No / The use of nanoparticles have provided numerous of advantages in medicine due to their unique physiochemical characteristics such as size, charge, shape and surface reactivity [1-4]. Understanding the interaction between engineered nanomaterials and living matter has attracted increasing attention in recent years. Toxicity of nanoparticles was studied in different cell types and cell lines. Nano-SiO2 has good stability, easy dispensability, and melting degeneration, and is widely used in rubber, paints, biomedical and biotechnology fields [5]. In this study, the LDH assay and the MTT assay were applied to evaluate the cytotoxicity of in vitro Silicon dioxide nanoparticles (SiO2-NP, 20nm) on cultured cell lines. Human lung adenocarcinoma epithelial cell line (A549) were used as a lung related cell line and human keratinocyte cell line (HaCaT) as a skin related cell line representing different uptake routes. The percentage cytotoxicity of the silicon dioxide nanoparticles was measured once cultured in a 24 hour incubation period. The concentration of the SiO2 nanoparticles chosen was 10, 50, 100 and 200µg/ml. To measure the cytotoxicity of nanoparticle on cultured cell lines, we used 104*cells/100 µl of cell culture media being placed in a 96 well rounded bottom plate with the LDH assay. The extracellular lactate dehydrogenase release was measured by using a colorimetric CytoTox 96 non-radioactive assay kit and the absorbance was recorded at 492nm. The MTT assay was used to evaluate mitochondrial activity which includes cell growth and cell death. This has been performed by inserting a premixed optimized dye solution in the culture wells. The Absorbance was recorded at 570 nm, from the recorded absorbance is directly proportional to the number of live cells. In order to maintain the cell lines, they were placed in a plastic T-75cm² tissue culture flasks grown in Dulbecco's Modified Eagle's Medium. Studies were performed in the absence of serum. Cytotoxicity was found in both cells the A549 and HaCaT cells and cytotoxicity increased as concentration of the silicon dioxide increased. The percentage cytotoxicity calculated was higher in HaCaT cells compared to the A549 cells. A cell count assay was plated in order to display the cell number of both the HaCaT and A549 cells. The cell count reaffirmed that cytotoxicity did occur as the cell count decreased as the concentration of the silicon dioxide increased compared to the control. These results show that silicon dioxide nanoparticles acted differently in two different cell types and that the metabolic rate of a cell can be used to determine the nanoparticles affect. Further understanding of the mechanism involving the ROS generation could provide more information on how silicon dioxide nanoparticles increase cytotoxicity. / Physiology 2015 conference abstract