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Abstract
We report the synthesis ofAu nanoparticles, with tunable longitudinal plasmon band
and shape selectivity, mediated by starch in the presence of ultrasonic waves. The
synthesis was carried out by reduction of HAuCl4, at various concentrations, using
H2O2 as the reducing agent. When the reactions were carried out in the absence of
ultrasonic waves, there was no occurrence of the longitudinal resonance band, while
the transverse plasmon resonance band shifted toward a higher wavelength. Transmission
electron microscopic measurements revealed an increase in particle sizes with increasing
higher initial HAuCl4 concentration. On the other hand, in the presence of ultrasonic
waves, as the initial concentration of HAuCl4 was increased, while the transverse
plasmon resonance band remained the same, the longitudinal plasmon resonance band
increasingly shifted toward a higher wavelength. Transmission electron microscopic
measurements revealed the change in shape from spherical to triangular to hexagonal
particles with increasing initial HAuC14 concentration. We also report that the starch-stabilized
nanoparticles could be precipitated from the solution by a starch digesting enzyme
which also binds with the particles resulting in its precipitation.