Synthesis, assembly, and biofunctionalization of silica-coated gold nanorods for colorimetric biosensing

An efficient silica coating process using an improved Stober method has been used to prepare silica-coated gold nanorods (Au-rod@SiO2). The resulting pure and clean silica surface of the gold nanorods (GNRs) is important for the facile self-assembly of Au-rod@SiO2 films on poly(4-vinylpyridine) (PVP) modified quartz substrates and offers versatile functional groups, such as the amino group, for the immobilization of biomolecules by well-established silica surface modification protocols. The subsequent covalent bioconjugation of amino-functionalized Au-rod@SiO2 films with goat anti-human-immunoglobulin G (anti-hIgG) is successfully employed for the colorimetric detection of h-IgG in a model reaction based on the specific binding affinity between the proteins. Significantly, the protein-recognition event on the Au-rod@SiO2 films can not only be monitored by changes in the absorption of light, but is also observable by the naked eye.