Encapsulation of photoactive porphyrinoids in polyelectrolyte hollow microcapsules viewed by fluorescence lifetime imaging microscopy (FLIM)

Fluorescence Lifetime Imaging Microscopy (FLIM) was used to investigate the encapsulation of porphyrinoids in multilayer hollow microcapsules assembled layer by layer with poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). The lifetime colour contrast enables the discrimination of fluorophore interactions at the microcapsule interface or deeper localized in the microcapsule shell. The coupling of functionalized porphyrin derivatives with oppositely charged polyelectrolyte made the microcapsule pH responsive. FLIM images were also obtained from aluminium monosulfonate phthalocyanine (AlPcS1) included in a lipid vesicle deposited on the surface of a modified microcapsule with dispersed gold nanoparticles (AuNP). In this case, a heterogeneous distribution of both quenched and enhanced fluorescence intensities was mapped from various fluorescence spots. These effects, undetected in the absence of AuNP, were accompanied by a decrease of lifetimes attributed to the contribution of plasmonic effects induced by AuNP. Fluorescence lifetime contrast-based imaging provides new insights in the field of polyelectrolyte microcapsules.