AFM)-based nanotechnological approaches to highly sensitive detection of proteins is a perspective direction in biomedical research. These approaches use AFM chips to concentrate the target proteins from the test solution volume (buffer solution, diluted biological fluid) onto the chip surface for their subsequent registration on the chip surface by AFM. Atomic force microscope is a molecular detector that enables protein detection at ultra-low (subfemtomolar) concentrations in single-molecule counting mode. Due to extremely high sensitivity of AFM, its application for multiplexed protein detection is of great interest for use in proteomics and diagnostic applications. In this study, AFM chips containing an array of sensor areas have been fabricated. Magnetron sputtering of chromium and tungsten nanolayers has been used to form optically visible metallic marks on the AFM chip surface to provide necessary precision of AFM probe positioning against each sensor area for scanning. It has been demonstrated that the marks formed by magnetron sputtering of Cr and W are stable on the surface of the AFM chips during the following activation and intensive washing of this surface. The results obtained in our present study allow application of the developed chips for multiplexed protein analysis by AFM.

  18. Intrinsically High-Q Dynamic AFM Imaging in Liquid with a Significantly Extended Needle Tip

    PubMed Central

    Minary-Jolandan, Majid; Tajik, Arash; Wang, Ning; Yu, Min-Feng

    2012-01-01

    Atomic force microscope (AFM) probe with a long and rigid needle tip was fabricated and studied for high Q factor dynamic (tapping mode) AFM imaging of samples submersed in liquid. The extended needle tip over a regular commercially-available tapping mode AFM cantilever was sufficiently long to keep the AFM cantilever from submersed in liquid, which significantly minimized the hydrodynamic damping involved in dynamic AFM imaging of samples in liquid. Dynamic AFM imaging of samples in liquid at an intrinsic Q factor of over 100 and an operation frequency of over 200 kHz was demonstrated. The method has the potential to be extended to acquire viscoelastic materials properties and provide truly gentle imaging of soft biological samples in physiological environments. PMID:22595833

  19. AFM of biological complexes: what can we learn?

    PubMed Central

    Gaczynska, Maria; Osmulski, Pawel A.

    2009-01-01

    The term “biological complexes” broadly encompasses particles as diverse as multisubunit enzymes, viral capsids, transport cages, molecular nets, ribosomes, nucleosomes, biological membrane components and amyloids. The complexes represent a broad range of stability and composition. Atomic force microscopy offers a wealth of structural and functional data about such assemblies. For this review, we choose to comment on the significance of AFM to study various aspects of biology of selected nonmembrane protein assemblies. Such particles are large enough to reveal many structural details under the AFM probe. Importantly, the specific advantages of the method allow for gathering dynamic information about their formation, stability or allosteric structural changes critical for their function. Some of them have already found their way to nanomedical or nanotechnological applications. Here we present examples of studies where the AFM provided pioneering information about the biology of complexes, and examples of studies where the simplicity of the method is used toward the development of potential diagnostic applications. PMID:19802337

  20. Sub-diffraction nano manipulation using STED AFM.

    PubMed

    Chacko, Jenu Varghese; Canale, Claudio; Harke, Benjamin; Diaspro, Alberto

    2013-01-01

    In the last two decades, nano manipulation has been recognized as a potential tool of scientific interest especially in nanotechnology and nano-robotics. Contemporary optical microscopy (super resolution) techniques have also reached the nanometer scale resolution to visualize this and hence a combination of super resolution aided nano manipulation ineluctably gives a new perspective to the scenario. Here we demonstrate how specificity and rapid determination of structures provided by stimulated emission depletion (STED) microscope can aid another microscopic tool with capability of mechanical manoeuvring, like an atomic force microscope (AFM) to get topological information or to target nano scaled materials. We also give proof of principle on how high-resolution real time visualization can improve nano manipulation capability within a dense sample, and how STED-AFM is an optimal combination for this job. With these evidences, this article points to future precise nano dissections and maybe even to a nano-snooker game with an AFM tip and fluorospheres.

  1. Mounting of Escherichia coli spheroplasts for AFM imaging.

    SciTech Connect

    Sullivan, Claretta J; Morrell-Falvey, Jennifer L; Allison, David P; Doktycz, Mitchel John

    2005-11-01

    The cytoplasmic membrane of Escherichia coli (E. coli) is the location of numerous, chemically specific transporters and recognition elements. Investigation of this membrane in vivo by atomic force microscopy (AFM) requires removal of the cell wall and stable immobilization of the spheroplast. AFM images demonstrate that spheroplasts can be secured with warm gelatin applied to the mica substrate just before the addition of a spheroplast suspension. The resulting preparation can be repeatedly imaged by AFM over the course of several hours. Confocal fluorescence imaging confirms the association of the spheroplasts with the gelatin layer. Gelatin molecules are known to reorder into a network after heating. Entrapment within this gelatin network is believed to be responsible for the immobilization of spheroplasts on mica.

  2. Optical response of magnetic fluorescent microspheres used for force spectroscopy in the evanescent field.

    PubMed

    Bijamov, Alex; Shubitidze, Fridon; Oliver, Piercen M; Vezenov, Dmitri V

    2010-07-20

    Force spectroscopy based on magnetic tweezers is a powerful technique for manipulating single biomolecules and studying their interactions. The resolution in magnetic probe displacement, however, needs to be commensurate with molecular sizes. To achieve the desirable sensitivity in tracking displacements of the magnetic probe, some recent approaches have combined magnetic tweezers with total internal reflection fluorescence microscopy. In this situation, a typical force probe is a polymer microsphere containing two types of optically active components: a pure absorber (magnetic nanoparticles for providing the pulling force) and a luminophore (semiconducting nanoparticles or organic dyes for fluorescent imaging). To assess the system's capability fully with regard to tracking the position of the force probe with subnanometer accuracy, we developed a body-of-revolution formulation of the method of auxiliary sources (BOR-MAS) to simulate the absorption, scattering, and fluorescence of microscopic spheres in an evanescent electromagnetic field. The theoretical formulation uses the axial symmetry of the system to reduce the dimensionality of the modeling problem and produces excellent agreement with the reported experimental data on forward scattering intensity. Using the BOR-MAS numerical model, we investigated the probe detection sensitivity for a high numerical aperture objective. The analysis of both backscattering and fluorescence observation modes shows that the total intensity of the bead image decays exponentially with the distance from the surface (or the length of a biomolecule). Our investigations demonstrate that the decay lengths of observable optical power are smaller than the penetration depth of the unperturbed excitation evanescent wave. In addition, our numerical modeling results illustrate that the expected sensitivity for the decay length changes with the angle of incidence, tracking the theoretical penetration depth for a two-media model, and is

  3. Quantum state readout of individual quantum dots by electrostatic force detection

    NASA Astrophysics Data System (ADS)

    Miyahara, Yoichi; Roy-Gobeil, Antoine; Grutter, Peter

    2017-02-01

    Electric charge detection by atomic force microscopy (AFM) with single-electron resolution (e-EFM) is a promising way to investigate the electronic level structure of individual quantum dots (QDs). The oscillating AFM tip modulates the energy of the QDs, causing single electrons to tunnel between QDs and an electrode. The resulting oscillating electrostatic force changes the resonant frequency and damping of the AFM cantilever, enabling electrometry with a single-electron sensitivity. Quantitative electronic level spectroscopy is possible by sweeping the bias voltage. Charge stability diagram can be obtained by scanning the AFM tip around the QD. e-EFM technique enables to investigate individual colloidal nanoparticles and self-assembled QDs without nanoscale electrodes. e-EFM is a quantum electromechanical system where the back-action of a tunneling electron is detected by AFM; it can also be considered as a mechanical analog of admittance spectroscopy with a radio frequency resonator, which is emerging as a promising tool for quantum state readout for quantum computing. In combination with the topography imaging capability of the AFM, e-EFM is a powerful tool for investigating new nanoscale material systems which can be used as quantum bits.

  4. Sampling Protein Form and Function with the Atomic Force Microscope*

    PubMed Central

    Baclayon, Marian; Roos, Wouter H.; Wuite, Gijs J. L.

    2010-01-01

    To study the structure, function, and interactions of proteins, a plethora of techniques is available. Many techniques sample such parameters in non-physiological environments (e.g. in air, ice, or vacuum). Atomic force microscopy (AFM), however, is a powerful biophysical technique that can probe these parameters under physiological buffer conditions. With the atomic force microscope operating under such conditions, it is possible to obtain images of biological structures without requiring labeling and to follow dynamic processes in real time. Furthermore, by operating in force spectroscopy mode, it can probe intramolecular interactions and binding strengths. In structural biology, it has proven its ability to image proteins and protein conformational changes at submolecular resolution, and in proteomics, it is developing as a tool to map surface proteomes and to study protein function by force spectroscopy methods. The power of AFM to combine studies of protein form and protein function enables bridging various research fields to come to a comprehensive, molecular level picture of biological processes. We review the use of AFM imaging and force spectroscopy techniques and discuss the major advances of these experiments in further understanding form and function of proteins at the nanoscale in physiologically relevant environments. PMID:20562411

  5. Digital force-feedback for protein unfolding experiments using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Bippes, Christian A.; Janovjak, Harald; Kedrov, Alexej; Muller, Daniel J.

    2007-01-01

    Since its invention in the 1990s single-molecule force spectroscopy has been increasingly applied to study protein (un-)folding, cell adhesion, and ligand-receptor interactions. In most force spectroscopy studies, the cantilever of an atomic force microscope (AFM) is separated from a surface at a constant velocity, thus applying an increasing force to folded bio-molecules or bio-molecular bonds. Recently, Fernandez and co-workers introduced the so-called force-clamp technique. Single proteins were subjected to a defined constant force allowing their life times and life time distributions to be directly measured. Up to now, the force-clamping was performed by analogue PID controllers, which require complex additional hardware and might make it difficult to combine the force-feedback with other modes such as constant velocity. These points may be limiting the applicability and versatility of this technique. Here we present a simple, fast, and all-digital (software-based) PID controller that yields response times of a few milliseconds in combination with a commercial AFM. We demonstrate the performance of our feedback loop by force-clamp unfolding of single Ig27 domains of titin and the membrane proteins bacteriorhodopsin (BR) and the sodium/proton antiporter NhaA.

  6. Nano-Bio-Mechanics of Neuroblastoma Cells Using AFM

    NASA Astrophysics Data System (ADS)

    Bastatas, Lyndon; Matthews, James; Kang, Min; Park, Soyeun

    2011-10-01

    We have conducted an in vitro study to determine the elastic moduli of neurobalstoma cell lines using atomic force microscopy. Using a panel of cell lines established from neuroblastoma patients at different stages of disease progress and treatment, we have investigated the differences in elastic moduli during a course of cancer progression and chemotherapy. The cells were grown on the hard substrates that are chemically functionalized to enhance adhesion. We have performed the AFM indentation experiments with different applied forces from the AFM probe. For the purpose of the comparison between cell lines, the indentations were performed only on cell centers. The obtained force-distance curves were analyzed using the Hertz model in order to extract the elastic moduli. We have found that the elastic moduli of human neuroblastoma cells significantly varied during the disease progression. We postulate that the observed difference might be affected by the treatment and chemotherapy.

  7. Atomic force microscopy as an advanced tool in neuroscience

    PubMed Central

    Jembrek, Maja Jazvinšćak; Šimić, Goran; Hof, Patrick R.; Šegota, Suzana

    2015-01-01

    This review highlights relevant issues about applications and improvements of atomic force microscopy (AFM) toward a better understanding of neurodegenerative changes at the molecular level with the hope of contributing to the development of effective therapeutic strategies for neurodegenerative illnesses. The basic principles of AFM are briefly discussed in terms of evaluation of experimental data, including the newest PeakForce Quantitative Nanomechanical Mapping (QNM) and the evaluation of Young’s modulus as the crucial elasticity parameter. AFM topography, revealed in imaging mode, can be used to monitor changes in live neurons over time, representing a valuable tool for high-resolution detection and monitoring of neuronal morphology. The mechanical properties of living cells can be quantified by force spectroscopy as well as by new AFM. A variety of applications are described, and their relevance for specific research areas discussed. In addition, imaging as well as non-imaging modes can provide specific information, not only about the structural and mechanical properties of neuronal membranes, but also on the cytoplasm, cell nucleus, and particularly cytoskeletal components. Moreover, new AFM is able to provide detailed insight into physical structure and biochemical interactions in both physiological and pathophysiological conditions. PMID:28123795

  8. Single-molecule force spectroscopy of membrane proteins from membranes freely spanning across nanoscopic pores.

    PubMed

    Petrosyan, Rafayel; Bippes, Christian A; Walheim, Stefan; Harder, Daniel; Fotiadis, Dimitrios; Schimmel, Thomas; Alsteens, David; Müller, Daniel J

    2015-05-13

    Single-molecule force spectroscopy (SMFS) provides detailed insight into the mechanical (un)folding pathways and structural stability of membrane proteins. So far, SMFS could only be applied to membrane proteins embedded in native or synthetic membranes adsorbed to solid supports. This adsorption causes experimental limitations and raises the question to what extent the support influences the results obtained by SMFS. Therefore, we introduce here SMFS from native purple membrane freely spanning across nanopores. We show that correct analysis of the SMFS data requires extending the worm-like chain model, which describes the mechanical stretching of a polypeptide, by the cubic extension model, which describes the bending of a purple membrane exposed to mechanical stress. This new experimental and theoretical approach allows to characterize the stepwise (un)folding of the membrane protein bacteriorhodopsin and to assign the stability of single and grouped secondary structures. The (un)folding and stability of bacteriorhodopsin shows no significant difference between freely spanning and directly supported purple membranes. Importantly, the novel experimental SMFS setup opens an avenue to characterize any protein from freely spanning cellular or synthetic membranes.

  9. MDM2-MDM4 molecular interaction investigated by atomic force spectroscopy and surface plasmon resonance.

    PubMed

    Moscetti, Ilaria; Teveroni, Emanuela; Moretti, Fabiola; Bizzarri, Anna Rita; Cannistraro, Salvatore

    Murine double minute 2 (MDM2) and 4 (MDM4) are known as the main negative regulators of p53, a tumor suppressor. They are able to form heterodimers that are much more effective in the downregulation of p53. Therefore, the MDM2-MDM4 complex could be a target for promising therapeutic restoration of p53 function. To this aim, a deeper understanding of the molecular mechanisms underlining the heterodimerization is needed. The kinetic and thermodynamic characterization of the MDM2-MDM4 complex was performed with two complementary approaches: atomic force spectroscopy and surface plasmon resonance. Both techniques revealed an equilibrium dissociation constant (KD ) in the micromolar range for the MDM2-MDM4 heterodimer, similar to related complexes involved in the p53 network. Furthermore, the MDM2-MDM4 complex is characterized by a relatively high free energy, through a single energy barrier, and by a lifetime in the order of tens of seconds. New insights into the MDM2-MDM4 interaction could be highly important for developing innovative anticancer drugs focused on p53 reactivation.

  10. Unraveling Hydrophobic Interactions at the Molecular Scale Using Force Spectroscopy and Molecular Dynamics Simulations.

    PubMed

    Stock, Philipp; Monroe, Jacob I; Utzig, Thomas; Smith, David J; Shell, M Scott; Valtiner, Markus

    2017-03-28

    Interactions between hydrophobic moieties steer ubiquitous processes in aqueous media, including the self-organization of biologic matter. Recent decades have seen tremendous progress in understanding these for macroscopic hydrophobic interfaces. Yet, it is still a challenge to experimentally measure hydrophobic interactions (HIs) at the single-molecule scale and thus to compare with theory. Here, we present a combined experimental-simulation approach to directly measure and quantify the sequence dependence and additivity of HIs in peptide systems at the single-molecule scale. We combine dynamic single-molecule force spectroscopy on model peptides with fully atomistic, both equilibrium and nonequilibrium, molecular dynamics (MD) simulations of the same systems. Specifically, we mutate a flexible (GS)5 peptide scaffold with increasing numbers of hydrophobic leucine monomers and measure the peptides' desorption from hydrophobic self-assembled monolayer surfaces. Based on the analysis of nonequilibrium work-trajectories, we measure an interaction free energy that scales linearly with 3.0-3.4 kBT per leucine. In good agreement, simulations indicate a similar trend with 2.1 kBT per leucine, while also providing a detailed molecular view into HIs. This approach potentially provides a roadmap for directly extracting qualitative and quantitative single-molecule interactions at solid/liquid interfaces in a wide range of fields, including interactions at biointerfaces and adhesive interactions in industrial applications.

  11. Mechanisms of small molecule–DNA interactions probed by single-molecule force spectroscopy

    PubMed Central

    Almaqwashi, Ali A.; Paramanathan, Thayaparan; Rouzina, Ioulia; Williams, Mark C.

    2016-01-01

    There is a wide range of applications for non-covalent DNA binding ligands, and optimization of such interactions requires detailed understanding of the binding mechanisms. One important class of these ligands is that of intercalators, which bind DNA by inserting aromatic moieties between adjacent DNA base pairs. Characterizing the dynamic and equilibrium aspects of DNA-intercalator complex assembly may allow optimization of DNA binding for specific functions. Single-molecule force spectroscopy studies have recently revealed new details about the molecular mechanisms governing DNA intercalation. These studies can provide the binding kinetics and affinity as well as determining the magnitude of the double helix structural deformations during the dynamic assembly of DNA–ligand complexes. These results may in turn guide the rational design of intercalators synthesized for DNA-targeted drugs, optical probes, or integrated biological self-assembly processes. Herein, we survey the progress in experimental methods as well as the corresponding analysis framework for understanding single molecule DNA binding mechanisms. We discuss briefly minor and major groove binding ligands, and then focus on intercalators, which have been probed extensively with these methods. Conventional mono-intercalators and bis-intercalators are discussed, followed by unconventional DNA intercalation. We then consider the prospects for using these methods in optimizing conventional and unconventional DNA-intercalating small molecules. PMID:27085806

  12. DNA interaction with DAPI fluorescent dye: Force spectroscopy decouples two different binding modes.

    PubMed

    Reis, L A; Rocha, M S

    2017-05-01

    In this work, we use force spectroscopy to investigate the interaction between the DAPI fluorescent dye and the λ-DNA molecule under high (174 mM) and low (34 mM) ionic strengths. Firstly, we have measured the changes on the mechanical properties (persistence and contour lengths) of the DNA-DAPI complexes as a function of the dye concentration in the sample. Then, we use recently developed models in order to connect the behavior of both mechanical properties to the physical chemistry of the interaction. Such analysis has allowed us to identify and to decouple two main binding modes, determining the relevant physicochemical (binding) parameters for each of these modes: minor groove binding, which saturates at very low DAPI concentrations ( CT ∼ 0.50 μM) and presents equilibrium binding constants of the order of ∼10(7) M(-1) for the two ionic strengths studied; and intercalation, which starts to play a significant role only after the saturation of the first mode, presenting much smaller equilibrium binding constants (∼10(5) M(-1) ).

