Showing papers in "Journal of Nanoparticle Research in 2009"

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

Abstract: 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.

The effect of particle size on the thermal conductivity of alumina nanofluids

Abstract: We present new data for the thermal conductivity enhancement in seven nanofluids containing 8–282 nm diameter alumina nanoparticles in water or ethylene glycol. Our results show that the thermal conductivity enhancement in these nanofluids decreases as the particle size decreases below about 50 nm. This finding is consistent with a decrease in the thermal conductivity of alumina nanoparticles with decreasing particle size, which can be attributed to phonon scattering at the solid–liquid interface. The limiting value of the enhancement for nanofluids containing large particles is greater than that predicted by the Maxwell equation, but is predicted well by the volume fraction weighted geometric mean of the bulk thermal conductivities of the solid and liquid. This observation was used to develop a simple relationship for the thermal conductivity of alumina nanofluids in both water and ethylene glycol.

Toxicity of nano- and micro-sized ZnO particles in human lung epithelial cells

Abstract: This is the first comprehensive study to evaluate the cytotoxicity, biochemical mechanisms of toxicity, and oxidative DNA damage caused by exposing human bronchoalveolar carcinoma-derived cells (A549) to 70 and 420 nm ZnO particles. Particles of either size significantly reduced cell viability in a dose- and time-dependent manner within a rather narrow dosage range. Particle mass-based dosimetry and particle-specific surface area-based dosimetry yielded two distinct patterns of cytotoxicity in both 70 and 420 nm ZnO particles. Elevated levels of reactive oxygen species (ROS) resulted in intracellular oxidative stress, lipid peroxidation, cell membrane leakage, and oxidative DNA damage. The protective effect of N-acetylcysteine on ZnO-induced cytotoxicity further implicated oxidative stress in the cytotoxicity. Free Zn2+ and metal impurities were not major contributors of ROS induction as indicated by limited free Zn2+ cytotoxicity, extent of Zn2+ dissociation in the cell culture medium, and inductively-coupled plasma-mass spectrometry metal analysis. We conclude that (1) exposure to both sizes of ZnO particles leads to dose- and time-dependent cytotoxicity reflected in oxidative stress, lipid peroxidation, cell membrane damage, and oxidative DNA damage, (2) ZnO particles exhibit a much steeper dose–response pattern unseen in other metal oxides, and (3) neither free Zn2+ nor metal impurity in the ZnO particle samples is the cause of cytotoxicity.

Acute toxicities of six manufactured nanomaterial suspensions to Daphnia magna

Abstract: The rapid growth of nanotechnology is stimulating research on the potential environmental impacts of manufactured nanomaterials (MNMs). This paper summarizes a comprehensive study on the 48-h acute toxicity of water suspensions of six MNMs (i.e., ZnO, TiO2, Al2O3, C60, SWCNTs, and MWCNTs) to Daphnia magna, using immobilization and mortality as toxicological endpoints. The results show that the acute toxicities of all MNMs tested are dose dependent. The EC50 values for immobilization ranged from 0.622 mg/L (ZnO NPs) to 114.357 mg/L (Al2O3 NPs), while the LC50 values for mortality ranged from 1.511 mg/L (ZnO NPs) to 162.392 mg/L (Al2O3 NPs). In these tests, TiO2, Al2O3, and carbon-based nanomaterials were more toxic than their bulk counterparts. Moreover, D. magna were found to ingest nanomaterials from the test solutions through feeding behaviors, which indicates that the potential ecotoxicities and environmental health effects of these MNMs cannot be neglected.

Fusarium solani : a novel biological agent for the extracellular synthesis of silver nanoparticles

Abstract: We report extracellular biosynthesis of silver nanoparticles by Fusarium solani (USM-3799), a phytopathogen causing disease in onion, when challenged with 1 mM silver nitrate (AgNO3). The formation of nanoparticles was characterized by visual observation followed by UV–Vis spectrophotometric analysis, which showed a peak at about 420 nm, which is very specific for silver nanoparticles. Further analysis carried out by Fourier Transform Infrared Spectroscopy (FTIR), provides evidence for the presence of proteins as capping agent, which helps in increasing the stability of the synthesized silver nanoparticles. Transmission Electron Microscopy (TEM) investigations confirmed that silver nanoparticles were formed. The synthesized silver nanoparticles were found to be polydispersed, spherical in the range of 5–35 nm with average diameter of 16.23 nm. Extracellular synthesis of nanoparticles could be highly advantageous from the point of view of synthesis in large quantities and easy downstream processing.

