Green synthesis of CuO nanoparticles using Cassia auriculata   leaf extract and in vitro evaluation of their biocompatibility with rheumatoid arthritis macrophages (RAW 264.7)

Purpose: To undertake green synthesis of copper oxide nanoparticles (CuO NPs) using Cassia auriculata leaf extract and evaluate their biocompatibility with rheumatoid arthritis macrophages (RAW 264.7 cell line).
Methods: CuO NPs were prepared by heating a mixture of 10 mL of 0.01 M CuSO₄ solution and 30 mL of C. auriculata extract at 80 °C for 1 h. The synthesized CuO NPs were characterized by x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UVVis), energy-dispersive x-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS). The cytotoxicity of the NPs against RAW 264.7 cells was studied using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.
Results: The gradual change in color of the reaction solution from brownish yellow to dark brown indicated CuO NP formation. TEM images revealed spherical, polydispersed NPs (mean particle size, 23 nm). FTIR results indicated capping of polyphenols on the surface of the NPs. Most RAW 264.7 cells (> 95 %) remained alive following exposure to CuO NPs at concentrations of up to 200 μg/mL, indicating biocompatible with the cells.
Conclusion: An eco-friendly, low-cost, biosynthetic method for CuO NP preparation has been successfully developed using C. auriculata leaf extract. Furthermore, the nanoparticles are biocompatible with RAW 264.7 cell line.

Keywords
Cassia auriculata extract; Copper oxide nanoparticles; RAW 264.7 cell line; Rheumatoid arthritis