Abstract
Particulate gold films were deposited on glass substrates by vapor deposition. Rabbit immunoglobulin G (IgG) was immobilized by physiosorption and then Alexa Fluor anti Rabbit IgG was bound to the protein-coated surfaces. Fluorescence was enhanced with increasing the Au thickness and reached saturation at 30 nm when Alexa Fluor555 anti IgG was used. We also examined the effect of silica spacers between the gold film and the labeled protein. The maximum enhancement was dependent on the thickness of silica and reach maximum at 10 nm. The maximum increase in intensity was about 6-fold. We also bound Alexa Fluor-680 anti IgG to the protein-coated surface, and the maximum enhancement was about 10-fold.
Highlights
Fluorescence detection is a central technology of the biosciences
The plasmon wavelength was red-shifted to 680 nm with increasing the thickness to 5 nm, showing that the particle size became larger for the thicker gold film (Fig. 1)
When the film thickness was over 10 nm, the plasmon absorbance disappeared, inferring that the metal film became continuous without the presence of individual particles
Summary
Fluorescence detection is a central technology of the biosciences. While fluorescence is a sensitive method there is a continuing need for increase sensitivity, as evidenced by the use of amplification methods such as ELISA [1,2] and PCR [3,4]. A large number of experiments have shown that fluorescence intensities can be increased 10-fold or more when the fluorophores are in close proximity to the silver particles. The silica layer was used to keep the fluorophores out of direct contact with the gold where quenching is expected to dominate over enhanced fluorescence.
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