Biogenic Synthesis, Characterization, and Evaluation of Larvicidal and Antibacterial Activities of Zinc Oxide Nanoparticles using Paspalum vaginatum Extract

The advantages of biological method of nanoparticle synthesis over chemical and physical methods cannot be overemphasized. However, its sustainability depends on the continuous availability of extracts used as reducing and capping agents. To prevent over-exploitation of a few plant sources for this, there is a need to increase available sources of suitable extracts. This study aimed to biogenically synthesize, characterize, and evaluate the larvicidal and antibacterial activities of zinc oxide nanoparticles using Paspalum vaginatum extract. Phytochemical assessment of the aqueous extract was done using gas chromatography–mass spectrometry (GC-MS) before zinc oxide nanoparticles (ZnONPs) biosynthesis using 0.05 M zinc nitrate hexahydrate. Following their characterization with Fourier transform infrared spectroscopy, X-ray diffraction (XRD) analysis, dynamic light scattering, ultraviolet-visible spectroscopy, and transmission electron microscopy, the antibacterial and larvicidal activities of the resulting ZnONPs were assayed. Results showed structures of ten (10) components of the extract. The XRD spectrum indicated the crystalline nature of synthesized ZnONPs, with hexagonal wurtzite structure. Their maximum absorbance of ultraviolet visible light occurred at 307 nm. Micrograph revealed their spherical shapes, with a mean size of 3.96±2.4 nm. Also, there was appreciable dose- and time-dependent larvicidal activity of synthesized ZnONPs against instar IV Anopheles sp larvae, with 88.3±0.0% mortality recorded after 26 h of exposure. At 53.3 µg/mL, synthesized ZnONPs recorded 11.33±7.2 mm and 6.0±2.2 mm growth inhibitions against Salmonella spp. and Escherichia coli, respectively. Results of this study confirm that P. vaginatum aqueous extract is suitable for the synthesis of ZnONPs with considerable antibacterial and larvicidal activities.