Iron oxide nanocrystals are of great scientific and technological interest. In this work, these materials are the starting point for producing a reactive nanoparticle whose surface resembles that of natural green rusts. Treatment of iron oxide nanoparticles with cysteamine leads to the reduction of iron and the formation of a brilliant green aqueous solution of nanocrystals rich in iron(II). These materials remained crystalline with magnetic and structural features of the original iron oxide. However, new low-angle X-ray diffraction peaks as well as vibrational features characteristic of cysteamine were found in the nanocrystalline product. X-ray absorption spectroscopy (XAS), X-ray photoemission (XPS) and Mössbauer spectroscopies indicated the presence of an iron(II)-rich phase with high sulfur content analogous to the iron–oxygen structures found in natural green rusts. Electron microscopy found that these structural components remained associated with the nonreduced iron oxide cores. These sulfur-rich analogs of natural green rusts are highly reactive and were able to rapidly degrade a model organic dye in water. This observation suggests possible actuation with a cysteamine treatment of inert and magnetic iron oxide particles at the point-of-use for environmental remediation.

Molecular-based contrast agents for magnetic resonance imaging (MRI) are often characterized by insufficient relaxivity, thus requiring the systemic injection of high doses to induce sufficient contrast enhancement at the target site. In this work, gadolinium oxide (Gd2O3) nanoplates are produced via a thermal decomposition method. The nanoplates have a core diameter varying from 2 to 22 nm, a thickness of 1 to 2 nm and are coated with either an oleic acid bilayer or an octylamine modified poly(acrylic acid) (PAA–OA) polymer layer. For the smaller nanoplates, longitudinal relaxivities (r1) of 7.96 and 47.2 (mM s)−1 were measured at 1.41 T for the oleic acid bilayer and PAA–OA coating, respectively. These values moderately reduce as the size of the Gd2O3 nanoplates increases, and are always larger for the PAA–OA coating. Cytotoxicity studies on human dermal fibroblast cells documented no significant toxicity, with 100% cell viability preserved up to 250 μM for the PAA–OA coated Gd2O3 nanoplates. Given the 10 times increase in longitudinal relaxivity over the commercially available Gd-based molecular agents and the favorable toxicity profile, the 2 nm PAA–OA coated Gd2O3 nanoplates could represent a new class of highly effective T1 MRI contrast agents.

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.

Polystyrene nanoring arrays with outer diameters ranging from 130 to 230 nm were fabricated using low cost and simple fabrication techniques, including nanosphere lithography, argon plasma treatment, immersion in organic solvents and sonication. These nanorings were developed from polystyrene nanospheres pre-assembled on substrates. Scanning electron microscopy revealed that the argon plasma treatment transformed polystyrene nanospheres into hollow cone-shaped nanostructures. X-ray photoelectron and Raman spectroscopy found that the argon plasma changed the composition of the polystyrene nanospheres by forming graphitic materials. The nanoring formation mechanism was discussed based on the instrument analyses.

To fully understand the biological and environmental impacts of nanomaterials requires studies that address both sublethal end points 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 end points, 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.

This work examines the effect of nanocrystal diameter and surface coating on the reactivity of cerium oxide nanocrystals with H2O2 both in chemical solutions and in cells. Monodisperse nanocrystals were formed in organic solvents from the decomposition of cerium precursors, and subsequently phase transferred into water using amphiphiles as nanoparticle coatings. Quantitative analysis of the antioxidant capacity of CeO2–x using gas chromatography and a luminol test revealed that 2 mol of H2O2 reacted with every mole of cerium(III), suggesting that the reaction proceeds via a Fenton-type mechanism. Smaller diameter nanocrystals containing more cerium(III) were found to be more reactive toward H2O2. Additionally, the presence of a surface coating did not preclude the reaction between the nanocrystal surface cerium(III) and hydrogen peroxide. Taken together, the most reactive nanoparticles were the smallest (e.g., 3.8 nm diameter) with the thinnest surface coating (e.g., oleic acid). Moreover, a benchmark test of their antioxidant capacity revealed these materials were 9 times more reactive than commercial antioxidants such as Trolox. A unique feature of these antioxidant nanocrystals is that they can be applied multiple times: over weeks, cerium(IV) rich particles slowly return to their starting cerium(III) content. In nearly all cases, the particles remain colloidally stable (e.g., nonaggregated) and could be applied multiple times as antioxidants. These chemical properties were also observed in cell culture, where the materials were able to reduce oxidative stress in human dermal fibroblasts exposed to H2O2 with efficiency comparable to their solution phase reactivity. These data suggest that organic coatings on cerium oxide nanocrystals do not limit the antioxidant behavior of the nanocrystals, and that their redox cycling behavior can be preserved even when stabilized.Keywords: antioxidant capacity; cerium oxide; Fenton-type reaction; nanocrystal; redox cycle

