The entangled bank unravels p.251
doi: 10.1038/462251a
Volume 462 Issue 7271
Editorials
p.252
doi: 10.1038/462252a
News
p.256
doi: 10.1038/462256a
Japanese science faces deep cuts p.258
doi: 10.1038/462258a
p.258
doi: 10.1038/462258b
Muon collider gains momentum p.260
doi: 10.1038/462260a
p.263
doi: 10.1038/462263a
p.264
doi: 10.1038/462264a
p.265
doi: 10.1038/462265a
News Features
p.266
doi: 10.1038/462266a
p.270
doi: 10.1038/462270a
p.272
doi: 10.1038/462272a
News & Views
p.291
doi: 10.1038/462291a
p.292
doi: 10.1038/462292a
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doi: 10.1038/462294a
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doi: 10.1038/462295a
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doi: 10.1038/462296a
Guiding light p.297
version="1.0"?> ]>With microfluidic devices gaining prominence for many applications in chemistry and biology, the hunt is on to find ways of accurately controlling the motion of liquid droplets. In Angewandte Chemie, Antoine Diguet et al. describe a method for using light to trap and move oil droplets floating on an aqueous solution (
This isn't the first time that light has been used to push droplets around. But Diguet and colleagues take a new approach based on the chromocapillary effect, in which light generates a tension gradient at a liquid–liquid interface. This gradient can induce an interfacial flow between droplets and bulk liquids, which propels the droplet in the opposite direction to the gradient.
The authors' technique depends on the compound dissolved in the bulk liquid. Diguet et al. used a surfactant that isomerizes in response to different wavelengths of light — it adopts a polar isomeric form when illuminated with ultraviolet light, and a less polar form when lit with visible light. The light-induced changes in polarity modulate the surface tension between the surfactant solution and oil droplets floating on its surface. So, when the authors partially illuminated such a droplet with ultraviolet light, the tension gradient caused the droplet to move away from the lit area. If they then partially irradiated the droplet with visible light, the droplet moved towards the lit area.
By combining ultraviolet and visible light, Diguet et al. made a chromocapillary trap that captured oil droplets cast onto the surface of the surfactant solution. The authors could then drag the droplets across the surface of the solution, at speeds of about 300 micrometres per second, simply by moving the trap around. The image above is a montage of superimposed frames from a movie, and shows a droplet (gold colour) being directed by a trap (cyan halo) along a heart-shaped path; the Petri dish is 5.1 centimetres in diameter.
Chromocapillary traps should work for various combinations of immiscible liquids, and could thus be useful for controlling droplets in micro- or millifluidic devices. The authors' system could also be used to safely handle dangerous liquids, or in light-responsive materials.
p.298
doi: 10.1038/462298a
Articles
Human DNA methylomes at base resolution show widespread epigenomic differences p.315
doi: 10.1038/nature08514
RNA polymerase II-TFIIB structure and mechanism of transcription initiation p.323
doi: 10.1038/nature08548
Letters
A limit on the variation of the speed of light arising from quantum gravity effects p.331
doi: 10.1038/nature08574
Coexistence of Fermi arcs and Fermi pockets in a high-Tc copper oxide superconductor p.335
doi: 10.1038/nature08521
Ultraflat graphene p.339
doi: 10.1038/nature08569
Evidence for warmer interglacials in East Antarctic ice cores p.342
doi: 10.1038/nature08564
Reconstruction of the history of anthropogenic CO2 concentrations in the ocean p.346
doi: 10.1038/nature08526
Mutation load and rapid adaptation favour outcrossing over self-fertilization p.350
doi: 10.1038/nature08496
Frequency of gamma oscillations routes flow of information in the hippocampus p.353
doi: 10.1038/nature08573
Systems-level dynamic analyses of fate change in murine embryonic stem cells p.358
doi: 10.1038/nature08575
Signal peptides are allosteric activators of the protein translocase p.363
doi: 10.1038/nature08559
Dynamic activation of an allosteric regulatory protein p.368
doi: 10.1038/nature08560
Review Articles
Light and shadow from distant worlds p.301
doi: 10.1038/nature08556
Human genetics illuminates the paths to metabolic disease p.307
doi: 10.1038/nature08532
