Surface plasmon resonance of colloidal Au-modified gold films

The effect of colloidal Au nanoparticle immobilization on surface plasmon resonance (SPR) reflectivity is reported. Immobilization of 25 nm diameter colloidal Au on to an evaporated Au film results in a large shift in plasmon angle, a broadened plasmon resonance and an increase in minimum reflectance. This results in increased SPR sensitivity, demonstrated in several ways, including a sandwich immunoassay for human IgG, enlargement of a 1.4 nm diameter Au cluster, and detection of displacement of surface-bound biotinylated colloidal Au by free biocytin in solution. Similarly large changes in reflectivity are realized upon binding of colloidal Au to electrolessly deposited Au films prepared entirely by wet-chemical methods. These results represent potentially significant advances in the generality and sensitivity of SPR.