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.

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.

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.

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.

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. 

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.

Jade Sterling
Science Writer
24 October 2021

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New research shows that ‘explosive’ cyclones off Antarctica, caused by increasing extreme atmospheric events, can contribute to ice shelf calving and, ultimately, sea level rise.

The finding comes after an international team of scientists, including Australian Antarctic Division physical scientist Dr Petra Heil, investigated the calving of a 1636 square kilometre, 210 metre-thick iceberg off the Amery Ice Shelf in East Antarctica.

The calving on 25 September 2019 occurred almost a decade earlier than scientists had expected (based on historical observations), from an existing rift across the front of the ice shelf.

Two explosive cyclone events just prior to the calving, were caused by unusual atmospheric conditions that fuelled sustained cyclones at the front of the ice shelf, and helped direct moist, warm air towards the ice shelf at the same time.

Dr Heil said these high latitude cyclones form in the extra-tropics, or mid-latitudes, and deepen as they move towards Antarctica.

They are marked by a deep central air pressure, are longer-lasting than ordinary cyclones, and bring clouds, high winds and often heavy precipitation.

“They form when the central pressure decreases by at least 24 hPa in 24 hours and they are stronger in the Indian Ocean sector of the Southern Ocean – near the Amery Ice Shelf – than elsewhere around Antarctica,” Dr Heil said.

“They are also more intense in the Southern Hemisphere than in the Northern Hemisphere.”

The team used satellite data and climate reanalysis (using models to analyse historical atmospheric observations) to understand the unusual atmospheric conditions at the time of the calving. They also looked at sea-ice conditions and ice movement over the Amery Ice Shelf.

Lead author of the study, Dr Diana Francis of Khalifa University in the United Arab Emirates, said they found an explosive cyclone formed over Cooperation Sea, to the west of the ice shelf, on 18 September 2019, generating surface winds of more than 72 kph.

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The Arabian heat low has intensified over the past 41 years, a trend thought to be caused by climate change

Climate researchers have predicted summer temperatures in the UAE will increase after they identified a strengthening of a key weather system associated with hotter air.

Scientists at Khalifa University of Science and Technology found the Arabian heat low has intensified and grown over the past four decades, a trend thought to be caused by climate change.

This low-pressure system is linked to the extremely high temperatures the Gulf region experiences each summer.

“This means that the region witnessed an increase in summer temperature extremes and this impacted larger areas,” said Dr Diana Francis of Khalifa University, one of the authors of a paper that details the research.

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Despite being a desert country, the UAE has all the necessary ingredients for fog, seeing up to 50 foggy nights per year. 

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Why is there so much fog in a desert country? On Dr. Diana Francis, Head of the ENGEOS Lab , explains why the , despite being a desert country, has all the necessary ingredients for fog, seeing up to 50 foggy nights per year

— جامعة خليفة للعلوم والتكنولوجيا (@KhalifaUni)

Winter in the UAE brings respite from the scorching summer temperatures for which this region is famed. It also brings foggy mornings, enveloping the country from the skyscrapers in Dubai to the dunes in Liwa.

Despite being a desert country, the UAE has all the necessary ingredients for fog, seeing up to 50 foggy nights per year. Dry desert conditions exist next to the warm seas of the Gulf, with moist air carried inland by the afternoon sea breeze cooled by the night desert surface.

“The fog that forms over the UAE is known as radiation fog and is caused by the rapid cooling of the desert surface at night during the winter,” explained Dr. Diana Francis, Head of the Environmental and Geophysical Sciences (ENGEOS) Lab at Khalifa University. “This cooling leads to cool air in the lower layers of the atmosphere, which condenses the water vapor present there. The UAE has an atmosphere rich in water vapor since it’s surrounded by water bodies, where sea breeze circulation brings large amounts of water vapor inland during the day, which is trapped and forms fog during the night.”

Fog can be considered as a low-lying cloud; it’s a visible aerosol of miniscule water droplets hovering above the ground. About 95 percent of the fog seen in the UAE is radiation fog, which is why it is so prevalent in the winter and not the summer. The other 5 percent is advection fog, meaning it forms over the surrounding seas and moves over the UAE. Regardless of the type of fog, when the sun rises and warms the country in the morning, the fog dissipates.

The desert part of the country also plays a vital role in the weather over the UAE. When the winds over the country are calm, the moist air blown in from the sea earlier in the day mixes with the dust and sand in the air from the desert. This dust acts as the catalyst for fog development.

“Dust is the main component in the aerosol load present in the atmosphere over the UAE,” explained Dr. Francis. “Aerosols act as condensation nuclei for water vapor, causing the water to condense around the dust particles in the air. This is the same principle that leads to the condensation of water vapor on the mirror when you shower—the mirror is the aerosol particle. Given how much of the atmosphere is sand from the desert and the large capacity of the desert to cool down quickly at night, it makes sense that two of the hot spots for fog formation in the UAE are the Sweihan desert and the South West of Abu Dhabi. Both  are desert areas, with fog forming over these places, expanding, and then merging together, particularly over Abu Dhabi airport.”

ENGEOS lab research work shows that Abu Dhabi airport experiences more low visibility events than Dubai or Al Ain due to the fog that starts nearby. The fog is most frequent between 20 and 100 kilometers inland but can extend up to 200 kilometers inland over the desert, and tends to occur the most in December and January, even though the fog season lasts between September and March.

“At ENGEOS we perform now-casting of fog formation, spatial cover and duration using satellite observations and artificial intelligence techniques,” said Dr. Francis. “We also forecast fog formation, time of occurrence, intensity and duration one day in advance using modelling. We found that fog can occur any time between 7pm and 11am local time, but the highest number of events occur between 3am and 7am. This information is critical for operations at Abu Dhabi airport and the transport sector in general to reduce the risks related to fog and low visibility.”

Jade Sterling
Science Writer
28 March 2021

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