By getting biological fluids to surf on acoustic waves in oil, Duke University engineers have developed a technology that could form the basis of a small-scale, programmable biomedical chip. The chip would be also rewritable, making it possible to reuse it for a variety of purposes from on-site diagnostics to laboratory-based research.

Presented as a proof-of-concept demonstration, the device can handle droplets measuring between one nanoliter to 100 microliters in size; can move droplets slowly or quickly depending on user preferences; and can split, move and mix droplets in any pattern desired.

Because they rely on solid surfaces, existing lab-on-a-chip systems have a major drawback: traces of the samples being transported get absorbed, contaminating the device. "There are a lot of protein-laden fluids and certain reagents that tend to stick to the chips that are handling them," explained Tony Jun Huang, a mechanical engineering and materials science professor at Duke. "This is especially true of biological samples like undiluted blood, sputum and fecal samples.”

By contrast, the new device prevents droplets from leaving behind any trace of themselves by means of a thin layer of inert, immiscible oil. The oil is made to function like the surface of a subwoofer through the vibration of piezoelectric transducers just below it; by controlling the sound waves, vertical vortexes form small “dimples” that can hold droplets. Modulating the sound waves allows the droplets to be passed along the surface of the oil.

"Our contactless, liquid-handling mechanism inherently eliminates cross-contamination associated with surface adsorption and the need for surface modification," said Huang. "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 wants next to create a fully automated lab-on-a-chip platform that can support complex operations with dozens of droplets simultaneously.

The research appears in Nature Communications.