Electrochemically deposited silver structures with nanowires 50-100 nm in diameter show high fluorescence amplification and strongly reduced fluorescence lifetimes. Both quantities depend on the structure thickness. With increasing thickness the fluorescence amplification proportionally increases and the fluorescence lifetime decreases. This thickness dependence is caused by fluorophore interaction with a system of plasmon excitations in coupled nanowires extending over micrometer size regions. Thus the amplification is attributed to a combination of extended structure area and strong plasmonic coupling between nanowires which also help to radiatively scatter the fluorescence emission.

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Using the effect of the fluorescence enhancement in close proximity to metal nanostructures, we have been able to demonstrate ultrasensitive immunoassays suitable for the detection of biomarkers. Silver fractal-like structures have been grown by electrochemical reduction of silver on the surface of glass slides. A model immunoassay was performed on the slide surface with rabbit IgG (antigen) noncovalently immobilized on the slide, and rhodamine red-X-labeled antirabbit IgG conjugate was subsequently bound to the immobilized antigen. The fluorescence signal was measured from the glass-fractal's surface using a confocal microscope, and the images were compared to the images from the same surface not coated with fractals. Our results showed significant enhancement (more than 100-fold) of the signal detected on fractals compared to bare glass. We thus demonstrate that such fractal-like structures can assist in improving the signals from assays used in medical diagnostics, especially those for analytes with molecular weight under 100 kDa.