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Biosensors are the devices that detect the presence of biological analyte for example biomolecules, microorganisms etc. and convert this biological response to electrical one. There are 3 generation of biosensors-

First generation biosensors: Here the reaction product diffuses to the transducer and electrical response is created. Biocatalyst and transducer can be separated and are functionally active in absence of another one.

Second generation biosensors: To generate enhanced response a mediator is used between reaction and transducer. Hence removal of any one either biocatalyst or transducer can affect the functioning of others.

Third generation biosensors: Here response is directly caused by reaction and neither product nor mediator is involved directly e.g., biochip.

History of Biosensors:-

Leland C. Clark, Jr in 1956 developed the 1st true biosensor for oxygen detection. He is known as the ‘father of biosensors’ his biosensor is used to gauge oxygen in the blood, and in this sensor the electrode used is referred as the Clark electrode or oxygen electrode. Then in 1962 he demonstrated an amperometric enzyme electrode for the detection of glucose. Later, the first potentiometric biosensor was discovered to detect urea and in 1969 by Guilbault and Montalvo, Jr. Eventually, in 1975 Yellow Spring Instruments (YSI) developed the first commercial biosensor.

Biosensor detection process:-

A biosensor consists of analyte (a substance of interest that needs detection.), bioreceptor (molecule that specifically recognizes the analyte), transducer (an element that converts one form of energy into another), electronics (processes the transduced signal and prepares it for display), display (consists of a user interpretation system such as the liquid crystal display of a computer).

Hence the overall process is as follows: immobilization of biological material🡪surface treatment of sensors/transducer🡪 interaction of analyte with biological material🡪 recognition by transducer🡪conversion of biological signal into electrical signal🡪 signal amplification 🡪 conversion into numerical form using algorithm 🡪 communicate and display.

Types of Biosensors:-

There are various types of biosensors some of them are-

Enzyme-based biosensors: In 1967 first enzyme-based sensor was discovered by Updike and Hicks. Its developed-on immobilization techniques, adsorption of enzymes like oxidoreductases, polyphenol oxidases, peroxidases, and amino-oxidases. So, a transducer is used to merge an enzyme to generate a signal that is directly proportional to the target analyte. Thereby, the signal is amplified and stored.

Immunosensors biosensors: Antibodies have high affinity for their respective antigen. The antibodies bind to pathogens or toxins and interact with components of the host's immune system. These types of biosensors are based on affinity ligand solid-state devices where the immunochemical reactions are connected to a transducer.

Tissue-based biosensors: Diviès formed the first microbe-based or cell-based sensor. Tissues for these come from plants and animals. Membranes, chloroplasts, mitochondria, and microsomes were used for organelle-based sensors. This type of biosensor has high stability, and longer detection time with reduced specificity.

DNA biosensors: These were formulated on the characteristic that single-strand nucleic acid molecule is able to recognize and bind to its complementary strand in a sample due to the formation of stable hydrogen bonds between the two nucleic acid strands. Used in testing of genetical and diseases.

Piezoelectric biosensors: They are of 2 types, the quartz crystal microbalance and the surface acoustic wave device. They are based on the measurement of changes in resonance frequency of a piezoelectric crystal due to mass changes on the crystal structure(oscillation change).

Thermal biosensors : Also known as calorimetric biosensors, work on the property of adsorption or production of heat which in turn changes the temperature of medium where the reaction is occurring. They are constructed using immobilized enzymes and temperature sensors. These thermometric biosensors can detect serum cholesterol, urea, glucose, penicillin G and uric acid.

Magnetic biosensors: They are miniaturized biosensors that uses paramagnetic or super-paramagnetic particles or crystals for detecting biological interactions by measuring changes in magnetic properties or magnetically induced effects. It has great potential in terms of sensitivity and size.

Optical biosensors: It consists of a light source and optical components to generate a light beam with specific characteristics that is proportional to the concentration of the measured analyte. To send this light to a modulating agent, a modified sensing head is used along with a photodetector. These biosensors mainly involve transducing elements like antibodies and enzymes.

Fluorescent biosensors: They are imaging agents used in cancer and drug discovery. They enable insights into the role and regulation of enzymes at cellular level. (Green fluorescent protein) GFP-based and genetically encoded FRET (Förster resonance energy transfer) biosensors play a vital role.

Wearable biosensors: These are the digital devices used to wear on the human body. They come in various systems like tattoos, smart dresses, smart watches which measure the blood glucose, blood pressure, heart rate, oxygen etc. They are the sign of world improvement and their use helps in diagnosing human status. Using these biosensors can help people from not getting hospitalized as biosensors assist them in their health status.

Smart watch with various sensors

Resonant biosensors: A transducer in the form of acoustic wave is connected to a bio-element or antibody. Now the target molecule is connected to the membrane causes the alteration in membrane mass. This change in mass causes the alteration in transducer’s resonant frequency. Eventually, this frequency change can be measured.

Applications of Biosensors:-

Biosensors are ubiquitous in various fields- in drug discovery, disease detection, in medical industry like common healthcare checking, in environmental monitoring, in soil quality monitoring, in food quality monitoring, in defense and fighting bioterrorism, in cell metabolism, in plant studies, in fermentation industries, in water quality management, prosthetic devices, in marine life for detection of eutrophication using nitrite and nitrate sensors and many more.

Future Prospects:-

Biosensors are the blend of biotechnology and microelectronics. These are essential devices to measure analytes like gases, organic and inorganic substances, bacteria and ions.

Future work must aim at explaining the mechanism of interaction between biomolecules and nanomaterials on the electrode surface or nanofilms and using novel properties to form a new generation of biosensors. However, biosensors based on nanomaterials show great attractive prospects in clinical diagnosis, process control, food analysis and environmental monitoring in the near future.

Lot of research is needed in developing various biosensors for various purposes and so this technology should be commercially available.

Funds need to be mobilized to manufacture biosensors on a large scale for the general public too.

Application of biosensors will be enhanced with commercial market exposure.

Real time monitoring will help clean and hygiene the environment and various areas too.

Challenges in commercial production of Biosensors:-

Only a few biosensors are commercially available like lateral flow pregnancy tests and electrochemical glucose sensors. Some issues that contribute to this factor i.e. less production of commercial biosensors are hazard related problems with biosensors, manufacturing components of biosensors require huge cost and it isn’t stable and easy to produce and also require more time to produce commercially. Response of biosensors after several months of stagnant period shows decreased performance in any application.

Muskaan Kabra

Department of Biochemistry and Biotechnology

St. Xavier's College, Ahmedabad


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