You are right that it is very difficult to coat the bare IONPs with Au, Ag, because you know that the bare surface of IONPs is only covered by hydroxy moieties, which have very poor ligation affinity to the metal precursors resulting very minute surface coverage and formation of mostly the free metal particles. To overcome this, during IONPs fabrication you can use some stabilizers or surface active moieties that provide suitable functionality for ligation of the metal ion precursors in the dispersion medium and can facilitate to occur the nucleation onto the surface of IONPs. I mean you have to confirm the physio or chemisorption of the metal precursors onto the IONPs surface rather than free in the medium then add quantitative amount of reducing agent to form the metal particles. Best of luck.

Thanks Rahman, i am using oleic acid as stabilizer, then performing gold nanoparticles formation using IONPs dispersion. But very few coated particles are found.

Dear Kumar

Please follow these papers:

1. http://pubs.rsc.org/en/content/articlehtml/2015/cc/c4cc10413g

2. https://pubs.acs.org/doi/abs/10.1021/acsami.5b00368

3. https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.200400427