Fungal nano: UV-Vis tests the metal

Skip to Navigation

Ezine

  • Published: Jun 1, 2016
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Fungal nano: UV-Vis tests the metal

Fungal fixers

Fungi could help researchers make metal nanoparticles from salts much more efficiently than conventional processes, according to a review published in the journal Nanoscale Research Letters. (Photo by David Bradley)

Fungi can help researchers make metal nanoparticles from salts much more efficiently than conventional processes, according to a review published in the journal Nanoscale Research Letters.

Khwaja Salahuddin Siddiqi of the Aligarh Muslim University, in Uttar Pradesh, India and Azamal Husen of the University of Gondar, in Ethiopia, explain how various fungi secrete enzymes and proteins as reducing agents for metals that could be exploited in a fermentation type process to mass produce nanoparticles. The aim would be to solve the problems of controlling nanoparticle size and shape and stability. They explain how biogenic nanoparticles have been successfully characterised using thermogravimetric analysis, X-ray diffractometry, SEM/TEM, zeta potential measurements, UV-Vis spectroscopy and Fourier transform infrared (FTIR) spectroscopy.

Biogenesis

"Chemical methods for the synthesis of nanoparticles are common, but their use is limited," the team says, not least because of the toxic agents required for their preparation and environmental concerns regarding solvent use and emissions. "Biogenic methods employing plant extracts are more popular, innocuous, inexpensive, and environmentally friendly as they do not leave hazardous residues to pollute the atmosphere," the team adds. Microbes have also been used as they too offer efficiency in terms of bioaccumulation of the metal from a feedstock, precipitation, biomineralization, and biosorption.

While some fungi that might be used instead of bacteria are pathogenic, as long as healthy and safety are taken into account, they offer the potential to produce far greater biomass, far more quickly than bacteria from which nanoparticles might then be generated. Moreover, the team asserts, the fungal mycelia (hairs) offer a vast surface area in a small volume for interaction with a metal-bearing feedstock and given the higher rate of metal-grabbing protein secretion in fungi compared to bacteria, the conversion of metal salts to metal nanoparticles can be very rapid.

The critical process involves the fungus simply protecting itself from otherwise toxic metals in its environment. For instance, when fungi are exposed to metal salts such as silver nitrate or gold chloride, the exude enzymes and metabolites that chelate or otherwise take up and sequester the toxic metal ions. In so doing, the metal ions are concomitantly reduced, often by naphthoquinones and anthraquinones metabolites present, to an insoluble form that aggregates as metal nanoparticles. Nitrate reductase from a particular fungus might lead to ferric salt reduction to iron nanoparticles. Cadmium, mercury, lead and thallium might also be sequestered to nanoparticle form for various applications using fungi, the team points out.

Mouldy nanoparticles

The resulting relatively uniform nanoparticles might then be used in a wide range of technologies, including using them as antimicrobial agents in medicine, ironically enough. Different fungal enzymes and protection mechanisms would generate different sizes and shapes of nanoparticle and be optimal with different metal salts. For instance, the silver nanoparticles biogenerated by Aspergillus fumigates are not necessarily the same size as those made by Fusarium oxysporum even if the salt concentration, pH, and temperature are exactly the same. A wide range of fungi and yeasts have now been shown to aggregate metal nanoparticles and their UV-Vis spectra and other analytical characteristics are always of interest. Some fungi even seem capable of generating semiconducting nanoparticles with particularly intriguing spectroscopic absorption characteristics.

Biogenic nanoparticles with a role in drug delivery, magnetic resonance imaging, catalysis, environmental sensing, textile engineering, and the food sector and plant disease management are increasingly common and the use of fungi to recover precious and toxic metals from waste is on the increase too. Comprehensive protocols must now be developed to allow us to take full control of the morphology of such biogenerated metal nanoparticles for new applications in medicine, agriculture, and technology, the team concludes. "We are currently looking for a comprehensive protocol to control the geometrical shape, size and stability of nanoparticles," Husen told SpectroscopyNOW.

Related Links

Nanoscale Res Lett 2016, 11, 98: "Fabrication of Metal Nanoparticles from Fungi and Metal Salts: Scope and Application"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

Follow us on Twitter!

Social Links

Share This Links

Bookmark and Share

Microsites

Suppliers Selection
Societies Selection

Banner Ad

Click here to see
all job opportunities

Copyright Information

Interested in separation science? Visit our sister site separationsNOW.com

Copyright © 2017 John Wiley & Sons, Inc. All Rights Reserved