Electrochemical transducers and

Analytes Enzyme classes Electrochemical transducer and indicated species or effects... 

The measurements of electrochemical impedance, voltammetric (po-larographic) analysis, and spectroelectrochemistry represent a basis for analysis of molecules of biological significance in bulk of solution and at interfaces. These principles are reviewed in the first four chapters. The next three chapters demonstrate how these principles are utilized in voltammetric and interfacial analysis of biomacromolecules such as nucleic acids, proteins, polysaccharides, and viruses in vitro, in the development of biosensors with electrochemical transducers and in in vivo voltammetry. The last two chapters of this volume are devoted to the principles of electrophoresis used for separation analysis of biomolecules and to the theoretical principles and practical description of the patch-clamp technique to an extent suitable for those wishing to initiate research in electrophysiology. 

The modification of electrodes with enzymes and other biological macromolecules was well underway before 1978, and a detailed history of this field is beyond the scope of the present paper. A brief discussion of biological systems is given, however, to place them in context with other modification layers. A recent review by Frew and Hill (121) discusses past and future strategies for design of electrochemical biosensors. Topics discussed were enzyme electrodes, electron transfer mediators, conducting salts, electrochemical immunoassay, enzyme labels, and cell-based biosensors. In general, the bioactive molecule or cell is immobilized in proximity to an electrochemical transducer and exposed to the analyte solution for real-time analysis. 

Fig. 1. Schematic representation of a battery system also known as an electrochemical transducer where the anode, also known as electron state 1, may be comprised of lithium, magnesium, zinc, cadmium, lead, or hydrogen, and the cathode, or electron state 11, depending on the composition of the anode, may be lead dioxide, manganese dioxide, nickel oxide, iron disulfide, oxygen, silver oxide, or iodine.

Junge, W., Lill, H., and Engelbrecht, S., 1997. ATP. syntlia.se An electrochemical transducer with rotatory mechanics. Trends in Biochemical Sciences 22 420-423. 

Other useful sensors rely on the coupling of microorganisms and electrochemical transducers. Changes in the respiration activity of the microorganism, induced by the target analyte, result in decreased surface concentration of electroactive metabolites (e.g., oxygen), which can be detected by the transducer. 

The presence of polymer, solvent, and ionic components in conducting polymers reminds one of the composition of the materials chosen by nature to produce muscles, neurons, and skin in living creatures. We will describe here some devices ready for commercial applications, such as artificial muscles, smart windows, or smart membranes other industrial products such as polymeric batteries or smart mirrors and processes and devices under development, such as biocompatible nervous system interfaces, smart membranes, and electron-ion transducers, all of them based on the electrochemical behavior of electrodes that are three dimensional at the molecular level. During the discussion we will emphasize the analogies between these electrochemical systems and analogous biological systems. Our aim is to introduce an electrochemistry for conducting polymers, and by extension, for any electrodic process where the structure of the electrode is taken into account. 

There are mainly three types of transducers used in immunosensors electrochemical, optical, and microgravimetric transducers. The immunosensors may operate either as direct immunosensors or as indirect ones. For direct immunosensors, the transducers directly detect the physical or chemical effects resulting from the immunocomplex formation at the interfaces, with no additional labels used. The direct immunosensors detect the analytes in real time. For indirect immunosensors, one or multiple labeled bio-reagents are commonly used during the detection processes, and the transducers should detect the signals from the labels. These indirect detections used to need several washing and separation steps and are sometimes called immunoassays. Compared with the direct immunosensors, the indirect immunosensors may have higher sensitivity and better ability to defend interference from non-specific adsorption. 

G.C. Fiaccabrino and M. Koudelka-Hep, Thin-film microfabrication of electrochemical transducers. Electroanalysis 10, 217-222 (1998). 

Other enzymes have also been immobilized on CNTs for the construction of electrochemical biosensors. Deo et al. [115] have described an amperometric biosensor for organophosphorus (OP) pesticides based on a CNT-modified transducer and OP hydrolase, which is used to measure as low as 0.15 pM paraoxon and 0.8 pM parathion with... 

Among the different carbonaceous materials, GC and pyrolytic graphite (PG) and the graphite-powder-based composites such as carbon paste (CP) are the most popular choices as electrochemical transducer materials. 

Leclerc M. Optical and electrochemical transducers based on functionalized conjugated polymers. Adv Mater 1999 11 1491-1498. 

Immunosensors have been designed which use both direct and indirect immunoassay technology to detect specific analytes within a minute or less in a variety of matrices (see Fig. 9). Indirect immunosensors may employ ELA, FLA, or CLIA principles whereby enzyme-, fluorophore- or chemiluminescent-labeled analyte competes with the target (nonlabeled) analyte for binding sites on the immobilized antibody. Unbound (free) labeled analyte is then quantitated using an electrochemical, optical, or electromechanical transducer and compared to the amount of target analyte in the sample. 

M.J. Schoening, Voltohmmetry —a new transducer principle for electrochemical sensors. In V.M. Mirsky (Ed.), Ultrathin Electrochemical Chemo- and Biosensors. Technology and Performance, Springer, Berlin, 2004. 

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