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Effect of Ligand Charge on Electron-Transfer Rates of Water-Soluble Gold Nanoparticles

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journal contribution
posted on 28.05.2015, 00:00 by David Crisostomo, Rachel R. Greene, David E. Cliffel
As the use of nanoparticles as biological and electronic platforms increases, research must be conducted to determine the kinetics of varying types of particles. In this paper, we determine the forward heterogeneous electron-transfer rate constant (kf) of water-soluble monolayer-protected gold nanoparticles using a scanning electrochemical microscope (SECM). Using SECM approach curves, we were able to determine the electron-transfer rates of water-soluble nanoparticles protected with a variety of ligands: tiopronin, glutathione, and trimethylammonium undecenyl mercaptan. Our results show the electron-transfer rate is largely dependent on the charge presented by the ligand shell. Fixed charges on ligands inhibit the tunneling of the electron through the protecting monolayer, making ligand charge a dominant factor in electron-transfer rates. By changing the ligand charge on tiopronin-protected gold nanoparticles through pH, we show the electron-transfer rate is inversely proportional with pH and decreases dramatically as the ligands move from an uncharged to a negatively charged species.