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In the last decade the utilization of silver nanoparticles in consumer related products is strongly enhanced. Therefore, many studies focus on investigations regarding their toxicological potential. This includes investigations concerning uptake, distribution and excretion of the particles. However, little attention was paid to changes of physical and chemical properties of the particles in the human body. A major question is if the particles are size and shape persistent and can survive the digestion process. 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. We synthesized poly(acrylic acid) stabilized ultra-small silver nanoparticles with a radius of 3.1 nm and a size distribution width of 20%. The artificial digestion process mimics the gastro-intestinal passage and simulates the oral, gastric and small intestinal conditions. Additionally, we used as food components oil, starch, skimmed milk powder and mixture thereof to provide a preferably realistic environment. Large aggregates of up to 56 nm were determined in the absence of food additives. In contrast, the presence of oil and starch limit the radii of aggregates to about 10 nm. Only small aggregates of 6 nm radii were found in the presence of milk powder. It prevents primary particles from etching in the intestinal juice. Our results indicate that the silver nanoparticles can pass the digestion process in a nanoscale form but undergo a strong and food-dependent transformation in their state of aggregation.
Creating the Silver Standard: Development of a Silver Nanoparticle Reference Material using SAXS
(2017)
The utilization 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 high variety of products, which ranges from food containers over children toys and textiles. Therefore, research on the toxicological potential of 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 use of a wide range of silver nanoparticles, which show a broad size distribution. To overcome this problem we report on the synthesis of ultra-small silver nanoparticles and their quantitative characterization by small-angle X-ray scattering. The particles are highly stable and show no aggregation for more than six months. SAXS analysis via a Monte Carlo data evaluation procedure reveal a narrow size distribution of the silver cores with a mean volume weighted radius of 3.0 nm and a distribution width of 0.6 nm. Dynamic light scattering provides a hydrodynamic radius of 10.0 nm and a PDI of 0.09. The particles are stabilized with poly(acrylic acid) (PAA) forming a shell with a thickness of 7.0 nm. It is foreseen to use these thoroughly characterized particles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. As a first step the particles are used in the first world-wide inter-laboratory comparison of SAXS. This study reveals that SAXS shows highly reproducible results for particles in the sub-20 nm region independently on the type of instrument used. Furthermore, 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. With this flexible system first applications regarding biological application in an artificial digestion procedure have been performed. Thereby the changes in size distribution and aggregation state were monitored by SAXS.