Exceeding a resolving power of 50 for virus size determination by differential mobility analysis.

A recently described DMA designed for high resolution viral particle analysis (Perez-DMA; Perez-Lorenzo et al, 2020) is modified to decrease the relative peak full width at half maximum (FWHM) below previously achieved ≈3.3%. The electrode radii at the outlet slit (R 1  = 1.01 cm; R 2  = 2 cm) and the working length are almost unchanged (L = 114.9 vs. 116 mm). The laminarization trumpet and the radius of the curve merging the trumpet to the working section are both considerably widened to improve gas flow laminarization. DMA evaluation with salt clusters is improved by reducing the flow resistance at the gas outlet, to reach substantially larger sheath gas flow rates Q near 1700 L/min. Tests with tetraheptylammonium bromide clusters with a center rod diverging at 3° demonstrate FWHM<2.7%, without indications of performance loss due to turbulence even at 1700 L/min. Correcting these high flow rate data for diffusive broadening reveals a maximal DMA FWHM in the limit of non-diffusing particles and zero sample flow, FWHM∞ = 1.8%. An uncorrected peak width approaching 2% is independently demonstrated at much lower flow rates of sheath gas with two recently described bee virus particle standards having singularly narrow size distributions at mean diameters of 38 and 17 nm. Correcting raw 38 nm particle peak widths for broadening due to diffusion and aerosol to sheath gas flow rate ratio q/Q shows an even more ideal response with FWHM∞<1%, where this value includes nonidealities in the DMA as well as possible lack of monodispersity in the viral particles.

Singularly Narrow Viral Size and Mobility Standards from the 38.3 nm Chronic Bee Paralysis Virus and Its 17.5 nm Satellite.

The chronic bee paralysis virus (CBPV), extracted from sick or dead bees, was studied by mobility measurements via electrospray charge reduction with a differential mobility analyzer (DMA) of unusually high resolution. Three different particles are observed. The most abundant one contributes a mobility peak at 38.3 nm, approximately as expected for CBPV. The peak is very sharp in spite of the nonisometric nature of CBPV. We also observe a previously unreported weaker well-resolved shoulder 4.8% more mobile, perhaps due to empty (genome-free) particles. Another sharp peak appearing at approximately 17.51 nm is likely associated with the known icosahedral CBPV satellite (CBPVS). The 17.51 and 38.3 nm peaks offer size and mobility standards much narrower than previously reported at any size above 5 nm, with relative full peak width at half-maximum (FWHM) in mobility approaching 2% (∼1% in diameter). Slight but clear imperfections in the DMA response and the electrospraying process suggest that the real width of the viral mobility distribution is less than 2%.