PEG linkers have been widely used in drug discovery, ADC development, bioconjugation and labeling, nanoparticle drug delivery, and polyethylene glycol. PEG linkers are chemically functionalized polyethylene glycol linkers. Due to their water solubility and non-immunogenicity, PEG linkers are particularly attractive as very powerful tools in the scientific community for conjugation, drug discovery, nanoparticle drug delivery, chemical biology, and biomarkers. There are two classes of PEG, monodisperse and polydisperse. Monodisperse PEG linkers have precise numbers of PEG units with specific chemical structures and precise molecular weights. Whereas polydisperse PEG is a polymer with an average molecular weight.