(654c) Structural Insights into DNA-Stabilized Silver Clusters through Analytical Ultracentrifugation

Noble-metal nanoparticles with sizes approaching their Fermi wavelengths (~0.5 nm for Ag) display remarkable optical properties owing to the discretization of their electronic states. Among these, silver clusters stabilized by DNA (Ag_NDNA) stand out for their exceptional stability and tunability in optical properties. Selection of the stabilizing DNA or RNA sequence guides the formation of Ag_NDNA clusters, controlling the synthesized particle size to including between ~10-24 Ag atoms. These particles are then excellent candidates for a number of applications including sensing schemes and for use as novel nanophotonic elements in devices. However, applications involving Ag_NDNAs remain limited by the lack of mechanistic understanding regarding their photo-physical and folding pathways in response to stimuli, and this lack of understanding is largely due to challenges in obtaining structural information about the particles in solution.

In this work we address the structural characterization of the particles through in situ characterization with analytical ultracentrifugation (AUC). In AUC, the sedimentation rate of the AgNPs is monitored during centrifugation and structural information can be extracted from modelling of the concentration boundary of the particles as a function of time. This information is amplified through the use of density contrast variation experiments, in which a deuterated solvent is utilized to enable precise determination of the particle density in the given solvent system. For AG15DNA NPs this is of particular interest for aqueous - salt buffer and water-ethanol mixtures in which significantly different NP optical properites have been hypothesized as being due to structural rearrangement of the particle. Data and analysis of the sedimentation behavior measured of purified Ag15DNA NPs will be presented for both as produced and aged particles in both solvent systems, shedding new light on the differential behavior and structures of the particles in these systems.