OPSS-PEG(8)-COOH is a heterobifunctional PEG linker with an ortho-pyridyl disulfide (OPSS) group for thiol-specific conjugation and a reactive carboxyl (COOH) group for amide bond formation. The OPSS enables attachment to biomolecules like proteins, peptides, or antibodies via disulfide bonds with cysteine residues. Used in bioconjugation and drug delivery systems, its PEG (polyethylene glycol) chain enhances solubility, reduces immunogenicity, and prolongs circulation time in biological systems. Commonly applied in targeted cancer therapies, where it helps deliver drugs selectively to tumor cells while minimizing side effects. Also utilized in diagnostic imaging to improve the stability and efficiency of contrast agents. Its amphiphilic nature makes it suitable for creating micelles or nanoparticles for encapsulating hydrophobic drugs, improving their bioavailability and therapeutic efficacy.