Synthesis of Silver-Modified Nanoceria Formulations Through Solution-Based Nanoengineering and Their Unique Efficacies Towards (Non-) Enveloped Virus Species

The utility of noble metal species in catalysis has been further broadened by investigations into their complex substrate interactions (catalyst-substrate/support effects). Such studies highlight the impact of chemical environment on material character as emergent phenomena (<i>e.g.</i> varied plasmon character, unique reaction selectivity (reactivity)). In the presented study, noble metal silver’s limited solubility in and surface-phase formation on redox-active cerium oxide nanoparticles is overcome by manipulating the unique chemistry of ionic silver in aqueous solution. In particular, the oxidation of silver and, thereby, the final nanomaterial synthesis products, are <i>nanoengineered</i> by top-down chemical etching process to remove contaminant silver (oxide) phases post-synthesis (utilizing Tollen’s reagent, [Ag(NH₃)₂]⁺, formation from silver (oxide)) (<i>AgCNP1</i>) or selective-oxidation of Ce³⁺ over silver by hydrogen peroxide (H₂O₂+Ag⁰,Ag₂O → Ag⁺+H₂O+(radical oxygen species)), bottom-up process, to preclude silver (oxide) particle phase formation (<i>AgCNP2</i>). Each synthesis produces surface/near-surface silver-phases of varied oxidation states (evidenced by x-ray photoelectron spectroscopy) due to the unique crystal environments evolved by each synthetic route (evidenced by transmission electron microscopy, x-ray diffraction, electroanalysis). Further, synthesis conditions and product silver phase character strongly impact cerium site reduction in each formulation (25.8 and 53.7 %Ce as Ce³⁺ for AgCNP1 and 2, respectively). Biomedically-relevant, reactive oxygen species modulating enzyme-mimetic catalysis assays (peroxide-degrading: catalase, superoxide radical scavenging: superoxide dismutase) were performed for each formulation, which correlate catalytic redox activity with extent of cerium reduction in the formulations. The complex nature of the silver surface phase character and silver/ceria-mediated surface catalysis activity of each formulation were further highlighted in studies demonstrating their unique efficacy towards inactivation of enveloped (OC43 <i>coronavirus</i>) and/or non-enveloped (RV14 <i>rhinovirus</i>) viruses. Specificity towards virus character is further studied through electroanalytical methods (electrochemical impedance spectroscopy, circuit modeling) and adsorption studies.