Enhanced Dispersity of Gold Nanoparticles Modified by -Carboxyl Alkanethiols Under the Impact of Poly(ethylene glycol)s

The physisorption of nonionic surfactant poly (ethylene glycol) (PEG) series and the chemisorption of carboxyl-terminated alkanethiols on surface of gold nanoparticles (AuNPs) were investigated. The physical adsorption of oligo (ethylene glycol) moieties introduced a tiny red shift of surface plasmon resonance (SPR) of AuNPs, indicating the formation of a protective layer of PEG molecules around gold surface. The subsequent chemisorption of -carboxyl alkanethiols was performed under the protection of PEG molecules, and the aggregation of metal nanoparticles did not appear by TEM observation. The successful adsorption of -carboxyl alkanethiol on gold surface was demonstrated according to FT-IR spectrum and the prior adsorbed PEG molecules could be washed out by centrifugation. Furthermore, the presence of nonionic surfactant even displayed a protective role in centrifugal process. The dispersity of modified AuNPs with peripheral functional groups was enhanced under the protection of PEG molecules as an important advantage in further biological applications.