The atomic force microscope (AFM) was used to study a series of self-assembled systems: alkanethiol self-assembled monolayer (SAM), diblock copolymer thin film, solid supported lipid bilayer membrane, and microgel with double interpenetrating polymer network. In the first system, packing and restructuring of self-assembled monolayers as exhibited by several alkanethiol systems (1-hexanethiol, 1-decanethiol, 11-ferrocenyl-1-undecanethiol) is demonstrated using conducting probe AFM (CP-AFM). Pressure is induced by an AFM tip, and simultaneously, electrical behavior is measured via detection of tunneling currents between metallic tip and substrate. The behavior is fit using a mechanical model that attempts to predict the observed junction resistance as a function of applied force with consideration for mechanical restructuring of the monolayer at higher loads. CP-AFM is also used to study self-assembled thin film of the diblock copolymer polystyrene- block-polyferrocenylsilane (PS-b-PFS) on gold substrate. Simultaneous height and electrical current imaging verify the phase separation of the two blocks of the polymer and additionally, distinguish each block due to differential conductivity. The phase separation of multi-component phospholipid bilayers (phosphatidylcholine/ sphingomyelin/ cholesterol) on supporting substrate into liquid-ordered and liquid-disordered phases is demonstrated using both topographical imaging, and the use of force map analysis through tip indentation and rupture measurements. The segregation and differential mechanical stiffness of the phases help to understand the important role of mechanical stability and rigidity membranes. An automated batch analysis process was implemented to facilitate the procedure. The mechanical properties of microfluidically produced microgels (cross-linked sodium alginate and poly(N-isopropylacrylamide)) are measured using indentation experiments, to evaluate the suitability of these gels as cell-mimics. Nanoscale heterogeneities were avoided by using a tipless cantilever. This body of work shows that the alginate content of these microgels can be varied to tune their mechanical properties and that a platform for mechanical measurement of cell and cell-mimics is possible.

In this study, it was nanoimprint focused on the anti-adhesion technique between the grating structure silicon molds below 200nm half-pitch and polymer materials (H-PDMS). The nano-groove structure molds with different depths and widths were made by FIB. During the process of molding by soft-lithography, an anti-adhesion layer needed being plated between the silicon and PDMS mold, which was in order to get completely formed H-PDMS soft mold and prevent defective mold caused by the adhesion problem on the surface. There were three kinds of method of plating anti-adhesion layer which were the liquid immersion, vapor deposition, and fluorine doped DLC film. The PFOTCS was used as mold releasing agent in the methods of liquid immersion and vapor deposition, and the contact angle was measured to realize the ability of anti-adhesion. In the method of fluorine doped DLC film, in addition to measuring the anti-adhesion ability for each sample through contact angle with water, the AFM was also applied to measure the degree of adhesion on the surface for each film. And the contact angles with water between each film were also compared. The methods of plating anti-adhesion film with lower degree of adhesion on the surface could be acquired and discussed by means of the above-mentioned ways to fabricate the molds with good formability

We study the conformational change of insulin fibril growth from three aspects: the impact of (i) incubation time; (ⅱ) nano-particles; (iii) and ion added. We used circular dichroism (CD) spectroscopy and fourier transform infrared spectroscopy (FT-IR) to obtain the structural transition of the insulin, and gain the morphology information of fibril by atomic force microscopy (AFM) and transmission electron microscopy (TEM). We show that the insulin transform from £\-helix to £]-sheet structure as increased incubated time. The addition of Au nanoparticles (NPs) caused the formation of coordination bond with insulin fiber and produced shorter and thicker insulin fibril . The Fe3O4 NPs, on the other hand, offered only van der Waals interaction toward insulin fibril. Hence they could be used to separate insulin fibril from solution. Finally, addition of salts can induce the conformation changes of insulin fibril ten times faster than that without salts. And the insulin fibril fragment was two or three times shorter than that produced without salts. At high salt concentration, insulin formed amorphous aggregates. This phenomenon was attribute to anions from salt: covering the surface charge of insulin fibril, they weaken the original electrostatic repulsion among insulin fibrils and result in their aggregation.

