Biosensors determining particular analyte

Biosensors are the analytical systems, which contain sensitive biological elements and detectors. Plant cells as a possible biosensors have natural structure that determinates their high activity and stability. Criteria in the screening of the plant cells as biosensors for allelopathy should be as under (i) Reaction is fast based on the time of response, (ii) Reaction is sensitive to small doses of analysed compounds or their mixtures and (iii) Methods of detection viz., biochemical, histochemical, biophysical (in particular, spectral changes in absorbance or fluorescence) are easy in laboratory and in the field conditions. The search of biosensors in active plant species is suitable to determine the mechanisms of action of biologically active substances or external factors of the environment (Roshchina and Roshchina, 2003 Roshchina, 2004 2005 c)). 

However, it should be mentioned that there is a flexible hand-held electrochemical instrument on the market, which can be programmed to be used in a variety of voltammetric/amperometric modes in the field [209]. Although the majority of biosensor applications described in this review were for single analyte detection, it is very likely that future directions will involve development of biosensor arrays for multi-analyte determinations. One example of this approach has been described in an earlier section, where five OPs could be monitored with an array of biosensors based on mutant forms of AChE from D. melanogaster [187]. This array has considerable potential for monitoring the quality of food, such as wheat and fruit. Developments and applications of biosensors in the area of food analysis are expected to grow as consumer demand for improved quality and safety increases. Another area where biosensor developments are likely to increase significantly is in the field of environmental analysis, particularly with respect to the defence of public... 

Proteins are present at various concentrations in samples from very different origins and the determination of their concentration is of particular interest. Biosensors offer an alternative to the classical analytical methods due to their inherent specificity, simplicity, relative low cost and rapid response. 

Interferences are of particular importance for devices destined for continuous use in very complex matrices. Biosensors are tested for interferences not just from species that are expected to bind to or react with the particular chemical recognition agent employed the end use of the biosensor is considered, and components of that sample matrix are examined for potential interference. Test assays are conducted in the sample matrix, and compared with results obtained in simple buffers in order to determine analyte recovery. 

Enantiospecificity occurs when the analytical method can determine only one of the enantiomers. In this regard, biosensors that used l or d type enzymes, e.g., L-amino acid oxidase or (l-AAOD, D-amino acid oxidase or d-AAOD), can be considered enantiospecific for classes of l or d enantiomers because the enzyme will be able to catalyze the reaction of only one particular enantiomer. 

We believe that data mining techniques will find utility in the future in determining accurate outputs from complex piezoelectric sensors yet to be developed. In the future, ever more complex biosensors and chemical sensors will be created on piezoelectric platforms. The accurate analyses of complex multidimensional inputs from such sensors may critically depend upon the use of machine learning algorithms. Such algorithms will learn to identify characteristic non-linear features of the inputs and associate them accurately with particular outputs (classification activity), such as an analyte concentration, that are then reported to the end-user. 

Various analytical methods now employ amperometric measurements as part of their procedures. In particular, amperometric titrations have been widely used for the analysis of various substances in samples ranging from water to radioactive materials. Also, amperometric sensors, such as the dissolved oxygen probe and various amperometric biosensors, are widely used for clinical, environmental, and industrial monitoring. Furthermore, amperometric detectors have gained considerable use since the 1970s in high-performance liquid chromatographic determination of various substances and in flow injection analysis. 

The electrodes determine mainly the output of the electroenzymatic process. In contrast, the analytical selectivity is determined by the specificity of the signal-producing interaction of the enzyme with the analyte. Moreover, the properties of the enzyme, such as its specific activity, influence the dynamic range, and the sensitivity of biosensors. In this respect, account has to he taken of the fact that enzymatic processes are susceptible to deviations from their optimal environmental conditions in particular, their thermal and chemical stabUity is limited. These peculiarities decisively determine the limits of apphcabUity of enzymes. 

The determination of pesticides has become increasingly important in recent years because of the widespread use of these compounds, which is due to their large range of biological activity and a relatively low persistence. The development of biosensors for pesticides is the subject of considerable interest, particularly in the areas of food and environmental monitoring. Several enzymes such as cholinesterase enzymes (AChE, BChE) and urease have been used in the design of direct electrochemical biosensors for the detection of pesticides (Larsen et al., 2007). Analytical devices based on the inhibition of cholinesterase have been widely used for the detection of organic phosphate compounds and carbamate pesticides. 

The sensitivity, s, of a biosensor is defined by the ratio s = Aa/Am, around the measured value, and determines the suitability of the sensor for use in a particular application. It is possible that m is not the actual quantity to be measured, but simply a function of that quantity. This is the case for potentiometric biosensors in which the amplitude of the signal is proportional to the logarithm of the analyte concentration, according to the Nemst Law ... 

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