Electrochemical biosensors biorecognition elements

Electrochemical DNA biosensors are based on the use of nucleic acids or analogues as biorecognition element and electrochemical techniques for the transduction of the physical chemical signal. Two aspects are essential in the development of hybridization biosensors, sensitivity and selectivity. Traditional methods for detecting the hybridization event are too slow and require special preparation. Therefore, there is an enormous interest in developing new hybridization biosensors, and the electrochemical represent a very good alternative [108]. 

As has been already discussed, the biological recognition element is the selective part in biosensors however, the overall function of the biosensor is determined by the proper combination of the biological recognition element with the transducer, with respect to the signal-transduction process. Thus, after the discussion of the nature, the properties, and the apphcabUity of different biological compounds, suitable combinations of biorecognition elements with electrochemical transducers are described in Sect. 2.11.1.4. 

To the best of our knowledge, the ideal reagent-free electrochemical immunosen-sor for on-the-spot analysis has yet to be developed. Systems reported in the literature as electrochemical immunosensors, some of which are listed and denoted by I under assay type in Table 2, are based primarily on one factor the immobilization of the sensing Ab or Ag directly on the electrode [124, 125]. The schematic of an electrochemical immunosensor, thus defined, is shown in Fig. 6. It should be noted that electrochemical immunosensors are often categorized as electrochemical biosensors, which covers any type of electrochemical sensor consisting of a biorecognition element placed directly over or in close proximity to the electrode [126]. 

Materials used in electrochemical biosensors can greatly benefit from nanotechnology. Nanomaterials are especially used to immobilize the recognition elements and improve the transport of the electrical signal from the biorecognition element to the electrode surface (the transducer). A weak immobilization protocol affects the biosensor stability during use and storage and prejudices the overall functionality of the biosensor [85-89]. 

Traditionally, antibodies have been the main biorecognition elements used. Antibodies have been applied in various biosensor platforms including electrochemical, fluores-cent, o and colorimetric assays. Antibodies provide varying stringency of interactions depending on whether they are monoclonal or polyclonal. Monoclonal antibodies... 

Enzymes have been widely used as biorecognition elements in biosensors as they are able to catalyze reactions that produce electrochemical, optical, and thermal sig-nals." " Most popularly, glucose oxidase is widely used in electrochemical glucose biosensors that have found wide usage in clinical and medical settings. Enzymes offer ease of immobilization on transducers by physical adsorption, covalent linkage, and... 

Among the biological recognition elements enzymes are by far the most important. The reason for this lies in the fact that these molecules provide not only the recognition of analyte-substrate, but also have the catalytic function important for the amplification of the signal. Enzymes are quite flexible molecules and have various complex conformations with sometimes different catalytic activity. The biorecognition molecules can be integrated in biosensors with a variety of electrochemical transducers (Table 1). 

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