X-ray photoelectron spectroscopy of metal oxide nanoparticles: chemical composition, oxidation state and functional group content.

Surface chemistry drives the interaction of a material with its surroundings, therefore it can be used to understand and influence the fate of nanomaterials when used as functional materials or when released to the environment. Here we have used X-ray photoelectron spectroscopy (XPS) to probe the chemical composition, oxidation state and functional group content of the near surface region of four families of commercially available metal oxide nanoparticles from several different suppliers. The analyzed nanoparticles varied in size and surface functionalization (unfunctionalized amine, stearic acid, and PVP-coated samples).

Titanium dioxide nanoparticles - physicochemical characterization and cytotoxic risk.

Titanium dioxide (TiO) nanoparticles (NPs) are incorporated into numerous consumer products yet data as to potential adverse health effects remains inconclusive. In this paper we physically characterize 16 nanoforms of TiO from different manufacturers of different size, crystalline structure and surface chemistry. Physical measurements of the particles were performed and compared with those provided by manufacturers revealing several discrepancies.

Cellulose nanomaterial metrology: microscopy measurements.

Cellulose nanomaterials are increasingly used for a wide variety of applications. Adequate characterization of these materials is required for quality control during production, to distinguish between materials synthesized by different methods, by different suppliers or from difference cellulose biomass sources, to facilitate development of applications and for regulatory purposes. Here we review recent microscopy measurements for the three main types of cellulose nanomaterials: cellulose nanocrystals, individual cellulose nanofibrils and cellulose nanofibrils.

Characterization and Cellular Toxicity Studies of Commercial Manganese Oxide Nanoparticles.

Manganese oxide nanoparticles (MnO NPs) are finding applications in several environmentally important areas such as farming and energy storage. MnO NPs span a range of metal oxidation states that open up a wide range of applications in catalysis as well. As a result, it is important to understand how such materials can impact human health through incidental exposure.

Physical Characterization and Cellular Toxicity Studies of Commercial NiO Nanoparticles.

Nickel oxide (NiO) nanoparticles from several manufacturers with different reported sizes and surface coatings were characterized prior to assessing their cellular toxicity. The physical characterization of these particles revealed that sizes often varied from those reported by the supplier, and that particles were heavily agglomerated when dispersed in water, resulting in a smaller surface area and larger hydrodynamic diameter upon dispersion. Cytotoxicity testing of these materials showed differences between samples; however, correlation of these differences with the physical properties of the materials was not conclusive.

Surface chemistry of metal oxide nanoparticles: NMR and TGA quantification.

Surface functionalization is widely used to control the behavior of nanomaterials for a range of applications. However, methods to accurately quantify surface functional groups and coatings are not yet routinely applied to nanomaterial characterization. We have employed a combination of quantitative NMR (qNMR) and thermogravimetric analysis (TGA) to address this problem for commercial cerium, nickel, and iron oxide nanoparticles (NPs) that have been modified to add functional coatings with (3-aminopropyl)triethoxysilane (APTES), stearic acid, and polyvinylpyrrolidone (PVP).

Interlaboratory Comparison on the Quantification of Total and Accessible Amine Groups on Silica Nanoparticles with qNMR and Optical Assays.

Risk assessment of nanomaterials requires not only standardized toxicity studies but also validated methods for nanomaterial surface characterization with known uncertainties. In this context, a first bilateral interlaboratory comparison on surface group quantification of nanomaterials is presented that assesses different reporter-free and labeling methods for the quantification of the total and accessible number of amine functionalities on commercially available silica nanoparticles that are widely used in the life sciences. The overall goal of this comparison is the identification of optimum methods as well as achievable measurement uncertainties and the comparability of the results across laboratories.

Comprehensive framework for human health risk assessment of nanopesticides.

Nanopesticides are not only in an advanced state of research and development but have started to appear on the market. Industry and regulatory agencies need a consolidated and comprehensive framework and guidance for human health risk assessments. In this perspective we develop such a comprehensive framework by exploring two case studies from relevant product types: an active ingredient delivered with a nanocarrier system, and a nanoparticle as an active ingredient.

Characterization of Commercial Metal Oxide Nanomaterials: Crystalline Phase, Particle Size and Specific Surface Area.

