Quantitative Assessment of the Physical Virus Titer and Purity by Ultrasensitive Flow Virometry

Rapid quantification of viruses is vital for basic research on viral diseases as well as clinical application of virus-based products. Here, we report the development of a high-throughput single-particle method to enumerate intact viral particles by ultrasensitive flow virometry, which detects single viruses as small as 27 nm in diameter. The nucleic acid dye SYTO 82 was used to stain the viral (or vector) genome, and a laboratory-built nano-flow cytometer (nFCM) was employed to simultaneously detect the side-scatter and fluorescence signals of individual viral particles. Using the bacteriophage T7 as a model system, intact virions were completely discriminated from empty capsids and naked viral genomes. Successful measurement of the physical virus titer and purity was demonstrated for recombinant adenoviruses, which could be used for gene delivery, therapeutic products derived from phage cocktails, and infected cell supernatants for veterinary vaccine production.

Automated summary

The development of a high-throughput single-particle method for quantifying intact viral particles is crucial for both basic research on viral diseases and clinical application. By using nucleic acid dye and a laboratory-built nano-flow cytometer, different types of viral particles can be effectively discriminated.