Single-molecule quantum tunnelling sensors

Single-molecule sensors are pivotal tools for elucidating chemical and biological phenomena. Among these, quantum tunnelling sensors occupy a unique position, due to the exceptional sensitivity of tunnelling currents to sub-ångström variations in molecular structure and electronic states. This capability enables simultaneous sub-nanometre spatial resolution and sub-millisecond temporal resolution, allowing direct observation of dynamic processes that remain concealed in ensemble measurements. This review outlines the fundamental principles of electron tunnelling through molecular junctions and highlights the development of key experimental architectures, including mechanically controllable break junctions and scanning tunnelling microscopy-based approaches. Applications in characterising molecular conformation, supramolecular binding, chemical reactivity, and biomolecular function are critically examined. Furthermore, we discuss recent methodological advances in data interpretation, particularly the integration of statistical learning and machine learning techniques to enhance signal classification and improve throughput. This review highlights the transformative potential of quantum-tunnelling-based single-molecule sensors to advance our understanding of molecular-scale mechanisms and to guide the rational design of functional molecular devices and diagnostic platforms.