background image
¡°We expect this method to have a broad
impact,¡± Richter said. ¡°We may include less
of the antimicrobial ingredient without los-
ing 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 synthe-
size the particles under continuous flow
Funding was provided by the U.S. Environ-
mental Protection Agency, the National Sci-
ence Foundation and NC State. Researchers
from the EPA, University of Hull, Wagenin-
gen University and University College Lon-
don participated in the study.
(source: kulikowski ¨C
An abstract of the paper follows:
¡®An environmentally benign antimicrobial nanoparticle based on a
silver-infused lignin core¡¯
Authors: Alexander P. Richter, Joseph S. Brown, Bhuvensh Bharti and Orlin
D. Velev, North Carolina State University; Amy Wang, Sumit Gangwal,
Keith Houck and Elaine A. Cohen Hubal, U.S. EPA; Vesselin N. Paunov,
University of Hull; and Simeon D. Stoyanov, Wageningen University and
University College London
Published: July 13, 2015, online in Nature Nanotechnology
Abstract: Silver nanoparticles have antibacterial properties, but their use
has been a cause for concern because they persist in the environment.
Here, we show that lignin nanoparticles infused with silver ions and coated
with a cationic polyelectrolyte layer form a biodegradable and green alter-
native to silver nanoparticles. The polyelectrolyte layer promotes the ad-
hesion of the particles to bacterial cell membranes and, together with sil-
ver ions, can kill a broad spectrum of bacteria, including Escherichia coli,
Pseudomonas aeruginosa and quaternary-amine-resistant Ralstonia sp.
Ion depletion studies have shown that the bioactivity of these nanoparti-
cles is time-limited because of the desorption of silver ions. High-through-
put bioactivity screening did not reveal increased toxicity of the particles
when compared to an equivalent mass of metallic silver nanoparticles
or silver nitrate solution. Our results demonstrate that the application of
green chemistry principles may allow the synthesis of nanoparticles with
biodegradable cores that have higher antimicrobial activity and smaller
environmental impact than metallic silver nanoparticles.
Environmentally Safe Method To Combat Bacteria Developed
Nanoscale particles combine antimicrobial potency of silver with lignin; kills E. coli
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July 13, 2015: North Carolina State Univer-
sity researchers have developed an effec-
tive and environmentally benign method to
combat bacteria by engineering nanoscale
particles that add the antimicrobial potency
of silver to a core of lignin, a ubiquitous sub-
stance found in all plant cells. The findings
introduce ideas for better, greener and safer
nanotechnology and could lead to enhanced
efficiency of antimicrobial products used in
agriculture and personal care.
In a study published in Nature Nanotech-
nology, NC State engineer Orlin Velev and
colleagues show that silver-ion infused
lignin nanoparticles, which are coated with a
charged polymer layer that helps them ad-
here to the target microbes, effectively kill
2015 AUGUST #6-7
a broad swath of bacteria, including E. coli and other harmful microor-
As the nanoparticles wipe out the targeted bacteria, they become de-
pleted of silver. The remaining particles degrade easily after disposal
because of their biocompatible lignin core, limiting the risk to the envi-
¡°People have been interested in using silver nanoparticles for antimicro-
bial purposes, but there are lingering concerns about their environmen-
tal impact due to the long-term effects of the used metal nanoparticles
released in the environment,¡± said Velev, INVISTA Professor of Chemical
and Biomolecular Engineering at NC State and the paper¡¯s corresponding
author. ¡°We show here an inexpensive and environmentally responsible
method to make effective antimicrobials with biomaterial cores.¡±
The researchers used the nanoparticles to attack E. coli, a bacterium
that causes food poisoning; Pseudomonas aeruginosa, a common
disease-causing bacterium; Ralstonia, a genus of bacteria containing
numerous soil-borne pathogen species; and Staphylococcus epidermis,
a bacterium that can cause harmful biofilms on plastics ¨C like catheters
¨C in the human body. The nanoparticles were effective against all the
The method allows researchers the flexibility to change the nanoparticle
recipe in order to target specific microbes. Alexander Richter, the paper¡¯s
first author and an NC State Ph.D. candidate who won a 2015 Lemelson-
MIT Student Prize, says that the particles could be the basis for reduced
risk pesticide products with reduced cost and minimized environmental