Magnesium-Powered Microbots Could Help Clean Contaminated Water Supplies

While magnesium bubbles propel the bots, layers of iron, gold, and silver attract and kill as much as 80 percent of E. coli in experimental water samples.

It is true, however, that people in developing countries have higher risk of getting bacterial diseases from their water supply. The bacteria E. coli kills millions of people each year, according to the World Health Organization, with children in Asia and Africa at particular risk. Thousands of others die each year from cholera and other water-borne bacterial diarrheal diseases.

Scientists have been investigating effective water purification methods for decades, but many traditional practices are either impractical or ineffective. In addition, the rise of antibiotic-resistant bacteria has made some classic purification agents, such as chlorine, not as effective as they once were.

But an emerging technology shows promise: tiny nanobots that can zoom through water and kill bacteria. 

A recent study, published in the journal ACS Applied Materials & Interfaces, details the development of “Janus microbots” that can safely and effectively trap and kill bacteria in water. 

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The tiny spherical microbots are split into two halves. One half is made of magnesium, which reacts with water to create hydrogen bubbles. These bubbles push the bot forward through the water, acting like a motor that lets the microbot swim.

The other side of the microbot is layered with iron and gold, and studded with silver nanoparticles. The iron makes the bots magnetic, meaning that they can be easily removed from the water once they’ve finished cleaning. The gold traps disease-causing bacteria, and the silver nanoparticles, which have an antibacterial property, kill the pathogens.

This simple design was shown to be effective: After 15 minutes in heavily contaminated water, the bots killed 80 percent of the E. coli bacteria in experimental water samples. Though the authors of the new study only tested the bots with E. coli, previous research has shown that silver nanoparticles are capable of killing many other species of bacteria, including those that cause cholera and typhus. And since the bots can be picked up by a magnet from the water once they’ve finished cleaning, they don’t leave any toxic residue behind.

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There are limits to the nanobots’ power, though. For one, they can only swim around for about 15 minutes, at which point the magnesium chemical reaction stops and they need to be pulled out of the water. An 80 percent kill rate is better than nothing, but still leaves behind some bacteria. The researchers hypothesized that with more bots, the amount of E. coli killed would rise.

Cost and the extent to which rural communities might adopt the technology were not discussed in the study. And, while the bots are good at trapping bacteria, they wouldn’t get rid of other contaminants more commonly found in the US water supply, including heavy metals like lead.

The study was funded by European government agencies and the Max Planck Institute for Intelligent Systems