Conjugates of gold nanoparticles and poly(ethylene glycol): Formation in hydrosol, direct transfer to organic medium, and stability of organosols

A onestage method has been developed for phase transfer of gold nanoparticles (NPs) with a diameter of 17.2 +/- 0.5 nm from a hydrosol to an organic medium (chloroform). The method is based on the high affinity of thiolated poly(ethylene glycol) (TPEG) for nonpolar solvents and the capability of its molecules for chemisorption on a gold NP surface with the formation of a dense monolayer. Results of thermo-gravimetric analysis have been used to determine the maximum packing density (a parts per thousand 0.85 nm(-2)) of TPEG molecules on the surface of Au NPs with the aforementioned diameter. It has been shown that TPEG can play the roles of both an NP stabilizer and a phase transfer agent. Therewith, the degree of NP transfer from water to chloroform is a parts per thousand 90%. The stability to aggregation of the obtained organosols has been found to increase with the chemisorption value of PEG molecules. It has been demonstrated that these organosols can be used to form two-dimensional ensembles of gold NPs on planar substrates.