Quantum dots (QDs) hold promise for several biomedical, life sciences and photovoltaic applications. Substantial production volumes and environmental release are anticipated. QD toxicity may be intrinsic to their physicochemical properties, or result from the release of toxic components during breakdown. We hypothesized that developing zebrafish could be used to identify and distinguish these different types of toxicity. Embryos were exposed to aqueous suspensions of CdSe core / ZnS shell QDs functionalized with either poly-L-lysine or poly(ethylene glycol) terminated with methoxy, carboxylate, or amine groups. Toxicity was influenced by the QD coating, which also contributed to the QD suspension stability. At sublethal concentrations, many QD preparations produced characteristic signs of Cd toxicity that weakly correlated with metallothionein expression, indicating that QDs are only slightly degraded in vivo. QDs also produced distinctly different toxicity that could not be explained by Cd release. Using the zebrafish model, we were able to distinguish toxicity intrinsic to QDs from that caused by released metal ions. We conclude that developing zebrafish provide a rapid, low-cost approach for assessing structure-toxicity relationships of nanoparticles.

We investigate the assembly of block copolymer-nanoparticle composite films on chemically nanopatterned substrates and present fully three-dimensional simulations of a coarse grain model for these hybrid systems. The location and distribution of nanoparticles within the ordered block copolymer domains depends on the thermodynamic state of the composite in equilibrium with the surface. Hierarchical assembly of nanoparticles enables applications in which the ability to precisely control their locations within periodic and nonregular geometry patterns and arrays is required.

Once released into the environment, engineered nanomaterials may be transformed by microbially mediated redox processes altering their toxicity and fate. Little information currently exists on engineered nanomaterial transformation under environmentally relevant conditions. Here, we report the development of an in vitro biomimetic assay for investigation of nanomaterial transformation under simulated oxidative environmental conditions. The assay is based on the extracellular hydroquinone-driven Fenton’s reaction used by lignolytic fungi. We demonstrate the utility of the assay using CdSecore/ZnSshell quantum dots (QDs) functionalized with poly(ethylene glycol). QD transformation was assessed by UV-Visible spectroscopy, inductively-coupled plasma-optical emission spectroscopy, dynamic light scattering, transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX). QDs were readily degraded under simulated oxidative environmental conditions: the ZnS shell eroded and cadmium was released from the QD core. TEM, electron diffraction analysis and EDX of transformed QDs revealed formation of amorphous Se aggregates. The biomimetic hydroquinone-driven Fenton’s reaction degraded QDs to a larger extent than did H2O2 and classical Fenton’s reagent (H2O2 + Fe2+). This assay provides a new method to characterize transformations of nanoscale materials expected to occur under oxidative environmental conditions.

The toxicity of engineered nanoparticles is expected to depend in part on their stability in biological systems. To assess the biodurability of engineered nanomaterials in the human digestive system, we adapted an in vitro assay previously used to evaluate the bioaccessibility of metals in contaminated soils. The compositions of the simulated gastric and intestinal fluids, temperature and residence times were designed to closely mimic conditions in the stomach and duodenum of the small intestine. We demonstrated the utility of the assay using CdSecore/ZnSshell quantum dots functionalized with polyethylene glycol (PEG) thiol of two different molecular masses (PEG350 and PEG5000). Under gastric conditions, removal of the PEG ligand diminished the stability of PEG350-quantum dot suspensions, while PEG5000-quantum dots were severely degraded. Inclusion of the glycoprotein mucin, but not the digestive protein pepsin, in simulated gastric fluids provided both PEG350- and PEG5000-coated quantum dots partial protection from transformations induced by gastric conditions.

We have investigated the surface photochemical properties of Fe "doped" and (Fe,N) codoped homoepitaxial rutile TiO 2 (110) films grown by plasma-assisted molecular beam epitaxy. Fe does not incorporate as an electronic dopant in the rutile lattice but rather segregates to the film surface. However, codeposition of Fe with N enhances the solubility of Fe, and DFT calculations suggest that codopant complex formation is the driving force behind the enhanced solubility. The codoped films, in which a few atomic percent of Ti (O) are replaced with Fe (N), exhibit significant disorder compared to undoped films grown under the same conditions, presumably due to dopant-induced strain. Codoping redshifts the rutile bandgap into the visible. However, the film surfaces are photochemically inert with respect to hole-mediated decomposition of adsorbed trimethyl acetate. The absence of photochemical activity may result from dopant-induced trap and/or recombination sites within the film. This study indicates that enhanced visible light absorptivity in TiO 2 does not necessarily result in visible light initiated surface photochemistry.