ENHANCEMENT OF MOLECULAR FLUORESCENCE NEAR-THE-SURFACE OF COLLOIDAL METAL-FILMS

Fluorescence enhancement was studied on sliver colloidal metal films ( CMFs) using two systems: (1) Langmuir-Blodgett monolayers of fluoresce in-labeled phospholipids separated from the surface of the films by sp acer layers of octadecanoic acid and (2) biotin-fluorescein conjugates captured by avidin molecules adsorbed on top of a multilayer structur e formed by alternating layers of bovine serum albumin-biotin conjugat e (BSA-biotin) and avidin. The dependence of fluorescence intensity on the number of lipid or protein spacer layers deposited on the surface of the CMF was investigated. The results demonstrate the requirement for adsorbate location within the region between Ag particles for maxi mal enhancement. The density of avidin molecules on the surface of the BSA-biotin/avidin multilayers adsorbed on the CMF was also determined . A procedure for forming a rigid, uniform silica layer around the Ag particles on the CMF is described. The layer protects the particles fr om undesirable chemical reactions such as etching by halide ions, for example, and provides the requisite stability for bioanalytical applic ations. Colloidal films composed of Ag particles covered by similar to 10-nm-thick silica layers were tested for fluorescence enhancement us ing goat immunoglobulin and a conjugate of rabbit anti-goat immunoglob ulin with 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino)hexanoate. An enhancement factor of similar to 20 was obtained.