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NANOTECHNOLOGY IN THE FOOD CHAIN - Favv

NANOTECHNOLOGY IN THE FOOD CHAIN - Favv

100 Threshold-based

100 Threshold-based detection of projected particles in micrographs using the ‘Detection module’ of iTEM allows measuring hundreds of individual particles simultaneously. These quantitative measurements include the electron density, size, shape, perimeter and surface area. Distributions of these parameters can be expressed on a number basis (Figure B). Electron tomographic reconstruction allowed visualizing the morphology of the silica NPs in three dimensions. Tilt series of micrographs were recorded semiautomatically assisted by Explore 3D (FEI). These were aligned and reconstructed using Inspect 3D (FEI). Reconstructions were visualized using AMIRA (Mercury). Artefacts inherent to the analysis of projections of NPs were detected and interpreted. An estimation of the surface area, volume (Figure C) and volume specific surface area of NPs in suspension was obtained. Volume: 204208 nm³ A B C Surface area: 52889 nm² Figure (A) Micrograph showing an aggregate with subunits; (B) Annotated micrograph showing a mixture of NPs categorized by mean diameter; (C) Electron tomographic reconstruction of a SiO2 aggregate. Bar 50 nm.

Quantitative analysis of the physical characteristics of gold and silver nanoparticles by advanced transmission electron microscopy Elke Van Doren, Pieter-Jan De Temmerman, Michel Abi Daoud Francisco & Jan Mast CODA-CERVA, Groeselenberg 99, B-1180, Brussels, Belgium E-mail: jamas@var.fgov.be Silver and gold nanoparticles (NPs) are commercially distributed on the internet at an international level as food supplements. The question of toxicological risks arises directly, because from a nutritional physiology point of view, noble metals are not required and because gold NPs have catalytic effects, while silver NPs have a biocidal effect. The latter is the basis of the use of Ag NPs as antimicrobial agents in food packaging, refrigerators and kitchen appliances. To evaluate the possible health risks of these applications, knowledge of the physical characteristics of these metallic NPs is an important factor. By its high resolution, transmission electron microscopy (TEM) is one of the few techniques that allow direct visualization of such nanomaterials. Conventional sample preparation techniques coupled to TEM imaging and (semi)automatic, thresholdbased detection of NPs in electron micrographs are evaluated to categorize the particles as NPs and to measure their physical properties on a per-particlebasis. Standard operating procedures were developed for this purpose. Conventional TEM imaging using a Tecnai Spirit TEM (FEI, Eindhoven, The Netherlands) operating at 120 kV allows directly visualizing the structure, size and shape and agglomeration state of preparations of gold and silver NPs (Figure A). Digital micrographs were made using a 4*4 k Eagle CCD-camera (FEI) and stored in an iTEM database (Olympus, Münster, Germany) together with imaging and sample preparation data and of (intermediate) results. Threshold-based detection of projected particles in micrographs using the ‘Detection module’ of iTEM allows to measure hundreds of individual particles simultaneously. These quantitative measurements include the electron density, size, shape, perimeter and surface area. Distributions of these parameters can be expressed on a number basis (Figure B). 101

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