These labels with long lifetime in the range between 32 and 9 ns are excitable in the UV or blue region and are useful as polarization probes for the measurement of high MW analytes (small proteins) or for lifetime-based applications. They exhibit long lifetimes that are not environment sensitive.

SeTau-425-NHS for example was used to measure high-molecular-weight analytes such as BSA directly in an FP assay (more under Fluorescence Polarization). Importantly the FLT of these labels does not change upon covalent attachment to proteins or other analytes. For more information we refer you to Lifetime Applications.