A multiplexed separation of iron oxide nanocrystals using variable magnetic fields.

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.

Reaction of water-stable C60 aggregates with ozone.

While the reactivity of C60 has been described in a variety of organic solvents, little information is available regarding aqueous-based reactions due to solubility limitations. In this study, a reaction between C60, as a nanoscale suspension, and dissolved ozone in the aqueous phase was investigated. Findings indicate a facile reaction occurs, resulting in aggregate dissolution concurrent with formation of water-soluble fullerene oxide species.

Forming biocompatible and nonaggregated nanocrystals in water using amphiphilic polymers.

High-quality nanocrystals formed in organic solvents can be completely solubilized in water using amphiphilic copolymers containing poly(ethylene glycol) or PEG. These copolymers are generated using a maleic anhydride coupling scheme that permits the coupling of a wide variety of PEG polymers, both unfunctionalized and functionalized, to hydrophobic tails. Thermogravimetric analysis, size exclusion chromatography, cryogenic transmission electron microscopy, and infrared spectroscopy all indicate that the copolymers effectively coat the nanocrystals surfaces.

Low-field magnetic separation of monodisperse Fe3O4 nanocrystals.

Magnetic separations at very low magnetic field gradients (<100 tesla per meter) can now be applied to diverse problems, such as point-of-use water purification and the simultaneous separation of complex mixtures. High-surface area and monodisperse magnetite (Fe3O4) nanocrystals (NCs) were shown to respond to low fields in a size-dependent fashion. The particles apparently do not act independently in the separation but rather reversibly aggregate through the resulting high-field gradients present at their surfaces.

Antibacterial activity of fullerene water suspensions: effects of preparation method and particle size.

Fullerene research in biological systems has been hindered by the compound's relative insolubility in water. However, C60 molecules can be made to aggregate, forming stable fullerene water suspensions (FWS) whose properties differ from those of bulk solid C60. There are many different protocols for making FWS.

Solvothermal synthesis and characterization of anatase TiO2 nanocrystals with ultrahigh surface area.

Phase-pure, ultrafine nanocrystalline anatase with high specific surface area (up to 250 m(2) g(-1)) was obtained upon injection of a titanium alkoxide precursor into ethanol with designed volume of water under mild solvothermal conditions (<200 degrees C, 2 h). Primary particle sizes were tuned by adjusting various reaction parameters, with the smallest grain sizes occurring at low temperatures (140-150 degrees C), low initial alkoxide concentrations, and intermediate hydrolysis ratios (r identical with[H2O]/[Ti(OR)4]=5-10). Additionally, variations in the reaction temperature result in changes in particle morphology and distribution, with high-temperature samples exhibiting bimodal distributions of small spherical and larger cubic particles that suggest grain growth via Ostwald ripening.

Characterization of nanocrystalline CdSe by size exclusion chromatography.

High-performance size exclusion chromatography (HPSEC) is a powerful tool for probing the size and size distribution of complex materials. Here we report its application to the analysis of cadmium selenide nanocrystals produced in organic solvents. If nanocrystal-column interactions are minimized, this method provides an accurate measure of nanocrystal hydrodynamic diameter directly in solution; such information is complementary to TEM in that it can measure the thickness of various capping agents.

Analytical ultracentrifugation for characterizing nanocrystals and their bioconjugates.

Analytical ultracentrifugation (AU) provides a general way to probe the polydispersity of nanoparticles and the formation of bioconjugates in solution. Unconjugated gold nanocrystals show sedimentation coefficient distributions that are in agreement with size distributions as measured by TEM. AU is sensitive to the size/shape changes elicited by conjugation, in this case to lactose repressor (LacI).

Virus crystals as nanocomposite scaffolds.

The generation of long-range three-dimensional nanoscopic patterns is a major goal in materials chemistry. Here we report a strategy for creating such systems using virus crystals as scaffolds which can be infiltrated with metal specifically palladium and platinum. The inorganic component effectively packs within the porous macromolecular crystal architecture, providing a route for patterning these materials on the nanometer length scale.

Synthesis of monodisperse iron oxide nanocrystals by thermal decomposition of iron carboxylate salts.

Iron oxide (Fe(3)O(4), magnetite) nanocrystals of 6 to 30 nm with narrow size distributions (sigma = 5-10%) were prepared by the pyrolysis of iron carboxylate salts.

Recycling size exclusion chromatography for the analysis and separation of nanocrystalline gold.

Recycling size exclusion chromatography (RSEC) provides a high-resolution technique for the analysis and separation of materials based on size. We show here the application of this method to gold nanocrystals stabilized by thiols. Alternate recycling is more effective at separating nanomaterials as compared to closed-loop recycling because of its improved efficiency and high resolution.