Engineers have demonstrated a versatile microfluidic lab-on-a-chip that uses sound waves to create tunnels in oil to manipulate and transport droplets touch-free. The technology could form the basis of a small-scale, programmable, rewritable biomedical chip that is completely reusable to enable on-site diagnostics or laboratory research. The system achieves rewritable routing, sorting, and gating of droplets with minimal external control, which are essential functions for the digital logic control of droplets.
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 one major drawback: 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 uses a thin layer of inert, immiscible oil to stop droplets from leaving behind any trace of themselves. Just below the oil, a grid of piezoelectric transducers vibrates 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.
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 meticulously 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 that can transport droplets along an x or y axis, based on two different streaming patterns. 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 a 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. The next step is to combine the miniaturized radio-frequency power supply and control board for large-scale integration and dynamic planning.