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The Study of the Phase Transfer of Gold Nanoparticles by Surface Modification

D. Brad Akers1, Gregory Von White II1, and Christopher L. Kitchens2. (1) Chemical and Biomolecular Engineering, Clemson University, 105 Sumter Ct, Central, SC 29630, (2) Chemical & Biomolecular Engineering, Clemson University, 127 Earle Hall, Clemson, SC 29634

Metal nanoparticles are of great interest for diverse applications due to their unique properties; however, for sensing and other targeted applications, it is necessary to design the surface chemistry to enable their desired function. We have synthesized citrate-stabilized, spherical gold nanoparticles 3-5 nm in diameter and subsequently exchanged the surface-capping citrate with a model alkanethiol in a stirred, biphasic water/hexane medium. The change in surface chemistry switches the particle solubility preference from the aqueous to the organic environment. We have instigated the nanoparticle phase transfer with time resolved UV-Visible absorbance spectroscopy of the aqueous phase, monitoring a diminishing central peak around 500 nm throughout the phase transfer. The absorbance peak indicates a consistent size distribution of stable nanoparticles within the aqueous layer throughout the transfer. TEM images of the organic phase were taken at strategic intervals up t = 20 hours. Nanospheres from the aqueous phase were analyzed with TEM for time t = 0 minutes and t = 20 hours. The particle distributions were essentially the same for the organic layer over time, suggesting that particle size—and consequently surface energy—was not a dominant factor in the kinetic mechanism for the phase transfer.