Phase transfer of surface-modified gold nanoparticles by hydrophobization with alkylamines

The complete transfer from an aqueous to an organic solution of negatively charged carboxylate- and sulfonate-modified gold nanoparticles in the presence of primary amines is demonstrated. The transfer of carboxylate-modified gold nanoparticles to chloroform was found to be dependent on the pH of the aqueous phase. The sulfonate-modified gold nanoparticles readily transferred to chloroform in the presence of sodium chloride. Fourier transform infrared measurements showed that the transfer of particles occurred via acid-base pair formation between the carboxylate or sulfonate moieties on the nanoparticles and the protonated amine groups of the alkylamines. The transfer of the gold nanoparticles to the organic phase occurred under similar conditions for alkylamines with C-12 and C-18 chain lengths. Transmission electron microscopy studies showed that the phase-transferred gold nanoparticles arranged into ordered arrays upon evaporation of the organic solvent.