Nanometer-spaced metal gratings for highly sensitive surface-enhanced Raman spectroscopy

Constructing surface-enhanced Raman scattering (SERS) substrates is a recognized and effective approach for amplifying Raman signals. However, the simultaneous acquisition of nanostructured substrates with high enhancement factors and repeatability poses challenges due to cost and technological limitations. Here, we developed nanometer-spaced metal gratings (NSMGs) with high sensitivity and uniformity for SERS applications by combining nanoimprint techniques with a flexible polydimethylsiloxane (PDMS) substrate. The grating spacing of NSMGs could be adjusted by capitalizing on the stretchability of PDMS, resulting in the acquisition of SERS gratings with different nano-sized gaps (minimum ∼22 nm ) under a single imprinting mold with wide spacing. Importantly, the hotspots on the substrate can be flexibly tailored by the spacing adjustment, leading to the further enhancement of SERS signal, maximum up to nine-fold. Besides, the target molecule could be easily squeezed into the metal gaps with a strong localized electromagnetic field through active stretching and releasing of the substrate, which can further amplify the SERS signal. The high sensitivity and versatility of NSMGs were further proved by the label-free detection of rhodamine 6G (R6G) and adenine at nanomolar level. The proposed NSMG substrate is cost-effective and can be mass-produced, which has great potential for SERS applications.