Physical chemical characterization of nanomaterials is critical to assessing quality control during production, evaluating the impact of material properties on human health and the environment, and developing regulatory frameworks for their use. We have investigated a set of 29 nanomaterials from four metal oxide families (aluminum, copper, titanium and zinc) with a focus on the measurands that are important for the basic characterization of dry nanomaterials and the determination of the dose metrics for nanotoxicology. These include crystalline phase and crystallite size, measured by powder X-ray diffraction, particle shape and size distributions from transmission electron microscopy, and specific surface area, measured by gas adsorption.

Particle Size Distributions for Cellulose Nanocrystals Measured by Transmission Electron Microscopy: An Interlaboratory Comparison.

Particle size is a key parameter that must be measured to ensure reproducible production of cellulose nanocrystals (CNCs) and to achieve reliable performance metrics for specific CNC applications. Nevertheless, size measurements for CNCs are challenging due to their broad size distribution, irregular rod-shaped particles, and propensity to aggregate and agglomerate. We report an interlaboratory comparison (ILC) that tests transmission electron microscopy (TEM) protocols for image acquisition and analysis.

Acellular oxidative potential assay for screening of amorphous silica nanoparticles.

Silica nanoparticles (SiNPs) are used in a wide range of consumer products, engineering and medical applications, with likelihood of human exposure and potential health concerns. It is essential to generate toxicity information on SiNP forms and associated physicochemical determinants to conduct risk assessment on these new materials. To address this knowledge gap, we screened a panel of custom synthesized, well-characterized amorphous SiNPs pristine and surface-modified (-C3-COOH, -C11-COOH, -NH, -PEG) of 5 different sizes: (15, 30, 50, 75, 100 nm) for their oxidative potential using an acellular assay.

A Multi-Method Approach for Quantification of Surface Coatings on Commercial Zinc Oxide Nanomaterials.

Surface functionalization is a key factor for determining the performance of nanomaterials in a range of applications and their fate when released to the environment. Nevertheless, it is still relatively rare that surface groups or coatings are quantified using methods that have been carefully optimized and validated with a multi-method approach. We have quantified the surface groups on a set of commercial ZnO nanoparticles modified with three different reagents ((3-aminopropyl)-triethoxysilane, caprylsilane and stearic acid).

Quantification of surface functional groups on silica nanoparticles: comparison of thermogravimetric analysis and quantitative NMR.

Thermogravimetric analysis (TGA) coupled with evolved gas analysis-FT-IR has been examined as a potential method to study the functional group content for surface modified silica nanoparticles. A comparison with a quantitative solution NMR method based on analysis of groups released after dissolution of the silica matrix is used to provide benchmark data for comparison and to assess the utility and limitations of TGA. This study focused primarily on commercially available silicas and tested whether it was possible to use a correction based on bare silica to account for the significant mass loss that occurs due to condensation of surface hydroxyl groups and loss of matrix-entrapped components at temperatures above ∼200 °C.

Characterization of Size and Aggregation for Cellulose Nanocrystal Dispersions Separated by Asymmetrical-Flow Field-Flow Fractionation.

Cellulose nanocrystals (CNCs) derived from various types of cellulose biomass have significant potential for applications that take advantage of their availability from renewable natural resources and their high mechanical strength, biocompatibility and ease of modification. However, their high polydispersity and irregular rod-like shape present challenges for the quantitative dimensional determinations that are required for quality control of CNC production processes. Here we have fractionated a CNC certified reference material using a previously reported asymmetrical-flow field-flow fractionation (AF4) method and characterized selected fractions by atomic force microscopy (AFM) and transmission electron microscopy.

Quantification and Stability Determination of Surface Amine Groups on Silica Nanoparticles Using Solution NMR.

Surface chemistry is a critical factor for determining the behavior of a nanomaterial after incorporation in composites, devices, and biomedical products, and is also important for nanotoxicology studies. We have developed an optimized protocol for dissolution of aminated silicas and determination of functional-group contents by quantitative H NMR (qNMR) analysis of the released amines. A number of variables were optimized for the dissolution protocol, including the base concentration, mass of silica, time, temperature, and method of sample agitation, in order to achieve adequate NMR signals for quantification.

Ensemble and Single Particle Fluorescence Characterization of Dye-Labeled Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) have been covalently labeled with both fluorescein and rhodamine and studied by a combination of UV-vis absorption spectroscopy and ensemble and single molecule fluorescence spectroscopy. For all samples, the fluorescence anisotropy and lifetimes were consistent with effects expected for covalently bound dye molecules. Low dye loading levels (∼0.

