Characterization of Nanoparticles

Measurement Processes for Nanoparticles

Vasile-Dan Hodoroaba, Wolfgang Unger, Alexander Shard

• Publisher: Elsevier
• Year: 2019
• Print ISBN: 9780128141823
• eBook ISBN: 9780128141830
• Topic: Physical Sciences
• Subtopic: Nanoscience

Characterization of Nanoparticles: Measurement Processes for Nanoparticles surveys this fast growing field, including established methods for the physical and chemical characterization of nanoparticles. The book focuses on sample preparation issues (including potential pitfalls), with measurement procedures described in detail. In addition, the book explores data reduction, including the quantitative evaluation of the final result and its uncertainty of measurement. The results of published inter-laboratory comparisons are referred to, along with the availability of reference materials necessary for instrument calibration and method validation. The application of these methods are illustrated with practical examples on what is routine and what remains a challenge.In addition, this book summarizes promising methods still under development and analyzes the need for complementary methods to enhance the quality of nanoparticle characterization with solutions already in operation.- Helps readers decide which nanocharacterization method is best for each measurement problem, including limitations, advantages and disadvantages- Shows which nanocharacterization methods are best for different classes of nanomaterial- Demonstrates the practical use of a method based on selected case studies

Chapter 1

Introduction

Alexander G. Shard^a; Vasile-Dan Hodoroaba^b; Wolfgang E.S. Unger^{b a} National Physical Laboratory, Teddington, United Kingdom
^b Bundesanstalt für Materialforschung und -prüfung (BAM), Berlin, Germany

Abstract

The purpose of this book is to provide a comprehensive collection of analytical methods that are commonly used to measure nanoparticles, providing information on one, or more, property of importance. The chapters provide up-to-date information and guidance on the use of these techniques, detailing the manner in which they may be reliably employed. Within this chapter, we detail the rationale and context of the whole book, which is driven by the observation of a low level of reproducibility in nanoparticle research. The aim of the book is to encourage awareness of both the strengths and weaknesses of the various methods used to measure nanoparticles and raise awareness of the range of methods that are available. The editors of the book have, for many years, been engaged in European projects and standardization activities concerned with nanoparticle analysis and have identified authors who are experts in the various methods included within the book. This has produced a book that can be used as a definitive guide to current best practice in nanoparticle measurement.

Keywords

Nanoparticle; Size; Size distribution; Shape; Chemistry; Coating; Concentration; Standards; Charge; Characterization

Abbreviations

ACS American Chemical Society

CCQM Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology

DLS dynamic light scattering

ISO International Organization for Standardization

OECD The Organisation for Economic Co-operation and Development

REACH Registration, Evaluation, Authorisation and Restriction of Chemicals

VAMAS Versailles Project on Advanced Materials and Standards

Acknowledgements

We are deeply indebted to the contributors to this book for their considerable efforts in writing the chapters for this book and for their patience with the compilation and editing process. We are indebted to Gabriela Capile and her colleagues from Elsevier for assisting us in the collation and organization of this work.

Rationale

The purpose of this book is to provide a succinct collection of measurement methods that may be applied to nanoparticles to determine their most important physical and chemical properties. Nanoparticles are increasingly used in innovative products manufactured by advanced industries and provide enhanced, unique properties of great commercial and societal value. The demand for high-performance materials places increasingly stringent tolerances on the properties of nanoparticles. Additionally, the risk assessment of new nanoparticles requires fit-for-purpose measurements by physical and chemical methods to ensure that valid toxicity and ecotoxicity conclusions are reached.

The major purpose of this work is to summarize the most useful and widely available methods to measure important physical and chemical properties of high-performance nanoparticles. The aim is to support the drive for reproducibility and confidence in the nanoparticle supply chain and to help manufacturers to produce the correct physical and chemical property data needed to prepare registration dossiers under current and future regulation. In Europe, for instance, this binding registration process is regulated under REACH. Europe's manufacturers and importers of chemicals have a general obligation to register each nanoform substance manufactured or imported in relevant quantities. In the registration dossier, they must identify the risks linked to the substances they produce and market based on valid measurement procedures. There are similar obligations in other economies also.

Context

In 2016, the editors of ACS Nano stated ‘It is now time for the nanomaterials community to consolidate and to agree on methods of characterization and minimum levels of analysis of materials’ [1], and this book, in part, is aimed at addressing this challenge. In that editorial, they provided an example of toxic surfactants adsorbed on gold nanoparticles: the unknown presence of which could skew the assessment of gold nanoparticle toxicity [2]. There are many examples of the influence of nanoparticle coatings on biological effects, and coatings are present on virtually all particles whether they are intended or not. Size measurement alone is insufficient and, whilst the editorial suggested a range of ‘standard’ measurement techniques, none of the listed methods would have identified the presence of the toxic adsorbate.

Furthermore, the OECD council recommended in 2013 that ‘…the approaches for the testing and assessment of traditional chemicals are in general appropriate for assessing the safety of nanomaterials but may have to be adapted to the specificities of nanomaterials’ [3]. As a consequence, the OECD Working Party on Manufactured Nanomaterials (WPMN) launched projects to further explore the need for revisions of existing test guidelines and the preparation of new ones. Projects of the Working Party within the remit of this book are addressing (i) the determination of the (volume) specific surface area of manufactured nanomaterials, (ii) particle size and size distribution of manufactured nanomaterials, (iii) an identification and quantification of the surface chemistry and coatings of nano- and microscale materials, and (iv) environmental transformations of nanomaterials. The last project is rather challenging for nanoforms that are neither soluble nor have high dissolution rate but morphological, chemical transformation, and other abiotic degradation has to be carefully measured.