•TiO2 and ZnO nanomaterials incorporated into sunscreens were evaluated for ROS production.•Presented here chemical assays were ideal tools to assess photoactivity of sunscreen pigments.•TiO2 was inactive upon UV irradiation; coatings render its surfaces non-reactive.•ZnO nanomaterials produced substantial amounts of ROS upon UVA illumination.•ZnO in sunscreens is either uncoated or ineffectually coated to limit its intrinsic property.Most commercial sunscreens that use inorganic pigments (TiO2 and ZnO) employ materials with nanoscale dimensions so that the products are both transparent and smooth upon application. However, certain types of TiO2 and ZnO nanoparticles are well known for their ability to produce reactive oxygen species (ROS) upon UV illumination. Consumers would not be protected from the adverse effects of sun exposures if photoactive nanomaterials were employed in sunscreens. To evaluate whether this is the case, eight different commercial sunscreens, as well as nanoscale pigments derived from these products, were exposed to ultraviolet light and evaluated for ROS production. Redundant and complementary assays for detecting reactive oxygen species included dichlorofluorescein fluorescence, luminol chemiluminescence, and the decolorization of dyes (Congo red and Rose Bengal). Additionally, spin trap (POBN and DMPO) electron paramagnetic resonance spectroscopy provided quantitative measures of ROS generation upon UV illumination. Nanoscale TiO2 from neat sunscreens was relatively inactive upon illumination; inert oxide coatings such as alumina and silica apparently render the titania surfaces non-reactive. In contrast, ZnO derived from sunscreens produced substantial amounts of ROS upon UVA illumination. The photocatalytic activity of nanoscale ZnO suggests that more effective sunscreens would rely on strategies, such as surface coatings, designed to limit its ROS generation under ultraviolet illumination. Finally, the simple chemical assays presented here are ideal screening tools for ensuring sunscreen pigments were inert under ultraviolet illumination.

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.Keywords: antioxidant; cerium oxide; crystal growth; nanocrystal; phase transfer; water-soluble;

Many of the solution phase properties of nanoparticles, such as their colloidal stability and hydrodynamic diameter, are governed by the number of stabilizing groups bound to the particle surface (i.e., grafting density). Here, we show how two techniques, analytical ultracentrifugation (AUC) and total organic carbon analysis (TOC), can be applied separately to the measurement of this parameter. AUC directly measures the density of nanoparticle–polymer conjugates while TOC provides the total carbon content of its aqueous dispersions. When these techniques are applied to model gold nanoparticles capped with thiolated poly(ethylene glycol), the measured grafting densities across a range of polymer chain lengths, polymer concentrations, and nanoparticle diameters agree to within 20%. Moreover, the measured grafting densities correlate well with the polymer content determined by thermogravimetric analysis of solid conjugate samples. Using these tools, we examine the particle core diameter, polymer chain length, and polymer solution concentration dependence of nanoparticle grafting densities in a gold nanoparticle–poly(ethylene glycol) conjugate system.

