A biosensor is a receptor-transducer integrated device, able to supply analytical quantitative and highly selective information, using a biological recognizing element. The biosensor change a chemical information into a measurable signal thanks to 2 basic components serially linked each other: the biological recognizing system and a chemical physical transducer.
The recognizing system translates the information, typically the concentration of a analyte, from a biological status to a chemical signal, with a high level of selectivity vs the analyte to be measured.
The transducer, transfers the signal out of the recongnizing system to the electrical status, being the biological element in direct contact with the transducing element.
Then, the transducer is linked to the electronic instrument which allows the signal to be processed into Data.
Many type of biosensors are available depending on the recognizing system adopted (enzymes, antibodies, cellules,….) or the way of transducing the signal (amperometric, potentiometric, field effect transistor or coductivity).
In case of enzymatic biosensors, one or more enzymes are immobilized on the surface of the transducing element (frequently a metal electrode) providing to catalize a high selective reaction to the substrate under measure. An integrated detector provide to monitor the answers.
Amperometric sensors aer based on a current generated by oxidation or reduction of a chemical which is electrically active. Tipically Redox reactions are achieved by maintaining constant the work electrode (metal or carbonate) or the electrode array vs the reference electrode. The resulting current is directly linked to the bulk concentration of the electrically active body. Biocatalytic reactions are generally chosen in such a way to be considered as being proportional to the current products in steady state.