Plasmonic Electronic Raman Scattering as Internal Standard for Spatial and Temporal Calibration in Quantitative Surface-enhanced Raman Spectroscopy

Abstract

Ultrasensitive surface-enhanced Raman spectroscopy (SERS) still faces difficulties in quantitative analysis because of its susceptibility to local optical field variations at plasmonic hotspots in metallo-dielectric nanostructures. Current SERS calibration approaches using Raman tags have inherent limitations due to spatial occupation competition with analyte molecules, spectral interference with analyte Raman peaks, and photodegradation. Here, we report that plasmon-enhanced electronic Raman scattering (ERS) signals can serve as an internal standard for spatial and temporal calibration of molecular Raman scattering (MRS) signals at the same hotspots, enabling rigorous quantitative SERS analysis. We observe a linear dependence between ERS and MRS signal intensities upon spatial and temporal variations of excitation optical fields, manifesting the |E|^4 enhancements for both ERS and MRS processes at the same hotspots. Furthermore, we find that the performance limit of ERS calibration is caused by the effects from orientation variations of analyte molecules at hotspots.