Photobleaching-Driven Ratiometric Fluorescent Switching of ZGO:Mn Nanorods/RhB for Iodine Vapor Monitoring with Integrated Gas-Phase Separation

Abstract Conventional fluorescent sensors generally rely on complex, time-consuming structural engineering of recognition moieties. By contrast, leveraging photobleaching for eco-friendly, reagent-free signal transduction has long been impeded by irreversible fluorophore degradation. Additionally, direct liquid-phase detection of trace radioactive iodine species (I2 or I−) persistently suffers from severe matrix interference. Herein, we engineered a novel photobleaching-driven ratiometric fluorescent platform that exploits the marked difference in photostability between structurally robust manganese-doped zinc gallate nanorods (ZGO:Mn NRs) and photo-stable rhodamine B (RhB) fluorophores. Under low-power UV irradiation, photogenerated superoxide radicals and holes induce pronounced self-quenching of ZGO:Mn NRs without compromising their crystalline structure. Upon exposure to I2, these reactive species are rapidly scavenged, restoring the intrinsic green luminescence of the nanorods and producing a distinct orange-to-green color transition. The ratiometric probe exhibits excellent sensitivity, with a limit of detection (LOD) as low as 1.54 nM. To eliminate matrix interference, we seamlessly integrate a custom 3D-printed miniaturized gas-phase separation module, which converts nonvolatile I− into volatile I2, with a smartphone-based machine-vision readout system. The system was successfully applied to detect trace iodide in complex soil, raw lake water, and kelp extract samples, with recoveries ranging from 94.7% to 105.6%, demonstrating great promise for nuclear regulatory monitoring.