Biosensors Conductimetric

Electrochemical biosensors are the most common especially when the biological component is an enzyme. Many enzyme reactions involve electroactive species being either consumed or generated and can be monitored by ampero-metric, potentiometric or conductimetric techniques, although the latter are the least developed and will not be discussed further. 

An enzyme biosensor consists of an enzyme as a biological sensing element and a transducer, which may be amperometric, potentiometric, conductimetric, optical, calorimetric, etc. Enzyme biosensors have been applied to detecting various substrates (Table 3.1), which are selectively oxidized or reduced in enzyme-catalyzed processes depending on the nature of substrates and enzymes used (oxidases or reductases) to construct sensors. 

Applications. An example of practical approach based on polymer-imprinted materials is the development of biosensors for the detection of the herbicides atrazine [87] and 2,4-dichlorophenoxyacetic acid (2,4-D) [88]. The first one is based on conductimetric detection and it uses an atrazine selective polymeric matrix generated from triethylene glycol dimethacrylate... 

Biosensors evanescence SPR, absorbance), Electrochemical methods (amperometric, conductimetric, potentiometric), piezoelectric acoustic, colorimetric, mechanical, thermal methods et al., 2002 Baeumner, 2003 Nakamura and Karube, 2003... 

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). 

Measurements of the cell conductance represent the third electrochemical transduction mode. The resulting sensing devices thus rely on the biological or chemical modulation of the surface conductivity. Despite the promise of conductimetric devices, their exploitation in modern biosensors is still in its infancy. 

Electrochemical sensor fabrication has dominated the analytical application of polymers. In some sensors the polymer film acts as a membrane for the preconcentration of ions or elements before electrochemical detection. Polymers also serve as materials for electrode modification that lower the potential for detecting analytes. In addition, some polymer films function as electrocatalytic surfaces. Using a polymer in biosensors is a very rapidly developing area of electroanalytical chemistry. Polymeric matrix modifiers have been applied as diffusional barriers in constructing not only sensitive amperometric biosensors, but also electrochemical sensors that apply potentiometric, conductimetric, optical, and gas-sensing transducer systems. The principles, operations, and application of potentiometric, conductimetric, optical and gas sensors are described in Refs. 13, 39-41. In this chapter, we focus mainly on amperometric biosensors based on redox enzymes. 

Conductivity measurements are much less chemically specific and so are not considered in detail in this volume, although Chapter 2.11 describes some biosensors that operate on conductimetric principles. It is also important to note, in passing, the use of conductimetric methods in analysis [3], particularly for capillary electrophoresis [4, 5] and in ion chromatography [6]. 

Sheppard NF Jr, Mears D, Guiseppi-Elie A (1996) Model of an immobilized enzyme conductimetric urea biosensor. Biosens Bioelectron 11 967-979... 

Earlier studies of indirect conductimetric biosensors based on CEPs have been described by Wrighton and coworkers. The devices of Wrighton and coworkers [34] used an ingenious connection to a third electrode to potentiate the response of the CEP that was set between a pair of interdigitated microelectrodes (Figure 12.3). In this configuration, when the applied voltage to the microelectrodes is zero... 

Amperometric enzyme electrodes are at the leading edge of biosensors as far as the body of scientific publications as well as the development of the commercially available devices is concerned. Only a few conductimetric enzyme electrodes and EN(zyme)-FETs have been described. 

Lesho, M. J., The design of conductimetric biosensors based on environmentally responsive hydrogels, Ph.D. thesis. Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, 1996. 

Amperometric and conductimetric gas sensors have been devised for the detection of oxygen, hydrogen, ammonia, sulfur dioxide and methane. Enzyme-based biosensors such as cholesterol or glucose electrodes for blood analysis depend on the oxidation of cholesterol or glucose oxidase, respectively, to produce hydrogen peroxide that is detected amjjerometricaUy (Fig. 3). 

Other electrochemical biosensors may be utilized for the design of BioETs mainly one can think of using conductimetric and/or impedimetric enzyme-based biosensors that might be utilizable as the others above. However, there remain the fields of optical sensing and gravimetric sensing (employing quartz crystal microbalance, bulk or surface acoustic wave devices), two fields rarely used up to now in conjunction with biosensors. [10]... 

There are the first examples, the ones referred to a multiplex multi-specificity case. Per example in a work from the group of Soldatkin, in Ukraine, an array of conductimetric enzyme biosensors for simultaneous determination of carbohydrates maltose, lactose, sucrose and glucose were developed [55]. Several enzyme... 

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