Cells were cultured on glass-based Petri dishes and stained with 10 µm acridine orange, the signal was collected by exciting samples with 405 nm and 488 nm lasers, and emission was collected at 542 nm (represented by red) and 494 nm (represented by green), respectively and imaged with confocal scanning microscope (CLSM, LSM 710, Carl Zeiss, Germany)