Bis-PEG4-acid is widely used as a linker in bioconjugation and drug delivery systems. Its PEG (polyethylene glycol) spacer provides excellent solubility and reduces immunogenicity, making it ideal for attaching therapeutic molecules like antibodies, peptides, or small molecules to nanoparticles or other carriers. The terminal carboxylic acid groups enable easy functionalization through amide bond formation, facilitating the creation of stable conjugates. In proteomics, it serves as a crosslinker for protein-protein interactions or protein immobilization on surfaces. Additionally, it is employed in the development of hydrogels and biomaterials, where its hydrophilic properties enhance biocompatibility and stability.