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Brief Communications

Nature 426, 515-516 (4 December 2003) | doi:10.1038/426515a

Open Innovation Challenges

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On-chip manipulation of free droplets

Orlin D. Velev, Brian G. Prevo & Ketan H. Bhatt

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Tiny free-floating drops can be driven across a liquid medium by an electric field.

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'Lab-on-a-chip' systems resemble factories with permanently rigged pipes, but their prefabricated microchannels could have problems in delivering materials such as suspended particles, biological cells or proteins, which may adhere to the walls and clog the channels. More flexible microfluidic systems allow liquids to be transported as droplets on a solid surface1, 2, 3, 4, 5, 6, 7, 8, 9, 10, but these suffer from similar drawbacks where the droplets are in contact with solid walls. Here we describe a liquid–liquid microfluidic system for manipulating freely suspended microlitre- and nanolitre-sized droplets of water or hydrocarbon, which float on a denser, perfluorinated oil and are driven by an alternating or constant electric field applied by arrays of electrodes below the oil. These microfluidic chips could be used as a versatile tool in microscale transport and mixing and in chemical and materials synthesis.