Phyllanthin-assisted biosynthesis of silver and gold nanoparticles: a novel biological approach

Abstract: The anisotropic gold and spherical–quasi-spherical silver nanoparticles (NPs) were synthesized by reducing aqueous chloroauric acid (HAuCl4) and silver nitrate (AgNO3) solution with the extract of phyllanthin at room temperature. The rate of reduction of HAuCl4 is greater than the AgNO3 at constant amount of phyllanthin extract. The size and shape of the NPs can be controlled by varying the concentration of phyllanthin extract and thereby to tune their optical properties in the near-infrared region of the electromagnetic spectrum. The case of low concentration of extract with HAuCl4 offers slow reduction rate along with the aid of electron-donating group containing extract leads to formation of hexagonal- or triangular-shaped gold NPs. Transmission electron microscopy (TEM) analysis revealed that the shape changes on the gold NPs from hexagonal to spherical particles with increasing initial concentration of phyllanthin extract. The Fourier transform infrared spectroscopy and thermogravimetric analyses reveal that the interaction between NPs and phyllanthin extract. The cyclic voltammograms of silver and gold NPs confirms the conversion of higher oxidation state to zero oxidation state. Anisotropic gold and silver nanoparticles were synthesized by a simple procedure using phyllanthin extract as reducing agent. The rate of bioreduction of AgNO3 is lower than the HAuCl4 at constant concentration of phyllanthin extract. The required size of the nanoparticles can be prepared by varying the concentration of phyllanthin with AgNO3 and HAuCl4.

Generation of nanoparticles by spark discharge

Abstract: The production of nanoparticles by microsecond spark discharge evaporation in inert gas is studied systematically applying transmission electron microscopy, mobility analysis and BET surface area measurement. The method of spark discharge is of special interest, because it is continuous, clean, extremely flexible with respect to material, and scale-up is possible. The particle size distributions are narrow and the mean primary particle size can be controlled via the energy per spark. Separated, unagglomerated particles, 3–12 nm in size, or agglomerates can be obtained depending on the flow rate. The nanoparticulate mass produced is typically 5 g/kWh. A formula is given, which estimates the mass production rate via thermal conductivity, evaporation enthalpy and the boiling point of the material used. We showed that with gas purified at the spot, the method produced gold particles that were so clean that sintering of agglomerated particles occurred at room temperature. The influence of a number of parameters on the primary particle size and mass production rate was studied and qualitatively understood with a model of Lehtinen and Zachariah (J Aerosol Sci 33:357–368, 2002). Surprisingly high charging probabilities for one polarity were obtained. Spark generation is therefore of special interest for producing monodisperse aerosols or particles of uniform size via electrical mobility analysis. Qualitative observations in the present study include the phenomenon of material exchange between the electrodes by the spark, which opens the possibility of producing arbitrary mixtures of materials on a nanoscale. If spark generation of nanoparticles is performed in a standing or almost standing gas, an aerogel of a web-like structure forms between surfaces of different electrical potential.

Microbial synthesis of silver nanoparticles by Bacillus sp.

Abstract: A silver resistant Bacillus sp. was isolated through exposure of an aqueous AgNO3 solution to the atmosphere. Silver nanoparticles were synthesized using these airborne bacteria (Bacillus sp.). Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analyses confirmed that silver nanoparticles of 5–15 nm in size were deposited in the periplasmic space of the bacterial cells; a preferable cell surface location for the easy recovery of biogenic nanoparticles.

Exposure to nanoscale particles and fibers during machining of hybrid advanced composites containing carbon nanotubes

Abstract: This study investigated airborne exposures to nanoscale particles and fibers generated during dry and wet abrasive machining of two three-phase advanced composite systems containing carbon nanotubes (CNTs), micron-diameter continuous fibers (carbon or alumina), and thermoset polymer matrices. Exposures were evaluated with a suite of complementary instruments, including real-time particle number concentration and size distribution (0.005–20 μm), electron microscopy, and integrated sampling for fibers and respirable particulate at the source and breathing zone of the operator. Wet cutting, the usual procedure for such composites, did not produce exposures significantly different than background whereas dry cutting, without any emissions controls, provided a worst-case exposure and this article focuses here. Overall particle release levels, peaks in the size distribution of the particles, and surface area of released particles (including size distribution) were not significantly different for composites with and without CNTs. The majority of released particle surface area originated from the respirable (1–10 μm) fraction, whereas the nano fraction contributed ~10% of the surface area. CNTs, either individual or in bundles, were not observed in extensive electron microscopy of collected samples. The mean number concentration of peaks for dry cutting was composite dependent and varied over an order of magnitude with highest values for thicker laminates at the source being >1 × 106 particles cm−3. Concentration of respirable fibers for dry cutting at the source ranged from 2 to 4 fibers cm−3 depending on the composite type. Further investigation is required and underway to determine the effects of various exposure determinants, such as specimen and tool geometry, on particle release and effectiveness of controls.

