Nanocrystalline ceria is an interesting inorganic material for biological application that can exhibit antioxidant properties due to facile electron transfer between cerium(III) and cerium(IV). In this work, ceria nanocrystals with uniform and tunable size, surface chemistry, and variable cerium(III) content were formed via the high temperature thermal decomposition of ceria precursors including cerium acetylacetonate hydrate, cerium oleylamine, and cerium nitrate hexahydrate. When combined with organic acid and amine surfactants at temperatures between 260 and 320 °C, these cerium precursors decomposed to yield near-spherical cerium oxide nanocrystals with diameters ranging from 3 to 10 nm. For all shapes of nanocrystals, the smallest primary particle sizes had the most cerium(III) content. Both poly(acrylic acid)–octyl amine as well as oleic acid could be used to transfer the hydrophobic nanocrystals into water; acute in vitro toxicology studies revealed that even at high concentrations (e.g., 10 ppm) 3 nm nanocrystalline ceria suspensions had had no measurable effect on human dermal fibroblasts (HDF). Additionally, hydrogen peroxide effectively converted cerium(III) to cerium(IV) without any change in the colloidal stability of the nanocrystals. These data illustrate that highly uniform nanocrystalline cerium oxide formed in organic solutions can be a potential antioxidant in the aqueous environments relevant for biological applications.

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To fully understand the biological and environmental impacts of nanomaterials requires studies which address both sub-lethal endpoints and multigenerational effects. Here we use a nematode to examine these issues as they relate to exposure to two different types of quantum dots, core (CdSe) and core-shell (CdSe/ZnS), and to compare the effect to those observed after cadmium salt exposures. The strong fluorescence of the core-shell QDs allowed for the direct visualization of the materials in the digestive track within a few hours of exposure. Multiple endpoints, including both developmental and locomotive, were examined at QD exposures of low (10 mg/L Cd), medium (50 mg/L Cd), and high concentrations (100 mg/L Cd). While the core-shell QDs showed no effect on fitness (lifespan, fertility, growth, and three parameters of motility behavior), the core QDs caused acute effects similar to those found for cadmium salts suggesting that biological effects may be attributed to cadmium leaching from the more soluble QDs. Over multiple generations, we commonly found that for lower life-cycle exposures to core QDs the parents response was generally a poor predictor of the effects on progeny. At the highest concentrations, however, biological effects found for the first generation were commonly similar in magnitude to those found in future generations.

In this paper, nanoscale iron oxide/quantum dot (QD) complexes were formed in an efficient and versatile reaction that relied on the nucleation of chalcogenides on preformed iron oxide nanocrystals. Iron oxide nanocrystals acted as seeds for the growth of CdSe quantum rods (QRs), CdSe QDs, and CdSe@ZnS QDs. A zinc sulfide shell was added to protect the CdSe core in the complex chemically and provide a reasonable fluorescence quantum yield (∼5%). High-resolution transmission electron microscopy revealed that QDs shared an interface with iron oxide, yielding structures that resemble pincushions with QDs or QRs studding the surface of the iron oxide. These complexes only formed under specific conditions of temperature, injection rate, and surfactant composition that minimized the formation of unbound QDs. As a superparamagnetic material, iron oxide provided a high purity (∼89%) of complexed materials without unbound QDs. The quantitative photoluminescence quantum yields of the purified complexes correlated with the number of QDs per iron oxide. These nanoscale complexes retained the size-dependent optical and magnetic properties of each component.

The increased bioavailability of nanoparticles engineered for good dispersion in water may have biological and environmental impacts. To examine this issue, the authors assessed the biological effects in nematodes as they relate to exposure to silver nanoparticles (AgNPs) of different sizes at low (1 mg/L Ag), medium (10 mg/L Ag), and high concentrations (100 mg/L Ag). Over multiple generations, the authors found that the smallest particle, at 2 nm, had a notable impact on nematode fertility. In contrast, the largest particle, at 10 nm, significantly reduced the lifespan of parent nematodes (P0) by 28.8% and over the span of 3 generations (F1–F3). In addition, a computer vision system automatically measured the adverse effects in body length and motility, which were not size-dependent.