Jean-Christophe Baret and colleagues, Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany, have used high AC voltage of up to 1000 V to control exactly how many droplets flow through tiny channels on a plastic chip per second. The tiny water droplets are only visible under the microscope. The higher the applied voltage, the quicker the succession of the droplets – the higher their frequency.

To translate these frequencies into musical notes, the researchers added a fluorescent agent to the water, so that the droplets emitted light when illuminated with a laser. A photomultiplier tube converted the light into electric signals, which in turn were used to create the respective notes with a sound card.

The frequencies differ from the original note by up to 5 %. This is roughly equivalent to a half-tone. Due to the mechanical properties of the microfluidic chip, the intervals between the successive droplets are not always identical. Also the electric voltage changes with a slight delay.

The ability to control the movement of droplets with a high degree of precision using electric voltage is seen as a significant step in the development of a medical chip laboratory. Electric fields could, e.g., be used to sort out infected cells or mutated DNA.

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• The Microfluidic Jukebox,
  Say Hwa Tan, Florine Maes, Benoît Semin, Jérémy Vrignon, Jean-Christophe Baret,
  Sci. Rep. 2014.
  DOI: 10.1038/srep04787

• “Music Video”
  The first test of the researchers was to play the Ode to Joy from Beethoven.