The obligation to register new nanoforms, there are hundreds of them every year, will lead to a big workload in testing. A possible workaround can be the development of grouping and read-across approaches that are based on the use of several sets of information: data obtained by measurement methods as described in this book, information on fundamental behaviour and reactivity of specified nanomaterials, and the toxicological data of relevant REACH endpoints or assays. The first step in the read-across workflow is the identification of appropriate characterization methods for the nanoforms in the substance. Currently, it is assumed that the minimum parameters that should be measured are composition (including impurities), particle size (in one or more dimensions), particle shape, and surface chemistry (chemical identity).

Recent research activities have been attempting the effective prediction of nanomaterial's health and environmental risks using existing or newly generated data and newly developed predictive hazard assessment models based on refined hazard-correlated endpoints. Achieving this goal requires the development of multiscale algorithms in nanoinformatics, which link existing and emerging data and advance the current state-of-the-art in silico modelling and predictive toxicology approaches.

In summary, it is therefore essential to establish the key measurement methods to support the manufacture, performance, and reliability of nanomaterials and to enable safe-by-design concepts. Many types of innovative nanoparticles exist: metals used in catalysis, medical applications and conductive inks; metal oxides employed in fuel cells and ferrofluids and as contrast agents for magnetic resonance imaging; semiconductors used as quantum dots and rods for bioimaging, photonics, display, and lighting technologies; and organic particles used for electronic applications, drug delivery vehicles, fluorescent reporters, and advanced coatings. In these applications, one of the important properties defining material performance is the size of the particles and, related to this, the size distribution. For monodisperse nanomaterials, particularly those which are spherical, the measurement of size is not a contentious issue; the currently accepted uncertainty is typically of the order of 1 nm [4], with dynamic light scattering (DLS) producing somewhat inaccurate results. However, DLS is a convenient and precise method and therefore is useful and, indeed, highly used in academic and industrial contexts where accuracy is not a priority.

The measurement of size distribution is far more challenging than measuring the average size of a population. This may be appreciated by considering a normal distribution and the error in estimating a mean value compared with the error in estimating a standard deviation from the sampled data. A sample size of ~ 10 is more than sufficient to establish the mean, but a sample size of more than 100 is required to have confidence that the standard deviation of the sample is within 10% of the standard deviation of the population. Therefore, it involves considerable effort to measure accurate size distributions using microscopies.

Relevance

The production of nanoparticles is of growing economic importance, an example being the number of medicines which are now formulated as nanoparticles. It is hard to assess the size of the nanomedicine market because this often incorporates drugs conjugated to polyethylene glycol or proteins. If these are included, the market size is greater than 100 billion, to an extent that it does not matter whether the units are US dollars, Euros, or pound sterling. Although these are technically nanoparticles in terms of size and certain measurement techniques that could be commonly employed, chemical measurements have a far greater importance, and the nature of these materials means that, for example, advanced mass spectrometries provide a majority of the required information. The main nonconjugate forms of nanomedicine on the market, where nanoparticle measurement is essential, consist of liposomes, nanocrystals, polymers, emulsions, virosomes, and magnetic particles [5].

In 2012, the OECD [6] and ISO [7] both presented a list of nanoparticle properties, which should be measured in a standardized manner. A number of the OECD measurements relate to the properties of dry powders, which are not of major concern for high value nanomaterials; some others, such as ‘redox potential’, ‘radical formation potential’, and ‘photocatalytic activity’, are functional measurements, which are hard to define. Nevertheless, these lists contain properties that are appropriate and may be succinctly listed as size, size distribution, aggregation state, shape, surface area, composition, surface chemistry, and surface charge. It is interesting to note that the concentration of nanoparticles is not listed as ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Chapter 1: Introduction
• Chapter 2.1.1: Characterization of nanoparticles by scanning electron microscopy
• Chapter 2.1.2: Characterization of nanomaterials by transmission electron microscopy: Measurement procedures
• Chapter 2.1.3: Scanning probe microscopy (SPM)
• Chapter 3.1.1: Single particle inductively coupled plasma mass spectrometry (spICP-MS)
• Chapter 3.1.2: Particle Tracking Analysis (PTA)
• Chapter 3.1.3: Electrospray-differential mobility analysis (ES-DMA)
• Chapter 3.1.4: Tunable resistive pulse sensing (TRPS)
• Chapter 3.2.1: Dynamic light scattering (DLS)
• Chapter 3.2.2: Small angle x-ray scattering (SAXS)
• Chapter 3.2.3: Ultraviolet–visible spectrophotometry
• Chapter 3.2.4: Acoustic spectroscopy for particle size measurement of concentrated nanodispersions
• Chapter 3.2.5: Zeta-potential measurements
• Chapter 3.3.1: Analytical centrifugation
• Chapter 3.3.2: Field-flow fractionation (FFF) with various detection systems
• Chapter 4.1: Volume-specific surface area by gas adsorption analysis with the BET method
• Chapter 4.2: Preparation of nanoparticles for surface analysis
• Chapter 4.3.1: X-ray photoelectron spectroscopy
• Chapter 4.3.2: Auger electron spectroscopy
• Chapter 4.4: Energy-dispersive X-ray spectroscopy (EDS)
• Chapter 4.5.1: Low-energy ion scattering (LEIS)
• Chapter 4.5.2: Rutherford backscattering spectroscopy (RBS) and medium energy ion scattering (MEIS)
• Chapter 4.6: Vibrational spectroscopy
• Chapter 4.7: Secondary ion mass spectrometry
• Chapter 5: International standards in nanotechnologies
• Chapter 6: Conclusions and perspectives
• Index