NPL is currently a world leader in the analysis of nanoparticle suspensions. This approach is ideal when investigating the properties of nanomaterials in-situ, for example the detection and quantification of agglomerates. Techniques currently available are:

Size and size distribution, detection of agglomerates

• Dynamic light scattering (DLS)
• Differential centrifugal sedimentation (DCS)
• Nanoparticle tracking analysis (NTA)

The most suitable is dependent on the material being analysed.

Stability of dispersion (sedimentation and agglomeration over time)

A key factor in studying the fate of nanomaterials in the environment is measuring how their properties change with time. Most critically the ability to form agglomerates which will affect the size distribution. The stability of nanoparticle suspension are determined by Turbidity measurements combined with other analytical method (Electron Microscopy, DLS and ELS, NTA, etc.)

Turbidity measurements can be performed over a length of time of interest (e.g. 10 h with reading every hour, 7 days with reading every day, etc.)

Zeta potential measurement

This is related to the effective charge of a nanoparticle surface. This is affected by both the particle and the suspension medium. This factor is critical determining the fate of suspended nanomaterials. If the nanoparticles rely on electrostatic stabilization and the charge is high enough (typically > 30 mV or < -30 mV) the particles will repel each other and the suspension will remain stable. Too low and the particles will tend to form agglomerates.

Particle density measurements

Density of particles can be measured utilizing the DCS technique, along with the particle size and size distribution. The size range of the particles that can be analysed depends on their constituent materials.

Photocatalytic properties

The ability of nanoparticles to catalyse the production of reactive oxygen species (ROS) under irradiation (typically by solar simulator) is measured by using specific optical probes. ROS that are detected are typically superoxide radicals, hydroxyl radicals and hydrogen peroxide. The general photocatalytic activity can also be measured by means of unspecific probes.

Example of multi-technique approach to nanoparticle characterisation.
Electron microscopy reveals the nature of the primary particle.
NTA reveals and quantifies the presence of agglomerates.
This can be confirmed and additional analysis preform by techniques such as DLS.

Contact

Customer Service tel: +44 20 8943 8637
E-mail: nanoanalysis_enquiries@npl.co.uk