Transducers impedimetric

Currently, immunosensors provide a powerful tool for monitoring biospecific interactions in real time or for deriving information about the binding kinetics of an immunoreaction or the structure/function relationships of molecules. Amperometric, potentiometric, conductive, and impedimetric transducers have been applied in direct and indirect electrochemical immunoassays. 

Impedimetric measurements are inherently nonselective, but the modification of electrode surfaces with selective recognition agents has resulted in selective sensing devices based on impedimetric transducers. Reviews of immunosensors and cell-based biosensors include sections on impedance transduction [177, 250, and references therein]. A review of bioelec-tronic noses, devices intended to mimic the human olfactory system in detecting and identifying odors, includes interdigital structures for complex impedance measurements and arrays of capacitive sensor elements [251]. 

Biosensors are analytical devices that are able to detect biological components. SAMs and lipid bilayers are often used as platforms for the immobilization of biosensors [532-534], but other supports, such as Si—SiOa [535-537], Ti02 [538], and polymers [539, 540], can also be used. Electrochemical biosensors [541, 542] might use potentiometric, field-effect transistor, amperometric, or impedimetric transducers. 

The transducers most commonly employed in biosensors are (a) Electrochemical amperometric, potentiometric and impedimetric (b) Optical vibrational (IR, Raman), luminescence (fluorescence, chemiluminescence) (c) Integrated optics (surface plasmon resonance (SPR), interferometery) and (d) Mechanical surface acoustic wave (SAW) and quartz crystal microbalance (QCM) [4,12]. 

Electrochemical biosensors have some advantages over other analytical transducing systems, such as the possibility to operate in turbid media, comparable instrumental sensitivity, and possibility of miniaturization. As a consequence of miniaturization, small sample volume can be required. Modern electroanalytical techniques (i.e., square wave voltammetry, chronopotentiometry, chronoamperometry, differential pulse voltammetry) have very low detection limit (1(T7-10 9 M). In-situ or on-line measurements are both allowed. Furthermore, the equipments required for electrochemical analysis are simple and cheap when compared with most other analytical techniques (2). Basically electrochemical biosensor can be based on amperometric and potentiometric transducers, even if some examples of conductimetric as well as impedimetric biosensor are reported in literature (3-5). 

Electrochemical genosensors for the detection of bacteria were introduced about a decade ago. Miniaturization and advanced microfabrication technology have made it compatible with bacteria DNA diagnostic. This technology is cost effective, fast, and accurate. The bioaffinity and biocatalysis reactions generate either amper-ometric, voltametric, impedimetric, or conductimetric signals on screen-printed transducer chips (SPC), which is proportional to the number of immobilized DNA copies on the SPC surface. 

Mainly electrochemical (amperometric, potentiometric, impedimetric, or conductometric) and optical (IR, Raman, fluorescence, absorption, reflection, evanescence field, or surface plasmon resonance) transducers are used as the basis for biosensors. However, beside these there are other, less often employed transducers that make use of the piezoelectric effect, surface acoustic waves, or detection of heat generated in enzyme reactions [40, 41]. In the context of this work, the focus is on the specific features of electrochemical transducers. An overview showing the different fields of apphcation can be found in Sect. 2.11.1.5 (Table 2). 

Impedimetric [535, 543-547] biosensors monitor biointeractions using impedance. Biomaterials that can interact with electronic transducers include proteins such as, for example, enzymes, antibodies or antigens, and oligonucleotides or DNA fragments. This is a relatively new domain, and a Scopus search for impedimetric biosensor shows less than 200 citations. 

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