Surface-enhanced Raman Spectroscopy (SERS) is a powerful optical sensing technique widely used in fields like medicine, microbiology, and environmental analysis. Planar SERS substrates are preferred for their ease of integration into lab-on-chip systems and superior reproducibility. Substrate performance is assessed using metrics like enhancement factor, sensitivity, and reproducibility. Many experimental and post-processing factors can influence these metrics and their interpretations, with one of the most critical being the illumination area—essentially, the number of hotspots generating the signal. We investigated with Raman mapping the impact of the illumination area on five SERS substrates showing that a larger illumination area improves reproducibility on random structures, while it sacrifices resolution. Furthermore, a larger illumination area leads to more stable signals, particularly in irregular nanostructures, yielding higher sensitivity. In conclusion, choosing a SERS substrate should consider the trade-off between uniformity for resolution and larger illumination area for signal reproducibility.
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