  13. On the effects of intercalators in DNA condensation: a force spectroscopy and gel electrophoresis study.

    PubMed

    Rocha, M S; Cavalcante, A G; Silva, R; Ramos, E B

    2014-05-08

    In this work we have characterized the effects of the intercalator ethidium bromide (EtBr) on the DNA condensation process by using force spectroscopy and gel electrophoresis. We have tested two condensing agents: spermine (spm(4+)), a tetravalent cationic amine which promotes cation-induced DNA condensation, and poly(ethylene glycol) (PEG), a neutral polymer which promotes DNA ψ-condensation. Two different types of experiments were performed. In the first type, bare DNA molecules disperse in solution are first treated with EtBr for intercalation, and then the condensing agent is added to the sample with the purpose of verifying the effects of the intercalator in hindering DNA condensation. In the second experiment type, the bare DNA molecules are first condensed, and then the intercalator is added to the sample in order to verify its influence on the previously condensed DNA. The results obtained with the two different experimental techniques used agree very well, indicating that previously intercalated EtBr can hinder both cation-induced and ψ-condensation, being more efficient in the first case. On the other hand, EtBr has little effect on the previously formed cation-induced condensates, but is efficient in unfolding the ψ-condensates.

  14. Investigating the mechanical properties of zona pellucida of whole human oocytes by atomic force spectroscopy.

    PubMed

    Andolfi, Laura; Masiero, Elena; Giolo, Elena; Martinelli, Monica; Luppi, Stefania; Dal Zilio, Simone; Delfino, Ines; Bortul, Roberta; Zweyer, Marina; Ricci, Giuseppe; Lazzarino, Marco

    2016-08-08

    The role of mechanics in numerous biological processes is nowadays recognized, while in others, such as the fertilization process, it is still neglected. In the case of oocytes the description of their mechanical properties could improve the comprehension of the oocyte-spermatozoon interaction and be helpful for application in in vitro fertilization (IVF) clinics. Herein the mechanical properties of whole human oocytes (HOs) immediately after retrieval are investigated by indentation measurements with atomic force spectroscopy under physiological conditions. Measurements are performed on immature (metaphase I - MI) and mature (metaphase II - MII) HOs. According to their morphological characteristics MII-HOs are classified as "suitable" and "rejected"; these latter would be usually rejected for intracytoplasmic sperm injection (ICSI). For all maturation stages we observe that the elastic response of the zona pellucida (ZP) outer layer was different and distinguishable from the rest of the ZP-HO. The elasticity of this ZP outer layer varies with maturation and quality: stiffness decreases from immature MI to good quality MII, up to poor-quality rejected MII. An indirect analysis with IVF outcome indicates that the ZP outer layer of analysed HOs donated by women who achieved pregnancy is stiffer than that of HOs from women with negative outcome. Our findings suggest that mechanical properties can represent important oocyte quality indicators that may be exploited for the design of innovative ICSI dedicated cell sorters.

  15. Structural investigations on native collagen type I fibrils using AFM

    SciTech Connect

    Strasser, Stefan; Zink, Albert; Janko, Marek; Heckl, Wolfgang M.; Thalhammer, Stefan . E-mail: stefan.thalhammer@gsf.de

    2007-03-02

    This study was carried out to determine the elastic properties of single collagen type I fibrils with the use of atomic force microscopy (AFM). Native collagen fibrils were formed by self-assembly in vitro characterized with the AFM. To confirm the inner assembly of the collagen fibrils, the AFM was used as a microdissection tool. Native collagen type I fibrils were dissected and the inner core uncovered. To determine the elastic properties of collagen fibrils the tip of the AFM was used as a nanoindentor by recording force-displacement curves. Measurements were done on the outer shell and in the core of the fibril. The structural investigations revealed the banding of the shell also in the core of native collagen fibrils. Nanoindentation experiments showed the same Young's modulus on the shell as well as in the core of the investigated native collagen fibrils. In addition, the measurements indicate a higher adhesion in the core of the collagen fibrils compared to the shell.

  16. Studying the mechanism of CD47-SIRPα interactions on red blood cells by single molecule force spectroscopy

    NASA Astrophysics Data System (ADS)

    Pan, Yangang; Wang, Feng; Liu, Yanhou; Jiang, Junguang; Yang, Yong-Guang; Wang, Hongda

    2014-08-01

    The interaction forces and binding kinetics between SIRPα and CD47 were investigated by single-molecule force spectroscopy (SMFS) on both fresh and experimentally aged human red blood cells (hRBCs). We found that CD47 experienced a conformation change after oxidation, which influenced the interaction force and the position of the energy barrier between SIRPα and CD47. Our results are significant for understanding the mechanism of phagocytosis of red blood cells at the single molecule level.The interaction forces and binding kinetics between SIRPα and CD47 were investigated by single-molecule force spectroscopy (SMFS) on both fresh and experimentally aged human red blood cells (hRBCs). We found that CD47 experienced a conformation change after oxidation, which influenced the interaction force and the position of the energy barrier between SIRPα and CD47. Our results are significant for understanding the mechanism of phagocytosis of red blood cells at the single molecule level. Electronic supplementary information (ESI) available: Experimental section. See DOI: 10.1039/c4nr02889a

  17. Scanning hall probe microscopy (SHPM) using quartz crystal AFM feedback.

    PubMed

    Dede, M; Urkmen, K; Girişen, O; Atabak, M; Oral, A; Farrer, I; Ritchie, D

    2008-02-01

    Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of approximately 50 nm and 7 mG/Hz(1/2) at room temperature. In the SHPM technique, scanning tunneling microscope (STM) or atomic force microscope (AFM) feedback is used to keep the Hall sensor in close proximity of the sample surface. However, STM tracking SHPM requires conductive samples; therefore the insulating substrates have to be coated with a thin layer of gold. This constraint can be eliminated with the AFM feedback using sophisticated Hall probes that are integrated with AFM cantilevers. However it is very difficult to micro fabricate these sensors. In this work, we have eliminated the difficulty in the cantilever-Hall probe integration process, just by gluing a Hall Probe chip to a quartz crystal tuning fork force sensor. The Hall sensor chip is simply glued at the end of a 32.768 kHz or 100 kHz Quartz crystal, which is used as force sensor. An LT-SHPM system is used to scan the samples. The sensor assembly is dithered at the resonance frequency using a digital Phase Locked Loop circuit and frequency shifts are used for AFM tracking. SHPM electronics is modified to detect AFM topography and the frequency shift, along with the magnetic field image. Magnetic domains and topography of an Iron Garnet thin film crystal, NdFeB demagnetised magnet and hard disk samples are presented at room temperature. The performance is found to be comparable with the SHPM using STM feedback.

  18. Force.

    ERIC Educational Resources Information Center

    Gamble, Reed

    1989-01-01

    Discusses pupil misconceptions concerning forces. Summarizes some of Assessment of Performance Unit's findings on meaning of (1) force, (2) force and motion in one dimension and two dimensions, and (3) Newton's second law. (YP)

  19. Investigation of the influence of UV irradiation on collagen thin films by AFM imaging.

    PubMed

    Stylianou, Andreas; Yova, Dido; Alexandratou, Eleni

    2014-12-01

    Collagen is the major fibrous extracellular matrix protein and due to its unique properties, it has been widely used as biomaterial, scaffold and cell-substrate. The aim of the paper was to use Atomic Force Microscopy (AFM) in order to investigate well-characterized collagen thin films after ultraviolet light (UV) irradiation. The films were also used as in vitro culturing substrates in order to investigate the UV-induced alterations to fibroblasts. A special attention was given in the alteration on collagen D-periodicity. For short irradiation times, spectroscopy (fluorescence/absorption) studies demonstrated that photodegradation took place and AFM imaging showed alterations in surface roughness. Also, it was highlighted that UV-irradiation had different effects when it was applied on collagen solution than on films. Concerning fibroblast culturing, it was shown that fibroblast behavior was affected after UV irradiation of both collagen solution and films. Furthermore, after a long irradiation time, collagen fibrils were deformed revealing that collagen fibrils are consisting of multiple shells and D-periodicity occurred on both outer and inner shells. The clarification of the effects of UV light on collagen and the induced modifications of cell behavior on UV-irradiated collagen-based surfaces will contribute to the better understanding of cell-matrix interactions in the nanoscale and will assist in the appropriate use of UV light for sterilizing and photo-cross-linking applications.

  20. Structural studies of sulfur passivated GaAs(001) surfaces with LEED and AFM

    NASA Astrophysics Data System (ADS)

    Wang, Xuewen; Ke, Yenjin; Milano, Steve; Tao, Nongjian; Darici, Yesim

    1997-03-01

    We present the results of auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and atomic force microscopy (AFM) analysis of sulfur passivating layers on the GaAs(001) surface. The GaAs surfaces were passivated with both inorganic ((NH_4)_2S) and organic (ODT) S-based compounds. We prepared the inorganic sulfur-passivated GaAs(001) surfaces with a wet chemical treatment using (NH_4)_2S solution. This was followed by thermal annealing of the treated sample in ultra high vacuum. After ex-situ and in-situ treatments the surface resulted in a (2X1) LEED pattern. The LEED data (I-V curves) was recorded and compared with dynamical LEED calculations for different structural models for the sulfur passivated GaAs(110) surface. The results showed that sulfur passivated (2X1) surface structure is an arsenic-sulfur dimer on gallium terminated substrate. The ex-situ AFM results also showed a (2X1) structure for the inorganic passivation and a very smooth surface for the organic ODT in ethanal treated sample.

  1. How does the molecular linker in dynamic force spectroscopy affect probing molecular interactions at the single-molecule level?

    NASA Astrophysics Data System (ADS)

    Taninaka, Atsushi; Aizawa, Kota; Hanyu, Tatsuya; Hirano, Yuuichi; Takeuchi, Osamu; Shigekawa, Hidemi

    2016-08-01

    Dynamic force spectroscopy (DFS) based on atomic force microscopy, which enables us to obtain information on the interaction potential between molecules such as antigen-antibody complexes at the single-molecule level, is a key technique for advancing molecular science and technology. However, to ensure the reliability of DFS measurement, its basic mechanism must be well understood. We examined the effect of the molecular linker used to fix the target molecule to the atomic force microscope cantilever, i.e., the force direction during measurement, for the first time, which has not been discussed until now despite its importance. The effect on the lifetime and barrier position, which can be obtained by DFS, was found to be ˜10 and ˜50%, respectively, confirming the high potential of DFS.

  2. Spectrin-ankyrin interaction mechanics: A key force balance factor in the red blood cell membrane skeleton.

    PubMed

    Saito, Masakazu; Watanabe-Nakayama, Takahiro; Machida, Shinichi; Osada, Toshiya; Afrin, Rehana; Ikai, Atsushi

    2015-01-01

    As major components of red blood cell (RBC) cytoskeleton, spectrin and F-actin form a network that covers the entire cytoplasmic surface of the plasma membrane. The cross-linked two layered structure, called the membrane skeleton, keeps the structural integrity of RBC under drastically changing mechanical environment during circulation. We performed force spectroscopy experiments on the atomic force microscope (AFM) as a means to clarify the mechanical characteristics of spectrin-ankyrin interaction, a key factor in the force balance of the RBC cytoskeletal structure. An AFM tip was functionalized with ANK1-62k and used to probe spectrin crosslinked to mica surface. A force spectroscopy study gave a mean unbinding force of ~30 pN under our experimental conditions. Two energy barriers were identified in the unbinding process. The result was related to the well-known flexibility of spectrin tetramer and participation of ankyrin 1-spectrin interaction in the overall balance of membrane skeleton dynamics.

  3. Characterization of Gd loaded chitosan-TPP nanohydrogels by a multi-technique approach combining dynamic light scattering (DLS), asymetrical flow-field-flow-fractionation (AF4) and atomic force microscopy (AFM) and design of positive contrast agents for molecular resonance imaging (MRI)

    NASA Astrophysics Data System (ADS)

    Rigaux, G.; Gheran, C. V.; Callewaert, M.; Cadiou, C.; Voicu, S. N.; Dinischiotu, A.; Andry, M. C.; Vander Elst, L.; Laurent, S.; Muller, R. N.; Berquand, A.; Molinari, M.; Huclier-Markai, S.; Chuburu, F.

    2017-02-01

    Chitosan CS—tripolyphosphate TPP/hyaluronic acid HA nanohydrogels loaded with gadolinium chelates (GdDOTA ⊂ CS-TPP/HA NGs) synthesized by ionic gelation were designed for lymph node (LN) MRI. In order to be efficiently drained to LNs, nanogels (NGs) needed to exhibit a diameter ϕ < 100 nm. For that, formulation parameters were tuned, using (i) CS of two different molecular weights (51 and 37 kDa) and (ii) variable CS/TPP ratio (2 < CS/TPP < 8). Characterization of NG size distribution by dynamic light scattering (DLS) and asymetrical flow-field-flow-fractionation (AF4) showed discrepancies since DLS diameters were consistently above 200 nm while AF4 showed individual nano-objects with ϕ < 100 nm. Such a difference could be correlated to the presence of aggregates inherent to ionic gelation. This point was clarified by atomic force microscopy (AFM) in liquid mode which highlighted the main presence of individual nano-objects in nanosuspensions. Thus, combination of DLS, AF4 and AFM provided a more precise characterization of GdDOTA ⊂ CS-TPP/HA nanohydrogels which, in turn, allowed to select formulations leading to NGs of suitable mean sizes showing good MRI efficiency and negligible toxicity.

  4. Characterization of Gd loaded chitosan-TPP nanohydrogels by a multi-technique approach combining dynamic light scattering (DLS), asymetrical flow-field-flow-fractionation (AF4) and atomic force microscopy (AFM) and design of positive contrast agents for molecular resonance imaging (MRI).

    PubMed

    Rigaux, G; Gheran, C V; Callewaert, M; Cadiou, C; Voicu, S N; Dinischiotu, A; Andry, M C; Vander Elst, L; Laurent, S; Muller, R N; Berquand, A; Molinari, M; Huclier-Markai, S; Chuburu, F

    2017-02-03

    Chitosan CS-tripolyphosphate TPP/hyaluronic acid HA nanohydrogels loaded with gadolinium chelates (GdDOTA ⊂ CS-TPP/HA NGs) synthesized by ionic gelation were designed for lymph node (LN) MRI. In order to be efficiently drained to LNs, nanogels (NGs) needed to exhibit a diameter ϕ < 100 nm. For that, formulation parameters were tuned, using (i) CS of two different molecular weights (51 and 37 kDa) and (ii) variable CS/TPP ratio (2 < CS/TPP < 8). Characterization of NG size distribution by dynamic light scattering (DLS) and asymetrical flow-field-flow-fractionation (AF4) showed discrepancies since DLS diameters were consistently above 200 nm while AF4 showed individual nano-objects with ϕ < 100 nm. Such a difference could be correlated to the presence of aggregates inherent to ionic gelation. This point was clarified by atomic force microscopy (AFM) in liquid mode which highlighted the main presence of individual nano-objects in nanosuspensions. Thus, combination of DLS, AF4 and AFM provided a more precise characterization of GdDOTA ⊂ CS-TPP/HA nanohydrogels which, in turn, allowed to select formulations leading to NGs of suitable mean sizes showing good MRI efficiency and negligible toxicity.

  5. Activity in the premotor area related to bite force control--a functional near-infrared spectroscopy study.

    PubMed

    Takeda, Tomotaka; Shibusawa, Mami; Sudal, Osamu; Nakajima, Kazunori; Ishigami, Keiichi; Sakatani, Kaoru

    2010-01-01

    The purpose of this study was to elucidate the influence of bite force control on oxygenated hemoglobin (OxyHb) levels in regional cerebral blood flow as an indicator of brain activity in the premotor area. Healthy right-handed volunteers with no subjective or objective symptoms of problems of the stomatognathic system or cervicofacial region were included. Functional near-infrared spectroscopy (fNIRS) was used to determine OxyHb levels in the premotor area during bite force control. A bite block equipped with an occlusal force sensor was prepared to measure clenching at the position where the right upper and lower canine cusps come into contact. Intensity of clenching was shown on a display and feedback was provided to the subjects. Intensity was set at 20, 50 and 80% of maximum voluntary teeth clenching force. To minimize the effect of the temporal muscle on the working side of the jaw, the fNIRS probes were positioned contralaterally, in the left region. The findings of this study are: activation of the premotor area with bite force control was noted in all subjects, and in the group analysis OxyHb in the premotor cortex was significantly increased as the clenching strengthened at 20, 50 and 80% of maximum voluntary clenching force. These results suggest there is a possibility that the premotor area is involved in bite force control.

  6. Leading Change: Transitioning the AFMS into a High Reliability Organization

    DTIC Science & Technology

    2016-02-16

    AIR WAR COLLEGE AIR UNIVERSITY LEADING CHANGE: TRANSITIONING THE AFMS INTO A HIGH RELIABILTY ORGANIZATION by Robert K. Bogart...academic research paper are those of the author and do not reflect the official policy or position of the US government, the Department of Defense, or Air ...University. In accordance with Air Force Instruction 51-303, it is not copyrighted, but is the property of the United States government. iii

  7. Adiabatic Compression Sensitivity of AF-M315E

    DTIC Science & Technology

    2015-07-01

    the development of green rocket propellants . The Air Force Research Laboratory’s (AFRL) monopropellant, AF-M315E, has been selected for...art rocket fuels and propellants . A known quantity of liquid propellant is placed in a metal U-tube and held isothermally in a preheated mixture of... Propellant Infusion Mission (GPIM) program. As the propulsion system developed by Aerojet- Rocketdyne for this propellant advances in maturity, studies

  8. Morphological and Structural Changes on Human Dental Enamel After Er:YAG Laser Irradiation: AFM, SEM, and EDS Evaluation

    PubMed Central

    Rodríguez-Vilchis, Laura Emma; Olea-Mejìa, Oscar Fernando; Sánchez-Flores, Ignacio; Centeno-Pedraza, Claudia

    2011-01-01

    Abstract Objective: The purpose of this study was to evaluate, using atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), the morphological and structural changes of the enamel after irradiation with the Er:YAG laser. Background data: A previous study showed that subablative Er:YAG laser irradiation produced undesirable morphological changes on the enamel surface, such as craters and cracks; however, the enamel acid resistance was not increased. Methods: Fifty-two samples of human enamel were divided into four groups (n = 13): Group I was the control (no laser irradiation), whereas Groups II, III, and IV were irradiated with the Er:YAG 100 mJ (12.7 J/cm2), 100 mJ (7.5 J/cm2), and 150 mJ (11 J/cm2), respectively, at 10 Hz with water spray. The morphological changes were observed by AFM and SEM. The weight percentages (wt%) of calcium (Ca), phosphorus (P), oxygen (O) and chlorine (Cl) were determined in the resultant craters and their periphery using EDS. Kruskal–Wallis and Mann–Whitney U tests were performed (p ≤ 0.05) to distinguish significant differences among the groups. Results: The AFM images showed cracks with depths between 250 nm and 750 nm for Groups II and IV, respectively, and the widths of these cracks were 5.37 μm and 2.58 μm. The interior of the cracks showed a rough surface. The SEM micrographs revealed morphological changes. Significant differences were detected in Ca, P, and Cl in the crater and its periphery. Conclusions: AFM observations showed triangular-shaped cracks, whereas craters and cracks were evident by SEM in all irradiated samples. It was not possible to establish a characteristic chemical pattern in the craters. PMID:21417912

  9. Nanoscale infrared (IR) spectroscopy and imaging of structural lipids in human stratum corneum using an atomic force microscope to directly detect absorbed light from a tunable IR laser source.

