Multilayer Microcapsules for FRET Analysis and Two-Photon-Activated Photodynamic Therapy

Microcapsules obtained by layer-by-layer assembly provide a good platform for biological analysis owing to their component diversity, multiple binding sites, and controllable wall thickness. Herein, different assembly species were obtained from two-photon dyes and traditional photosensitizers, and further assembled into microcapsules. Fluorescence resonance energy transfer (FRET) was shown to occur between the two-photon dyes and photosensitizers. Confocal laser scanning microscopy (CLSM) with one- and two-photon lasers, fluorescence lifetime imaging microscopy (FLIM), and time-resolved fluorescence spectroscopy were used to analyze the FRET effects in the microcapsules. The FRET efficiency could easily be controlled through changing the assembly sequence. Furthermore, the capsules are phototoxic upon one- or two-photon excitation. These materials are thus expected to be applicable in two-photon-activated photodynamic therapy for deep-tissue treatment.