The Condensation of Water on Adsorbed Viruses.

Abstract

The wetting and dewetting behavior of biological nanostructures and to a greater degree single molecules is not well-known even though their contact with water is the basis for all biology. Here, we show that environmental electron microscopy (EM) can be applied as a means of imaging the condensation of water onto viruses. We captured the formation of submicrometer water droplets and filaments on single viral particles by environmental EM and by environmental transmission EM. The condensate structures are compatible with capillary condensation between adsorbed virus particles and with known droplet shapes on patterned surfaces. Our results confirm that such droplets exist down to <50 nm. The viruses preserved their shape after a condensation/evaporation cycle as expected from their stability in air and water. Moreover we developed procedures that overcome problems of beam damage and of resolving structures with a low atomic number.

Nanoscale wetting of viruses by ionic liquids

“…That is, a liquid filament (F) with a negatively curved meniscus (F -) coexists with thin liquid filaments W, which are pinned (p) to the upper edge of a wall (here a virus). Similar patterns were observed for water/TMV by electron microscopy [35], although at lower resolution. This is indeed expected, based on the similarity of the surface tensions.…”

“…13 The environmental SEM (ESEM) technique, in conjunction with very good control of a water vapor atmosphere of several hundred Pa, has allowed us to image similar structures of TMV/liquid water [35]. However, the fast spreading dynamics has not allowed recording images analogous to Fig.…”

“…We show that the cylindrical nature of the TMV particles, the virions, leads to the formation of nanoscale liquid filament structures that propagate along the patterns. The use of non-volatile ILs allows a detailed study of the wetting of complex nanostructures driven by surface tension only, in the absence of any capillary condensation effects [35]. Interestingly, the spontaneous spreading of ILs in the form of nanoscale liquid filaments shows their capability to act as a localized negative stain for the high resolution imaging of nanoscale biological objects by STEM.…”

Surface Chemistry Can Unlock Drivers of Surface Stability of SARS-CoV-2 in a Variety of Environmental Conditions

“… 27 Therefore, an understanding of the effect of humidity on surface stability and adsorption of this novel virus is crucial. Water molecules in the liquid phase condense from its vapor phase on various surfaces (e.g., between virus particles and solid substrates) and create liquid bridges with a curvature, which is related to the relative humidity “ h ” expressed by the Kelvin equation 28 ( Equation 1 ). When the solid surfaces are fixed in one dimension, as for structures with a high aspect ratio, the interface curvature radii “ r ” is determined by: …”

Multifrequency Force Microscopy of Helical Protein Assembly on a Virus

“…In our experimental conditions we did not find evidences of water menisci formation or capillary interactions, for example strong adhesion forces that reflect in the φ 1 signal, and that could affect the topography, giving rise to unrealistic TMV geometries. We took special attention to the environmental conditions because it is known that TMV surface features can be obscured even by very thin water films 49 . Standard AFM tips mounted on rectangular cantilevers (Multi75Al, nominal f res = f 1 = 75 kHz, spring constant = 3 N/m and tip radius R < 10 nm, BudgetSensors) and super sharp (SSS-SEIHR, nominal f res = f 1 = 130 kHz, spring constant = 15 N/m and tip radius R = 2 nm, Nanosensors) were used in experiments, obtaining similar results.…”