Mal-PEG2-acid is widely used in bioconjugation and drug delivery systems. Its primary application involves linking molecules, such as proteins, peptides, or drugs, to other entities like nanoparticles or targeting ligands. The maleimide group in Mal-PEG2-acid reacts specifically with thiol groups, enabling stable covalent bonds with cysteine residues in proteins or other thiol-containing molecules. This property makes it valuable in antibody-drug conjugates (ADCs), where it helps attach cytotoxic drugs to antibodies for targeted cancer therapy. Additionally, it is utilized in modifying biomolecules to enhance their solubility, stability, or bioavailability. Its PEG spacer also reduces immunogenicity and improves pharmacokinetics, making it a key component in therapeutic and diagnostic applications.