Nanoparticles have unique thermal, optical, physical, chemical, magnetic and electrical properties compared to their bulk material counterparts. These features can be exploited for next generation biosensors, electronics, catalysts and antimicrobials. Metallic nanoparticles are one important and widely studied group of materials, showing great diversity and many different uses
Over the past few decades interest in metallic nanoparticles and their synthesis has greatly increased. This has resulted in the development of numerous ways of producing metallic nanoparticles using chemical and physical methods. However, drawbacks such as the involvement of toxic chemicals and the high-energy requirements of production make it difficult for them to be widely implemented.
An alternative way of synthesising metallic nanoparticles is by using living organisms such as bacteria, fungi and plants. In order to survive in environments containing high levels of metals, organisms have adapted by evolving mechanisms to cope with them. These mechanisms may involve altering the chemical nature of the toxic metal so that it no longer causes toxicity, resulting in the formation of nanoparticles of the metal concerned. Thus nanoparticle formation is the “by-product” of a resistance mechanism against a specific metal, and this can be used as an alternative way of producing them. This “green” method of biological nanoparticle production is a promising approach that allows synthesis in aqueous conditions, with low energy requirements and low-costs.
There are important links between the way nanoparticles are synthesised and their potential uses. Silver nanoparticles (AgNPs) have been shown in numerous studies to display antibacterial properties. With the rise in antibiotic resistance in recent years and the development of fewer new antibiotics, research has begun to focus on these antibacterial nanoparticles as potential new medical tools. Silver nanoparticles have also been used as optical sensors for the formation of small molecule adsorbates. Whereas catalysts based on Pt nanoparticles have been shown to exhibit high activity for the electrooxidation of formic acid.
Research has focused heavily on prokaryotes as a means of synthesising metallic nanoparticles. They provide advantages such as their abundance in the environment and their ability to adapt to extreme conditions. They are also fast growing, inexpensive to cultivate and easy to manipulate. Growth conditions such as temperature, oxygenation and incubation time can be easily controlled.
U.S. Army researchers announces groundbreaking advance in nanoparticle production
U.S. Army has announced in March 2019 that at the U.S. Army Combat Capabilities Development Command (CCDC) Chemical Biological Center biologist Alena Calm, research scientist Kelley Betts, research chemical engineer Michael Kim, Ph.D., and biologist Frank Kragl are developing methods to characterize and scale up the production of these nanoparticles to better understand how biologically-derived nanoparticles could improve Army capabilities.
A variety of microbes have the ability to synthesize intracellular metal nanoparticles that could be harnessed for use in future military applications. One of these organisms, the bacteria Magnetospirillum gryphiswaldense, sequesters magnetite to form intracellular chains of microbial nanoparticles called magnetosomes. These biologically-derived nanoparticles require much less energy to make than their synthetic counterparts and have a number of superior qualities such as high chemical purity, low toxicity, good biocompatibility and environmentally-friendly production.
The initial goal was to explore the ability of these nanoparticles to provide customizable, environmentally-friendly electromagnetic pulse protective materials that fit well within the Army’s Energy Security and Sustainability Strategy. Current capabilities, such as the Faraday cage, can be expensive and cumbersome in field-forward environments.
Now that they have determined how to grow the bacteria on a large scale, they’re investigating military uses for the nanoparticles that they produce. While their use in medicine is well-documented in applications such as magnetic imaging, immunoassays and cancer therapeutics, their potential in military applications remain undiscovered.
“We’ve learned how to grow them in small and large scales. We’ve gotten to the stage of making and characterizing nanoparticles, and we’re in the process of figuring out what they can do,” Calm said. “In the next steps, we’d like to learn about what they can do for the Army. We keep getting more ideas on how to use these.”
Because nanoparticles have both broad and interdisciplinary applications, they could potentially impact the development of a variety of defense-related materials such as new classes of sensors, microelectronic devices, specialized coatings useful for next-generation combat vehicle design and functionalized textiles such as Solider uniforms and protective suit systems.
Currently, scientists at the Center’s Toxicology and Obscuration Sciences Division are electrospinning the nanoparticles in a polymer. “If we can spin these into fibers, the material could be tested for an assortment of capabilities,” Betts said. The Center’s Biotechnology Branch is partnering with the University of Delaware’s College of Engineering to determine the possibilities.
This research was jumpstarted through the Center’s FY18 Innovative Development of Employee Advanced Solutions (IDEAS) Program, which is designed to promote innovation and advanced development of new ideas and projects, and was subsequently supported by the Center’s Biological Engineering for Advanced Materials Solutions Grand Challenge. In 2019, the newly-awarded IDEAS project titled: A Biologically-derived Transformer- “More than meets the eye…” will look to leverage these living organic materials to develop a first-of-its-kind, highly efficient, biologically-grown electronic transformer by using living bacterial cultures to grow a working laminated transformer core.
The CCDC Chemical and Biological Center is the first Defense Department laboratory to develop a process for scaling up the production of magnetosomes.
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