What is a biosensor?
Biosensor is a sensor device made up of a transducer with biological recognition characteristics for elements such as DNA, enzymes, antibodies, and cells etc. The main principle of operation is that the electrical current produced by the transducer is directly related to the concentration or change in concentration of a recognition element in the mechanical, chemical or biological domain. Biosensor is exactly this type of device and the interface it represents is a biological to electronic interface. It is not limited to electronics; it can be an interface between biological and optical systems as well. In a sense, it is the information and modern electronics technology’s interface to biosystems that enables us to dig deep into the mysteries of biological life that we had never dug before. Great strides are being made in the field of nanomaterials and nanodevices, as they get coupled up in the shape of biosensors to biological systems leading to hitherto unimaginable progress in the field of medical diagnostics and research. Biosensors are destined to have a great future ahead as they unveil the underlying bioscience phenomena and provide information that can be logged and analyzed for the purpose of application or research. No matter how complex or large this information database may be, thanks to the advanced computational power available to modern technology, analytics can be produced to decipher complex biological phenomena with the help of these biosensor interfaces. Biosensors are great substitutes to more complex way of monitoring environmental pollution, food hazards, and medical diagnostic techniques.

Biosensor technology combines biological elements and micro-electronic devices together to develop a variety of analytical devices. These include Protein sensors, DNA sensors, and LoC (Lab-on-a-Chip) devices etc. Biosensors, in general, may include some biological entities like microorganisms, enzymes, etc. along with materials that have been biologically derived like engineered proteins, recombinant antibodies, aptamers etc. or even bio-mimic like imprinted polymers, biomimetic catalysts, synthetic receptors, combinatorial ligands, etc. Traditionally, only enzymes and antibodies used to be integrated into the biosensors but since their development in the 1970s, alternative biological materials along with the synthetic recognition elements came into play as well. These are then coupled with either a physicochemical transducer or an optical, electrochemical, magnetic, thermometric, piezoelectric, or a micromechanical transducing microsystem. The concentration of the analyte is directly proportional to the signal generated by the transducer (within a certain range of operation). This signal is then converted to a digital output which is used either on a display or fed into a computing system for further processing.

Biosensors have several uses in fields such as the environment, biomedical research, medicine, drug discovery, food safety and hazard, process industries, security and even defense. Biosensors are an ideal example of the interface between biological materials and electronics, and even micro- and nano- electronics. Information processing, and information storage, related to biological fuel cells, bionics and biomaterials could be achieved using bioelectronics and biosensors that are at the core of this field of research and applications.
While it would be quite imaginative to list down all the various applications in various fields, some of these would include: Biological fuel cells, Biocomputing, Aptasensors, DNA chips and nucleic acid sensors, Commercial biosensors, manufacturing and markets, Enzyme biosensors, Electronic noses, Mobile diagnostics and telecommuting, Immunosensors, Lab-on-a-chip, microfluidics and µTAS, Organism- and whole cell-based biosensors, Nanomaterials and Nanoanalytical systems, Natural and synthetic receptors, Printed biosensors and organic electronics, Infectious disease detection, Single-cell detection/analysis, and Personal health monitoring etc.

Research related to biosensors
A lot of research has already been conducted related to biosensors. 3D bio-printing is now being developed and it leads to biosensors with live cells in 3D microenvironments. Similarly, a new wireless mouth-guard biosensor with an aim to detect salivary uric acid level in real-time and also continuously was fashioned. Great new modifications have already been applied to the electrochemical glucose biosensors and they have come a long way with much more stable results than ever before. Harmonic measurements are achievable through the use of electrochemical biosensors although this area requires further research and development. Gene therapy is now possible for genetic disorders through biomarkers that are a part of the modern bio-fabrication that is going on centered around bio-sensing technologies. Pesticide residues have always been a great source of concern since the 1950s and now thanks to biosensors, these residues are measurable without getting into complicated technologies like Chromatography and Mass Spectrometry.

Fabrication of Biosensors
In biosensors, the biological recognition element is the one that interacts with a target analyte. The transducer converts the physicochemical event into a digital electronic signal. Conductive, semiconductive or piezoelectric materials are employed as electrodes. The structural materials are dependent on the research application and so does the transducing technique employed, and manufacture of the transducer itself. A variety of different materials can be utilized to bind bio-recognition elements to the transducer. These can include noble metals film or nanoparticles, metal oxides, conductive and non-conductive polymers, carbon nanotubes (CNTs) and microfibers etc. These materials are deposited on the biosensor using such techniques as vacuum evaporation, electrodeposition, and even printing.
Polymers and monomers with biologically relevant side are used due to their suitable properties as well. In recent years, carbon surfaces have started to attract the scientists and the manufacturers of biosensors. For Proteins and DNA sensing, biological recognition elements on the surface of the sensor make it attractive to the target analyte with the intent of sensing and measuring its concentration.

Future applications
Until now we have been largely familiar with monitoring and control of electromechanical and chemical systems. Biosensors will enable us to monitor and control biological systems and phenomena as well. This would be a great leap towards understanding the organic and living world with the use of technology.
Biosensors are the interface between biology and technological world. In future the biosensor applications could extend well beyond our imagination into such uses as ‘independent’ or self-controlled biosensors that could be use in buildings or vehicles, for remote patient monitoring, and even control, and for various hygiene related materials, and for our food and water etc.

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