Reverse contrast and substructures in protein micro-patterns on 3D polymer surfaces

We characterize an approach enabling protein patterning over broad polymer areas based on selective protein adsorption on surfaces of spin-cast amino-terminated polystyrene structured topographically with elastomer molds (capillary force lithography) and passivated locally against adsorption with poly(ethylene oxide)-silanes printed with flat elastomer stamps (inverted micro-contact printing). Atomic force microscopy reveals uniformity of $PS-NH_{2}$ films with stripes of grooves and elevations alternating with periodicity $4 < \lambda < 200 \mu m$. Film morphologies, prior and after selective adsorption of model protein, are mapped with optical and fluorescence microscopes, respectively. The examination with the Fourier analysis shows that elevated regions of polymer relief are replicated as dark or bright stripes on fluorescent micrographs for elevations forming plateaus ($>3 \mu m$) or narrow ridges, respectively. Reverse contrast in protein micro-patterns is induced by modified relief geometry, which affects surface flux of silanes from stamp to polymer surface both within and away from contact zones of micro-contact printing. In addition, protein substructures with a fraction $\lambda/n$ of relief periodicity are observed on surfaces with elevated ridges (n = 2) and plateaus (n = 2 and 4). This is due to the locally modified protein adsorption with silane concentration and surface topography, respectively.