Biosensors are analytical devices that detect biological processes and convert them into electrical signals. They consist of a bioreceptor that recognizes the analyte, and a transducer that converts the bioreceptor's signal into a measurable electrical output. Leland C. Clark Jr. is considered the father of biosensors for inventing the Clark Electrode, the first biosensor used to measure oxygen levels in blood and liquids. Common types of biosensors include electrochemical, optical, and piezoelectric biosensors. Examples include glucose monitoring devices and pregnancy test kits. Biosensors have applications in fields like healthcare, environmental monitoring, food analysis, and industrial process control.