Increasing the antioxidant capacity of ceria nanoparticles with catechol-grafted poly(ethylene glycol).

Ceria nanoparticles are remarkable antioxidants due to their large cerium(III) content and the possibility of recovering cerium(III) from cerium(IV) after reaction. Here we increase the cerium(III) content of colloidally stable nanoparticles (e.g., nanocrystals) using a reactive polymeric surface coating. Catechol-grafted poly(ethylene glycols) (PEG) polymers of varying lengths and architectures yield materials that are non-aggregating in a variety of aqueous media. Cerium(IV) on the ceria surface both binds and oxidizes the catechol functionality, generating a dark-red colour emblematic of surface-oxidized catechols with a concomitant increase in cerium(III) revealed by X-ray photoemission spectroscopy (XPS). The extent of ceria reduction depends sensitively on the architecture of the coating polymer; small and compact polymer chains pack with high density at the nanoparticle surface yielding the most cerium(III). Nanoparticles with increased surface reduction, quantified by the intensity of their optical absorption and thermogravimetric measures of polymer grafting densities, were more potent antioxidants as measured by a standard TEAC antioxidant assay. For the same core composition nanoparticle antioxidant capacities could be increased over an order of magnitude by tailoring the length and architecture of the reactive surface coatings.

When function is biological: Discerning how silver nanoparticle structure dictates antimicrobial activity.

Silver nanomaterials have potent antibacterial properties that are the foundation for their wide commercial use as well as for concerns about their unintended environmental impact. The nanoparticles themselves are relatively biologically inert but they can undergo oxidative dissolution yielding toxic silver ions. A quantitative relationship between silver material structure and dissolution, and thus antimicrobial activity, has yet to be established. Here, this dissolution process and associated biological activity is characterized using uniform nanoparticles with variable dimension, shape, and surface chemistry. From this, a phenomenological model emerges that quantitatively relates material structure to both silver dissolution and microbial toxicity. Shape has the most profound influence on antibacterial activity, and surprisingly, surface coatings the least. These results illustrate how material structure may be optimized for antimicrobial properties and suggest strategies for minimizing silver nanoparticle effects on microbes.

Electroless plating of thin gold films directly onto silicon nitride thin films and into micropores.

A method to directly electrolessly plate silicon-rich silicon nitride with thin gold films was developed and characterized. Films with thicknesses <100 nm were grown at 3 and 10 °C between 0.5 and 3 h, with mean grain sizes between ∼20 and 30 nm. The method is compatible with plating free-standing ultrathin silicon nitride membranes, and we successfully plated the interior walls of micropore arrays in 200 nm thick silicon nitride membranes. The method is thus amenable to coating planar, curved, and line-of-sight-obscured silicon nitride surfaces.