MXenes for sensing technology: from fundamental properties to diverse applications

MXenes, an emerging class of two-dimensional transition metal carbides and nitrides, have revolutionized sensing technologies due to their excellent electrical conductivity, tunable surface chemistry, and mechanical flexibility. This review examines MXene-based sensors across five critical domains: gas sensing for detecting volatile compounds (e.g., NH₃, NO₂) with parts per billion (ppb)-level sensitivity; electrochemical/optical biosensing for biomarkers and disease diagnostics; piezoresistive pressure/strain sensing, which achieves high sensitivity (gauge factors exceeding 100, even more than 8000) and ultralow detection limits (as low as a few Pascal); piezoresistive/acoustic energy-harvesting sensing for sound wave detection with a sensitivity below 0.1 Pascal and thermoresistive-based thermal sensing for precise temperature sensitivity lower than 0.1% °C^-1. We elucidate how surface terminations (-O, -F, -OH) and composite engineering enhance performance through tailored structure-property relationships. The synergy of MXenes' hydrophilicity, biocompatibility, and multimodal sensing capabilities enables advanced applications. Challenges and future perspectives highlight smart systems, sustainable synthesis routes, and interdisciplinary strategies to overcome current barriers, positioning MXenes as transformative materials for next-generation sensing platforms toward diverse applications.