For years, scientists have been working to develop "labs on a chip," portable devices that would perform complex analyses usually only possible in a chemistry laboratory. Such tools would also allow testing of extremely small amounts of expensive or hazardous materials. Now, researchers say a new technology that relies on microscopic bubbles may bring these nifty devices a step closer to reality.
The big stumbling block for lab-on-a-chip prototypes has been their cumbersome valves and controls, which have rendered them too slow for critical applications, such as large-scale analyses for pharmaceutical companies or in counterterrorism screenings. The new technology, called bubble logic, employs nano-sized droplets of chemicals to mimic the actions of the electrons moving through the circuits of a microprocessor. The droplets travel through tiny channels filled with water or oil--whichever fluid the droplets don't dissolve in--and switch paths automatically based on subtle differences in their mass or diameter. In doing so, they can deliver precise amounts of material to exact locations. "Bubble logic merges chemistry with computation, allowing a digital bit to carry a chemical payload," says computer scientist Neil Gershenfeld of the Massachusetts Institute of Technology in Cambridge.
Reporting in today's issue of Science, Gershenfeld and colleagues describe how they designed the new technology using the presence or absence of a sequence of bubbles as a substitute for the conventional "on" or "off" binary language of computer circuits. The end result is devices composed of little more than glass tubes and liquid that perform as microprocessors. The same basic design could accommodate bubbles consisting of a wide variety of substances, depending on the task at hand or chemical analyses required. Although still orders of magnitude slower than conventional computers, bubble logic can operate about 100 times faster than existing microfluidic chips, the researchers say. That should be fast enough to create chemical "memories" that could store thousands of substances the way computers store data and then retrieve and distribute those substances quickly.
The research "makes one wonder how far it is possible to go in constructing microfluidic 'thinking devices,' " says chemist Irving Epstein of Brandeis University in Waltham, Massachusetts.