I'm trying to switch the caps of my gold nanoparticles to from an aqueous citrate-capped solution to an organic thiol-capped solution. I've tried various ways to do this, all of which being variations of mixing the Ct-capped nanoparticles with the desired thiol in an organic solvent, with the idea that the thiol has a higher affinity for the gold and will displace the citrate, resulting in the desired thiol-capped hydrophobic nanoparticles in the organic layer. The Ct-capped nanoparticles range in diameters from ~6 to 24nm.
This procedure is described in countless papers and it just doesn't work that easily. Does anybody have any experience/advice/suggestions for this? I've tried using some phase transfer catalysts, different variations of equivalencies and solvents, and still to no avail.