Rhodanese-enabled signal conversion and nanoporous gold electrotransduction for dual sensing of cyanide and sulfite in environmental waters.

Cyanide and sulfite are environmentally relevant pollutants that require reliable monitoring because of their toxicity, industrial use, and potential co-occurrence in contaminated waters. However, conventional methods often involve laborious pretreatment, expensive instrumentation, and matrix interference, limiting rapid environmental analysis. Here, we report a rhodanese-coupled nanoporous gold (NPG) electrochemical platform for dual detection of cyanide and sulfite using an NPG-modified glassy carbon electrode (NPG/GCE). The NPG interface enabled sensitive sulfite oxidation with a distinct peak at +0.14 V, whereas cyanide was indirectly quantified through the Rdl2-catalyzed stoichiometric reaction between cyanide and thiosulfate. This reaction produces thiocyanate and sulfite in a 1:1 ratio, and the generated sulfite, rather than thiocyanate, was selected as the electroactive reporter. This signal-conversion strategy converted poorly electroactive cyanide into a readily detectable species. The platform showed a linear range of 0.1-2000 μM for direct sulfite detection and 0.1-1000 μM for indirect Rdl2-assisted cyanide detection based on the generated sulfite oxidation signal, with corresponding detection limits of 50.44 nM and 48.42 nM, respectively. It also exhibited good operational and Rdl2 storage stability, acceptable anti-interference performance, and satisfactory spike-recovery results in environmental water samples, with recoveries of 97.63%-110.09% for sulfite and 96.90%-108.20% for cyanide. This system integrates Rdl2 specificity with NPG-based signal amplification, offering a simple enzymatic signal-conversion strategy for electrochemical monitoring of poorly electroactive pollutants.