When ever we take the absorption or transmission spectra of nobel metal nanoparticles using a UV-VIS spectrometer, there is a strong absorption due to the localsied surface palsmon resonance of the particular nanoparticles. But apart from that what are the other types of absorption can occur?
What about simple Rayleigh scattering? It is elastic scattering, but will certainly strongly affect transmission.
Generally not. But if you prepare the gold nanoparticles with proteins or any plant extract you get a peak for protein also around 400 nm.
Please see the following article:
Potential therapeutic and diagnostic applications of one-step in situ biosynthesized gold nanoconjugates (2-in-1 system) in cancer treatment
I do agree with Prof Sudip Mukherjee, there will be other absorption parts that might arise from the UV-vis spectra. First of all, it would be the characteristic absorption spectra of the surface activators (SAs) that you used to block the size of the particles such as polymers, hydrophobic-hydrophilic agents -CTAB, TOAB, and/or other organic agents - trisodium citrate, ... You can check them by measuring the UV-vis spectra of those SAs, and try to see the spectra of the particles containing solution after each time centrifugation. You could experience that those characteristic spectra decrease by the mean centrifugation times, but they still exist.
On the other hand, I do believe that you modified the surface of the noble metal particles in order to employ them for some other applications such as bioimaging, detection ... The absorption of the named bioactive molecules might occur when they attached to the surface of the particles. Pls measure the individual spectra of those molecules (thiolated-biotine or thiolated oligo chain,...), it might be a quite good evident for proving their connective presence onto the particles.
For smaller size nano-particles only dipolar mode will exist but if the particle size is large, multipolar mode excitation definitely exist. you need to look multipole excitation theory.
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