The uptake of CNTs by Stylonychia mytilus and their distribution during the dividing process of the cells were observed with optical microscope for the first time. The dose-effect relationship between concentration of CNTs and surviving rate of Stylonychia mytilus was measured. The surviving rates were found to be about 111%

107%

75%

70%

53%

43%

38% on the fifth day after adding CNTs for the concentrations of 0.1

0.5

1

5

10

50

200 μg·mL?1

respectively. The result showed that high concentration of CNTs exhibited a dose-dependent inhibition to the cells

whereas very low concentration of CNTs was likely to stimulate the growth of the cells. To understand the inhibition from the CNTs

the propidium iodide was used to dye the macronucleus of Stylonychia mytilus. Images from fluorescent microscope showed that the damage occurred on the macronucleus and membrane of the cells.