Levitation’s what you need

Welcome! A veritable feast for you this month – indeed you join us just as our cups are in danger of falling into the ‘over runneth’ category. We have for you the world’s smallest cup of coffee, a sound more intense than a rocket launch heard from 3ft away and toothpicks…that fly.

You want to read about those things right? Who wouldn’t? But you are busy people – if nothing else you’d no doubt like to get on with the crossword at the bottom of the page. Fear not however, in a moment of dazzling efficiency we have found something for you that combines all of these in one handy bite size story.

It is a story that began more than a century ago and has had biochemists, among others, in a tizz ever since. In 1902 Lord Rayleigh – or to give him his full title John William Strutt, 3rd Baron Rayleigh, Order of Merit don'tyouknow– introduced the concept of acoustic radiation pressure. In a nutshell this is the basic property of waves – electromagnetic or acoustic – to exert a steady, albeit relatively weak, force.

It took until the 1990’s before scientists really started to realise some of the potential of this basic property – including a major surge in various biomedical applications. But it has taken until today to be able to report that work on the acoustic radiation force has reached its zenith. Indeed it has reached the goal of any research as far as we are concerned – it has been used to levitate some toothpicks. Not only that, but rotate them as well.

Researchers from the Swiss Federal Institute of Technology (ETH) in Zurich have built an acoustic levitator from two platforms which can ‘trap’ the toothpicks between them. One platform emits and the other reflects acoustic waves – which then reinforce and cancel out in a manner that creates a powerful stationary wave. And powerful it has to be – in order to take on and beat gravity the levitator had to generate a staggering 160 decibels of sound. This is significantly louder than the 120 decibels you would expose your ‘shell-likes’ to if you unfortunately found yourself 3ft away from a rocket launch. Cunningly, the researchers used ultrasound so they didn’t deafen themselves – which we imagine would really take the edge of the fun of toothpick levitation.

So far so what, surely this is just an amusing trick?

Not a bit of it. You see the real breakthrough is the ability of lead researcher Daniele Foresti and his team to manipulate the materials that they levitate. By making the acoustic platform of many tiny squares, and making each 15mm x 15mm square its own sound-emitting device, the team are able to "pass" materials from one of these platforms to another.

Of course it isn’t just toothpicks that can levitated – much more importantly it can be done with droplets of liquid. This opens up the possibility of remotely controlled chemical reactions that are contactless, meaning chemical tests could be carried out without any contamination. And just like that the entire pharmaceutical, biochemical and genetics community have their attention well and truly grabbed.

The challenge of totally contamination free reactions has been chased for decades – but has taken on particular relevance in recent years as it can seriously hinder DNA transfection. And that is precisely the next goal of Foresti – he wants to introduce DNA into a cell…as it hovers in his specially constructed acoustophoretic chamber.

But before he gets to that, his current work – published in PNAS – needed to prove the concept – and prove it he did in the most spectacular fashion. Presumably after donning a baristas outfit and a chirpy ‘Starbucks’ smile he introduced a single drop of water and a single coffee grain, and in an instant produced the world’s smallest cup of coffee. Proof not only of the concept of acoustic levitation, but also that coffee really is the lubricator of scientific success.