    PubMed

    Marcott, Curtis; Lo, Michael; Kjoller, Kevin; Domanov, Yegor; Balooch, Guive; Luengo, Gustavo S

    2013-06-01

    An atomic force microscope (AFM) and a tunable infrared (IR) laser source have been combined in a single instrument (AFM-IR) capable of producing ~200-nm spatial resolution IR spectra and absorption images. This new capability enables IR spectroscopic characterization of human stratum corneum at unprecendented levels. Samples of normal and delipidized stratum corneum were embedded, cross-sectioned and mounted on ZnSe prisms. A pulsed tunable IR laser source produces thermomechanical expansion upon absorption, which is detected through excitation of contact resonance modes in the AFM cantilever. In addition to reducing the total lipid content, the delipidization process damages the stratum corneum morphological structure. The delipidized stratum corneum shows substantially less long-chain CH2 -stretching IR absorption band intensity than normal skin. AFM-IR images that compare absorbances at 2930/cm (lipid) and 3290/cm (keratin) suggest that regions of higher lipid concentration are located at the perimeter of corneocytes in the normal stratum corneum.

  10. XPS and AFM Study of GaAs Surface Treatment

    SciTech Connect

    Contreras-Guerrero, R.; Wallace, R. M.; Aguirre-Francisco, S.; Herrera-Gomez, A.; Lopez-Lopez, M.

    2008-11-13

    Obtaining smooth and atomically clean surfaces is an important step in the preparation of a surface for device manufacturing. In this work different processes are evaluated for cleaning a GaAs surface. A good surface cleaning treatment is that which provides a high level of uniformity and controllability of the surface. Different techniques are useful as cleaning treatments depending on the growth process to be used. The goal is to remove the oxygen and carbon contaminants and then form a thin oxide film to protect the surface, which is easy to remove later with thermal desorption mechanism like molecular beam epitaxy (MBE) with minimal impact to the surface. In this study, atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to characterize the structure of the surface, the composition, as well as detect oxygen and carbon contaminant on the GaAs surface. This study consists in two parts. The first part the surface was subjected to different chemical treatments. The chemical solutions were: (a)H{sub 2}SO{sub 4}:H{sub 2}O{sub 2}:H{sub 2}O(4:1:100), (b) HCl: H{sub 2}O(1:3), (c)NH{sub 4}OH 29%. The treatments (a) and (b) reduced the oxygen on the surface. Treatment (c) reduces carbon contamination. In the second part we made MOS devices on the surfaces treated. They were characterized by CV and IV electrical measurements. They show frequency dispersion.

  11. Quantitative force and dissipation measurements in liquids using piezo-excited atomic force microscopy: a unifying theory.

    PubMed

    Kiracofe, Daniel; Raman, Arvind

    2011-12-02

    The use of a piezoelectric element (acoustic excitation) to vibrate the base of microcantilevers is a popular method for dynamic atomic force microscopy. In air or vacuum, the base motion is so small (relative to tip motion) that it can be neglected. However, in liquid environments the base motion can be large and cannot be neglected. Yet it cannot be directly observed in most AFMs. Therefore, in liquids, quantitative force and energy dissipation spectroscopy with acoustic AFM relies on theoretical formulae and models to estimate the magnitude of the base motion. However, such formulae can be inaccurate due to several effects. For example, a significant component of the piezo excitation does not mechanically excite the cantilever but rather transmits acoustic waves through the surrounding liquid, which in turn indirectly excites the cantilever. Moreover, resonances of the piezo, chip and holder can obscure the true cantilever dynamics even in well-designed liquid cells. Although some groups have tried to overcome these limitations (either by theory modification or better design of piezos and liquid cells), it is generally accepted that acoustic excitation is unsuitable for quantitative force and dissipation spectroscopy in liquids. In this paper the authors present a careful study of the base motion and excitation forces and propose a method by which quantitative analysis is in fact possible, thus opening this popular method for quantitative force and dissipation spectroscopy using dynamic AFM in liquids. This method is validated by experiments in water on mica using a scanning laser Doppler vibrometer, which can measure the actual base motion. Finally, the method is demonstrated by using small-amplitude dynamic AFM to extract the force gradients and dissipation on solvation shells of octamethylcyclotetrasiloxane (OMCTS) molecules on mica.

  12. Mining the “glycocode”—exploring the spatial distribution of glycans in gastrointestinal mucin using force spectroscopy

    PubMed Central

    Gunning, A. Patrick; Kirby, Andrew R.; Fuell, Christine; Pin, Carmen; Tailford, Louise E.; Juge, Nathalie

    2013-01-01

    Mucins are the main components of the gastrointestinal mucus layer. Mucin glycosylation is critical to most intermolecular and intercellular interactions. However, due to the highly complex and heterogeneous mucin glycan structures, the encoded biological information remains largely encrypted. Here we have developed a methodology based on force spectroscopy to identify biologically accessible glycoepitopes in purified porcine gastric mucin (pPGM) and purified porcine jejunal mucin (pPJM). The binding specificity of lectins Ricinus communis agglutinin I (RCA), peanut (Arachis hypogaea) agglutinin (PNA), Maackia amurensis lectin II (MALII), and Ulex europaeus agglutinin I (UEA) was utilized in force spectroscopy measurements to quantify the affinity and spatial distribution of their cognate sugars at the molecular scale. Binding energy of 4, 1.6, and 26 aJ was determined on pPGM for RCA, PNA, and UEA. Binding was abolished by competition with free ligands, demonstrating the validity of the affinity data. The distributions of the nearest binding site separations estimated the number of binding sites in a 200-nm mucin segment to be 4 for RCA, PNA, and UEA, and 1.8 for MALII. Binding site separations were affected by partial defucosylation of pPGM. Furthermore, we showed that this new approach can resolve differences between gastric and jejunum mucins.—Gunning, A. P., Kirby, A. R., Fuell, C., Pin, C., Tailford L. E., Juge, N. Mining the “glycocode”—exploring the spatial distribution of glycans in gastrointestinal mucin using force spectroscopy. PMID:23493619

  13. 3D Color Digital Elevation Map of AFM Sample

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This color image is a three dimensional (3D) view of a digital elevation map of a sample collected by NASA's Phoenix Mars Lander's Atomic Force Microscope (AFM).

    The image shows four round pits, only 5 microns in depth, that were micromachined into the silicon substrate, which is the background plane shown in red. This image has been processed to reflect the levelness of the substrate.

    A Martian particle only one micrometer, or one millionth of a meter, across is held in the upper left pit.

    The rounded particle shown at the highest magnification ever seen from another world is a particle of the dust that cloaks Mars. Such dust particles color the Martian sky pink, feed storms that regularly envelop the planet and produce Mars' distinctive red soil.

    The particle was part of a sample informally called 'Sorceress' delivered to the AFM on the 38th Martian day, or sol, of the mission (July 2, 2008). The AFM is part of Phoenix's microscopic station called MECA, or the Microscopy, Electrochemistry, and Conductivity Analyzer.

    The AFM was developed by a Swiss-led consortium, with Imperial College London producing the silicon substrate that holds sampled particles.

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  14. Measurement methods in atomic force microscopy.

    PubMed

    Torre, Bruno; Canale, Claudio; Ricci, Davide; Braga, Pier Carlo

    2011-01-01

    This chapter is introductory to the measurements: it explains different measurement techniques both for imaging and for force spectroscopy, on which most of the AFM experiments rely. It gives a general overview of the different techniques and of the output expected from the instrument; therefore it is, at a basic level, a good tool to properly start a new experiment. Concepts introduced in this chapter give the base for understanding the applications shown in the following chapters. Subheading 1 introduces the distinction between spectroscopy and imaging experiments and, within the last ones, between DC and AC mode. Subheading 2 is focused on DC mode (contact), explaining the topography and the lateral force channel. Subheading 3 introduces AC mode, both in noncontact and intermittent contact case. Phase imaging and force modulation are also discussed. Subheading 4 explains how the AFM can be used to measure local mechanical and adhesive properties of specimens by means of force spectroscopy technique. An overview on the state of the art and future trends in this field is also given.

  15. Image Force Microscopy

    NASA Astrophysics Data System (ADS)

    Rajapaksa, Indrajith

    In this thesis we describe an enhancement to the Atomic force microscope (AFM) to simultaneously gather topographic features and spectroscopic information .Compared to the current state of the art of near-field excitation and far-field detection AFM imaging techniques our system uses a radical new approach near-field excitation and near-field detection. By placing the detector in the near-field we achieve high signal to noise and single molecular resolution. The origin of our near-field detector signal is the image force gradient due to the interaction of the stimulated molecular dipole with its image on the metal probe. We designed and built an optical and electronic system to capture this signal and simultaneously image nano-scale surface topography and optical image force gradient. By varying the wavelength of the excitation beam we measure the induced optical image force gradient spectra of molecules on surface. These spectra show good agreement with the absorption spectra of the bulk molecules measured by conventional absorption spectroscopy. We show that image force gradient is directly proportional to the optical absorption dipole strength. Using Finite Element 3D electromagnetic simulations and using Lorentz model for the excited molecular dipole we showed that the image force gradient has a decay length of 1nm, making the theoretical resolution of this microscopy technique approximately 1 nm. This rapid decay was measured experimentally .This resolution was seen by the high contrasting spectroscopic images of molecules on the surface. In follow on experiments this technique was extended to provide surface Raman spectroscopy and microscopy at molecular resolution. We create an image force gradient interaction through optical parametric down conversion between stimulated Raman excited molecules on a surface and a cantilevered nanometer scale probe brought very close to it. Spectroscopy and microscopy on clusters of molecules have been performed. Single

  16. Three-dimensional interaction force and tunneling current spectroscopy of point defects on rutile TiO2(110)

    NASA Astrophysics Data System (ADS)

    Baykara, Mehmet Z.; Mönig, Harry; Schwendemann, Todd C.; Ünverdi, Ã.-zhan; Altman, Eric I.; Schwarz, Udo D.

    2016-02-01

    The extent to which point defects affect the local chemical reactivity and electronic properties of an oxide surface was evaluated with picometer resolution in all three spatial dimensions using simultaneous atomic force/scanning tunneling microscopy measurements performed on the (110) face of rutile TiO2. Oxygen atoms were imaged as protrusions in both data channels, corresponding to a rarely observed imaging mode for this prototypical metal oxide surface. Three-dimensional spectroscopy of interaction forces and tunneling currents was performed on individual surface and subsurface defects as a function of tip-sample distance. An interstitial defect assigned to a subsurface hydrogen atom is found to have a distinct effect on the local density of electronic states on the surface, but no detectable influence on the tip-sample interaction force. Meanwhile, spectroscopic data acquired on an oxygen vacancy highlight the role of the probe tip in chemical reactivity measurements.

  17. Force Spectroscopy of Collagen Fibers to Investigate Their Mechanical Properties and Structural Organization

    PubMed Central

    Gutsmann, Thomas; Fantner, Georg E.; Kindt, Johannes H.; Venturoni, Manuela; Danielsen, Signe; Hansma, Paul K.

    2004-01-01

    Tendons are composed of collagen and other molecules in a highly organized hierarchical assembly, leading to extraordinary mechanical properties. To probe the cross-links on the lower level of organization, we used a cantilever to pull substructures out of the assembly. Advanced force probe technology, using small cantilevers (length <20 μm), improved the force resolution into the sub-10 pN range. In the force versus extension curves, we found an exponential increase in force and two different periodic rupture events, one with strong bonds (jumps in force of several hundred pN) with a periodicity of 78 nm and one with weak bonds (jumps in force of <7 pN) with a periodicity of 22 nm. We demonstrate a good correlation between the measured mechanical behavior of collagen fibers and their appearance in the micrographs taken with the atomic force microscope. PMID:15111431

  18. Combination STM/AFM and AFM Images of Magnetic Domains

    NASA Astrophysics Data System (ADS)

    Yi, L.; Gallagher, M.; Howells, S.; Chen, T.; Sarid, D.

    1991-12-01

    By employing a cantilevered tip in a scanning tunneling microscope, one obtains images that show an enhancement of features associated with forces whose derivatives vary along the direction of scanning. The theory of this process is described together with experimental results showing magnetic domains on a gold coated floppy disk. Also shown are atomic force microscopy images of a ferrofluid-developed magnetic tape.

  19. Thermochemical nanolithography fabrication and atomic force microscopy characterization of functional nanostructures

    NASA Astrophysics Data System (ADS)

    Wang, Debin

    This thesis presents the development of a novel atomic force microscope (AFM) based nanofabrication technique termed as thermochemical nanolithography (TCNL). TCNL uses a resistively heated AFM cantilever to thermally activate chemical reactions on a surface with nanometer resolution. This technique can be used for fabrication of functional nanostructures that are appealing for various applications in nanofluidics, nanoelectronics, nanophotonics, and biosensing devices. This thesis research is focused on three main objectives. The first objective is to study the fundamentals of TCNL writing aspects. We have conducted a systematic study of the heat transfer mechanism using finite element analysis modeling, Raman spectroscopy, and local glass transition measurement. In addition, based on thermal kinetics analysis, we have identified several key factors to achieve high resolution fabrication of nanostructures during the TCNL writing process. The second objective is to demonstrate the use of TCNL on a variety of systems and thermochemical reactions. We show that TCNL can be employed to (1) modify the wettability of a polymer surface at the nanoscale, (2) fabricate nanoscale templates on polymer films for assembling nano-objects, such as proteins and DNA, (3) fabricate conjugated polymer semiconducting nanowires, and (4) reduce graphene oxide with nanometer resolution. The last objective is to characterize the TCNL nanostructures using AFM based methods, such as friction force microscopy, phase imaging, electric force microscopy, and conductive AFM. We show that they are useful for in situ characterization of nanostructures, which is particularly challenging for conventional macroscopic analytical tools, such as Raman spectroscopy, IR spectroscopy, and fluorescence microscopy.

  20. AFM nanoscale indentation in air of polymeric and hybrid materials with highly different stiffness

    NASA Astrophysics Data System (ADS)

    Suriano, Raffaella; Credi, Caterina; Levi, Marinella; Turri, Stefano

    2014-08-01

    In this study, nanomechanical properties of a variety of polymeric materials was investigated by means of AFM. In particular, selecting different AFM probes, poly(methyl methacrylate) (PMMA), polydimethylsiloxane (PDMS) bulk samples, sol-gel hybrid thin films and hydrated hyaluronic acid hydrogels were indented in air to determine the elastic modulus. The force-distance curves and the indentation data were found to be greatly affected by the cantilever stiffness and by tip geometry. AFM indentation tests show that the choice of the cantilever spring constant and of tip shape is crucially influenced by elastic properties of samples. When adhesion-dominated interactions occur between the tip and the surface of samples, force-displacement curves reveal that a suitable functionalization of AFM probes allows the control of such interactions and the extraction of Young' modulus from AFM curves that would be otherwise unfeasible. By applying different mathematical models depending on AFM probes and materials under investigation, the values of Young's modulus were obtained and compared to those measured by rheological and dynamic mechanical analysis or to literature data. Our results show that a wide range of elastic moduli (10 kPa-10 GPa) can be determined by AFM in good agreement with those measured by conventional macroscopic measurements.

  1. Theoretical modelling of AFM for bimetallic tip-substrate interactions

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Ferrante, John

    1991-01-01

    Recently, a new technique for calculating the defect energetics of alloys based on Equivalent Crystal Theory was developed. This new technique successfully predicts the bulk properties for binary alloys as well as segregation energies in the dilute limit. The authors apply this limit for the calculation of energy and force as a function of separation of an atomic force microscope (AFM) tip and substrate. The study was done for different combinations of tip and sample materials. The validity of the universality discovered for the same metal interfaces is examined for the case of different metal interactions.

  2. The influence of aminophylline on the nanostructure and nanomechanics of T lymphocytes: an AFM study

    NASA Astrophysics Data System (ADS)

    Huang, Xun; He, Jiexiang; Liu, Mingxian; Zhou, Changren

    2014-09-01

    Although much progress has been made in the illustration of the mechanism of aminophylline (AM) treating asthma, there is no data about its effect on the nanostructure and nanomechanics of T lymphocytes. Here, we presented atomic force spectroscopy (AFM)-based investigations at the nanoscale level to address the above fundamental biophysical questions. As increasing AM treatment time, T lymphocytes' volume nearly double increased and then decreased. The changes of nanostructural features of the cell membrane, i.e., mean height of particles, root-mean-square roughness (Rq), crack and fragment appearance, increased with AM treatment time. T lymphocytes were completely destroyed with 96-h treatment, and they existed in the form of small fragments. Analysis of force-distance curves showed that the adhesion force of cell surface decreased significantly with the increase of AM treatment time, while the cell stiffness increased firstly and then decreased. These changes were closely correlated to the characteristics and process of cell oncosis. In total, these quantitative and qualitative changes of T lymphocytes' structure and nanomechanical properties suggested that AM could induce T lymphocyte oncosis to exert anti-inflammatory effects for treating asthma. These findings provide new insights into the T lymphocyte oncosis and the anti-inflammatory mechanism and immune regulation actions of AM.

  3. Evolution of nano-rheological properties of Nafion¯ thin films during pH modification by strong base treatment: A static and dynamic force spectroscopy study

    NASA Astrophysics Data System (ADS)

    Eslami, Babak; López-Guerra, Enrique A.; Raftari, Maryam; Solares, Santiago D.

    2016-04-01

    Addition of a strong base to Nafion® proton exchange membranes is a common practice in industry to increase their overall performance in fuel cells. Here, we investigate the evolution of the nano-rheological properties of Nafion thin films as a function of the casting pH, via characterization with static and dynamic, contact and intermittent-contact atomic force microscopy (AFM) techniques. The addition of KOH causes non-monotonic changes in the viscoelastic properties of the films, which behave as highly dissipative, softer materials near neutral pH values, and as harder, more elastic materials at extreme pH values. We quantify this behavior through calculation of the temporal evolution of the compliance and the glassy compliance under static AFM measurements. We complement these observations with dynamic AFM metrics, including dissipated power and virial (for intermittent-contact-mode measurements), and contact resonance frequency and quality factor (for dynamic contact-mode measurements). We explain the non-monotonic material property behavior in terms of the degree of ionic crosslinking and moisture content of the films, which vary with the addition of KOH. This work focuses on the special case study of the addition of strong bases, but the observed mechanical property changes are broadly related to water plasticizing effects and ionic crosslinking, which are also important in other types of films.

  4. Robust high-resolution imaging and quantitative force measurement with tuned-oscillator atomic force microscopy.

    PubMed

    Dagdeviren, Omur E; Götzen, Jan; Hölscher, Hendrik; Altman, Eric I; Schwarz, Udo D

    2016-02-12

    Atomic force microscopy (AFM) and spectroscopy are based on locally detecting the interactions between a surface and a sharp probe tip. For highest resolution imaging, noncontact modes that avoid tip-sample contact are used; control of the tip's vertical position is accomplished by oscillating the tip and detecting perturbations induced by its interaction with the surface potential. Due to this potential's nonlinear nature, however, achieving reliable control of the tip-sample distance is challenging, so much so that despite its power vacuum-based noncontact AFM has remained a niche technique. Here we introduce a new pathway to distance control that prevents instabilities by externally tuning the oscillator's response characteristics. A major advantage of this operational scheme is that it delivers robust position control in both the attractive and repulsive regimes with only one feedback loop, thereby providing an easy-to-implement route to atomic resolution imaging and quantitative tip-sample interaction force measurement.

