Label-Free Analysis of Single Viruses with a Resolution Comparable to That of Electron Microscopy and the Throughput of Flow Cytometry

Viruses are by far the most abundant biological entities on our planet, yet existing characterization methods are limited by either their speed or lack of resolution. By applying a laboratory-built high-sensitivity flow cytometer (HSFCM) to precisely quantify the extremely weak elastically scattered light from single viral particles, we herein report the label-free analysis of viruses with a resolution comparable to that of electron microscopy and the throughput of flow cytometry. The detection of single viruses with diameters down to 27 nm is described. T7 and lambda bacteriophages, which differ in size by as little as 4 nm, could be baseline-resolved. Moreover, subtle structural differences of the same viral particles can be discriminated. Using monodisperse silica nanoparticles as the size reference standards, the virus sizes measured by the HSFCM are in agreement with the equivalent particle diameters derived from their structural dimensions. The HSFCM opens a new avenue for virus characterization.