The mechanism of metal nanoparticle formation in plants: limits on accumulation

Abstract: Metal nanoparticles have many potential technological applications. Biological routes to the synthesis of these particles have been proposed including production by vascular plants, known as phytoextraction. While many studies have looked at metal uptake by plants, particularly with regard to phytoremediation and hyperaccumulation, few have distinguished between metal deposition and metal salt accumulation. This work describes the uptake of AgNO3, Na3Ag(S2O3)2, and Ag(NH3)2NO3 solutions by hydroponically grown Brassica juncea and the quantitative measurement of the conversion of these salts to silver metal nanoparticles. Using X-ray absorption near edge spectroscopy (XANES) to determine the metal speciation within the plants, combined with atomic absorption spectroscopy (AAS) for total Ag, the quantity of reduction of AgI to Ag0 is reported. Transmission electron microscopy (TEM) showed Ag particles of 2–35 nm. The factors controlling the amount of silver accumulated are revealed. It is found that there is a limit on the amount of metal nanoparticles that may be deposited, of about 0.35 wt.% Ag on a dry plant basis, and that higher levels of silver are obtained only by the concentration of metal salts within the plant, not by deposition of metal. The limit on metal nanoparticle accumulation, across a range of metals, is proposed to be controlled by the total reducing capacity of the plant for the reduction potential of the metal species and limited to reactions occurring at an electrochemical potential greater than 0 V (verses the standard hydrogen electrode).

Electrochemical method for the synthesis of silver nanoparticles

Abstract: The article deals with a novel electrochemical method of preparing long-lived silver nanoparticles suspended in aqueous solution as well as silver powders. The method does not involve the use of any chemical stabilising agents. The morphology of the silver nanoparticles obtained was studied using transmission electron microscopy, scanning electron microscopy, atomic force microscopy and dynamic light scattering measurements. Silver nanoparticles suspended in water solution that were produced by the present technique are nearly spherical and their size distribution lies in the range of 2 to 20 nm, the average size being about 7 nm. Silver nanoparticles synthesised by the proposed method were sufficiently stable for more than 7 years even under ambient conditions. Silver crystal growth on the surface of the cathode in the electrochemical process used was shown to result in micron-sized structures consisting of agglomerated silver nanoparticles with the sizes below 40 nm.

Crystal structure mediates mode of cell death in TiO2 nanotoxicity

Abstract: Certain properties that nanoparticles possess differentiate them from their bulk counterparts, and these characteristics must be evaluated prior to nanoparticle studies and include: size, shape, dispersion, physical and chemical properties, surface area, and surface chemistry. Early nanotoxicity studies evaluating TiO2 have yielded conflicting data which identify either size or crystal structure as the mediating property for nano-TiO2 toxicity. However, it is important to note that none of these studies examined size with the crystal structure composition controlled for or examined crystal structure while controlling the nanoparticle size. The goal of this study was to evaluate the role of size and crystal structure in TiO2 nanotoxicity while controlling for as many other nanoproperties as possible using the HEL-30 mouse keratinocyte cell line as a model for dermal exposure. In the size-dependent studies, all the nanoparticles are 100% anatase, and aggregate sizes were determined in order to take into account the effect of agglomeration on size-dependent toxicity. In addition, varying crystal structures were assessed while the size of the nanoparticles was controlled. We were able to identify that both size and crystal structure contribute to cytotoxicity and that the mechanism of cell death varies based on crystal structure. The 100% anatase TiO2 nanoparticles, regardless of size, induced cell necrosis, while the rutile TiO2 nanoparticles initiated apoptosis through formation of reactive oxygen species (ROS).

