A fluorescent nanoprobe for real-time monitoring of intracellular singlet oxygen during photodynamic therapy

Sensing of intracellular singlet oxygen ( 1 O 2 ) is required in order to optimize photodynamic therapy (PDT). An optical nanoprobe is reported here for the optical determination of intracellular 1 O 2 . The probe consists of a porous particle core doped with the commercial 1 O 2 probe 1,3-diphenylisobenzofuran (DPBF) and a layer of poly-L-lysine. The nanoparticle probes have a particle size of ~80 nm in diameter, exhibit good biocompatibility, improved photostability and high sensitivity for 1 O 2 in both absorbance (peak at 420 nm) and fluorescence (with excitation/emission peaks at 405/458 nm). Nanoprobes doped with 20% of DPBF are best suited even though they suffer from concentration quenching of fluorescence. In comparison with the commercial fluorescent 1 O 2 probe SOSG, 20%-doped DPBF-NPs (aged) shows higher sensitivity for 1 O 2 generated at an early stage. The best nanoprobes were used to real-time monitor the PDT-triggered generation of 1 O 2 inside live cells, and the generation rate is found to depend on the supply of intracellular oxygen. A fluorescent nanoprobe featured with refined selectivity and improved sensitivity towards 1 O 2 was prepared from the absorption-based probe DBPF and used to real-time monitoring of the generation of intracellular 1 O 2 produced during PDT.