The purpose of this study was to characterize the micromechanical properties of various structural components in asphalt using Atomic Force Microscopy (AFM). The focus of the study was based on nano-indentation experiments performed within a micro-grid of asphalt phases in order to determine micromechanical properties such as stiffness, adhesion and elastic/plastic behavior. The change in microstructure and micromechanical behavior due to oxidative aging of the asphalt was also a primary focus of the study. The experiment was performed with careful consideration of AFM artifacts, which can occur due to factors such as geometry of the cantilever tip, hysteresis, filtering methods and acoustic vibrations. The materials used in this study included asphalts AAB, AAD and ABD from the Materials Reference Library (MRL) of the Strategic Highway Research Program (SHRP), chosen due to variations in crude source, chemical composition and elemental analysis for each asphalt type. The analysis of nano-indentation creep measurements corresponding to phase-separated regions ultimately revealed heterogeneous domains in asphalt with different mechanical properties, and oxidative aging was found to induce substantial microstructural change within these domains, including variations in phase structure, phase properties and phase distribution. The form and extent of these changes, however, were different for each asphalt studied. Data analysis and information collected during this study were used for comparisons to existing models and asphalt data, which validated results and established correlations to earlier, related studies. From these comparisons, it was found that data parallels followed expected trends; furthermore, analogous interpretations and distinctions were made between results from this study and the micellar and microstructural models of asphalt. This study of micromechanical properties that govern asphalt behavior has yielded information essential to the advancement of hot mix asphalt (HMA) performance, including a new asphalt “weak zone” hypothesis and a foundation of data for implementation into new and existing asphalt models.

A magnetic force microscope (MFM) is a special type of scanning force microscope which measures the stray field above a ferromagnetic sample with the help of a ferromagnetic cantilever. The aim of this project was to design and build a MFM head and interface it with a commercial scanning probe electronics controller with the help of an appropriate force sensor. The MFM head and the force sensor were to be designed to work at low temperatures (down to 4 K) and in high vacuum. During this work, a magnetic force microscope (MFM) head was designed. Its design is symmetrical and modular. Two dimensional views were prepared to ensure proper geometry and alignment for the various modules. Based on these views, individual parts in the various modules were manufactured and combined for the final assembly of the head. This MFM head has many essential and advanced features which were incorporated during the design process. Our MFM head has an outside diameter of 5 cm and thus has a low thermal mass. The head operates inside a 100 cm long vacuum can which is kept in a cold bath inside a superinsulated dewar. Other features of this MFM head include thermal compensation of the important parts, flexibility to use commercial MFM cantilevers and a large scan range compared to the previous designs. Some of the anticipated system specifications are: 1) room temperature scanning range of 175?? 175 ??m, 2) low temperature scanning range between 35-50 ??m, 3) smallest detectable magnetic force in the range of one pN and 4) smallest detectable magnetic force gradient in the range of 10-3 to 10 -5 N/m. This MFM head was interfaced to a commercial scanning probe electronics apparatus by designing a fiber-optic interferometer as the sensor for the detection of the cantilever deflection. The fiber-optic sensor also has features of its own such as stability, compactness and low susceptibility to noise because of all-fiber construction. With this MFM head, we hope to image many magnetic samples which were previously impossible to image at Texas A&M.