In quest of a systematic framework for unifying and defining nanoscience

Abstract: This article proposes a systematic framework for unifying and defining nanoscience based on historic first principles and step logic that led to a “central paradigm” (i.e., unifying framework) for traditional elemental/small-molecule chemistry. As such, a Nanomaterials classification roadmap is proposed, which divides all nanomatter into Category I: discrete, well-defined and Category II: statistical, undefined nanoparticles. We consider only Category I, well-defined nanoparticles which are >90% monodisperse as a function of Critical Nanoscale Design Parameters (CNDPs) defined according to: (a) size, (b) shape, (c) surface chemistry, (d) flexibility, and (e) elemental composition. Classified as either hard (H) (i.e., inorganic-based) or soft (S) (i.e., organic-based) categories, these nanoparticles were found to manifest pervasive atom mimicry features that included: (1) a dominance of zero-dimensional (0D) core–shell nanoarchitectures, (2) the ability to self-assemble or chemically bond as discrete, quantized nanounits, and (3) exhibited well-defined nanoscale valencies and stoichiometries reminiscent of atom-based elements. These discrete nanoparticle categories are referred to as hard or soft particle nanoelements. Many examples describing chemical bonding/assembly of these nanoelements have been reported in the literature. We refer to these hard:hard (H-n:H-n), soft:soft (S-n:S-n), or hard:soft (H-n:S-n) nanoelement combinations as nanocompounds. Due to their quantized features, many nanoelement and nanocompound categories are reported to exhibit well-defined nanoperiodic property patterns. These periodic property patterns are dependent on their quantized nanofeatures (CNDPs) and dramatically influence intrinsic physicochemical properties (i.e., melting points, reactivity/self-assembly, sterics, and nanoencapsulation), as well as important functional/performance properties (i.e., magnetic, photonic, electronic, and toxicologic properties). We propose this perspective as a modest first step toward more clearly defining synthetic nanochemistry as well as providing a systematic framework for unifying nanoscience. With further progress, one should anticipate the evolution of future nanoperiodic table(s) suitable for predicting important risk/benefit boundaries in the field of nanoscience.

Enhanced transport of zerovalent iron nanoparticles in saturated porous media by guar gum

Abstract: In order to ensure adequate mobility of zerovalent iron nanoparticles in natural aquifers, the use of a stabilizing agent is necessary. Polymers adsorbed on the nanoparticle surface will give rise to electrosteric stabilization and will decrease attachment to the surface soil grains. Water saturated sand-packed columns were used in this study to investigate the transport of iron nanoparticle suspensions, bare or modified with the green polymer guar gum. The suspensions were prepared at 154 mg/L particle concentration and 0.5 g/L polymer concentration. Transport experiments were conducted by varying the ionic strength, ionic composition, and approach velocity of the fluid. Nanoparticle deposition rates, attachment efficiencies, and travel distances were subsequently calculated based on the classical particle filtration theory. It was found that bare iron nanoparticles are basically immobile in sandy porous media. In contrast, guar gum is able to ensure significant nanoparticle transport at the tested conditions, regardless of the chemistry of the solution. Attachment efficiency values for guar gum-coated nanoparticles under the various conditions tested were smaller than 0.066. Although the calculated travel distances may not prove satisfactory for field application, the investigation attested the promising role of guar gum to ensure mobility of iron nanoparticles in the subsurface environment.

How interdisciplinary is nanotechnology

Abstract: Facilitating cross-disciplinary research has attracted much attention in recent years, with special concerns in nanoscience and nanotechnology. Although policy discourse has emphasized that nanotechnology is substantively integrative, some analysts have countered that it is really a loose amalgam of relatively traditional pockets of physics, chemistry, and other disciplines that interrelate only weakly. We are developing empirical measures to gauge and visualize the extent and nature of interdisciplinary interchange. Such results speak to research organization, funding, and mechanisms to bolster knowledge transfer. In this study, we address the nature of cross-disciplinary linkages using “science overlay maps” of articles, and their references, that have been categorized into subject categories. We find signs that the rate of increase in nano research is slowing, and that its composition is changing (for one, increasing chemistry-related activity). Our results suggest that nanotechnology research encompasses multiple disciplines that draw knowledge from disciplinarily diverse knowledge sources. Nano research is highly, and increasingly, integrative—but so is much of science these days. Tabulating and mapping nano research activity show a dominant core in materials sciences, broadly defined. Additional analyses and maps show that nano research draws extensively upon knowledge presented in other areas; it is not constricted within narrow silos.

