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

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Researchers in the US have developed a way to manipulate and mix droplets of fluids by having them surf on acoustic waves in oil.

acoustic waves
A photo showing the digital acoustofluidic device with a drop of blood floating on the carrier layer of fluorinated oil

The group, from Duke University in North Carolina, claims that the technology could form the basis of a reusable and programmable biomedical chip for applications ranging from diagnostics to laboratory-based research.

So-called lab-on-a-chip systems have played an increasingly important role in the biomedical and pharmaceutical sectors, but because these devices rely on solid surfaces their application has been hindered by problems related to surface absorption.

"There are a lot of protein-laden fluids and certain reagents that tend to stick to the chips that are handling them," said Tony Jun Huang, the William Bevan Professor of Mechanical Engineering and Materials Science at Duke. "This is especially true of biological samples like undiluted blood, sputum and faecal samples. Our technology is well-suited for processing these difficult samples."

According to a study in the journal Nature Communications the new lab-on-a-chip platform gets around this problem by using a thin layer of inert, immiscible oil to stop droplets from leaving behind any trace of themselves. Just below the oil, a series of piezoelectric transducers vibrate when electricity is passed through them. Just like the surface of a subwoofer, these vibrations create sound waves in the thin layer of oil above them.

By carefully controlling the sound waves, the researchers create vertical vortexes that form small dimples in the oil to either side of the active transducer. These dimples can hold droplets with volumes ranging from one nanolitre to 100 microlitres and pass them along the surface of the oil as the sound waves are modulated and different transducers are activated.

"Our contactless liquid-handling mechanism inherently eliminates cross-contamination associated with surface adsorption and the need for surface modification," Huang said. "It enables reusable paths for the droplets to be dynamically processed on arbitrary routes without cross-talk between each other, exponentially increasing the allowable number of combinations of reagent inputs on the same device."

Huang said that the group now plans to develop a more advanced version of the technology that can handle complex operations with dozens of droplets simultaneously.