It has been recognized that ROS production in cancer cells triggered by PDT is one of the main mechanisms. ROS can induce damages to mitochondria, endoplasmic reticulum, and other organelle, thereby inducing apoptosis 17. DCFH‐DA staining showed that there had more ROS in the nano‐AE PDT group as well as nano‐AE transfection coupled with PDT group compared with other groups (P < 0.05). Compared to control groups, the production of ROS had quadrupled in SGC‐7901 cells as early as 1 h after PDT (Fig. 7). The data suggested that nano‐AE PDT generated ROS and lead to apoptosis.