posted on 2015-03-03, 00:00authored byAshley
M. Smith, Lauren E. Marbella, Kathryn A. Johnston, Michael J. Hartmann, Scott E. Crawford, Lisa M. Kozycz, Dwight S. Seferos, Jill E. Millstone
We use nuclear magnetic resonance
spectroscopy methods to quantify
the extent of ligand exchange between different types of thiolated
molecules on the surface of gold nanoparticles. Specifically, we determine
ligand density values for single-moiety ligand shells and then use
these data to describe ligand exchange behavior with a second, thiolated
molecule. Using these techniques, we identify trends in gold nanoparticle
functionalization efficiency with respect to ligand type, concentration,
and reaction time as well as distinguish between functionalization
pathways where the new ligand may either replace the existing ligand
shell (exchange) or add to it (“backfilling”). Specifically,
we find that gold nanoparticles functionalized with thiolated macromolecules,
such as poly(ethylene glycol) (1 kDa), exhibit ligand exchange efficiencies
ranging from 70% to 95% depending on the structure of the incoming
ligand. Conversely, gold nanoparticles functionalized with small-molecule
thiolated ligands exhibit exchange efficiencies as low as 2% when
exposed to thiolated molecules under identical exchange conditions.
Taken together, the reported results provide advances in the fundamental
understanding of mixed ligand shell formation and will be important
for the preparation of gold nanoparticles in a variety of biomedical,
optoelectronic, and catalytic applications.