Used in bioconjugation for linking molecules in drug development and bioanalytical research. Its NHS ester reacts efficiently with primary amines on proteins, peptides, or amine-modified biomolecules, forming stable amide bonds. The PEG2 spacer improves solubility and reduces steric hindrance, enhancing reaction efficiency and target accessibility. Commonly applied in preparing antibody-drug conjugates (ADCs), labeling biomolecules with fluorophores or biotin, and surface immobilization in biosensors or microarrays. The Ald--Ph group allows orthogonal conjugation via aldehyde-reactive chemistry, enabling site-specific modifications in complex biological systems.