Both colloidal iron oxide and aluminum ferrite nanocrystals can initiate the growth of vertically aligned carbon nanotube (CNT) carpets through water-assisted chemical vapor deposition (CVD). The outer diameters of the CNTs ranged from 3 to 18 nm, and this dimension correlated well with the diameters of the starting nanocrystals. The smallest particles (4 nm aluminum ferrite nanocrystals) yielded CNT carpets with high percentages (60%) of single-walled CNT species, whereas larger particles (iron oxide nanocrystals over 25 nm) formed carpets with more double, triple, and larger multiwalled structures. CNTs grown by aluminum ferrite nanocrystals were uniformly of higher quality (IG/ID = 11.4) than comparable materials formed from pure iron oxides (IG/ID = 9.8). We speculate that the presence of aluminum in the nanocatalyst may slow the acetylene decomposition at the catalyst surface, leading to less production of amorphous carbon material.

Despite the many processes developed for carbon nanotube synthesis, few if any of these control the carbon nanotube diameter and length simultaneously. Here, we report a process whereby we synthesize vertically aligned carbon nanotube arrays (VA-CNT) using water-assisted chemical vapor deposition from solution processed premade and near-monodisperse iron oxide nanoparticles. Utilizing a dendrimer-assisted iron oxide nanoparticle monolayer deposition technique, the synthesis of high quality VA-CNTs is observed with a surprising degree of walls uniformity and diameters that correlate closely with the catalyst particle size. Specifically, we utilize 8.3 and 15.4 nm nanoparticle sizes to grow uniform, large diameter VA-CNTs. We observe control of the VA-CNT diameter and number of walls based on the nanoparticle size, with the 8.3 nm nanoparticles growing over 90% four-walled CNTs. Additionally, there is a sparse population of VA-CNTs with large diameters and few walls that tend to flatten into nanostructures resembling paired-layer graphene nanoribbons.Keywords: catalyst; catalyst support; nanoparticles; vertically aligned carbon nanotubes;

The size-dependent magnetic properties of nanocrystals are exploited in a separation process that distinguishes particles based on their diameter. By varying the magnetic field strength, four populations of magnetic materials were isolated from a mixture. This separation is most effective for nanocrystals with diameters between 4 and 16 nm.

TiO2 and ZnO nanomaterials are widely used to block ultraviolet radiation in many skin care products, yet product labels do not specify their dimensions, shape, or composition. The absence of this basic information creates a data gap for both researchers and consumers alike. Here, we investigate the structural similarity of pigments derived from actual sunscreen products to nanocrystals which have been the subject of intense scrutiny in the nanotoxicity literature. TiO2 and ZnO particles were isolated from eight out of nine commercial suncare products using three extraction methods. Their dimension, shape, crystal phase, surface area, and elemental composition were examined using transmission and scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller (BET) specific surface area analysis, energy dispersive X-ray and inductively coupled plasma optical emission spectroscopy. TiO2 pigments were generally rutile nanocrystals (dimensions ~25 nm) with needle-like or near-spherical shapes. ZnO pigments were wurtzite rods with a short axes less than 40 nm and longer dimensions often in excess of 100 nm. We identify two commercial sources of TiO2 and ZnO nanocrystals whose physical and chemical features are similar to the pigments found in sunscreens. These particular materials would be effective surrogates for the commercial product and could be used in studies of the health and environmental impacts of engineered nanomaterials contained in sunscreens.

Arsenic contamination in groundwater is a severe global problem, most notably in Southeast Asia where millions suffer from acute and chronic arsenic poisoning. Removing arsenic from groundwater in impoverished rural or urban areas without electricity and with no manufacturing infrastructure remains a significant challenge. Magnetite nanocrystals have proven to be useful in arsenic remediation and could feasibly be synthesized by a thermal decomposition method that employs refluxing of FeOOH and oleic acid in 1-octadecene in a laboratory setup. To reduce the initial cost of production, $US 2600/kg, and make this nanomaterial widely available, we suggest that inexpensive and accessible “everyday” chemicals be used. Here we show that it is possible to create functional and high-quality nanocrystals using methods appropriate for manufacturing in diverse and minimal infrastructure, even those without electricity. We suggest that the transfer of this knowledge is best achieved using an open source concept.

