Rapid industrialization and urbanization have significantly increased wastewater discharge into natural water bodies, thereby emphasizing the critical importance ofprecise long-term pollutant monitoringat urban sewage outfalls to protect aquatic ecosystems. Free chlorine (FC), widely used in disinfection, poses significant ecological risks when over-discharged. However, achieving reliable long-term FC monitoringat discharge points remains a substantial challenge. In this study,we developed a continuously responsive surface-enhanced Raman scattering (SERS) sensor for long-term on-site FC monitoring.The sensor integrated a flexible SERS probe functionalized with 4-aminothiophenol (4-ATP) for selective FC detection, and acompact floating roller device for continuous signal acquisition. The sensor exhibited a low detection limit of 4.16 ppb and accurately quantified FC concentrations in real-world water samples, showcasinghigh sensitivity and reliability.Long-term deployment atsewage treatment plant (STP) outfalls further validated its robust monitoring capabilities under actual environmental conditions. This innovative SERS sensor offers a practical and accurate solution for long-term on-site FC monitoring, highlighting its potential as a scalable approach for environmental monitoring applications.?
?
