This research is dedicated to develop novel batch fabrication procedures for two distinct AFM (Atomic Force Microscope) probes integrated with electrodes enabling electrical sample characterization and electrochemical sample surface profiling respectively. These AFM probes allow for highly accurate control of the probe positioning, low contact force and sample surface imaging with high lateral resolution. As an electrical characterization tool, a nickel micro four-point probe integrated with solid nickel tips was developed. Low electrical resistance of the probe and contact resistance were achieved due to the solid nickel cantilever and tips. Low aspect ratio solid metal tips reduced contact resistance resulting in stable electrical measurement. Conductivity loss easily experienced while using metal coated AFM cantilevers was overcome by solid nickel tip integration to the electrically conductive AFM cantilevers. The fabrication method introduces selective conical nickel tip etching in silicon dioxide etching chambers. A novel batch fabrication method for SECM-AFM (Scanning Electrochemical Microscope-Atomic Force Microscope) tip integrated with a ring electrode was developed as a tool for electrochemical imaging as well as topological imaging. The electroactive area at an exactly defined distance above the apex of the AFM tip is fabricated using an inverse silicon mold technique. The electrode at a deliberately chosen distance from the end of a scanning probe tip allowing electrochemical sample imaging separated from sample topology imaging. The ring electrode coated with polymer entrapping enzymes enabled the probe to detect ATP from living epithelial cells.

The human body is an intricate network of many highly regulated biochemical processes and cell adhesion is one of them. Cell adhesion is mediated by specific interactions between molecules on apposing cell surfaces and is critical to many physiological and pathological processes like inflammation and cancer metastasis. During inflammation, blood-borne circulating leukocytes regularly stick to and roll on the vessel walls, which consist in part, adhesive contacts mediated by the selectin family of adhesion receptors (P-, E- and L-selectin). This is the beginning of a multi-step cascade that ultimately leads to leukocyte recruitment in areas of injury or infection. In vivo, selectin-mediated interactions take place in a hydrodynamic milieu and hence, it becomes imperative to study these interactions under very similar conditions in vitro. The goal of this project was to characterize the kinetic and mechanical properties of selectin interactions with different physiologically relevant ligands and selectin-specific monoclonal antibodies (mAbs) under a mechanically stressful milieu, using atomic force microscopy (AFM). Elasticity studies revealed that bulk of the complex compliance came from the selectins, with the ligands or mAbs acting as relatively stiffer components in the stretch experiments. Furthermore, molecular elasticity was inversely related to selectin length with the Consensus Repeats (CRs) behaving as Hookean springs in series. Besides, monomeric vs. dimeric interactions could be clearly distinguished from the elasticity measurements. L-selectin dissociation studies with P-selectin Glycoprotein Ligand 1 (PSGL-1) and Endoglycan revealed that catch bonds operated at low forces while slip bonds were observed at higher forces. These results were consistent with previous P-selectin studies and suggested that catch bonds could contribute to the shear threshold for L-selectin-mediated rolling By contrast, only slip bonds were observed for L-selectin-antibody interactions, suggesting that catch bonds could be a common characteristic of selectin-ligand interactions. Force History studies revealed that off-rates of L-selectin-sPSGL-1 (or 2-GSP-6) interactions were not just dependent on applied force, as has been widely accepted but in fact, depended on the entire history of force application, thus providing a new paradigm for how force could regulate bio-molecular interactions. Characterizing selectin-ligand interactions at the molecular level, devoid of cellular contributions, is essential in understanding the role played by molecular properties in leukocyte adhesion kinetics. In this aspect, data obtained from this project will not only add to the existing body of knowledge but also provide new insights into mechanisms by which selectins initiate leukocyte adhesion in shear.

Atomic force microscopy (AFM) is adapted to the measurement of adhesion forces between indoor-air-pollutant bioparticulates and synthetic carpet fiber materials. This novel technology is used to characterize the adhesion and release of a model bioparticulate, the bacterium E. coli on Nylon. This knowledge will lead to expanded studies of a wider range of biocontaminants, and ultimately to the ability to design carpet and rugs upholstery that reduce the spread of indoor air pollutants. Such an advance would improve life significantly for the 20+ million Americans who suffer from asthma, and countless others who are afflicted with allergies and illness spread via bioparticulates.

