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

Sensing of intracellular singlet oxygen (O-1(2)) is required in order to optimize photodynamic therapy (PDT). An optical nanoprobe is reported here for the optical determination of intracellular O-1(2). The probe consists of a porous particle core doped with the commercial O-1(2) probe 1,3-diphenylisobenzofuran (DPBF) and a layer of poly-L-lysine. The nanoparticle probes have a particle size of similar to 80 nm in diameter, exhibit good biocompatibility, improved photostability and high sensitivity for O-1(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 O-1(2) probe SOSG, 20%-doped DPBF-NPs (aged) shows higher sensitivity for O-1(2) generated at an early stage. The best nanoprobes were used to real-time monitor the PDT-triggered generation of O-1(2) inside live cells, and the generation rate is found to depend on the supply of intracellular oxygen.