Using theoretical considerations and MD simulation techniques, we show that the rupture strength of H-bond assemblies is governed by geometric confinement effects, suggesting that clusters of at most 3-4 H-bonds break concurrently, even under uniform shear loading of a much larger number of H-bonds. This universally valid result leads to an intrinsic strength limitation that suggests that shorter strands with less H-bonds achieve the highest shear strength. Our finding explains how the intrinsic strength limitation of H-bonds is overcome by the formation of a nanocomposite structure of H-bond clusters, thereby enabling the formation larger, much stronger beta-sheet structures. Our results explain recent experimental proteomics data, suggesting a correlation between the shear strength and the prevalence of beta-strand lengths in biology.

The distribution of electric field in and near the surface of the electrophoretic cell determines the motion of proteins in the buffer and along the surface. This is a complicated problem, influenced by buffer ion concentration, electrode configuration, and surface and substrate conductivities. Steady state calculations approximating the experimental geometry were made for different arrangements of electrodes using MAFIA (Computer Simulation Technologies) program and ESTAT programs. Electric field distributions in both conducting surfaces like ITO (Indium Tin Oxide) (Kevley Technologies), gold and aluminum and non conducting surfaces were studied. In order to measure the EOF of the buffer neutrally charged fluorescent Poly-Styrene beads of 1 μm diameter were included in the buffer and imaged using confocal microscope. It was observed that the electric filed was highly modified by various factors like the conducting nature of the surface, position of the electrodes, salt concentration in the buffer and distance from the separation surface.

Pressure-area isotherms and fluorescence microscopy were used to investigate the impact of chitosan on the competitive adsorption between lung surfactant (LS) and serum proteins at the air-liquid interface. Isotherms demonstrate an optimum chitosan concentration to mediate LS adsorption; higher concentrations actually reduce the amount of LS which can adsorb. Fluorescence microscopy images show the transition from a serum protein to LS-covered interface for the optimum chitosan concentration; this transition goes through a sharply phase separated coexistence region. The results suggest that the cationic chitosan molecules mediate adsorption of the negatively charged LS aggregates by reducing the electrostatic barrier imposed by negatively charged interfacial serum proteins.

Self-assembly in water at pH 6 and 10 of a wedge-shaped bolaamphiphile (1), bearing amino and glucose hydrophilic headgroups, was found to give two types of nanotubes with different inner diameters of 20 and 80 nm, respectively. X-ray diffraction and IR measurement revealed that the nanotubes have distinct inner and outer surfaces covered with amino and glucose headgroups, respectively. The nanotubes were able to effectively encapsulate an anionic spherical protein, ferritin, and DNA into the hollow cylinder under neutral pH conditions. Positively charged amino groups in the nanotube hollow cylinder proved to accelerate the encapsulation of the anionic biomacromolecules via electrostatic interaction. Covalent modification of the amino groups with a fluorescent donor dye on the inner surface of the nanotube allowed us to achieve the construction of an optical recognition system for encapsulation of guest molecules. Fluorescence resonance energy transfer (FRET) from the fluorescent donor located on the inner surface to the ferritin labeled with fluorescent acceptor enabled us to visualize the encapsulation and transportation features of the ferritin in the nanochannel shaped by the hollow cylinder structure.

Bio-conjugated nanomaterials play a promising role in the development of novelsupramolecular structures, molecular machines, and biosensing devices. In this study, lipid-capped gold nanoparticles were synthesized and allowed to form a self-assembled monolayer structure. The nanoparticles were prepared by a phase transfer method, which involved the reduction of potassium tetrachloroaurate(III) by sodium citrate in an aqueous solution and the simultaneous transfer of the reduced species to an organic medium containing DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine). The gold nanoparticles were characterized using Uv-vis spectroscopy and dynamic light scattering (DLS) particle-size analysis. In addition, the resulting nanoparticles were examined using transmission electron microscopy (TEM). The Langmuir-Blodgett (LB) technique was used to assemble the DMPC-capped nanoparticles onto a water subphase at room temperature. The measurement of the compression isotherm confirmed the assemblage of lipid capped gold nanoparticles. This method of synthesis of ordered structures utilizing molecular interactions of lipids will be useful in developing novel metamaterials and nanocircuits.

