Microfluidic device quickly captures, releases proteins

By Mark A. DeSorbo

ALBUQUERQUE, N.M.—The tiny line of gold fingers of a new microfluidic device are the piano keys that when tickled allow this new lab-on-chip to sing songs of particle analysis to the tunes of contamination control, drug discovery, homeland defense and lab chromatography.

The device, reported in the journal Science, separates proteins from each other and solutions by electrically heating the tiny gold lines to alter surface properties, say Sandia National Laboratories researchers Dale Huber and Bruce Bunker.

Thin resistive gold heater elements are suspended over a silicon nitride membrane. The elements, fed electrical current by the gold conductor lines, give researchers piano-key control in heating different portions of the device to capture and release proteins for closer analysis.
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And those tiny gold fingers, each about a third of the width of a human hair, send current through selected lines, electrically mimicking chemical separation methods of industry-standard chromatographs, says Huber.

The device, which was manufactured in ISO Class 5 and Class 6 cleanrooms, can easily fit into the hand-held sensors that could aid in detecting anything from contamination sources in cleanrooms, cell-signaling proteins produced by the body that indicate disease, to near-instantaneously concentrating classes of suspect proteins for immediate analysis.

“Before the symptoms of the disease, the body creates cell-signaling proteins, and those proteins kick the immune system going,” says Bunker. “If you can detect these proteins, you can tell you've been exposed to something hours or even days before the onset of symptoms.”

The device, for which Sandia has applied for a patent, works by sending minute currents of electricity for microseconds through the gold crosspieces, called heat lines, to warm a 4-nm-thick polymer film.

Huber, who developed the N-isopropyl acrylamide (polyNIPAM) film, says the material responds to heat by changing from a hydrophilic (water-loving) to a hydrophobic (water-hating) state. The water-heating state makes it easy for the film to adsorb proteins passing over it in an aqueous solution, while the cooler hydrophilic state means the proteins will be carried away by water molecules and released in a natural cleansing action.

“There might only be a concentration of several thousand in a milliliter of solution,” Huber says. “You can flow that entire liter of solution over the film, which grabs all of the microbes. Then you turn the material off and it releases into another aqueous solution—so, now it will be a million times more concentrate than it was before, and easier to detect and analyze.”


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