  5. Probing the role of metal cations on the aggregation behavior of amyloid β-peptide at a single molecule level by AFM

    NASA Astrophysics Data System (ADS)

    Xie, Yang; Wang, Jianhua; Liu, Chundong

    2016-09-01

    With the development of nanotechnology, understanding of intermolecular interactions on a single molecule level by atomic force spectroscopy (AFM) has played an important role in molecular biology and biomedical science. In recent years, some research suggested that the presence of metal cations is an important regulator in the processes of misfolding and aggregation of the amyloid β-protein (Aβ), which may be an important etiological factor of Alzheimer's disease. However, the knowledge on the principle of interactions between Aβ and metal cations at the single molecule level is still poor understood. In this paper, the amyloid β-protein (Aβ) was fabricated on substrate of mixed thiol-modified gold nanoparticles using self-assembled monolayer method and the adhesion force in the longitudinal direction between metal cations and Aβ42 were investigated by AFM. The role of metal ions on Aβ aggregation is discussed from the perspective of single molecular force. The force results showed that the specific adhesion force F i and the nonspecific force F 0 between a single Aβ-Aβ pair in control experiment were calculated as 42 ± 3 and 80 pN, respectively. However, F i between a single Aβ-Aβ pair in the presence of Cu2+, Zn2+, Ca2+ and Al3+ increased dramatically to 84 ± 6, 89 ± 3, 73 ± 5, 95 ± 5 pN successively, which indicated that unbinding between Aβ proteins is accelerated in the presence of metal cations. What is more, the imaging results showed that substoichiometric copper cations accelerate the formation of fibrils within 3 days. The combined atomic force spectroscopy and imaging analysis indicate that metal cations play a role in promoting the aggregating behavior of Aβ42.

  6. A simple and efficient quasi 3-dimensional viscoelastic model and software for simulation of tapping-mode atomic force microscopy

    SciTech Connect

    Solares, Santiago D.

    2015-11-26

    This study introduces a quasi-3-dimensional (Q3D) viscoelastic model and software tool for use in atomic force microscopy (AFM) simulations. The model is based on a 2-dimensional array of standard linear solid (SLS) model elements. The well-known 1-dimensional SLS model is a textbook example in viscoelastic theory but is relatively new in AFM simulation. It is the simplest model that offers a qualitatively correct description of the most fundamental viscoelastic behaviors, namely stress relaxation and creep. However, this simple model does not reflect the correct curvature in the repulsive portion of the force curve, so its application in the quantitative interpretation of AFM experiments is relatively limited. In the proposed Q3D model the use of an array of SLS elements leads to force curves that have the typical upward curvature in the repulsive region, while still offering a very low computational cost. Furthermore, the use of a multidimensional model allows for the study of AFM tips having non-ideal geometries, which can be extremely useful in practice. Examples of typical force curves are provided for single- and multifrequency tappingmode imaging, for both of which the force curves exhibit the expected features. Lastly, a software tool to simulate amplitude and phase spectroscopy curves is provided, which can be easily modified to implement other controls schemes in order to aid in the interpretation of AFM experiments.

  7. A simple and efficient quasi 3-dimensional viscoelastic model and software for simulation of tapping-mode atomic force microscopy

    DOE PAGES

    Solares, Santiago D.

    2015-11-26

    This study introduces a quasi-3-dimensional (Q3D) viscoelastic model and software tool for use in atomic force microscopy (AFM) simulations. The model is based on a 2-dimensional array of standard linear solid (SLS) model elements. The well-known 1-dimensional SLS model is a textbook example in viscoelastic theory but is relatively new in AFM simulation. It is the simplest model that offers a qualitatively correct description of the most fundamental viscoelastic behaviors, namely stress relaxation and creep. However, this simple model does not reflect the correct curvature in the repulsive portion of the force curve, so its application in the quantitative interpretationmore » of AFM experiments is relatively limited. In the proposed Q3D model the use of an array of SLS elements leads to force curves that have the typical upward curvature in the repulsive region, while still offering a very low computational cost. Furthermore, the use of a multidimensional model allows for the study of AFM tips having non-ideal geometries, which can be extremely useful in practice. Examples of typical force curves are provided for single- and multifrequency tappingmode imaging, for both of which the force curves exhibit the expected features. Lastly, a software tool to simulate amplitude and phase spectroscopy curves is provided, which can be easily modified to implement other controls schemes in order to aid in the interpretation of AFM experiments.« less

  8. A simple and efficient quasi 3-dimensional viscoelastic model and software for simulation of tapping-mode atomic force microscopy.

    PubMed

    Solares, Santiago D

    2015-01-01

    This paper introduces a quasi-3-dimensional (Q3D) viscoelastic model and software tool for use in atomic force microscopy (AFM) simulations. The model is based on a 2-dimensional array of standard linear solid (SLS) model elements. The well-known 1-dimensional SLS model is a textbook example in viscoelastic theory but is relatively new in AFM simulation. It is the simplest model that offers a qualitatively correct description of the most fundamental viscoelastic behaviors, namely stress relaxation and creep. However, this simple model does not reflect the correct curvature in the repulsive portion of the force curve, so its application in the quantitative interpretation of AFM experiments is relatively limited. In the proposed Q3D model the use of an array of SLS elements leads to force curves that have the typical upward curvature in the repulsive region, while still offering a very low computational cost. Furthermore, the use of a multidimensional model allows for the study of AFM tips having non-ideal geometries, which can be extremely useful in practice. Examples of typical force curves are provided for single- and multifrequency tapping-mode imaging, for both of which the force curves exhibit the expected features. Finally, a software tool to simulate amplitude and phase spectroscopy curves is provided, which can be easily modified to implement other controls schemes in order to aid in the interpretation of AFM experiments.

  9. Fabrication of a new substrate for atomic force microscopic observation of DNA molecules from an ultrasmooth sapphire plate.

    PubMed

    Yoshida, K; Yoshimoto, M; Sasaki, K; Ohnishi, T; Ushiki, T; Hitomi, J; Yamamoto, S; Sigeno, M

    1998-04-01

    A new stable substrate applicable to the observation of DNA molecules by atomic force microscopy (AFM) was fabricated from a ultrasmooth sapphire (alpha-Al2O3 single crystal) plate. The atomically ultrasmooth sapphire as obtained by high-temperature annealing has hydrophobic surfaces and could not be used for the AFM observation of DNA. However, sapphire treated with Na3PO4 aqueous solution exhibited a hydrophilic character while maintaining a smooth surface structure. The surface of the wet-treated sapphire was found by x-ray photoelectron spectroscopy and AFM to be approximately 0.3 nm. The hydrophilic surface character of the ultrasmooth sapphire plate made it easy for DNA molecules to adhere to the plate. Circular molecules of the plasmid DNA could be imaged by AFM on the hydrophilic ultrasmooth sapphire plate.

  10. Fabrication of a new substrate for atomic force microscopic observation of DNA molecules from an ultrasmooth sapphire plate.

    PubMed Central

    Yoshida, K; Yoshimoto, M; Sasaki, K; Ohnishi, T; Ushiki, T; Hitomi, J; Yamamoto, S; Sigeno, M

    1998-01-01

    A new stable substrate applicable to the observation of DNA molecules by atomic force microscopy (AFM) was fabricated from a ultrasmooth sapphire (alpha-Al2O3 single crystal) plate. The atomically ultrasmooth sapphire as obtained by high-temperature annealing has hydrophobic surfaces and could not be used for the AFM observation of DNA. However, sapphire treated with Na3PO4 aqueous solution exhibited a hydrophilic character while maintaining a smooth surface structure. The surface of the wet-treated sapphire was found by x-ray photoelectron spectroscopy and AFM to be approximately 0.3 nm. The hydrophilic surface character of the ultrasmooth sapphire plate made it easy for DNA molecules to adhere to the plate. Circular molecules of the plasmid DNA could be imaged by AFM on the hydrophilic ultrasmooth sapphire plate. PMID:9545030

  11. Accurate formula for conversion of tunneling current in dynamic atomic force spectroscopy

    NASA Astrophysics Data System (ADS)

    Sader, John E.; Sugimoto, Yoshiaki

    2010-07-01

    Recent developments in frequency modulation atomic force microscopy enable simultaneous measurement of frequency shift and time-averaged tunneling current. Determination of the interaction force is facilitated using an analytical formula, valid for arbitrary oscillation amplitudes [Sader and Jarvis, Appl. Phys. Lett. 84, 1801 (2004)]. Here we present the complementary formula for evaluation of the instantaneous tunneling current from the time-averaged tunneling current. This simple and accurate formula is valid for any oscillation amplitude and current law. The resulting theoretical framework allows for simultaneous measurement of the instantaneous tunneling current and interaction force in dynamic atomic force microscopy.

  12. {beta}-connectin studies by small-angle x-ray scattering and single-molecule force spectroscopy by atomic force microscopy

    SciTech Connect

    Marchetti, S.; Carla, M.; Gambi, C. M. C.; Sbrana, F.; Vassalli, M.; Toscano, A.; Pacini, A.; Fratini, E.; Tiribilli, B.

    2011-05-15

    The three-dimensional structure and the mechanical properties of a {beta}-connectin fragment from human cardiac muscle, belonging to the I band, from I{sub 27} to I{sub 34}, were investigated by small-angle x-ray scattering (SAXS) and single-molecule force spectroscopy (SMFS). This molecule presents an entropic elasticity behavior, associated to globular domain unfolding, that has been widely studied in the last 10 years. In addition, atomic force microscopy based SMFS experiments suggest that this molecule has an additional elastic regime, for low forces, probably associated to tertiary structure remodeling. From a structural point of view, this behavior is a mark of the fact that the eight domains in the I{sub 27}-I{sub 34} fragment are not independent and they organize in solution, assuming a well-defined three-dimensional structure. This hypothesis has been confirmed by SAXS scattering, both on a diluted and a concentrated sample. Two different models were used to fit the SAXS curves: one assuming a globular shape and one corresponding to an elongated conformation, both coupled with a Coulomb repulsion potential to take into account the protein-protein interaction. Due to the predominance of the structure factor, the effective shape of the protein in solution could not be clearly disclosed. By performing SMFS by atomic force microscopy, mechanical unfolding properties were investigated. Typical sawtooth profiles were obtained and the rupture force of each unfolding domain was estimated. By fitting a wormlike chain model to each peak of the sawtooth profile, the entropic elasticity of octamer was described.

  13. An Atomic Force Microscopy based investigation of specific biomechanical properties for various types of neuronal cells

    NASA Astrophysics Data System (ADS)

    Spedden, Elise; White, James; Kaplan, David; Staii, Cristian

    2012-02-01

    Here we describe the use of Atomic Force Microscope (AFM) based techniques to characterize and explore the influence of biochemical and biomechanical cues on the growth and interaction of neuronal cells with surrounding guidance factors. Specifically, we use AFM topography and AFM force spectroscopy measurements to systematically investigate the morphology, elasticity, and real time growth of neuronal processes in the presence of different types of extracellular matrix proteins and growth factors. We therefore create a series of systems containing specified neuron densities where the type of the underlying growth promoting protein is different from sample to sample. For each system we measure key biomechanical parameters related to neuronal growth such as height and elastic modulus at multiple growth points on several types of neurons. We show that systematic measurements of these parameters yield fundamental information about the role played by substrate-plated guidance factors in determining elastic and morphological properties of neurons during growth.

  14. Surface Microstructure of Mo(C)N Coatings Investigated by AFM

    NASA Astrophysics Data System (ADS)

    Kuznetsova, T.; Zubar, T.; Chizhik, S.; Gilewicz, A.; Lupicka, O.; Warcholinski, B.

    2016-12-01

    MoCN coatings have been formed by cathodic arc evaporation using the mixture of acetylene and nitrogen and pure molybdenum target. The surface structure, in conjunction with x-ray data, was analyzed by atomic force microscopy (AFM). The AFM results show differently shaped grain forms on the surface of coatings investigated. The increase in carbon in chemical coatings composition results in the reduction in surface grain size and the increase in roughness of the coatings.

  15. Nanoscale rippling on polymer surfaces induced by AFM manipulation

    PubMed Central

    2015-01-01

    Summary Nanoscale rippling induced by an atomic force microscope (AFM) tip can be observed after performing one or many scans over the same area on a range of materials, namely ionic salts, metals, and semiconductors. However, it is for the case of polymer films that this phenomenon has been widely explored and studied. Due to the possibility of varying and controlling various parameters, this phenomenon has recently gained a great interest for some technological applications. The advent of AFM cantilevers with integrated heaters has promoted further advances in the field. An alternative method to heating up the tip is based on solvent-assisted viscoplastic deformations, where the ripples develop upon the application of a relatively low force to a solvent-rich film. An ensemble of AFM-based procedures can thus produce nanoripples on polymeric surfaces quickly, efficiently, and with an unprecedented order and control. However, even if nanorippling has been observed in various distinct modes and many theoretical models have been since proposed, a full understanding of this phenomenon is still far from being achieved. This review aims at summarizing the current state of the art in the perspective of achieving control over the rippling process on polymers at a nanoscale level. PMID:26733086

  16. Direct observation of the anchoring process during the adsorption of fibrinogen on a solid surface by force-spectroscopy mode atomic force microscopy

    PubMed Central

    Hemmerlé, J.; Altmann, S. M.; Maaloum, M.; Hörber, J. K. H.; Heinrich, L.; Voegel, J.-C.; Schaaf, P.

    1999-01-01

    Atomic force microscopy in a force-spectroscopy mode has been used to investigate the kinetics of the adsorption process of fibrinogen molecules on a silica surface. An original “approach/retraction” cycle of the tip/surface was used for this purpose. Fibrinogen molecules were adsorbed on the atomic force microscopy tip and were brought into contact with the silica surface for different interaction times varying from 5 to 2,000 ms. Multiple consecutive ruptures were observed. The mean number of ruptures nr per cycle increases steadily with the interaction time as well as the mean strength fr which varies from 300 pN for 5 ms to 1,400 pN for 2,000 ms. The minimal interaction time for a fibrinogen molecule to bind strongly to a silica surface during an adsorption process appears to lie between 50 and 200 ms. The histograms of the distances between two consecutive ruptures in one cycle exhibit maxima around 20–25 nm. This length is comparable to the characteristic distance between D and E globules of one fibrinogen molecule and suggests that fibrinogen molecules mainly adsorb through their D and E globules. PMID:10359776

  17. Manufacturing process of nanofluidics using afm probe

    NASA Astrophysics Data System (ADS)

    Karingula, Varun Kumar

    A new process for fabricating a nano fluidic device that can be used in medical application is developed and demonstrated. Nano channels are fabricated using a nano tip in indentation mode on AFM (Atomic Force Microscopy). The nano channels are integrated between the micro channels and act as a filter to separate biomolecules. Nano channels of 4 to7 m in length, 80nm in width, and at varying depths from 100nm to 850 nm allow the resulting device to separate selected groups of lysosomes and other viruses. Sharply developed vertical micro channels are produced from a deep reaction ion etching followed by deposition of different materials, such as gold and polymers, on the top surface, allowing the study of alternative ways of manufacturing a nanofluidic device. PDMS (Polydimethylsiloxane) bonding is performed to close the top surface of the device. An experimental setup is used to test and validate the device by pouring fluid through the channels. A detailed cost evaluation is conducted to compare the economical merits of the proposed process. It is shown that there is a 47:7% manufacturing time savings and a 60:6% manufacturing cost savings.

  18. Topographical and Chemical Imaging of a Phase Separated Polymer Using a Combined Atomic Force Microscopy/Infrared Spectroscopy/Mass Spectrometry Platform

    SciTech Connect

    Tai, Tamin; Karácsony, Orsolya; Bocharova, Vera; Van Berkel, Gary J.; Kertesz, Vilmos

    2016-02-18

    This article describes how the use of a hybrid atomic force microscopy/infrared spectroscopy/mass spectrometry imaging platform was demonstrated for the acquisition and correlation of nanoscale sample surface topography and chemical images based on infrared spectroscopy and mass spectrometry.

  19. Characterization of the specific interaction between the DNA aptamer sgc8c and protein tyrosine kinase-7 receptors at the surface of T-cells by biosensing AFM.

    PubMed

    Leitner, Michael; Poturnayova, Alexandra; Lamprecht, Constanze; Weich, Sabine; Snejdarkova, Maja; Karpisova, Ivana; Hianik, Tibor; Ebner, Andreas

    2017-04-01

    We studied the interaction of the specific DNA aptamer sgc8c immobilized at the AFM tip with its corresponding receptor, the protein tyrosine kinase-7 (PTK7) embedded in the membrane of acute lymphoblastic leukemia (ALL) cells (Jurkat T-cells). Performing single molecule force spectroscopy (SMFS) experiments, we showed that the aptamer sgc8c bound with high probability (38.3 ± 7.48%) and high specificity to PTK7, as demonstrated by receptor blocking experiments and through comparison with the binding behavior of a nonspecific aptamer. The determined kinetic off-rate (koff = 5.16 s(-1)) indicates low dissociation of the sgc8c-PTK7 complex. In addition to the pulling force experiments, simultaneous topography and recognition imaging (TREC) experiments using AFM tips functionalized with sgc8c aptamers were realized on the outer regions surface of surface-immobilized Jurkat cells for the first time. This allowed determination of the distribution of PTK7 without any labeling and at near physiological conditions. As a result, we could show a homogeneous distribution of PTK7 molecules on the outer regions of ALL cells with a surface density of 325 ± 12 PTK7 receptors (or small receptor clusters) per μm(2). Graphical Abstract The specific interaction of the DNA aptamer sgc8c and protein tyrosine kinase-7 (PTK7) on acute lymphoblastic leukemia (ALL) cells was characterized. AFM based single molecule force spectroscopy (SMFS) yielded a kinetic off-rate of 5.16 s(-1) of the complex. Simultaneous topography and recognition imaging (TREC) revealed a PTK7 density of 325 ± 12 molecules or clusters per μm(2) in the cell membrane.

  20. Automated assembly of holder chips to AFM probes

    NASA Astrophysics Data System (ADS)

    Reinhart, Gunther; Jacob, Dirk; Fouchier, Marc

    2001-10-01

    At the Belgian institute IMEC techniques for the production of electrically conductive atomic force microscope (AFM) probes are developed. To facilitate handling of the fragile probes, holder chips are required. The assembly of such holder chips, which can be split up into the application of solder paste, the positioning of the holder chip and the soldering of the chip, is a crucial manufacturing step, that, until now, was performed manually for economic reasons. With the help of a modular micro assembly tool, developed by the Institute for Machine Tools and Industrial Management (iwb) of the Technische Universitaet Muenchen, an economical automated assembly of the holder chips was developed. Thanks to our integrated sensor technology, even the automated assembly onto the extremely fragile membranes of moulded AFM probes was possible. In particular, the dispensing process of the solder paste onto the membranes was improved by the integration of a non-contact sensor for the needle clearance.

  1. Development of a combined atomic force microscopy and side-view imaging system for mechanotransduction research

    NASA Astrophysics Data System (ADS)

    Beicker, Kellie N.

