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Biosensors

 

A biosensor is defined as a device that produces a measurable signal proportional to the concentration of the target analyte, usually incorporating a biological sensing element and measuring signals derived from biological interactions. Biosensors are self-contained integrated analytical devices that convert a biological response into quantifiable and processable signals. Biosensors required for measurement should have rapid detection, be accurate, be easy to operate, have a low response time, and be low-cost, highly sensitive, and reliable.

Working Principle of Biosensors

Biosensors are operated based on the principle of signal transduction. These components include a bio-recognition element, a biotransducer and an electronic system composed of a display, processor and amplifier. The bio-recognition element, essentially a bioreceptor, is allowed to interact with a specific analyte. The transducer measures this interaction and outputs a signal. The intensity of the signal output is proportional to the concentration of the analyte. The signal is amplified (using an Op-Amp based Amplifier) and then it is  passed through a Low Pass RC Filter. Signal Processing Unit or a Signal Conditioning Unit is accountable for performing the this process of amplifying and filtering the signal. The output of the signal processing unit is termed as an analog signal. This output is equivalent to the biological quantity being measured. The analog signal can be exhibited directly on an LCD display but usually, this analog signal is passed to a Microcontroller, where the analog signal is converted into digital signal. This is done since it is easy to analyse, process or store a digital signal.

Biosensors can be classified into four categories based on the type of transducer:

Electrochemical

The electrochemical biosensor is one of the typical sensing devices based on transducing the biochemical events to electrical signals. In this type of sensor, an electrode is a key component that is employed as a solid support for immobilization of biomolecules and electron movement. It transduces biochemical events such as enzyme-substrate reaction and antigen-antibody interaction to electrical signals. The 1st version of electrochemical biosensor was glucose biosensor which was developed by Clark. This biosensor has paved the path for biosensors in medical diagnostics. Electrochemical biosensor is actually a promising development in the field of clinical diagnosis, food-processing quality control and environmental monitoring. It is used for the diagnosis of a variety of diseases including cancers. Electrochemical nanobiosensors for monitoring biomolecular interactions has helped realize reagent-free, label-free, noninvasive, on site, in situ and online measurements of parameters of interest in a variety of matrices or mediums.

Optical

Optical biosensor is a compact analytical device having a biorecognition element integrated with a transducer system. Optical biosensors emit an optical signal, which is directly proportional to the concentration of the analyte. The biorecognition elements used by biosensors are generally biological materials, including enzymes, antibodies, antigens, receptors, nucleic acid, whole cells and tissues. Optical biosensing can be performed in a label-free or label-based manner. Label-free protocols involve interaction of the analyte with the transducer for signal detection while label-based protocols label the analyte and the optical signal is generated by colorimetric, fluorescent or luminescent methods. Optical biosensors provide high specificity, sensitivity and cost-effectiveness.

Piezoelectric

Piezoelectric biosensors are a group of analytical devices working on a principle of affinity interaction recording. A piezoelectric platform is a sensor part working on the principle of oscillations change due to a mass bound on the piezoelectric crystal surface. Piezoelectric immunosensor can detect antigens in the picogram range and also detect antigens in the gas phase as well as the liquid phase. Piezoelectric Biosensors work by measuring the change in frequency which occurs when the antigen binds to the antibody receptor. They are used in a wide variety of detection based applications as biological transducers, for example detection of cancer by detecting specific cancer biomarkers, determining drug effectiveness, DNA hybridization detection and detection of the hepatitis C virus etc.

Thermal

Thermal sensors measure the change in temperature via the change of electrical properties of sensor materials. There are two basic types of temperature sensing contact and non-contact. Contact temperature sensing requires the sensor to be in direct physical contact with the media or object being sensed. It can be used to monitor the temperature of solids, liquids or gases over an extremely wide temperature range. Non-contact measurement interprets the radiant energy of a heat source in the form of energy emitted in the infrared portion of the electromagnetic spectrum. This method can be used to monitor non-reflective solids and liquids but is not effective with gases due to their natural transparency. Thermal sensors have been intensively developed and used in a wide range of applications from monitoring of industrial processes to environmental control. Thermal sensors are capable of measuring various thermal signals such as temperature, flow, acceleration and angular velocity.

Applications of biosensors

There are numerous applications in various fields such as water quality monitoring, food sample analysis, drug and medicine analysis, blood-sugar detection, contamination in water and soil, and DNA-based sensors. For the waste water treatment process, mostly water quality parameters such as organic matter content, oxygen consumption rate, chemical oxygen demand (COD), BOD, pH, heavy metals, bacterial load, and specific ionic concentration can be monitored using biosensor techniques. In environmental monitoring applications, optical and thermal biosensors can be used for organic matter detection. Heavy metals contents are generally detected by electrochemical and piezoelectric sensors. Similarly, optical biosensors utilized for identifying the bacterial content in effluent samples. Highly selective biosensors contribute to advances in next-generation medicines such as individualized medicine and ultrasensitive point-of-care detection of markers for diseases.

References

John Fontes,Chapter 20 - Temperature Sensors, Editor(s): Jon S. Wilson, Sensor Technology Handbook, Newnes, 2005, Pages 531-561,ISBN 9780750677295, https://doi.org/10.1016/B978-075067729-5/50060-4.

Ibrahim A. Matter, Osama M. Darwesh, Hamdy A.B. Matter, Chapter 11 - Nanosensors for herbicides monitoring in soil, Editor(s): Abdeltif Amrane, Dinesh Mohan, Tuan Anh Nguyen, Aymen Amine Assadi, Ghulam Yasin, Nanomaterials for Soil Remediation, Elsevier, 2021, Pages 221-237, ISBN 9780128228913, https://doi.org/10.1016/B978-0-12-822891-3.00011-6.

Akifumi Kawamura, Takashi Miyata, 4.2 - Biosensors, Editor(s): Mitsuhiro Ebara, Biomaterials Nanoarchitectonics, William Andrew Publishing, 2016, Pages 157-176, ISBN 9780323371278, https://doi.org/10.1016/B978-0-323-37127-8.00010-8.


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