Electrochemical transduction

Later on, such S-layer-based sensing layers were also used in the development of optical biosensors (optodes), where the electrochemical transduction principle was replaced by an optical one [97] (Fig. 10c). In this approach an oxygen-sensitive fluorescent dye (ruthenium(II) complex) was immobilized on the S-layer in close proximity to the glucose oxidase-sensing layer [97]. The fluorescence of the Ru(II) complex is dynamically quenched by molecular oxygen. Thus, a decrease in the local oxygen pressure as a result of... 

Electroanalytical techniques, such as conductometry [174], potentiometry [22], voltammetry [6], chronoamperometry [25] and EIS [175], have been used extensively for transduction of the detection signal in the MIP-based chemosensors. The chemosensor response may be due to different interfacial phenomena occurring at the electrode-electrolyte interface [16], which will be discussed below in the respective sections. The electrochemical transduction scheme can be devised for accurate measurements tailored to the analytes exhibiting either faradic or non-faradic electrode behaviour. In many instances, the detection medium is an inert buffer solution [24]. In order to enhance the chemosensor response, some of the... 

This procedure can be applied irrespectively of whether the analyte is electroactive or electroinactive (Case b in Scheme 4). Here, the template is removed from the MIP film with a suitable solvent solution. Next, the chemosensor with template-free MIP is immersed in the test solution for analyte preconcentration. Analyte determination can be carried out with the chemosensor in the same test solution. Alternately, the determination can be performed in another solution. For an electroactive analyte, the chemosensor is removed from the test solution (after preconcentration) and transferred to a blank electrolyte solution followed by the analyte determination. In the case of an electroinactive analyte, the chemosensor is transferred to solution of an electroactive competitor for displacement of this analyte from the MIP film. All the electrochemical transductions, i.e. conductometric, impedimetric, potentiometric, chronoamperometric and voltammetric, are operative under this scheme. In particular, voltammetry and chronoamperometry can be used for determination of both electroactive and electroinactive analytes. This approach as well as the relevant experimental design will be elaborately discussed below in the same section. 

DNA biosensors based on electrochemical transduction of hybridization couple the high specificity of hybridization reactions with the excellent sensitivity and portability of electrochemical transducers. The ultimate goal of all researches is to design DNA biosensors for preparing a basis for the future DNA microarray system. 

When natural or synthetic DNA molecules interact with electrode surfaces adsorption occurs. The knowledge about the adsorption of nucleic acids onto the electrode surface leads to the development of DNA-modified electrodes, also called electrochemical DNA biosensors [3-6,19-24], An electrochemical DNA biosensor is an integrated receptor-transducer device that uses DNA as the biomolecular recognition element to measure specific binding processes with DNA, using electrochemical transduction. 

Electrochemical transduction of the hybridisation event can be classified into two categories label-based and label-free approaches. The label-based approach can be further subdivided into intercalator/groove binder, non-intercalating marker, and NP. The label-free approach is based on the intrinsic electroactivity of the DNA purine bases or the change in interfacial properties (e.g., capacitance and electron transfer resistance) upon hybridisation [49],... 

Another approach to electrochemical transduction by chemical recognition is the incorporation of the imprinted polymer as the active ingredient in a membrane of an ISE. ISEs are devices which, when incorporated in an electrochemical cell with an appropriate reference electrode, produce a potential that varies predictably with the concentration of a certain ion in solution. If the response of the electrode follows theory, the response is Nernstian and is given by the Nernst equation ... 

Photonic activation of electrobiocatalytic functions of redox proteins and the electrochemical transduction of recorded photonic signals... 

Electrochemical immunoassays include a wide variety of devices based on the coupling of immunological reactions with electrochemical transduction. All of them involve the immobilization of an immunoreagent component on the surface of the electrode transducer. Electrochemical detection is based on the direct intrinsic redox behavior either of an analyte species or of some reporter molecule. For the detection no expensive equipment is needed, with the measurement of either a simple current or a voltage charge. Different electrochemical detection strategies are used, but ampero-metric detection is most widely used. Potentiometric and conductometric detection are applied in different assays as well. 

Such structural information could provide strong arguments concerning the chemical structures of the polymers and can be extremely important for bioimmobilization purposes. In addition, it offers valuable information about the distribution and geometry of the resulting layer. On the other hand, the stability of this film and the active surface area strongly affect the performance (especially reproducibility and stability) of the final biosensor device, particularly when electrochemical transduction schemes are employed. Such parameters can be determined using electrochemical procedures. 

Alkylphenols and their ethoxylates Immunosensor using electrochemical transduction mg L 1 range 19... 

During the last decade the number of application of MIP-based sensors has increased dramatically. The high selectivity and affinity of MIPs for target analytes make them ideal recognition elements in the development of sensors. Capacitive (Panasyuk etal., 2001), conductimetric (Piletsky et al., 1995), field effect (Lahav et al., 2004), amper-ometric (Kritz and Mosbach, 1995), and voltammetric (Pizzariello et al., 2001), electrochemical transduction systems have been used. Sensors based on conductimetric transduction have been developed by Piletsky et al. (1995) for the analysis of herbicides. A system using a TiC>2 sol-gel system, and with a linear range of 0.01-0.50 mg L-1 for atrazine, without interference of simazine, and chloroaromatic acids has been described by Lahav et al. (2004). 

The use of molecular switches in solution phase has recently received attention (de Silva et al., 1997). Photochemical logic gates shown AND, OR, XOR, NOR, and INH functionality have been reported, whereas electrochemical storage of information via electroswitchable systems (Katz et al., 2004), electrochemical transduction of photonically or electrochemically encoded information, and electrochemi-cal/photochemical information processing (Willner et al., 2001 Perez-Inestrosa... 

The photonic activation of molecular mechanical functions in solution is often limited by its lack of integration. The electrochemical transduction of... 

The purpose of this chapter is to summarize the principles of electrochemical sensors, with focus on the transduction mechanism. The most common form of electrochemical sensor, the enzyme electrode, will be used below for illustrating the principles of electrochemical transduction. Here, the biocatalytic recognition of the substrate, by an immobilized enzyme layer, is followed by electrochemical measurement of the product or depleted cofactor (figure 5.2). The choice of the appropriate electrochemical transducer is governed by the nature of the substrate, the desired analytical performance, and the shape and size of the device. 

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. 

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