I am conjugating a drug on gold nanoparticles. The unbound drug absorbs well between 350-400 nm. The naked gold nanoparticle absorbs between 250-500 nm. After conjugation of the drug to the nanoparticle, the UV features of the drug are skewed and blue shifted. I thought of creating a standard curve of the plain drug and calculate the amount of drug on the nanoparticle by correlation. However, because of this aforementioned problem, I do not know if it is a good idea to use the same technique.

The drug also shows fluorescence. If I take an excitation scan of the nanoparticle keeping fluorescence at 500 nm constant, the excitation spectra matches to that of unbound drug. Also exciting at 350 nm, the fluorescence spectra of the nanoparticles matches with that of the drug. Gold nanoparticles has absolutely no contribution in the fluorescence spectra. I proceeded to make a standard curve of fluorescence with different concentrations of the drug and calculate the amount of drug on the nanoparticle by correlation of fluorescence intensities. Is fluorescence a correct technique to use for quantification of the amount of drug? Any help would be appreciated.

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