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Excelling in brevity but lacking in applicability, the 2011 EU nanomaterial definition has become a source of anguish for scientists and industry alike. Repeated pleas and discussions with our own envoy have demonstrated the strength of their resolve: this definition is unlikely to change. Manufacturers of many materials (cosmetics, pigments, foodstuffs, etc.) will have to characterise and label all their products accordingly, a task still impossible for lack of a clear metrological approach towards this goal. Therefore, the onus has fallen on the scientists to come up with a practicable measurement technique allowing inexpensive classification covering large swathes of the material landscape. Small-angle X-ray Scattering (SAXS) probes the size range in question, and can - with due care - deliver a bulk-averaged volume-weighted size distribution. Like any other real-world measurement method, however, it is not (and can never be) a universal solution. This presentation will clarify the SAXS technique, provide several application examples for nanomaterial characterisation, and will detail the limitations and pitfalls that accompany its abilities. At the end of this presentation, you will have the information to judge whether the technique is amenable to your materials or not.
Although aluminium is one of the most common elements in the biosphere, up to now little is known about its impact on human health. aluminium and its chemical derivatives are highly abundant in food, food contact materials and consumer products. Humans are exposed to aluminium via the gastrointestinal tract (GI tract). Exposition can change substantially due to consumer behavior since aluminium is also a compound of numerous food additives. Recently, aluminium exposition is increasingly considered to cohere with cancer and neurodegenerative disorders. Lately, due to an increasing attentiveness on this topic, limiting values for food additives have been tightened by the EFSA. However, cellular effects of aluminium and especially aluminium-containing nanomaterials, that represent a significant part of chemicals found in food products, are widely unknown and in the focus of our research activities, for example in the bilateral SolNanoTOX project. We established an in vitro simulation system of the GI tract, where nanomaterials undergo the different physiological, chemical and proteinbiochemical conditions of saliva, gastric juice and the intestine. The artificially digested nanomaterials, as well as soluble aluminium chloride as ionic control substance, were subjected to several analytical and biochemical methods to characterize their change of appearance and their cytotoxic effects on intestinal cellular models. We observed the fate of the nanomaterials during typical pH-values of saliva, gastric and intestinal juice with Dynamic light scattering measurements and ICP-MS in the single particle mode. After observable disappearance at pH 2 the particles recovered in the simulated intestinal fluid. The simulation of the GI tract, mainly the change of pH settings, can lead to a certain chemical activation of aluminium that can increase bioavailability in the intestine after oral uptake of aluminium-containing food products. In vitro assays like CTB, MTT and cellular impedance measurements showed that there were no acute cytotoxic effects measurable after a period up to 48h after incubation, comparable to undigested particles. In contrast, high amounts of aluminium ions showed synergistic effects on cell viability compared to non-digested aluminium ions. Although toxicological potential of Al ions to healthy tissue appears to be low, increased hazardous potential cannot be ruled out to pre-damaged tissue and can have a relevance in risk assessment for special consumer groups with for example chronical intestinal inflammation or dietary eating behavior combined with high exposure to Al-containing food products.
Aluminium and its chemical derivatives are highly abundant in food, food contact materials and consumer products. Up to now little is known about its derivatization and uptake during digestion and its impact on human health. As part of the SolNanoTOX project, different aluminium species were investigated during an artificial digestion process that mimics the saliva, the stomach and the intestine regarding pH-values, duration time, chemical environment and enzymatic composition.
Two different nanomaterials (Al, Al2O3) and a soluble ionic AlCl3 control were digested and investigated by different analytical methods regarding core radius, hydrodynamic diameter, agglomeration and dissolution behavior in biological media.
The fate of nanoparticles during typical pH-values of saliva, gastric and intestinal juice was studied with dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and ICP-MS in the single particle mode. After disappearance at pH 2 the nanoparticles were detected again in the intestinal fluid, as measured by DLS. During all artificial digestion stages Al nanoparticles had a constant average SAXS radius. In contrast, the radii of Al2O3 nanoparticles changed concentration-dependently. Highest radii were observed in the stomach fluid while intestinal fluid was found to cause full recovery of the primary particles. Dissolution of digested nanoparticles in cell culture media showed a bimodal size distribution of primary particles and aggregates.
