Additional Important Considerations in Surface-Enhanced Raman Scattering Enhancement Factor Measurements

Despite considerable progress, the issues for precise evaluation of the surface-enhanced Raman scattering (SERS) substrate enhancement factor (EF) have not yet been completely solved until now. Herein, we verify that key aspects of probe molecules including initial concentration, footprint, and diffusion kinetics need to be taken into account for the experimental SERS EF measurement. The three factors collectively affect the surface coverage and thereby the determination of the number of probe molecules on the SERS substrate. We recommend that the measurement of the SERS EFs should be performed with complete surface coverage of probe molecules at steady-state equilibrium using relatively high initial concentrations. It has been demonstrated for the first time that the SERS EFs are independent of the initial concentration of probe molecules when exceeding the threshold initial concentration for complete surface coverage. This study highlights the importance of probe molecules in terms of diffusion kinetics and surface coverage for the accurate determination of the SERS EFs, which has yet to be addressed in the literature.