    Key metrics for understanding cell response to mechanical stimuli include rearrangement of the cytoskeletal and nucleoskeletal structure, induced strains and biochemical distributions; however, structural information during applied stress is limited by our ability to image cells under load. In order to study the mechanics of single cells and subcellular components under load, I have developed a unique imaging system that combines an atomic force microscope (AFM) with both vertical light-sheet (VLS) illumination and a new imaging technique called PRISM - Pathway Rotated Imaging for Sideways Microscopy. The combined AFM and PRISM system facilitates the imaging of cell deformation in the direction of applied force with accompanying pico-Newton resolution force measurements. The additional inclusion of light-sheet microscopy improves the signal-to-noise ratio achieved by illumination of only a thin layer of the cell. This system is capable of pico-newton resolution force measurements with simultaneous side-view high frame rate imaging for single-molecule and single-cell force studies. Longer-term goals for this instrument are to investigate how external mechanical stimuli, specifically single-molecule interactions, alter gene expression, motility, and differentiation. The overall goal of my dissertation work is to design a tool useful for mechanobiology studies of single cells. This requires the design and implementation of PRISM and VLS systems that can be coupled to the standard Asylum AFM on inverted optical microscope. I also examine the strategy and implementation of experimental procedures and data analysis pipelines for single-cell and single-molecule force spectroscopy. These goals can be broken down as follows: • Performed single-molecule force spectroscopy experiments. • Performed single-cell force spectroscopy experiments. • Constructed and characterized the side-view microscopy system. • Applied combined AFM and side-vew microscopy system.

  2. Studying single red blood cells under a tunable external force by combining passive microrheology with Raman spectroscopy.

    PubMed

    Raj, Saurabh; Wojdyla, Michal; Petrov, Dmitri

    2013-04-01

    The dynamic micromechanical and structural properties of single human red blood cells are studied using a combination of dual trap optical tweezers and confocal Raman spectroscopy. Such a combination permits us to show a direct relationship between the rheological properties and chemical structure conformation. The frequency dependence of the complex stiffness of the cells was measured using both one and two probe response functions under identical experimental conditions. Both the microrheology and Raman measurements were performed at different stretching forces applied to the cell. A detailed analysis of the auto- and cross-correlated probe motions allows exploring the local and overall viscoelastic properties of the cells over a controlled range of the deformations. The observed growth of the cell viscoelasticity with stretching was associated with structural changes in the cell membrane monitored via the Raman spectroscopy.

  3. Resonant optical gradient force interaction for nano-imaging and -spectroscopy

    NASA Astrophysics Data System (ADS)

    Yang, Honghua U.; Raschke, Markus B.

    2016-05-01

    The optical gradient force provides optomechanical interactions, for particle trapping and manipulation, as well as for near-field optical imaging in scanning probe microscopy. Based on recent spectroscopic experiments, its extension and use for a novel form of chemical scanning probe nano-imaging was proposed. Here, we provide the theoretical basis in terms of spectral behavior, resonant enhancement, and distance dependence of the optical gradient force from numerical simulations in a coupled nanoparticle model geometry. We predict an asymmetric line shape of the optical gradient force for molecular electronic or vibrational resonances, corresponding to the real part of the dielectric function of the sample materials. Yet the line shape can become symmetric and absorptive for collective polaritonic excitations. The corresponding magnitudes of the force range from fN to pN, respectively. The distance dependence scales considerably less steeply than simple point dipole model predictions due to multipole effects. The combination of these characteristics of the optical gradient force offers the chance to experimentally distinguish it from competing processes such as thermal expansion induced forces. In addition we provide a perspective for further resonant enhancement and control of optical forces.

  4. Bubble colloidal AFM probes formed from ultrasonically generated bubbles.

    PubMed

    Vakarelski, Ivan U; Lee, Judy; Dagastine, Raymond R; Chan, Derek Y C; Stevens, Geoffrey W; Grieser, Franz

    2008-02-05

    Here we introduce a simple and effective experimental approach to measuring the interaction forces between two small bubbles (approximately 80-140 microm) in aqueous solution during controlled collisions on the scale of micrometers to nanometers. The colloidal probe technique using atomic force microscopy (AFM) was extended to measure interaction forces between a cantilever-attached bubble and surface-attached bubbles of various sizes. By using an ultrasonic source, we generated numerous small bubbles on a mildly hydrophobic surface of a glass slide. A single bubble picked up with a strongly hydrophobized V-shaped cantilever was used as the colloidal probe. Sample force measurements were used to evaluate the pure water bubble cleanliness and the general consistency of the measurements.

  5. Probing physical properties at the nanoscale using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Ditzler, Lindsay Rachel

    Techniques that measure physical properties at the nanoscale with high sensitivity are significantly limited considering the number of new nanomaterials being developed. The development of atomic force microscopy (AFM) has lead to significant advancements in the ability to characterize physical properties of materials in all areas of science: chemistry, physics, engineering, and biology have made great scientific strides do to the versatility of the AFM. AFM is used for quantification of many physical properties such as morphology, electrical, mechanical, magnetic, electrochemical, binding interactions, and protein folding. This work examines the electrical and mechanical properties of materials applicable to the field of nano-electronics. As electronic devices are miniaturized the demand for materials with unique electrical properties, which can be developed and exploited, has increased. For example, discussed in this work, a derivative of tetrathiafulvalene, which exhibits a unique loss of conductivity upon compression of the self-assembled monolayer could be developed into a molecular switch. This work also compares tunable organic (tetraphenylethylene tetracarboxylic acid and bis(pyridine)s assemblies) and metal-organic (Silver-stilbizole coordination compounds) crystals which show high electrical conductivity. The electrical properties of these materials vary depending on their composition allowing for the development of compositionally tunable functional materials. Additional work was done to investigate the effects of molecular environment on redox active 11-ferroceneyl-1 undecanethiol (Fc) molecules. The redox process of mixed monolayers of Fc and decanethiol was measured using conductive probe atomic force microscopy and force spectroscopy. As the concentration of Fc increased large, variations in the force were observed. Using these variations the number of oxidized molecules in the monolayer was determined. AFM is additionally capable of investigating

  6. The dynamics and pH-dependence of Ag43 adhesins' self-association probed by atomic force spectroscopy

    NASA Astrophysics Data System (ADS)

    Jacquot, Adrien; Sakamoto, Chizuko; Razafitianamarahavo, Angelina; Caillet, Céline; Merlin, Jenny; Fahs, Ahmad; Ghigo, Jean-Marc; Duval, Jérôme F. L.; Beloin, Christophe; Francius, Grégory

    2014-10-01

    Self-associating auto-transporter (SAAT) adhesins are two-domain cell surface proteins involved in bacteria auto-aggregation and biofilm formation. Antigen 43 (Ag43) is a SAAT adhesin commonly found in Escherichia coli whose variant Ag43a has been shown to promote persistence of uropathogenic E. coli within the bladder. The recent resolution of the tri-dimensional structure of the 499 amino-acids' β-domain in Ag43a has shed light on the possible mechanism governing the self-recognition of SAAT adhesins, in particular the importance of trans-interactions between the L shaped β-helical scaffold of two α-domains of neighboring adhesins. In this study, we use single-molecule force spectroscopy (SMFS) and dynamic force spectroscopy (DFS) to unravel the dynamics of Ag43-self association under various pH and molecular elongation rate conditions that mimic the situations encountered by E. coli in its natural environment. Results evidenced an important stretchability of Ag43α with unfolding of sub-domains leading to molecular extension as long as 150 nm. Nanomechanical analysis of molecular stretching data suggested that self-association of Ag43 can lead to the formation of dimers and tetramers driven by rapid and weak cis- as well as slow but strong trans-interaction forces with a magnitude as large as 100-250 pN. The dynamics of cis- and trans-interactions were demonstrated to be strongly influenced by pH and applied shear force, thus suggesting that environmental conditions can modulate Ag43-mediated aggregation of bacteria at the molecular level.Self-associating auto-transporter (SAAT) adhesins are two-domain cell surface proteins involved in bacteria auto-aggregation and biofilm formation. Antigen 43 (Ag43) is a SAAT adhesin commonly found in Escherichia coli whose variant Ag43a has been shown to promote persistence of uropathogenic E. coli within the bladder. The recent resolution of the tri-dimensional structure of the 499 amino-acids' β-domain in Ag43a has shed

  7. Conformational rearrangements in the transmembrane domain of CNGA1 channels revealed by single-molecule force spectroscopy

    PubMed Central

    Maity, Sourav; Mazzolini, Monica; Arcangeletti, Manuel; Valbuena, Alejandro; Fabris, Paolo; Lazzarino, Marco; Torre, Vincent

    2015-01-01

    Cyclic nucleotide-gated (CNG) channels are activated by binding of cyclic nucleotides. Although structural studies have identified the channel pore and selectivity filter, conformation changes associated with gating remain poorly understood. Here we combine single-molecule force spectroscopy (SMFS) with mutagenesis, bioinformatics and electrophysiology to study conformational changes associated with gating. By expressing functional channels with SMFS fingerprints in Xenopus laevis oocytes, we were able to investigate gating of CNGA1 in a physiological-like membrane. Force spectra determined that the S4 transmembrane domain is mechanically coupled to S5 in the closed state, but S3 in the open state. We also show there are multiple pathways for the unfolding of the transmembrane domains, probably caused by a different degree of α-helix folding. This approach demonstrates that CNG transmembrane domains have dynamic structure and establishes SMFS as a tool for probing conformational change in ion channels. PMID:25963832

  8. Interaction of an anticancer peptide fragment of azurin with p53 and its isolated domains studied by atomic force spectroscopy.

    PubMed

    Bizzarri, Anna Rita; Santini, Simona; Coppari, Emilia; Bucciantini, Monica; Di Agostino, Silvia; Yamada, Tohru; Beattie, Craig W; Cannistraro, Salvatore

    2011-01-01

    p28 is a 28-amino acid peptide fragment of the cupredoxin azurin derived from Pseudomonas aeruginosa that preferentially penetrates cancerous cells and arrests their proliferation in vitro and in vivo. Its antitumor activity reportedly arises from post-translational stabilization of the tumor suppressor p53 normally downregulated by the binding of several ubiquitin ligases. This would require p28 to specifically bind to p53 to inhibit specific ligases from initiating proteosome-mediated degradation. In this study, atomic force spectroscopy, a nanotechnological approach, was used to investigate the interaction of p28 with full-length p53 and its isolated domains at the single molecule level. Analysis of the unbinding forces and the dissociation rate constant suggest that p28 forms a stable complex with the DNA-binding domain of p53, inhibiting the binding of ubiquitin ligases other than Mdm2 to reduce proteasomal degradation of p53.

  9. Conformational rearrangements in the transmembrane domain of CNGA1 channels revealed by single-molecule force spectroscopy

    NASA Astrophysics Data System (ADS)

    Maity, Sourav; Mazzolini, Monica; Arcangeletti, Manuel; Valbuena, Alejandro; Fabris, Paolo; Lazzarino, Marco; Torre, Vincent

    2015-05-01

    Cyclic nucleotide-gated (CNG) channels are activated by binding of cyclic nucleotides. Although structural studies have identified the channel pore and selectivity filter, conformation changes associated with gating remain poorly understood. Here we combine single-molecule force spectroscopy (SMFS) with mutagenesis, bioinformatics and electrophysiology to study conformational changes associated with gating. By expressing functional channels with SMFS fingerprints in Xenopus laevis oocytes, we were able to investigate gating of CNGA1 in a physiological-like membrane. Force spectra determined that the S4 transmembrane domain is mechanically coupled to S5 in the closed state, but S3 in the open state. We also show there are multiple pathways for the unfolding of the transmembrane domains, probably caused by a different degree of α-helix folding. This approach demonstrates that CNG transmembrane domains have dynamic structure and establishes SMFS as a tool for probing conformational change in ion channels.

  10. Influence of atomic tip structure on the intensity of inelastic tunneling spectroscopy data analyzed by combined scanning tunneling spectroscopy, force microscopy, and density functional theory

    NASA Astrophysics Data System (ADS)

    Okabayashi, Norio; Gustafsson, Alexander; Peronio, Angelo; Paulsson, Magnus; Arai, Toyoko; Giessibl, Franz J.

    2016-04-01

    Achieving a high intensity in inelastic scanning tunneling spectroscopy (IETS) is important for precise measurements. The intensity of the IETS signal can vary by up to a factor of 3 for various tips without an apparent reason accessible by scanning tunneling microscopy (STM) alone. Here, we show that combining STM and IETS with atomic force microscopy enables carbon monoxide front-atom identification, revealing that high IETS intensities for CO/Cu(111) are obtained for single-atom tips, while the intensity drops sharply for multiatom tips. Adsorption of the CO molecule on a Cu adatom [CO/Cu/Cu(111)] such that the molecule is elevated over the substrate strongly diminishes the tip dependence of IETS intensity, showing that an elevated position channels most of the tunneling current through the CO molecule even for multiatom tips, while a large fraction of the tunneling current bypasses the CO molecule in the case of CO/Cu(111).

  11. Statistics of reversible transitions in two-state trajectories in force-ramp spectroscopy

    SciTech Connect

    Diezemann, Gregor

    2014-05-14

    A possible way to extract information about the reversible dissociation of a molecular adhesion bond from force fluctuations observed in force ramp experiments is discussed. For small loading rates the system undergoes a limited number of unbinding and rebinding transitions observable in the so-called force versus extension (FE) curves. The statistics of these transient fluctuations can be utilized to estimate the parameters for the rebinding rate. This is relevant in the experimentally important situation where the direct observation of the reversed FE-curves is hampered, e.g., due to the presence of soft linkers. I generalize the stochastic theory of the kinetics in two-state models to the case of time-dependent kinetic rates and compute the relevant distributions of characteristic forces. While for irreversible systems there is an intrinsic relation between the rupture force distribution and the population of the free-energy well of the bound state, the situation is slightly more complex if reversible systems are considered. For a two-state model, a “stationary” rupture force distribution that is proportional to the population can be defined and allows to consistently discuss quantities averaged over the transient fluctuations. While irreversible systems are best analyzed in the soft spring limit of small pulling device stiffness and large loading rates, here I argue to use the stiffness of the pulling device as a control parameter in addition to the loading rate.

  12. Tip Characterization Method using Multi-feature Characterizer for CD-AFM

    PubMed Central

    Orji, Ndubuisi G.; Itoh, Hiroshi; Wang, Chumei; Dixson, Ronald G.; Walecki, Peter S.; Schmidt, Sebastian W.; Irmer, Bernd

    2016-01-01

    In atomic force microscopy (AFM) metrology, the tip is a key source of uncertainty. Images taken with an AFM show a change in feature width and shape that depends on tip geometry. This geometric dilation is more pronounced when measuring features with high aspect ratios, and makes it difficult to obtain absolute dimensions. In order to accurately measure nanoscale features using an AFM, the tip dimensions should be known with a high degree of precision. We evaluate a new AFM tip characterizer, and apply it to critical dimension AFM (CD-AFM) tips used for high aspect ratio features. The characterizer is made up of comb-shaped lines and spaces, and includes a series of gratings that could be used as an integrated nanoscale length reference. We also demonstrate a simulation method that could be used to specify what range of tip sizes and shapes the characterizer can measure. Our experiments show that for non re-entrant features, the results obtained with this characterizer are consistent to 1 nm with the results obtained by using widely accepted but slower methods that are common practice in CD-AFM metrology. A validation of the integrated length standard using displacement interferometry indicates a uniformity of better than 0.75%, suggesting that the sample could be used as highly accurate and SI traceable lateral scale for the whole evaluation process. PMID:26720439

  13. FACS-sorted particles reduce the data variance in optical tweezers-assisted dynamic force spectroscopy measurements.

    PubMed

    Stangner, T; Singer, D; Wagner, C; Gutsche, C; Ueberschär, O; Hoffmann, R; Kremer, F

    2013-08-01

    By combining optical tweezers-assisted dynamic force spectroscopy experiments with fluorescence activated cell sorting (FACS), we demonstrate a new approach to reducing the data variance in measuring receptor-ligand interactions on a single molecule level by ensuring similar coating densities. Therefore, the carboxyfluorescein-labelled monophosphorylated peptide tau226-240[pThr231] is anchored on melamine resin beads and these beads are sorted by FACS to achieve a homogeneous surface coverage. To quantify the impact of the fluorescence dye on the bond parameters between the phosphorylated peptide and the corresponding phosphorylation specific anti-human tau monoclonal antibody HPT-104, we perform dynamic force spectroscopy and compare the results to data using unsorted beads covered with the non-fluorescence peptide analogue. Finally, we demonstrate that the data variance of the relative binding frequency is significantly decreased by a factor of 3.4 using pre-sorted colloids with a homogeneous ligand coating compared to using unsorted colloids.

  14. FACS-sorted particles reduce the data variance in optical tweezers-assisted dynamic force spectroscopy measurements

    NASA Astrophysics Data System (ADS)

    Stangner, T.; Singer, D.; Wagner, C.; Gutsche, C.; Ueberschär, O.; Hoffmann, R.; Kremer, F.

    2013-08-01

    By combining optical tweezers-assisted dynamic force spectroscopy experiments with fluorescence activated cell sorting (FACS), we demonstrate a new approach to reducing the data variance in measuring receptor-ligand interactions on a single molecule level by ensuring similar coating densities. Therefore, the carboxyfluorescein-labelled monophosphorylated peptide tau226-240[pThr231] is anchored on melamine resin beads and these beads are sorted by FACS to achieve a homogeneous surface coverage. To quantify the impact of the fluorescence dye on the bond parameters between the phosphorylated peptide and the corresponding phosphorylation specific anti-human tau monoclonal antibody HPT-104, we perform dynamic force spectroscopy and compare the results to data using unsorted beads covered with the non-fluorescence peptide analogue. Finally, we demonstrate that the data variance of the relative binding frequency is significantly decreased by a factor of 3.4 using pre-sorted colloids with a homogeneous ligand coating compared to using unsorted colloids.

  15. Unraveling the Secrets of Bacterial Adhesion Organelles Using Single-Molecule Force Spectroscopy

    NASA Astrophysics Data System (ADS)

    Axner, Ove; Björnham, Oscar; Castelain, Mickaël; Koutris, Efstratios; Schedin, Staffan; Fällman, Erik; Andersson, Magnus

    Many types of bacterium express micrometer-long attachment organelles (so-called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Force-measuring optical tweezers (FMOT) have since then been used to unravel the biomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin are situated at the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g., urine flow. It has been found that many types of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.

  16. Analysis of adhesive binding forces between laminin-1 and C2C12 muscle cell membranes measured via high resolution force spectroscopy

    NASA Astrophysics Data System (ADS)

    Gluck, George; Gilbert, Richard; Ortiz, Christine

    2002-03-01

    Laminins are a family of glycoproteins that regulate cell differentiation, shape, and motility through interactions with various cell surface receptors. Here, we have directly measured the biomolecular adhesive binding forces between a cantilever / probe tip that was covalently attached with laminin-1 and membrane receptors on C2C12 muscle cells using the technique of high-resolution force spectroscopy (HRFS). On retraction of the probe tip away from the membrane surface, discrete, long-range adhesive unbinding events were always observed. Statistical analysis of the data revealed an initial broad distribution of heterogeneous unbinding events (occurring at separation distances, D=0-2µm from the point of maximum compression) of magnitude 92.23±37.87pN followed by a narrow distribution of homogeneous unbinding events (occurring at D > 2µm) of magnitude 38.16±9.10pN, which is suggestive of an individual biomolecular adhesive interaction. On-going studies include loading rate dependence and effect of dystroglycan mutation.

