High-Sensitivity and Stable Cellular Fluorescence Imaging by Patterned Silver Nanocap Arrays

Patterned silver nanocap arrays (PSNAs) prepared on porous anodic alumina templates by a simple coating technique yield enhanced sensitivity and stability in cellular fluorescence imaging. Microstructural analysis, surface-enhanced Raman scattering mapping, and finite difference time domain simulation indicate that the hot spots are evenly distributed on the substrate. Ag1522 or Chinese Hamster Ovary cells are labeled by phalloidin-fluorscein isothiocyanate (P-FITC) on the cytoskeletons and the fluorescence signals from the fluorophores bound on the cell cytoskeletons on the PSNAs are enhanced 8-fold compared to those on glass used in conventional imaging. In addition to the intensity enhancement, the photostability is improved dramatically. Spectral analysis suggests that the PSNAs can create more excitons in the light-emitting P-FITC because of plasmon resonance energy transfer from the silver nanocaps to the nearby P-FITC. They can also act as plasmonic antennae by converting a part of the nonradiative near-field emission from the fluorophores to the far field consequently enhancing the emission.