Biomedical Engineering Reference
In-Depth Information
nanoparticles with certain reproducible morphology due to the diversely
varying composition and structure of plants from dif erent origins. h e
dii culty increases further, if the production of nanoparticles with desired
morphology is achieved by certain functional groups on a particular part
of the plant biomass. For example, Au nanoparticles could be accumulated
throughout the epidermis, cortex and vascular tissue of
Brassica juncea
.
However, the size distribution of nanoparticles within the plant tissues
was found to be location-dependent, with a broader range of particle
sizes exhibited by the nanoparticles formed within aboveground tissues
as compared to those root-located nanoparticles [160]. h us, in order to
use an easy and safe green method in scale up and industrial production of
well-dispersed metal nanoparticles, plant extracts are certainly better than
living plants.
8.2.1.5
Biosynthesis of Metal Nanoparticles by Biomolecules
8.2.1.5.1 Reducing Sugars
Reducing sugars such as monoses, dioses and oligoses are polyols with dis-
sociated aldehyde or ketonic groups [100]. h e ability of dif erent sugars as
reducing agents for the synthesis of metallic nanoparticles was demonstrated
by Panigrahi
et al.
[161]. h eir study shows that nanoparticles with uniform
size can be produced if fructose was used, whereas particles of variable sizes
were generated if glucose and sucrose were used. h e role of reducing sug-
ars was demonstrated when sucrose was used as a non-reducing sugar. It
was found that in the preparation of Ag nanoparticles by using sucrose as a
reducing agent, no Ag nanoparticles were produced when AgNO
3
was used
as Ag precursor, whereas the production of Au nanoparticles was observed
when HAuCl
4
was used as Au precursor [161]. h is phenomenon suggests
that instead of the non-reducing sucrose, the actual compounds responsible
for the bioreduction of nanoparticles were glucose and fructose produced
from sucrose at er being hydrolyzed by the chloroauric acid. Succinoglycan,
an important acidic polysaccharide of
Sinorhizobium meliloti
consisting of
one galactose and seven glucose residues, was demonstrated to be useful for
the production of Ag nanoparticles in controlled pH environments. As pro-
posed by the authors [161], one reducing sugar in the succinoglycan pro-
vided one electron to reduce Ag
+
to Ag(0) only under a basic condition. h e
aldehyde group of reducing sugar was oxidized to carboxyl group by nucleo-
philic addition of OH
-
, which reduced Ag
+
to Ag(0) [162]. A similar mecha-
nism could also apply to the bioreduction of tetrachloroaurate ions by the
reducing sugars present in the lemongrass extract as proposed by Shankar
et al.
[163]. h e growth of Au nanotriangles was believed to be a result of
