Labeled electroactive

Radioactive tracer techniques. In electrochemistry, the procedure is essentially the same as in studies of chemical reactions the electroactive substance or medium (solvent, electrolyte) is labelled, the product of the electrode reaction is isolated and its activity is determined, indicating which part of the electroactive substance was incorporated into a given product or which other component of the electrolysed system participated in product formation. Measurement of the exchange current at an amalgam electrode by means of a labelled metal in the amalgam (see page 262) is based on a similar principle. 

In amperometry, the current produced by the oxidation or reduction of an electroactive analyte species at an electrode surface is monitored under controlled potential conditions. The magnitude of the current is then related to the quantity of analyte present. However, as both antibody and antigen are not intrinsically electroactive, a suitable label must be introduced to the immunocomplex to promote an electrochemical reaction at the immunosensors. In this respect, enzyme labels including the... 

M. Akram, M.C. Stuart, and D.K.Y. Wong, Signal generation at an electrochemical immunosensor via the direct oxidation of an electroactive label. Electroanalysis 18, 237-246 (2006). 

J. Wang, G. Liu, and Y. Lin, Bioassay label based on electroactive silica beads. Small 2, 1134-1138... 

Chemical reaction steps Even if the overall electrochemical reaction involves a molecular species (O2). it must first be converted to some electroactive intermediate form via one or more processes. Although these processes are ultimately driven by depletion or surplus of intermediates relative to equilibrium, the rate at which these processes occur is independent of the current except in the limit of steady state. We therefore label these processes as chemical processes in the sense that they are driven by chemical potential driving forces. In the case of Pt, these steps include dissociative adsorption of O2 onto the gas-exposed Pt surface and surface diffusion of the resulting adsorbates to the Pt/YSZ interface (where formal reduction occurs via electrochemical-kinetic processes occurring at a rate proportional to the current). 

The amperometric immunosensors reported so far rely on various methodological principles including use of a Clark electrode for detecting oxygen formation or depletion, an electrochemically active product yielded in an enzyme reaction or an antigen labelled with an electroactive species. 

Titration of electroactive substance A with another electroactive substance B was carried out at the potential at which both A and B are reducible at cathode. The current vs volume of titrant B curve and label the diagram accordingly sketched ... 

Heyrovsky etal. [114] have shown that voltammetric behavior of isomeric end-labeled-SH deoxyoligonucleotides on HMDE depends on the dislocation of the electroactive components along the strand, as well as on their adsorptivity compared to the adsorptivity of other parts of the molecule. 

The amperometric transduction of an immunoreaction consists in the post-labeling of the detected target by an enzyme able to catalyze the production or the consumption of electroactive species. The electrochemical oxidation or reduction of the latter at a constant potential applied to the immunosensor provides thus a current, whose intensity is proportional to the amount of immobilized target. 

Most electrochemical immunosensors use antibodies or antigens labelled with an enzyme that generates an electroactive product which can be detected at the electrochemical transducer surface. The combination of high enzyme activity and selectivity with the sensitive methods of electrochemical detection provides a basis for the development of immunosensors. Horse radish peroxidase (HRP) and alkaline phosphatase (AP) are popular enzyme labels and can be used with a variety of substrates. 

Electrochemical immunosensors based on screen-printed electrodes have recently been applied to the detection of environmental pollutants such as PCBs, PAHs, pesticides [17-20] and of important molecules in clinical and food field [21-23]. In this case, the screen-printed electrodes are both the solid-phase for the immunoassay and the electrochemical transducers antibody or antigen molecules are directly immobilised at the sensor surface (transducer) and one of these species is enzyme-labelled in order to generate an electroactive product which can be detected at the screen-printed electrode surface. 

Other methods of detection of hybridisation event consist of the use of labels. These labels can be divided into electroactive and enzymatic labels. The schemes commonly used for detection are scheme b or c. The scheme selected to detect the hybridisation event depends on whether the target is labelled with a marker by PCR amplification or using a labelling kit, or whether a labelled synthetic detector oligonucleotide is used. These methods are usually the most sensitive, but the need of a labelling step makes them more complex, tedious and... 

Different immunoassays have been developed in CE microchips for detecting immunoglobulins, such as mouse IgG. Enzymatic (alkaline phosphatase) [39] or electroactive (ferrocene) [38] labelled anti-mouse... 

The formation of double-stranded DNA upon hybridisation is commonly detected in connection with the use of an appropriate electroactive hybridisation intercalator or labelling DNA by a simple electroactive molecule or an adequate NP. 

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