Hi, have you tried to determine the amount of your organic compound attached to nanoparticles by any other method (e.g. activity)? One of the possibility is that amount of your drug is really low and it is the reason why you observe only solvents signals. If yes, give yourself the question: Should I observed such amount of the drag if is not attached to NP by NMR?

Hi Mr. Krężel, thanks for the suggestion. The quantification of the organic compounds  is currently undergoing by TGA analysis. Previously I have also verified the presence of the polymer functional groups on my nanoparticles by FTIR analysis-the results showed similar peaks as the polymer standards. What eludes me is that the peaks of these polymers also did not appear on my H-NMR spectrum. 

I have a simple question.  The NMR you are using is solution NMR.  Is it possible that the organic ligand is coating the nanoparticles?  In this case one would need solid states NMR, not solution state NMR, to detect it. .      .   Were this true, this would imply the nanoparticle have very high affinity for the ligand of interest. .     .

Dear Josua  - I fully agree with Michaels explanation for the absense of signals from your capping agent and your drug molecules. If it is possible to add an excess of the drug molecules will you then see NMR signals from these appearing ? If the "free". drug molecules are in reasonable fast dynamic exchange with the bound ones you should see a line witdth of the drug NMR signals that would depend on the free to bound ratio.

Maybe I am too optimistic  - the black cat may only be seen using infrared light :-) !

@MP: I apologize for my late reply. Thank you very much for your thorough feedback.