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. 2014 Aug;462-463:199-206.
doi: 10.1016/j.virol.2014.06.005. Epub 2014 Jul 5.

Quantitative Real-Time Single Particle Analysis of Virions

Free PMC article

Quantitative Real-Time Single Particle Analysis of Virions

Susanne Heider et al. Virology. .
Free PMC article


Providing information about single virus particles has for a long time been mainly the domain of electron microscopy. More recently, technologies have been developed-or adapted from other fields, such as nanotechnology-to allow for the real-time quantification of physical virion particles, while supplying additional information such as particle diameter concomitantly. These technologies have progressed to the stage of commercialization increasing the speed of viral titer measurements from hours to minutes, thus providing a significant advantage for many aspects of virology research and biotechnology applications. Additional advantages lie in the broad spectrum of virus species that may be measured and the possibility to determine the ratio of infectious to total particles. A series of disadvantages remain associated with these technologies, such as a low specificity for viral particles. In this review we will discuss these technologies by comparing four systems for real-time single virus particle analysis and quantification.

Keywords: Flow-field-fractionation; Multiple-angle laser light scanning; NanoSight; Nanoparticle tracking analysis; Single particle analysis; Tunable resitive pulse sensing; Virus titer; VirusCounter.


Fig. 1
Fig. 1
Comparison of strategies for measuring viral concentrations. (A) Levels of stringency in virus titer measurement. The type of parameter measured influences the stringency and thus the level of titers measured: measuring infectivity will always give lower titers than measuring particle numbers, protein or nucleic acid amounts based measurements. In this case, infectious titers (measured by flow cytometry after reporter gene transduction), total particle number (measured by TRPS), reverse transcriptase levels (measured by PERT assay) and viral RNA containing a GFP reporter (measured by RT qPCR) were determined in triplicate for 8 different preparations of lentiviral particles, derived from the stable producing cell line STAR-A-HV (ECACC no. 04072115). Viral preparations were concentrated by ultracentrifugation (2 h, 56,000g, 4 °C in a Beckmann XL70 ultracentrifuge using a SW32ti rotor). Concentrations for each preparation are shown together with the respective means and standard error of the mean (SEM). TRPS—tunable resistive pulse sensing; PERT—product-enhanced reverse transcriptase assay; qPCR—quantitative polymerase chain reaction. (B) Average vs. distribution. While the two distributions depicted are clearly distinct, they yield the same average (indicated by the vertical dotted line). When using ensemble methods, subpopulations may be hidden, indicating the importance of single particle analysis.

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