In summary, simulation of the gastrointestinal tract, mainly the change of pH settings, has provided evidence that the bioavailability of Al is likely to increase during the passage of the gut after oral uptake of aluminium-containing food products.
In the last decade the utilization of silver nanoparticles in consumer related products is enhanced. Therefore, many studies focus on investigations regarding their toxicological potential. This includes investigations concerning uptake, distribution and excretion of the particles. So far, little attention was paid to changes of physical and chemical properties in the human body. During processes like digestion, the question arises whether they can pass this barrier in a nanoscale form. In this study we analytically monitored the changes in the size distribution of colloidal silver during an artificial digestion process with the help of small angle x-ray scattering (SAXS). Therefore, we synthesized polyacrylic acid stabilized ultra-small silver nanoparticles with a radius of 3 nm and a size distribution width of 18%. The artificial digestion process mimics the gastro-intestinal passage and simulates the oral, gastric and small intestinal conditions. Additionally, food components like oil, starch, glucose and skimmed milk powder are used to provide a preferably realistic environment.
In absence of any food components the low pH initiates aggregation of the particles in the stomach. However, the particles unexpectedly stabilize in a defined cluster form with a mean radius of 12 nm. By the use of the food components oil and starch we observed that the particles are dispersed again. Now we found a bimodal size distribution of primary particles and aggregates. In contrast to that, with skimmed milk powder only a slight aggregation occurs in the stomach. In the gastric tract the particle distribution is stabilized at a mean volume weighted radius of 5 nm. Hence, skimmed milk powder acts as a colloidal stabilizer. For comparison we also used silver nitrate as a control substance. Surprisingly, we observed a formation of nanoparticles already in the saliva. During the digestion process the distribution narrows and finally in the intestine it shows a stable distribution with a mean volume weighted radius of 3 nm and a small fraction of aggregates. These results indicate that the silver nanoparticles can pass the digestion process in a nanoscale form but undergo a transformation in the size distribution. However, even from pure silver nitrate nanoparticle formation can be observed. This sketches a complex mechanism in which not only food components but also silver ions cause changes in nanoparticle size and aggregation.
Cellular effects of Al-, Ti- and Zn-containing nanomaterials on intestinal cell lines in vitro
(2016)
Aluminium-, titanium- and zinc-containing chemicals are highly abundant in food, food contact materials and consumer products. Physical and chemical conversion might lead to a certain amount of nanoscaled particles that can be taken up by the gastrointestinal tract. Nanospecific effects such as higher reactivity, increased surface or altered uptake can increase hazardous potential for human health. The aim of this study as part of the european SolNanoTOX project is to characterize toxicological effects of Al-, Zn- and Ti-containing nanomaterials on intestinal cell lines.
While toxicological potential of zinc species has been well studied, little is known about the effects of aluminium- and titanium-species. We have performed toxicological experiments on the human intestinal cell line Caco-2 for numerous endpoints: Cellular ATP and glutathione levels, apoptosis, necrosis, vesicular uptake, oxidative stress, growth rate and cell cycle modification. While zinc-containing controls showed toxic responses, our utilized aluminium- (elementary Al, γ-Al2O3) and titanium-species (TiO2, rutile) did not. Nevertheless, we detected some differences between both different aluminium nanoparticle species and aluminium ions with regard to cell viability. We also provide strong evidence for particle-specific uptake of aluminium and titanium in the intestinal cell line Caco-2.
In summary, among the different tested endpoints, Al- and Ti-containing nanomaterials did not show any toxicity in intestinal cell lines in vitro. Nevertheless, this absence of effect was not due to an absence of exposure, since particle-specific uptake was reported. Metal particle uptake over a long time might therefore be relevant for risk assessment of aluminium- and titanium-containing food products.
Core or coating material – What dictates the uptake and translocation of nanoparticles in vitro?
