Streptavidin- and SuperAvidin?-coated polymer beads are used in immunology, nucleic acid, and cell separation or visualization workflows. Streptavidin is a tetrameric protein with a net negative charge at neutral pH that reduces nonspecific binding of unbiotinylated proteins. SuperAvidin? is a proprietary version that has a higher binding affinity for biotinylated ligands and lower nonspecific binding than streptavidin.