The precise manipulation of small amounts of liquids is key in many scientific and technological processes involving physics, chemistry and biology. Digital microfluidics, where drops are individually controlled on open surfaces, offers a promising alternative to conventional channel-based microfluidics. The EU-funded DIOPTRA (Digital optofluidics for remote actuation of liquids) initiative worked to develop a digital optofluidic toolbox for on-demand droplet manipulation. The researchers investigated two different mechanisms via liquid-liquid and liquid-solid interfaces. DIOPTRA used the chromocapillary effect to manipulate droplets on a light-sensitive solution as a liquid-liquid interface. The researchers wished to control a large number of droplets on demand with a microprojector. For liquid-solid systems, DIOPTRA applied a new wetting mechanism to control water droplets on solid surfaces. The researchers placed heat-responsive polymers on top of strongly adsorbing solids and used the temperature gradient to move the droplets. The researchers successfully developed thermosensitive polymer-based surfaces and demonstrated how these surfaces can control droplets when combined with directed light. DIOPTRA successfully used this technique to organise particles on solid substrates from evaporating drops containing a photosurfactant. These results open up a new range of optofluidic operations for physics, chemistry and biology researchers.
Droplet manipulation, light-based system, liquids, microfluidics, DIOPTRA, digital optofluidics