Improving nanoparticle size measurement accuracy for safety assessment

Researcher holding pill

EMPIR nanoparticle project contributes to new written standard and other outputs

The project

Nanomaterials and nanoparticles are finding applications across a wide range of technology sectors, from medicine and food to transportation and construction. In order to assess these new materials for potential risks to health and the environment, they need to be well-characterised. The measurement of constituent nanoparticle size, shape, and size distribution are important factors for the risk evaluation process.

EMPIR project Improved traceability chain of nanoparticle size measurements (17NRM04, nPSize) is working to assess a range of traceable nanoparticle measurement approaches, including Scanning Electron Microscopy (also in Transmission Mode), Atomic Force Microscopy and Small Angle X-ray Scattering, and deliver improved calibration methods to users. For the techniques under investigation, physical models of their response to a range of nanoparticle types are developed. Validated reference materials will also be used for an inter-comparison of measurement systems, with an evaluation of the associated measurement uncertainty. With project contributions to standards development work, manufacturers will be better placed to assess the human and environmental risks posed by nanomaterials across a whole range of products.

The project research, which has been running for two years, has produced a number of outputs including those outlined below:

New standard published

The ISO standard 21363 Nanotechnologies — Measurements of particle size and shape distributions by transmission electron microscopy was published in August 2020, with significant contribution from the project consortium, as the first full international standard under the ISO Technical Committee TC 229 Nanotechnologies, Joint Working Group JWG 2 Measurement and Characterization.

The following description of the standard appears on the web page linked above: ‘This document specifies how to capture, measure and analyse transmission electron microscopy images to obtain particle size and shape distributions in the nanoscale. The document broadly is applicable to nano-objects as well as to particles with sizes larger than 100 nm. The exact working range of the method depends on the required uncertainty and on the performance of the transmission electron microscope. These elements can be evaluated according to the requirements described in this document.’

Reference nanoparticles

A unique set of 11 well-defined novel reference nanoparticle candidates of various materials, sizes, shapes and concentrations meeting the stakeholder requirements has been developed. Their pre-characterisation has been completed. Materials were selected according to their use, i.e. for titania, silica and gold; shapes should be non-spherical; size should be below 100 nm, monodisperse as well as polydisperse; and for the first time: well-known number concentration. All these have been considered by the project consortium in the new set of 11 nPSize materials. Full details can be seen on the project website.

The high-quality of the reference nanoparticles developed has already attracted interest from the scientific community. Recently, an image of the nPSize gold nanocubes with monodispersed size distribution was selected as a finalist for the 2020 Microscopy Today Micrograph Awards (see image C1-5) and eventually won the 3rd prize.

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Workshop on reference nanomaterials

111 experts from public institutes, academia, industries, JRC, DIN, ISO, CEN and the EU participated in a workshop organised by PTB and BAM looking at current and future needs for reference nanomaterials. A keynote presentation gave details of a recent survey led by the JRC on the needs for reference materials and representative test materials in the area of nanotechnologies. The proceedings of the workshop are available.

Training courses

A second training course entitled nPSize - Metrology for Measurement of Nanoparticle Size by Electron Microscopy & Atomic Force Microscopy was run as an online event by VSL and BAM in October 2020. Exactly 100 attendees took part in the one-day event, many of them being either PhD-students and post-docs in research institutions or representative of industries manufacturing nanoparticles.

Future training courses on accurate analysis of NPs by Small Angle X-Ray Scattering (SAXS) are already being prepared for the start of 2021 by CEA with contributions from PTB and BAM. The video presentations from these courses will be available via Youtube. For further information please contact

Book published

A number of the project partners contributed to a new book Characterization of Nanoparticles - measurement processes for nanoparticles, with the project coordinator as an editor. It combines the concepts and new results from the current project with results obtained by previously completed EMPIR project Metrology for innovative nanoparticles (14IND12, Innanopart).

Upcoming VAMAS inter-laboratory studies

The EMPIR project coordinator and VAMAS/TWA 34 Nanoparticle Populations have just agreed to start a new project on the measurement of size and concentration of two nPSize materials, silica bimodal, 30 and 60 nm with two different relative number concentrations 1:1 and 10:1, and measurement of size, shape and concentration of bipyramidal titania as an extension of the case study in ISO 21363. The call for participation will be available via the VAMAS website.

Project Coordinator Vasile-Dan Hodoroaba from BAM said

‘The unique combination of project partners, each with their own area of expertise, has enabled a new quality in the evaluation of size and shape of complex nanoparticles by developing a new set of reference nanomaterials and new measurement procedures including physical modelling, machine learning and their combination’.

These EMPIR projects are co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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Figure: a) A calculated back focal plane image with θ=70°, ϕ=345° and z0 = 60nm. b) A measured back focal plane image of an NV-center. From J. Christinck et al., Appl. Phys. B 126, 161 (2020). Copyright PTB, published with kind permission of PTB
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