Used in bioconjugation for crosslinking proteins and labeling biomolecules. It reacts selectively with thiol groups (cysteine residues) in proteins to form stable thioether bonds, making it ideal for preparing protein-protein conjugates or attaching fluorescent dyes, biotin, or other probes. Commonly used in preparing immunoassays, enzyme labeling, and immobilizing biomolecules on surfaces. Its iodoacetyl group ensures high reactivity and specificity toward sulfhydryls, while the sulfo-NHS ester enables water solubility and efficient coupling to primary amines under mild conditions. Suitable for applications requiring controlled, site-specific modifications in aqueous buffers at near-neutral pH.