Risk-based classification system of nanomaterials

Abstract: Various stakeholders are increasingly interested in the potential toxicity and other risks associated with nanomaterials throughout the different stages of a product’s life cycle (e.g., development, production, use, disposal). Risk assessment methods and tools developed and applied to chemical and biological materials may not be readily adaptable for nanomaterials because of the current uncertainty in identifying the relevant physico-chemical and biological properties that adequately describe the materials. Such uncertainty is further driven by the substantial variations in the properties of the original material due to variable manufacturing processes employed in nanomaterial production. To guide scientists and engineers in nanomaterial research and application as well as to promote the safe handling and use of these materials, we propose a decision support system for classifying nanomaterials into different risk categories. The classification system is based on a set of performance metrics that measure both the toxicity and physico-chemical characteristics of the original materials, as well as the expected environmental impacts through the product life cycle. Stochastic multicriteria acceptability analysis (SMAA-TRI), a formal decision analysis method, was used as the foundation for this task. This method allowed us to cluster various nanomaterials in different ecological risk categories based on our current knowledge of nanomaterial physico-chemical characteristics, variation in produced material, and best professional judgments. SMAA-TRI uses Monte Carlo simulations to explore all feasible values for weights, criteria measurements, and other model parameters to assess the robustness of nanomaterial grouping for risk management purposes.

Toxicity of amorphous silica nanoparticles in mouse keratinocytes

Abstract: The present study was designed to examine the uptake, localization, and the cytotoxic effects of well-dispersed amorphous silica nanoparticles in mouse keratinocytes (HEL-30). Mouse keratinocytes were exposed for 24 h to various concentrations of amorphous silica nanoparticles in homogeneous suspensions of average size distribution (30, 48, 118, and 535 nm SiO2) and then assessed for uptake and biochemical changes. Results of transmission electron microscopy revealed all sizes of silica were taken up into the cells and localized into the cytoplasm. The lactate dehydrogenase (LDH) assay shows LDH leakage was dose- and size-dependent with exposure to 30 and 48 nm nanoparticles. However, no LDH leakage was observed for either 118 or 535 nm nanoparticles. The mitochondrial viability assay (MTT) showed significant toxicity for 30 and 48 nm at high concentrations (100 μg/mL) compared to the 118 and 535 nm particles. Further studies were carried out to investigate if cellular reduced GSH and mitochondria membrane potential are involved in the mechanism of SiO2 toxicity. The redox potential of cells (GSH) was reduced significantly at concentrations of 50, 100, and 200 μg/mL at 30 nm nanoparticle exposures. However, silica nanoparticles larger than 30 nm showed no changes in GSH levels. Reactive oxygen species (ROS) formation did not show any significant change between controls and the exposed cells. In summary, amorphous silica nanoparticles below 100 nm induced cytotoxicity suggest size of the particles is critical to produce biological effects.

Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale: state-of-the-art, potential, and perspectives

Abstract: This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems and devices at the nanoscale. These techniques include spectroscopic ellipsometry, polarimetry, and reflectance anisotropy. We give an overview of the various ellipsometry strategies for the measurement and analysis of nanometric films, metal nanoparticles and nanowires, semiconductor nanocrystals, and submicron periodic structures. We show that ellipsometry is capable of more than the determination of thickness and optical properties, and it can be exploited to gain information about process control, geometry factors, anisotropy, defects, and quantum confinement effects of nanostructures.

Fabrication and characterization of iron oxide nanoparticles filled polypyrrole nanocomposites

Abstract: The effect of iron oxide nanoparticle addition on the physicochemical properties of the polypyrrole (PPy) was investigated. In the presence of iron oxide nanoparticles, PPy was observed in the form of discrete nanoparticles, not the usual network structure. PPy showed crystalline structure in the nanocomposites and pure PPy formed without iron oxide nanoparticles. PPy exhibited amorphous structure and nanoparticles were completely etched away in the nanocomposites formed with mechanical stirring over a 7-h reaction. The thermal stability of the PPy in the nanocomposites was enhanced under the thermo-gravimetric analysis (TGA). The electrical conductivity of the nanocomposites increased greatly upon the initial addition (20 wt%) of iron oxide nanoparticles. However, a higher nanoparticle loading (50 wt%) decreased the conductivity as a result of the dominance of the insulating iron oxide nanoparticles. Standard four-probe measurements indicated a three-dimensional variable-range-hopping conductivity mechanism. The magnetic properties of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic stirring was observed to have a favorable effect on the protection of iron oxide nanoparticles from dissolution in acid. A tight polymer structure surrounds the magnetic nanoparticles, as compared to a complete loss of the magnetic iron oxide nanoparticles during conventional mechanical stirring for the micron-sized iron oxide particles filled PPy composite fabrication.