  17. DNA-duplex linker for AFM-SELEX of DNA aptamer against human serum albumin.

    PubMed

    Takenaka, Musashi; Okumura, Yuzo; Amino, Tomokazu; Miyachi, Yusuke; Ogino, Chiaki; Kondo, Akihiko

    2017-02-15

    DNA-duplex interactions in thymines and adenins are used as a linker for the novel methodology of Atomic Force Microscope-Systematic Evolution of Ligands by EXpotential enrichment (AFM-SELEX). This study used the hydrogen bonds in 10 mer of both thymines (T10) and adenines (A10). Initially, the interactive force in T10-A10 was measured by AFM, which returned an average interactive force of approximately 350pN. Based on this result, DNA aptamers against human serum albumin could be selected in the 4th round, and 15 different clones could be sequenced. The lowest dissociation constant of the selected aptamer was identified via surface plasmon resonance, and it proved to be identical to that of the commercial aptamer. Therefore, specific hydrogen bonds in DNA can be useful linkers for AFM-SELEX.

  18. Probing ternary solvent effect in high Voc polymer solar cells using advanced AFM techniques

    DOE PAGES

    Li, Chao; Soleman, Mikhael; Lorenzo, Josie; ...

    2016-01-25

    This work describes a simple method to develop a high Voc low band gap PSCs. In addition, two new atomic force microscopy (AFM)-based nanoscale characterization techniques to study the surface morphology and physical properties of the structured active layer are introduced. With the help of ternary solvent processing of the active layer and C60 buffer layer, a bulk heterojunction PSC with Voc more than 0.9 V and conversion efficiency 7.5% is developed. In order to understand the fundamental properties of the materials ruling the performance of the PSCs tested, AFM-based nanoscale characterization techniques including Pulsed-Force-Mode AFM (PFM-AFM) and Mode-Synthesizing AFMmore » (MSAFM) are introduced. Interestingly, MSAFM exhibits high sensitivity for direct visualization of the donor–acceptor phases in the active layer of the PSCs. Lastly, conductive-AFM (cAFM) studies reveal local variations in conductivity in the donor and acceptor phases as well as a significant increase in photocurrent in the PTB7:ICBA sample obtained with the ternary solvent processing.« less

  19. Investigation of mussel adhesive protein adsorption on polystyrene and poly(octadecyl methacrylate) using angle dependent XPS, ATR-FTIR, and AFM

    SciTech Connect

    Baty, A.M.; Suci, P.A.; Tyler, B.J.; Geesey, G.G.

    1996-02-10

    Despite many years of research effort, the molecular interactions that are responsible for microbial adhesion and fouling of surfaces remain obscure. An understanding of these interactions would contribute to the development of surfaces that resist colonization of microorganisms. The irreversible adsorption of mussel adhesive proteins (MAP) from the marine mussel Mytilus edulis has been investigated on polystyrene (PS) and poly(octadecyl methacrylate) (POMA) surfaces using angle resolved X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrometry, and atomic force microscopy (AFM). Angle resolved XPS was used to quantify the elemental composition with depth of the upper 90 {angstrom} of the surface, and AFM was used to obtain the surface topography. The adsorption pattern of MAP, revealed by AFM images, is distinctly different on the two polymer surfaces and suggests that the substratum influences protein adhesion. The depth profiles of MAP, obtained from angle resolved XPS, show differences in nitrogen composition with depth for MAP adsorbed to PS and POMA. Infrared spectra of hydrated adsorbed MAP revealed significant differences in the amide III region and in two bands which may originate from residues in the tandemly repeated sequences of MAP. This data demonstrates that the chemistry of the polymer film that is present at the protein-polymer interface can influence protein-protein and protein-surface interactions.

  20. Tissue section AFM: In situ ultrastructural imaging of native biomolecules

    PubMed Central

    Graham, Helen K.; Hodson, Nigel W.; Hoyland, Judith A.; Millward-Sadler, Sarah J.; Garrod, David; Scothern, Anthea; Griffiths, Christopher E.M.; Watson, Rachel E.B.; Cox, Thomas R.; Erler, Janine T.; Trafford, Andrew W.; Sherratt, Michael J.

    2010-01-01

    Conventional approaches for ultrastructural high-resolution imaging of biological specimens induce profound changes in bio-molecular structures. By combining tissue cryo-sectioning with non-destructive atomic force microscopy (AFM) imaging we have developed a methodology that may be applied by the non-specialist to both preserve and visualize bio-molecular structures (in particular extracellular matrix assemblies) in situ. This tissue section AFM technique is capable of: i) resolving nm–µm scale features of intra- and extracellular structures in tissue cryo-sections; ii) imaging the same tissue region before and after experimental interventions; iii) combining ultrastructural imaging with complimentary microscopical and micromechanical methods. Here, we employ this technique to: i) visualize the macro-molecular structures of unstained and unfixed fibrillar collagens (in skin, cartilage and intervertebral disc), elastic fibres (in aorta and lung), desmosomes (in nasal epithelium) and mitochondria (in heart); ii) quantify the ultrastructural effects of sequential collagenase digestion on a single elastic fibre; iii) correlate optical (auto fluorescent) with ultrastructural (AFM) images of aortic elastic lamellae. PMID:20144712

  1. Nanogap based graphene coated AFM tips with high spatial resolution, conductivity and durability.

    PubMed

    Lanza, Mario; Gao, Teng; Yin, Zixuan; Zhang, Yanfeng; Liu, Zhongfan; Tong, Yuzhen; Shen, Ziyong; Duan, Huiling

    2013-11-21

    After one decade of analyzing the intrinsic properties of graphene, interest into the development of graphene-based devices and micro electromechanical systems is increasing. Here, we fabricate graphene-coated atomic force microscope tips by growing the graphene on copper foil and transferring it onto the apex of a commercially available AFM tip. The resulting tip exhibits surprising enhanced resolution in nanoscale electrical measurements. By means of topographic AFM maps and statistical analyses we determine that this superior performance may be related to the presence of a nanogap between the graphene and the tip apex, which reduces the tip radius and tip-sample contact area. In addition, the graphene-coated tips show a low tip-sample interaction, high conductivity and long life times. The novel fabrication-friendly tip could improve the quality and reliability of AFM experiments, while reducing the cost of AFM-based research.

  2. Ultrafast force-clamp spectroscopy to probe lac repressor-DNA interactions

    NASA Astrophysics Data System (ADS)

    Monico, Carina; Capitanio, Marco; Belcastro, Gionata; Vanzi, Francesco; Pavone, Francesco S.

    2013-06-01

    We recently developed an ultrafast force-clamp laser trap capable to probe, under controlled force, bimolecular interactions with unprecedented temporal resolution. Here we present the technique in the framework of protein-DNA interactions, specifically on Lactose repressor protein (LacI). The high temporal resolution of the method reveals the kinetics of both short- and long-lived interactions of LacI along the DNA template (from ˜100 μs to tens of seconds), as well the dependence on force of such interaction kinetics. The two kinetically well-distinct populations of interactions observed clearly represent specific interactions with the operator sequences and a fast scanning of LacI along non-cognate DNA. These results demonstrate the effectiveness of the method to study the sequence-dependent affinity of DNA-binding proteins along the DNA and the effects of force on a wide range of interaction durations, including μs time scales not accessible to other single-molecule methods. This improvement in time resolution provides also important means of investigation on the long-puzzled mechanism of target search on DNA and possible protein conformational changes occurring upon target recognition.

  3. Unfolding DNA condensates produced by DNA-like charged depletants: A force spectroscopy study

    NASA Astrophysics Data System (ADS)

    Lima, C. H. M.; Rocha, M. S.; Ramos, E. B.

    2017-02-01

    In this work, we have measured, by means of optical tweezers, forces acting on depletion-induced DNA condensates due to the presence of the DNA-like charged protein bovine serum albumin (BSA). The stretching and unfolding measurements performed on the semi-flexible DNA chain reveal (1) the softening of the uncondensed DNA contour length and (2) a mechanical behavior strikingly different from those previously observed: the force-extension curves of BSA-induced DNA condensates lack the "saw-tooth" pattern and applied external forces as high as ≈80 pN are unable to fully unfold the condensed DNA contour length. This last mechanical experimental finding is in agreement with force-induced "unpacking" detailed Langevin dynamics simulations recently performed by Cortini et al. on model rod-like shaped condensates. Furthermore, a simple thermodynamics analysis of the unfolding process has enabled us to estimate the free energy involved in the DNA condensation: the estimated depletion-induced interactions vary linearly with both the condensed DNA contour length and the BSA concentration, in agreement with the analytical and numerical analysis performed on model DNA condensates. We hope that future additional experiments can decide whether the rod-like morphology is the actual one we are dealing with (e.g. pulling experiments coupled with super-resolution fluorescence microscopy).

  4. Atomic force microscope with combined FTIR-Raman spectroscopy having a micro thermal analyzer

    SciTech Connect

    Fink, Samuel D.; Fondeur, Fernando F.

    2011-10-18

    An atomic force microscope is provided that includes a micro thermal analyzer with a tip. The micro thermal analyzer is configured for obtaining topographical data from a sample. A raman spectrometer is included and is configured for use in obtaining chemical data from the sample.

  5. Adsorption Behavior of Cellulose and Its Derivatives toward Ag(I) in Aqueous Medium: An AFM, Spectroscopic, and DFT Study.

    PubMed

    Zhu, Chuantao; Dobryden, Illia; Rydén, Jens; Öberg, Sven; Holmgren, Allan; Mathew, Aji P

    2015-11-17

    The aim of this study was to develop a fundamental understanding of the adsorption behavior of metal ions on cellulose surfaces using experimental techniques supported by computational modeling, taking Ag(I) as an example. Force interactions among three types of cellulose microspheres (native cellulose and its derivatives with sulfate and phosphate groups) and the silica surface in AgNO3 solution were studied with atomic force microscopy (AFM) using the colloidal probe technique. The adhesion force between phosphate cellulose microspheres (PCM) and the silica surface in the aqueous AgNO3 medium increased significantly with increasing pH while the adhesion force slightly decreased for sulfate cellulose microspheres (SCM), and no clear adhesion force was observed for native cellulose microspheres (CM). The stronger adhesion enhancement for the PCM system is mainly attributed to the electrostatic attraction between Ag(I) and the negative silica surface. The observed force trends were in good agreement with the measured zeta potentials. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analyses confirmed the presence of silver on the surface of cellulose microspheres after adsorption. This study showed that PCM with a high content of phosphate groups exhibited a larger amount of adsorbed Ag(I) than CM and SCM and possible clustering of Ag(I) to nanoparticles. The presence of the phosphate group and a wavenumber shift of the P-OH vibration caused by the adsorption of silver ions on the phosphate groups were further confirmed with computational studies using density functional theory (DFT), which gives support to the above findings regarding the adsorption and clustering of Ag(I) on the cellulose surface decorated with phosphate groups as well as IR spectra.

  6. AFM-Based Single Molecule Techniques: Unraveling the Amyloid Pathogenic Species

    PubMed Central

    Ruggeri, Francesco Simone; Habchi, Johnny; Cerreta, Andrea; Dietler, Giovanni

    2016-01-01

    Background A wide class of human diseases and neurodegenerative disorders, such as Alzheimer’s disease, is due to the failure of a specific peptide or protein to keep its native functional conformational state and to undergo a conformational change into a misfolded state, triggering the formation of fibrillar cross-β sheet amyloid aggregates. During the fibrillization, several coexisting species are formed, giving rise to a highly heterogeneous mixture. Despite its fundamental role in biological function and malfunction, the mechanism of protein self-assembly and the fundamental origins of the connection between aggregation, cellular toxicity and the biochemistry of neurodegeneration remains challenging to elucidate in molecular detail. In particular, the nature of the specific state of proteins that is most prone to cause cytotoxicity is not established. Methods: In the present review, we present the latest advances obtained by Atomic Force Microscopy (AFM) based techniques to unravel the biophysical properties of amyloid aggregates at the nanoscale. Unraveling amyloid single species biophysical properties still represents a formidable experimental challenge, mainly because of their nanoscale dimensions and heterogeneous nature. Bulk techniques, such as circular dichroism or infrared spectroscopy, are not able to characterize the heterogeneity and inner properties of amyloid aggregates at the single species level, preventing a profound investigation of the correlation between the biophysical properties and toxicity of the individual species. Conclusion: The information delivered by AFM based techniques could be central to study the aggregation pathway of proteins and to design molecules that could interfere with amyloid aggregation delaying the onset of misfolding diseases. PMID:27189600

  7. Ultrastable Atomic Force Microscopy for Biophysics

    NASA Astrophysics Data System (ADS)

    Churnside, Allison B.

    Atomic force microscopy (AFM) is a multifunctional workhorse of nanoscience and molecular biophysics, but instrumental drift remains a critical issue that limits the precision and duration of experiments. We have significantly reduced the two most important types of drift: in position and in force. The first, position drift, is defined as uncontrolled motion between the tip and the sample, which occurs in all three dimensions. By scattering a laser off the apex of a commercial AFM tip, we locally measured and thereby actively controlled its three-dimensional position above a sample surface to <0.4 A (Deltaf = 0.01--10 Hz) in air at room temperature. With this enhanced stability, we demonstrated atomic-scale (˜1 A) tip-sample stability and registration over tens of minutes with a series of AFM images. The second type of drift is force drift. We found that the primary source of force drift for a popular class of soft cantilevers is their gold coating, even though they are coated on both sides to minimize drift. When the gold coating was removed through a simple chemical etch, this drift in deflection was reduced by more than an order of magnitude over the first 2 hours after wetting the tip. Removing the gold also led to ˜ 10-fold reduction in reflected light, yet short-term (0.1--10 s) force precision improved. With both position and force drift greatly reduced, the utility of the AFM is enhanced. These improvements led to several new AFM abilities, including a five-fold increase in the image signal-to-noise ratio; tip-registered, label-free optical imaging; registered tip return to a particular point on the sample; and dual-detection force spectroscopy, which enables a new extension clamp mode. We have applied these abilities to folding of both membrane and soluble proteins. In principle, the techniques we describe can be fully incorporated into many types of scanning probe microscopy, making this work a general improvement to scanning probe techniques.

  8. LET Spectrum Measurements In CR-39 PNTD With AFM

    SciTech Connect

    Johnson, C. E.; DeWitt, J. M.; Benton, E. R.; Yasuda, N.; Benton, E. V.

    2011-06-01

    Energetic protons, neutrons, and heavy ions undergoing collisions with target nuclei of varying Z can produce residual heavy recoil fragments via intra-nuclear cascade/evaporation reactions. The particles produced in these non-elastic collisions generally have such extremely short range ({approx}<10 {mu}m) that they cannot be directly observed by conventional detection methods including CR-39 plastic nuclear track detector (PNTD) that has been chemically etched for analysis by standard visible light microscopy. However, high-LET recoil fragments having range on the order of several cell diameters can be produced in tissue during radiotherapy using proton and carbon beams. We have developed a method to analyze short-range, high-LET tracks in CR-39 plastic nuclear track detector (PNTD) using short duration chemical etching ({approx}<1 {mu}m) following by automated atomic force microscope (AFM) scanning. The post-scan data processing used in this work was based on semi-automated matrix analysis opposed to traditional grey-scale image analysis. This method takes advantage of the 3-D data obtained via AFM to achieve robust discrimination of nuclear tracks from other features inherently present in the post-etch detector surface. Through automation of AFM scanning, sufficient AFM scan frames were obtained to attain an LET spectrum spanning the LET range from 200-1500 keV/{mu}m. In addition to our experiments, simulations were carried out with the Monte Carlo transport code, FLUKA. To demonstrate this method, CR-39 PNTD was exposed to the proton therapy beam at Loma Linda University Medical Center (LLUMC) at 60 and 230 MeV. Additionally, detectors were exposed to 1 GeV protons at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). For these exposures CR-39 PNTD, Al and Cu target foils were used between detector layers.

  9. Quantitative nano-mechanics of biological cells with AFM

    NASA Astrophysics Data System (ADS)

    Sokolov, Igor

    2013-03-01

    The importance of study of living cells is hard to overestimate. Cell mechanics is a relatively young, yet not a well-developed area. Besides just a fundamental interest, large practical need has emerged to measure cell mechanics quantitatively. Recent studies revealed a significant correlation between stiffness of biological cells and various human diseases, such as cancer, malaria, arthritis, and even aging. However, really quantitative studies of mechanics of biological cells are virtually absent. It is not even clear if the cell, being a complex and heterogeneous object, can be described by the elastic modulus at all. Atomic force microscopy (AFM) is a natural instrument to study properties of cells in their native environments. Here we will demonstrate that quantitative measurements of elastic modulus of cells with AFM are possible. Specifically, we will show that the ``cell body'' (cell without ``brush'' surface layer, a non-elastic layer surrounding cells) typically demonstrates the response of a homogeneous elastic medium up to the deformation of 10-20%, but if and only if a) the cellular brush layer is taken into account, b) rather dull AFM probes are used. This will be justified with the help of the strong condition of elastic behavior of material: the elastic modulus is shown to be independent on the indentation depth. We will also demonstrate that an attempt either to ignore the brush layer or to use sharp AFM probes will result in the violation of the strong condition, which implies impossibility to use the concept of the elastic modulus to describe cell mechanics in such experiments. Examples of quantitative measurements of the Young's modulus of the cell body and the cell brush parameters will be given for various cells. Address when submitting: Clarkson University, Potsdam, NY 13699

  10. LET Spectrum Measurements In CR-39 PNTD With AFM

    NASA Astrophysics Data System (ADS)

    Johnson, C. E.; DeWitt, J. M.; Benton, E. R.; Yasuda, N.; Benton, E. V.

    2011-06-01

    Energetic protons, neutrons, and heavy ions undergoing collisions with target nuclei of varying Z can produce residual heavy recoil fragments via intra-nuclear cascade/evaporation reactions. The particles produced in these non-elastic collisions generally have such extremely short range (˜<10 μm) that they cannot be directly observed by conventional detection methods including CR-39 plastic nuclear track detector (PNTD) that has been chemically etched for analysis by standard visible light microscopy. However, high-LET recoil fragments having range on the order of several cell diameters can be produced in tissue during radiotherapy using proton and carbon beams. We have developed a method to analyze short-range, high-LET tracks in CR-39 plastic nuclear track detector (PNTD) using short duration chemical etching (˜<1 μm) following by automated atomic force microscope (AFM) scanning. The post-scan data processing used in this work was based on semi-automated matrix analysis opposed to traditional grey-scale image analysis. This method takes advantage of the 3-D data obtained via AFM to achieve robust discrimination of nuclear tracks from other features inherently present in the post-etch detector surface. Through automation of AFM scanning, sufficient AFM scan frames were obtained to attain an LET spectrum spanning the LET range from 200-1500 keV/μm. In addition to our experiments, simulations were carried out with the Monte Carlo transport code, FLUKA. To demonstrate this method, CR-39 PNTD was exposed to the proton therapy beam at Loma Linda University Medical Center (LLUMC) at 60 and 230 MeV. Additionally, detectors were exposed to 1 GeV protons at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). For these exposures CR-39 PNTD, Al and Cu target foils were used between detector layers.

