This work reports an efficient method to fabricate large-area flexible substrates for surface enhanced Raman scattering (SERS) application. Our technique is based on a single-step direct imprint process via porous anodic alumina stamps. Periodic hexagonal arrangements of porous anodic alumina stamps are transferred to the polyethylene terephthalate substrates by mechanically printing process. Printed nanocaps will turn into “hot spots” for electromagnetic enhancement with a deposited gold film by high vacuum evaporation. The gaps between the nanocaps are controllable with a tight correspondence to the thickness of the deposited gold, which dramatically influence the enhancement factor. After covered with a single-layer graphene sheet, the gold nanocap substrate can be further optimized with an extra enhancement of Raman signals, and it is available for the trace detection of probe molecules. This convenient, simple, and low-cost method of making flexible SERS-active substrates potentially opens a way towards biochemical analysis and disease detection.

A single-step nanoimprint process for direct patterning of metallic nanostructures at room temperature is described. Porous anodic alumina (PAA) is used for stamps and the structure can be optimized by adjusting the PAA fabrication parameters. The periodic hexagonal cells on the PAA stamps are transferred to the metals by mechanically pressing the stamps into the substrate, and various metal nanopatterns with different hardnesses and elastic moduli such as Sn, Zn, Al, Ag, Mg and Cu are fabricated. Metal nanopits or nanoislands with well defined spacing between 75 and 150 nm can be readily produced using the metal direct imprinting process. The mechanical properties of the PAA stamps and effects of imprinting pressure on the height of the transferred patterns are also investigated.

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Surface-enhanced fluorescence, a burgeoning technique in biological detection, provides largely enhanced fluorescence signal by exciting localized surfaces plasmons resonance with fluorescent dyes. Nanostructure and surroundings brings great impact on the emission signal, however, insufficient physics about the process limits further improvement on the nanostructure design. In this study, optical properties of Rhodamin-6G molecules on patterned silver nano-island arrays are tailored by precisely controlling the distance between the dyes and silver arrays. The fluorescence signal depends on the distance and the largest enhancement of 10 folds is achieved when the distance is 10 nm. The results are theoretically corroborated by finite difference time domain simulation and applied to cytoskeleton fluorescence imaging using phalloidin-fluorescein isothiocyanate. Our study provides insights into the physical mechanisms associated with the fluorescence enhancement and quenching, and our experiments suggest potential applications to high-sensitivity sub-cell imaging.