How dense is a virus/virion in relation to water?

[Aero51]

I am doing a project for my fluids class pertaining to particle tracking. As a sample application, I would like to simulate a virus traveling through a filter or (most simply) a very narrow tube in laminar flow conditions. I need the density of an individual virus particle (a virion as Wikipedia says) to resolve the buoyant forces. Right now I have found very low density viruses to be about 1.03 g/ml or about 1030 kg/m^3 (just under the density of water). I have no physical intuition, but that number seems very large for a virus. I would think if their density was almost as high as water that there would be no such thing as an "airborne virus" simply because it would sink to the ground. Does anyone have a good reference?

 

[mfb]

The density of water is a good approximation for all cells and cell-like structures, usually water is the main component.

Virus particles are so small that buoyancy (and gravity in general) is negligible in realistic setups - sure, if your air is perfectly motionless, on average the particle will sink, but if that happens on a timescale of hours (or even longer) you can neglect it. Brownian motion is relevant for those particles, too.

 

[Ygggdrasil]

Viruses have about the same density as water. They can be airborne when they become aerosolized small water droplets.

A typical way to purify viruses is by density gradient centrifugation. Essentially, you set up a gradient in centrifuge tube with a high concentration of a salt or sugar solution at the bottom of the tube and a lower concentration on top. You then add the virus in and centrifuge overnight so that the virus migrates to where it's density matches the density of the surrounding solution. Here's a paper that estimates the density of hepatitis C virus using this method and also discusses the density of other viruses: http://vir.sgmjournals.org/content/73/3/715.full.pdf

 

[Aero51]

Thank you for the information. According to my calculations the Brownian motion is generally small, but may not be negligible. For instance, I would like to model a filtration system. We have a fully developed laminar flow in a tube of a diameter D. What diameter would be required to say, stop 90% of virions traveling through a filter channel of 100 microns in length? I am not planning on including the wall attraction just yet, but I have included the drag forces, buoyant forces and the Saffman lift force. The Brownian motion of the particle will help enhance the catching frequency. If this is not a good application, what would you suggest?

 

[LudusRex]

I can provide some insight into the density of viruses and how it relates to their behavior in fluids. First, it is important to note that the density of a virus can vary depending on the specific type of virus and its individual characteristics. However, on average, the density of a virus particle is around 1.03 g/ml or 1030 kg/m^3, which is just slightly lower than the density of water.

This may seem like a high density for such a small particle, but it is important to remember that viruses are not solid objects. They are made up of genetic material (DNA or RNA) surrounded by a protein coat, and sometimes a lipid envelope. This composition contributes to their overall density. Additionally, the density of a virus can be affected by its shape and size, as well as the environment in which it is found.

In terms of their behavior in fluids, viruses are considered to be neutrally buoyant, meaning they neither sink nor float in water. This is due to their density being similar to that of water. However, in air, the density of viruses is significantly lower than that of the surrounding air, which allows them to remain suspended and travel through the air as an "airborne virus."

I would recommend consulting scientific literature or databases to find specific information on the density of the virus you are studying. Additionally, it may be helpful to consider the fluid dynamics of the environment in which the virus is traveling, as this can also affect its behavior and movement.