Can I see the COVID virus under the microscope

Most people when they hear the word ‘microorganism’, think bacteria, fungi, amoebas – and viruses such as COVID-19.

But almost no one has seen a virus, at least through conventional microscopes.

The reason is simple – when it comes to microorganisms, there’s tiny and then there’s tiny.   

Why can’t I see COVID with an ordinary microscope?

The coronavirus is just too darn small.

Microorganisms such as bacteria are already small – with a diameter of between 0.2 and 2 micrometres. They’re so small they’re hard to see even with the high magnification of a compound light microscope, but they are still hundreds of times larger than a virus.

Viruses are measured not in micrometres, but in nanometres.

Even with the best light microscope, it’s just not possible to get the magnification and resolution needed to capture an image of a virus like COVID.

What’s the problem?

Most viruses are so small that the problem doesn’t lie with the microscope – the problem is the wavelength of light itself.

The wavelength of visible light ranges from about 400 to 700 nanometres. The coronavirus on the other hand is just 50 nanometres. Photons of light are just too big to get the job done.

So, what do you do when light itself isn’t small enough? You turn to the …

Electron microscope

Electron microscopes were originally developed in the 1930s for just this situation.

Commonly referred to as Scanning Electron Microscopes or SEM for short.

When the wavelengths of optical light were too large, researchers turned to something far smaller – the humble electron.

Instead of light, electron microscopes fire a stream of electrons at or through a sample, producing images with thousands of times greater magnification and resolution. They can visualise objects down to 0.1 nanometres and are even capable of imaging atoms.

With this kind of resolving power, the nano-scale world of the coronavirus is no longer inaccessible to humans. The only trouble is that electron microscopes are sophisticated and expensive instruments that you can usually only find in research institutes or universities.

Fortunately, we can all be grateful that laboratories and universities around the world have managed to produce and share detailed images of COVID and other viruses, helping researchers to understand their structure so that better treatments and vaccines can be developed.

An interesting exception

As mentioned above, viruses like COVID are normally invisible to a conventional light microscope. But in recent years a new kind of virus has been discovered – the giant virus.

They’re so large that upon discovery many species were mistakenly identified as bacteria. After all, until very recently no one had ever knowingly seen a virus through a light microscope.

Giant viruses are a surprisingly diverse and numerous bunch, and their origins are still a contested mystery – were they normal-sized viruses that evolved using host DNA?