Thiol functionalized methoxyl polyethylene glycol, PEG thiol (mPEG-SH) is a monofunctional PEG derivative that can be used to modify proteins, peptides and other materials. Thiol groups also have high affinity to gold surface and are widely used for gold nanoparticles or gold film modification. PEGylation can increase solubility and stability and reduce immunogenicity of peptides and proteins. It can also suppress the non-specific binding of charged molecules to the modified surfaces.