Silver nanostructure coated beads enhance fluorescence for sensitive immunoassays and bioimaging

While the principle of fluorescence enhancement of metal nanostructures is well known, the utility of this effect in practical methodologies used in analytical laboratories remains to be established. In this work we explored the advantage of fluorescence enhancement for flow cytometry and bioimaging. We reported the observation of metal-enhanced fluorescence emission of fluorophores located on the surface of silver nanostructure-coated silica beads, suitable for flow cytometry detection. The fluorescence enhancement was investigated using a model AlexaFluor 430 IgG immunoassay. Approximately 8.5-fold higher fluorescence intensities at 430 nm excitation was observed from silvered ~400 nm silica beads deposited on glass as compared to the control sample. Enhanced fluorescence signals, by a factor of ~2, were also observed in imaging of cells labeled with the europium chelate, 4,4´-bis(1”,1”,1”,2”,2”,3”,3”-heptafluoro-4”,6”-hexanedion-6”-yl)chlorosulfo-o-terphenyl-Eu³⁺ (BHHCT-Eu³⁺), when such silver-coated silica beads were used as substrates. These results indicated that silver nanostructures-coated silica beads are able to provide intensified fluorescence signals for bioassays and bioimaging.