Inter-flake modulation of MXenes for advanced sensing applications

MXenes have emerged as highly promising two-dimensional materials for advanced sensing applications owing to their high electrical conductivity, rich surface chemistry, hydrophilicity, mechanical flexibility, and compositional diversity. While many MXene-based sensors have been interpreted primarily from the perspective of surface-mediated interactions on individual flakes, practical sensing devices are typically constructed from assembled architectures, including films, fibers, aerogels, hydrogels, and composite networks. In these systems, inter-flake regions can make important contributions to the generation and transmission of macroscopic sensing signals by influencing charge transport, ion and molecular diffusion, and local interfacial interactions at the device level. This review focuses on inter-flake modulation as a key design principle for MXene-based sensing systems. We begin by briefly outlining the intrinsic material properties that make MXenes attractive for sensing, then discuss the fundamental inter-flake properties of MXene assemblies, including interlayer spacing, flake orientation, structural porosity, and the chemical microenvironment, with emphasis on their characterization, modulation strategies, and impacts on sensing performance. We further summarize representative advances in inter-flake modulation of MXene assemblies for smart sensing scenarios, spanning piezoresistive sensing, chemiresistive sensing, and electrochemical sensing. Finally, we discuss key challenges and opportunities for optimizing inter-flake structures toward future MXene-based sensing systems. We believe this work will provide useful guidance and new perspectives for future advanced MXene materials and devices in smart sensing applications.