Enzymatic biosensors

As often happens for the electrode coatings that are the subject of this monograph, enzymatic biosensors constitute an area in which ICP-modified electrodes have found the highest number of applications and, for this reason, the number of review articles written in this specific field is particularly high [140-145]. Table 2.5 reports a selection made from the very high number of amperometric biosensors found in the literature, aiming to give an idea of the applications proposed. 

Electrodes Samples Type of determination Data processing algorithm Ref. 

aud PPy-modified electrodes includiug different anions Standard solutions Discrimination between soluticms containing chemical species representative of different tastes sweet, bitter, acid, salty, and astringcmt PCA [130] 

PPy-modified electrodes including different anions, bare carbon paste electrode, carbon paste electrodes modified with pbtalocyanine, Au disk electrode Red wines Discrimination of wines possessing altered organoleptic characteristics PLS, PCA [138] 

PPy-modified electrodes doped with differemt counterions carbon paste electrodes modified with metallophtha-locyanine complexes carbon paste electrodes modified with perylene imide derivatives Red wines Discrimination between wine samples aged in oak barrels of different characteristics PCA, SIMCA [131] 

Impedance spectroscopy has been extensively used to follow changes of the interfacial properties of electrodes upon immobilization of enzymes and to characterize biocatalytic processes at enzyme-modified electrodes. Faradaic impedance spectroscopy can be used to study the kinetics of the electron transfer originating from bioelectrocatalytic reactions. It should be noted, that for characterizing redox-active biomolecules by impedance spectroscopy no additional redox probe is added to the electrolyte solution, and the measured electron-transfer process corresponds to the entire bioelectrocatalytic reaction provided by the biocatalyst. Under the condition that the enzyme is not saturated by the substrate, the electron-transfer resistance of the electrode is also controlled by the substrate concentration. Thus, the substrate concentration can be analyzed by the impedance spectroscopy following values [9]. 

Shamsipur et al. prepared a robust and effective catalase (CAT)-nanocomposite film modified-glassy carbon electrode using multiwalled carbon nanotubes (MWCNTs) and a room temperature ionic liquid, l-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), by a layer-by-layer self-assembly method [21]. The ionic liquid assembled 

Another recent example reports a label-free electrochemical impedimetric immunosensor for the sensitive detection of metabolite of furaltadone, 5-morpholino-3-amino-2-oxazolidone (AMOZ), one of the most common nitrofuran antibacterial agents 

Under the optimized conditions, the relative change in impedance was proportional to the logarithmic value of AMOZ concentrations in the range of 1.0 to 1.0 x 10 ng/ml (r = 0.9991) with the detection limit of l.Ong/ml. The impedimetric immunosensor was successfully applied to the determination of AMOZ in animal derived food samples, such as chicken muscle, pork, swine casing, shrimp, egg, and honey, with good agreement with the results obtained by HPLC-MS/MS [24], 

An example of the selective detection of E. coli involved an impedimetric immunosensor developed using SAM-modified gold screen-printed electrodes (SPEs) [27]. In this 

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Electrogenerated chemiluminescence (ECL) has proved to be useful for analytical applications including organic analysis, ECL-based immunosensors, DNA probe assays, and enzymatic biosensors. In the last few years, the electrochemistry and ECL of compound semiconductor nanocrystallites have attracted much attention due to their potential applications in analytical chemistry (ECL sensors). 

M. Trojanowicz, Determination of pesticides using electrochemical enzymatic biosensors. 

M.D. Rubianes and G.A. Rivas, Enzymatic biosensors based on carbon nanotubes paste electrodes. Electroanalysis 17, 73—78 (2005). 

The feasibility of amperometric sucrose and mercury biosensors based on the immobilization of invertase, glucose oxidase, and muta-rotase entrapped in a clay matrix (laponite) was investigated by Mohammadi et al. [31]. In this work, the effect of pH of a tri-enzymatic biosensor in which the optimum pH of the three enzymes is different (Invertase, pH 4.5 Glucose oxidase, pH 5.5 and Mutarotase, pH 7.4) [41] was studied. The pH effect on the biosensor response was analyzed between pH 4 and 8 and the highest activity was found at pH 6.0. In order to improve the selectivity of the invertase toward mercury and to avoid silver interference, a medium exchange technique was carried out. The biosensor was exposed to mercury in an acetate buffer solution at pH 4 while the residual activity was evaluated with phosphate buffer solution at pH 6 [41]. 

M. Albareda-Silvert, A. Merkoci and S. Alegret, Configurations used in the design of screen printed enzymatic biosensors. A review, Sens. Actuators B, 69 (2000) 153-163. 

Enzymatic Biosensors andTheir Biomimetic Analogs Advanced Analytical Appliances... 

As a rule, the combined immobilization of oxidase and peroxidase on the electrode allows the determination of metabolite (S) concentration, even if negligibly small. This type of biosensor is the main one used for detection of any particular compound in blood or other multicomponent system glucose, ethanol, cholesterol, proteins, amino acids, etc. For example, for patients with diabetes a rapid analysis of their blood for glucose concentration is a vitally important procedure. We will not attempt to discuss in full all the existing types of biosensor we will just note that enzymatic and cell biosensors are the most widespread types of these appliances. Enzymatic biosensors are more appropriate to the subject of the current monograph and, therefore, they will be discussed below. 

Biomimetic analogs of existing enzymatic biosensors have been designed with broader functional abilities using inorganic biomimics, which is one of the strategic directions in the branch of super-sensitive analytical systems. The development of model systems is the... 

The utilization of a DNA matrix to aid enzyme immobilization is a promising alternative for the development of new biosensors and its application in flow systems. A DNA-tyrosinase carbon paste electrode [95] showed excellent performance for detection of cathecol in a FIA system and suggests that other enzymatic biosensors can benefit from the presence of DNA. 

In design of biosensors most often used are enzymes from oxidoreductases and hydrolases however, in very broad literature on this subject, applications of many other enzymes can be found. The analytical characteristics of enzymatic biosensor depend on numerous factors. Besides the origin of enzyme (type of natural material, from which the enzyme was isolated), the most significant is a mode of immobilization. It affects significantly kinetics of enzyme and diffusional limitations of the immobilization matrix. Although there is a general belief that enzymes should be immobilized in a hydrophilic environment, a successful immobilization of enzyme in carbon paste with silicon oil105 initiated development of numerous biosensors with enzyme... 

More recently, other types of enzymatic biosensors have developed based on thermistor or opto-electronic sensors. Pogacnik and Franko (2003) presented a photother-mal biosensor for the determination of low concentrations of organophosphate and carbamates pesticides in vegetables without sample treatment. 

D., (1995) Validation of an enzymatic biosensor with various liquid chromatographic techniques for determining organophosphorus pesticides and carbaryl in freeze-dried waters. Anal. Chim. Acta, 311, 265-271... 

Miscoria, SA., Barrera, G. D., and Rivas, G. A. (2005) Enzymatic biosensor based on carbon paste electrodes modified with gold nanoparticles and polyphenol oxidase. Electroanalysis 17, 1578-1582... 

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