Thanks to a new sound-based control system, a microfluidic processor can precisely manipulate droplets with an exceptionally broad range of volumes. The minimalist device is compatible with many substrates, including metals, polymers and glass. It is also biocompatible, and its developers at the Hong Kong Polytechnic University say it could be a transformative tool for applications in biology, chemistry and lab-on-a-chip systems.
Nano- and microfluidic systems use the principles of micro- and nanotechnology, biochemistry, engineering and physics to manipulate the behaviour of liquids on a small scale. Over the past few decades, they have revolutionized fluid processing, enabling researchers in a host of fields to perform tasks on chips that would previously have required painstaking test-tube-based work. The benefits include real-time, high-throughput testing for point-of care diagnostics using tiny sample sizes.
Microfluidics also play a role in several everyday technologies, including inkjet printer heads, pregnancy tests and, as the world recently discovered, tests for viruses like SARS-Cov2, which causes COVID-19. Indeed, the latter example involves a whole series of fluidic operations, as viral RNA is extracted from swabs, amplified and quantified using the polymerase chain reaction (PCR).
In each of these operations, it is vital to avoid contaminating the sample with other fluids. Researchers have therefore been striving to develop contactless techniques – for instance, those that rely on light, heat or magnetic and electric fields to move the fluids around. However, such approaches often require strong fields or high temperatures that can damage delicate chemical or biological samples.
In recent years, scientists have experimented with using acoustic fields instead. However, this method was previously found to work only for certain types of fluids, and with a limited volume range from hundreds of nanolitres (nL) to tens of microlitres (μL).
Versatile, residue-free fluid control
The new sound-controlled fluidic processor (SFP) developed by Liqiu Wang and colleagues is not bound by this limit. Thanks to an ultrasonic transducer and a liquid-infused slippery surface that minimizes adhesion of the samples, it can manipulate droplets with volumes of between 1 nL to 3000 μL. “By adjusting the sound source’s position, we can shape acoustic pressure fields to push, pull, mix or even split droplets on demand,” explains Wang. “This method ensures versatile, residue-free fluid control.”
The technique’s non-invasive nature and precision make it ideal for point-of-care diagnostics, drug screening and automated biochemical assays, Wang adds. “It could also help streamline reagent delivery in high-throughput systems,” he tells Physics World.
A further use, Wang suggests, would be fundamental biological applications such as organoid research. Indeed, the Hong Kong researchers demonstrated this by culturing mouse primary liver organoids and screening for molecules like verapamil, a drug that can protect the liver by preventing harmful calcium buildup.
Wang and colleagues, who report their work in Science Advances, say they now plan to integrate their sound-controlled fluidic processor into fully automated, programmable lab-on-a-chip systems. “Future steps include miniaturization and incorporating multiple acoustic sources for parallel operations, paving the way for next-generation diagnostics and chemical processing,” Wang reveals.
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