| Self-assembled soft nanostructures open the era of new research by enabling the controlled positioning of protein or genes at the nanoscale on surfaces. Selective immobilization of these biological molecules at high density is enormously important for high throughput analysis of molecules and efficient disease diagnostics. Specifically, a controlled attachment and alignment of filamentous actin (F-actin) is useful for constructing nanoscale tracks to guide motor proteins underlying molecular transport devices. This dissertation explores amphiphilic block copolymers and hydrogels as templates to attach and orient F-actin. A morphological transition of asymmetric poly(styrene-b-acrylic acid) (PS-b-PAA) films is observed by in-situ scanning probe microscopy (SPM) in aqueous media. Upon initial exposure to buffer solution at pH 7.4, spherical PAA domains swell through a glassy PS surface layer to form negatively charged mushroom caps. With further exposure, the PAA caps coalesce to produce a smooth, highly wettable surface. However, if films are exposed to a buffer solution containing 3-aminopropyltriethoxysilane (APTES) for 1h, the PAA domain swelling is greatly reduced and the mushroom caps stabilize at a diameter of 33 nm. This stabilization results from a cross-linking reaction between PAA and APTES, which also converts the PAA domains from a net negative to net positive charge. By varying molecular weights of PAA block in PS-b-PAA, the feature size and spacing can be tuned. To demonstrate an application for this template with positively charged domains, a cytoskeletal filament, F-actin with a net negative charge, is organized on the PS-b-PAA template via electrostatic interactions under physiological conditions. F-actin shows a tendency to align along the modified PAA mushroom caps. We also demonstrate a novel route to control attachment of F-actin on hydrogel films. By incorporating an amine-terminated silane, the hydrogel surface charge and surface topography is varied. With increasing silane content, F-actin reorients from perpendicular to parallel to the hydrogel surface, ceases to wobble, and forms mainly elongated or cyclic structures. F-actin coverage reaches a maximum at 2.5vol% silane and declines at higher silane content. This biphasic behavior is explained by the simultaneous increase in surface charge and the self-assembly of a micron scale pattern of positively-charged islands. |
