Strep-Tactin®XT is a streptavidin variant, which binds to the Strep-tag®II and Twin-Strep-tag® with high affinity and specificity. It is available as conjugate with DY-649 for fast and directed detection of N-terminally, C-terminally as well as internally tagged Strep-tag®II or Twin-Strep-tag® fusion proteins in applications like ELISA, FACS, immunohistochemistry, and immunocytochemistry. The absorption/emission maxima for DY-649 are 655/676 nm