Techniques for measuring the size of nanoparticles

Compared with the number of techniques for measuring the size of a particle greater than 1 micron, there are very few techniques that are able to accurately measure the size of small particles, particularly those less than 10 nanometres.

Dynamic Light Scattering (DLS), sometimes called Photon Correlation Spectroscopy (PCS) or Quasi-Elastic Light Scattering (QELS) is the only technique able to measure particles in a solution or dispersion in a fast, routine manner with little or no sample preparation.

Photon Correlation Spectroscopy has the advantages of small measurement times, typically in seconds or at most a few minutes, with the sample having been through the minimum of preparation.

The minimal or entire lack of sample preparation ensures that the sample is measured as it actually is.

The preparation required for other techniques can change the properties of the particles, for example aggregates can be created or destroyed.

The technique is only suitable for ‘hard’ materials, i.e. those not affected by the preparation technique and is poor from a statistical point of view as only tens or hundreds of particles are measured.

Electron microscopy
This suffers from the same disadvantages as the AFM techniques, however they both can give more information about the shape and surface structure of the particle than an ensemble technique like DLS.