Food microbes beware: It’s raining nanobombs

Demokritou Lab
Philip Demokritou (in blue coat) with his lab team, from left: Georgios Pyrgiotakis, Pallavi Vedantam, and Caroline Cirenza.

March 18, 2015 — Can super-tiny droplets of water sprayed at strawberries, spinach, and lettuce kill deadly food pathogens?

Philip Demokritou, associate professor of aerosol physics and director of the Laboratory for Environmental Health NanoSciences at Harvard T.H. Chan School of Public Health, thinks so. And if this new technology can be successfully scaled up, he says it could be a “game-changer” in the fight against toxic microorganisms, including E. coli, salmonella, and listeria. The U.S. Centers for Disease Control estimates that each year in the U.S. approximately 48 million people get sick, 128,000 are hospitalized and 3,000 die from the consumption of food contaminated with pathogenic microorganisms.

In a U.S. Department of Agriculture-funded study published in mid-February in the journal Environmental Science & Technology, Demokritou and colleagues describe how nano-sized, charged water particles called Engineered Water Nanostructures (EWNS) can inactivate foodborne bacteria on both stainless steel surfaces and on the surfaces of tomatoes. They found a dose-response relationship in the study; that is, the more EWNS they used, and the longer the EWNS were in contact with the pathogens, the more the deadly bugs were destroyed.

Results from the study suggest that the new nanotechnology-based approach could provide an environmentally friendly and inexpensive alternative to current food decontamination methods, which often involve substances containing chlorine or ammonia that can leave unhealthy residue on produce.

“We cannot continue to battle infectious diseases using chemical warfare,” said Demokritou. “This new method is chemical-free, leaves no residues, and uses very little electricity.” Preliminary findings also suggest that inhalation of EWNS appears to be safe—in a study led by Demokritou and his team last year, the researchers found that mice exposed to inhaled EWNS showed no adverse lung injury and inflammation at doses higher than those used in airborne bacteria inactivation experiments.

How does it work? The EWNS—which Demokritou and his team spent three years developing—are produced by aerosolizing water and passing it through a strong electric field, in a process called electrospraying. The resulting “engineered” particles are just 25 nanometers in diameter, 4,000 times smaller than the width of a human hair. They remain airborne in indoor conditions for hours due to their high electric charge and contain substances called Reactive Oxygen Species (ROS) that are generated during their synthesis by splitting water molecules apart. Their nanoscale size makes the nanoparticles highly mobile. They are, in essence, like tiny bombs that can move around and interact with microorganisms on fresh produce. When they bounce onto toxic microorganisms, they zap them out of existence, Demokritou explains. After they destroy the pathogens, they disintegrate back into water vapor, leaving no chemical residues.

Georgios Pyrgiotakis, research associate in the Department of Environmental Health and first author of the new study, explained that the team experimented with two different ways of delivering EWNS on surfaces. In one method, EWNS were delivered to surfaces via diffusion by simply allowing EWNS to move around and find bacteria on surfaces; in another, an electric field was used to steer the EWNS—using their electric charge—directly onto test surfaces. The latter targeted delivery method proved quicker and more effective. Microbiologist Pallavi Vedantam, a postdoctoral fellow in the Center for Nanotechnology and Nanotoxicology and part of Demokritou’s team, called the results exciting. “This could revolutionize the technology we currently use to disinfect produce post-harvest,” she said.

Next steps for the researchers will be to refine and scale up their new food decontamination method. They’ll figure out how much time and how many EWNS are needed for maximum pathogen destruction, and they’ll test the method on other kinds of food pathogens and spoilage microorganisms.

Demokritou envisions products using EWNS to eliminate food pathogens at any point along the “farm-to-fork” continuum—after the food has been harvested, during transport, at supermarkets, or in home refrigerators. The technology also has potential in other applications, such as wound healing, air disinfection, and art or artifact preservation, he said.

“This can be deadly against many classes of infectious agents,” said Demokritou. And although no method will be 100% effective against pathogens, EWNS could at least provide a viable alternative to current methods, he said. “The 20th century model uses chemicals for everything, especially in the battle against infectious agents,” he said. “We have to start thinking in a more sustainable way. Nanotechnology can help a lot.”

Karen Feldscher

— photo and video: Craig LaPlante