IntroductionImmunosensor or commonly known as biosensor has come together by combining biological receptors and sensor to create a single device. It is a device for the detection of an analyte. The analytical device that allows a sample to be analyzed for the presence of a specific compound is the sensor and the use of a biological material to interact specifically with the analyte is called a biosensor. Biosensor involves converting a chemical flow of information into an electrical signal and is classified based on common types of bioreceptors. In general, the goal of the biosensor is to enable rapid and convenient testing at the point of concern and care where the sample was obtained. A biosensor consists of three components: a bioreceptor, a biotransducer and an electronic system. The bioreceptor is also known as the bio-recognition component. This is where it uses biomolecules from 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 of a bioreceptor is that necessary to have high selectivity for the analyte among the matrix of a other chemical or biological compound. Bioreceptor the molecule must be immobilized near the transducer. Common types of interaction with bioreceptors: i. Antibody/antigen interactions: Biosensors use the very specific binding affinity of an antibody for a specific antigen. The antibody followed the principle of a lock and key and this antigen will only bind to the correct formation. The disadvantages of using antibodies are that the binding capacity is highly dependent on the conditions of test such as pH level and temperature and the interaction of this test between the antigen. ..... middle of paper ......a genetically engineered form of a native protein or enzyme.• The protein is configured to detect a specific analyte and the resulting signal is read by an instrument detection method, for example a fluorometer or luminometer.The advantages of these biosensors are that they have accurate results, minute detection capability, easy to use, versatile availability and 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 application such as glucose monitoring in diabetic patients, detection of pathogen biosensors and protein engineering. Environmental application such as detection of pesticides and river water contaminants such as heavy metal ion. detection of toxicity level before and after bioremediation.