sf9 cells were seeded in a 24-well plate at a density of 1 × 104 cells per well in culture media TC-100 with 10% foetal bovine serum (Sigma) for 24 h at 27 °C. Then, the cells in 9 wells were equally split into three groups. Group 1 was left as the controls. Group 2 and 3 were incubated with 9 and 12 μL Hg2+ for 40 min, respectively. Next, 10, 15 or 20 μL of RATU was added into 3 wells in group 2 (and group 3) respectively. After incubated for another 40 min, the cells were observed and imaged on a Nikon Eclipse Ti inverted fluorescence microscope excited with green light.