PORTLAND, Ore. Bubble memory technology is backthis time in a microfluidic version for logic applications rather than the magnetic approach taken by Texas Instruments in the 1970s.
Invented by scientists at the Massachusetts Institute of Technology, the microfluidic bubbles are used for logic, not memory. Bubble logic can encode on-chip process control for microfluidic devices, in lieu of electronic circuitry, the researchers claimed.
"Our bubble trains encode information, with the presence of a bubble representing a "1" while its absence implies a '0'," said Manu Prakash, a research assistant at MIT's Center for Bits and Atoms, where bubble logic was invented. "Thus a bubble is a single bit of information, but now a bit of information can'also carry a'material [or] chemical payload. This is a powerful paradigm as a computation also results in physical material processing at the same time."
The work was performed with Neil Gershenfeld, director of the Center for Bits and Atoms.
Bubble logic promises to enable microfluidic "labs-on-a-chip" that incorporate computer-like control for the processing of chemicals without electronic circuitry. By encoding bubbles into the chemical flow itself, the MIT team demonstrated that microfluidic devices can carry their own process control information without the need for an external microprocessor.
Microfluidic devices demonstrated by the researchers were about 100 times faster than the external valves and control systems used in current microfluidic chips, but were about 1,000 times slower than a microprocessor.
Microfluidic labs-on-a-chip use nanoliters of chemicals that speed up reactions, enabling tests to be performed in minutes rather than hours or even days. The small amount of reagents needed makes testing much cheaper. In addition, the push-button control provided by application-specific channels on a microfluidic chip mean testing could move from the lab to the field.
Without bubble logic to encode process control information, however, current microfluidic labs-on-a-chip must rely on interfaces with electronic circuitry and battery powered microprocessors. Using bubble logic, process control information could be encoded into the chemical flow itself, allowing valves to be automatically opened and closed in the correct sequence to perform specific tests.
According to the researchers, bubble logic is encoded into long trains of molecules moving lock-step through a microfluidic device, permitting chemicals to be gated into the proper microfluidic reaction chambers. After the reaction takes place, the same chemical flow gates the results out of the reaction chambers and into read-out channels which indicate the results.
"We have tested numerous schemes for readout," said Prakash. "The easiest is optical, but we have numerous other'readouts based on applications which include pressure transients [and] capacitive sensing."
Besides tests, bubble-logic controlled processes could synthesize compounds, sort biological cells and deposit anything from chemicals for etching to ink for print-heads.
The MIT researchers also demonstrated logic controlled microfluidic devices using nitrogen bubbles, but other types of gas would also work. Current demonstrations at the MIT Center include bubble logic controlled gates, memories, amplifiers and oscillators.
Funding for the project was provided by the National Science Foundation.
Texas Instruments took the first crack at magnetic-based bubble memory technology around 1975.