A laser-based, single nano-particle tracking analysis system was described in the March issue of Microscopy Today. The LM series of analyzers from NanoSight allows nanoscale particles such as viruses to be directly and individually visualised in liquids in real time, from which high-resolution particle size distribution profiles can be obtained, figure 1. The technique is fast, robust, accurate, and low cost representing an attractive alternative or complement to expensive and more complex methods of nano-particle analysis such as dynamic light scattering (photon correlation spectroscopy) or electron microscopy.

By simultaneously and directly measuring the diffusion coefficient of each and every particle, the dedicated Nanoparticle Tracking Analysis (NTA) software suite allows the user to automatically count and size the viruses in a sample. Results are displayed as graphs of size against count of individual particles (or size versus relative brightness), thus overcoming the limitations inherent in other particle analysis systems that generate only mean particle size distribution data with resolution.