Platinum nanoparticle oxidase-like enzyme for colorimetric and photothermal dual-mode detection of sulfide ions

Monitoring sulfide ions (S 2- ) in environmental matrices is critical for environmental safety and pollution control. In this work, a novel dual-mode colorimetric and photothermal (PT) point-of-care testing (POCT) platform was developed for S 2- assay. The synthesized platinum nanoparticles (Pt NPs) exhibited exceptional oxidase-like activity, catalyzing the oxidation of 3,3 ' ,5,5 '-tetramethylbenzidine (TMB) to its oxidized form (oxTMB), causing a color change from colorless to blue. Additionally, oxTMB exhibits significant PT effects under nearinfrared 808 nm laser irradiation. The presence of S 2- induced the aggregation of Pt NPs, markedly inhibiting their oxidase-like activity, thereby establishing an inverse relationship between the concentration of S 2- and both the RGB value and temperature change in TMB solution. The limits of detection (LODs) were calculated to be 1.5 mu M and 4.4 mu M for colorimetric and photothermal analysis using a digital thermometer and smartphone, respectively. The S 2- in lake water and fuel residue was analyzed, yielding satisfactory results. This method offers low-cost, straightforward, and swift advantages, underscoring its potential for POCT in environmental monitoring.