Study On The Biological Effects Of Photocatalytic Graphene - TiO 2 Complexes

Objective To prepare graphene-TiO2compounds which have excellent photocatalytic activity, good dispersity and the ability of responding to visible light. Study the killing effect of photoexcited graphene-TiO2with ultraviolet or visible light on hepatoma carcinoma cells (HepG2) and plasmid DNA. The mechanism was explorated preliminarily.Methods Graphene-TiO2compounds with different doping ratios of graphene were prepared by hydrothermal reduction method. Graphene-TiO2compounds were characterized by XRD, FTIR, TEM, BET and UV-Vis. The compounds, which had good dispersity and excellent photocatalytic activity was screened for the research of biological effect. HepG2cells were employed to conduct the experiment of killing cancer cells in vitro with photoexcited graphene-TiO2compounds. The effect of photoexcited graphene-TiO2compounds on the survival rate of HepG2cells was measured by MTT assay, and the morphology of HepG2cells treated by graphene-TiO2compounds was observed by inverted fluorescence microscope. The effects of light source, time of irradiation and the concentration of graphene-TiO2compounds on photocatalytic killing effect of HepG2cell were investigated. Plasmid DNA was used as the object to detect the changes of supercoiled structure and content of8-OHdG, which was treated with photoexcited graphene-TiO2by gel electrophoresis and HPLC, respectively. The apoptosis rate, mitochondrial membrane potential (MMP) and intracellular calcium concentration of HepG2cells were detected by flow cytometry. The mode of the killing effect on HepG2cells by photocatalytic graphene-TiO2compounds was investigated.Results Graphene-TiO2compounds were successfully prepared, and the results displayed that the titanium dioxide in prepared graphene-TiO2compounds was still anatase phase. Nanometer TiO2dispersed on the graphene carrier intensively and uniformly. Graphene-TiO2was mesoporous material, the pore structure was abundant and the specific surface area was larger. The introduction of graphene increased the absorption ability of ultraviolet light, meanwhile, the photoresponsive range of TiO2was extended to visible region. Graphene-TiO2compounds with20%graphene doping had the highest photocatalytic activity. Photoexcited graphene-TiO2compounds had stronger killing efficiency than that of TiO2under ultraviolet light or visible light. The killing effect of graphene-TiO2compounds was showed in the style of neorobiosis and apoptosis. Under ultraviolet light or visible light, photoexcited graphene-TiO2compounds led to the decrease in the ratio of the super-coiled DNA and the oxidative damage effects than that of TiO2. The apoptosis rate increased, the MMP of HepG2cells decreased and intracellular calcium concentration increased by photoexcited graphene-TiO2compounds. Its intensity was stronger than that of pure TiO2.Conclusion The photocatalytic efficiency of killing HepG2cells were improved by doping TiO2 with graphene carrier. Furthermore, the photoresponsive range of TiO2was extended, and so that the HepG2cells could be killed under visible light, which could avoid the damage induced by ultraviolet. Photocatalytic graphene-TiO2compounds killed the HepG2cells by apoptosis pathway.