Fluorescent and Electrochemical Sensing With Nitrogen‐Doped MXene Quantum Dots: From Design Principles to High‐Performance Detection

Nitrogen‐doped MXene quantum dots (N‐MQDs) have emerged as a versatile class of nanomaterials with tunable electronic structures, stable photoluminescence, and adaptable surface functionalities, making them highly promising for advanced chemical and biological sensing. Nitrogen incorporation modulates the lattice, introduces defect sites, and reconstructs surface electronic states, enabling controlled bandgap tuning, charge redistribution, and enhanced exciton dynamics. These structural and electronic modifications provide the foundation for high‐performance fluorescent and electrochemical detection, allowing sensitive, selective, and reversible signal transduction. N‐MQDs demonstrate ultrasensitive detection of small biomolecules, neurotransmitters, metal ions, pharmaceuticals, and oxidative stress markers, with detection limits in the nanomolar to sub‐micromolar range. The combination of quantum confinement and nitrogen‐induced electronic perturbations further amplifies their analytical responsiveness. Importantly, N‐MQD‐based sensors maintain performance in complex matrices, including biological fluids, environmental water, and food samples, highlighting their translational potential. This review systematically addresses the design principles, interfacial interaction mechanisms, and performance evaluation of N‐MQDs, providing a comprehensive perspective on their integration into next‐generation sensing platforms. Overall, nitrogen doping transforms MQDs into modular, high‐performance probes capable of bridging fundamental materials science and real‐world analytical applications.