Sizing of polydisperse silver nanoparticle suspensions - comparison of AF4 coupled to online DLS with batch mode DLS

Dynamic light scattering (DLS) is a well-established and powerful analytical technique for sizing of nanoparticles in suspensions. Due to its easy applicability it has found its place in analytical laboratories all around the world.

However, DLS has significant drawbacks when it comes to the characterization of polydisperse samples. This is due to the Rayleigh approximation that states that the intensity of the scattered light (I) is proportional to the particle diameter (d) to the power of six (I α d6). That means, for example, a 60 nm particle scatters one million times as much light as a 6 nm particle, thereby heavily biasing the measurement towards any larger particles present in a mixture, ultimately leading to overestimated particle sizes. One possibility to overcome this drawback is the separation of polydisperse samples by field-flow fractionation prior to DLS analysis and then using DLS as an online detector to accurately measure each monodisperse size fraction as it elutes.

This application note presents a comparison of DLS in batch mode with asymmetrical flow field-flow fractionation (AF4) coupled with DLS (AF4-DLS) for the measurement of a mixture of silver nanoparticles (AgNP) of different sizes (20 nm, 40 nm, 60 nm). The results obtained clearly highlight the advantage of using a powerful fractionation technology prior to DLS analysis for polydisperse samples.