Metallic particles, silver in particular, can significantly enhance the fluorescence of dye molecules in the immediate
vicinity (5-20 nm) of the particle. This magnifying effect can be theoretically explained/predicted by considering the
change of photonic mode density near the fluorophore due to coupling to the conducting surface. We are using this
method to observe fluorescence from a single ribosomal particle in a project aimed at acquiring sequence information
from the translating ribosome (NIH's $1000 Genome Initiative). Several quartz slides with silver nanostructures were
made using electron beam lithography techniques. The structures were approximately 50 nm high silver tiles measuring
400-700 nm on the side, and were spaced differently over a total area of 1 mm x 1 mm on any given quartz slide. In a
preliminary experiment, we coated this surface with the Alexa 647-labeled antibodies and collected single molecule
images using the MicroTime 200 (PicoQuant) confocal system. We showed that the fluorescence intensity measured
over the silver islands film was more than 100-fold higher than fluorescence from a comparable site on uncoated section
of the quartz slide. No noticeable photobleaching was seen. The fluorescence lifetime was very short, about 200 ps or
less (this is the resolution limit of the system). The method has great promise for investigations of biologically relevant
single molecules.
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