Particle Size Analysis of Viruses
and Virus-Like Particles

A virus particle consists of several parts including the genetic material (DNA or RNA), a protein coat that protects these genes, and in some cases an envelope of lipids that surrounds the protein coat when they are outside a cell. The size of viruses ranges from a few tens to a few hundreds of nm, which is equal to 1/100 to 1/1000 of the cell (a few to a few tens of μm in size) of any other common living organism. Influenza vaccines are now produced by growing the virus in fertilized eggs, then multiplying and inactivating it. The picture below is an electron micrograph of an influenza virus. 

Image of an influenza virus
Image of an influenza virus

Virus-like particles (VLP) are meant to mimic the virus of interest in everything except the genetic material. Due to this similarity (particular in terms of conformation) VLPs prove useful in the study of virus behavior and also vaccine development. The size of VLPs is similar to that of viruses and may be measured using either dynamic light scattering or laser diffraction technologies. The ability of laser diffraction to measure from nanometers to thousands of microns makes it well suited for VLP development. Depending on how the VLP is manufactured it's possible that fragments of starting material will be present in the sample at larger sizes than the VLP itself. The size of these particles can either be too large for dynamic light scattering to measure or present a difficult challenge for the lower resolution of that technique.


Size of Viruses using Dynamic Light Scattering

The SZ-100 Nanoparticle Analyzer has been successfully applied to analyze transparent bioparticles, such as influenza viruses and vaccines, with good accuracy. The particle diameter of any bioparticle determined by dynamic light scattering is usually larger than that from an electron micrograph. The reason for this is that hydrates and proteins around the cell move together, causing the particle to meet with resistance, which in turn causes DLS measurements to yield a larger particle size.

The result below for an influenze virus reported a mean size of 127.6 nm, with good repeatability. The measurement was made in the standard glass cell at the 90 degree scattering angle.

Particle size distribution for an influenza virus as measured by the SZ-100.
Particle size distribution for an influenza virus as measured by the SZ-100.
Size results for an influenza virus as measured by the SZ-100.
Size results for the influenza virus.

Size of Virus-Like Particles using Laser Diffraction

The LA-960 Particle Size Analyzer measuring range stretches from 10 nanometers to 5 millimeters. This is more than sufficient to measure virus-like particle samples -- including those containing material larger than several microns. An example size result (below) shows three separate populations. The finest population is the VLP itself. The LA-960 can report size metrics for the entire population as well as metrics for each individual population using the Multimodal Report.

Particle size distribution and results for a VLP material as measured by the LA-960.
Click to enlarge: Particle size distribution and results for a VLP material as measured by the LA-960.

Summary

The HORIBA SZ-100 and LA-960 particle size analyzers can measure the size of viruses and virus-like particles quickly and accurately. Additionally, the SZ-100 can measure the zeta potential of these materials.


Particle Analyzers for Virus and VLP Applications

SZ-100 Nanopartica Series Instruments

Industry's widest range and highest precision measurement instrument for Nanoparticle characterization.

LA-960

The LA-960 uses Mie Scattering (laser diffraction) to measure particle size of suspensions or dry powders. The speed and ease-of-use of this technique makes it the popular choice for most applications.