Sample preparation for qNMR Fluorescence quenching upon click-reaction with N 3 groups 10 solutions of 0.0164 mg/mL of nanoparticles (2.4 • 10 14 particles) with increasing amounts of fluorescent dye (AF488-DBCO) were prepared by diluting 32.8 µL of 1 mg/mL of nanoparticles in PBS (Dulbecco PBS, pH = 7.4) followed by addition of 0 -56.2 µL of a 0.01 mg/mL stock solution of the dye prepared in MQ water corresponding to 0 -15 eq equivalents of the dye w.r.t. to the number of NPs. The amount of PBS buffer was varied to keep the concentration of the particles constant (total volume = 2 mL) and the concentration of the dye in the stock solution was confirmed from the absorbance at 492 nm. All solutions were prepared in brown glass vials and kept in the dark after preparation to prevent photodegradation of the dye. The reactions were allowed to stir at RT for 72 hours in the dark before the PL measurements to ensure that the click reaction had reached completion. In parallel, reference solutions with the same concentration of the DBCO-carrying dye, but without nanoparticles, were prepared and kept under the same conditions. The measurement parameters and dye concentrations were chosen such that the emission intensity of the sample with maximum concentration did not exceed 10 6 counts to avoid saturation of the PL detector.