ISO/TR 27609:2020 — Nanotechnologies — Overview of Nanomaterial Characterization

Characterisation is the foundation upon which all nanomaterial science, technology, and regulation is built. Without reliable characterisation data, it is impossible to establish meaningful structure-property relationships, ensure batch-to-batch consistency, demonstrate regulatory compliance, or conduct reproducible toxicological studies. ISO/TR 27609:2020 provides a comprehensive technical overview of the characterisation techniques applicable to manufactured nanomaterials, serving as an essential reference for researchers, quality control professionals, and regulatory scientists. This article synthesises the key technical content of the standard, highlighting the principles, capabilities, and limitations of the major characterisation methods.

The Characterisation Landscape: A Multi-Technique Approach

ISO/TR 27609 establishes that no single technique can fully characterise a nanomaterial. A complete characterisation requires a battery of complementary methods addressing six fundamental parameter categories: (1) size and size distribution, (2) shape and morphology, (3) chemical composition and purity, (4) surface properties (chemistry, area, charge), (5) crystal structure and polymorphism, and (6) physical properties (density, porosity, solubility, dispersion stability). The standard provides a detailed mapping of which techniques address which parameters, enabling researchers to design efficient characterisation strategies tailored to their specific nanomaterial and application context.

A key contribution of the standard is its systematic comparison of technique capabilities across nanomaterial types. For example, electron microscopy (SEM, TEM, STEM) provides excellent spatial resolution and morphological information but requires vacuum conditions and may introduce drying or beam-damage artefacts. Light scattering methods (DLS, NTA) operate in liquid suspension and provide ensemble statistics but are model-dependent and may not resolve multimodal distributions. X-ray methods (XRD, SAXS, XPS) provide crystallographic and chemical information with high precision but require relatively large sample volumes and may not detect amorphous or poorly crystalline phases. The standard encourages cross-validation, where at least two independent techniques confirm each critical parameter.

Technique Selection and Data Quality

ISO/TR 27609 provides practical guidance on selecting characterisation techniques based on the specific information needed, the nature of the nanomaterial, and the intended application. For routine quality control in manufacturing, rapid techniques with high throughput and robustness — such as DLS for size and zeta potential for surface charge — are preferred. For regulatory submission or research publication, the standard recommends a more comprehensive approach, including imaging techniques for direct visualisation and spectroscopic methods for chemical confirmation. In all cases, the standard emphasises the importance of method validation, including determination of measurement uncertainty, limit of detection, and inter-laboratory reproducibility.

The standard dedicates significant attention to sample preparation, which is widely recognised as the largest source of variability in nanomaterial characterisation. Detailed guidance is provided for dispersion protocols (including the use of surfactants, sonication parameters, and dispersion stability verification), substrate preparation for microscopy, and sample mounting for spectroscopic analysis. The concept of “measurement traceability” is introduced, linking instrument calibration to internationally recognised reference standards (e.g., NIST, IRMM, BAM) and ensuring that measurement results can be compared across laboratories and over time.

Emerging Techniques and Future Directions

ISO/TR 27609 also surveys emerging characterisation techniques that, while not yet widely adopted in routine analysis, offer significant potential for addressing current characterisation gaps. These include: cryo-electron microscopy (cryo-TEM/cryo-SEM) for characterising nanomaterials in their native hydrated state; in situ TEM for observing dynamic processes such as sintering, catalysis, and phase transformations; hyperspectral imaging (Raman, FTIR, EDX) for spatially resolved chemical mapping; and single-particle ICP-MS for ultra-trace elemental analysis at the individual nanoparticle level. The integration of these advanced methods with machine learning-based image analysis and data fusion approaches is identified as a key future direction for the field.

From an engineering perspective, the standard highlights the growing need for inline and at-line characterisation methods that can be integrated into manufacturing processes for real-time quality control. While most current characterisation methods are laboratory-based and off-line, the development of process analytical technology (PAT) tools for nanomaterials — such as in-line UV-Vis spectroscopy, focused beam reflectance measurement (FBRM), and acoustic attenuation spectroscopy — is identified as a critical priority for industrial-scale nanomaterial production.

Frequently Asked Questions