Bacteria-Sized Metallic Microrobots Decompose Microplastic

Ranging from urban environments to pristine wilderness, tiny pieces of plastic are everywhere. It is not easy to deteriorate plastic pieces, it can take centuries for them to degrade completely. Enzymes activated by daylight could speed up the process, but getting these compounds to interconnect with microplastics is challenging. In a proof-of-concept study, scientists reporting in ACS Applied Materials & Interfaces reveal self-propelled microrobots that can swim, attach to plastics and break them down.

Metallic microrobots (dark blue dots) colonize a rough piece of microplastic under visible light, breaking down the plastic into tinier molecules. Source: Adapted from ACS Applied Materials & Interfaces 2021

While plastic products are present everywhere whether it’s indoor commodities such as utensils, shelves, or plastic waste and broken pieces litter the outdoors. Microplastics — The smallest of these are less than 5 mm in size — are difficult to separate and remove. Furthermore, they can adsorb pollutants and heavy metals, conceivably harming living beings if accidentally consumed. So, previous scientists suggested a low-energy approach to get rid of plastics in the environment by using enzymes that use daylight to produce very reactive compounds that break down these kinds of polymers. Nevertheless, getting the enzymes and small plastic pieces to interconnect with each other is challenging and usually demands pretreatments or bulky mechanical stirrers, which aren’t readily scaled up. Martin Pumera and his associates wanted to produce a sunlight-propelled enzyme that moves toward and latches onto microparticles and dismantles them.

To modify an enzyme material into light-driven microrobots, the scientists made star-shaped particles of bismuth vanadate and then uniformly coated the 4-8 μm-wide structures with magnetic iron oxide. These microrobots could swim down a network of channels and combine with microplastic pieces adjacent to their entire lengths. The scientists noticed that under visible light, microrobots actively glommed onto four basic varieties of plastics. The team then illuminated four plastic pieces coated with the microrobot enzyme for a week in a dilute hydrogen peroxide solution. They noticed that the plastic dropped 3% of its weight and that the outside texture for all varieties changed from smooth to pitted, and small molecules and components of the plastics were observed in the left-over solution. The scientists say the self-propelled microrobot enzymes pave the way toward operations that can capture and degrade microplastics in hard-to-reach areas.

Journal Reference: 

“A Maze in Plastic Wastes: Autonomous Motile Photocatalytic Microrobots against Microplastics” by Soňa Hermanová, Yulong Ying, Seyyed Mohsen Beladi-Mousavi, Jan Plutnar, and Martin Pumera, 19 May 2021, ACS Applied Materials & Interfaces.

DOI: 10.1021/acsami.1c04559

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