The various elements in the sensing process are described below • Analyte

The various elements in the sensing process are described below
• Analyte: A substance whose chemical and physical characteristics are being identified and measured. Example is that glucose is an ‘analyte’ in a biosensor created to detect glucose.
• Bioreceptor: In essence a biosensor is mainly the combination of a bioreceptor and transducer. A compound or a molecule which specifically decodes or recognizes the analyte is known as a bioreceptor. Enzymes, various proteins, tissue, cells, organelles, deoxyribonucleic acid (DNA), microoranisms and antibodies are some examples of bioreceptors. A certain biosensor is defined by its specific bioreceptor. The process of signal generation in the form of light, heat, pH, charge or mass change, etc upon interaction with the analyte is termed bio-recognition. High selectivity for the analyte in a host of other biochemical components is a key requirement of the bioreceptor.
• Transducer: The transducer is an element which transform one form of energy to another. In a biosensor the function of the transducer is to convert the specific bio-recognition event into a measurable signal. Most transducers produce either optical, thermal or electrical signals which are usually proportional to the amount of analyte–bioreceptor interactions.
• Electronics: The extended part of a biosensor which processes the converted signal and prepares it for interpretation and display. It consists of simple (i.e potentiostat) and/or complicated circuitries which performs signal conditioning such as amplification and conversion of signals from analogue into the digital form. The processed signals are then output to the display unit of the biosensor.
• Display: The display may consist of an LCD ( liquid crystal display) or a direct printer which generates data, graphs or curves useful or understood by the user. The output could either be in ready form or may still need some manipulation by software or connected as output in some automated feed control mechanism.
The International Union of Pure and Applied Chemistry (IUPAC) first used and defined the term “biosensor” in 1992. Afterwards biosensors has experienced exponential growth to become a major field in 21st century engineering worldwide.
However the history of biosensors actually dates back to as early as 1906 when M. Cremer demonstrated that the concentration of an acid in a liquid is proportional to the electric voltage that results between parts of that solution located on opposing locations of a glass membrane. After some three years later in 1909 the concept of hydrogen ion concentration or pH was put forward by Søren Peder Lauritz Sørensen. However it took more than ten years (1922) when a glass electrode for pH measurements was realized by W.S. Hughes.. In the years from 1909 and 1922, J. M. Nelson, and Edward G. Griffin were the first scientists to experiment in immobilizing or restricting movement in enzymes by making them assimilate or absorb invertase or saccharase on activated charcoal and a gelatinuous aluminum hydroxide.
Historically the first ‘true’ biosensor was designed and created by Prof Leland C. Clark, Jr in 1956 for oxygen detection and eventual measurement. He then become famously acknowledged as the ‘father of biosensors’ and his invention and subsequent developments of the oxygen detector electrode bears his name: ‘Clark electrode’.
An amperometric enzyme electrode’s presentation for the discovery of the presence of glucose by Leland Clark in 1962 was succeeded by the invention of the first potentiometric biosensor to observe and measure urea in 1969 by George G. Guilbault, and Joseph G. Montalvo Jr. A year after in 1970 the ISFET ion sensor was invented and exhibited by Prof Piet Bergveld to quantify concentrations of ions in compounds and substances. The ISFET’ or Ion-senstive Field Effect Transistors’s current changes when the pH or ion concentration fluctuates.
Eventually in 1972, at Ohio the first commercial biosensor was launched by Yellow Spring Instruments (YSI) into the mass public for the first time . Ever since the development of the i-STAT sensor, remarkable progress has been achieved in the field of biosensors. Among them is the invention of the first immunosensor and the pO2 and pCO2 Optode in 1975, the first artificial pancreas in 1976, the first fibre optic pH sensor in 1980, the first Surface Plasmon Resonance devide in 1983, a Glucose Amperometric Biosensor using ferrocene in 1984 and so many more. The field is now a multidisciplinary area of research which connects the principles of basic sciences (physics, chemistry and biology) with fundamentals of micro/nano-technology, electronics and applicatory medicine. A total of over 84000 reports on the topic of ‘biosensors’ from 2005 to 2015 has been indexed in the database ‘Web of Science’ .