Silver nanoparticles have shown immense potential in many biomedical applications, specifically wound healing. These nanoparticles reduce the degree of inflammation in wounds and increase the rate of wound healing overall in a dose-dependent manner. Moreover, silver nanoparticles exhibit antibacterial and antimicrobial properties. While the mechanism of action for silver nanoparticles is not clear, current studies focus on the effect of silver nanoparticles on recipient cells and tissues. It is shown that silver nanoparticles are more toxic to these recipient cells in comparison to other metal nanoparticles. This suggests that the bactericidal properties of the silver nanoparticles are size dependent. Our present work investigates the toxicity level of silver nanoparticles on specific immune circulating cells. The approach is to report the LD50 level as a function of the ratio of the nanoparticles concentration (ppm) to the cell concentration (cell number/ml) used in the assays. This method allows a normalization of the LD50 capable to compare the toxicity of the nanoparticle on different types of cells. Next, the localization of the silver nanoparticles within the cells will be determined, and the toxic mode of action of the nanoparticles will be modulated by the modification of the synthesis method.

Developments in the field of proteomics are highly encouraging for medical researchers. While gel electrophoresis offers a successful means for protein recognition, it requires the use of a relatively large system and a rather long period of time. Here, a protocol is developed for electrophoresis of proteins using flat surfaces based on the principles of electrophoresis of DNA on flat surfaces. By further adapting this system, it is hoped to create a portable device for protein electrophoresis. Droplets of fluorescently tagged proteins such as albumin, casein, poly-L-lysine and their mixtures were placed on glass surfaces in an electrophoretic cell and allowed to dry. TBE buffer was added to the cell and the migration of the salt complexes was monitored using confocal microscopy. We show that different protein - salt complexes have different mobilities on a flat surface. The shape and size distributions of the protein-salt complexes and their mixtures on surfaces were also studied using atomic force microscopy and were found to be dependent upon the proteins. It is observed that the native charge of the proteins play a dominant role in the migration of the protein-salt complexes in the electrophoretic cell. From the morphology of the protein droplets it is observed that large aggregates are formed when oppositely charged proteins are mixed. Light scattering measurements and zeta potential measurements confirm the difference in the size and shape of the aggregates in solution leading to different mobilities of the protein-salt aggregates during electrophoresis.

Imaging live cells using atomic force microscopy (AFM) is perhaps the most challenging role within which the tool can be deployed. The procedure requires that the target cells be maintained under thermostated physiological fluids in order that viability is retained. Furthermore, once the imaging probe has engaged with the target cells, the use of appropriate imaging forces that guarantee reasonable spatial resolution must be weighed against the need to maintain a ‘light touch’ so that the integrity of this most delicate structure is not compromised. The purpose of the present study was ostensibly to image live cells (PtK2 epithelial cells) in-vitro and to examine those force regimes and tip properties that lead to best imaging. Interestingly, by employing ultra low imaging forces (FL < 100pN) whilst operating in contact mode, as opposed to ‘tapping’ mode, it was possible to achieve spatial resolutions in the range of about 25nm, which was sufficient to resolve the constituent fibres of the cytoskeletal network and other subcellular detail. Emipircally, certain tips were found to generate better resolution images than others, and we characterized those tips by imaging a commercial ion-beam etched spike array to determine not only the radius of curvature at the active imaging tip, but also the general morphology of the apex region. Force distance curves could be obtained which allowed a Hertzian analysis of the cellular elasticity. In this instance a value for the Young's modulus, EC, was determined to be 75kPa. Time-lapse imaging in this low force regime allowed the non-intrusive observation of cytoskeletal reorganisation during motility over extended periods of up to 7 hours.

