N-GQDs as quenching/enhancing nano-probes for the detection of persistent organic pollutants

Persistent organic pollutants remain among the most challenging environmental contaminants due to their persistence, bioaccumulation, and long-range ecological toxicity. In recent years, nitrogen-doped graphene quantum dots (N-GQDs) have emerged as highly promising fluorescent nano-probes for ultrasensitive POP detection because of their tunable electronic structure, high surface activity, excellent aqueous dispersibility, and controllable photophysical behavior. This review discusses the structural engineering, dopant modulation, and morphological control of N-GQDs as key determinants of fluorescence quenching and enhancement performance. Particular emphasis is placed on the mechanistic foundations of photophysical transduction pathways, including photoinduced electron transfer, fluorescence resonance energy transfer, trap-state passivation, and competitive displacement mechanisms governing “turn-off” and “turn-on” sensing responses. The review further evaluates recent advances in analytical sensing architectures, ratiometric platforms, hybrid multimodal systems, and field-deployable devices for environmental monitoring applications. Importantly, current limitations involving structural heterogeneity, mechanistic ambiguity, matrix interference, and poor reproducibility are analyzed. Finally, future perspectives focusing on artificial intelligence-assisted nanomaterial design, hybrid sensing technologies, and standardized fabrication strategies are proposed to accelerate the transition of N-GQDs from laboratory-scale fluorescent materials to reliable environmental sensing platforms for next-generation pollutant surveillance.