The amine-reactive biotin-PEG3, SE is a pegylated, water-soluble reagent for simple and efficient biotin labeling of antibodies, proteins and other primary amine-containing macromolecules?for subsequent detection with streptavidin, avidin or NeutrAvidin? biotin-binding protein. This molecule has a?PEG3 spacer to improve water soluibility and?facilitate reactivity with the molecule and eventual accessibility of the biotin to avidin or streptavidin.