Two-dimensional transition metal carbides and/or nitrides (MXenes) and their applications in sensors

Due to its excellent electrical conductivity, good hydrophilicity, excellent mechanical properties, large and adjustable interlayer spacing, rich surface functional groups and large specific surface area, MXenes have attracted great attention in energy storage and conversion, sensors, electromagnetic shielding and biomedical fields. The unique surface chemistry, graphene-like morphology, high hydrophilicity, satisfactory biocompatibility and easy to form composite materials make MXenes an ideal material for sensor applications. In the past years, great efforts have been devoted to the design and fabrication of various MXene-based sensors. This review briefly introduces the structure, main synthesis methods and properties of MXenes, and then focuses on the application of MXenes and/or its composite materials in pressure sensors, strain sensors, gas sensors, humidity sensors, temperature sensors, electrochemical (bio) and optical/photoelectric sensors. The sensing mechanism, preparation method, properties and application fields of various sensors are discussed, and the performance of various MXene-based sensors is compared. Finally, we discuss and look forward to the future opportunities and challenges.