With increasing concerns about environmental pollution, opiate abuse and terrorism, people have become more sensitive to hazardous substances that threaten public health and safety. Raman spectroscopy is a very useful analytical tool, giving molecular fingerprint information even with portable readers. However, since inelastic (Raman) scattering of light is inherently weak, the Raman-based sensors cannot detect the substances in trace amounts. The extraordinary enhancement of Raman signals from molecules adjacent to metallic nanostructures, which is called as surface-enhanced Raman scattering (SERS), has been discovered by Professor Van Duyne in 1976. Over the past 40 years, scientists have continuously expanded the theoretical understanding of the plasmonic phenomena and developed various nanomaterials to be SERS-active.
From a practical point-of-view, cost-effective high-throughput methods of fabricating SERS substrates are in great demand. In this regard, we introduce a novel approach for fabricating SERS substrates on plastic films. Maskless plasma etching of a plastic film produces nano-protrusions on the surface, which serving as selective growth sites for nanostructure development during the subsequent metal deposition step. These simple two steps result in ultrahigh density (>100/μm2) plasmonic nanopillar arrays. Besides of SERS performance (i.e., enhancement factor > 107), the reproducibility and uniformity are thoroughly examined in 4 inch wafer scale. The detections of forensic drugs (heroin, Fentanyl, methamphetamine) and explosives (TNT, RDX, PETN) in low concentrations have been demonstrated on our SERS substrates (KIMStrates) using a portable Raman reader (Metrohm Raman Ltd.). We strongly believe that this economical and reliable SERS substrate can be a material platform for ultrasensitive Raman sensors in various applications of SERS technology.