Environmental Engineering Reference
In-Depth Information
(a)
(b)
(c)
(d)
100nm
1 μm
500 nm
100 nm
fiGure 18.3
TeM images at different magnifications (a-d) of thin sections of stained Verticillium cells after reaction with Aucl
4
ions for
72 h. Reprinted with permission from Ref. [28]. © 2001, Wiley-Vch Verlag Gmbh, Weinheim, Fed. Rep. of Germany.
18.2.2.1 Fungi-Assisted Intracellular Nanoparticle Synthesis
In continuation with the earlier discussion, various research
groups reported different fungi for nanoparticle synthesis; for example, Mukherjee et al. reported the eukaryotic microorganism
Verticillium
sp. (AAT-Ts-4) for the biological synthesis of gold nanoparticles (Fig. 18.3). Gold particles of size 20 nm were
prepared on the surface and on the cytoplasmic membrane of fungal mycelium [28].
Recently, Vigneshwaran et al. prepared silver nanoparticles up to 9 nm in size using silver nitrate in the presence of
Aspergillus
flavus
on the surface of its cell wall and incubated for 72 h [29].
18.2.2.2 Fungi-Assisted Extracellular Nanoparticle Synthesis
extracellular synthesis of nanoparticles has many applica-
tions as unnecessary adjoining cellular components are absent from the cell. Because of the enormous secretory components
that are involved in the reduction and capping of nanoparticles, fungi produce nanoparticles extracellularly. In this regard
shankar et al. found an endophytic fungus,
Colletotrichum
sp., isolated from the leaves of the geranium plant, which is helpful
in the synthesis of spherical gold nanoparticles [22]. Bhainsa and d'souza reported the synthesis of silver nanoparticles by use
of
Aspergillus fumigatus
with silver nitrate. The spherical and triangular shape nanoparticles were observed in the range of
5-25 nm [24]. This is the fastest reduction protocol by a biological method and is faster than even physical and chemical
methods. cationic proteins secreted by
F. oxysporum
were used for the synthesis of zirconia nanoparticles when incubated with
zirconium fluoride [30].
It was also found that
F. oxysporum
produced optoelectronic nanocrystalline material Bi
4
in the size range of 5-8 nm with
quasi-spherical morphology by extracellular mechanism, when bismuth nitrate was added as precursor [31].
18.2.3
actinomycete-Mediated synthesis of nanoparticles
Actinomycetes have popularly been known as ray fungi. A novel extremophilic actinomycete, the
Thermomonospora
sp. was
found to synthesize extracellular spherical gold nanoparticles with size up to 8 nm [32]. The obtained nanoparticles were stable
for more than 6 months. In contrast, the alkalotolerant actinomycete
Rhodococcus
sp. intracellularly accumulated gold nanopar-
ticles with a dimension of 5-15 nm. The availability of reductases on the cell wall reduced ionic Au and accumulated as Au on
the cell wall and on the cytoplasmic membrane [33].
18.2.4
yeast-Mediated synthesis of nanoparticles
lin et al. reported baker's yeast,
Saccharomyces cerevisiae
, for the reduction of Au
3+
to metallic gold in the peptidoglycan layer
of the cell wall by the aldehyde group present in reducing sugars [34]. extracellular hexagonal silver nanoparticles in the size
range of 2-5 nm were reported by using yeast MKy3 [35]. yeast
Pichia jadinii
(
Candida utilis
) has been used for intracellular
synthesis of gold nanoparticles up to 100 nm size with spherical, triangular, and hexagonal morphologies [36, 37]. however, Jha
et al. reported
S. cerevisiae
for the synthesis of spherical-shaped face-centered cubic unit cell antimony oxide (sb) nanoparticles
in the size of 2-10 nm at room temperature [38].
