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Total virus titer in minutes

Abstract: In this Application Note, we review how using nanoparticle tracking analysis, have been employed for the direct visualization, concentration measurement and sizing of bacteriophages and viruses


The titer of bacteriophage 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 this gives a direct count of individual infective virus particles, non-infective virus particles do not produce plaques, and 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 visualized 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 complement to existing methods of nanoparticle analysis such as Dynamic Light Scattering (DLS), Photon Correlation Spectroscopy (PCS) or Electron Microscopy (EM).

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