SeTau-660-NHS (K9-4159) is our latest addition to our squaraine rotaxane dyes, which is extremely bright (Φ. ε = 120,000) compared to Alexa 660 (Φ. ε = 48,800) or Alexa 680 (Φ. ε = 68,800) and with one of the longest fluorescence lifetimes (3.3 ns) of NIR reporters!