Green Synthesis of Zinc Oxide Nanoparticles Using Monotheca buxifolia Leaf Extract; Their Biological Activities and Use in Fabrication of Nano-Biosensor

In this study, the green synthesis of zinc nanoparticles (ZnONPs) was carried out using the Monotheca buxifolia leaf extract. Various instrumental techniques were used to characterize and evaluate ZnONPs biological potentials like antimicrobial, hair growing, antioxidant, and bio sensing activities. The antibacterial potentials in terms of the zone of inhibition, the minimum inhibitory concentration (MIC), and the minimum bactericidal concentration (MBC) were measured against four strains of bacteria viz., Klebsiella pneumonia, Escherichia coli, Salmonella typhi, and Staphylococcus aureus. The lowest MIC and MBC were recorded for S. typhi (60 and 90 µg/mL, respectively). Likewise, the antioxidant potential was measured using DPPH and 2,2'-azinobis-bis-3-ethylbenzthiazoline-6-sulfonic acid (ABTS) assays, and a significant free radical scavenging activity was observed for both the leaf extract and ZnONPs. Keeping in view the traditional use of that plant for the hair growth, the potential effect of the leaf extract and ZnONPs was also examined using rabbits as experimental animals where a moderate degree of enhancement in the rate of the hair growth was noticed for ZnONPs. In addition, an efficient ZnONPs-based bacterial biosensor was fabricated which successfully detected the presence of different bacterial strains using distilled water. A direct relation was observed between the amount of current and the bacterial population. Comparatively, ZnONPs showed good antioxidant, antimicrobial, and hair growth activities in comparison to those of the leave extract. The antibacterial spectrum of the synthesized ZnONPs was also evident from the conduction of current in the sensor as the medium used in the cell was distilled water, and electrolytes were released from bacterial cells lysed by ZnONPs. Further in vitro and in vivo experiments are needed to ascertain the observed biological potentials.