Mechanism of Nitrogen-Doped Ti₃C₂ Quantum Dots for Free-Radical Scavenging and the Ultrasensitive H₂O₂ Detection Performance

MXene quantum dots feature favorable biological compatibility and superior optical properties, offering great potential for biomedical applications such as reactive oxygen species (ROS) scavenging and fluorescence sensing. However, the ROS scavenging mechanism is still unclear and the MXene-based materials for ROS sensing are still scarce. Here, we report a nitrogen-doped titanium carbide quantum dot (N-Ti3C2 QD) antioxidant with effective ROS scavenging ability. The doped nitrogen atoms promote the electrochemical interaction between N-Ti3C2 QDs and free radicals and thus enhance their antioxidant performance. Density functional theory (DFT) simulations reveal the hydroxyl radical quenching process and confirm that the doped N element promotes the free-radical absorption ability, especially for −F and −O functional groups in N-Ti3C2 QDs. Furthermore, N-Ti3C2 QDs show rapid, accurate, and remarkable sensitivity to hydrogen peroxide in the range of 5 nM–5.5 μM with a limit of detection of 1.2 nM within 15 s, which is the lowest detection limit of the existing fluorescent probes up to now. Our results provide a new category of antioxidant materials, a real-time hydrogen peroxide sensing probe, promoting the research and development of MXene in bioscience and biotechnology.