Biotin-PE-maleimide (N-Biotinyl-N'-[2-(N-maleimido)ethyl]piperazine) is a bulky, membrane-impermeable, sulfhydryl-containing reagent with a relatively large molecular size. Biotin-PE-maleimide can be used for biotin labeling (such as thiol groups) and detection of proteins or other biomolecules.