Surface-Enhanced Raman Scattering in Au Nanostructures with Submolecular Gaps for Molecular Size Detection.

Nanostructures for surface-enhanced Raman scattering (SERS) are widely studied to enhance the intensity of Raman-scattered light. The main stream of SERS substrate design is smaller nanogaps; however, there has been limited investigation of the nanostructures that cause a reduction in Raman scattering intensity. This study presents a systematic approach for molecular characterization using the intensity reduction in Au-based nanostructures with nanometer-order gaps. The nanostructures were fabricated by sputtering on glass substrates, and their gap sizes were evaluated using resistive spectroscopy. When 4-mercaptobenzoic acid molecules were attached to the nanostructures, an intensity reduction was observed when the gaps were extremely small, nearly in contact with each other. Experimental results, supported by finite element analysis, indicate that this arises from an interplay between the molecular size and the gap size. These findings suggest that this approach provides a potential framework for molecular size detection based on controlled nanostructures.