Metal-enhancement study of dual functional photosensitizers with aggregation-induced emission and singlet oxygen generation

Photosensitizers with aggregation-induced emission (AIE-PS) are attractive for image-guided photodynamic therapy due to their dual functional role in generating singlet oxygen and producing high fluorescent signal in the aggregated state. However, their brightness and treatment efficiency maybe limited in current practice. Herein we report the first systematic investigation on the metal-enhanced fluorescence (MEF) and singlet oxygen generation (ME-SOG) ability of our newly synthesized AIE-photosensitizers. The Ag@AIE-PS of varied sizes were prepared via layer-by-layer assembly with controlled distance between silver nanoparticles (AgNPs) and AIE-PS. A maximum of 6-fold enhancement in fluorescence and 2-fold increment in SOG were observed for the 85nmAg@AIE-PS. Comprehensive characterization and simulation were conducted to unravel the plasmon-enhancement mechanisms of Ag@AIE-PS. Results show that MEF of AIE-PS is determined by the enhanced electric field around AgNPs, while ME-SOG is dictated by the scattering efficiency of the metal core, where bigger AgNPs would result in larger enhancement factor. Furthermore, the optimum distance between AgNPs and AIE-PS to achieve maximum SOG enhancement is shorter than that required for the highest MEF. The correlation of MEF and ME-SOG found in this study is useful for designing new a generation of AIE-photosensitizers with high brightness and treatment efficiency towards practical theranostic application in the future.