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Tiny magnetic robots can help remove some of the smallest plastic particles from polluted water.

Most plastics eventually end up as tiny fragments that then hide in our environment, food and drinking water. There is no consensus on the health implications of ingesting plastic yet, but early research suggests that plastic particles can enter organs within the body and that this process gets easier as the particles get smaller.

However, efficiently detecting and removing the tiniest of plastics, or nanoplastics, from water is still a challenge, says at the Brno University of Technology in the Czech Republic. He and his colleagues thought tiny robots could help.

They built their spherical robots about 200 nanometres in size from a metallic, magnetic material. The researchers immersed trillions of these robots in 5 millilitres of water that was also filled with billions of particles of polystyrene plastic of similar size. Then, they exposed this mix to a magnetic field, which made the robots move within it. As the nanobots moved, they stuck to polystyrene particles because of an electrostatic attraction.

To keep track of how many nanoplastics the robots were capturing, Pumera and his colleagues used a special dye that made the plastic glow red. When they added this dye to water samples before treatment, the water took on a rich red colour. They then added the nanobots to undyed water samples and, after about 2 hours, removed the robots – and the plastics they were attached to – with another magnet. At this point, adding the dye to the water made it glow a weak red colour, from which the team could calculate that the nanobots had removed more than 90 per cent of the nanoplastics.

at the Brno University of Technology who worked on the project says that because the robots can move and because they selectively attach to nanoplastics, they may offer a more efficient way to remove them than conventional methods like filtration.

But the nanobots may not be equally effective in every environment, says at the Pennsylvania State University. They could be suitable for water treatment facilities where water composition is more well understood, but more experiments are needed to assess how they would perform in places like the ocean where there are many different types of nanoplastics of different shapes and sizes, as well as other pollutants, she says.

The team is hoping to conduct those experiments next and tweak the design of the robots as necessary, says Pumera.