Particle suspension and re-suspension of nano-particles
Try mercaptoacetate surface treatment to put a negative charge on their surfaces for repulsion around pH 8 or 9 basic solution.  Uncoordinated mercaptoacetate is oxidatively dimerized to the disulfide by air (oxygen).  The drug S-mercaptocysteine as its salt (basic pH) should be more aggressive toward binding.  3-Mercapto-1-propanesulfonic acid will bind at lower pH.

The dose must be low enough that you do not disaggregate your particles, especially over time.  You can permeable membrane desalt an excess.