This bifunctional crosslinker, Mal-amido-PEG5-C2-NHS ester, is widely used in bioconjugation processes for linking biomolecules such as proteins, peptides, or antibodies to other molecules or surfaces. The maleimide group selectively reacts with sulfhydryl (-SH) groups on cysteines to form stable thioether bonds, while the NHS ester group efficiently reacts with primary amines to form stable amide bonds. The PEG5 spacer enhances water solubility, reduces steric hindrance, and provides flexibility, improving conjugation efficiency. The C2 alkyl chain adds precise spacing between functional groups. It is commonly applied in drug delivery systems to attach therapeutic agents to targeting molecules, as well as in the development of diagnostic assays, biosensors, and bioconjugate-based therapeutics, where precise and stable molecular linkages are essential. The water-soluble PEG chain helps maintain the stability and functionality of conjugated biomolecules in aqueous environments.