Direct Blue Light-Induced Autocatalytic Oxidation of o-Phenylenediamine for Highly Sensitive Visual Detection of Triaminotrinitrobenzene

o-Phenylenediamine (OPD)-based chromogenic reactions are worthy tools for the development of visual colorimetric assays. The chromogenic reactions are usually triggered by various oxidants, which is not easily tunable and incompatible with some analytes. Herein, we report that direct blue light irradiation can induce the autocatalytic oxidation of OPD to generate 2,3-diaminophenazine (oxidized-state OPD, oxOPD). The autocatalytic photo-oxidation reaction mechanism of OPD is mainly ascribed to the resonant energy transfer between ectronically excited oxOPD and dissolved oxygen to form singlet state oxygen with a high oxidation capacity, which accelerates the oxidation of OPD. We demonstrate that under neutral and alkaline environment, the photoinduced autocatalytic oxidation of OPD is able to be further enhanced by triaminotrinitrobenzene (TATB) explosive because of its inhibition effect on the aggregation caused quenching phenomenon of oxOPD. On this basis, a straightforward visual colorimetric assay for TATB with a tunable dynamic range is developed. This assay is capable of detecting TATB explosive concentrations as low as 2.7 nM. Notably, the obvious color change after addition of TATB enables a naked-eye readout with the lowest detectable TATB concentrations of 60 nM.