Abstract
Suitable immobilization of a biorecognition element, such as an antigen or antibody, on a transducer surface is essential for development of sensitive and analytically reliable immunosensors. In this review, we report on (1) methods of antibody prefunctionalization using electroactive probes, (2) methods for immobilization of such conjugates on the surfaces of electrodes in electrochemical immunosensor construction and (3) the use of antibody-electroactive probe conjugates as bioreceptors and sensor signal generators. We focus on different strategies of antibody functionalization using the redox active probes ferrocene (Fc), anthraquinone (AQ), thionine (Thi), cobalt(III) bipyridine (Co(bpy)33+), Ru(bpy)32+ and horseradish peroxidase (HRP). In addition, new possibilities for antibody functionalization based on bioconjugation techniques are presented. We discuss strategies of specific, quantitative antigen detection based on (i) a sandwich format and (ii) a direct signal generation scheme. Further, the integration of different nanomaterials in the construction of these immunosensors is presented. Lastly, we report the use of a redox probe strategy in multiplexed analyte detection.
Highlights
Electrochemical immunosensors are a type of integrated devices that provide selective quantitative or semi-quantitative analytical information using biorecognition phenomenon between an antibody (Ab) and antigen (Ag) with an electrochemical transducer [1]
The interactions between Ab and Ag can be observed using different labels, such as radioactive, chemiluminescent and fluorophore compounds. Enzymes are another group of labels, including horseradish peroxidase (HRP), alkaline phosphatase (ALP), laccase and glucose oxidase (GOx), which need some substrates added to the testing solution, such as hydroquinone, catechol, o-aminophenol, naphthyl phosphate, p-aminophenol phosphate, ferrocene and glucose [3]
We suggest application of Antibody drug conjugates (ADCs) technology based on the reduction of molecules, as for example ferrocene or other compounds
Summary
Electrochemical immunosensors are a type of integrated devices that provide selective quantitative or semi-quantitative analytical information using biorecognition phenomenon between an antibody (Ab) and antigen (Ag) with an electrochemical transducer [1]. In the past few years, the enzyme-linked immunosorbent assay (ELISA) used for specific detection of different analytes has become very popular and commonly used in laboratory practice This method, depending on the format of the assay (i.e., direct, sandwich or competitive) could be useful for the detection of both antigens and antibodies. The possible solution for increasing the sensitivity of immunosensors based on electroactive labels as compared with immunosensors based on enzyme labels is increasing the number of redox active molecules attached to antibodies. This issue will be more deeply discussed . A sandwich-type-format immunosensor consists of an unlabelled primary capture antibody and an electrochemically-detectable, redox-active label-conjugated signalling secondary antibody (Figure 1A). The other label worth mentioning is tris(bipyridine)ruthenium(II) [Ru(bpy)3 ]2+ , which combines the possibilities of electrochemical detection with electrochemiluminescence (ECL) [16,17]
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