(+)-Biotin-PEG2-NHS Ester is a heterobifunctional crosslinking reagent. Its molecular structure consists of a biotin moiety, a polyethylene glycol (PEG) spacer of two units, and an N-hydroxysuccinimide (NHS) ester reactive group. The PEG linker provides hydrophilicity and reduces steric hindrance, while the NHS ester reacts efficiently with primary amines (e.g., on lysine residues of proteins or amine-modified surfaces) to form stable amide bonds. This compound is primarily used in life science research for biotinylation. The biotin tag enables strong, specific binding to streptavidin or avidin, facilitating applications such as protein purification, pull-down assays, Western blot detection, ELISA, and immunofluorescence imaging. The PEG2 spacer enhances solubility and accessibility. Furthermore, derivatives with similar biotin-PEG-NHS architectures are utilized in the development of advanced therapeutic modalities, including antibody-drug conjugates (ADCs) and proteolysis-targeting chimeras (PROTACs), where they serve as functional components of the linker-payload construct. It is sensitive to moisture and should be stored desiccated at low temperatures. Handling requires standard precautions for organic reagents, particularly avoiding inhalation and contact with skin or eyes.