From workplace air measurement results toward estimates of exposure? Development of a strategy to assess exposure to manufactured nano-objects

Abstract: In the past few years, an increasing number of studies on workplace air measurements on manufactured nano-materials and -objects have been published. Most of the studies had a more explorative character, so a direct interpretation to workers” exposure for a given exposure situation, activity, or process is not a straight-forward process. In general, the studies use a quite similar package of devices for near real-time monitoring of particle number- and mass concentration in size ranges <100 nm up to 10 μm, and the collection of samples for off-line characterization of air samples. Various approaches for addressing background concentrations and its use to indicate the potential for exposure to nano-objects could be observed. Within the EU-sponsored NANOSH project, a harmonized approach for measurement strategy, data analysis and reporting was developed. In addition to time/activity–concentration profiles as reported by most studies, this approach enables a first step to estimate the potential for exposure to manufactured nano-objects, more quantitatively. The NANOSH data will be collated into a base, which may form the starting point for a harmonized database facilitating overall analysis in near future, to derive estimates for exposure for several exposure situations.

Rheological behaviour of ethylene glycol-titanate nanotube nanofluids

Abstract: Experimental work has been performed on the rheological behaviour of ethylene glycol based nanofluids containing titanate nanotubes over 20–60 °C and a particle mass concentration of 0–8%. It is found that the nanofluids show shear-thinning behaviour particularly at particle concentrations in excess of ~2%. Temperature imposes a very strong effect on the rheological behaviour of the nanofluids with higher temperatures giving stronger shear thinning. For a given particle concentration, there exists a certain shear rate below which the viscosity increases with increasing temperature, whereas the reverse occurs above such a shear rate. The normalised high-shear viscosity with respect to the base liquid viscosity, however, is independent of temperature. Further analyses suggest that the temperature effects are due to the shear-dependence of the relative contributions to the viscosity of the Brownian diffusion and convection. The analyses also suggest that a combination of particle aggregation and particle shape effects is the mechanism for the observed high-shear rheological behaviour, which is also supported by the thermal conductivity measurements and analyses.

Comparison of four mobility particle sizers with different time resolution for stationary exposure measurements

Abstract: Exposure to airborne ultrafine and nanoparticles has raised increased interest over the recent years as they may cause adverse health effects. A common way to quantify exposure to airborne particles is to measure particle number size distributions through electrical mobility analysis. Four mobility particle sizers have been subject to a detailed intercomparison study, a TSI Fast Mobility Particle Sizer (FMPS), a Grimm Sequential Mobility Particle Sizer (SMPS+C), and two TSI Scanning Mobility Particle Sizers (SMPSs), equipped with two different condensation particle counters (CPC). The instruments were challenged with either NaCl or diesel soot particles. The results indicate that the sizing of all tested instrument was similar with only the FMPS size distributions consistently shifted toward smaller particle sizes. The Grimm SMPS generally measured higher concentrations and broader distributions than the TSI instruments. The two Grimm DMAs agreed well with each other; however, the TSI SMPS results showed a reproducible dependence on the flow rates. While TSI and Grimm SMPS delivered consistent results for sodium chloride (NaCl) and diesel soot, the FMPS seemed to react differently to the changing particle source than the SMPSs, which may be caused by either the different morphology or particle size dependent effects. For NaCl particles, the FMPS delivered the narrowest distributions and concentrations comparable with TSI SMPSs, whereas for diesel soot, it delivered the broadest distributions and higher concentrations than TSI SMPSs.

Evaluating the Control Banding Nanotool: A qualitative risk assessment method for controlling nanoparticle exposures

Abstract: Control banding (CB) strategies offer simplified processes for controlling worker exposures in the absence of firm toxicological and exposure information. The nanotechnology industry is an excellent candidate for applying such strategies with overwhelming uncertainties of work-related health risks posed by nanomaterials. A recent survey shows that a majority of nanomaterial producers are not performing a basic risk assessment of their product in use. The CB Nanotool, used internationally, was developed to conduct qualitative risk assessments to control nanoparticle exposures. Nanotoxicology experts have requested standardization of toxicological parameters to ensure better utility and consistency of research. Such standardization would fit well in the CB Nanotool’s severity and probability risk matrix, therefore enhancing the protection of nanotechnology industry workers. This article further evaluates the CB Nanotool for structure, weighting of risk factors, and utility for exposure mitigation, and suggests improvements for the CB Nanotool and the research needed to bolster its effectiveness.

