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Partic. vol. 45 pp. 49-57 (August 2019)
doi: 10.1016/j.partic.2018.05.007

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

Agnieszka Dudkiewicza,b,c,*, Angela Lehnerd, Qasim Chaudhrye, Kristian Molhavef, Guenter Allmaierd, Karen Tiedeg, Alistair B.A. Boxallb, Peter Hofmannh, John Lewisa

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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