TS biotin ethylenediamine (Biotin ethylenediamine thiosulfate, sodium salt) is a highly selective thiol labeling probe. Similar to the MTS group, TS (thiosulfate) group is capable of reacting with thiols at nearly neutral pH. However, unlike the MTS group , which is neutral, TS is negatively charged and thus probes bearing a TS group are ideal for specifically labeling thiols exposed at the exterior cell surface because charged probes are less likely to enter cells.  It's available in 3 variations: Biotin, Biotin-X, and Biotin-XX. The X and XX spacer should facilitate the interaction between biotin and avidin or streptavidin.  TS Biotin-X ethylenediamine   Biotin-X ethylenediamine thiosulfate, sodium salt  C20H34N5NaO7S3  MW: 575.7  Off-white solid soluble in DMSO or water  Store desiccated at -20°C