Strongly enhancing discrimination of sample concentrations via analyte-induced hot spots: Leveraging combined signal and signal-to-background ratio in SERS measurement

Abstract

Surface-enhanced Raman scattering (SERS) has been extensively used for the detection of various chemical and biological species. However, accurately quantifying analyte concentrations through SERS remains a challenge. Here, we report a new method that significantly enhancing the accuracy of quantification. We fabricated SERS substrates by thermally depositing Ag nanoparticles (AgNPs) on glass slides which were treated with plasma in an air‑oxygen mixture. The introduction of an analyte onto a plasma-treated substrate induced the aggregation of AgNPs, resulting in the formation of multiple hot spots referred to as analyte-induced hot spots, which exhibited strong Raman enhancing abilities. The degree of aggregation was conclusively shown to positively correlate with the analyte concentration, leading to heightened sensitivity towards concentration variations in both the signal (S) and signal-to-background ratio (SBR) in SERS measurements. With heightened sensitivity, both S and SBR exhibit the potential to effectively differentiate between analyte solutions with twofold concentration differences, evident from distinct error bar separations. This distinct separation applies to S and SBR across various concentrations, successfully broadening the detection range. The broadened range was successfully demonstrated in the detection of adenine solution, spanning from 2 × 10⁻⁶ and 5 × 10⁻⁴ M. To validate the practical applicability of our method in real sample analysis, we established the broadened detection range for thiram in apple juice to be from 2 × 10⁻⁷ to 5 × 10⁻⁵ M.