Development of a sample preparation approach to measure the size of nanoparticle aggregates by electron microscopy--颗粒学报PARTICUOLOGY

Dudkiewicz, A., Lehner, A., Chaudhry, Q., Molhave, K., Allmaier, G., Tiede, K., . . . Lewis, J. (2019). Development of a sample preparation approach to measure the size of nanoparticle aggregates by electron microscopy. Particuology, 45, 49-57. https://doi.org/10.1016/j.partic.2018.05.007

Development of a sample preparation approach to measure the size of nanoparticle aggregates by electron microscopy

Agnieszka Dudkiewicz ^{a b c *}, Angela Lehner ^d, Qasim Chaudhry ^e, Kristian Molhave ^f, Guenter Allmaier ^d, Karen Tiede ^g, Alistair B.A. Boxall ^b, Peter Hofmann ^h, John Lewis ^a

a The Food and Environment Research Agency, Sand Hutton, York Y041 1LZ, UK
b Department of Environment, The University of York, Heslington, York YO10 5DD, UK
c National Centre for Food Manufacturing, The University of Lincoln, Holbeach PE12 7AG, UK
d Research Group Bio- and Polymer Analysis, Institute of Chemical Technologies and Analytics, TU Wien (Vienna University of Technology), Getreidemarkt 9, A-1060 Vienna, Austria
e University of Chester, Parkgate Road, Chester CH1 4BJ, UK
f Department of Micro and Nanotechnology, Technical University of Denmark, DTU Bldg 345b, Lyngby 2800, Denmark
g Research Centre for Global Food Security and Ecosystems, University of Hohenheim, Wollgrasweg 43, 70155 Stuttgart, Germany
h Department of Geoinformatics — Z_GIS, University of Salzburg, Schillerstr. 30, A-5020 Salzburg, Austria

10.1016/j.partic.2018.05.007

Volume 45, August 2019, Pages 49-57

Received 12 February 2018, Revised 22 May 2018, Accepted 23 May 2018, Available online 29 November 2018, Version of Record 10 June 2019.

E-mail: agnieszkaidudkiewicz@gmail.com

Highlights

• A new approach for the measurement of nanoparticle aggregates using electron microscopy.

• Determination of a sample preparation protocol that did not introduce agglomeration.

• Comparison of measurements between electron microscopy and reference methods.

• Skewing artefact introduced by sample preparation was refined using mathematical solution.

• Mathematical solution differed for gold and silica nanoparticles.

Abstract

Electron microscopy (EM) is widely used for nanoparticle (NP) sizing. Following an initial assessment of two sample preparation protocols described in the current literature as "unperturbed", we found that neither could accurately measure the size of NPs featuring a broad size distribution, e.g., aggregates. Because many real-world NP samples consist of aggregates, this finding was of considerable concern. The data showed that the protocols introduced errors into the measurement by either inducing agglomeration artefacts or providing a skewed size distribution towards small particles (skewing artefact). The focus of this work was to develop and apply a mathematical refinement to correct the skewing artefact. This refinement provided a much improved agreement between EM and a reference methodology, when applied to the measurement of synthetic amorphous silica NPs. Further investigation, highlighted the influence of NP chemistry on the refinement. This study emphasised the urgent need for greater and more detailed consideration regarding the sample preparation of NP aggregates to routinely achieve accurate measurements by EM. This study also provided a novel refinement solution applicable to the size characterisation of silica and citrate-coated gold NPs featuring broad size distributions. With further research, this approach could be extended to other NP types.

Graphical abstract

Keywords

Nanoparticles; Aggregates; Measurement; Electron microscopy; Sample preparation; Artefacts

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