In recent decades, various research groups in the field of materials science have invested time and resources to answer the following question: is it possible to develop new techniques capable of producing silver particles on a nanometric scale (i.e., one billionth of a meter), thus enhancing the optical, catalytic and bactericidal properties of silver? A group of Brazilian investigators has taken a step forward in this contest.
In a research carried out within the Center for Development of Functional Materials (CDMF), one of the Research, Innovation & Dissemination Centers (RIDCs) funded by the São Paulo Research Foundation - FAPESP, they 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.
New technique provides economic feasibility
A Professor at UFSCar and executive director for the CDMF, Elson Longo says that CDMF's researchers developed an innovative method of obtaining nanocomposites three years ago. These nanocomposites were comprised of silver nanoparticles coupled to a silver tungstate semiconductor crystal by transmission electron microscopy.
However, the high cost of transmission electron microscopes limited plans of large-scale production of these materials for real-world applications. "The transmission electron microscope used to obtain this material costs approximately 1.3 million euros," Longo said. The technique involved electron-beam irradiation of silver tungstate, which resulted in promising bactericides whereby the silver tungstate semiconductor attracts bacterial agents that are then are neutralized by silver nanoparticles.
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," said the coordinator of the FAPESP-funded research center.
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.
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 http://www.bv.fapesp.br/en/3).
"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.
Towards the scale-up of the formation of nanoparticles on α-Ag2WO4 with bactericidal properties by femtosecond laser irradiation 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 & Juan Andrés Scientific Reports volume 8, Article number: 1884 (2018) doi:10.1038/s41598-018-19270-9
São Paulo Research Foundation (FAPESP)