SERS Substrate Enhancement Factor (SSEF) determination using Gas Chromatography-Mass spectrometry (GC-MS): A...

The "SERS Substrate Enhancement Factor" (SSEF) is one of the most precise metrics for the quantification of surface-enhanced Raman scattering (SERS) enhancement factors (EFs). However, a major challenge in determining the SSEF lies in accurately quantifying the number of molecules contributing to the measured intensities in both SERS and conventional Raman measurements, denoted as N_SERS and N_Raman. Here, we present a method to quantify N_SERS using Gas Chromatography-Mass Spectrometry (GC-MS) by measuring the residual concentrations of analyte molecules in the solutions used to immerse the SERS substrates. Significant differences in analyte concentration were observed due to adsorption onto the SERS surfaces, which translates to N_SERS. 4-Methylbenzenethiol (4-MBT) was selected as an analyte substance due to its strong interaction with the gold and silver surfaces of the SERS substrates. To determine N_Raman, a highly concentrated solution of 4-MBT in diethyl ether was measured. We describe in detail the optical calculations used to determine the "Effective Excitation Volume" V_eff, which is probed during the conventional Raman measurement and how N_Raman was derived from V_eff. Sixteen SERS substrates with varying preparation parameters were fabricated according to a full factorial experimental design and their SERS performance was compared using the SSEF. For SERS substrate fabrication, quartz wafers were structured via thermal dewetting in combination with reactive ion etching. The measurement technique proposed in this work significantly simplifies the otherwise demanding quantification of N_SERS and N_Raman, thereby rendering the precise quantification of SERS enhancements based on the SSEF readily accessible.