Biohybridization of Supported Gold Nanoassemblies on Silicon

Abstract

Understanding the molecular interactions of bio-organic molecules with metal nanoassemblies on a semiconductor surface is important to developing potential applications involving hybrid bio-organic metal interfaces. Here, we provide the first study of room-temperature growth evolution of l-cysteine on three notable Au nanoassemblies supported on the Si(111)7×7 surface. Our results indicate unidentate and/or bidentate arrangement of adsorbed cysteine on the Si substrate through Si–N and/or Si–S linkages, while in coexistence with the supported Au monomers and dimers. Similar to thiol-containing molecules adsorbed on other noble metals, cysteine chemisorbs via the S atom in neutral form on the supported Au nanocrystallite film. On the supported gold honeycomb nanonetwork, cysteine undergoes unidentate chemisorption through the thiol group with Au atoms and through the amino group with Si adatoms, which enables the remaining free functional groups to selectively bond with different incoming molecules. Instead of the “universal” three-stage growth found for cysteine adsorption on a pristine Si(111)7×7 surface, we observe the two-stage growth of cysteine on the supported gold honeycomb nanonetwork (i.e., without a transitional layer), similar to that found on a gold single-crystal surface. The formation of the ultrathin gold-silicide layer (honeycomb) has effectively transformed the semiconductor surface to a metal-like surface.