Transducer physicochemical

The reaction between the analjrte and the bioreceptor produces a physical or chemical output signal normally relayed to a transducer, which then generally converts it into an electrical signal, providing quantitative information of analytical interest. The transducers can be classified based on the technique utilized for measurement, being optical (absorption, luminescence, surface plasmon resonance), electrochemical, calorimetric, or mass sensitive measurements (microbalance, surface acoustic wave), etc. If the molecular recognition system and the physicochemical transducer are in direct spatial contact, the system can be defined as a biosensor [76]. A number of books have been published on this subject and they provide details concerning definitions, properties, and construction of these devices [77-82]. 

The physicochemical change of the biologically active material resulting from the interaction with the analyte must be converted into an electrical output signal by an appropriate transducer. On the one hand, unspecific, but broadly applicable transducers may be used, which indicate general parameters such as reaction enthalpy (thermistor), mass change (piezoelectric crystal), or layer thickness (reflectometry). On the other hand, a specific indication may be achieved with potentio-metric or amperometric electrodes for species such as H+, OH-, CO2, NH3, or H2O2, or with optical methods such as photometry or fluori-metry. 

Biosensors are the offspring of the first successful marriage between biotechnology and modem electronics. The biomolecules are responsible for the specific recognition of the analyte whereas the physicochemical transducer supplies an electrical output signal which is amplified by the spatially separated electronic component. 

Biosensor An integrated device incorporating a biological/ biomimetic recognition system either integrated within or intimately associated with a physicochemical transducer [68]. Biosensors are chemical sensors in which the recognition system utilizes a biochemical mechanism [6]. 

Chemical sensor A device that converts chemical information such as the presence/concentration of specific sample components into a measurablel signal [66]. Chemical sensors contain two basic functional units connected in a series a chemical (molecular) recognition system (receptor) and a physicochemical transducer [6]. It is capable of continuously recognizing the presence and/or concentration of a chemical constituent in a liquid or gas and converting this information in real time to an electrical or optical signal. 

Electrochemical DNA-based biosensor A biosensor that integrates DNA (generally a nucleic acid) as the biological recognition element and an electrode as the physicochemical transducer. 

Physicochemical electrochemical transducers See Electrode/working electrode... 

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