Spatial Heterogeneity of Sulfate in Tap Water across China: Insights from a Rapid and Reliable Surface-Enhanced Raman Spectroscopy Analysis

As a key anion in the biogeochemical cycle and life science, the analysis of trace-level sulfate anion (SO42–) is a routine yet laborious laboratory task. Traditional lab-based methods are inadequate for real-time, high-spatiotemporal-resolution screening and tracking on national/global scales. To address this challenge, a surface-enhanced Raman spectroscopy (SERS)-based strategy was developed, achieving sensitive qualitative analysis (≥1 μg/L) within 1 min/sample and accurate quantitative analysis (relative standard deviation < 10%) within 3–5 min/sample for SO42– in diverse water samples. The selective capture and detection of SO42– are realized via intermolecular hydrogen bonding with the adsorbed thiourea, using positively charged Au NPs as the SERS substrate. The rapid screening of SO42– levels in tap water from major cities across China displayed high spatial heterogeneity, consistent with recently reported theoretical prediction, influenced by an overall interplay of climatic, hydro-geochemical, and anthropogenic drivers. Critically, this SERS platform is expected to establish a high-throughput sensing framework for monitoring SO42– dynamics on national/global scales, generating spatially resolved real-time data sets that empower data-driven sulfur cycle modeling. Moreover, it holds potential to revolutionize real-time environmental monitoring of other environmentally relevant anions, such as nitrate, nitrite, and perchlorate.