Improves antibacterial activity and oxidation stability of curpous oxide nanoparticles against clinical bacterial strains

Abstract

Bacteria had caused severe demerits to the public health sector. Yet, conventional antibiotic application as an antibacterial route had led to misuse and overuse of antibiotics and led to antibiotic-resistant bacteria. Therefore, nanoparticles as a novel antibacterial agent had been highly studied due to their high surface area-to-volume ratio, and unique physical, and chemical characteristics. Copper (Cu)-based nanoparticles (NPs) had been widely studied due to copper’s low cost and high abundance. Nevertheless, Cu-based NPs had suffered from oxidative instability that caused batch-to-batch variation and affected the performance of Cu-based NPs as antibacterial agents. Besides, nanotoxicity had also hindered Cu-based NPs’ antibacterial application. Herein, we produced cuprous oxide (Cu2O) nanoparticles (Cu2ONPs) and treated them with thermal oxidation treatment for 18 (18-Cu2ONPs) and 36 hours (36-Cu2ONPs). The successful formation of Cu2ONPs was verified by Ultraviolet-visible (UV-Vis) spectra, X-ray diffraction analysis and selected area electron diffraction (SAED). The application of thermal oxidation improved the cupric oxide (CuO) content, size reduction of Cu2ONPs and improvement of Zeta potential negativity. The Cu2ONPs were then applied to an antibacterial test (minimum bactericidal concentration (MBC) test) on E. coli, Methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis (S. epidermidis) and Acinetobacter baumannii (A. baumannii) to investigate the effect of thermal oxidation treatment on the antibacterial performance of Cu2ONPs. Finally, a (3-(4,5-Dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide) MTT test was carried out to investigate the biocompatibility of Cu2ONPs produced. The Cu2ONPs produced show broad-spectrum (Gram-positive and Gram-negative) and drug-resistance strains with antibacterial properties MBC value of 50 ppm. Surprisingly, the oxidized Cu2ONPs (18-Cu2ONPs and 36-Cu2ONPs) cause slight production of CuO and defect which exhibits improved antibacterial activity with MBC of 1.25 ppm. Finally, the Cu2ONPs produced are acquired with excellent biocompatibility with half-maximum growth inhibitory concentration (IC50) value of 164, 131 and 112 ppm for Cu2ONPs, 18-Cu2ONPs and 36-Cu2ONPs, respectively. This is higher than the MBC value required for antibacterial activity. Our results pave the route for manufacturing biocompatible and antibacterial Cu2ONPs with improved antibacterial activity with good biocompatibility via thermal oxidation treatment.