Surface-adsorbed silver half-shells as a platform for surface-enhanced immunoassays; optimization through morphological control.

We have investigated the effectiveness of surface-adsorbed silver half-shells for inducing the surface-enhanced fluorescence phenomenon. Our simple structure consists of a dense monolayer of monodispersive latex sphere covered by thermally evaporated silver, some tens of nm thick. In order to increase its effectiveness as a platform for immunoassay, we explored three physical parameters; the diameter of the latex sphere, the deposition thickness and the adsorption density of the latex sphere. The maximum enhancement of 25.5 was achieved using the sphere with 56 nm diameter with 10 nm silver deposited. As for the adsorption density, the maximum fluorescence signal was achieved with a relatively sparse adsorption density, 12.5 per microm(2) vs. 105.9 per microm(2), corresponding to the full coverage. With the adsorption density also optimized, the enhancement was further increased by a factor of three.