Detection by Fluorescence Polarization FP

The steady-state polarization of (Re-L) -HSA was sensitive to the binding of anti-FI S A, resulting in a significant increase in luminescence polarization. Consequently (Re-L) -HSA can be used as a tracer in a competitive immunoassay with unlabeled HSA acting as an antigen (Fig. 8.18). 

The sensitivity of the assay is in the 100 nM range. Use of this organometalhc rhenium tracer has made it possible to extend the range of use of the hapten assay technique in which it is widely employed to include high molecrdar weight analytes (10 to 10 D). 

Use of Oiganometallic Complexes as Substrates or Co-substrates for Enzyme Immunoassay 

In the mid 1970s, immunoassay sensitivity was greatly increased with the arrival of the enzymo immunoassay (EIA) [21-24]. In this type of assay, an enzyme attached to the detection antibody (cf Fig. 8.2B) or to the analyte allows amplification of the signal. These types of assay are currently the most widespread. Derivatives of ferrocene have been used in this type of assay, several of which are discussed below. This is in fact an extension of the term MIA. In fact, the organo-metaUic complex as used here is not the tracer but the substrate or co-substrate (redox mediator) of an enzyme. 

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