Atomic force microscopy (AFM) can be used to acquire high-resolution topographical images of surfaces, but has the additional capability of detecting the local nanometer scale mechanical properties. For these reasons, it becomes a standard research tool in the surface science recently. In this paper, we used AFM to measure the several properties of two different human hepatocellular carcinoma cell lines, Hep G2 ( known as well differentiated and more highly carcinomatous hepatoma cell lines ) and SK-HEP-1 ( known as poorly differentiated and more lightly carcinomatous hepatoma cell lines ) cells fixed on the glass substrate, which including the surface morphology and the relationship between the cantilever deflections and loading forces ( force curve ). Considered the heterogeneous characteristics of the cell surface, the preferred experimental method is to make pixel-by-pixel force curves in a designated area ( force map ) , both adhesion forces and elasticity associated with different locations on the cell surfaces will be obtained. Finally, we use Hertzian model to calculate Young's modulus of Hep G2 and SK-HEP-1 respectively. Based on these results, we can understand the surface properties of two human hepatocarcinoma cell lines with different differentiated stage. The results showed the difference of the morphology, height, cell migration, degree of cell aggregation, roughness, elasticity, adhesive force of two cells. SK-HEP-1 cell has the wide distance of the folds, better cell migration, homogeneous properties of elasticity. It can be assumed that the SK-HEP-1 cells have a dense network structure of actin filaments under the cell membrane like branches (branched networks); Hep G2 cell has the narrow distance of the folds, poor cell migration, heterogeneous properties of elasticity. It can be assumed that the Hep G2 cells have the individual actin filaments and cross-linked network structure of actin filaments under the cell membrane. The above results can be speculated that the elastic properties of the membrane surface will be influenced of actin filaments.

In this study, we developed the manufacturing pathways of carbon nanofibers (CNF) and activated carbon nanofibers (ACNF) via the ¡§melt-spinning¡¨ method. A novel route based on the solvent-free core/sheath melt-spinning of polypropylene/ (phenol formaldehyde-polyethylene) (PP/(PF-PE)) to prepare CNF. The approach consists of three main steps: co-extrusion of PP (core) and a polymer blend of PF and PE (sheath), followed by melt-spinning, to form the core/sheath fibers; stabilization of core/sheath fibers to form the carbon fiber precursors; and carbonization of carbon fiber precursors to form the final CNF. Both scanning electron microscopy and transmission electron microscopy images reveal long and winding CNF with diameter 100 - 600 nm and length greater than 80 £gm. With a yield of ~ 45 % based on its raw material PF, the CNF exhibits regularly oriented bundles which curl up to become rolls of wavy long fibers with clean and smooth surface. Results from X-ray diffractometry, energy dispersive X-ray, Raman spectroscopy, and selected area electron diffraction patterns further reveal that the CNF exhibits a mixed phase of carbon with graphitic particles embedded homogeneously in an amorphous carbon matrix. The carbon atoms in CNF are evenly distributed in a matrix having a composition of 90 % carbon element and 10 % in oxygen element. A series of ACNF have also been prepared based on the chemical activation on the thus-prepared CNF; their morphological and microstructure characteristics were analyzed by scanning electron microscopy, atomic force microscopy (AFM), Raman spectroscopy, and X-ray diffractometry, with particular emphasis on the qualitative and quantitative AFM analysis. The effect of activating agent, potassium hydroxide and phosphorous acid, is compared; factors affecting the surface morphology and microstructure of ACNF are analyzed. The ACNF also exhibits a mixed phase of carbon with graphitic particles embedded homogeneously in an amorphous carbon matrix. The resulting ACNF consists of 73 % C element and 27 % O element. The total pore volume of the all activated ACNF is larger than that of un-activated CNF. It can be inferred that chemical activation by KOH results in increased micropore volume in carbon nanofibers; while the micropores produced by the chemical activation of H3PO4 may further be activated and then enlarged to become the mesopores at the expense of micropore volume. For the concentration effect of KOH on ACNF, it can be inferred that high concentration KOH activation results in increased SBET and micropore volume in carbon nanofibers. The average pore diameter of ACNF gradually decreases as the KOH concentration increases.

Supported lipid bilayers (SLBs) are unique model systems for biological membranes. SLBs can be formed by fusing liposomes on solid substrates, which can be characterized by a variety of surface analytical techniques, such as Atomic Force Microscopy (AFM), X-ray diffraction, Quartz Crystal Microbalance (QCM), etc. In this study we used AFM to investigate the dynamic process of the formation of SLBs from liposomes in solutions containing metal ions and phase separation between different lipids as a function of temperature. Divalent cations, Ni2+ in particular, was found to be critical to the deposition of bilayers. Lipid rafts are plasma membrane microdomains rich in sphingolipid and cholesterol forming a liquid ordered phase surrounded by a liquid disordered phase. Lipid rafts are insoluble in cold non-ionic detergents, also called Detergent Resistant Membranes (DRMs). The interaction behaviors between detergent (Triton X-100) and mixed bilayers (DOPC/DPPC and DOPC/SpM) were studied by AFM. The way lipid bilayers were solubilized by Triton X-100 was quite different below and above its critical micelle concentration (CMC), and the SpM domains were found to be resistant to detergent extraction in the cold.

