Light microscopes are handy optical instruments that come with a variety of essential uses, such as in studying various microorganisms, including parasites, bacteria, and fungi. However, they also come with many limitations.
While a light microscope can be extremely beneficial in bacteriology and pathology, can the same be said for, say, virology? Can viruses be seen with a light microscope? If yes, how? If now, what microscopes can be used to study viruses?
These are all questions we will answer in this article.
Can viruses be seen with a light microscope?
The answer is yes and no. There are now modern developments with light microscopy equipment that come with a significantly increased range and resolution of around 350 to 40 nanometers, more than well enough to study live viruses in superior detail.
However, these optical microscopes are not your conventional light microscopes, and often employ complementary techniques and tools to work. These nano imaging systems may make use of things like transparent microspheres, reflectance imaging sensors, and ultraviolet light.
So, the answer is, with a conventional light microscope, viewing viruses may be an almost impossible task, but it can definitely work with a modified light microscope that features an extraordinarily high resolution, and is equipped with a light source that delivers a significantly short wavelength of light waves to be able to image something as small as virus particles.
Here is a comparison of the same virus particles on a sample that is viewed through a scanning electron microscope versus a modified light microscope. While there is a wide disparity in resolution, it’s clear that the viruses can be identified with the light microscope.
How it works
These modified light microscopes not only have the capability to view submicroscopic organisms such as viruses, but it can also image thousands of these virus particles at once, and automatically count and size the virus particles.
Different types of viruses, such as the ebola virus and the zika virus, can also be identified by using different light wavelengths. This, coupled with a multiplexed analysis of the sample, can easily characterize each individual virus particle.
This unprecedented ability of light microscopy to be able to be used for observing viruses comes with many useful benefits, the most important one being that it enables researchers and medical practitioners to detect viruses quickly, and thus deliver a cure and a vaccine.
Moreover, even with all the modifications and upgrades, these microscopes are still much easier to use, cheaper, and more accessible than the typical microscopes used for this task, such as electron microscopes.
Having said all of these things, there are still a lot of issues surrounding the use of light microscopes in the study of viruses. This is mainly because this is a relatively recent technology that is still continuously being developed.
Hence, many other microscopy techniques are still preferred and more commonly used to study virus particles. But, why is this so important, anyway? What is it with viruses that they can’t be imaged with just a simple light microscope?
What is a virus?
A virus is defined as an infectious agent that infects the living cells of all life forms, including humans, animals, plants, and other microorganisms. In fact, even bacteria can be infected by a virus.
Generally, viruses are infinitesimally small submicroscopic particles that are easily around 100 to 500 times smaller than any bacteria. Virus particles, called virions, typically measure at only about 400 to 25 nanometers.
This is often beyond the limit of most light microscopes, including the conventional compound microscope with a resolution of only 200 nm. As such, it’s almost impossible to study viruses through light microscopy, unless you simply want to see a giant virus’ general morphology.
This is a microscope image of a live virus inside its host. You can clearly see various cells and tissue sections surrounding the virus particles, and how these particles are distributed within the host.
Different viruses have different sizes and shapes, depending on the type of virus family they belong to, but they are generally helical or icosahedral, and come in minutes size when compared to other microscopic organisms
Apart from these things, common characteristics of viruses include the fact that these are not living cells, but rather, they live off of the host in order to survive and reproduce. These particles are equipped with receptor-binding proteins that enable them to attach to the host.
What microscopy techniques can be used to observe viruses?
While it can be difficult to observe viruses with a light microscope, many different types of microscopy techniques can be utilized to study virus particles, and these include electron microscopy, atomic force microscopy, fluorescence microscopy, and dark field microscopy.
Take a look at this three-dimensional image reconstruction of the chikungunya virus, as observed through cryo-electron microscopy techniques. The structure of the virus particle is clearly visible and distinguished.
Here are the most common microscopy techniques used to observe viruses:
There are various types of electron microscopy used to image virus particles, including immunoelectron microscopy, electron tomography, transmission electron microscopy, and cryo-electron microscopy.
Transmission electron microscopy is a sophisticated technique that allows for the detailed imaging and observation of nanosized specimens, including, of course, virus particles, by making use of electron beams rather than visible light to illuminate the specimen.
Meanwhile, cryo-electron microscopy is a specialized type of electron microscopy that works by freezing the specimen in liquid nitrogen to be able to study its physical structure through the rendition of a three-dimensional image.
Take a look at this high-resolution image of the H1N1 influenza virus as seen under a transmission electron microscope. The clarity of detail is superb, enabling the viewer to identify several characteristics of each particle.
Other types of microscopy
Aside from electron microscopy, which can often be costly and complicated, there are other types of microscopy techniques that can be utilized to view virus particles, such as fluorescence microscopy and total internal reflection dark field microscopy.
Fluorescence microscopy is used to quantify the concentration of virus cells in a sample. It works by using fluorochromes to track viral DNA in the cells of the host, and as the viruses are identified, they are then viewed under a confocal microscope.
Finally, total internal reflection dark field microscopy makes use of a perforated mirror to identify and track larger virus particles without any need for labeling. The downside is that this technique is quite complicated and requires several procedures to work.
Viruses are submicroscopic particles that are hundreds of times smaller than bacteria and are infectious to various living organisms. Due to their small size, these virus particles are often difficult to study, especially with the use of conventional light microscopes.
However, there are modified light microscopes that are up to the task, as well as a variety of other microscopy techniques equipped with the right specifications and capabilities to study virus particles in great detail.