2.5 Mitochondrial membrane potential measurement

The apoptosis signaling pathway is triggered when cells are under a toxic or an unfavorable environment. MMP decreases during apoptosis. Therefore, MMP can serve as an early indicator of cell apoptosis. The method used for MMP measurement was based on a previous study (Smiley et al., 1991). The cells were washed with PBS after treatment with ICG and NIR laser irradiation. The cells were then incubated with the JC-1 dye (Thermo Fisher Scientific) at 37°C for 30 min in a cell culture incubator. Finally, the fluorescence intensity was analyzed using a fluorescence microscope and a fluorescence spectrometer. The cells treated with 50 μM carbonyl cyanide 3-chlorophenylhydrazone (CCCP) were used as positive controls because CCCP is a common MMP disruptor.