Characterizing the state of nanoparticles (such as size, surface charge, and degree of agglomeration) in aqueous suspensions and understanding the parameters that affect this state are imperative for toxicity investigations. In this study, the role of important factors such as solution ionic strength, pH, and particle surface chemistry that control nanoparticle dispersion was examined. The size and zeta potential of four TiO2 and three quantum dot samples dispersed in different solutions (including one physiological medium) were characterized. For 15 nm TiO2 dispersions, the increase of ionic strength from 0.001 M to 0.1 M led to a 50-fold increase in the hydrodynamic diameter, and the variation of pH resulted in significant change of particle surface charge and the hydrodynamic size. It was shown that both adsorbing multiply charged ions (e.g., pyrophosphate ions) onto the TiO2 nanoparticle surface and coating quantum dot nanocrystals with polymers (e.g., polyethylene glycol) suppressed agglomeration and stabilized the dispersions. DLVO theory was used to qualitatively understand nanoparticle dispersion stability. A methodology using different ultrasonication techniques (bath and probe) was developed to distinguish agglomerates from aggregates (strong bonds), and to estimate the extent of particle agglomeration. Probe ultrasonication performed better than bath ultrasonication in dispersing TiO2 agglomerates when the stabilizing agent sodium pyrophosphate was used. Commercially available Degussa P25 and in-house synthesized TiO2 nanoparticles were used to demonstrate identification of aggregated and agglomerated samples.

Characterization of size, surface charge, and agglomeration state of nanoparticle dispersions for toxicological studies

Stability of commercial metal oxide nanoparticles in water.

The aim of this study was to establish and validate a practical method to disperse nanoparticles in physiological solutions for biological in vitro and in vivo studies. TiO2 (rutile) dispersions were prepared in distilled water, PBS, or RPMI 1640 cell culture medium. Different ultrasound energies, various dispersion stabilizers (human, bovine, and mouse serum albumin, Tween 80, and mouse serum), various concentrations of stabilizers, and different sequences of preparation steps were applied. The size distribution of dispersed nanoparticles was analyzed by dynamic light scattering and zeta potential was measured using phase analysis light scattering. Nanoparticle size was also verified by transmission electron microscopy. A specific ultrasound energy of 4.2 × 105 kJ/m3 was sufficient to disaggregate TiO2 (rutile) nanoparticles, whereas higher energy input did not further improve size reduction. The optimal sequence was first to sonicate the nanoparticles in water, then to add dispersion stabilizers, and finally to add buffered salt solution to the dispersion. The formation of coarse TiO2 (rutile) agglomerates in PBS or RPMI was prevented by addition of 1.5 mg/ml of human, bovine or mouse serum albumin, or mouse serum. The required concentration of albumin to stabilize the nanoparticle dispersion depended on the concentration of the nanoparticles in the dispersion. TiO2 (rutile) particle dispersions at a concentration lower than 0.2 mg/ml could be stabilized by the addition of 1.5 mg/ml albumin. TiO2 (rutile) particle dispersions prepared by this method were stable for up to at least 1 week. This method was suitable for preparing dispersions without coarse agglomerates (average diameter < 290 nm) from nanosized TiO2 (rutile), ZnO, Ag, SiOx, SWNT, MWNT, and diesel SRM2975 particulate matter. The optimized dispersion method presented here appears to be effective and practicable for preparing dispersions of nanoparticles in physiological solutions without creating coarse agglomerates.

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Optimized dispersion of nanoparticles for biological in vitro and in vivo studies

Th antibacterial activity of metal oxide nanoparticles has received marked global attention as they can be specifically synthesized to exhibit significant toxicity to bacteria. The importance of their application as antibacterial agents is evident keeping in mind the limited range and effectiveness of antibiotics, on one hand, and the plethora of metal oxides, on the other, along with the propensity of nanoparticles to induce resistance being much lower than that of antibiotics. Effective inhibition against a wide range of bacteria is well known for several nano oxides consisting of one metal (Fe3O4, TiO2, CuO, ZnO), whereas, research in the field of multi-metal oxides still demands extensive exploration. This is understandable given that the relationship between physicochemical properties and biological activity seems to be complex and difficult to generalize even for metal oxide nanoparticles consisting of only one metal component. Also, despite the broad scope that metal oxide nanoparticles have as antibacterial agents, there arise problems in practical applications taking into account the cytotoxic effects. In this respect, the consideration of polymetallic oxides for biological applications becomes even greater since these can provide synergetic effects and unify the best physicochemical properties of their components. For instance, strong antibacterial efficiency specific of one metal oxide can be complemented by non-cytotoxicity of another. This review presents the main methods and technological advances in fabrication of nanostructured metal oxides with a particular emphasis to multi-metal oxide nanoparticles, their antibacterial effects and cytotoxicity.

