'Killer paper' could prolong shelf life of foods
By Ben Coxworth
January 19, 2011
Silver is a known killer of harmful bacteria, and has already been incorporated into things such as antibacterial keyboards, washing machines, water filters, and plastic coatings for medical devices. Now, scientists have added another potential product to the list: silver nanoparticle-impregnated “killer paper" packaging, that could help keep food from spoiling.
Led by Aharon Gedanken from Israel’s Bar-Ilan University, the team discovered that paper could be covered with silver nanoparticles through the application of ultrasonic radiation – a process known as ultrasonication. It involves the formation and subsequent collapse of acoustic bubbles near a solid surface, which creates microjets that throw the desired nanoparticles onto that surface. To the team’s knowledge, this was only the second time that ultrasonication had ever been attempted on paper.
Unlike previous attempts at creating antibacterial paper, this one-step method was reportedly quite effective, and produced a smooth, homogenous, long-lasting coating. By varying the nanoparticle concentration and the application time, the thickness of the coating could be varied as needed. When exposed to E. coli and S. aureus bacteria, both of which cause food poisoning, the paper killed them all off within three hours.
The scientists stated that the ultrasonication process could also be used to apply other nanomaterials to paper, which could be used to tweak its hydrophobicity, conductivity, or texture.
While the addition of ionic silver to foods has been used in the past to ward off bacteria, the paper would reportedly serve as a longer-term solution, as it would act as a slow-release reservoir for the silver. Germany’s Fraunhofer Institute for Process Engineering and Packaging has previously looked into the use of sorbic acid-coated plastic as an antibacterial food wrap.
The killer paper research was recently published in the journal Langmuir.