Used in bioconjugation for site-specific labeling of cysteine residues in proteins and peptides. The iodoacetate group reacts selectively with thiol groups, forming a stable thioether bond, while the NHS ester enables coupling to primary amines. Commonly applied in preparing fluorescent or biotinylated probes for imaging, detection, and pull-down assays. Also utilized in crosslinking studies and targeted drug delivery systems where precise attachment to sulfhydryl groups is required. Stable under physiological conditions, making it suitable for labeling biomolecules in mild buffers.