Biosensors are molecular sensors that combine a biological recognition mechanism with a physical transduction technique.

B. A. Cornell, V. L. B. Braach-Maksvytis, L. G. King, P. D. J. Osman, B. Raguse, L. Wieczorek & R. J. Pace* Co-operative Research Centre for Molecular Engineering & Technology, 126 Greville Street, Chatswood NSW 2067, Australia.

A biosensor is a device consisting of a biological component (as an enzyme or bacterium) that reacts with a target substance and an electrochemical or optical component that detects the resulting products or by-products and emits a signal (https://www.merriam-webster.com/dictionary/biosensor). Also, is an analytical device that combines a biological component with a physicochemical detector (https://en.wikipedia.org/wiki/Biosensor)