PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Chapter 3: Multi-Technique Approach for Characterization of Gold Nanoparticles
incoming light, which allows the further modulation of optical effects through alignment
[163,164]. Figure 3.3 shows variation of UV-visible spectra with the change in the particle
morphology. One-peak SPR peak for spherical nanoparticles transforms to two-peaks SPR
for nanorods which typically display longitudinal and transverse plasmon resonances
(electron oscillations along or across their long axis, respectively). Rod length affects
longitudinal plasmon wavelength (a strong extinction peak in the upper visible or nearinfrared
parts of the spectrum). As the aspect ratio increases, the position of the longitudinal
plasmon band red-shifts and the transverse plasmon band position stay relatively constant.
Thus, the particle shape dictates what wavelengths of light can be absorbed, and elastically
scattered; gold nanorods of moderate aspect ratio (2 – 5) display plasmon bands with tunable
maxima from ~700 to 900 nm and high-aspect ratio nanorods exhibit a longitudinal plasmon
band past 1500 nm [163,164,167].
Figure 3.3. UV-visible absorption spectra of different gold nanostructures, e.g.
nanoparticles/spheres, decahedra and nanorods.
UV-visible absorbance spectra can also be used to investigate different ligands
(proteins, antibodies etc.) on the nanoparticles (Figure 3.4). The adsorption of ligand onto
gold nanoparticle surface results in red shift in absorbance peak for the nanoparticle. It is
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