Amino-PEG3-acid (CAS No. 784105-33-5) is a carboxylic acid derivative containing a triethylene glycol (PEG3) spacer arm, with the structure H₂N-(CH₂CH₂O)₃-CH₂COOH and a molecular weight of 237.25. It is produced through chemical synthesis, starting from ethylene glycol, with amino and carboxyl groups introduced via multi-step polymerization. Strict control of reaction conditions is required to ensure monodispersity. This product enhances solubility through its hydrophilic PEG chain. The amino group can react with NHS esters, carboxylic acids, etc., while the carboxyl group can couple with antibodies or drugs. It is widely used in the synthesis of antibody-drug conjugates (ADCs), construction of PROTAC molecules, and biomolecular labeling, serving as an important linker in the biopharmaceutical field.