An Analyte-Derived Turn-On Fluorescent Nanozyme Sensor Enabled by a Programmable Light-Driven Cascade for o-Nitroaniline Detection

Conventional fluorescence sensing of o-nitroaniline (o-NA) is frequently limited by unstable exogenous fluorophores and interference-prone “turn-off” readouts. Here, we develop a probe-free, analyte-derived “turn-on” platform based on commercial nano-TiO2 with programmable charge migration to drive a light-triggered reduction–oxidation cascade. Oxalic acid acts as a hole scavenger to prioritize the electron-driven reduction of o-NA to o-phenylenediamine, while Cu2+ dynamically regulates electron flow and markedly enhances peroxidase-like activity to generate reactive oxygen species that efficiently oxidize the intermediate into the strongly emissive 2,3-diaminophenazine. This establishes a fundamentally new “self-luminescence” signal-from-none mechanism in which fluorescence arises uniquely from the target’s directional conversion, thereby minimizing batch effects and suppressing false positives from structurally similar nitroaromatics. The platform exhibits a linear detection range of 2.0–40 μM and a detection limit of 0.23 μM, supporting compliance-oriented monitoring in real water matrices.