Incorporation of Gold Nanorods and Their Enhancement of Fluorescence in Mesostructured Silica Thin Films

Gold nanorods with longitudinal surface plasmon resonance wavelengths ranging from 544 to 840 nm have been coated with silica at varying thicknesses. Silica-coated Au nanorods are vitreophilic, and mesostructured composite thin films have thereafter been prepared by dispersing silica-coated Au nanorods in the silica precursor solution. Au nanorods are distributed relatively uniformly in the resultant films and their incorporation amounts can be readily varied. Mesostructured composite films containing both Au nanorods and fluorophores have been further fabricated. Each Au nanorod in these films can be treated as being embedded in a uniform array of fluorophores. Dark-field and fluorescence imaging have been carried out in the same area of the films to correlate the scattering from single nanorods with the fluorescence from the surrounding fluorophores. An exact correspondence between the bright spots on the dark-field image and those on the fluorescence image indicates that the fluorescence of the fluorophores is enhanced by nearby Au nanorods. The fluorescence enhancement is found to be dependent on different fluorophores and gets larger as the thickness of the precoated silica layer on Au nanorods becomes thinner.