Introduction Immunosensor or commonly known as biosensor came together by combining a biological receptor and a sensor to create a single device. It is a device for detecting an analyte. The analytical device that works to analyze a sample for the presence of a specific compound is the sensor and using a biological material to specifically interact with the analyte is known as a biosensor. The biosensor involves the conversion of a chemical flow of information into an electrical signal and is classified according to common types of bioreceptors. Overall, the purpose of the biosensor is to enable rapid and convenient testing at the point of interest and care where the sample was collected. There are three components that constitute a biosensor-bioreceptor, a biotransducer and an electronic system.a. Bioreceptor is also known as biorecognition component. It is where it uses biomolecules of organisms such as enzymes, antibodies, nucleic acid and a cell as a whole. It is designed to interact with the specific analyte of interest to produce an effect measurable by the transducer. The key requirement for a bioreceptor is to have high selectivity for the analyte among the array of other chemical or biological compounds. Bioreceptor the molecule must be immobilized near the transducer. Common types of bioreceptor interactions: i. Antibody/Antigen Interactions: Biosensors utilize the very specific binding affinity of the antibody for a specific antigen. The antibody follows the lock and key principle and the antigen binds only to the correct formation.The disadvantages of using the antibody are that the binding capacity is highly dependent on the test conditions such as pH level and temperature and the interaction of this test between the antigen. ..... middle of paper ...... a genetically modified form of a native protein or enzyme.• The protein is configured to detect a specific analyte and the resulting signal is read by a detection instrument, such as a fluorometer or luminometer. the advantages of these biosensors are the accuracy of the results, the minute detection capability, the ease of use, the versatility and the availability of continuous monitoring. The biosensor has a wide range of applications depending on how it is used. It is used as medical application, industrial application, environmental applications, military applications and drug development. Medical applications such as glucose monitoring in diabetic patients, protein engineered biosensor detection and pathogen detection. Environmental applications such as detection of pesticides and river water contaminants such as heavy metal ion. toxic level level detection before and after bioremediation.