Conceptual limitations and extensions of lung-deposited Nanoparticle Surface Area Monitor (NSAM)

Abstract: Nanoparticle Surface Area Monitor (NSAM, TSI model 3550 and Aerotrak 9000) is an instrument designed to measure airborne surface area concentrations that would deposit in the alveolar or tracheobronchial region of the lung. It was found that the instrument can only be reliably used for the size range of nanoparticles between 20 and 100 nm. The upper size range can be extended to 400 nm, where the minimum in the deposition curves occurs. While the fraction below 20 nm usually contributes only negligibly to the total surface area and is therefore not critical, a preseparator is needed to remove all particles above 400 nm in cases where the size distribution extends into the larger size range. Besides limitations in the particle size range, potential implications of extreme concentrations up to the coagulation limit, particle material (density and composition) and particle morphology are discussed. While concentration does not seem to pose any major constraints, the effect of different agglomerate shapes still has to be further investigated. Particle material has a noticeable impact neither on particle charging in NSAM nor on the deposition curves within the aforementioned size range, but particle hygroscopicity can cause the lung deposition curves to change significantly which currently cannot be mimicked with the instrument. Besides limitations, possible extensions are also discussed. It was found that the tendencies of the particle deposition curves of a reference worker for alveolar, tracheobronchial, total and nasal depositions share the same tendencies in the 20–400 nm size range and that their ratios are almost constant. This also seems to be the case for different individuals and under different breathing conditions. By means of appropriate calibration factors NSAM can be used to deliver the lung deposited surface area concentrations in all these regions, based on a single measurement.

Airborne nanoparticle exposures associated with the manual handling of nanoalumina and nanosilver in fume hoods

Abstract: Manual handling of nanoparticles is a fundamental task of most nanomaterial research; such handling may expose workers to ultrafine or nanoparticles. Recent studies confirm that exposures to ultrafine or nanoparticles produce adverse inflammatory responses in rodent lungs and such particles may translocate to other areas of the body, including the brain. An important method for protecting workers handling nanoparticles from exposure to airborne nanoparticles is the laboratory fume hood. Such hoods rely on the proper face velocity for optimum performance. In addition, several other hood design and operating factors can affect worker exposure. Handling experiments were performed to measure airborne particle concentration while handling nanoparticles in three fume hoods located in different buildings under a range of operating conditions. Nanoalumina and nanosilver were selected to perform handling experiments in the fume hoods. Air samples were also collected on polycarbonate membrane filters and particles were characterized by scanning electron microscopy. Handling tasks included transferring particles from beaker to beaker by spatula and by pouring. Measurement locations were the room background, the researcher’s breathing zone and upstream and downstream from the handling location. Variable factors studied included hood design, transfer method, face velocity/sash location and material types. Airborne particle concentrations measured at breathing zone locations were analyzed to characterize exposure level. Statistics were used to test the correlation between data. The test results found that the handling of dry powders consisting of nano-sized particles inside laboratory fume hoods can result in a significant release of airborne nanoparticles from the fume hood into the laboratory environment and the researcher’s breathing zone. Many variables were found to affect the extent of particle release including hood design, hood operation (sash height, face velocity), work practices, type and quantity of the material being handled, room conditions, and the adequacy of the room exhaust.

ICP-MS: a powerful technique for quantitative determination of gold nanoparticles without previous dissolving

Abstract: A direct and simple inductively coupled plasma mass spectroscopy (ICP-MS) method for the determination of gold nanoparticles (AuNP) with different particle sizes ranging from 5 to 20 nm and suspended in aqueous solutions is described. The results show no significant difference compared to the determination of the same AuNPs after digestion, as claimed by the literature. The obtained limit of quantification of the method is 0.15 μg/L Au(III) that corresponds to 4.40 × 109 AuNP/L, considering spherical AuNPs 15 nm sized. Spike recovery experiments have shown that the sample matrix is a significant factor influencing the accuracy of the measurement. Spike recoveries from 93% to 95% are found for AuNP samples prepared in trisodium citrate, while for deionized H2O a spike recovery of around 80% was obtained. The sample preparation mode along with the ICP-MS parameters have been optimized and found to be crucial so as to achieve the required accuracy for the direct quantification of AuNP suspensions. The effect of the nanoparticle size upon the ICP-MS signal also was studied, and only significant differences due to the chemical environment and not to the AuNPs size were found.

