Enhanced fluorescence images for labeled cells on silver island films.

Silver island films (SIFs) were deposited on glass substrates to serve as supports. T-Lymphocytic (PM1) cell lines were labeled by Alexa Fluor 680-dextran conjugates on the membranes or by YOYO in the nuclei. The fluorescence images of the cell lines were recorded in the emission intensity and lifetime using scanning confocal microscopy. The fluorescence signals by the fluorophores bound on the cell membranes were enhanced significantly by SIF supports as compared with those on the glass. In addition to the increase in the intensity, there was a dramatic shortening of the emission lifetime. In contrast to the Alexa Fluor 680 fluorophores on the membranes, the YOYO fluorophores intercalated in the cell nuclei were not influenced significantly by the silver islands. This result can be interpreted by an effect of the distance on coupling between the fluorophores and metal particles: the fluorophores on the cell membranes are localized within, but the fluorophores in the cell nuclei are beyond the region of metal-enhanced fluorescence. Thus, the metal supports can be used to improve the detection sensitivity for target molecules on cell surfaces when they are fluorescently labeled.