Effects of Nano-TiO2 on Chlamydomonas reinhardtii Cell Surface under UV, Natural Light ConditionsCHEN Xiaojuan1, LU Ruirui2, LIU Peng2* LIU Peng(刘鹏)，Email: chemliupwhut.edu.cnFunded by the National Natural Science Foundation of China (No. 51579159)., Li Xi21Key Laboratory of Ecological Impacts of Hydraulic-Projects and Restoration of Aquatic Ecosystem of Ministry of Water Resources, Institute of Hydroecology, Ministry of Water Resources and Chinese Academy of Sciences. Wuhan 430079, PR. China2Department of Chemistry, School of Sciences, Wuhan University of Technology, Wuhan 430070, PR. ChinaAbstract: The effects of nano-TiO2 on aquatic ecosystem have attracted more and more attention. Cell surface of aquatic organisms constitutes a primary site for the interaction and a barrier for the nano-TiO2 biological effects. In the present study, the biological effects of nano-TiO2 on a unicellular green algae Chlamydomonas reinhardtii were studied by observing the changes of the cell surface morphology and functional groups under UV or natural light. By SEM, the cell surface morphology of C. reinhardtii was changed under UV light, nano-TiO2 with UV light or natural light, which indicated that photocatalysis damaged cell surface. It was also observed that cell surface was surrounded by TiO2 nanoparticles. The ATR-FTIR spectra showed that the peaks of functional groups such as C-N, -C=O, -C-O-C and P=O, which were the important components of cell wall and membrane, all depressed by the photocatalysis of nano-TiO2 under UV light or natural light. The photocatalysis of nano-TiO2 promoted peroxidation of functional groups on the surface of C. reinhardtii cells, which led to the damages of cell wall and membrane. Key words: nano-TiO2; Chlamydomonas reinhardtii; biological effects; cell surface morphology; functional groups1 IntroductionNanomaterials (NMs) contain natural or man-made particles, with at least one dimension of 100 nm or less, that are increasingly being used for commercial purposes, especially in industry, such as construction materials, fillers, opacifiers, catalysts, semiconductors, cosmetics, microelectronics, and drug carriers 1, 2. Because of its good thermal stability, chemical resistance and optical catalytic properties, nano titanium dioxide (nano-TiO2) is among the first nanomaterials made readily commercially available to a wide variety of research activities 3. Nano-TiO2 has been used for a wide variety of applications, including self-cleaning, surface coatings, light-emitting diodes, solar cells, disinfectant sprays, sporting goods, water treatment agents and topical sunscreens, et al 4, 5. Nano-TiO2 is also used in construction and building materials as an additive. The widespread use could lead to significant release of nano-TiO2 into water by many ways 6. Some analytical evidences on TiO2 nanoparticle release into the environment have been published in recent years 7-9. The concerns about the effects of nano-TiO2 on aquatic environment have raised prompting extensive investigations of nano-TiO2 biological effects on the aquatic organisms, including algae, invertebrates and fish 10-12. As one main biota forming the basis of the food web in aquatic ecosystems in aquatic ecosystem, algae is used to asset the aquatic risk of pollution and toxin in the government environment reports 3, 13. A number of studies of nano-TiO2 on algae have appeared and been summarized in several papers in recent years 3, 10, 13, 14. Chlamydomonas reinhardtii is one of the species used the most for the nano-TiO2 biological effects, due to its unique advantages for genetic, biochemical, and cell biological approaches. Biological effect characterizations of C. reinhardtii exposed to nano-TiO2 included growth inhibition, photosynthesis inhibition, ROS generation, lipid peroxidation stress, stress response genes high expression and new protein synthesis 15-18. As we know, algae cell surface constitutes a primary site for interaction and a barrier for the entrance of nanoparticles. However, the effects of nano-TiO2 on C. reinhardtii cell surface are not clear, and the effect mechanisms of nano-TiO2 on cell walls and membranes are as yet poorly understood 19. The present work aimed to determine the effects of nano-TiO2 under UV, natural light conditions on C. reinhardtii cell surface by observing the changes of cell morphology, cell surface function groups.2 Experimental2.1 MaterialsDegussa P25 provided by Shenshi Chem was used in this study. It contains 80 wt % anatase and 20 wt % rutile, with the average Brunauer EmmettTeller (BET) surface area of 50 m2 g-1 and an average particle size of about 20-30 nm 20. It was dispersed in water by ultrasonic disperse process for 30 min with a good dispersion without agglomeration.Chlamydomonas reinhardtii was obtained from FACHB collection (Freshwater Algae Culture Collection of the Institute of Hydrobiology, the Chinese Academy