BS3 (Sulfo-DSS) is a homobifunctional amine-specific crosslinking reagent based on NHS-ester reactive groups for selective conjugation of primary amines.

BS3 contains two sulfo-NHS ester groups at both ends of a 8-carbon spacer.

The sulfo moieties provide excellent water solubility and allows BS3 to be used in acqueous buffer solutions without the need of organic solvents that may cause protein perturbation.