NanoFASE partners Alison Crossley (Senior Research Fellow, Oxford Materials Characterisation Service, Oxford University Begbroke Science Park) and Barry Park (Director, GBP Consulting Ltd) attended a UK Royal Society of Chemistry/National Physical laboratory Symposium on 24th April 2018 on Nanoparticle concentration – critical needs and state-of-the-art measurement. The event was attended by over 100 international delegates. The programme comprised speakers from the UK, Germany, Sweden, USA, Russia, Australia and New Zealand.

Alison Crossley presented a poster entitled "Analytical considerations following accidentally discharged potentially nano-sized material into a river" acknowledging the NanoFASE project. The meeting attracted a large number of high quality posters (30) mostly by PhD students with several describing novel and emerging methods for measuring nanoparticle concentration. This was an extremely interesting symposium with a series of excellent speakers providing an insight into current characterisation techniques.

As a service to the Nano community the talks and respective speakers are detailed below:

• The Keynote Talk was given by Dr Richard Brown of NPL, the winner of L S Theobald Lecture awarded in memory of Leslie Stuart Theobald, an academic of Imperial College. The Lectureship is awarded to someone who has made a significant contribution to analytical chemistry in an area of work relevant to the Analytical Methods Committee of the Royal Society of Chemistry Analytical Division. Dr Brown talked about the significant reductions in black smoke, down one order of magnitude, and polyaromatic hydrocarbons, down three orders of magnitude, that have been achieved leading to a decrease in pollution over the past thirty or more years. However, he indicated that traffic still creates pollution problems. He quoted the Royal College of Physicians report of 2016 which stated that 40,000 deaths per year in the UK result from air pollution. He also noted the response from Professor Sir David Spiegelhalter of Cambridge University who has talked of huge uncertainties surrounding this figure. Dr Brown wished for better data than were quoted in the Royal College of Physicians report and noted that effects on cardiovascular disease are not reflected in current legislation. He indicated that particle number concentration would be a preferred measurement to use rather than particle mass. He did recognise that huge reductions in particles have been determined over the past twelve years, based on data from many sites in major cities and elsewhere. He seeks to apply a rigorous metrology approach based on stable measurements that are comparable and coherent so that the data can be of value in an epidemiological study. Within this, it is key to define measurands and specify methods.
• Andrea Jaase of German Federal Institute for Risk Assessment (BfR) talked about Linking nanomaterial physico-chemical properties with cellular uptake and toxicity. She noted the concerns about toxicity of nanoparticles and indicated that characterisation leading to toxicity is too simple and that it is important to add interactions between the nanomaterial and the system taking account of the initial dose delivered and the internal dose achieved. ICPMS was noted as the gold standard for quantifying nanoparticle uptake in cells with cellular uptake being size dependent. There is a need to focus and differentiate between mass and number information regarding delivery to cells. Jaase also expressed concern about difficulties in getting round robin data published indicating that it is important to determine and report variability of data across laboratories and techniques. 
• A speaker from Sweden, Fredrik Hook from Chalmers University, gave a talk on Single nanoparticle analytics: from viruses via exosomes to drug delivery carriers and claimed an association with Astra Zeneca although did not elaborate on the association. He discussed a 2D flow nanometry concept in the context of improved characterisation of individual nanoparticles of diagnostic and therapeutic significance.
• Nanoparticle reference materials: lessons learned and the case for concentration measurements was the topic from Vince Hackley of NIST. He described the importance of having accredited reference nanomaterials and explained what NIST has to offer. Over 1200 reference materials are available and are provided with a certificate with certified values. He noted that reference gold nanoparticles are sold worldwide with c.50/50 US/Rest of the world. C.46% are supplied to industry with c.42% to government bodies and the balance to academia. It was also interesting to note that over 100 published papers had referenced these gold nanoparticles with 27 of them referring to spICPMS. Hackley provided insights into potential problems with storage of nanoparticles in suspension with losses to container surfaces particularly problematic for low concentrations. He also advised on using multiple techniques to seek to include the smallest particles in an analysis.
• Michael Krumrey of Physikalisch-Technisdhe Bundesanstalt in Berlin talked about Nanoparticle concentration with Small Angle X-ray Scattering (SAXS) and noted that Dynamic Light Scattering (DLS), Small Angle X-ray Scattering (SAXS) is an ensemble method where nanoparticles can be studied in liquid suspension. He noted that traceable size determination of spherical nanoparticles using SAXS is already established with an ISO standard available.
• Susana Nunez of LGC Ltd discussed Determination of number concentration of inorganic nanoparticles using spICPMS: recent developments and remaining challenges. She talked about key challenges of spICPMS for achieving accurate number concentration of nanomaterials and talked about the need for effective sample preparation.
• Nikolai Khlebtsov from the Russian Academy of Sciences gave a talk on Determination of size and concentration of gold and silica nanoparticles from absorption and turbidity spectra, but it was extremely difficult to decipher the data he presented as the slides were very dense.
• Victoria Coleman of the National Measurement Institute Australia gave a talk on Relative nanoparticle concentration with benchtop methods. She commented that there are no certified reference materials available that are specifically designed for measurements of nanoparticle number concentration, but reflected that a number of single particle techniques used for particle size distribution analysis also claim to measure number concentration – these include particle tracking analysis (PTA) and resonant mass measurement (RMM). She had used size-monodisperse gold nanoparticles and specifically prepared modal distributions of these particles to create dilution series for investigating nanoparticle concentrations.
• Kuba Tatarkiewicz of Manta Instruments Inc in San Diego presented a talk on What does it take to accurately measure the concentration of particles in colloids? Manta have developed their own NTA – MANTA – multispectral advanced nanoparticle tracking analysis and have four patents on the technology. They used blue, green and red lasers for different particle size bands and to help, NIST produced four component mix for exploratory studies. He presented results from studies on this four component mix and for other colloids and also discussed calibrating instruments that use MANTA.
• Hans van der Voorn of Izon Science gave a talk on Nanoparticle concentration measurement is essential and, fortunately, quite easy and expressed concern that most published papers are not reproducible with c.80% of cancer papers not reproducible. He supported his argument by claiming that Dynamic Light Scattering was the "worst of the main techniques". He compared IZON’s Tunable Resistive Pulse Sensing (TRPS) with NTA/PTA and noted that TRPS can be made accurate for concentration to a few percent on a linear scale whereas NTA is at best accurate on a log scale. He also reminded the audience that unmeasured does not mean "not there".
• Hanna Jankecvics Jones from Malvern Panalytical gave a talk on Advances in particle concentration from Malvern Panalytical. She noted that the NTA process has its own ISO standard and then went on to describe the enhanced capability to be found in the new autosampler accessory for Nanosight’s particle tracking analysis (PTA) instrument NS300 kit which gives improved repeatability with increased sample throughput.  Round robin test data were shown supporting the claims for the upgraded equipment. Finally, it was noted that temperature control is key as change in viscosity can lead to change in size measurements so need to equilibrate to temperature.
• Denis Koltsov of BREC Solutions Ltd closed the symposium with a talk on Particle tracking analysis for particle counting. As Chair of the ISO TC 229 committee on nanotechnology, he was able to give details of the current status on standards for nanotechnology. He began by explaining the interactions between ISO, CEN, OECD etc and confirmed that published standards related on nanotechnology now stand at 40 with a further 52 under development. The Particle tracking Analysis method is covered in ISO 19430:2016 with three PTA equipment companies involved in its preparation. Part 2 is pending with particle counting and number concentration to be included. In closing, he reminded the audience of the importance of reference materials.