(436f) Monitoring Ligand Exchange on the Surface of Gold and Silver Nanoparticles and the Implications on Nanoparticle – Phospholipid Assemblies for Drug Delivery Applications

Gold and silver nanoparticles have been getting increasing amount of attention due to their stability, optical properties and low toxicity in the field of consumer products and biomedicines. Gold and silver nanoparticles with various surface chemistries have been synthesized in order to take advantage of the size, shape and morphology dependent properties of the nanoparticles which vary greatly from the bulk properties. The nanoparticle surface can be functionalized with varieties of ligands to satisfy the particular application of choice. Hence it is important to predict the interactions of the nanoparticles with the ligands. In this treatise, Fluorescent Resonant Energy Transfer (FRET) was used to predict the relative binding strengths of fluorescently tagged functional groups spectrofluorometrically.  Nanoparticles bound with fluorescently tagged ligands were titrated into a known concentration of non-fluorescently tagged unbound ligands and the fluorescence intensity was monitored until the exchange reached equilibrium. Isothermal titration calorimetry (ITC) was used to support the thermodynamic changes of the ligand exchange reactions in-situ and real time, quantitative data was obtained on ligand binding. 

Hydrophilic cationic, anionic, and nonionic nanoparticles ranging from 3 to 20 nm in diameter were used to induce simulated drug delivery from small unilamellar vesicles (SUVs).  Fluorescence spectroscopy was used to measuring the efflux of encapsulated fluorescent marker dye from the vesicles, triggered by nanoparticle exposure. SUVs containing self-quenched entrapped fluorescein were prepared using DPPC and DPPG lipids and subjected to nanoparticles. Initially the fluorescence is low due to self-quenching but increases as the entrapped dye leaks out of the liposomes (with time, temperature or due to interactions with the nanoparticles resulting in the change of stability or permeability of the lipid bilayer). This extent of change in fluorescence signal in the form of relative fluorescence of the leaked marker dye was used to determine the change in membrane permeability.