Scientists have designed a device that can levitate materials using sound. Daniele Foresti and colleagues at ETH Zurich in Switzerland used their acoustic levitator to create this explosive mid-air reaction between a tiny water droplet and a grain of sodium. The levitator works by sending powerful ultrasound waves between an emitting surface and a reflector, which bounces them back. Where the emitted and reflected waves meet, they interfere and create stable areas that can trap small pieces of material. The positions of the waves can then be altered to move the hovering material around.

The team were able to watch chemical reactions in mid-air, mix water droplets with instant coffee granules and even levitate a toothpick. They say the levitator could have important applications in research. As the technique is completely contactless, it could be useful for processes such as DNA transfection that are vulnerable to contamination.