Gap-Mode Tip-Enhanced Raman Scattering on Au Nanoplates of Varied Thickness.

Gold nanoplates (AuNPLs) enable the gap-mode configuration of tip-enhanced Raman spectroscopy (TERS). This allows for low-concentration molecular sensing and high-resolution imaging. Compared with non-gap-mode TERS, the gap plasmon provides significantly higher enhancement factors. In addition, AuNPLs exhibit a lightning rod or edge effect, further enhancing the laser field and increasing the spectroscopic sensitivity. In this study, we investigate the relationship between the thickness of AuNPLs and the intensity of the spontaneous Raman signal produced by 4-nitrobenzenethiol, a reporter molecule used in TERS. Our experimental and theoretical results show that the intensity of TERS spectra increases with an increase in the thickness of the AuNPLs. This study of the thickness dependence of AuNPL allows us to find a configuration with maximal nanoplasmonic effects. Moreover, the electromagnetic interaction of the AuNPL with the tip, positioned near the AuNPL's edge, results in a plasmonic nanoantenna configuration for field enhancement, with important promise for future applications to nanobioimaging and biosensing.