This document discusses nanobiosensors, including their classification, working principles, history, and applications. Nanobiosensors combine biological components with nano-scale physicochemical detectors. They are classified based on the type of nanomaterial used, such as nanoparticles, nanotubes, or nanowires. Carbon nanotube-based biosensors that function as field-effect transistors are described. The document also reviews recent developments in electrochemical, fiber-optic, and carbon nanotube biosensors, as well as potential applications in biological and environmental detection.