Dear Maulik,

I would say you can try something like DLS, UV-VIS spectroscopy, Small Angle X-ray Scattering and confirm it in SEM or TEM. This will tell you the size distribution of the nanoparticles and if they are stable.

If you want to check if you got some chemicals on the nanoparticles, you should have the solution clear of the chemicals and then dissolve the gold and estimate the concentration of your chemical in that solution.

If you want a quality check whether your chemistry works, then try something which will be clustering the nanoparticles only in case it works:

AuNP@Antibody-Antigen-Antibody@AuNP

You can read our paper, where we estimate the amount of DNA on AuNP and its functionality as well as the size distribution..

Article Surface Passivation Improves the Synthesis of Highly Stable ...

I recommend you a simple one-step immunoassay to examine the quality of the AuNP-antibody or AuNP-antigen conjugates:

www.nanodiscoveryinc.com