Green Synthesis of Copper-Doped Zinc Oxide Nanoparticles by Using Solanum Incanum Leaves Extract for Enhanced Antimicrobial and Antioxidant Activities

Abstract

Nanoparticles could become an indispensable, viable therapeutic option for treating drug resistant infections. Nanometer-scale material synthesis using a green approach has received attention. The aim of the study was to synthesize bitter apple (Solanum incanum) leaf extract aided ZnO nanoparticles, and ZnO- ceftriaxone conjugate for the evaluation of antimicrobial and antioxidant activities. The green synthesis parameters such as as temperature, pH, and volume ratio of the precursor to plant extract was optimized. The synthesized metal nanoparticle nanocomposite and conjugate were subjected to characterization and biological activity tests. The FESEM-EDS elemental mapping analysis proved the novelty of the green synthesis approach in synthesizing single ZnO and copper doped ZnO composite with good dopant distribution. The XRD and TEM analysis of the synthesized nanomaterials showed nanometer-scale sizes (7-50 nm). The optical property adjustments from 3.04 to 2.97 eV for indirect Kubelka-Munk functions were confirmed from DRS-UV-vis analysis. The angle shift on the XRD pattern analysis confirmed the perfect dopant inclusion in the host lattice relative to a single ZnO. The lattice fringe values from HRTEM analysis confirmed the existence of both CuO and ZnO crystals with local heterojunctions. The conjugation of ceftriaxone with synthesized zinc oxide was highly confirmed by the peak at 270 nm on the UV-vis spectroscopy. Doping and heterojunctions have crucial values in charge transfer and visible light harvesting behavior, as proved by the PL analysis. The synergistic effects of doped composites and antibiotic conjugate showed greater antibacterial activity against both the gram-positive and gram-negative bacteria. The highest antibacterial activity was observed in the order of 43.3% <49.5%<71.5%<79.5% for ZnO<CuO<ZnO-AB<GCD-Z10.5, respectively. Similarly, the reduction in the MIC, MBC, and tolerance test values was also observed in the order of ZnO<CuO<ZnO-AB<GCD-Z10.5, respectively. This was plausibly a result of more reactive oxygen species (ROS) generation through bacteria-cell-catalyst interaction and the release of metal ions. The antioxidant activity of the doped nanoparticles and ceftriaxone-ZnO conjugate was analysed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay. Their antioxidant potential was found to be in the order of ZnO<CuO<GCD-Z10.5<ZnO-AB, respectively. Thus, the overall analysis leads to the conclusion that the potentiality of synthesized materials has a future outlook for biological and medical applications, especially in the development of antimicrobials for combating antibiotic resistance bacteria.