In vitro evaluation with P1 and P1-SO. (a) ROS generation in HeLa cells with DCFH-DA, cells were incubated with P1 or P1-SO for 2 h under 5% oxygen level under irradiation for 6 min (690 nm, 400 mW/cm2) (scale bar, 50 nm). (b) Calcein-AM and PI stained HeLa cells were incubated with P1 and P1-SO and then exposed under 690 nm laser irradiation (400 mW/cm2) for 6 min under 5% oxygen level (scale bar, 100 μm). (c) and (d) MTT assay of P1 and P1-SO under 5% oxygen level with and without irradiation. (e) and (f) Flow cytometry quantification of apoptosis of HeLa cells incubated with P1 and P1-SO under 5% oxygen level with 690 nm laser irradiation (400 mW/cm2).