Molecular-Level Investigations Combining Nanoscale Lithography and Atomic Force Microscopy

Abstract

In this dissertation, nanostructures of octadecyltrichlorosilane (OTS) and were prepared using particle lithography and evaluated using characterizations with atomic force microscopy (AFM). The nanostructures of OTS were used as a resist for patterning fibronectin, an extracellular matrix protein. Particle lithography provides a practical and reproducible approach to generate billions of nanostructures comprised of organic thin films or nanomaterials. A film of mesospheres can be applied as a surface mask to define the periodicity and size of nanopatterns using processes of self-assembly. A close-packed arrangement of mesospheres is produced spontaneously when monodisperse solutions of latex or silica are dried on a flat surface. Organosilanes attach to surfaces by successive steps of hydrolysis and condensation. Nanoscopic amounts of water are required to initiate the hydrolysis step of the reaction, if too much water is present the molecules cross-link to form polymer strands. The location of nanoscopic residues of water on the surface influence the geometry of the nanostructures produced with particle lithography. Three particle lithography approaches for preparing OTS nanostructures were evaluated using strategies for solution immersion, contact printing and vapor deposition. Surface platforms of organosilanes provided a foundation for building more complex molecular architectures by defining discrete surface sites for further steps of chemical patterning. Nanoscale patterning using organosilane chemistry was used to prepare test platforms to investigate protein binding and immunoassays at the molecular level. Studies with organosilanes provide groundwork for investigations with protein patterning to investigate the activity of fibronectin. The head groups of self-assembled monolayers (SAMs) were designed to selectively resist protein adsorption in areas surrounding small islands of protein-adhesive SAMs. A spatially selective platform for binding proteins was prepared to study protein binding at the molecular level using organosilane SAMs combined with particle lithography. Fibronectin attached selectively to the surface of (3-trimethoxysilylpropyl) diethylenetriamine SAMs to form nanopatterns over broad areas (microns). The periodicity and surface coverage of the nanostructures was determined by the diameter of the silica mesospheres. Studies with atomic force microscopy were used to evaluate the thickness and arrangement of SAMs, proteins and antibodies at each step of the fabrication procedure.