Lignin Nanoparticles Use Silver To Beat The Pulp Out Of Bacteria

Antimicrobial silver nanoparticles appear in a wide variety of products, including medical equipment and even socks. But silver nanoparticles can linger in the environment and may pose a threat to natural ecosystems. Now, an international research team has developed potentially eco-friendly, silver-infused nanoparticles that effectively combat bacteria (Nat. Nanotechnol. 2015, DOI: 10.1038/nnano.2015.141).

The new antimicrobial is built around lignin, a by-product of wood pulp processing. The team’s lignin nanoparticle cores carry only 5 to 10% of the metal used in traditional silver nanoparticles, says Orlin D. Velev of North Carolina State University, who led the team. The start-up company Benanova, led by NC State graduate student Alexander P. Richter, is working to commercialize these lignin-based products.

The researchers believe their new particles mitigate potential environmental hazards by using biodegradable cores and a small silver payload. “You don’t need the whole nanoparticle to be silver,” Velev tells C&EN. “You just need something benign to carry and release silver ions.”

Velev and his colleagues chose lignin. The researchers bound silver ions to nanoscopic clumps of lignin by bathing the particles in an aqueous silver nitrate solution.

Finally, the team coated the nanostructures’ surfaces with a cationic polyelectrolyte to create positively charged particles that could attach to negatively charged bacterial membranes. The particles could then attack the microbes with their silver-ion payload.

“This is an interesting and important approach,” says Virender K. Sharma, who specializes in green chemistry and public health at Texas A&M University. Sharma, who was not involved with the study, points out that the particles are effective against a range of bacteria, but he would like to see more experiments to compare the bacterial pathways affected by the new particles and by conventional nanosilver.

The team will continue to study and develop these particles, but Velev believes he and his colleagues have already demonstrated a powerful approach to green nanoengineering: Start with an abundant, ec0-friendly material and make deliberate, eco-conscious choices to functionalize it. “Only then will you get a really efficient particle that does the job right,” Velev says.