Photoluminescence Mechanisms and Optical Sensing Applications of MXene Quantum Dots for Pesticide Detection in Vegetable Matrices.

The widespread occurrence of pesticide residues and inorganic contaminants in vegetables requires rapid, sensitive, and reliable analytical approaches for food safety monitoring. MXene quantum dots (MQDs) have attracted significant attention as advanced luminescent nanomaterials due to their tunable photoluminescence, surface chemistry, and strong interfacial interactions. This review provides a mechanism-oriented overview of MQDs-based optical sensing platforms for detecting contaminants in vegetable matrices, emphasizing photoluminescence behavior and signal modulation mechanisms. The influence of key structural parameters, including quantum confinement, surface terminations, heteroatom doping, and defect engineering, is discussed in relation to emission properties and sensing performance. Fundamental photophysical processes, including charge transfer, energy transfer, and inner filter effects (IFE), are analyzed to clarify fluorescence responses during analyte recognition. Various sensing strategies, such as fluorescence probes, ratiometric sensors, dual-mode optical platforms, and MQDs-assisted nanozyme systems, are highlighted, demonstrating high sensitivity and practical applicability. In hybrid nanozyme platforms, MQDs primarily act as interfacial electronic mediators and catalytic enhancers by facilitating charge transfer and improving interactions with catalytic components rather than functioning as independent catalytic centers. Remaining challenges include matrix interference, reproducibility, stability, and mechanistic understanding. Future perspectives focus on integrating MQDs with portable devices and data-driven technologies for real-time food safety monitoring.