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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