Dear A.K.Singh

You should make different acidic concentrations and try to see the spectral variation of LSPR for Au nanoparticles. Some acidic mediums have different effects. You should consider various acidic solutions for your experiments.

With regards

Dear Anand Kumar Singh,

From a theoretical point of view, the localised surface plasmon resonance (LSPR) is highly dependant on the medium surrounding the plamonic nanoparticle. Simply put, a change in the refractive index can lead to a shift in the Fano resonance observed experimentally in the UV-VIS spectrum. This is the basis of various theoretical, numerical and experimental studies of plasmonic bionsensors.

From a practical viewpoint, it could be more complex (isn't it always!). Gold (Au) is considered to an inert plasmonic material. However, it is plausible that localised surface chemistry of the Au nanoparticle is changing as a result of pH variation directly. Another issue could be the aggregation of the nanoparticles. Finally, make sure that you have used the medium to blank first, before analysing the medium + nanoparticles together.

Arezou Zarei proposes a good approach: try comparing the pH dependant spectral variation with results in the literature.

Good luck!

As gold is a material which is hard for the acidic reaction. LSPR is dependent mainly on the refractive index of the surrounding medium around the gold nanoparticle. Once the medium is not reactive with the nanoparticles, one can see the shift in LSPR peak as per the refractive index of the medium. It may be acidic or basic in nature.

Arezou Zarei Mam . Thank You very much for your spectacular answer.