Bis-PEG5-NHS ester is widely used in bioconjugation for linking biomolecules such as proteins, peptides, and antibodies. Its primary application lies in crosslinking amine-containing molecules due to the reactivity of the NHS ester groups with primary amines, forming stable amide bonds. The PEG5 spacer provides water solubility and increases the distance between linked molecules, reducing steric hindrance and improving bioactivity. This makes it ideal for creating protein-protein or protein-label conjugates in immunoassays, diagnostic probes, and drug delivery systems. It is also used in surface functionalization of nanoparticles and biosensors, where controlled spacing and orientation of biomolecules are critical. The hydrophilic PEG linker helps minimize non-specific binding and enhances stability in biological environments.