Biomedical Engineering Reference
In-Depth Information
Surfactin, a well-studied lipopeptide biosurfactant, synthesized by
Bacillus
sp., can form micelles at a very low concentration of 0.005% (Sen, 1997). Liao
et al. (2010) prepared Surfactin-stabilized supermagnetic ironoxide nanoparticles
(SPION) that can serve as a contrast agent for magnetic resonance imaging. The as-
synthesized SPION particles in organic solvent dispersed easily in aqueous phase, to
form a stable suspension of spherical nanoparticles. Singh et al. (2011) used Surfactin
in the synthesis of cadmium sulfide nanoparticles. Results showed no evidence of
color change or agglomeration over a period of 120 days. The improved stability of
nanoparticles was due to the interaction of cadmium sulfide nanoparticles with the
free amine groups of Surfactin. The presence of Surfactin had not only stabilized
the particles but also acted as the capping agents during synthesis, which confined
the phase-transitioned cubic nanoparticles size to 3-4 nm. Concentration of biosur-
factants has always played a significant role in determining the structure of nanopar-
ticles. The thickness of the petals in the rose-like ZnO nanostructure was greatly
affected by the concentration of initial Surfactin in the precursor solution (Reddy
et al., 2011). Increase in Surfactin concentration decreased the thickness of petals.
The as-synthesized ZnO nanoparticles were further tested for their efficacy in the
photocatalytic degradation of methylene blue.
Reddy et al. (2009) studied the effect of pH on size and stability of gold nanopar-
ticle obtained through Surfactin-mediated synthesis. Nanoparticles were found to
be more stable at pH 7 and 9, while they were aggregated within 24 h at pH 5.
Furthermore, particles were of uniform size and shape at pH 7, but polydispersed at
pH 5 and 9.
Other structures like porous microtubules were also reported for the synthesis
of metal nanoparticles using biosurfactants. Rehman et al. generated rhamnolipid
microtubules by refluxing native rhamnolipids with gold salts. These micro-
tubules served as templates for the synthesis and self-assembly of gold nanopar-
ticles to obtain rhamnolipid gold nanoparticle composite microtubules. Further
heat treatment of these composite microtubules yielded porous gold microwire-
like structures that find applications in electronics, optics, catalysis, and sensing.
Similarly, Narayanan et al. (2010) used rhamnolipid for capping ZnS nanoparticles
in an aqueous medium. SAXS analysis revealed uniformly dispersed nanospheres
with the size range of 4.5 nm.
MICROEMULSION-BASED NANOPARTICLE SYNTHESIS
Biomolecules as building blocks in nanoparticle synthesis can maintain and integrate
the structural and functional diversity of biosystems with the inherent properties of
nanomaterials (Rehman et al., 2010). One of the most important and challenging
steps that influences the overall properties of final product is the generation of a suit-
able self-assembled microstructure. Various customized protocols have been devel-
oped for the self-assembly of biosurfactants to obtain microstructures of required
sizes and shapes. Elucidating the underlying mechanisms in the formation of micro-
emulsion is important in designing a controlled process for nanoparticle synthesis.
Microemulsion systems are pseudoternary systems that require the formation of a
clear homogeneous system comprising water, oil, surfactant, and an alcohol-based
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