Magnetic particles transform water droplets into skilled tightrope walkers

By placing tiny magnetic particles inside ordinary water droplets, you can turn them into liquid acrobats. Droplets can climb steps, jump over obstacles, and initiate chemical reactions. This level of control could be useful for drug delivery and the creation of more complex lab-on-a-chip technologies.

Fan Shilin He and his colleagues at Sun Yat-sen University in China created a surface with tiny grooves and covered it with a superhydrophobic, or wet-resistant, varnish. They know that a water droplet resting on such a groove can spontaneously jump up due to the pressure difference between the bottom of the droplet, which is deformed by the small groove, and the rounded and less constrained top part. I did.

The researchers wanted to create this pressure difference on demand. They added small magnetic particles to each droplet and placed an electromagnet beneath the groove. When the electromagnet was turned on, some of the particles, or droplets, were drawn into the groove. When I turned it off, the water droplet shape bounced and flew upwards as if from a slingshot.

Using this technique, the team was able to enable droplets to hop down millimeter-scale stairs and overcome small obstacles. The researchers were also able to direct a droplet into the narrow space between two wires and connect a circuit to light a light bulb.

Xiao Yan Researchers from China’s Chongqing University say this is a creative way to control pressure-based droplet jumps and could become a valuable tool for precisely transporting chemical droplets. It has said.

In one experiment, researchers plunged and mixed droplets into a liquid chemical sample under a microscope lens, allowing them to observe the resulting chemical reaction from start to finish. Another experiment involved mixing two droplets with a third in a closed box, which would have been ruined if the researchers had had to open the box to let air in. The reaction was initiated remotely.

Such precise chemical control can be applied to drug delivery. Huang hopes the technology will also advance “lab-on-a-chip” technology, an effort to miniaturize complex biochemical experiments that typically require a lot of space and glassware. He proposes a “lab-on-stacked chip” in which droplets jump vertically between levels to generate many reactions in parallel.