Mal-amido-PEG1-C2-NHS ester is a noncleavable antibody-drug conjugate (ADC) linker that incorporates a maleimide functional group and an N-hydroxysuccinimide (NHS) ester. The NHS ester offers a means to specifically modify primary amines (-NH2) present in proteins, amine-modified oligonucleotides, and other amine-containing molecules[1][2].