Abstract
The streptavidin-based enrichment of biotin-tagged molecules is a common methodology that is routinely used across multiple disciplines in biomedical research. Numerous and varied formats of immobilized streptavidin and related proteins are available, but predicting which product is most apt for a given application is complicated by the fact that there are numerous technical considerations and no universal reporting standards for describing the binding capacity of the beads. Here, we define criteria that should be considered when performing a fit-for-purpose evaluation of streptavidin beads. We also describe a colorimetric competitive displacement assay, the streptAVIdin binDing capacITY (AVIDITY) assay, a fast, easy, and inexpensive absorbance-based method to measure the binding capacity of streptavidin beads, which can be used to compare different products and evaluate variation among many of the same product. We expect that the fit-for-purpose criteria and the AVIDITY assay will benefit users across disciplines to make informed decisions regarding the most apt streptavidin bead products for their own experiments.