Influence of metal oxide nanoparticles on the cell wall structure of Nannochloropsis oculata

The algal cell wall is the primary site for interaction with nanoparticles and creates a barrier against the entry of nanoparticles into its cell. Therefore, the effect of zinc oxide (ZnO), copper (II) oxide (CuO) and iron (III) oxide (Fe2O3) nanoparticles was investigated on the cell wall structure of Nannochloropsis oculata. Calculation of EC50 using microalgae cell count showed that the order of nanoparticles toxicity in N. oculate was CuO>ZnO>Fe2O3. The interaction of ZnO, CuO and Fe2O3 nanoparticles with microalgae cell wall was proved in FTIR analysis. The highest interaction of the studied nanoparticles was with carbonyl (C=O), methoxy (C-O) and methyl (C-H) functional groups of N. oculata cell wall. On the other hand, transmission electron microscopy (TEM) images showed that ZnO and CuO nanoparticles caused the shrinkage of cell wall. The accumulation of these nanoparticles was observed on the surface of the cell wall. Accumulation of nanoparticles and shrinkage of the cell wall could be the possible reason for the higher toxicity of CuO and ZnO nanoparticles than Fe2O3 nanoparticles in N. oculata.