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Process Adds Antimicrobial Silver Particles to Plants

Silver bar

(Armin Kübelbeck, CC-BY-SA, Wikimedia Commons)

14 July 2015. Engineers at North Carolina State University developed a process that adds biodegradable nanoparticles infused with silver to plant fibers that can kill a broad range of bacteria. A team from the lab of chemical engineering professor Orlin Velev, with colleagues from the U.S. Environmental Protection Agency and institutions in the U.K. and Netherlands, published its findings yesterday in the journal Nature Nanotechnology (paid subscription required).

North Carolina State University, in Raleigh, filed a patent application for the environmentally friendly nanoparticle technology, with Velev and first author Alexander Richter listed as its inventors. Velev and Richter, a doctoral candidate at NC State, also founded Benanova Inc. to commercialize the technology as an alternative to pesticides in agriculture. Richter is the company’s CEO.

Velev and associates sought to find an inexpensive and environmentally-friendly method for adding the antibacterial benefits of silver to plant tissue to reduce the risk of food poisoning in crops, and in coatings to reduce growth of bacterial biofilms on medical devices. “People have been interested in using silver nanoparticles for antimicrobial purposes,” says Velev in a university statement, “but there are lingering concerns about their environmental impact due to the long-term effects of the used metal nanoparticles released in the environment.”

The researchers devised a process that adds silver to lignin, the polymer substance that binds and gives strength to cells and fibers in plants, but aside from wood and straw, has little economic value. Their technique infuses silver ions into lignin nanoparticles coated with positively charged polyelectrolytes that help the nanoparticles bind to bacteria. The bacteria then absorb the silver, killing the bacteria, but leaving the biocompatible lignin.

Lab tests reported in the journal article show the silver-infused lignin nanoparticles killed a number of common harmful bacteria including E. coli associated with food poisoning, Pseudomonas aeruginosa known to cause infections on medical devices in hospitals, and Ralstonia solanacearum, a soil-borne bacteria causing disease in crops. Other tests show levels of silver in the plants exposed to this process are reduced as the bacteria absorb the silver, while silver nanoparticles used alone to kill bacteria remain in the environment.

The researchers say the process can be adapted to infuse other kinds of agents, such as antifungal compounds for pest control, into environmentally benign nanoparticles made from lignin. This is the value proposition of Benanova Inc., the company founded by Velev and Richter, where they say the process can deliver their payloads more efficiently than conventional pest control methods in agriculture, thus reducing the use of pesticides. The company says its techniques can be used as well with environmental clean-ups and in antimicrobial paints and coatings.

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