Elucidating the structure-function relationships of membrane proteins is critical for the design of therapeutic agents to treat disease and for understanding numerous cellular processes such as signal transduction and molecular or ion transport. Recent advances in the application of correlated single molecule imaging techniques have provided new insights into protein-protein and protein-membrane interactions. To demonstrate the potential of these approaches, we have used in situ atomic force microscopy and single molecule fluorescence microscopy to characterize the interactions between membrane receptors and their soluble ligands, examine the monomer-dimer equilibrium in a family of adhesion receptors, and elucidate protein-mediated membrane restructuring of a supported lipid bilayer. Building on these studies, we examined the CorA ion transporter protein. We demonstrated single molecule resolution of reconstituted CorA molecules in supported lipid bilayers using a correlated AFM-TIRF microscopy platform. This approach provided new insights into a purported mechanism of CorA activation that involved ion binding.

No description available.

Elucidating the structure-function relationships of membrane proteins is critical for the design of therapeutic agents to treat disease and for understanding numerous cellular processes such as signal transduction and molecular or ion transport. Recent advances in the application of correlated single molecule imaging techniques have provided new insights into protein-protein and protein-membrane interactions. To demonstrate the potential of these approaches, we have used in situ atomic force microscopy and single molecule fluorescence microscopy to characterize the interactions between membrane receptors and their soluble ligands, examine the monomer-dimer equilibrium in a family of adhesion receptors, and elucidate protein-mediated membrane restructuring of a supported lipid bilayer. Building on these studies, we examined the CorA ion transporter protein. We demonstrated single molecule resolution of reconstituted CorA molecules in supported lipid bilayers using a correlated AFM-TIRF microscopy platform. This approach provided new insights into a purported mechanism of CorA activation that involved ion binding.

The aim of the thesis was to design a methodology for in-situ evaluation of degradation of selected magnesium alloys using AFM in SBF solutions. Study of the degradation of magnesium alloys in a chemically different corrosive environments of simulated body fluid (SBF - Hank's solution). For the pilot study were used magnesium alloys AZ31 and AZ61, manufactured by advanced method of squeeze casting. Part of the thesis was to evaluate the influence of the chemical composition and structure on the degradation properties of these alloys.

With extensive development of nanotechnology in last few years, scientists have discovered that nanoparticles (NPs) can be used as an efficient Drug Delivery System (DOS). In order to develop better NPs based drug delivery tool, it is imperative to understand the interaction between the NPs and the cell membrane. In our earlier studies, cerium oxide nanoparticles (CNPs) have been reported to have therapeutic properties, specifically against abnormalities associated with oxidative stress. Therefore, CNPs with different sizes and morphology were selected to understand the interaction with cell. We analyzed the mechanical property of human nasal septum tumor cells membranes using Atomic Force Microscopy (AFM) with and without CNPs. In particular, Force-Distance spectroscopy mode was used to estimate the elasticity of cells membrane. Different concentrations (0, 50, 125 and 250 µM) of CNPs were added to the cells (squamous cells; CCL30) and incubated for different time periods (0, 15, 30 and 60 minutes). Cell membrane elasticity/Young's modulus was calculated using a modified Hertz model. Changes in the cell elasticity were observed in high concentration of CNPs when treated with one hour. Significant changes in cell elasticity were observed at high concentration of CNPs for one hour of incubation. No significant change in cell elasticity was observed over one hour time period for 50 µM of CNPs. Moreover, by using selected inhibitors to block different cell mediated internalization pathways, we also investigated the correlation between the cellular uptake and the tracking of NPs with their size. Specifically, similar change in cell elasticity was observed after blocking the cell energy production for CNPs with smaller diameter (3-5 nm). On the other hand, bigger size NPs (20-30 nm) showed no change in cell elasticity after blocking the cell energy production. These results indicate that 3-5 nm particles internalize cell by non-energy dependent pathway i.e. passive diffusion whereas 20-30 nm particles entered in cell by energy dependent pathways i.e. endocytosis of particles. Further, we have also identified the cellular uptake of 20-30 nm particles is by enclosing those CNPs in membrane vesicles in caveolae-mediated endocytosis mechanism. In summary, these results indicate that the nanoparticles-cell interaction has pronounced influence on the shape and size of the nanoparticles. These interactions can be further monitored by real time mechanical property measurement of cell membrane.