Fabrication of Large-Area Flexible SERS Substrates by Nanoimprint Lithography

We demonstrate the nanofabrication of flexible plasmonic sensors comprising of gold nanocones achieved by nanoimprint lithography on polycarbonate (PC) sheets. Thermal imprinting was performed consistently over a large area (roughly the size of a 6 in. wafer) with a batch process; this can be extended to a continuous process using UV roll-to-roll nanoimprinting. This provides a process to scale up the fabrication of continuous imprinted rolls of PC sheets at an optimal rate of 3–5 m/min. The geometry of the peaks and the valleys of the nanocones in the as-imprinted PC is defined by the nickel mold used during imprinting; however, the gaps between the nanocones are tailored by varying the thickness of the gold deposited onto the substrate. Two different thicknesses of gold were deposited to study the effect of geometry on plasmonic sensing. The resulting PC sheet with gold coating enables highly sensitive detection of analytes by Surface Enhanced Raman Spectroscopy (SERS) by virtue of plasmonic hotspots generated at the valleys, whose presence was confirmed by scattering scanning near-field optical microscopy. This is promising, particularly when the SERS substrate developed is highly reproducible, cost-effective, transparent, and flexible, finding application in nanoplasmonic sensing and on-field environmental monitoring, where rigid SERS substrates would not be appropriate.