HO-PEG8-CH2COOH is a polyethylene glycol (PEG)-based linker commonly used in biomedical research and pharmaceutical development. It serves as a hydrophilic spacer to conjugate therapeutic agents, biomolecules, or nanoparticles, enhancing solubility, biocompatibility, and circulation time in vivo. The carboxylic acid terminus enables amide bond formation with amine groups, facilitating the PEGylation of proteins, antibodies, or drugs to reduce immunogenicity and improve targeted delivery. Applications include the design of drug delivery systems, surface modification for imaging probes, and synthesis of conjugates for cancer therapy and diagnostics.