Enzymatic labeling methods enzyme conjugation

A sandwich immunoassay is another widely used detection scheme and involves the use of two antibodies. The first antibody is immobilized on the fiber and is used to capture the antigen, and the second antibody, which is conjugated to a fluorescent dye or enzyme, is used to generate the signal (Fig. 16c). When an enzyme is used for antibody labeling, the enzymatic conversion of a nonflu-orescent substrate to a fluorescent product is measured. The enzyme-labeling method is more sensitive since the signal is amplified by the enzymatic reaction. 

The ESI-MS is used for simultaneous detection of enzymatic products and chemically identical standards, which are distinguished by the deuterium labeling (Gerbert et al., 1999). The method starts with the design of a synthetic conjugate molecule that contains a target substrate for the desired enzyme. The conjugate molecule... 

The attachment of the ferrocene groups to small molecules has been used in two main classes of biosensor in the first, the conjugate is an enzyme substrate such that a shift in its redox potential occurs following enzymatic modification. An example is ferrocenylethyl phosphate (Figure 9) that facilitates the electrochemical assay of alkaline phosphatase, a common enzyme label for immunoassays. The redox potential of the alcohol product is lower than the phosphate ester and hence by poising the potential, the product can be selectively measured and so the alkaline phosphatase activity measured. The sensitivity of this method was further enhanced by the use of stripping voltammetry to detect the product. ... 

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