Nanocavity-supported plasmonic nanograss for uniform and highly sensitive surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) serves as an ultrasensitive and non-destructive spectroscopy technique that identifies trace analytes and enables numerous applications in the field of sensors, monitors, etc. Here, we theoretically proposed and experimentally demonstrated the nanocavity-supported silver nanograss (NSSN) used to construct a uniform and highly sensitive SERS substrate for analyzing various molecules. This is a sandwich nanostructure composed of silver nanograss, aluminum oxide (Al 2 O 3 ) nanocavity, and gold mirror on a silicon wafer. Originating from the homogeneous nanograss fabricated by the oblique-angle deposition, the relative standard deviation (RSD) of 4-mercaptobenzoic acid (4-MBA) SERS signals on multiple sites was down to 4.67%. Additionally, NSSN achieved a 20-fold enhancement of 4-MBA Raman signals compared to the pure nanograss on a silicon wafer (PNSW), which was attributed to a nanocavity-enhanced localized electric field. Moreover, the NSSN was used to detect the Rhodamine 6G (R6G) and Crystal Violet (CV) molecules with detection limits of 10 −9 M and 10 −8 M, respectively. The results indicate that NSSN possesses good performance integration in terms of uniformity, local field enhancement, and highly sensitive detection of multiple analytes compared to nanoparticle-based SERS substrates, suggesting that it is a promising platform for developing biomedical sensing, environmental monitoring, medical diagnosis, etc.