(422d) Monitoring Ligand Exchange On the Surface of Gold Nanoparticles Using Isothermal Titration Calorimetry

Ligand exchange is an important factor in the function and end fate of nanomaterials.  A better understanding of binding strengths of various functional groups to the surface of gold nanoparticles, GNPs, is needed in order to better predict how they will behave in natural and biological environments. Fluorescent Resonance Energy Transfer (FRET) was used to develop a hierarchy of competitive binding strengths of 5 fluorescently tagged functional groups using fluorescence spectroscopy. The functional groups investigated were; COOH, NH₂, OH, SH, and SO₃.GNPs bound with fluorescently tagged ligands were titrated into a known concentration of non-fluorescently tagged unbound ligands and the fluorescence intensity was monitored until ligand exchanged reached equilibrium. The study resulted in the following hierarchy with the lowest observed binding strength listed first; OH < NH₂ < COOH < SO3 < SH. Kinetics of the FRET data was used to calculate competitive binding constants. Isothermal Titration Calorimetry, ITC, was performed with the same ligands used in the FRET experiments in order to confirm the binding energies obtained from the FRET results.