Assay formats homogeneous

Immunoassays can be classified according to different criteria. The particular type selected has a strong influence on the assay performance with regard to precision and sensitivity. The main criteria include [3, 22, 23] (1) labeled or unlabeled assay formats, with different type of labels (2) competitive or non-competitive immunoassays, and (3) homogeneous or heterogeneous immunoassays. These classifications can also be extended to MIP-ILAs (Fig. 2) ... 

Enzyme assay methods for screening have been augmented by new screening technologies that allow homogeneous assay formats. Scintillation proximity... 

Homogeneous immunoassay using FRET is an attractive assay format, since the antigen-antibody binding reaction is much accelerated compared to that of solid phase sandwich im-... 

Fluorescence-based readouts build by far the most important basis of protease assays for HTS and compound profiling in the drug discovery industry today. These assay formats became increasingly popular in the 1990s (Burbaum and Sigal, 1997 Silverman et al., 1998). The basics of fluorescence are very well described in detail by Lakowicz (2006). This discussion will be restricted to biochemical protease assays in homogeneous formats based on fluorescence readouts that are suitable for HTS and automated compound profiling. 

In principle, intensity measurement is no different from the well-based immunoblot or other homogeneous well-based assay format such as an in-cell Western. However, because individual nuclei are identified and used as the mask, precise normalization to cell number can be achieved. In addition, microscopy with high quality cameras offers much higher signal-to-noise ratios, thus making many more assays possible. Finally, if a threshold can be set and cells classified as responders or non-responders, an intensity-based assay can be turned into a cytometry assay. 

Assay format Solid phase (chip-based) Homogeneous Homogeneous Homogeneous (bead-based)... 

The mentioned assays led to atrazine residue recoveries between 25 and 1000%, which is a variation that might be due to the high complexity of the sample matrix and the non-homogeneity of the standards used [77]. Improved characteristics were obtained after a better characterization of the used standards [78]. A further improvement was achieved by replacing the anti-humic acid antibodies, used for capturing the analjde, with basic proteins [79,80]. These are easily available and have the advantage that a broader variety of humic acids can be bound therefore, the assay should be independent of the composition of a particular soil. The use of this assay format improved both the sensitivity and signal intensity. 

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