Where Electrochemistry Meets Light: MXene Quantum Dots for Dual‐Mode Ultrasensitive Ion Sensing

The ultrasensitive detection of ionic species is of critical importance for environmental monitoring, biomedical diagnostics, and industrial analysis, yet remains challenging due to the limitations of conventional sensing platforms. In recent years, MXene quantum dots (MQDs) have emerged as a new class of luminescent nanomaterials that uniquely bridge electrochemistry and photophysics. Owing to their quantum‐confined dimensions, rich surface chemistry, and intrinsic electrical conductivity, MQDs simultaneously support electrochemiluminescent (ECL) and fluorescent (FL) emission, enabling dual‐mode ion sensing within a single material platform. This review provides a comprehensive overview of the fundamental mechanisms governing ECL and FL in MQDs, with particular emphasis on the roles of surface states, defect chemistry, and charge transfer pathways. Advanced nanocomposite and interfacial engineering strategies designed to enhance stability, signal amplification, and selectivity are systematically discussed. Representative applications in ultrasensitive ion detection are compared, highlighting how dual‐mode sensing improves analytical reliability and robustness in complex matrices. Finally, emerging trends toward coupled ECL–FL intelligence, system‐level stability, and real‐world deployability are outlined. By unifying mechanistic insight with materials engineering and sensing performance, this review aims to guide the rational design of next‐generation MQD‐based ion‐sensing platforms.