The effective water dispersion of highly uniform nanoparticles synthesized in organic solvents is a major issue for their broad applications. In an effort to overcome this problem, iron oxide and cadmium selenide nanocrystals were surrounded by lipid bilayers to create stable, aqueous dispersions. The core inorganic particles were originally generated in oleic acid and 1-octadecene. When these organic solutions were mixed with water and a sparing amount of excess fatty acid, up to 70% of the nanoparticles transferred into the aqueous phase. This simple approach was applied to two different nanocrystal types, and nanocrystal diameters ranging from 5 to 15 nm. In all cases, the resulting materials were stable, nonaggregated suspensions that retained their original magnetic and optical properties. The phase transfer efficiency is maximum when very little oleic acid is added (e.g. 0.2 w/w %). At higher concentrations, above the critical micelle concentration, the formation of micelles begins to compete with bilayer generation leading to less effective phase transfer. Unlike other approaches for water dispersion that rely on amphiphiles with significant water solubility, the fatty acids used in this work are only sparingly soluble in water. As a result, there is minimal dynamic exchange between free and bound surface agents and the resulting aqueous solutions contain little residual free organic carbon. Thermogravimetric analysis (TGA) confirmed the presence of bilayers around the nanocrystal cores. The particle size, size distribution, process yield, and colloidal stability were found using a suite of methods including transmission electron microscopy, small angle X-ray scattering, dynamic light scattering, inductively coupled plasma−optical emission spectroscopy, and ultraviolet−visible spectroscopy. Bilayer−nanocrystal complexes possess many of the same size-dependent features as the original materials, and as such offer new avenues for exploring and exploiting the interface between nanocrystals and biology.Keywords: bilayer-nanocrystal; fatty acid; iron oxide; nonpolar; quantum dots; SAXS

Centrifugation is an increasingly important technique for nanomaterial processing. Here, we examine this process for gold, cadmium selenide, and iron oxide nanocrystals using an analytical ultracentrifuge. Such data provide an accurate measure of the sedimentation coefficients for these materials, and we find that this parameter has a significant dependence on the size and surface coating. Conventional models for particle sedimentation cannot capture the behavior of these nanocrystals unless the density of the nanocrystals is described by a size-dependent term that accounts for both the inorganic core and the organic coating. Using this modification in the particle sedimentation framework, it is possible to estimate sedimentation coefficients from information about the nanocrystal core and surface coating dimensions. Such data are useful in choosing the speeds for a centrifugation process and are particularly important when bimodal nanocrystal distributions are present.Keywords: analytical ultracentrifugation; bimodal sample; cadmium selenide; iron oxide; nanocrystal density calculation; nanocrystals; polystyrene-coated gold

Higher environmental standards have made the removal of arsenic from water an important problem for environmental engineering. Iron oxide is a particularly interesting sorbent to consider for this application. Its magnetic properties allow relatively routine dispersal and recovery of the adsorbent into and from groundwater or industrial processing facilities; in addition, iron oxide has strong and specific interactions with both As(III) and As(V). Finally, this material can be produced with nanoscale dimensions, which enhance both its capacity and removal. The objective of this study is to evaluate the potential arsenic adsorption by nanoscale iron oxides, specifically magnetite (Fe3O4) nanoparticles. We focus on the effect of Fe3O4 particle size on the adsorption and desorption behavior of As(III) and As(V). The results show that the nanoparticle size has a dramatic effect on the adsorption and desorption of arsenic. As particle size is decreased from 300 to 12 nm the adsorption capacities for both As(III) and As(V) increase nearly 200 times. Interestingly, such an increase is more than expected from simple considerations of surface area and suggests that nanoscale iron oxide materials sorb arsenic through different means than bulk systems. The desorption process, however, exhibits some hysteresis with the effect becoming more pronounced with small nanoparticles. This hysteresis most likely results from a higher arsenic affinity for Fe3O4 nanoparticles. This work suggests that Fe3O4 nanocrystals and magnetic separations offer a promising method for arsenic removal.

Iron oxide (Fe3O4, magnetite) nanocrystals of 6 to 30 nm with narrow size distributions (σ = 5–10%) were prepared by the pyrolysis of iron carboxylate salts.