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Pure and multi metal oxide nanoparticles: synthesis, antibacterial and cytotoxic properties

Studies designed to investigate the environmental or biological interactions of nanoscale materials frequently rely on the use of ultrasound (sonication) to prepare test suspensions. However, the inconsistent application of ultrasonic treatment across laboratories, and the lack of process standardization can lead to significant variability in suspension characteristics. At present, there is widespread recognition that sonication must be applied judiciously and reported in a consistent manner that is quantifiable and reproducible; current reporting practices generally lack these attributes. The objectives of the present work were to: (i) Survey potential sonication effects that can alter the physicochemical or biological properties of dispersed nanomaterials (within the context of toxicity testing) and discuss methods to mitigate these effects, (ii) propose a method for standardizing the measurement of sonication power, and (iii) offer a set of reporting guidelines to facilitate the reproducibility of studies involving engineered nanoparticle suspensions obtained via sonication.

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Ultrasonic dispersion of nanoparticles for environmental, health and safety assessment--issues and recommendations.

Breakage of TiO2 agglomerates in electrostatically stabilized aqueous dispersions

Fractal analysis as a complimentary technique for characterizing nanoparticle size distributions

Thin film metal oxide coatings have been used commercially as electromagnetic filters from the UV to infrared regions for over half a century. Deposition onto a substrate has typically been accomplished using vapor deposition techniques [1‐3] and more recently sol‐gel methods. [4‐7] These coatings provide very good optical and mechanical performance when applied to substrates with similar thermal and mechanical properties. When conventional metal oxide coatings are applied to flexible, relatively soft substrates such as polymers, mismatches in mechanical properties can reduce interfacial adhesion or accelerate mechanical failures. [8,9] Theauthorsrecentlyshowedthatathinfilmpolymer nanocomposite can be applied to a polymer substrate and maintain adhesion even under high strains. [10] This paper describes the first time demonstration of an IR mirror using a relatively inexpensive method to apply complicated thin film dielectric stacks to a polymer substrate that can function effectively in high strain systems. Ultrathin layers of polymer nanocomposites can be used to develop electromagnetic filters, with improved mechanical performance, on compliant substrates such as polymers. Self-assembled polymer nanocomposite thin film layers composed of UV-cured acrylates and metal oxide nanoparticles were developed as antireflective coatings for ophthalmic lenses. [11,12] The primary failure mode in this application is associated with intrinsic stresses introduced during processing and thermal cycling of the plastic. Nanocomposite coatings outperform ceramic coatings on plastic substrates because the primary failures are ductile, limiting secondary cracks propagating from abrasions and thereby reducing haze. [10] Ceramic thin films in similar studies exhibited brittle fracture, which led to secondary cracks and higher haze measurements. [8,9] The use of nanoparticles at high packing densities,

Polymer nanocomposite thin film mirror for the infrared region.

Described herein are electrostatically stabilized nanoparticles. Methods of manufacturing non- agglomerated crystalline nanoparticles in water and polar solvents and encapsulation of nanoparticles to assemble room temperature curable transparent nanoparticles/polymer composites are also described.

Methods of making and using metal oxide nanoparticles

Metal oxide nanoparticles can be used in thin film polymer systems to engineer specific material properties while
maintaining visible transparency. High loadings of nanoparticles in a polymer can manipulate refractive index, modulus,
and UV absorption over a wide range. Because the polymer binders can be allowed to dominate the physical properties,
these systems are ideal where materials undergo large strains. While stable dispersions of sub-100nm diameter CeO2,
ZnO, and SiO2 are well understood and commercially available, our group also developed a stable dispersion of TiO2
nanoparticles. These metal oxides are significantly harder than the host polymer, have high UV absorption, and cover a
large refractive index range. Our group has successfully incorporated these materials into PMMA thin films with
loadings up to 60% by volume (approaching the theoretical close packing of spheres). These thin film nanocomposites
have been successfully incorporated into 30 layer, sharp cut optical filters that easily withstand large strains induced by
mechanical loading and thermal cycling. In these films we have adhered to the rule that nanoparticle diameter should be
one-tenth the wavelength of visible light. As the thickness of the overall filter stack increases, light scattering is
intensified, so the dimensions and refractive indices of the nanoparticles become critical for highly transparent systems.
We study here the interactions of particle dimensions, refractive index, loading, thickness, and transparency in
nanocomposites.

Natalia Mandzy

Papers

Breakage of TiO2 agglomerates in electrostatically stabilized aqueous dispersions

Fractal analysis as a complimentary technique for characterizing nanoparticle size distributions

Polymer nanocomposite thin film mirror for the infrared region.

Methods of making and using metal oxide nanoparticles

The role of nanoparticles in visible transparent nanocomposites