I have synthesized PVP coated iron oxide nanoclusters( approx. 250-300nm diameter) using hydrothermal method. But the nanoparticles are not very stable in water and keep falling down. How can I improve the stability of the nanoclusters? Should I use some post synthesis ligand exchange methods to replace the PVP with some other biocompatible ligands that will make the nanoclusters stable in water. Please help.
It would be pretty hard to have a stable dispersion for nanoparticles in this size regime. Large inorganic nanoparticles will settle down eventually no matter what you do. However, it might help a little bit (not a lot, though) if you introduce surface charge to the end of hydrophilic ligands; you can try to introduce charge by playing with solution pH.
Thank you Prof. Lee for your reply. But if the nanoclusters are not stable then is it possible to use them in biological applications. I am trying to study the contrast property of the nanoclusters for MR imaging. Please suggest/
If you want to use iron oxide nanoparticles for MR imaging, there are certain requirements for biological application: 1) The hydrophilic ligand coated nanopaticle should be smaller than 100 nm (ideally smaller than 50 nm). 2) The water solubility should be very good. 3) The nanoparticle should be superparamagnetic.
Why don't you check with my publications on MR imaging? Angew 2007, Angew 2011, Adv. Mater 2013, Chem Rev, 2015. CrystEngComm, 2015 (the last one for iron oxide nanoparticle synthesis) You will see that in certain cases it IS possible to obtain stable dispersion with suitable ligands even with quite large nanoparticles (but not in your size regime). If you still need more information, let me know.
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