NEWS OF THE WEEK NANOTECHNOLOGY
DRAWING WITH DNA Nanopipette allows voltage-controlled delivery of biomolecules to a surface
REPRODUCTION A miniature copy of Gina Candelori's "Degas Dancers" (right) was drawn with red and green DNA. On the left is the downsized original.
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C O M M O N PROBLEM E N -
countered when different materials are to be deposited on the same spot is that they don't land exactly on top of each other. The result is multiple imprints slightly misaligned—
what is called lack of registry. A tool has now been developed to address the problem for nanoscale applications: a doublebarreled nanopipette that gives researchers fine control when depositing molecules on a surface. David Klenerman of the University of Cambridge and his coworkers there and at Imperial College London use the nanopipette with scanning ion conductance microscopy to draw pictures on glass slides with fluorescent D N A as the pigment (Angew. Chem. Int. Ed. 2 0 0 5 , 4 4 , 6854). Each barrel of the nanopipette is filled with an electrolyte solution containing one of the components to be deposited. As the
SPECTROSCOPY
IONIC LIQUIDS IN HIGH VACUUM INSIDE VIEW Liquid samples are placed in an ultra-highvacuum chamber and exposed to X-rays. Species excited by the X-rays emit photoelectrons with specific binding energies.
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X-ray photoelectron spectroscopy used to probe room-temperature ionic liquids
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HEMISTS AT THE UNIVERSITY
ofNottingham, in England, have used anukra-high-vacuum (UHV) technique—X-ray photoelectron spectroscopy (XPS)—to investigate pure room-temperature ionic liquids and solutions of catalysts in ionic liquids (Chem. Commun., published online Oct. 17, dx.doi.org/10.1039/ b512311a). Team leader Peter Licence believes this is the first time any liquid sample has been investigated by any U H V spectroscopy. 2005
"Prior to our work, all samples studied by these techniques were either solids or frozen samples. Normal liquids simply evaporate under UHV. Ionic liquids have almost zero vapor pressure because they are composed entirely of ions. They therefore do not evaporate under UHV," he says. XPS provides information about the electronic states of different kinds of atoms in a compound and has sufficient sensitivity to distinguish between atoms of the same element situated in chemically distinct environments in a compound, Licence explains. "Our preliminary experiments
nanopipette approaches the surface, a droplet forms at the tip. A voltage applied between the two barrels determines which component and how much will be deposited. A variety of biological and synthetic molecules can be deposited. As a demonstration of the fine control and improved registry, Klenerman's team used red and green DNA, produced by fluorescence labeling, to reproduce artwork. Spots containing only one fluorophore show up as that color, whereas spots containing both fluorophores show up as yellow. Each image took about 30 minutes to generate. "We see it as a prototyping tool," Klenerman says. He plans to combine this technique with a method for imaging live cells. "We can imagine controllably dosing a receptor on a cell surface and seeing how much is required to make it respond," he says.—CELIA HENRY
have demonstrated that it is possible to obtain high-quality XPS data on pure ionic liquids as well as on ionic liquids doped with simple metal salts," he says. "We are therefore able to carry out in situ monitoring of catalysis in ionic liquids and obtain information about dissolved catalytic species. In principle, we could use this information to explain catalytic performance or selectivity." The Nottingham researchers obtained high-resolution X-ray photoelectron spectra of 1-ethyl3-metiiylimidazolium ethylsulfate, a commercial ionic liquid. They also used the technique to monitor the reduction of Pd2+ ions in a solution of a palladium catalyst in the liquid. Potential applications of XPS of ionic liquids are wide-ranging, says Licence. "They include the investigation of the dynamics of ionic liquid surfaces and interactions with solutes and the electrochemistry of ionic liquids in vacuo."—MICHAEL FREEMANTLE
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