Biomedical Engineering Reference
In-Depth Information
further for enhancing their structural, functional, and physicochemical properties.
The various functional groups and topological features of the biological macromol-
ecules can be exploited for the self-assembly of in situ synthesized nanostructures
without subjecting them to any harsh chemical treatments. It is believed that the
biotemplates-based nanoparticle synthesis with its tunable size, shape, and monodis-
persibility will turn out to be a competent alternative that can surpass the hitherto
achieved efficiencies by other conventional approaches.
METAL NANOPARTICLE SYNTHESIS
B
iosurfaCtants
as
C
aPPinG
a
Gents
Properties of Biosurfactants
Biosurfactants are surface-active molecules that are stable at extremes of pH,
temperature, and salinity. When compared to their synthetic counterparts, they have
unique properties such as bulky and complicated structures, multiple chiral centers,
ability to form supramolecular assemblies and liquid crystals, and other various
biological activities (Xie et al., 2005). Biosurfactants are biodegradable in nature
and are also reported to be nontoxic or less toxic as compared to synthetic surfac-
tants. The aforementioned superior properties of biosurfactants elevate their status to
“green molecules” for eco-friendly applications. One of the most important proper-
ties exploited in the nanoparticles synthesis is their micelle-forming ability. The non-
covalent interactions that arise due to solvophobic effects of hydrophobic tails form
the basis for self-aggregation into structures like micelles and vesicles. Micelles exist
in different morphologies, such as spherical, ellipsoidal, and cylindrical structures,
while vesicles are hollow spheres enveloped by bilayers of ampiphilic surfactants
(Engberts and Kevelam, 1996; Davies et al., 2006). Biosurfactants above the critical
micelle concentration (CMC) form micelles. Being amphiphiles, they can partition
at air-water or water-oil (hydrocarbon) interfaces. Their use as emulsifiers in the
food industry is attributable to this property.
The major concern in nanoparticle synthesis is tuning up these structures to
obtain aggregates with desired morphology and properties. The morphology of these
supramolecular structures can be significantly varied by changing the pH, tempera-
ture, surfactant concentration, and the ionic strength of solution.
Metal nanoparticles, owing to their size/shape-dependent, unique, and tunable
properties (e.g., quantum confinement Yanhong et al., 2004), plasmon resonance
(Hutter et al., 2001), and light scattering (Derkacs et al., 2008) etc., find applications
in wide areas such as electronics, optics, catalysis, and biotechnology. By controlling
the synthesis, it is possible to alter properties of nanosystems including surface area,
optical and electrical properties, and the accessibility of the guest species.
Experimental conditions, such as pH, temperature, viscosity of solution, and
processing conditions such as rate of reduction and adsorption mechanisms of sta-
bilizing/capping agents with metal ions are some of the factors that can be con-
trolled in the design of nanoparticles (Pradeep and Anshup, 2009; Ghorbani, 2011).
Particularly, capping agents play a very important role in determining the final
quality of the particles (Raveendran et al., 2003). It essentially reduces the tendency
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