The cytoskeleton is a diverse, multi-protein framework that plays a fundamental role in many cellular activities including mitosis, cell division, intracellular transport, cell motility, muscle contraction, and the regulation of cell polarity and organization. Furthermore, cytoskeletal filaments have been implicated in the pathogenesis of a wide variety of diseases including cancer, blood disease, cardiovascular disease, inflammatory disease, neurodegenerative disease, and problems with skin, nail, cornea, hair, liver and colon. Increasing evidence suggests that the distribution and organization of the cytoskeleton in living cells are affected by mechanical stresses and the cytoskeleton determines cell stiffness. We developed a fully nonlinear, constrained mixture model for adherent cells that allows one to account separately for the contributions of the primary structural constituents of the cytoskeleton and extended a prior solution from the finite elasticity literature for use in a sub-class of atomic force microscopy (AFM) studies of cell mechanics. The model showed that the degree of substrate stretch and the geometry of the AFM tip dramatically affect the measured cell stiffness. Consistent with previous studies, the model showed that disruption of the actin filaments can reduce the stiffness substantially, whereas there can be little contribution to the overall cell stiffness by the microtubules or intermediate filaments. To investigate the effect of mechanical stretching on cytoskeletal remodeling and cell stiffness, we developed a simple cell-stretching device that can be combined with an AFM and confocal microscopy. Results demonstrate that cyclic stretching significantly and rapidly alters both cell stiffness and focal adhesion associated vinculin and paxillin, suggesting that focal adhesion remodeling plays a critical role in cell stiffness by recruiting and anchoring F-actin. Finally, we estimated cytoskeletal remodeling by synthesizing data on stretch-induced dynamic changes in cell stiffness and focal adhesion area using constrained mixture approach. Results suggest that the acute increase in stiffness in response to an increased cyclic stretch was probably due to an increased stretch of the original filaments whereas the subsequent decrease back towards normalcy was consistent with a replacement of the highly stretched original filaments with less stretched new filaments.

In order to create informed predictive models that capture artery dependent responses during atherosclerosis progression and the long term response to hypertension, one needs to know the structural, biochemical and mechanical properties as a function of time in these diseased states. In the case of hypertension more is known about the mechanical changes; while, less is known about the structural changes over time. For atherosclerotic plaques, more is known about the structure and less about the mechanical properties. We established a congruent multi-scale model to predict the adapted salient arterial geometry, structure and biochemical response to an increase in pressure. Geometrical and structural responses to hypertension were then quantified in a hypertensive animal model. Eventually this type of model may be used to predict mechanical changes in complex disease such as atherosclerosis. Thus for future verification and implementation we experimentally tested atherosclerotic plaques and quantified composition, structure and mechanical properties. Using the theoretical models we can now predict arterial changes in biochemical concentrations as well as salient features such as geometry, mass of elastin, smooth muscle, and collagen, and circumferential stress, in response to hemodynamic loads. Using an aortic coarctation model of hypertension, we found structural arterial responses differ in the aorta, coronary and cerebral arteries. Effects of elevated pressure manifest first in the central arteries and later in distal muscular arteries. In the aorta, there is a loss and then increase of cytoskeleton actin fibers, production of fibrillar collagen and elastin, hyperplasia or hypertrophy with nuclear polypoid, and recruitment of hemopoeitic progenitor cells and monocytes. In the muscular coronary, we see similar changes albeit it appears actin fibers are recruited and collagen production is only increased slightly in order to maintain constant the overall ratio of ~55 percent. In the muscular cerebral artery, despite a temporary loss in actin fibers there is little structural change. Contrary to hypertensive arteries, characterizing regional stiffness in atherosclerotic plaques has not been done before. Therefore, experimental testing on atherosclerotic plaques of Apolipoprotein E Knockout mice was performed and revealed nearly homogenously lipidic plaques with a median axial compressive stiffness value of 1.5 kPa.

Atomic Force Microscopy (AFM) and Kelvin Probe Microscopy (KPM) are two surface characterization methods suitable for semiconductor nanocrystal applications. In this thesis work, an AFM system with KPM capability was developed and implemented. It was observed that, the effect of electrostatic interaction of the probe cantilever with the sample can be significantly reduced by using higher order resonant modes for Kelvin force detection. Germanium nanocrystals were grown on silicon substrate using different growth conditions. Both characterization methods were applied to the nanocrystal samples. Variation of nanocrystal sizes with varying annealing temperature were observed. Kelvin spectroscopy measurements made on nanocrystal samples using the KPM apparatus displayed charging effects.

The adhesion and removal of particles from surfaces is a contemporary problem in many industrial applications like Semiconductor manufacturing, Bioaerosol removal, Pharmaceuticals, Adhesives and Petroleum industry. The complexity of the problem is due to the variety of factors like roughness, temperature, humidity, fluid medium etc. that affect pull-off of particles from surfaces. In particle removal from surfaces using fluid motion, the dynamic effects of particle separation will play an important role. Thus it is essential to study the dynamic effects of particle removal. Velocity of pull-off and force duration effects are two important dynamic factors that might affect pull-off. Particle adhesion studies can be made using the Atomic Force Microscope (AFM). The velocity of pull-off and force duration can be varied while making the AFM measurements. The objective of the current work is to obtain the dependence of pull-off force on pull-off velocity. Experiments were conducted using AFM and the data obtained from the experiments is processed to obtain plots for pull-off force vs. particle size and pull-off force vs. pull-off velocity. The pull-off force is compared with the predictions of previous contact adhesion theories. A velocity effect on pull-off force is observed from the experiments conducted.