Two-dimensional (2D) materials have emerged as critical components in the design of high-performance nanosensors due to their superior physicochemical, electrical, and optical characteristics. Its improved surface-to-volume ratios, tunable bandgaps, and extremely thin topology provide outstanding sensitivity, selectivity, and rapid reactions for detecting different analytes. This chapter delves into an in-depth analysis of the recent developments in the application of 2D materials such as graphene, transition metal dichalcogenides, MXenes, and black phosphorus for chemical, biological, physical, and optical sensing applications. It addresses various categories of nanosensors, their structural elements, and the essential sensing methods, including electrochemical, chemo-resistive, and optical transduction. Special attention is given to flexible and wearable sensor technologies, real-time diagnostics, and integration into IoT platforms. Furthermore, the chapter highlights the excellent progress in gas-sensing and biosensing applications and the critical challenges related to material synthesis, device scalability, and environmental stability. Prospects emphasize hybrid nanostructures, advanced fabrication strategies, and data-driven approaches such as machine learning to optimize performance and broaden the practical applications of 2D-material-based nanosensors across healthcare, environmental monitoring, and industrial safety.