Used in bioconjugation processes to link molecules such as peptides, proteins, or dyes to other compounds through amine-reactive chemistry. The aldehyde group (Ald) enables selective reactions with aminooxy or hydrazide groups, forming stable oxime or hydrazone bonds under mild conditions. The PEG3 spacer improves solubility and reduces aggregation, while the pentafluorophenyl (Pfp) ester at the terminal end reacts efficiently with primary amines to form stable amide bonds. Commonly applied in the development of antibody-drug conjugates (ADCs), fluorescent probes, and targeted therapeutics where controlled, site-specific coupling is required. Its bifunctional design allows sequential conjugation steps, making it valuable in multi-step labeling and crosslinking strategies.