Silver nanoparticles are potent antimicrobials but they are expensive to manufacture and require toxic solvents to produce. A team of researchers from Khalifa University has found a new way to produce silver nanoparticles using biochemistry and magnetic fields.
Metal and metal oxide nanoparticles are useful in a wide variety of commercial applications and consumer products, with manufacturers taking advantage of their unique electrical, optical and catalytic properties. Silver nanoparticles are one such example, as due to their potent antimicrobial activity, they are often incorporated into soaps, wound-dressings, creams and biomedical devices, such as catheters and valves, which are especially susceptible to bacterial growth.
A team of researchers from Khalifa University and Carthage University developed a novel method to produce silver nanoparticles using baker’s yeast and a static magnetic field. They published their findings in Scientific Reports earlier this month.
The team included Prof. David Sheehan, Professor of Biochemistry and Dean of the College of Arts and Sciences, Dr. Siobhan O’Sullivan, Assistant Professor of Molecular Biology and Genetics, both from Khalifa University, and Ameni Kthiri , Dr. Selma Hamimed, Abdelhak Othmani, and Ahmed Landoulsi, from Carthage University, Tunisia.
“The aim of our work is to reduce the use of potentially harmful reagents in the manufacturing of silver nanoparticles in order to mitigate any health or environmental risks,” Prof. Sheehan explained.
“Green chemistry uses environmentally sustainable routes to design, and manufacture chemical products, and one popular approach to green metal nanoparticle synthesis is to use biological systems. Various bacteria, fungi, plants and biological waste products can catalyze the reactions that reduce metals and lead to useful nanostructures.”
Reduction is a chemical reaction in which an atom gains electrons from a reducing agent. Reducing agents can be natural or synthetic, with green synthesis methods sometimes involving plant-based extracts or microorganisms to eliminate the need for hazardous chemicals. Green synthesis has the added benefit of being cost-effective and efficient, as well as helping to stabilize the resulting nanoparticles. The methods used also offer the ability to fine-tune nanoparticle size by controlling the amount and type of reducing agent used.
A variety of plant and microbial systems have been used to prepare silver nanoparticles, including seaweed, curry leaf, and lactobacilli. Some cells contain or secrete enzymes that are biochemical routes to metal reduction, but the exact way they work is poorly understood.
Additionally, the antimicrobial properties of the resulting silver nanoparticles depend on their average diameter – the smaller the nanoparticle, the more effective against bacteria. When silver nanoparticles were developed using baker’s yeast, Saccharomyces cerevisiae, they ranged between 11 and 25 nanometers.
Prof. Sheehan and his research team introduced a static magnetic field to the biosynthesis in their new approach. The nanoparticles from this method were significantly smaller than those typically produced biosynthetically, ranging from 2 to 12 nanometers in size. Plus, the nanoparticles obtained using the magnetic field were highly crystalline, stable and near-uniform in shape. Most importantly, the antibacterial activity was greater than that seen in the control cultures.
When a static magnetic field (SMF) is applied to this synthesis method, the nanoparticles produced are significantly smaller.
Magnetic fields are force fields created by a magnet, or as a consequence of the flow of electricity. A static magnetic field is one which does not vary with time, characterized by steady direction, flow rate and strength. They are constant and arise from a variety of sources including the Earth’s own magnetic field, direct current transmission lines, and domestic electrical devices, including microwaves and mobile phones.
The medical imaging technique, magnetic resonance imaging (MRI), uses strong magnetic fields to generate images of the organs in the body because they can “readily penetrate biological material and interact with charged species such as ions and proteins,” Prof. Sheehan said.
While the interactions between biological specimens and magnetic fields remain somewhat mysterious, studies have shown profound effects of static magnetic fields on mammalian and microbial cells, including inducing oxidative stress.
The researchers found that Saccharomyces cerevisiae, the baker’s yeast bacteria they used in their experiment to develop silver nanoparticles, experienced oxidative stress and a profound reduction in growth rate when exposed to a weak static magnetic field.
To investigate the effects of a magnetic field on the silver nanoparticle synthesis, the research team added silver nitrate to S. cerevisiae cultures both in the presence and absence of a static magnetic field. They found that the nanoparticles developed with a magnetic field were notably smaller and more bactericidal, or better at preventing the growth of bacteria.
The research team hypothesized that the silver nanoparticles were formed by reduction of the silver nitrate due to the adsorption of silver ions on the surface of the S. cerevisiae metabolic products, such as enzymes and polysaccharides present. The nitrate collected into the pores of the metabolic products, leaving the silver nanoparticles free in solution.
The research team also suggested that the static magnetic field creates waves through the liquid where the reaction takes place, which enhances the decomposition of biomolecules through oxidative stress, releasing free radicals which then act as reducing agents.
This approach provides a novel green chemistry route to synthesizing metallic nanoparticles with important biomedical and commercial applications. Additionally, the team believes this is the first method to use static magnetic fields to produce metal nanoparticles from biosynthesis. As nanoparticles could provide a viable alternative to conventional antibiotics, making silver nanoparticles in a cost-effective, efficient, and environmentally-friendly way could be vital to global public health and the fight against antibiotic resistance.
24 October 2021