A new methodology has been developed to measure the maximum pressure that can be withstood by a bilayer lipid membrane (BLM) formed over porous substrates. A custom test fixture was fabricated to pressurize BLMs in very fine increasing increments until they fail. This experiment was performed on 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphatidylocholine (SOPC) BLMs formed over polycarbonate substrates with a single pore ranging from 5 to 20 microns in diameter. Failure pressure was found to be inversely proportional to pore diameter. The same set of experiments was repeated for BLMs that were formed from a mixture of SOPC and 50 mol% cholesterol (CHOL). The presence of cholesterol was found to increase the failure pressure of the BLMs by 56% on average. A model of the characteristic pressure curve from this experiment was developed based on the pressurization and flow of fluid through a porous substrate. The model was found to accurately fit the experimental pressure curves.

We investigated the efficient nucleation of silver nanoparticles on aldehyde-modified DNA strands. The aldehyde-bearing DNA was prepared by PCR incorporation of diol-modified synthetic deoxyuridine derivatives and subsequent cleavage of the diol groups to aldehyde functions using sodium periodate. Formerly unavailable dialdehyde-bearing DNA could be prepared by this mild and selective method. Both dialdehyde-DNA and monoaldehyde-DNA are capable of inducing silver nanoparticle formation without the addition of any external reductant. Interestingly, dialdehyde-DNA shows a different kinetic behavior and is about four times as efficient in silver nanoparticle formation as monoaldehyde-DNA. These data suggest a potentially unique mechanism of silver nanocluster formation induced by the dialdehyde groups. SEM measurements of fully metallized DNA strands show homogeneous metal coverage and selective metal deposition exclusively on the DNA template.

In experiments involving electrophoresis of proteins in gels, it was observed that the mobility of FITC tagged albumin (FITC albumin) was greater than that of TRITC tagged albumin (TRITC albumin). To further understand the effects of tagging proteins with fluorescent dyes, interactions of anionic proteins FITC albumin and untagged bovine serum albumin (BSA), with cationic protein ploy-L-lysine was studied using dynamical light scattering. It was found that aggregates formed by the interaction of FITC albumin with poly-L-lysine were larger than those formed by the interaction between poly-L-lysine and BSA. Using zeta potential measurements it was observed that irrespective of the fluorescent tags attached to them, the zeta potential values of cationic proteins changed from negative to positive with increasing amounts of poly-L-lysine. It was also observed that addition of small amounts of poly-L-lysine to solutions containing FITC albumin decreased the zeta potential drastically. To explain this data, we are proposing a model that suggests that low concentrations of poly-L-lysine serve as scaffold - like structures on which several FITC albumin molecules anchor. We conclude that FITC appears to change the surface charge of albumin significantly and thereby influencing its behavior in solution and its interaction with cationic poly-L-lysine.

Recent research at Virginia Tech have shown that active transporter proteins reconstituted into suspended bilayer lipid membranes (BLMs) formed across an array of pores in synthetic substrates can convert chemical energy available in adenosine triphosphate (ATP) into electricity. Experimental results from this work show that this system—called BioCell—is capable of 1.7μW of electrical power per square centimeter of BLM area and per 15μL of ATPase enzyme. In support of such a system, the lipid membrane, as host to active biological proteins and channels, must be formed evenly across a porous substrate, remain stable and yet fluid-like for protein folding and activation, and provide sufficient electrical insulation. We report on the formation and characterization using electrical impedance spectroscopy (EIS) of BLMs formed across two types of porous substrates: polycarbonate filters and single-aperture silicon substrates. Equivalent electrical circuits describing the lipid membranes and their supporting substrates are approximated to fit the measured responses. The results show that BLMs formed in some but not all of the 400nm pores of the filters, while the formation of BLMs on the single-aperture silicon substrates was much more consistent.