Increasingly scientists are developing lab-on-a-chip devices that can do the work of an entire lab on the area the size of a microchip. It is often important to route liquids in circuits to perform complex analysis tasks. While these chips are often small and portable, they rely on control machinery off the chip, negating their size advantage for many applications. Now researchers have developed a fluid version of a clock to help coordinate activity on these devices, according to research published in the Proceedings of the National Academy of Sciences. This work could help create a completely self-contained laboratory-system-on-a-chip with cost and distribution advantages for point-of-care diagnostics.
Lab-on-a-chip devices shrink beakers, flasks and other lab equipment into the form of channels, pumps and valves. These microfluidic devices ultimately may enable researchers to conduct thousands of experiments simultaneously at a fraction of the time, space, materials, cost and effort of what it might ordinarily have taken. Similar to how modern electronic devices route electrons, these mechanical systems and route fluids.
“The very first computers were mechanical,” says biomedical engineer Elliot Hui at the University of California, Irvine. “Although electronics has proven to be a far superior computing medium, the physical nature of mechanical computers has an immediacy and elegance that I find fascinating. The current interest in steampunk shows that popular culture shares this curiosity to some extent.”
Although scientists have successfully used microfluidic chips to perform a wide variety of biological and chemical experiments, they had yet to integrate clocks into these devices, which help electronics synchronize internal systems and coordinate with the outside world. As such, microfluidic chips have to rely on external timers and other control apparatus to work.
Now Hui and his colleagues have built a microfluidic circuit that can serve as a clock. “We are the first to produce a microfluidic frequency reference with adequate stability to provide timing control for typical microfluidic applications such as performing a diagnostic assay,” Hui says.
The device consists of a ring built from microfluidic valves and channels. Air pressure in the circuit drives the valves to open and close in a regular pattern. When operating for seven hours, the accuracy of the clock drifted by less than 1 percent per hour, suitable for controlling typical biochemical reactions for point-of-care diagnostics and many other lab-on-a-chip applications, the researchers said.
“It’s actually a pretty lousy clock in the conventional sense; you wouldn’t want to use it as a wristwatch, for example,” Hui says. “But for timing the length of biochemical reactions, this is very much sufficient.”
The researchers also used the clock to coordinate the timing of multiple valves for peristaltic pumping, similar to how the human body moves food down the gut.
“Due to the rapid and coordinated valve actuation pattern that is necessary, peristaltic pumps have always required control signals produced from off-chip,” Hui says. “We are the first to demonstrate pumps where the control circuitry is entirely integrated on-chip.
The clock “is an important step towards a full microfluidic computer, and the self-driving pump is an important step towards self-contained lab-on-a-chip devices,” Hui adds. “We are making good progress towards building a complete computer as well as building the biochemical assays that it will be designed to control.”