Dynamic light scattering (DLS) is widely used for ensemble characterization of hydrodynamic particle size, but I have a number of frustrations with the technique.
We measure our valuable samples in low concentrations and in very small volumes, so we use expensive, low volume, glass cells, which are optically superior to disposable plastic cuvettes, but we spend far too much time cleaning them, significantly reducing the productivity of our group.
Also, our samples range from monodisperse proteins to polymeric nanoparticles to liposomes, ranging from the nano-scale into the micro-scale and we need to have confidence that our data are precise and accurate across this entire scale, preferably, with a single technique. The commonly quoted upper size limit for DLS of 10µm is only possible by increasing the dispersant viscosity, but the whole point of DLS is to characterize the hydrodynamic properties of my sample in my dispersion: changing the viscosity is not an option!
The launch of the Zetasizer Ultra and its patented Capillary DLS technology now solves all of these problems, enabling seamless hydrodynamic characterization from Ångströms to 10’s of microns in a simple, high quality, disposable glass capillary cell with a minimum sample volume of 3µl. DLS seeks to characterize only diffusive motion, however, the latest research shows that the timescales associated with poor DLS results at larger particle sizes are not due to sedimentation! In fact, convective motion within large cuvettes, due to the active thermal control necessary for DLS, is the source of the error. Malvern Panalytical’s disposable glass capillary cells are 1mm x 1mm internally, suppressing this convective motion whilst allowing the instrument to maintain exquisite thermal control of the sample. The results shown in the graph above, demonstrate that the Zetasizer Ultra with the capillary cell, can now measure hydrodynamic properties from the nano- to the micro-scale in a single measurement and without altering the dispersion.