Throughout human history, fungi have been utilized as a source of food and harnessed to ferment and preserve foods and beverages. In the 20th century, humans have learned to harness fungi to protect human health (antibiotics, anti-cholesterol statins, and immunosuppressive agents), while industry has utilized fungi for large scale production of enzymes, acids, and biosurfactants. With the advent of modern nanotechnology in the 1980s, fungi have remained important by providing a greener alternative to chemically synthesized nanoparticle.
Background
A nanoparticle is defined as having one dimension 100 nm or less in size. Environmentally toxic or biologically hazardous reducing agents are typically involved in the chemical synthesis of nanoparticles so there has been a search for greener production alternatives. Current research has shown that microorganisms, plant extracts, and fungi can produce nanoparticles through biological pathways. The most common nanoparticles synthesized by fungi are silver and gold, however fungi have been utilized in the synthesis other types of nanoparticles including zinc oxide, platinum, magnetite, zirconia, silica, titanium, and cadmium sulfide and cadmium selenide quantum dots.
Silver nanoparticle production Synthesis of silver nanoparticles has been investigated utilizing many ubiquitous fungal species including Trichoderma, Fusarium, Penicillium, Rhizoctonia, Pleurotus and Aspergillus. Extracellular synthesis has been demonstrated by Trichoderma virde, T. reesei, Fusarium oxysporm, F. semitectum, F. solani, Aspergillus niger, A. flavus, A. fumigatus, A. clavatus, Pleurotus ostreatus, Cladosporium cladosporioides, Penicillium brevicompactum, P. fellutanum, an endophytic Rhizoctonia sp., Epicoccum nigrum, Chrysosporium tropicum, and Phoma glomerata, while intracellular synthesis was shown to occur in a Verticillium species, and in Neurospora crassa.
Gold nanoparticle production Synthesis of gold nanoparticles has been investigated utilizing Fusarium, Neurospora, Verticillium, yeasts, and Aspergillus. Extracellular gold nanoparticle synthesis was demonstrated by Fusarium oxysporum, Aspergillus niger, and cytosolic extracts from Candida albican. Intracellular gold nanoparticle synthesis has been demonstrated by a Verticillum species, V. luteoalbum,
Miscellaneous nanoparticle production In addition to gold and silver, Fusarium oxysporum has been used to synthesize zirconia, titanium, cadmium sulfide and cadmium selenide nanosize particles. Cadmium sulfide nanoparticles have also been synthesized by Trametes versicolor, Schizosaccharomyces pombe, and Candida glabrata. The white-rot fungus Phanerochaete chrysosporium has also been demonstrated to be able to synthesize elemental selenium nanoparticles.
Culture techniques and conditions Culture techniques and media vary depending upon the requirements of the fungal isolate involved, however the general procedure consist of the following: fungal hyphae are typically placed in liquid growth media and placed in shake culture until the fungal culture has increased in biomass. The fungal hyphae are removed from the growth media, washed with distilled water to remove the growth media, placed in distilled water and incubated on shake culture for 24 to 48 hours. The fungal hyphae are separated from the supernatant, and an aliquot of the supernatant is added to 1.0 mM ion solution. The ion solution is then monitored for 2 to 3 days for the formation of nanoparticles. Another common culture technique is to add washed fungal hyphae directly into 1.0 mM ion solution instead of utilizing the fungal filtrate. Silver nitrate is the most widely used source of silver ions, but silver sulfate has also been utilized. Choloroauric acid is generally used as the source of gold ions at various concentrations (1.0 mM and 250 mg to 500 mg of Au per liter). Cadmium sulfide nanoparticle synthesis for F. oxysporum was conducted using a 1:1 ratio of Cd2+ and SO42− at a 1 mM concentration. Gold nanoparticles can vary in shape and size depending on the pH of the ion solution. Gericke and Pinches (2006) reported that for V. luteoalbum small (cc.10 nm) spherical gold nanoparticles are formed at pH 3, larger (spherical, triangular, hexagon and rods) gold nanoparticles are formed at pH 5, and at pH 7 to pH 9 the large nanoparticles tend to lack a defined shape. Temperature interactions for both silver and gold nanoparticles were similar; a lower temperature resulted in larger nanoparticles while higher temperatures produced smaller nanoparticles.
Analytical techniques
Visual observations For externally synthesized silver nanoparticles the silver ion solution generally becomes brownish in color, but this browning reaction may be absent. For fungi that synthesize intracellular silver nanoparticles, the hyphae darken to a brownish color while the solution remains clear. In both cases the browning reaction is attributed to the surface plasmon resonance of the metallic nanoparticles. For external gold nanoparticle production, the solution color can vary depending on the size of the gold nanoparticles; smaller particles appear pink while large particles appear purple. Intracellular gold nanoparticle synthesis typically turns the hyphae purple while the solution remains clear. Externally synthesized cadmium sulfide nanoparticles were reported to make the solution color appear bright yellow.
… excerpt ends here. Continue reading the full article.
