Propargyl-PEG5-NHS Ester is widely used in bioconjugation and chemical biology for labeling and modifying biomolecules. Its NHS ester group reacts efficiently with primary amines, enabling the attachment of the PEG linker to proteins, peptides, or antibodies. The terminal propargyl group allows for further functionalization via click chemistry, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), making it a versatile tool for creating complex molecular architectures. This compound is particularly valuable in drug delivery systems, where it helps improve solubility, stability, and biocompatibility of therapeutic agents. It also plays a role in the development of biosensors and diagnostic tools by facilitating the precise attachment of detection moieties to biomolecules. Additionally, its PEG spacer provides flexibility and reduces steric hindrance, enhancing the performance of conjugated molecules in biological applications.