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

Sensing of intracellular singlet oxygen (1O2) is required in order to optimize photodynamic therapy (PDT). An optical nanoprobe is reported here for the optical determination of intracellular 1O2. The probe consists of a porous particle core doped with the commercial 1O2 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 1O2 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 1O2 probe SOSG, 20%-doped DPBF-NPs (aged) shows higher sensitivity for 1O2 generated at an early stage. The best nanoprobes were used to real-time monitor the PDT-triggered generation of 1O2 inside live cells, and the generation rate is found to depend on the supply of intracellular oxygen.