We demonstrated that the NMR quantification of azide-carrying ligands, either in the bound state or stripped from the NP surface, comes with several unsolved challenges. We presented two convenient alternatives based on fluorescence or UV-Vis spectroscopy, both having similar accuracy and precision. The first quantification method is based on fluorescence quenching of a fluorophore by photoinduced charge transfer to nitrocatechol ligands upon bioconjugation. The method is limited by the requirement for electron-accepting ligands.