Introduction to Biosensor

      A biosensor is defined as a detecting device that combines a transducer with a biologically sensitive and selective component. When a specific target molecule interacts with the biological component, a signal is produced, at transducer level, proportional to the concentration of the substance. Therefore biosensors can measure compounds present in the environment, chemical processes, food and human body at low cost if compared with traditional analytical techniques. According to the receptor type, biosensors can be classified as enzymatic biosensors, genosensors, immunosensors, etc. Biosensors can be also divided into several categories based on the transduction process, such as electrochemical, optical, piezoelectric, and thermal/calorimetric biosensors.

       Biosensor can be broken down into several components, namely; analyte, sample handling, bioreceptor, and tranducer. Analyte is what we want to be detected, such molecule of protein, toxin, peptide, vitamin, sugar, or metal ion. Sample handling is how to deliver analyte to the sensitive region (bioreceptor). It can be done for example by microfluidics and filtration. Bioreceptor is aimed to specifically recognize the analyte. There are some type of bioreceptors, such antibody with Fc and Fab, enzyme with active site, cell with membrane receptor, and polymer/hydrogel with competitive binding. Then, transducer will convert detection into specific variable (eletroactive substance, pH change, heat, light, or mass change).

       Due to recognition pattern, there are 3 kinds of signals probably being generated, signal from specific recognition, non-specific recognition and false specific recognition. Since the signal is very small corresponding to the size of molecules, an improving performance is added. Such magnetic bead, fluorescent dye, enzyme etc. will increase detection signal even though the signal error may occur. The common signal error source can be from inhomogenous sample, bubbles/flow artifacts, temperature, electromagnetic interferance, electronic unstability, and unstable chip/detection layer.

      Same with other sensors, biosensor has some main basic characteristics. Linearity, linearity of the sensor should be high for the detection of high substrate concentration. Sensitivity, sensitivity is value of the electrode response per substrate concentration. Selectivity, chemicals interference must be minimized for obtaining the correct result. Response time, response time is time necessary for having 95% of the response. Those characteristics highly depend on parts of biosensor. Therefore, to design a biosensor, analyte, sample handling, bioreceptor and transducer must be wisely chosen.