Reverse capture target assays

Fig. 8.5. Reverse capture assays allow an improvement of detectability by a decrease in background staining. Two oligomers (labeled and polyadenylated) are hybridized with the target (I, II) and captured with paramagnetic beads (PMB) covered with oligo-dT hairs (III). Nonspecifically adsorbed oligomers are usually tighter bound than hybrids to dT-hairs, allowing a selective desorption of specific hybrids (IV). These can be recaptured (V), followed by the determination of the amount of label bound.

Assays based on sandwich-hybridization are available in several platforms, such as sequential injection analysis (55), microtiter plate assays (61), and microfluidic devices (62). The LFA biosensor assays described in this chapter rely on the sandwich-hybridization of a nucleic acid sequence based amplified (NASBA) RNA target between a membrane immobilized capture probe and SRB-encapsulating liposome conjugated reporter probe. NASBA uses the enzymes avian myeloblastosis virus reverse transcriptase (AMV-RT), RNaseH, and T7 DNA dependent RNA polymerase in the presence of deoxyribonucleoside triphosphates and appropriate primers to amplify relatively few copies of target RNA into... 

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