Phase transfer of aqueous colloidal gold particles into organic solutions containing fatty amine molecules

We demonstrate the phase transfer of colloidal gold particles synthesized in an aqueous medium into toluene containing the cationic surfactant, octadecylamine (ODA). During vigorous shaking of the biphasic mixture, rapid transfer of the gold particles into the organic phase was observed. The phase transfer of the colloidal gold particles arises due to coupling of the gold particles with the organic phase ODA molecules via either coordination bond formation or weak covalent interaction. This process renders the particles sufficiently hydrophobic and soluble in the organic phase. The ODA-stabilized colloidal gold particles could be separated out in the form of a powder and readily dissolved in different organic solvents. The nature of binding of the ODA molecules to the gold particle surface was characterized using thermogravimetry/differential thermal analysis, as well as Fourier transform infrared spectroscopy. To the best of our knowledge, this is the first demonstration of the phase transfer of colloidal gold particles by direct co-ordination to primary amines. The protocol described herein does not require the use of acid, a feature common to similar phase transfer protocols involving alkanethiols as the co-ordinating and hydrophobizing agent.