Two-Phase Photobleaching Dequenching in Dye-Loaded Liposomes

A two-phase fluorescence dequenching was for the first time demonstrated in dye-loaded liposomes upon exposure to a prolonged duration of excitation. Liposomes encapsulating self-quenching concentrations (100 mM) of carboxyfluorescein were subjected to illumination under a 405 nm continuous-wave laser. Emission spectra collected over the span of exposure exhibited a peculiar behavior--two consecutive hikes in peak emission over time that were subsequently attributed to photobleaching induced dequenching. A mathematical model considering the effects of photobleaching on fluorescence quantum yield and absorption then accounted for the observed peaking. Specifically, the dequenching of dye in the outermost and bulk inner regions of the core, were ascribed to the first (fast, primary) and second (slow, secondary) peaking event, correspondingly. The occurrence of the latter was attributed to the combined effects of lower photobleaching rates and anomalous diffusion, stemming to a slower dequenching event. Results not only provided insight to future application of these liposomes in random lasing, but also highlight a potential method of optically tuning the extent of self-quenching.