Multi-wavelength colorimetric fingerprinting of sulfur compounds enabled by the differential inhibition of a Pt/Pd bimetallic nanozyme.

Sulfur-containing compounds (SCCs) are closely associated with food flavor, quality, and safety. Rapid and low-cost discrimination of multiple SCCs is therefore of great importance for food quality monitoring and safety control. Herein, we report a simple four-channel colorimetric sensor array based on a Pt/Pd bimetallic nanozyme that directly catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) without exogenous H2O2. The oxidized TMB exhibits a green color with four distinct absorption peaks at 370, 450, 652, and 880 nm. Upon addition of SCCs, the catalytic activity of Pt/Pd is inhibited to different extents, causing a progressive color change from green to blue. Notably, the inhibition leads to a decrease in absorbance at 450 nm, while the other three peaks increase, and the changes at each wavelength vary among different SCCs. By using the four absorption peaks as signal channels, a response fingerprint is generated for each SCC, enabling unambiguous discrimination. The inhibition mechanism was preliminarily investigated, revealing the oxidation of Pt/Pd after SCC binding. As a result, the sensor array successfully discriminated SCCs at different concentrations as well as in mixtures, and the practical applicability was validated in a beer matrix. Overall, this approach is simple, cost-effective, and requires no sophisticated instrumentation, offering great potential for on-site food safety monitoring.