July 10, 2003 As the old Hawaiian love song says, tiny bubbles really do make some people feel fine. Chemists, that is. But there is no wine involved this time, just water.
National Institute of Standards and Technology (NIST) chemists reported in the June 24 online edition of Langmuir that a process called microboiling shows promise for quick, simple and inexpensive chemical sensing. The process involves the formation of tiny vapor bubbles on a 200-nanometer-thick film of precious metal immersed in water and heated rapidly. By coating the metal microheater with a single layer of water-repelling molecules, the scientists dramatically altered the microboiling behavior. Bubbles formed more obviously and at lower temperatures, and the water in immediate contact with the metal got much hotter.
"It's astounding to me that we changed one functional group on the surface of that microheater and saw a dramatic change in the boiling behavior," says Michael Tarlov, a co-author of the paper.
The finding means that changes in boiling behavior should be useful for detecting specific substances. The water surrounding a microheater designed to bond with DNA or proteins, for example, might boil at a different temperature if the target molecules were attached to the coating. A change can be measured in just 5 microseconds, much faster than typical lab techniques. NIST scientists have found that the technique can detect surfactants, such as those used in detergents, and are studying its use in microfluidic (or lab-on-a-chip) devices.
The research also has other potential spin-offs, such as the use of designer coatings to improve efficiency in boilers and heat exchangers and the use of microheaters to simplify chemical manufacturing.
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