Spatial Dispersion in Electrochemically Generated Surface Composition Gradients Visualized with Covalently Bound Fluorescent Nanospheres

Abstract

Surface electrochemical potential gradients were prepared by poising the two ends of a thin Au strip at different potentials relative to a common solution Ag/AgCl reference couple. The small resistivity of the Au film resulted in a linear gradient in surface electrochemical potential, enabling spatially resolved electrochemistry. With no applied potential, a self-assembled monolayer (SAM) of an organothiol was formed on the electrode surface. Upon potential application the SAM was stripped in regions with local potentials cathodic of the reductive desorption potential, while regions sufficiently anodic of that potential maintained full monolayer coverage. A transition region was produced between the bare areas and those retaining full monolayer coverage. Carboxylic acid modified, fluorescently doped, polystyrene nanospheres can be reacted with amine-terminated thiols through the use of a water-soluble carbodiimide and N-hydroxysuccinimide. Fluorescence microscopy was used to image the nanosphere distribut...