(2016)
Nanoparticle size and shape are crucial parameters regarding the potential of nanoparticles to penetrate cell membranes and epithelial barriers. Current research in this field additionally focuses on the particle coating material. In order to distinguish between core- and coating-related effects in nanoparticle uptake and translocation behavior, this study investigated two nanoparticles equal in size, coating and charge but different in core material.
Silver and iron oxide coated with poly (acrylic acid) (PAS) were extensively characterized by TEM (transmission electron microscopy), SAXS (Small-Angle X-ray Scattering), ZetasizerTM and NanoSightTM. For uptake and transport studies the widely used human intestinal Caco-2 model in a TranswellTM-system with subsequent elemental analysis (AAS) was used. For evaluation and particle visualization transmission electron microscopy (TEM) and Ion Beam Microscopy (IBM) were conducted.
Although similar in size, charge and coating material, the behavior of particles in Caco-2 cells was quite different. The internalized amount was comparable, but PAA-coated iron oxide nanoparticles were additionally transported through the cells. By contrast, PAA-coated silver nanoparticles remained in the cells. Our findings suggest that the coating material influenced only the uptake of the nanoparticles whereas the translocation was determined by the core material.
In summary, a core-dependent effect on nanoparticle translocation was revealed. Both the uptake and transport of nanoparticles in and through cells should be considered when discussing nanoparticle fate and safety.
The use of silver nanoparticles in consumer related products has significantly increased over the last decade, especially due to their antimicrobial properties. Today they are used in a variety of products, which range from textiles over children toys and dietary supplements. Therefore, research on silver in a nanoscale form becomes increasingly important for a high amount of studies. Unfortunately the results of these studies are extremely diverse and do not lead to a consistent evaluation of the toxicity of silver nanoparticles. The central problem lies in the utilization of a wide range of silver nanoparticles, which show a broad size distribution. To overcome this problem we synthesized ultra-small core-shell silver nanoparticles by an up-scaled modification of the polyol process. The particles are highly stable and show no aggregation for more than six months. Small-angle X-ray scattering (SAXS) analysis reveal a narrow size distribution of the silver cores with a mean radius of RC = 3.0 nm and a distribution width of 0.6 nm. Dynamic light scattering (DLS) provides a hydrodynamic radius of RH = 10.0 nm and a PDI of 0.09. The surface of the particles is covered with poly(acrylic acid) (PAA) forming a shell with a thickness of 7.0 nm, which provides colloidal stability lasting for more than six months at ambient conditions. It is foreseen to use these thoroughly characterized particles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. The stabilizing ligand PAA can be easily exchanged by biomolecules to modify the surface functionality. Replacements of PAA with glutathione (GSH) and bovine serum albumin (BSA) have been performed as examples. We demonstrate that the particles effectively catalyze the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride. With PAA as stabilizer, the catalytic activity of (436 ± 24) L g-1 s-1 is the highest reported in literature for silver nanoparticles. GSH and BSA passivate the surface substantially resulting in lower catalytic activities of (77.6 ± 0.9) L g-1 s-1 and (3.47 ± 0.50) L g-1 s-1, respectively. The ultra-small particles were already used in the Nano Define project. Due to their small size it is possible to investigate the detection limits of different analytical techniques like electron microcopy, field flow fractionation or single particle tracking. In this project they serve as the calibration standard with the smallest radius.
Tracking silver nanoparticles: ultra-small silver refunctionalizable with fluorescent biopolymers
(2016)
We report on the synthesis of ultra-small silver nanoparticles and their quantitative characterization by small-angle X-ray scattering. The size distribution was derived by utilizing a Monte-Carlo data evaluation procedure reported by Pauw et al. Mean volume-weighted sizes are 3 nm with a size distribution width of 18 %. The particles should be used as reference materials for comparison of the result of different analytical methods among which are field-flow fractionation (FFF), dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and electron microscopy (EM). In addition further use of the particles is foreseen for comparison of studies on the toxicology of nanoparticles. Therefore the silver nanoparticles are transfunctionalized with fluorescent marked albumin (BSA-FITC) and also thoroughly characterized. With this it is possible to track silver nanoparticles and their behavior in interaction with cells.
Nanoscience, SAXS and you
(2017)