Silver nanoparticles (AgNPs) are used as antimicrobial agents in a wide variety of products. Uses include electronics, clothing, paints, sunscreens, cosmetics and medical devices. However, since AgNPs kill both target and friendly bacteria, the wisdom of their use has been questioned because their long-term persistence in the environment can be detrimental to the health of some natural ecosystems.
Recently, Dr. Orlin Velev and Alex Richter, a PhD student in his research group, have developed an alternative antimicrobial that's both effective and environmentally benign. The new antimicrobial is built around lignin, a by-product of wood pulp processing that's present in all woody plants and in some algal species.
The lignin nanoparticles are infused with silver ions, and are coated with a charged polymer layer. The polymer layer promotes the adhesion of the particles to bacterial cell membranes, which gives the silver ions killing access to the bacteria.
The Confocal image shows bacteria (green) with swarms of silver-loaded nanoparticles.
As the nanoparticles kill the targeted bacteria, they become depleted of silver and benign. The remaining particles degrade easily after disposal because of the biocompatible lignin core.
According to Dr. Velev, the new lignin nanoparticles have several major advantages. First, they carry only 5 to 10% of the metal used in traditional silver nanoparticles. Second, they're designed to be "time-selective," i.e. they kill most microbes within a certain time frame after application, then get depleted of silver ions and become benign. Finally, the nanoparticles are synthesized using green chemistry principles.
Alex, who's also a winner of the prestigious Lemelson-MIT Student Prize, has launched BENANOVA, a science startup that's commercializing this lignin-based product. According to Alex, "We expect this method to have a broad impact.".... "We may include less of the antimicrobial ingredient without losing effectiveness while at the same time using an inexpensive technique that has a lower environmental burden. We are now working to scale up the process to synthesize the particles under continuous flow conditions."
The research is reported in a recent paper in the journal Nature Nanotechnology. Funding for the research was provided by the U.S. Environmental Protection Agency, the National Science Foundation and NC State. Researchers from the EPA, University of Hull, Wageningen University and University College London participated in the study.