Amplified fluorescence imaging using photonic Ag nanotip array: A comparative study on surface morphology effects

We studied amplified fluorescence and applied to fluorescent cell imaging using plasmonic Ag substrates with the different surface nano-morphologies of tip and porous shapes. For a comparative study, we deliberately fabricated wafer-scale Ag nanotip array and nanoporous Ag substrates by a nanoimprint lithography and a chemical reduction route, respectively. Time-and space-resolved spectroscopy precisely evaluated metal -induced fluorescence characteristics by analyzing fluorescence intensity and lifetime modulations. For the standard molecular probe, the photonic Ag nanotip array showed slightly enhanced fluorescence compared to the cases on the irregular nanoporous Ag substrate and a bare glass. On the contrary, from the green fluorescent protein (GFP) expressed cell imaging study, fluorescence was remarkably amplified on the photonic nanotip array compared to that simply placed on a bare glass, whereas the GFP expressed cells suffered fluorescence quenching on the nanoporous Ag. The observed notable amplification of cell fluorescence on the photonic nanotip array is ascribed to the multiple constructive effects: the nanotip array for improved cell adherence, accumulated optical fields surrounding Ag nanotips, and photonic band-gap effect from the regularly arrayed nanotips.