“…For optimal quality control, single-particle analysis (SPA) would be preferred, since they allow following the distribution of key parameters (e.g., size) in the population, giving information about its heterogeneity [ 13 ]. Different approaches to SPA are in use (for comparison of methods see [ 13 , 14 ] and [ 15 ], among them electron microscopy (EM) and dynamic light scattering (DLS) approaches [ 16 ], nanoparticle tracking analysis (NTA) [ 11 , 14 , 17 , 18 ], flow virometry (FV) [ 19 , 20 ], and tunable resistive pulse sensing (TRPS) [ 13 , 21 , 22 ]. The latter is based on the Coulter principle, which states that particles pulled through a (physical) pore, while an electric current is applied, produce a change in impedance that is proportional to the volume of the particle traveling through the pore.…”