SERS Substrate Enhancement Factor (SSEF) determination using Gas Chromatography–Mass spectrometry (GC–MS): A simplified approach

The "SERS Substrate Enhancement Factor" (SSEF) is a widely used metric for the quantification of surface-enhanced Raman scattering (SERS) enhancement factors (EFs). However, a major challenge in determining the SSEF is the quantification of molecules contributing to the measured intensities for both SERS and conventional Raman measurements, denoted as NSERS and NRaman. This paper presents a method for quantifying NSERS using Gas Chromatography–Mass Spectrometry (GC–MS) by measuring the residual concentrations of analyte molecules in the sample solutions used for the immersion of SERS substrates. Due to the adsorption of analyte molecules onto the SERS surfaces, significant concentration differences occur, which translate to NSERS. 4-Methylbenzenethiol (4-MBT) was selected as an analyte substance due to its strong interaction with the gold and silver surfaces of SERS substrates. The measurement technique proposed in this work significantly simplifies the otherwise demanding quantification of NSERS. To determine NRaman, 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” Veff, which is probed during the conventional Raman measurement and how the number of molecules contributing to the Raman intensity was derived from Veff. To demonstrate our approach, 16 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.