by Will Li (’23) | March 21, 2022

Decades of environmental degradation have contaminated the world’s valuable water resources. From the water crisis in Flint, Michigan, to the accumulation of microplastics in oceans across the world, water pollution is one of humanity’s most pressing concerns. Millions have attempted to combat the issue through political action, cleanup organizations, and more recently, nanorobots. 

In March, a study by renowned Czech chemist Martin Pumera and his team introduced new magnetic, temperature-sensitive nanorobots that detect and remove chemical pollutants from water. Compared to previous nanobots designed for similar purposes, Pumera’s technology costs less to manufacture, can be easily recycled, and does not require a metal catalytic motor, a part which would rapidly oxidize and render the nanobots effectively useless.

Pumera’s nanobots proved highly effective at eliminating the heavy metal arsenic and the herbicide atrazine. Both carcinogenic pollutants pose health risks to numerous species. After ten minutes in a two-milliliter arsenic solution, 18.6 milligrams of nanorobots removed 59.7 percent of the arsenic; after one hundred minutes, they eliminated 65.2 percent. Similarly, 18.6 milligrams of nanobots removed 53.8 percent of atrazine after ten minutes and 61.5 percent after one hundred minutes in an atrazine solution.  

The biodegradable nanobots consist of magnetic iron oxide (Fe₃O₄) and a temperature-sensitive tri-block copolymer, called para-tertiary butyl catechol (PTBC), which is comprised of three distinct segments of polymers. PTBC also “acts like small hands that pick up and dispose of the pollutants,” according to an article published in science news outlet ZME Science. 

When the surrounding water temperature rose from 5°C to 25°C, the nanorobots self-assembled through weak Van der Waals attractions between the iron oxide and PTBC, clustered, and attracted pollutants that clung to them. At temperatures above 25°C, the nanorobots trapped the pollutants between themselves. But at temperatures below 5°C, the amount of iron and oxygen decreased and the nanorobots separated, indicating their ability to dispose of pollutants with merely a modification of temperature rather than external chemicals.

Controlled by a magnetic field, “the robot moves completely at the will of an operator, who can actively sweep the water and catch the pollutants,” explained Pumera. Operators can steer the pollutant-laden nanobots to a destination where researchers lower the temperature to extract the pollutants from the water.

Researchers then retrieve the robots with an external magnet. Unfortunately, the robots’ effectiveness at both collecting and discarding arsenic decreased after ten cycles of heating and cooling.

Pumera and his team only focused on two chemicals, but the “many other pollutants present in a real sample” could also attach to the nanobots, according to the study. The nanobots have additionally demonstrated success in the real world: they picked up 73 percent of arsenic and 72 percent of atrazine in tap water with five milligrams of pollutants per liter. In a time when it is critical to safeguard endangered environments, Pumera’s nanobots introduce an invaluable method for cleaning the world’s waterways.