  11. LET spectrum measurements in Cr-39 PNTD with AFM

    SciTech Connect

    Johnson, Carl Edward; De Witt, Joel M; Benton, Eric R; Yasuda, Nakahiro; Benton, Eugene V

    2010-01-01

    Energetic protons, neutrons, and heavy ions undergoing collisions with target nuclei of varying Z can produce residual heavy recoil fragments via intra-nuclear cascade/evaporation reactions. The particles produced in these non-elastic collisions generally have such extremely short range ({approx}< 10 {mu}m) that they cannot be directly observed by conventional detection methods including CR-39 plastic nuclear track detector (PNTD) that has been chemically etched for analysis by standard visible light microscopy. However, high-LET recoil fragments having range on the order of several cell diameters can be produced in tissue during radiotherapy using proton and carbon beams. We have developed a method to analyze short-range, high-LET tracks in CR-39 plastic nuclear track detector (PNTD) using short duration chemical etching ({approx}< 1 {mu}m) followed by automated atomic force microscope (AFM) scanning. The post-scan data processing used in this work was based on semi-automated matrix analysis opposed to traditional grey-scale image analysis. This method takes advantage of the 3-D data obtained via AFM to achieve robust discrimination of nuclear tracks from other features. Through automation of AFM scanning, sufficient AFM scan frames were obtained to attain an LET spectrum spanning the LET range from 200-1500 keV/{mu}m. In addition to our experiments, simulations were carried out with the Monte Carlo transport code, FLUKA. To demonstrate this method, CR-39 PNTD was exposed to the proton therapy beam at Loma Linda University Medical Center (LLUMC) at 60 and 230 MeV. Additionally, detectors were exposed to I GeV protons at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). For these exposures CR-39 PNTD, Al and Cu target foils were used between detector layers.

  12. High-speed AFM probe with micromachined membrane tip

    NASA Astrophysics Data System (ADS)

    Kim, Byungki; Kwak, Byung Hyung; Jamil, Faize

    2008-08-01

    This paper presents a micromachined silicon membrane type AFM tip designed to move nearly 1µm by electrostatic force. Since the tip can be vibrated in small amplitude with AC voltage input and can be displaced up to 1μm by DC voltage input, an additional piezo actuator is not required for scanning of submicron features. The micromachined membrane tips are designed to have 100 kHz ~ 1 MHz resonant frequency. Displacement of the membrane tip is measured by an optical interferometer using a micromachined diffraction grating on a quartz wafer which is positioned behind the membrane tip.

  13. Mechanically functional amyloid fibrils in the adhesive of a marine invertebrate as revealed by Raman spectroscopy and atomic force microscopy.

    PubMed

    S Mostaert, Anika; Crockett, Rowena; Kearn, Graham; Cherny, Izhack; Gazit, Ehud; C Serpell, Louise; P Jarvis, Suzanne

    2009-01-01

    Amyloid fibrils are primarily known in a pathogenic context for their association with a wide range of debilitating human diseases. Here we show a marine invertebrate (Entobdella soleae) utilizes functional amyloid fibrils comparable to those of a unicellular prokaryote (Escherichia coli). Thioflavin-T binding and Raman spectroscopy provided evidence for the presence of amyloid in the adhesive of Entobdella soleae. We elucidated that for these two very different organisms, amyloid fibrils provide adhesive and cohesive strength to their natural adhesives. Comparing the nanoscale mechanical responses of these fibrils with those of pathogenic amyloid by atomic force microscopy revealed that the molecular level origin of the cohesive strength was associated with the generic intermolecular β-sheet structure of amyloid fibrils. Functional adhesive residues were found only in the case of the functional amyloid. Atomic force microscopy provided a useful means to characterize the internal structural forces within individual amyloid fibrils and how these relate to the mechanical performance of both functional and pathogenic amyloid. The mechanistic link of amyloid-based cohesive and adhesive strength could be widespread amongst natural adhesives, irrespective of environment, providing a new strategy for biomimicry and a new source of materials for understanding the formation and stability of amyloid fibrils more generally.

  14. Hydrocarbons in phlogopite from Kasenyi kamafugitic rocks (SW Uganda): cross-correlated AFM, confocal microscopy and Raman imaging

    NASA Astrophysics Data System (ADS)

    Moro, Daniele; Valdrè, Giovanni; Mesto, Ernesto; Scordari, Fernando; Lacalamita, Maria; Ventura, Giancarlo Della; Bellatreccia, Fabio; Scirè, Salvatore; Schingaro, Emanuela

    2017-01-01

    This study presents a cross-correlated surface and near surface investigation of two phlogopite polytypes from Kasenyi kamafugitic rocks (SW Uganda) by means of advanced Atomic Force Microscopy (AFM), confocal microscopy and Raman micro-spectroscopy. AFM revealed comparable nanomorphology and electrostatic surface potential for the two mica polytypes. A widespread presence of nano-protrusions located on the mica flake surface was also observed, with an aspect ratio (maximum height/maximum width) from 0.01 to 0.09. Confocal microscopy showed these features to range from few nm to several μm in dimension, and shapes from perfectly circular to ellipsoidic and strongly elongated. Raman spectra collected across the bubbles showed an intense and convolute absorption in the range 3000–2800 cm‑1, associated with weaker bands at 1655, 1438 and 1297 cm‑1, indicating the presence of fluid inclusions consisting of aliphatic hydrocarbons, alkanes and cycloalkanes, with minor amounts of oxygenated compounds, such as carboxylic acids. High-resolution Raman images provided evidence that these hydrocarbons are confined within the bubbles. This work represents the first direct evidence that phlogopite, a common rock-forming mineral, may be a possible reservoir for hydrocarbons.

  15. Hydrocarbons in phlogopite from Kasenyi kamafugitic rocks (SW Uganda): cross-correlated AFM, confocal microscopy and Raman imaging.

    PubMed

    Moro, Daniele; Valdrè, Giovanni; Mesto, Ernesto; Scordari, Fernando; Lacalamita, Maria; Ventura, Giancarlo Della; Bellatreccia, Fabio; Scirè, Salvatore; Schingaro, Emanuela

    2017-01-18

    This study presents a cross-correlated surface and near surface investigation of two phlogopite polytypes from Kasenyi kamafugitic rocks (SW Uganda) by means of advanced Atomic Force Microscopy (AFM), confocal microscopy and Raman micro-spectroscopy. AFM revealed comparable nanomorphology and electrostatic surface potential for the two mica polytypes. A widespread presence of nano-protrusions located on the mica flake surface was also observed, with an aspect ratio (maximum height/maximum width) from 0.01 to 0.09. Confocal microscopy showed these features to range from few nm to several μm in dimension, and shapes from perfectly circular to ellipsoidic and strongly elongated. Raman spectra collected across the bubbles showed an intense and convolute absorption in the range 3000-2800 cm(-1), associated with weaker bands at 1655, 1438 and 1297 cm(-1), indicating the presence of fluid inclusions consisting of aliphatic hydrocarbons, alkanes and cycloalkanes, with minor amounts of oxygenated compounds, such as carboxylic acids. High-resolution Raman images provided evidence that these hydrocarbons are confined within the bubbles. This work represents the first direct evidence that phlogopite, a common rock-forming mineral, may be a possible reservoir for hydrocarbons.

  16. Germ direct observation by AFM under crystallization of self-organized assemblies of mono-protonated meso-tetraphenylporphine dimers

    NASA Astrophysics Data System (ADS)

    Udal'tsov, Alexander V.

    2016-08-01

    Assemblies consisting of mono-protonated meso-tetraphenylporphine dimers and water have been investigated by UV-vis spectroscopy in solution and atomic force microscopy (AFM) in thin layers. These assemblies self-organized into domains produce microcrystals in thin layer. Morphology of the microcrystals and characteristic features of crystallization germ on the top found by contact AFM indicate that surface tension of an aqueous layer on the domain generates the crystallization process. Estimations of the pressure producing the germ and bulk modulus (Bm) of microcrystals give 26.3±2.6 MPa and 3.72 GPa and Bm=12.7 GPa obtained for dried thin films. The former modulus is comparable with bulk modulus of water (2.174 GPa) that implies liquid crystals formation. Absorptions of longitudinal optical (LO) phonons with ћωLO=0.3761 and 0.3577 eV, which are arisen because of hole polaron moving through water, are found in the electronic spectra of the assemblies. The crystallization is suggested to occur due to Zundel cation (H5O2+) operation like the water-porphyrin matrix self-organization found earlier.

  17. Hydrocarbons in phlogopite from Kasenyi kamafugitic rocks (SW Uganda): cross-correlated AFM, confocal microscopy and Raman imaging

    PubMed Central

    Moro, Daniele; Valdrè, Giovanni; Mesto, Ernesto; Scordari, Fernando; Lacalamita, Maria; Ventura, Giancarlo Della; Bellatreccia, Fabio; Scirè, Salvatore; Schingaro, Emanuela

    2017-01-01

    This study presents a cross-correlated surface and near surface investigation of two phlogopite polytypes from Kasenyi kamafugitic rocks (SW Uganda) by means of advanced Atomic Force Microscopy (AFM), confocal microscopy and Raman micro-spectroscopy. AFM revealed comparable nanomorphology and electrostatic surface potential for the two mica polytypes. A widespread presence of nano-protrusions located on the mica flake surface was also observed, with an aspect ratio (maximum height/maximum width) from 0.01 to 0.09. Confocal microscopy showed these features to range from few nm to several μm in dimension, and shapes from perfectly circular to ellipsoidic and strongly elongated. Raman spectra collected across the bubbles showed an intense and convolute absorption in the range 3000–2800 cm−1, associated with weaker bands at 1655, 1438 and 1297 cm−1, indicating the presence of fluid inclusions consisting of aliphatic hydrocarbons, alkanes and cycloalkanes, with minor amounts of oxygenated compounds, such as carboxylic acids. High-resolution Raman images provided evidence that these hydrocarbons are confined within the bubbles. This work represents the first direct evidence that phlogopite, a common rock-forming mineral, may be a possible reservoir for hydrocarbons. PMID:28098185

  18. Characterization of microscale wear in a ploysilicon-based MEMS device using AFM and PEEM-NEXAFS spectromicroscopy.

    SciTech Connect

    Grierson, D. S.; Konicek, A. R.; Wabiszewski, G. E.; Sumant, A. V.; de Boer, M. P.; Corwin, A. D.; Carpick, R. W.

    2009-12-01

    Mechanisms of microscale wear in silicon-based microelectromechanical systems (MEMS) are elucidated by studying a polysilicon nanotractor, a device specifically designed to conduct friction and wear tests under controlled conditions. Photoelectron emission microscopy (PEEM) was combined with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and atomic force microscopy (AFM) to quantitatively probe chemical changes and structural modification, respectively, in the wear track of the nanotractor. The ability of PEEM-NEXAFS to spatially map chemical variations in the near-surface region of samples at high lateral spatial resolution is unparalleled and therefore ideally suited for this study. The results show that it is possible to detect microscopic chemical changes using PEEM-NEXAFS, specifically, oxidation at the sliding interface of a MEMS device. We observe that wear induces oxidation of the polysilicon at the immediate contact interface, and the spectra are consistent with those from amorphous SiO{sub 2}. The oxidation is correlated with gouging and debris build-up in the wear track, as measured by AFM and scanning electron microscopy (SEM).

  19. Atomic force microscopy to study intermolecular forces and bonds associated with bacteria.

    PubMed

    Lower, Steven K

    2011-01-01

    Atomic force microscopy (AFM) operates on a very different principle than other forms of microscopy, such as optical microscopy or electron microscopy. The key component of an AFM is a cantilever that bends in response to forces that it experiences as it touches another surface. Forces as small as a few picoNewtons can be detected and probed with AFM. AFM has become very useful in biological sciences because it can be used on living cells that are immersed in water. AFM is particularly useful when the cantilever is modified with chemical groups (e.g. amine or carboxylic groups), small beads (e.g. glass or latex), or even a bacterium. This chapter describes how AFM can be used to measure forces and bonds between a bacterium and another surface. This paper also provides an example of the use of AFM on Staphylococcus aureus, a Gram-positive bacterium that is often associated with biofilms in humans.

  20. Electrostatic binding and hydrophobic collapse of peptide-nucleic acid aggregates quantified using force spectroscopy.

    PubMed

    Camunas-Soler, Joan; Frutos, Silvia; Bizarro, Cristiano V; de Lorenzo, Sara; Fuentes-Perez, Maria Eugenia; Ramsch, Roland; Vilchez, Susana; Solans, Conxita; Moreno-Herrero, Fernando; Albericio, Fernando; Eritja, Ramón; Giralt, Ernest; Dev, Sukhendu B; Ritort, Felix

    2013-06-25

    Knowledge of the mechanisms of interaction between self-aggregating peptides and nucleic acids or other polyanions is key to the understanding of many aggregation processes underlying several human diseases (e.g., Alzheimer's and Parkinson's diseases). Determining the affinity and kinetic steps of such interactions is challenging due to the competition between hydrophobic self-aggregating forces and electrostatic binding forces. Kahalalide F (KF) is an anticancer hydrophobic peptide that contains a single positive charge that confers strong aggregative properties with polyanions. This makes KF an ideal model to elucidate the mechanisms by which self-aggregation competes with binding to a strongly charged polyelectrolyte such as DNA. We use optical tweezers to apply mechanical forces to single DNA molecules and show that KF and DNA interact in a two-step kinetic process promoted by the electrostatic binding of DNA to the aggregate surface followed by the stabilization of the complex due to hydrophobic interactions. From the measured pulling curves we determine the spectrum of binding affinities, kinetic barriers, and lengths of DNA segments sequestered within the KF-DNA complex. We find there is a capture distance beyond which the complex collapses into compact aggregates stabilized by strong hydrophobic forces and discuss how the bending rigidity of the nucleic acid affects this process. We hypothesize that within an in vivo context, the enhanced electrostatic interaction of KF due to its aggregation might mediate the binding to other polyanions. The proposed methodology should be useful to quantitatively characterize other compounds or proteins in which the formation of aggregates is relevant.

  1. Tensile mechanics of alanine-based helical polypeptide: force spectroscopy versus computer simulations.

    PubMed

    Afrin, Rehana; Takahashi, Ichiro; Shiga, Kazuki; Ikai, Atsushi

    2009-02-01

    In nature, an alpha-helix is commonly used to build thermodynamically stable and mechanically rigid protein conformations. In view of growing interest in the mechanical rigidity of proteins, we measured the tensile profile of an alanine-based alpha-helical polypeptide on an atomic-force microscope to investigate the basic mechanics of helix extension with minimal interference from side-chain interactions. The peptide was extended to its maximum contour length with much less force than in reported cases of poly-L-Glu or poly-L-Lys, indicating that chain stiffness strongly depended on the physicochemical properties of side chains, such as their bulkiness. The low tensile-force extension originated presumably in locally unfolded parts because of spontaneous structural fluctuations. In 50% trifluoroethanol, the well-known helix-promoting agent, the rigidity of the sample polypeptide was markedly increased. Computer simulations of the peptide-stretching process showed that a majority of constituent residues underwent a transition from an alpha-helical to an extended conformation by overcoming an energy barrier around psi approximately 0 degrees on the Ramachandran plot. The observed lability of an isolated helix signified the biological importance of the lateral bundling of helices to maintain a rigid protein structure.

  2. Spectroscopy of F26 to Probe Proton-Neutron Forces Close to the Drip Line

    NASA Astrophysics Data System (ADS)

    Lepailleur, A.; Sorlin, O.; Caceres, L.; Bastin, B.; Borcea, C.; Borcea, R.; Brown, B. A.; Gaudefroy, L.; Grévy, S.; Grinyer, G. F.; Hagen, G.; Hjorth-Jensen, M.; Jansen, G. R.; Llidoo, O.; Negoita, F.; de Oliveira, F.; Porquet, M.-G.; Rotaru, F.; Saint-Laurent, M.-G.; Sohler, D.; Stanoiu, M.; Thomas, J. C.

    2013-02-01

    A long-lived Jπ=41+ isomer, T1/2=2.2(1)ms, has been discovered at 643.4(1) keV in the weakly bound F926 nucleus. It was populated at Grand Accélérateur National d’Ions Lourds in the fragmentation of a S36 beam. It decays by an internal transition to the Jπ=11+ ground state [82(14)%], by β decay to Ne26, or β-delayed neutron emission to Ne25. From the β-decay studies of the Jπ=11+ and Jπ=41+ states, new excited states have been discovered in Ne25,26. Gathering the measured binding energies of the Jπ=11+-41+ multiplet in F926, we find that the proton-neutron π0d5/2ν0d3/2 effective force used in shell-model calculations should be reduced to properly account for the weak binding of F926. Microscopic coupled cluster theory calculations using interactions derived from chiral effective field theory are in very good agreement with the energy of the low-lying 11+, 21+, 41+ states in F26. Including three-body forces and coupling to the continuum effects improve the agreement between experiment and theory as compared to the use of two-body forces only.

  3. Correlative atomic force and confocal fluorescence microscopy: single molecule imaging and force induced spectral shifts (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Basché, Thomas; Hinze, Gerald; Stöttinger, Sven

    2016-09-01

    A grand challenge in nanoscience is to correlate structure or morphology of individual nano-sized objects with their photo-physical properties. An early example have been measurements of the emission spectra and polarization of single semiconductor quantum dots as well as their crystallographic structure by a combination of confocal fluorescence microscopy and transmission electron microscopy.[1] Recently, the simultaneous use of confocal fluorescence and atomic force microscopy (AFM) has allowed for correlating the morphology/conformation of individual nanoparticle oligomers or molecules with their photo-physics.[2, 3] In particular, we have employed the tip of an AFM cantilever to apply compressive stress to single molecules adsorbed on a surface and follow the effect of the impact on the electronic states of the molecule by fluorescence spectroscopy.[3] Quantum mechanical calculations corroborate that the spectral changes induced by the localized force can be associated to transitions among the different possible conformers of the adsorbed molecule.

  4. As Simple As Possible, but Not Simpler: Exploring the Fidelity of Coarse-Grained Protein Models for Simulated Force Spectroscopy

    PubMed Central

    Rottler, Jörg; Plotkin, Steven S.

    2016-01-01

    Mechanical unfolding of a single domain of loop-truncated superoxide dismutase protein has been simulated via force spectroscopy techniques with both all-atom (AA) models and several coarse-grained models having different levels of resolution: A Gō model containing all heavy atoms in the protein (HA-Gō), the associative memory, water mediated, structure and energy model (AWSEM) which has 3 interaction sites per amino acid, and a Gō model containing only one interaction site per amino acid at the Cα position (Cα-Gō). To systematically compare results across models, the scales of time, energy, and force had to be suitably renormalized in each model. Surprisingly, the HA-Gō model gives the softest protein, exhibiting much smaller force peaks than all other models after the above renormalization. Clustering to render a structural taxonomy as the protein unfolds showed that the AA, HA-Gō, and Cα-Gō models exhibit a single pathway for early unfolding, which eventually bifurcates repeatedly to multiple branches only after the protein is about half-unfolded. The AWSEM model shows a single dominant unfolding pathway over the whole range of unfolding, in contrast to all other models. TM alignment, clustering analysis, and native contact maps show that the AWSEM pathway has however the most structural similarity to the AA model at high nativeness, but the least structural similarity to the AA model at low nativeness. In comparison to the AA model, the sequence of native contact breakage is best predicted by the HA-Gō model. All models consistently predict a similar unfolding mechanism for early force-induced unfolding events, but diverge in their predictions for late stage unfolding events when the protein is more significantly disordered. PMID:27898663

  5. Atomic force microscopy: a versatile tool to probe the physical and chemical properties of supported membranes at the nanoscale.

