Used in bioconjugation to link molecules, especially in drug delivery systems and protein modification. The SH group reacts selectively with maleimides or gold surfaces, enabling attachment to proteins, peptides, or nanoparticles. The PEG-OH chain improves solubility, reduces immunogenicity, and extends circulation time of conjugated drugs. Commonly applied in developing targeted therapies, diagnostic probes, and surface coatings for biomedical devices. Also used in creating hydrogels and functionalizing materials for biosensors and lab-on-a-chip systems.