What does a virus sound like?

It might seem like a strange question - but it’s one that scientists have been attempting to grapple with in a bid to find out whether we can better defend ourselves against them, and also gain new insights into how they operate inside cells. Elad Harel at Michigan State University has got a way to shake virus particles with lasers and then “listen” to the vibrations to work out what shapes they are and what they’re made of. It’s amazing…

Elad - We wanted to know if we could track a virus by its sound. Do viruses make a sound? Can you induce them to make a sound?If they do, can we use that to track them and avoid some of the challenges with studying them nowadays?

Chris - They're also, some of them, one thirty thousandth of a millimetre across. Absolutely tiny. How on earth can you listen to something that small?

Elad - We've looked at very small objects before. We've looked at the nanoscale; a billionth of a metre. And we knew that we could measure these kinds of vibrations, we call them acoustic vibrations. We could do it on these metal nanoparticles. But from a very naive point of view, a virus is a small nanoparticle. It's very well organised and well structured. And we thought maybe it also produces some kind of ordered vibrations. We wanted to know if we could pick that up. We knew approximately where we would be looking.

It's about a frequency that's a million times higher than what humans can hear. It's something that you need very specialised instrumentation to detect. And the challenge really was the fact that a virus is embedded in a very complex environment. If you think about the virus in a cell, there are lots of other materials around it. And all of these materials also give rise to different sounds. So, could we pick up the sound in the background of everything else? Trying to pick up the sound of, say, an insect in a forest from hundreds of metres away. That was the technical challenge that we were facing.

Chris - How did you do it then? What was the apparatus that enabled you to tune in to the sound of a virus?

Elad - What was really amazing was that we could use light both to generate the sound and to detect the sound. So you can think of light as a hammer. Like when you bang on the table with a hammer, you bang on the nail, you're banging on the wall, you're really causing vibrations in that material. All those atoms that are in that material, in that table, in that wall, in that piece of glass, whatever it may be, they're all vibrating. So what we did is we used light as the hammer itself. So the light actually caused this virus particle to vibrate at this very, very high frequency.

And then to detect that, we used another laser pulse, which actually scattered off the vibrating virus particle. We capture this in a kind of stroboscopic way. So, that means that if you've ever been to a disco - or to a club - and you see that strobe light, right, and it kind of flashes on and off and you see these snapshots of people moving, that's kind of the idea where we hit this thing with a hammer, it starts vibrating, and then we wait a little bit of time, we take a picture of it. And then we repeat that over and over again, about 100 million times a second. And we build up a kind of a movie that shows a sound wave that goes up and down, up and down. This virus is really acting like a very small instrument.

Chris - Just out of interest, what virus was it that you were using as your test virus here?

Elad - It was a rhinovirus.

Chris - So, the common cold, the thing that every one of us is suffering with. Did you get it from someone in the lab?

Elad - We got it from a collaborator.

Chris - What, from his own nose? Or what I meant was, did someone donate the specimen of their own mucus because it's so common, isn't it? But more seriously, what is the purpose of this? Is it just that you're stressing the system to prove that you can do this with these tiny entities? Or is it that there may well be an application to being able to probe tissue that's got things like viruses lurking in it like this?

Elad - We see it as having two main applications. On one hand, diagnostics. You can imagine, with PCR tests, you can't detect whether the virus infection is active or not because the virus may have already ruptured and you're detecting really the genetic material inside of the virus. So here we have a method where we can detect the virus at the single virus level. That's just one virus particle. So we have the ultimate limit of sensitivity. And so you could imagine detecting viruses very, very early on before the onset of any symptoms. And because you could do it with light, you could even do it at a distance without making any physical contact.

On the other hand, we're primarily interested in the applications, understanding how viruses actually function. What are the dynamics of viruses? How does a virus assemble? How does a virus disassemble? How does a virus attach to a receptor? How does it get brought into the cell? If you can track that in real time, which is what we're trying to do now, you could develop antivirals by targeting any part of the virus life cycle to really speed up and streamline that process of trying to understand how drugs interrupt the binding or some other process where viruses can replicate and can infect you and make you sick.