Green synthesis and characterizations of zinc oxide nanoparticles using acorn fruit extract for antimicrobial, larvicidal and in silico activities

Antimicrobial resistance has become a serious global issue, because these microbes produce beta-Lactamase that degrades antibiotics. To overcome this issue, worldwide researchers have focused on nanoparticles. It is because of their unique chemical and biological properties and their use as an antimicrobial and larvicidal agent to get rid of infectious and vector-borne diseases. Therefore, this study aimed to synthesize zinc oxide nanoparticles using Acorn fruit as a novel and phytochemical-rich plant and evaluated their antimicrobial and larvicide potentials. These ZnO NPs synthesis were confirmed by Visual observation of color change from yellowish to dark brown and UV visible analysis. Fourier transform infrared spectroscopy (FTIR) of prepared nanoparticles revealed a sharp peak at 600-450 cm^{- 1} indicating the presence of Zn-O stretching vibration. The prominent, sharp peaks in the X-ray diffraction pattern verified the crystalline structure of ZnO NPs. With scanning electron microscopy (SEM), ZnO nanoparticles exhibiting a tiny size indicated good surface morphology. In biological activities these ZnO NPs revealed outstanding antibacterial efficacy against E. coli (minimum zone of inhibition 15 ± 02 mm at 10 µg/ml and maximum 24 ± 05 mm at 80 µg/ml) and S.aureus (minimum zone of inhibition 17 ± 03 mm at 10 µg/ml and 26 ± 02 mm at 80 µg/ml). In the in-silico analysis, these nanoparticles demonstrated a considerable interaction with the Beta-Lactamase binding site residues with a docking score of -8.2 kcal/mol. It confirms the successful inhibition of the given enzyme, which catalyzes a lot of antibiotics. Thus, these nanoparticles combated microbes by blocking their resistive enzyme, which is the novel property of these ZnO NPs. Furthermore, these ZnO NPs showed high mortality rates against the Culex quinquefasciatus larvae and the LC 50 and LC 90 values were found as 13.6 ppm and 45 ppm respectively. In histopathological observation, they found that these nanoparticles caused microvilli destruction. It also initiated mid-gut columnar cell vacuolization, passage of epithelial cell contents into the mid-gut lumen and ultimately cell death. Hence, the above findings propose that the synthesized ZnO NPs may be used for various environmental and anti-pathogenic applications.