Versatile gradients of chemistry, bound ligands and nanoparticles on alumina nanoporearrays

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Nanoporous alumina (PA) arrays produced by self-ordering growth, using electrochemicalanodization, have been extensively explored for potential applications based upon theunique thermal, mechanical and structural properties, and high surface-to-volume ratio ofthese materials. However, the potential applications and functionality of these materialsmay be further extended by molecular-level engineering of the surface of the pore rims. Inthis paper we present a method for the generation of chemical gradients on the surface ofPA arrays based upon plasma co-polymerization of two monomers. We further extend thesechemical gradients, which are also gradients of surface charge, to those of bound ligandsand number density gradients of nanoparticles. The latter represent a highlyexotic new class of materials, comprising aligned PA, capped by gold nanoparticlesaround the rim of the pores. Gradients of chemistry, ligands and nanoparticlesgenerated by our method retain the porous structure of the substrate, whichis important in applications that take advantage of the inherent properties ofthese materials. This method can be readily extended to other porous materials.