Dual detection and quantification of hypochlorite and sulfite ions via SERS spectroscopy by utilizing the redox reaction of tetramethylbenzidine

We developed a highly efficient, ultra-sensitive, and selective dual detection sensor for hypochlorite (ClO–) and sulfite (SO32–) ions based on surface-enhanced Raman scattering (SERS) spectroscopy. 3,3′,5,5′-Tetramethylbenzidine (TMB) is oxidized by ClO– under acidic conditions to diazotized oxTMB that, when electrostatically adsorbed onto Au nanoparticles (NPs), produces a strong Raman signal at 1605 cm−1. Meanwhile, oxTMB is reduced to TMB by SO32–, which significantly reduces the Raman signal. The linear detection range of the proposed sensor is 10–10 to 10–6 M with a detection limit of 59 pM for ClO– and 10–9 to 10–5 M with a detection limit of 5.4 nM for SO32–. In addition, the sensor was successfully applied to detect ClO– and SO32– in water samples.