    PubMed

    Picas, Laura; Milhiet, Pierre-Emmanuel; Hernández-Borrell, Jordi

    2012-12-01

    Atomic force microscopy (AFM) was developed in the 1980s following the invention of its precursor, scanning tunneling microscopy (STM), earlier in the decade. Several modes of operation have evolved, demonstrating the extreme versatility of this method for measuring the physicochemical properties of samples at the nanoscopic scale. AFM has proved an invaluable technique for visualizing the topographic characteristics of phospholipid monolayers and bilayers, such as roughness, height or laterally segregated domains. Implemented modes such as phase imaging have also provided criteria for discriminating the viscoelastic properties of different supported lipid bilayer (SLB) regions. In this review, we focus on the AFM force spectroscopy (FS) mode, which enables determination of the nanomechanical properties of membrane models. The interpretation of force curves is presented, together with newly emerging techniques that provide complementary information on physicochemical properties that may contribute to our understanding of the structure and function of biomembranes. Since AFM is an imaging technique, some basic indications on how real-time AFM imaging is evolving are also presented at the end of this paper.

  6. Combined use of atomic force microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry for cell surface analysis.

    PubMed

    Dague, Etienne; Delcorte, Arnaud; Latgé, Jean-Paul; Dufrêne, Yves F

    2008-04-01

    Understanding the surface properties of microbial cells is a major challenge of current microbiological research and a key to efficiently exploit them in biotechnology. Here, we used three advanced surface analysis techniques with different sensitivity, probing depth, and lateral resolution, that is, in situ atomic force microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry, to gain insight into the surface properties of the conidia of the human fungal pathogen Aspergillus fumigatus. We show that the native ultrastructure, surface protein and polysaccharide concentrations, and amino acid composition of three mutants affected in hydrophobin production are markedly different from those of the wild-type, thereby providing novel insight into the cell wall architecture of A. fumigatus. The results demonstrate the power of using multiple complementary techniques for probing microbial cell surfaces.

  7. Application of atomic force microscopy for characteristics of single intermolecular interactions.

    PubMed

    Safenkova, I V; Zherdev, A V; Dzantievf, B B

    2012-12-01

    Atomic force microscopy (AFM) can be used to make measurements in vacuum, air, and water. The method is able to gather information about intermolecular interaction forces at the level of single molecules. This review encompasses experimental and theoretical data on the characterization of ligand-receptor interactions by AFM. The advantage of AFM in comparison with other methods developed for the characterization of single molecular interactions is its ability to estimate not only rupture forces, but also thermodynamic and kinetic parameters of the rupture of a complex. The specific features of force spectroscopy applied to ligand-receptor interactions are examined in this review from the stage of the modification of the substrate and the cantilever up to the processing and interpretation of the data. We show the specificities of the statistical analysis of the array of data based on the results of AFM measurements, and we discuss transformation of data into thermodynamic and kinetic parameters (kinetic dissociation constant, Gibbs free energy, enthalpy, and entropy). Particular attention is paid to the study of polyvalent interactions, where the definition of the constants is hampered due to the complex stoichiometry of the reactions.

  8. In situ nanomanipulators as a tool to separate individual tobermorite crystals for AFM studies.

    PubMed

    Yang, Tianhe; Holzer, Lorenz; Kägi, Ralf; Winnefeld, Frank; Keller, Bruno

    2007-10-01

    Atomic force microscopy (AFM) studies of cementitious materials are limited, mainly due to the lack of appropriate sample preparation techniques. In porous autoclaved aerated concrete (AAC), calcium silicate hydrate (C-S-H) is produced in its crystalline form, tobermorite. The crystals are lath-like with a length of several micrometers. In this work, we demonstrate the application of nanomanipulators to separate an individual tobermorite crystal from the bulk AAC for subsequent AFM investigations. The nanomanipulators are operated directly in an environmental scanning electron microscope (ESEM). We studied the interaction between moisture and the tobermorite surface under controlled relative humidity (RH). The results of topography and adhesion force measurements with AFM suggest that the surface of tobermorite is hydrophobic, which contrasts the macroscopic material properties (e.g. moisture transport in capillary pores).

  9. High throughput nanofabrication of silicon nanowire and carbon nanotube tips on AFM probes by stencil-deposited catalysts.

    PubMed

    Engstrom, Daniel S; Savu, Veronica; Zhu, Xueni; Bu, Ian Y Y; Milne, William I; Brugger, Juergen; Boggild, Peter

    2011-04-13

    A new and versatile technique for the wafer scale nanofabrication of silicon nanowire (SiNW) and multiwalled carbon nanotube (MWNT) tips on atomic force microscope (AFM) probes is presented. Catalyst material for the SiNW and MWNT growth was deposited on prefabricated AFM probes using aligned wafer scale nanostencil lithography. Individual vertical SiNWs were grown epitaxially by a catalytic vapor-liquid-solid (VLS) process and MWNTs were grown by a plasma-enhanced chemical vapor (PECVD) process on the AFM probes. The AFM probes were tested for imaging micrometers-deep trenches, where they demonstrated a significantly better performance than commercial high aspect ratio tips. Our method demonstrates a reliable and cost-efficient route toward wafer scale manufacturing of SiNW and MWNT AFM probes.

  10. Hydration states of AFm cement phases

    SciTech Connect

    Baquerizo, Luis G.; Matschei, Thomas; Scrivener, Karen L.; Saeidpour, Mahsa; Wadsö, Lars

    2015-07-15

    The AFm phase, one of the main products formed during the hydration of Portland and calcium aluminate cement based systems, belongs to the layered double hydrate (LDH) family having positively charged layers and water plus charge-balancing anions in the interlayer. It is known that these phases present different hydration states (i.e. varying water content) depending on the relative humidity (RH), temperature and anion type, which might be linked to volume changes (swelling and shrinkage). Unfortunately the stability conditions of these phases are insufficiently reported. This paper presents novel experimental results on the different hydration states of the most important AFm phases: monocarboaluminate, hemicarboaluminate, strätlingite, hydroxy-AFm and monosulfoaluminate, and the thermodynamic properties associated with changes in their water content during absorption/desorption. This data opens the possibility to model the response of cementitious systems during drying and wetting and to engineer systems more resistant to harsh external conditions.

  11. Exploring the binding of 4-thiothymidine with human serum albumin by spectroscopy, atomic force microscopy, and molecular modeling methods.

    PubMed

    Zhang, Juling; Gu, Huaimin; Zhang, Xiaohui

    2014-01-30

    The interaction of 4-thiothymidine (S(4)TdR) with human serum albumin (HSA) was studied by equilibrium dialysis under normal physiological conditions. In this work, the mechanism of the interaction between S(4)TdR and human serum albumin (HSA) was exploited by fluorescence, UV, CD circular, and SERS spectroscopic. Fluorescence and UV spectroscopy suggest that HSA intensities are significantly decreased when adding S(4)TdR to HAS, and the quenching mechanism of the fluorescence is static. Also, the ΔG, ΔH, and ΔS values across temperature indicated that hydrophobic interaction was the predominant binding force. The CD circular results show that there is little change in the secondary structure of HSA except the environment of amino acid changes when adding S(4)TdR to HSA. The surface-enhanced Raman scattering (SERS) shows that the interaction between S(4)TdR and HSA can be achieved through different binding sites which are probably located in the II A and III A hydrophobic pockets of HSA which correspond to Sudlow's I and II binding sites. In addition, the molecular modeling displays that S(4)TdR-HSA complex is stabilized by hydrophobic forces, which result from amino acid residues. The atomic force microscopy results revealed that the single HSA molecular dimensions were larger after interaction of 4-thiothymidine. This work would be useful to understand the state of the transportation, distribution, and metabolism of the anticancer drugs in the human body, and it could provide a useful biochemistry parameter for the development of new anti-cancer drugs and research of pharmacology mechanisms.

  12. Molecular dynamics study on the mechanism of AFM-based nanoscratching process with water-layer lubrication

    NASA Astrophysics Data System (ADS)

    Ren, Jiaqi; Zhao, Jinsheng; Dong, Zeguang; Liu, Pinkuan

    2015-08-01

    The atomic force microscopy (AFM) based direct nanoscratching has been thoroughly studied but the mechanism of nanoscratching with water-layer lubrication is yet to be well understood. In current study, three-dimensional molecular dynamics (MD) simulations are conducted to evaluate the effects of the water-layer lubrication on the AFM-based nanoscratching process on monocrystalline copper. Comparisons of workpiece deformation, scratching forces, and friction coefficients are made between the water-lubricated and dry scratching under various thickness of water layer, scratching depth and scratching velocity. Simulation results reveal that the water layer has positive impact on the surface quality and significant influence on the scratching forces (normal forces and tangential forces). The friction coefficients of the tip in water-lubricated nanoscratching are significantly bigger than those in the dry process. Our simulation results shed lights on a promising AFM-based nanofabrication method, which can assist to get nanoscale surface morphologies with higher quality than traditional approaches.

  13. Visualization of internal structure of banana starch granule through AFM.

    PubMed

    Peroni-Okita, Fernanda H G; Gunning, A Patrick; Kirby, Andrew; Simão, Renata A; Soares, Claudinéia A; Cordenunsi, Beatriz R

    2015-09-05

    Atomic force microscopy (AFM) is a high resolution technique for studying the external and internal structures of starch granules. For this purpose granules were isolated from bananas and embedded in a non-penetrating resin. To achieve image contrast of the ultrastructure, the face of the cut blocks were wetted in steam and force modulation mode imaging was used. Images of starch from green bananas showed large variation of height across the granule due to a locational specific absorption of water and swelling of amorphous regions; the data reveal that the center of the granules are structurally different and have different viscoelastic properties. Images of starches from ripe bananas showed an even greater different level of organization: absence of growth rings around the hilum; the central region of the granule is richer in amylose; very porous surface with round shaped dark structures; the size of blocklets are larger than the green fruits.

  14. Graphene MEMS: AFM probe performance improvement.

    PubMed

    Martin-Olmos, Cristina; Rasool, Haider Imad; Weiller, Bruce H; Gimzewski, James K

    2013-05-28

    We explore the feasibility of growing a continuous layer of graphene in prepatterned substrates, like an engineered silicon wafer, and we apply this as a mold for the fabrication of AFM probes. This fabrication method proves the fabrication of SU-8 devices coated with graphene in a full-wafer parallel technology and with high yield. It also demonstrates that graphene coating enhances the functionality of SU-8 probes, turning them conductive and more resistant to wear. Furthermore, it opens new experimental possibilities such as studying graphene-graphene interaction at the nanoscale with the precision of an AFM or the exploration of properties in nonplanar graphene layers.

  15. Effect of AFM probe geometry on visco-hyperelastic characterization of soft materials

    NASA Astrophysics Data System (ADS)

    Boccaccio, Antonio; Lamberti, Luciano; Papi, Massimiliano; De Spirito, Marco; Pappalettere, Carmine

    2015-08-01

    Atomic force microscopy (AFM) nanoindentation is very suited for nano- and microscale mechanical characterization of soft materials. Although the structural response of polymeric networks that form soft matter depends on viscous effects caused by the relative slippage of polymeric chains, the usual assumption made in the AFM-based characterization is that the specimen behaves as a purely elastic material and viscous forces are negligible. However, for each geometric configuration of the AFM tip, there will be a limit indentation rate above which viscous effects must be taken into account to correctly determine mechanical properties. A parametric finite element study conducted on 12 geometric configurations of a blunt cone AFM tip (overall, the study included about 200 finite element analyses) allowed us to determine the limit indentation rate for each configuration. The selected tip dimensions cover commercially available products and account for changes in tip geometry caused by serial measurements. Nanoindentation rates cover typical experimental conditions set in AFM bio-measurements on soft matter. Viscous effects appear to be more significant in the case of sharper tips. This implies that, if quantitative data on sample viscosity are not available, using a rounded indenter and carrying out experiments below the limit indentation rate will allow errors in the determination of mechanical properties to be minimized.

  16. Viscometry of single nanoliter-volume droplets using dynamic force spectroscopy.

    PubMed

    Lee, Manhee; Kim, Bongsu; Kim, QHwan; Hwang, JongGeun; An, Sangmin; Jhe, Wonho

    2016-10-05

    The viscometry of minute amounts of liquid has been in high demand as a novel tool for medical diagnosis and biological assays. Various microrheological techniques have shown the capability to handle small volumes. However, as the liquid volume decreases down to nanoliter scale, increasingly dominant surface effects complicate the measurement and analysis, which remain a challenge in microrheology. Here, we demonstrate an atomic force microscope-based platform that determines the viscosity of single sessile drops of 1 nanoliter Newtonian fluids. We circumvent interfacial effects by measuring the negative-valued shear elasticity, originating from the retarded fluidic response inside the drop. Our measurement is independent of the liquid-boundary effects, and thus is valid without a priori knowledge of surface tension or contact angle, and consistently holds at a 1 milliliter-scale volume. Importantly, while previous methods typically need a much larger 'unrecoverable' volume above 1 microliter, our simple platform uses only ∼1 nanoliter. Our results offer a quantitative and unambiguous methodology for viscosity measurements of extremely minute volumes of Newtonian liquids on the nanoliter scale.

  17. Communication: Does force spectroscopy of biomolecules probe their intrinsic dynamic properties?

    SciTech Connect

    Makarov, Dmitrii E.

    2014-12-28

    In single-molecule pulling experiments, the molecule of interest is attached to a much larger object such as an atomic force microscope tip or a micrometer sized bead. The measured dynamics of molecular transitions is therefore affected by the hydrodynamic drag on the pulling instrument itself. By considering the transitions within the combined system (the molecule and the instrument), it is shown here that two distinct physical regimes exist: when the intrinsic stiffness of the molecule is greater than that of the linker connecting the molecule to the pulling setup then the pulling experiment probes the intrinsic dynamics of the molecule with only relatively small (and quantifiable) corrections resulting from the pulling setup. In contrast, when the stiffness of the linker exceeds that of the molecule, the molecular transition in question involves concerted motion of the molecule and the pulling setup and the hydrodynamic drag on the pulling instrument becomes the dominant source of friction along the molecular reaction coordinate. An analytical formula interpolating between these two cases is further derived. These results explain recent conflicting observations where some single-molecule pulling measurements report anomalously low diffusion coefficients along molecular reaction coordinates while others do not.

  18. Force Spectroscopy with Dual-Trap Optical Tweezers: Molecular Stiffness Measurements and Coupled Fluctuations Analysis

    PubMed Central

    Ribezzi-Crivellari, M.; Ritort, F.

    2012-01-01

    Dual-trap optical tweezers are often used in high-resolution measurements in single-molecule biophysics. Such measurements can be hindered by the presence of extraneous noise sources, the most prominent of which is the coupling of fluctuations along different spatial directions, which may affect any optical tweezers setup. In this article, we analyze, both from the theoretical and the experimental points of view, the most common source for these couplings in dual-trap optical-tweezers setups: the misalignment of traps and tether. We give criteria to distinguish different kinds of misalignment, to estimate their quantitative relevance and to include them in the data analysis. The experimental data is obtained in a, to our knowledge, novel dual-trap optical-tweezers setup that directly measures forces. In the case in which misalignment is negligible, we provide a method to measure the stiffness of traps and tether based on variance analysis. This method can be seen as a calibration technique valid beyond the linear trap region. Our analysis is then employed to measure the persistence length of dsDNA tethers of three different lengths spanning two orders of magnitude. The effective persistence length of such tethers is shown to decrease with the contour length, in accordance with previous studies. PMID:23199920

  19. Coffee Cup Atomic Force Microscopy

    ERIC Educational Resources Information Center

    Ashkenaz, David E.; Hall, W. Paige; Haynes, Christy L.; Hicks, Erin M.; McFarland, Adam D.; Sherry, Leif J.; Stuart, Douglas A.; Wheeler, Korin E.; Yonzon, Chanda R.; Zhao, Jing; Godwin, Hilary A.; Van Duyne, Richard P.

    2010-01-01

    In this activity, students use a model created from a coffee cup or cardstock cutout to explore the working principle of an atomic force microscope (AFM). Students manipulate a model of an AFM, using it to examine various objects to retrieve topographic data and then graph and interpret results. The students observe that movement of the AFM…

  20. The Atomic Force Microscopic (AFM) Characterization of Nanomaterials

    DTIC Science & Technology

    2009-06-01

    per response, including the time for reviewing instructions, searching existing data sources , gathering and maintaining the data needed, and completing...conditions may need to be determined. Later, Bumsu et al. [43] reported that α- terpineol and Texanol were better solvents than DMF due to their larger...chemical structures and higher viscosity (α- terpineol 36.5 cP, Texanol 18.3 cP, DMF 0.802 cP). This high viscosity may enhance the dispersity of the

  1. Probing ternary solvent effect in high Voc polymer solar cells using advanced AFM techniques

    SciTech Connect

    Li, Chao; Soleman, Mikhael; Lorenzo, Josie; Dhasmana, Nitesh; Chantharasupawong, Panit; Ievlev, Anton; Gesquiere, Andre; Tetard, Laurene; Thomas, Jayan

    2016-01-25

    This work describes a simple method to develop a high Voc low band gap PSCs. In addition, two new atomic force microscopy (AFM)-based nanoscale characterization techniques to study the surface morphology and physical properties of the structured active layer are introduced. With the help of ternary solvent processing of the active layer and C60 buffer layer, a bulk heterojunction PSC with Voc more than 0.9 V and conversion efficiency 7.5% is developed. In order to understand the fundamental properties of the materials ruling the performance of the PSCs tested, AFM-based nanoscale characterization techniques including Pulsed-Force-Mode AFM (PFM-AFM) and Mode-Synthesizing AFM (MSAFM) are introduced. Interestingly, MSAFM exhibits high sensitivity for direct visualization of the donor–acceptor phases in the active layer of the PSCs. Lastly, conductive-AFM (cAFM) studies reveal local variations in conductivity in the donor and acceptor phases as well as a significant increase in photocurrent in the PTB7:ICBA sample obtained with the ternary solvent processing.

  2. Two-Dimensional Measurement of n+-p Asymmetrical Junctions in Multicrystalline Silicon Solar Cells Using AFM-Based Electrical Techniques with Nanometer Resolution: Preprint

    SciTech Connect

    Jiang, C. S.; Moutinho, H. R.; Li, J. V.; Al-Jassim, M. M.; Heath, J. T.

    2011-07-01

    Lateral inhomogeneities of modern solar cells demand direct electrical imaging with nanometer resolution. We show that atomic force microscopy (AFM)-based electrical techniques provide unique junction characterizations, giving a two-dimensional determination of junction locations. Two AFM-based techniques, scanning capacitance microscopy/spectroscopy (SCM/SCS) and scanning Kelvin probe force microscopy (SKPFM), were significantly improved and applied to the junction characterizations of multicrystalline silicon (mc-Si) cells. The SCS spectra were taken pixel by pixel by precisely controlling the tip positions in the junction area. The spectra reveal distinctive features that depend closely on the position relative to the electrical junction, which allows us to indentify the electrical junction location. In addition, SKPFM directly probes the built-in potential over the junction area modified by the surface band bending, which allows us to deduce the metallurgical junction location by identifying a peak of the electric field. Our results demonstrate resolutions of 10-40 nm, depending on the techniques (SCS or SKPFM). These direct electrical measurements with nanometer resolution and intrinsic two-dimensional capability are well suited for investigating the junction distribution of solar cells with lateral inhomogeneities.

  3. AFM/MFM hybrid nanocharacterization of martensitic transformation and degradation for Fe-Pd shape memory alloy

    NASA Astrophysics Data System (ADS)

    Suzuki, Takayuki; Nagatani, Kohei; Hirano, Kazumi; Teramoto, Tokuo; Taya, Minoru

    2003-07-01

    Martensitic transfor