Scientists in Israel have developed what they call “killer paper,” packaging material coated with silver nanoparticles, each 1/50,000 the width of a human hair.
Because the Food and Drug Administration does not care for silver nanoparticles, we have begun researching zinc oxide as an alternative.
Aharon Gedanken, PhD
In lab tests, the paper reportedly showed potent antibacterial activity against common foodborne pathogens like E. coli and S. aureus, killing all the bacteria in three hours (Gottesman R, Shukla S, Perkas N, et al. Langmuir. 2011;27(2):720-726) from Langmuir.
The authors, led by Aharon Gedanken, PhD, professor emeritus of chemistry at Bar-Ilan University in Ramat Gan, Israel, suggest that nanoparticle-coated paper could help overcome the problem of antibiotic resistance and promote longer shelf life if used in food packaging.
To coat the paper with the nanoparticles, the scientists used a process they call “ultrasonication.” After preparing an aqueous solution containing silver ions and a reducing agent designed to convert them to metallic silver, they dip the material to be coated into the solution. “It can be a piece of paper, a piece of fabric, a flat surface of glass–any solid material, flat or curved, in various sizes,” Dr. Gedanken said. “Using an ultrasound-wave generator, which is a bit different from the type used to examine a fetus in utero, I pass ultrasonic waves through this mixture. That causes the formation of bubbles in the liquid, which then collapse and create nanosilver particles. As an aftereffect, ‘microjets’ of liquid squirt the nanoparticles at the solid surface at such a high speed that they become embedded in the fabric or the paper. “
Because of concerns about residue leaching into products wrapped in nanoparticle-coated paper, the scientists conducted two separate sets of measurements to assess this potential for contamination. After washing fabrics coated in silver nanoparticles, they found none in the washing solution. “Nonetheless, because the Food and Drug Administration [FDA] does not care for silver nanoparticles, we have begun researching zinc oxide as an alternative,” Dr. Gedanken said. “We have not tested it on foodborne pathogens yet, but against bacteria common in hospitals, and it is killing all of them so far. Given price and the FDA’s safety concerns, zinc oxide appears superior.”
Dr. Gedanken’s team has already begun scale-up of the process, developing a machine that can coat 50-meter rolls of paper, fabric, or aluminum foil.