Propargyl-PEG9-acid is widely used in bioconjugation and click chemistry applications due to its terminal alkyne group, which enables efficient and selective reactions with azide-functionalized molecules. It serves as a linker or spacer in the development of drug delivery systems, allowing for the attachment of therapeutic agents to targeting moieties or nanoparticles. The PEG (polyethylene glycol) chain enhances solubility, reduces immunogenicity, and improves the pharmacokinetics of conjugated molecules. This compound is also utilized in the synthesis of biosensors, where it facilitates the immobilization of biomolecules onto surfaces for detection purposes. Additionally, it plays a role in the preparation of hydrogels and other biomaterials for tissue engineering and regenerative medicine. Its versatility makes it a valuable tool in biotechnology and pharmaceutical research.