A novel approach to metal and metal oxide nanoparticle synthesis: the oil-in-water microemulsion reaction method

Abstract: A novel and straightforward approach, based on oil-in-water (o/w) microemulsions, was developed for the synthesis of inorganic nanoparticles at ambient conditions It implies the use of organometallic precursors dissolved in nanometre-scale oil droplets of o/w microemulsions Addition of reducing or oxidizing/precipitating agents results in the formation of metallic or metal oxide nanoparticles, respectively Nonionic o/w microemulsion systems were chosen, and several key compositions were selected for nanoparticle synthesis at 25 °C High Resolution Electron Microscopy revealed that small nanoparticles of metals (Pt, Pd and Rh) and nanocrystalline metal oxide (cerium (IV) oxide with cubic type crystalline structure confirmed by XRD), of less than 7 nm can be obtained in mild conditions

Neurotoxicity of low-dose repeatedly intranasal instillation of nano- and submicron-sized ferric oxide particles in mice

Abstract: Olfactory tract has been demonstrated to be an important portal for inhaled solid nanoparticle transportation into the central nervous system (CNS). We have previously demonstrated that intranasally instilled Fe2O3 nanoparticles could transport into the CNS via olfactory pathway. In this study, we investigated the neurotoxicity and size effect of repeatedly low-dose (130 μg) intranasal exposure of nano- and submicron-sized Fe2O3 particles (21 nm and 280 nm) to mice. The biomarkers of oxidative stress, activity of nitric oxide synthases and release of monoamine neurotransmitter in the brain were studied. Our results showed that significant oxidative stress was induced by the two sizes of Fe2O3 particles. The activities of GSH-Px, Cu,Zn-SOD, and cNOS significantly elevated and the total GSH and GSH/GSSG ratio significantly decreased in the olfactory bulb and hippocampus after the nano- and submicron-sized Fe2O3 particle treatment (p < 0.05). The nano-sized Fe2O3 generally induced greater alteration and more significant dose–effect response than the submicron-sized particle did. Some slight perturbation of monoamine neurotransmitters were found in the hippocampus after exposure to the two sizes of Fe2O3 particle. The TEM image showed that some ultrastructural alterations in nerve cells, including neurodendron degeneration, membranous structure disruption and lysosome increase in the olfactory bulb, slight dilation in the rough endoplasmic reticulum and lysosome increase in the hippocampus were induced by the nano-sized Fe2O3 treatment. In contrast, in the submicron-sized Fe2O3 treated mice, slightly swollen mitochondria and some vacuoles were observed in the olfactory bulb and hippocampus, respectively. These results indicate that intranasal exposure of Fe2O3 nanoparticles could induce more severe oxidative stress and nerve cell damage in the brain than the larger particle did. This is the first study to compare the neurotoxicity of nano- and submicron-sized Fe2O3 particles in the central nervous system after long-term and low-dose intranasal exposure.

Impact and structure of literature on nanoparticle generation by laser ablation in liquids

Abstract: The number of publications on laser ablation and nanoparticle generation in liquids increased by the factor of 15 in the last decade, with comparable high impact of the most cited articles in this field. A nearly unlimited variety of nanoparticle material, liquid matrix, and conjugative agent can be combined to a huge variety of colloids within a few minutes of laser processing. However, this diversification makes it hard to identify main research directions without a comprehensive literature overview. This investigation evaluates the impact and structure of the literature in this field tagging most prolific subjects and articles. Using an optimized search algorithm, the data sets derived from Science Citation Index (1998–2008) allow for statements on publication subject clusters, impact of articles and journals, as well as mapping global spots of activities.

Respiratory protection against airborne nanoparticles: a review

Abstract: As a precautionary measure, it is often recommended that workers take steps to reduce their exposure to airborne nanoparticles through the use of respiratory protective devices. The purpose of this study was to provide a review and analysis of the research literature and current recommendations on respirators used for protection against nanoparticles. Key research findings were that studies with particles as small as 4 nm have shown that conventional single-fiber filtration theory can be used to describe the filtration performance of respirators and that the most penetrating particle size for respirators equipped with commonly used electrostatic filter media is in the range of 30-100 nm. Future research needs include human laboratory and workplace protection factor studies to measure the respirator total inward leakage of nanoparticles. Industrial hygienists and safety professionals should continue to use traditional respirator selection guidance for workers exposed to nanoparticles.