![]() 8, 9, 10, 11, 12, 13 However, in practice, these techniques represent a rather expensive class of electron microscopy that require utmost delicacy and are time-consuming. CryoTEM and liquid-cell TEM are particularly interesting developments that in principle may overcome these issues. 3 The unambiguous discrimination between ‘true’ aggregates present in the sample and ‘formed’ aggregates, which were produced during sample preparation is very challenging in standard TEM. This process often results in the formation of nanoparticle aggregates 4, 5, 6 located in segregated patches at the perimeter of the dried droplet, which can be explained by surface dewetting 7 and the so-called ‘coffee-ring’ effect. TEM sample preparation typically consists of drop-casting and drying a particle suspension on a TEM grid. Measurements are typically performed in high-vacuum chambers on dry samples. Scanning (SEM) or transmission electron microscopes (TEM) are standard equipment in many companies and research facilities and their use is continually expanding. Here we describe a simple and almost universally-applicable approach that can eliminate artifacts found in conventional TEM micrographs taken for the analysis of suspended particulate nanomaterials. 3 Characterizing commercially-relevant materials, which often have highly non-uniform sizes and shapes, is particularly challenging. 2 Drying steps, unavoidable during sample preparation, can result in non-uniform particle deposition and particle aggregation. ![]() However, this technique is frequently plagued with issues related to artifacts, statistical reliability and interpretation. ![]() Electron microscopy is a so-called counting method, which determines individual nanoparticle size and can be used to construct the required number-weighted size distributions. With this definition, the median of the number-weighted size distribution was established as a definitive parameter in the legislation of nanomaterials. 1 Essentially, a “nanomaterial a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm – 100 nm”. In an attempt to ensure the safety of all applications of nanomaterials in products, the European Commission has issued a definition of the term ‘nanomaterial’ to be used in all European Union legislation. Nanomaterials are present in nearly all segments of modern life, including electronics, cosmetics, food products and healthcare.
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