Chemically driven design of N-doped MXene quantum dots for portable sensing and smartphone-integrated platforms.

Nitrogen-doped MXene quantum dots (N-MQDs) have recently emerged as versatile nanomaterials for portable sensing owing to their tunable surface chemistry, defect-rich structure, and favorable optical and electrochemical properties. This review presents a chemically driven perspective on the design of N-MQDs, emphasizing how controlled nitrogen incorporation, defect engineering, and surface termination modulation govern their functional behavior in miniaturized sensing systems. Rather than focusing solely on analytical performance, the discussion highlights material-level design principles that enable stable integration of N-MQDs into portable and smartphone-integrated platforms. Key strategies for physical anchoring, spatial organization, optical coupling, and mechanical robustness are critically examined to clarify how nanoscale chemical features translate into reliable platform-level performance. Representative examples of fluorescence-based, electrochemical, and dual-mode sensing architectures are summarized to illustrate the adaptability of N-MQDs across environmental and bioanalytical applications. By connecting chemical design with architectural integration, this review provides a unified framework for developing next-generation MQD-based sensing platforms compatible with decentralized, user-friendly, and smartphone-assisted diagnostics.