Viral particle analysis

Viral particle analysis

Virus quantification involves counting the number of viruses in a specific volume to determine the virus concentration. Virus quantification is usually based on measures of infectivity (plaque assays), genome copies (PCR) or viral antigens (ELISA). Each of these methods comes along with its intrinsic caveats. Traditional plaque titer assays are often referred to as functional assays, but they present a drawback in the delay they impose because of the time-consuming nature of these techniques. PCR and ELISA can only measure a single component of a virus, and therefore these methods are not capable of discriminating intact from non-intact particles hampering accurate quantification.

sFIDA combines the selectivity of an immunological assay with the sensitivity of high-resolution fluorescence microscopy. In sFIDA, viral particles are captured from the sample and fixed to a glass surface of a microtiter plate. Fluorescent detection probes directed against envelope, capsid and/or surface antigen epitopes of the virus are applied. Additionally, nucleic acid specific dyes enable further characterization of intact versus non-intact particles. As a final step, the surface is scanned by fluorescence microscopy to detect and count single viral particles to determine the absolute titer of intact viruses. sFIDA is amenable to high-throughput applications in a 384-well format on automated platforms.