New Nanoparticles Clean the Environment, Drinking Water

Nanoparticles are between 1 and 100 nanometers in size.Scientists can harness them for drug delivery, to combat disease, for filtering fresh drinking water, and much more.

Now, researchers from MIT and the Federal University of Goias in Brazil have developed a new technique that uses ultraviolet (UV) light to extract man-made pollutants from soil and water.

These pollutants, including pesticides and endocrine disruptors like bisphenol A, fight hard against natural degradation and disrupt systems in mammals and other animals. With the help of nanoparticles and UV light, removal of these toxins could be less expensive and time-consuming than current methods.

Lead author Nicolas Bertrand, a former professor at MIT’s Koch Institute for Integrative Cancer Research, told LabOutlook that he and colleagues stumbled upon the idea of using UV light while they were initially designing photo-sensitive polymers for drug delivery applications. Once they came up with a polymer that responded to UV light, they realized that this did not permeate well through skin and could cause damage to healthy cells.

“We therefore asked ourselves in which infrastructures UV light was already used,” Bertrand told LabOutlook. Knowing that UV radiation is used for removing bacteria from water, they developed the idea of using their discovery for water purification.

How it works

The nanoparticles are prepared from molecules (synthetic macromolecules commonly called plastics) that have a protective, hydrophilic (water-loving) shell and a hydrophobic (water-fearing) spherical core.

“The polymers are synthetized to ensure that when you shine UV light on them, the water-loving part is separated from the water-fearing part.When this happens on a nanoparticle, its protecting corona is removed and only the hydrophobic core remains. These ‘naked’ hydrophobic plastic beads are not stabilized anymore, and therefore clump together to minimize contacts with water,” Bertrand explained.

From there, these larger aggregates can easily be retrieved through filtration or sedimentation, with more than 95 percent of the nanoparticles removed from the water.

When the nanoparticle loses its protective layer, polymers are released into the water. While the polymer released (polyethylene glycol) is recognized as safe and used in various food, pharmaceutical and cosmetics products, it would be ideal if no material was released or if it could be used by parts of the ecosystem to further minimize environmental impact.

Bertrand’s nanoparticles

Still, even with the small amount of material released into the water, Bertrand’s nanoparticles have benefits compared with current purification processes. Some current techniques rely on chemical degradation of pollutants, which can potentially result in toxic by-products. Plus, these chemical degradation processes do not work on all types of chemicals.

“When unusual/unheard of molecules are found as contaminants (for example, the chemical spill in Elk River, WV, in January 2014), no data exist on the ability of these oxidizing agents to destroy the dangerous chemical, so their value is questionable,” Bertrand said. “Since it relies on non-specific absorption, our approach might be more versatile.”

Additionally, other processes, such as activated carbon extraction, require great energy to push large quantities of water through filters.

“In our technology, the nanoparticles float passively in the fluid until we precipitate them. Current water purification infrastructures have UV irradiation systems optimized to kill bacteria, this irradiation is more than sufficient to precipitate our nanoparticles,” Bertrand explained.

Bertrand told LabOutlook that one fundamental observation from this work is that small molecules passively absorb on the surface of the nanoparticle, and that the amounts absorbed correlate with the surface-to-volume ratio, meaning more absorption occurs on small nanoparticles.

“This is an important consideration for drug delivery because it could explain what happens with nanoparticles with high drug encapsulation and extensive burst release.”

Harnessing nanoparticles in Africa

Theresa Dankovich uses nanotechnology to purify drinking water in Africa. By filtering water through paper embedded with silver or copper nanoparticles, 99.9 percent water purity is achievable.

She calls it “The Drinkable Book.” Silver nanoparticles eliminate a wide variety of microorganisms, including bacteria and some viruses. While some silver and copper will seep from the nanoparticle-coated paper, the amount is minimal, Dankovich said, and is well below limits for metals put in place by the Environmental Protection Agency and World Health Organization.

Dankovich’s nonprofit company pAge Drinking Paper, works together with the nonprofit WATERisLIFE, to produce a book of this nanoparticle-embedded paper, which is put in a special holding device that water is then filtered through. One page can filter 26 gallons of drinking water; one book can filter a person’s water needs for four years.

Dankovich presented her technology along with results of recent field tests conducted in Africa and Bangladesh at the American Chemical Society (ACS) National Meeting earlier this month.

Drug delivery and beyond

The power of nanoparticles is also being harnessed to fight life-threatening lung diseases, such as cystic fibrosis. Researchers at Johns Hopkins University School of Medicine, Johns Hopkins University Department of Chemical and Biomolecular Engineering and Federal University of Rio de Janeiro in Brazil conducted a proof-of-concept study that found DNA-loaded nanoparticles could successfully pass through the hard-to-breach mucus barrier that covers conducting airways of lung-tissue. The mucus barrier–which serves as a protector from foreign materials and bacteria–unfortunately prevents targeted therapies from reaching the lungs. Other attempts to penetrate the barrier with nanoparticles were unsuccessful because they possessed a positive charge that caused them to be “sticky” and adhere to the negatively charged mucus covering the airways.

To circumvent this problem the team developed a simple method to densely coat the nanoparticles with a nonsticky polymer called PEG, neutralized the charge and created a non-sticky exterior.
Published in the Proceedings of the National Academy of Sciences, the proof-of-concept animal study demonstrates that placing corrective replacement genes or drugs inside a man-made biodegradable nanoparticle “wrapper” that patients inhale could penetrate the mucus barrier and one day be used to treat serious lung disorders. Since the delivery system is biodegradable it will not build up inside the body. The team also showed that a single-dose of inhaled delivery of the genes could theoretically last for several months.

“To our knowledge, this is the first biodegradable gene delivery system that efficiently penetrates the human airway mucus barrier of lung tissue,” said study author Jung Soo Suk, a biomedical engineer and faculty member at the Center for Nanomedicine at the Wilmer Eye Institute at Johns Hopkins.

Researchers funded by the National Institute of Biomedical Imaging and Bioengineering meanwhile, stopped brain cancer in rats by delivering gene therapy through nanoparticles. The nanoparticles deliver genes for an enzyme that converts a prodrug called ganciclovir into a glioma cell killer. There is no reliable treatment for glioma, which has a 5-year survival rate of 12 percent. As in cystic fibrosis, a current delivery method of gene therapy relies on using a virus, which can pose significant safety risks.

Challenges remain

Bertrand and other lead author Ferdinand Brandl both left MIT to join pharmacy schools in Quebec City, Canada and Regensburg, Germany, respectively.

Although their nanoparticle technology is solid, some challenges remain before it can be implemented in an industrial application.

As usual with lab-developed processes, “scale-up of production [is an issue]. For example, if we need to use it to purify huge quantities of water,” the researchers said.

As a next step, Bertrand said it would be interesting to design a system where no polymer is released, or where the material would be a natural ubiquitous molecule instead of a synthetic one. Work could also be done to improve the ability to remove increasing amounts of pollutants.