Presence and risks of nanosilica in food products

Presence of nano-sized silica during in vitro digestion of foods containing silica as a food additive

The presence, dissolution, agglomeration state, and release of materials in the nano-size range from food containing engineered nanoparticles during human digestion is a key question for the safety assessment of these materials. We used an in vitro model to mimic the human digestion. Food products subjected to in vitro digestion included (i) hot water, (ii) coffee with powdered creamer, (iii) instant soup, and (iv) pancake which either contained silica as the food additive E551, or to which a form of synthetic amorphous silica or 32 nm SiO(2) particles were added. The results showed that, in the mouth stage of the digestion, nano-sized silica particles with a size range of 5-50 and 50-500 nm were present in food products containing E551 or added synthetic amorphous silica. However, during the successive gastric digestion stage, this nano-sized silica was no longer present for the food matrices coffee and instant soup, while low amounts were found for pancakes. Additional experiments showed that the absence of nano-sized silica in the gastric stage can be contributed to an effect of low pH combined with high electrolyte concentrations in the gastric digestion stage. Large silica agglomerates are formed under these conditions as determined by DLS and SEM experiments and explained theoretically by the extended DLVO theory. Importantly, in the subsequent intestinal digestion stage, the nano-sized silica particles reappeared again, even in amounts higher than in the saliva (mouth) digestion stage. These findings suggest that, upon consumption of foods containing E551, the gut epithelium is most likely exposed to nano-sized silica.

Quantification of nanoparticles in aqueous food matrices using Particle-Induced X-ray Emission

Nanoparticles (NPs) of SiO(2) (15 nm) or Ag (20 - 40 nm) were dispersed in water, coffee and milk at several aqueous dilutions. The NPs dispersions concentrations were quantified with an ion beam technique: Particle-Induced X-ray Emission. Additional measurements in relation to the state of the NPs dispersions were done: particle size distribution by centrifuge liquid sedimentation and the extreme surface composition by X-ray photoelectron spectroscopy. The particle size distribution of SiO(2) and Ag NPs dispersions in water and Ag NPs in coffee remained mostly as primary particles with hydrodynamic diameters close to the reported pristine NPs diameter. SiO(2) NPs agglomerated in coffee. In milk, both NPs presented an adsorption with milk lipids. Extreme surface composition corroborated adsorption in milk and showed that SiO(2) agglomerates adsorb some coffee components. A linear tendency in the measurement of the concentration dilutions of all dispersions was measured, and a lack of media influence in the slope of each curve was found. Limits of detection with the current setup were estimated at 0.5 and 0.3 mg/ml for SiO(2) and Ag NPs, respectively.

STED microscopy and its applications: new insights into cellular processes on the nanoscale

For about a decade, superresolution fluorescence microscopy has been advancing steadily, maturing from the proof-of-principle stage to routine application. Of the various techniques, STED (stimulated emission depletion) microscopy was the first to break the diffraction barrier. Today, it is a prominent and versatile form of superresolution light microscopy. STED microscopy has shed a sharper light on numerous topics in cell biology, but also in material sciences. Both disciplines extend into the nanometer range, making detailed studies of structural and functional relationships difficult or even impossible to achieve using diffraction-limited microscopy. With recent advancements like spectral multiplexing or live-cell imaging, STED microscopy makes nanoscale materials and components of the cell accessible for fluorescence-based investigations. With multicolor superresolution imaging, even the interactions between biological and engineered nanostructures can be studied in detail. This review gives an introduction into the working principle of STED microscopy, provides a detailed overview of recent advancements and new techniques implemented for use with STED microscopy and shows how these have been applied in the life sciences and nanotechnologies.

Characterization of translocation of silver nanoparticles and effects on whole-genome gene expression using an in vitro intestinal epithelium coculture model

Applications of nanoparticles in the food sector are eminent. Silver nanoparticles are among the most frequently used, making consumer exposure to silver nanoparticles inevitable. Information about uptake through the intestines and possible toxic effects of silver nanoparticles is therefore very important but still lacking. In the present study, we used an in vitro model for the human intestinal epithelium consisting of Caco-2 and M-cells to study the passage of silver nanoparticles and their ionic equivalents and to assess their effects on whole-genome mRNA expression. This in vitro intestine model was exposed to four sizes of silver nanoparticles for 4 h. Exposure to silver ions was included as a control since 6-17% of the silver nanoparticles were found to be dissociated into silver ions. The amount of silver ions that passed the Caco-2 cell barrier was equal for the silver ion and nanoparticle exposures. The nanoparticles induced clear changes in gene expression in a range of stress responses including oxidative stress, endoplasmatic stress response, and apoptosis. The gene expression response to silver nanoparticles, however, was very similar to that of AgNO(3). Therefore, the observed effects of the silver nanoparticles are likely exerted by the silver ions that are released from the nanoparticles.