Influence of different cleaning processes on the surface chemistry of gold nanoparticles

In this paper we have investigated the effects of different cleaning methods (centrifugation and dialysis) on the surface chemistry and composition of 15 nm citrate stabilized gold nanoparticles (AuNPs). The Nuclear Magnetic Resonance (NMR) results indicates that three centrifugation cycles are sufficient to remove most of the citrate molecules, whilst CLS and DLS data reveal some nanoparticles aggregation when three centrifugation cycles are exceeded. Regarding the dialysis procedure, NMR analysis demonstrated that after nine cleaning cycles the citrate concentration is comparable to that measured after the first centrifugation (about 6E-04 mM) with an increase of the solution polydispersivity index. X-ray Photoelectron Spectroscopy results support the NMR findings and revealed a major hydrocarbon contamination after the nanoparticles cleaning process. Moreover, functionalization with 1H,1H,2H,2H-Perfluorodecanethiol hydrophobic thiols up to about 0.9 of a monolayer (ML) was achieved after two centrifugation cycles, whilst less of 0.6 ML was functionalized by simple thiol-citrate substitution in the pristine gold nanoparticle solution and after a 3 dialysis cyclesJRC.F.2-Consumer Products Safet