Novel technique achieves 32-fold increase in bactericidal capacity of nanoparticles

Researchers affiliated with the Center for Development of Functional Materials (CDMF) in São Paulo have developed a new method to obtain nanometric silver particles, currently used in various products.

By Elton Alisson  |  Agência FAPESP – In recent decades, various research groups in the field of materials science have embarked on a race to develop new techniques capable of producing nanometric silver particles and enhancing the optical, catalytic and bactericidal properties of silver. A nanometer is one billionth of a meter.

Researchers affiliated with the Center for Development of Functional Materials (CDMF), one of the Research, Innovation and Dissemination Centers (RIDCs) funded by FAPESP, have taken a step forward in this contest.

The researchers developed a new technological approach that generated silver nanoparticles with 32 times the bactericidal capacity of those currently used in food packaging, orthotics, and hospital and medical materials, among others.

The results of the study, conducted by researchers from the Federal University of São Carlos (UFSCar) and São Paulo State University (UNESP) in Brazil and from Spain’s Jaume I University and the Technical University of Liberec in the Czech Republic, were published in Scientific Reports.

“We succeeded in developing a novel solution for the production of silver nanoparticles that differ from those currently in existence and have far greater bactericidal capacity,” said Elson Longo, CDMF’s executive director and a professor at UFSCar, which hosts CDMF, in an interview given to Agência FAPESP. 

Three years ago, CDMF’s researchers developed an innovative method of obtaining nanocomposites comprising silver nanoparticles coupled to a silver tungstate semiconductor crystal by transmission electron microscopy.

Using this technique, which involves electron-beam irradiation of silver tungstate, they produced promising bactericides whereby the silver tungstate semiconductor attracts bacterial agents that are then are neutralized by silver nanoparticles.

Large-scale production of these materials for real-world applications using this technique, however, is limited by the high cost of transmission electron microscopes.

“The transmission electron microscope used to obtain this material costs approximately 1.3 million euros,” Longo said. “This makes large-scale production of the material completely unaffordable.”

To scale up production of these nanocomposites using a more competitive method, the researchers developed a novel technique consisting of pulsed laser irradiation of a silver tungstate semiconductor, with each pulse lasting only a femtosecond – one millionth of one billionth of a second (10^-15 s).

Analysis of the irradiated samples showed that interaction between the silver tungstate semiconductor and the femtosecond laser gave rise to large numbers of microstructures, which they characterized by transmission electron microscopy and found to be of two different types. 

“The new technique we developed resulted both in silver nanoparticles left on the semiconductor and in silver clusters,” Longo said.

To measure the bactericidal activity of the materials, the researchers placed samples of them in contact with methicillin-resistant strains of Staphylococcus aureus (MRSA), a bacterium that is resistant to numerous antibiotics and is frequently at the root of hospital-acquired infections.

Microscopic analysis showed a 32-fold increase in bactericidal activity for the laser-irradiated samples compared with silver nanoparticles produced by electron-beam irradiation. 

“The new technique offers the possibility of obtaining high-performance bactericidal compounds that are easy to produce,” Longo said.

Potential applications

The researchers have applied for a patent on the new technique and the two new classes of silver nanoparticle obtained by the technique.

The idea is to license the technology to Nanox, a spinoff from CDMF based in São Carlos, São Paulo State, and supported by FAPESP’s Innovative Research in Small Business Program (PIPE). 

“Nanox already sells silver nanoparticles worldwide and could benefit a great deal from the new technique for obtaining the material,” Longo said.

The researchers plan to evaluate use of the material in dental prosthetics and have begun trials to investigate the action of nanocomposites in cancer cells. 

Preliminary results of the experiments suggest the nanoparticles can eliminate tumor cells without affecting healthy cells.

The Scientific Reports article “Towards the scale-up of the formation of nanoparticles on α-Ag2WO4 with bactericidal properties by femtosecond laser irradiation” (doi:10.1038/s41598-018-19270-9) by Marcelo Assis, Eloisa Cordoncillo, Rafael Torres-Mendieta, Héctor Beltrán-Mir, Gladys Mínguez-Vega, Regiane Oliveira, Edson R. Leite, Camila C. Foggi, Carlos E. Vergani, Elson Longo and Juan Andrés can be read at: nature.com/articles/s41598-018-19270-9.