Biosensorlar are devices that detect analytes using a biological component and a transducer. Main concepts include biological recognition (enzymes, antibodies, nucleic acids, cells), signal transduction (electrochemical, optical, piezoelectric, thermal), amplification, and processing. Types include electrochemical (amperometric, potentiometric, conductometric), optical (fluorescence, SPR), piezoelectric (QCM), thermal, immunosensors, DNA sensors, cell-based, and nanobiosensors. Applications include healthcare, environmental, and food monitoring