A Broad-pH photozyme platform based on Mn, N co-doped carbon dots for colorimetric detection of thiram

Thiram, a widely used dithiocarbamate pesticide, can threaten ecological systems and human health through residual contamination. Here, manganese and nitrogen co-doped carbon dots (Mn, N-CDs) were harnessed as a photo-driven oxidase-like nanozyme to build a visual colorimetric assay for thiram. Under light irradiation, Mn, N-CDs can generate singlet oxygen ( 1 O 2 ) and superoxide (O 2 − ·) and maintain good photozyme activity over a broad pH range. The Mn, N-CDs/3,3′,5,5′-tetramethylbenzidine (TMB) mixture produces a blue oxidized product under illumination; after introducing thiram, the oxidation of TMB is suppressed because thiram consumes 1 O 2 and O 2 − ·, thereby producing a thiram concentration-dependent color-fading signal. Notably, extending the irradiation time enhances the analytical sensitivity by allowing the chromogenic reaction to approach a more stable readout. The proposed method can be coupled with smartphone-based RGB quantification to enable portable digital readout under natural light. In addition, satisfactory recoveries and repeatability were obtained in diverse real water samples. The proposed approach thus offers a feasible strategy for developing broad-pH-applicable, facile, and on-site colorimetric sensing for pesticide monitoring.