Why understanding the virus’ particle size and shape is critical

In view of the current COVID-19 outbreak, scientists are busy developing antivirals and vaccines to treat patients. China has given the go-ahead for researchers to begin human safety tests for an experimental coronavirus vaccine. Scientists in the United States have also begun clinical trials for a vaccine. In order to develop a viable vaccine or treatment, it is first important to characterize and understand the virus.

Being able to characterize the particle size of the virus can help scientists predict how it is spread. For instance, it could be used to understand the time that the infectious agent can remain suspended in the air, the distance across which it can be transported, as well as the site of deposition, viability and virulence of the virus, etc. 

Virus particles are typically very small in size – about 20 nm – 250 nm. Coronavirus ‘particles’ are spherical in shape with a diameter of approximately 0.13 µm. The smallest coronavirus ‘particles’ are about 0.06 µm, and the largest are about 0.14 µm.

Particles of such small sizes can remain suspended in the air for long periods. This presents a potential exposure risk to people both close to the source and at greater distances. A spherical particle of 4 μm in diameter takes 33 min to settle 1 m in still air, compared to a 1 μm particle that will take 8 hours to settle [1].

Infectious particles smaller than 10 μm tend to have more serious health implications as they are able to penetrate more deeply into the lower respiratory tract to establish infection. Therefore, particle size is central to the epidemiology of airborne pathogens.

Various viruses are present in the air constantly, but in small amounts which are generally not enough to cause disease in people with healthy immune systems. However, at higher concentrations, the risk of human infection increases dramatically [2]. Early detection of the virus is essential for prevention of the spread of viral infection. 

As such, characterization of the virus particles in terms of particle size and concentration is instrumental not only in early detection, but also in the development of treatments and vaccines.

Interested in learning more about the latest characterization tools that can be applied to virus and vaccine studies?

  • NanoSight: Utilizing Nanoparticle Tracking Analysis (NTA), Malvern Panalytical’s NanoSight allows one to visualize and measure nanoparticle concentration, particle size from 0.01 – 1 µm* in solution as well as characterize protein aggregation in real-time. This makes NTA a great companion for studies in viral vaccine research, nanotoxicology and biomarker detection, as well as the characterization of extracellular vesicles for disease state studies. Read more.
  • Zetasizer Ultra *NEW*: The Zetasizer Ultra is the world’s most capable combined DLS and ELS system, incorporating Non-Invasive Back Scatter (NIBS®) and, uniquely, Multi-Angle Dynamic Light Scattering (MADLS) technology for the measurement of particle and molecular size. NIBS provides the versatility and sensitivity to measure over a wide concentration range, while MADLS permits a higher resolution view into your sample’s size distribution for those critical measurements.
  • An extension to MADLS affords the ability to directly analyze particle concentration. The measurement of particle concentration is calibration-free, suitable for a wide range of materials, requires no or little dilution, and is quick to use – all of which make it ideal as a screening technique.  This is a unique capability of the Zetasizer Ultra which can even be applied to samples such as viruses and VLPs, which were previously very challenging to measure. Read more.

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