Strep-Tactin® conjugated with horseradish peroxidase (HRP) for fast and targeted detection of Strep-tag®II or Twin-Strep-tag® fusion proteins. Target proteins can be transferred to a blotting membrane or captured on a microplate prior to chromogenic or chemiluminescence detection using Strep-Tactin® HRP. Depending on the host organism, protein extracts may contain small amounts of biotinylated proteins. Biotin Blocking Buffer is recommended for blocking such biotinylated proteins on western blots prior to detection to prevent false positive bands. Biotin Blocking Buffer contains the tetrameric biotin binding protein avidin, which also selectively binds biotinylated proteins.