Learn how to use this product Strep-Tactin® is available conjugated to alkaline phosphatase (AP) for the specific detection of Strep-tag® and Twin-Strep-tag® fusion proteins. The proteins can be captured on a membrane or microplate. After the application of Strep-Tactin® AP, they can be visualized in a chromogenic reaction. Strep-Tactin® AP cross-reacts with biotin and biotinylated proteins (the biotin carboxyl carrier protein in E. coli), and to prevent the detection of false positives, 2.5 mg/ml avidin for biotin masking should be used.