Figure 1. Typical virus image produced by the NanoSight instrument.
Normally, the titer of phage and virus particles is established by plaque assay or, in the case of animal cell viruses, by a cell based bioassay. In these array systems infective virus particles are grown in confluent cell layers to produce plaques (zones of destroyed cells) which can be counted to determine the number of plaque forming units (pfu). While a direct count of individual infective virus particles, non-infective virus particles do not produce plaques and possible aggregates containing many virus particles will produce only single plaques. Often, the manufacturer needs to know the number of virus particles in the preparation, whether infective or not, and the degree, if any, to which the preparation is undergoing aggregation as an early indicator of limited shelf life.
Nanoparticle Tracking Analysis (NTA) allows nanoscale particles such as viruses and virus aggregates to be directly and individually visualised in liquids in real-time, from which high-resolution particle size distribution profiles can be obtained. The technique is fast, robust, accurate and low cost representing an attractive alternative or complement to existing methods of nanoparticle analysis such as Dynamic Light Scattering (DLS), Photon Correlation Spectroscopy (PCS) or Electron Microscopy (EM).
By simultaneously and directly measuring the diffusion coefficient of individual particles, the dedicated NTA software suite allows the user to automatically count and size the viruses and aggregates in a sample. Results are displayed as graphs of size against count of individual particles (or size vs. relative brightness). This particle-by-particle approach overcomes the limitations inherent to other particle analysis systems which only generate mean particle size distribution data.
- For more informaiton about Viral Vaccines visit the Application Notes
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- A review of Application and usage of NTA 2010-2011
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