Photostability measurements

Photostability measurements were performed by illuminating 3 mL of fluorescent nanoparticle solutions of the same optical density of 0.01 with white light of 450 W xenon lamp while monitoring intensity with a Horiba Fluorolog 3 (Horiba, Japan) fluorimeter. Optical densities of fluorescent free dye and particles were chosen to have the same 0.01 absorbance. The solutions were separately irradiated continuously using the white light source using a slit width of 14.7 nm. (For comparison, a 1 nm slit width was used when doing standard fluorescence measurements.) Initial fluorescence intensity was recorded at time zero and represents the maximum intensity. Fluorescence was recorded every 60 seconds following continuous exposure and normalized by the maximum intensity to produce a measure of % fluorescence remaining. Photostability measurements were performed for 10 minutes or in the linear kinetic range of photodegradation (up to 80–90% of the initial fluorescence).