Ratiometric fluorescent sensors based on MXene quantum dots: linking photophysics, architecture, and multi-analyte...

MXene quantum dots (MQDs) have recently emerged as highly promising nanomaterials for advanced food safety sensing due to their unique electronic structure, rich surface chemistry, and tunable photoluminescence. In this review-a comprehensive overview of MQD-based fluorescent and ratiometric platforms for food analysis-we systematically bridge fundamental photophysical mechanisms with architecture-level sensor design and real-world analytical performance. The discussion begins with the photophysical origins of MQD fluorescence, emphasizing the roles of quantum confinement, surface terminations, defect states, and transition metal d-orbitals in shaping emissive behavior. Building on this foundation, we analyze design strategies for single-emission and ratiometric sensing architectures, highlighting intrinsic and hybrid approaches that enhance signal reliability, self-calibration, and resistance to matrix interference. Recent advances in detecting biogenic amines, antibiotics, nitrite, and multi-analyte targets in complex food systems are critically evaluated, with particular attention to smartphone-integrated and dual-modal platforms. Finally, key translational challenges-including scalability, reproducibility, and regulatory integration-are outlined. Overall, MQD-based ratiometric sensors represent a transformative direction for rapid, robust, and field-deployable food safety monitoring technologies.