DBCO-PEG2-NHS ester is a click chemistry reagent featuring an azide group and an NHS ester, designed for copper-free Click Chemistry. It specifically and efficiently reacts with primary amines (e.g., lysine residue side chains or aminosilane-coated surfaces) under neutral or slightly basic conditions to form stable covalent bonds. The inclusion of a hydrophilic PEG spacer enhances water solubility and provides a flexible linkage, reducing steric hindrance during ligation. This compound, intended for research use only [1], is ideal for applications requiring precise and efficient bioconjugation.