S1420 Streptavidin Magnetic Beads are based on a 1 um carboxylate modified bead, they have very high binding capacity and low non-specific binding for proteins. S1421 Hydrophilic Streptavidin Magnetic Beads are based on a 2-3 um bead and gave lower binding capacity than S1420. S1421 has low non-specific binding for nucleic acid and are recommended for nucleic acid isolation applications.