Mechanistic and signal engineering of nitrogen-doped MXene quantum dots in electrochemical and...

Nitrogen-doped MXene quantum dots (N-MQDs) have recently attracted considerable attention as low-dimensional nanomaterials for electrochemical and electrochemiluminescence (ECL) sensing owing to their high electrical conductivity, tunable electronic structure, abundant surface-active sites, and pronounced quantum confinement effects. Nitrogen incorporation enables effective regulation of charge density, energy-level alignment, and radical stabilization, which collectively control electron transfer kinetics and luminescence efficiency. Despite growing interest, a unified mechanistic understanding linking nitrogen doping, signal modulation, and sensing performance remains limited. This review systematically examines the mechanistic principles and signal engineering strategies of N-MQDs in electrochemical and ECL sensing platforms. Key aspects, including electronic structure modulation, charge-transfer pathways, radical-mediated ECL processes, surface-state regulation, and quantum confinement effects, are discussed to establish structure-property-signal relationships. Advanced signal modulation approaches, such as excitation-dependent emission, ratiometric and multichannel detection, temporal and kinetic control, environmental responsiveness, and coreactant-driven amplification, are comprehensively reviewed. Recent applications in biosensing and environmental analysis are also evaluated with emphasis on analytical performance and sensor architectures. This review provides a comprehensive overview of recent advances in N-MQDs for ECL sensing, highlighting synthesis strategies, electronic properties, sensing mechanisms, and emerging applications.