Sound tunnels into rewritable lab-on-a-chip devices

Engineers have used sound waves to create tunnels in oil to manipulate and transport droplets, a microfluidic lab-on-a-chip advance that could improve on-site diagnostics or laboratory research.

The technology from a team at Duke University, North Carolina, could form the basis of a small-scale, programmable, rewritable biomedical chip that is completely reusable. The team’s results appear online on June 10 in Science Advances.

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Reusable lab-on-a-chip uses acoustic waves to manipulate fluid droplets

"Our new system achieves rewritable routing, sorting and gating of droplets with minimal external control, which are essential functions for the digital logic control of droplets," said Tony Jun Huang, the William Bevan Distinguished Professor of Mechanical Engineering and Materials Science at Duke. "And we achieve it with less energy and a simpler setup that can control more droplets simultaneously than previous systems."

According to Duke, automated fluid handling has driven the development of many scientific fields such as clinical diagnostics and large-scale compound screening. While ubiquitous in the modern biomedical research and pharmaceutical industries, these systems are bulky, expensive and do not handle small volumes of liquids well.

Lab-on-a-chip systems have been able to fill this space to some extent, but most are hindered by surface absorption. Because these devices rely on solid surfaces, the samples being transported inevitably leave traces of themselves behind that can lead to contamination.

The new lab-on-a-chip platform is said to use a thin layer of inert, immiscible oil to stop droplets from leaving behind any trace of themselves. Below the oil, a grid of piezoelectric transducers vibrate when electricity is passed through them, which create sound waves in the thin layer of oil above them.

These sound waves form complex patterns when they bounce off the top and bottom of the chip as well as when they run into one another. By planning the design of the transducers and controlling the frequency and strength of the vibrations causing the waves, the researchers are able to create vortices that, when combined, form tunnels that can push and pull droplets in any direction along the surface of the device.

"The new system uses dual-mode transducers, which can transport droplets along x or y axis based on two different streaming patterns," Huang said in a statement. "This is a big step up from our previous system, which simply created a series of dimples in the oil to pass droplets along on a single axis."

By using dual-mode transducers, the researchers were able to move droplets along two axes while simultaneously reducing the complexity of the electronics four-fold. They were also able to reduce the operating voltage of the transducers three-to-seven times lower than previous system, which allowed it to simultaneously control eight droplets. And by introducing a microcontroller to the setup, the researchers were able to program and automate much of the droplet movement.

The ability to control droplets in a manner similar to the logic systems found on a computer chip is essential to a wide variety of clinical and research procedures.

Aiding Huang in the creation of this upgraded system was Krishnendu Chakrabarty, the John Cocke Distinguished Professor of Electrical and Computer Engineering at Duke, and his PhD student Zhanwei Zhong.

"Our next step is to combine the miniaturised radio-frequency power-supply and control board designed by Professor Chakrabarty's team for large-scale integration and dynamic planning," said Huang. "We're also planning to integrate the ability to split droplets into two without having to touch them."