I have prepared gold nanoparticles of 80nm (by DLS) coated with biopolymer, Chondroitin Sulphate. The UV absorbance is observed at 540 nm, 730 nm, 965 and 1175nm. The 540 and 730 nm absorbance would be due to longitudinal and transverse SPR (as probably the particle shape is not spherical). Can anyone tell me the explanation of 965 nm and 1175 nm IR absorbance? Are these absorbance have any biological or clinical relevance? I guess there is no laser available suitable for this wavelength.
Have you imaged your particles? If you know their shapes, it might explain why you have 4 resonances. I wouldn't expect the resonances to be from the biopolymer, as the SPR usually shifts slightly in the presence of biomolecules; however, these molecules don't induce NEW resonance peaks that aren't otherwise there.
Depending on your application, do you need a laser? A diffuse lightsource such as a common light bulb emits at these wavelengths and could be used for spectroscopy.
I will take the images of the particles soon. I was actually looking for any literature on Gold nanoparticle which show UV-NIR absorbance till 1200 nm. The intended nanoparticle is for drug delivery and evaluation of hyperthermia by Infrared laser on cancer cells.
Well, the images will probably tell the story. If you look at manufactures of AuNanoRods they have specsheets that show how the plasmon resonance longitudinal peak shifts to long wavelengths as the aspect ratio of the rod increases. Like I said before, it's more likely that your resonances are mostly due to the shape of the particles, with slight deviations from bare particles induced by the coating.
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