New reference material candidates for traceable size measurement of non-spherical nanoparticles
Abstract
Size measurement of nanoparticles (NP) becomes a challenging analytical problem when non-spherical shapes must be traceably measured [1]. However, most industrial NPs have irregular shapes and broad size distribution making it often more complex to follow European regulatory to identify a material as a nanomaterial according to which accurate measurement of the smallest dimension and its size distribution is necessary.
The European research project nPSize - Improved traceability chain of nanoparticle size measurements aims to fill this gap by developing potential non-spherical reference nanoparticles, measurement procedures and physical modelling to improve the traceability chain, comparability and compatibility for NP size measurements between different methods. Therefore, new model NP with well-controlled shape has been synthesized and are supposed to be systematically characterized using the traceable methods scanning/transmission electron microscopy, atomic force microscopy and small angle X-ray scattering. Following NP candidates are under investigation with respect to their homogeneity and stability: (i) titania nanoplatelets (10-15 nm thickness x 50-100 nm lateral) [2], (ii) titania bipyramides (~60 nm length x 40 nm width) [3], (iii) titania acicular particles (100 nm length x 15-20 nm width; aspect ratio 5.5/6) [4], (iv) gold nanorods (~10 nm width x 30 nm length) [5], and (v) gold nanocubes (~55 nm x 55 nm x 55 nm) [6,7]. In addition, sample preparation procedures as well as measurement analysis procedures with evaluation of appropriate measurands and descriptors for each material class and method are being developed to support standardization. To underpin the traceability of the size measurement of non-spherical NP, physical modelling of the signals in e.g. electron microscopy techniques [8] will be used and in combination, the implementation of machine learning is aimed to facilitate measurement analysis procedures, especially regarding the accurate thresholding/segmentation of the NPs.