Biosensors Dr. Bhavesh Patel Principal V.P. and R.P.T.P. Science College, Vallabh Vidyanagar Email- bhavesh1968@rediffmail.com

What are biosensors? A device that uses specific biochemical reactions mediated by isolated enzymes, immuno systems, tissues, organelles or whole cells to detect chemical compounds usually by electrical, thermal or optical signals.

Principle of Biosensors

Required Characteristics Sensitivity Low detection limits Cost Simplicity Reliability Speed Accuracy Precision Utility Field portability Ruggedness Reproducibility Ease of calibration Stability Room for improvement

Types of biosensors Based on use of different biological material and sensor devices following are the main types – -Electro-chemical Biosensor -Amperometric Biosensor -Thermistor containing Biosensor -Bioaffinity sensor -Whole cell Biosensors -Opto-electronic Biosensor

Electro-chemical Biosensor This type of biosensor has been developed by using electronic device like field effect transmitors or light emitting diode. Field effect transmitors measures charge accumulation on their surface while light emitting diode measures photo response generated in a silica based chip as an alternating current. The field effect transmitor measures a biochemical reaction at the surface and induce in to current.

Amperometric Biosensor Amperometric biosensors are those which measures the reaction of anylate with enzyme and generate electrons directly or through a mediator. Enzyme electrodes are a new type of biosensor which have been designed for the assay of substrates such as urea, amino acid, glucose, alcohol and lactic acid. The enzyme is embedded in thin permeable membrane and produce oxygen, hydrogen, ammonia, carbon dioxide and other small molecules. This is detected by specific sensor.

Thermistor Containing Biosensors Thermistor is used to record even a small change in temperature (between 0.1- 0.001C) during biochemical reactions. By immobilizing enzymes like cholesterol oxidase, invertase, tyrosinase etc. thermistors have been developed. Thermistors are also developed for Ag-Ab with high sensitivity in case of thermometric Enzyme Linked Immunosorbant Assay (ELISA).

Bioaffinity Sensors This measures the concentration of the determinants i.e. substrates based on equilibrium binding. Such sensors involves the use of radiolabelled, enzymelabelled or fluorescence labelled substance. This type of biosensors are the use of lectin receptors for saccharides estimation, hormone receptors for hormone, drug receptors for drug, antibodies receptors for antigens and nucleic acid for inherited disease and finger printing.

Whole cell Biosensors In this device, either immobilized whole cell of microorganisms or their organelles are used. Azotobactor is used to measure concentration of nitrate within 5-10 min. The other organism used are Methylomonas for methane, Trichosporon for acetate and ethanol.

Opto-electronic Biosensors In this type of biosensor either enzymes or antibodies are immobilized on the surface of a membrane. For measuring color, biosensor with enzyme and dye is immobilized to a membrane. When substrate is catalysed to yield product, change in pH of the medium occur. This result in changes in dye membrane complex. The change in color is measured by using a light emitting diode and a photodiode.

Evolution of the Medical Biosensor Mid 1950’s - Leland C Clark invents an electrode that measures dissolved oxygen in the blood of patients undergoing surgery. He surrounded a platinum electrode and reference electrode with a plastic membrane permeable to gases. The voltage differential measured between the two gave the rate at which the oxygen was being diffused.

Clark extended this electrode idea to include glucose sensors. However these never made their way into routine patient care. This was due to flaws in accuracy when clots formed around the electrode.

Uses of Biosensors Environmental Monitoring Military Law Enforcement Medical

Present Applications of Biosensors Medical Care (both clinical and laboratory use) The determination of food quality The detection of environmental pollutants Industrial Process Control

Applications (cont’d.) Biosensors in process control will be able to measure materials in the process flow of temperature, pressure and the acidity readings. The development of biosensors in industry can improve manufacturing techniques, which would allow for a wider range of sensing molecules to be produced at a cheaper rate. In the field of medicine, tumor cells are used as a biosensor to monitor chemotherapeutic drug susceptibilities. Biosensors also play a role in the manufacturing of pharmaceuticals and replacement organs such as an artificial pancreas for diabetics.

Applications (cont’d.) It is found that biosensors are widely used in environmental testing by using a “flow-through” system to monitor wastewater (a flow-through system includes instruments using surface plasmon resonance). These censors are not only restricted to the use of molecules. Rather living microorganisms such as bacteria can be used to detect substances such as vitamin B12. Conclusively, biosensors play a part in the field of medicine, environmental quality, and industry mainly by identifying material and the degree of concentration present.

Example of biosensors Pregnancy test Detects the hCG protein in urine. Interpretation and data analysis performed by the user Glucos monitoring device (for diabetes patients) Monitors the glucose level in the blood. Interpretation and data analysis performed by a microprocessor.

Example of biosensors Infectous disease biosensor from RBS Data analysis and interpretatoin performed by a microprocessor Old time coal miners’ biosensor Data analysis and interpretation performed by the coal miner.

Research Biosensors Biacore Biosensor platform General and flexible, good tool for development of specific biosensors For a comprehensive list of research biosensor suppliers see: www.realtimebiosensor.com

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