Interaction of saponin 1688 with phase separated lipid bilayers.

Saponins are a diverse family of naturally occurring plant triterpene or steroid glycosides that have a wide range of biological activities. They have been shown to permeabilize membranes and in some cases membrane disruption has been hypothesized to involve saponin/cholesterol complexes. We have examined the interaction of steroidal saponin 1688-1 with lipid membranes that contain cholesterol and have a mixture of liquid-ordered (L) and liquid-disordered (L) phases as a model for lipid rafts in cellular membranes.

Correlating Cellulose Nanocrystal Particle Size and Surface Area.

Cellulose nanocrystals (CNCs) are negatively charged nanorods that present challenges for characterization of particle size distribution and surface area-two of the common parameters for characterizing nanomaterials. CNC size distributions have been measured by two microscopy methods: atomic force microscopy (AFM) and transmission electron microscopy (TEM). The agreement between the two methods is good for length measurements, after taking into consideration tip-convolution effects for AFM.

Synthesis and photochemical properties of PEGylated coumarin-caged ceramides for cell studies.

Caged ceramide analogues (C6-, C16-, C18-, C22- and C24-Cer) have been prepared by introducing a hydrophilic coumarin-based cage bearing a short polyethylene glycol (PEG) chain. (6-Bromo-7-mTEGylated-coumarin-4-yl)methyl (Btc) caged ceramide showed efficient photo-uncaging to release the parent ceramide upon direct exposure to 350 nm UV light; in contrast (7-mTEGylated-coumarin-4-yl)methyl (Tc) caged ceramide was photolysed more slowly. In preliminary experiments, Btc-caged ceramides were taken up by cells and their photolysis led to decreases in cell viability, but not to activation of caspase enzymes, suggesting that either reactive oxygen species or an alternate caspase-independent pathway may be responsible for the decreases in cell viability caused by photolysis of caged ceramides.

Membrane order parameters for interdigitated lipid bilayers measured via polarized total-internal-reflection fluorescence microscopy.

Incorporating ethanol in lipid membranes leads to changes in bilayer structure, including the formation of an interdigitated phase. We have used polarized total-internal-reflection fluorescence microscopy (pTIRFM) to measure the order parameter for Texas Red DHPE incorporated in the ethanol-induced interdigitated phase (LβI) formed from ternary lipid mixtures comprising dioleoylphosphatidylcholine, cholesterol and egg sphingomyelin or dipalmitoylphosphatidylcholine. These lipid mixtures have 3 co-existing phases in the presence of ethanol: liquid-ordered, liquid-disordered and LβI.

Changes in order parameters associated with ceramide-mediated membrane reorganization measured using pTIRFM.

The enzymatic generation of ceramide has significant effects on the biophysical properties of lipid bilayers and can lead to the extensive reorganization of cell membranes. We have synthesized and characterized a headgroup-labeled fluorescent lipid probe (NBD-ceramide, NBD-Cer) and demonstrated that it can be used for polarized total internal reflection fluorescence microscopy experiments to probe changes in membrane order that result from ceramide incorporation. NBD-Cer measures significantly higher order parameters for the liquid-ordered (Lo) domains ([P2] = 0.

Force spectroscopy measurements show that cortical neurons exposed to excitotoxic agonists stiffen before showing evidence of bleb damage.

In ischemic and traumatic brain injury, hyperactivated glutamate (N-methyl-D-aspartic acid, NMDA) and sodium (Nav) channels trigger excitotoxic neuron death. Na(+), Ca(++) and H2O influx into affected neurons elicits swelling (increased cell volume) and pathological blebbing (disassociation of the plasma membrane's bilayer from its spectrin-actomyosin matrix). Though usually conflated in injured tissue, cell swelling and blebbing are distinct processes.

Lipid Phase Separation and Protein-Ganglioside Clustering in Supported Bilayers Are Induced by Photorelease of Ceramide.

Photolysis of 6-bromo-7-hydroxycoumarinyl-caged ceramide was used to generate ceramide with spatial and temporal control in supported lipid bilayers prepared from mixtures of caged ceramide and phospholipids. The caged ceramide molecules are randomly distributed in fluid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers, and upon photolysis with long wavelength UV light small ordered ceramide domains are formed that phase separate from the bulk fluid membrane. Irradiation of a spatially restricted area leads to the transient formation of ceramide-enriched gel phase domains that equilibrate via lipid diffusion with the surrounding unirradiated membrane.