This document discusses nanosensors, including their definition, types, and applications. It describes four main types of nanosensors: optical nanosensors, bio-nanosensors, chemical nanosensors, and physical nanosensors. Specific examples are given for each type, such as proximity sensors for optical nanosensors. Applications discussed include PEPPLES for intracellular sensing, a twin-action nanosensor that responds to both metal ions and temperature, and a multimodal nanosensor capable of detecting multiple electromagnetic characteristics.