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The effect of post-synthesis aging on the ligand exchange activity of iron oxide nanoparticles
Kathleen Davis1, Michael Vidmar2, Airat Khasanov2
1Department of Materials Science and Engineering, Clemson University, Clemson, SC, United States; Center for Optical Materials Science and Engineering Technologies (COMSET), Clemson University, Anderson, SC, United States.
Hypothesis:
Ligand exchange is a widely-used method of controlling the surface chemistry of nanomaterials. Exchange is dependent on many factors including the age of the core particle being modified. Aging of the particles can impact surface structure and composition, which in turn can affect ligand binding.
Experiments:
To quantify the effects of aging on ligand exchange, we employed a technique to track the exchange of radiolabeled 14C-oleic acid with unlabeled, oleic acid bound to iron oxide nanoparticles. Liquid scintillation counting (LSC) was used to determine the amount of 14C-oleic acid adsorbing to the particles throughout the duration of the exchange for particles aged for 2days, 7days, and 30days.
Findings:
Results revealed an increase in the total amount of ligands exchanged with aging up to 30days. Kinetic analysis of these results revealed a significant decrease in the overall rate of ligand exchange between 2 and 30days. The change in extent of adsorption with age could suggest increased availability of free binding sites. A follow-up study comparing exchange with oxidized and unoxidized particles suggested this increase in ligand adsorption may be due to changes in the Fe2+/Fe3+ ratio on the surface as the particles aged.