There are currently two established ways to attach a DNA-label to the detection antibody. One is through streptavidin-biotin linkage and the other by covalent coupling using a heterobifunctional cross-linking agent. The strep-tavidin-biotin link is usually assembled stepwise by incubating one component at a time during the assay. This is rather straight forward but requires additional incubation and washing steps, which increase technical variation. The covalent antibody/DNA conjugate is prepared in advance and purified. This reduces the number of reaction components, making the assay easier to optimize.
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