Antioxidant and Antimicrobial Potentials of Nicotiana glauca Graham Leaves Extracts and Synthesized Silver Nanoparticles: A Phytochemical Approach

Nicotiana glauca is a medicinal plant that belongs to the genus Nicotiana, traditionally used for the treatment of many diseases. This study aims to screen the phytochemical content of leaf extracts of Nicotiana glauca, synthesize silver nanoparticles using the extracts, and evaluate their antioxidant and antimicrobial activities. The leaf samples were collected, air-dried, and ground into powder. The leaf powder was macerated with distilled water, methanol, n-hexane, and chloroform to extract the phytochemicals. Phytochemical analysis was performed using standard methods. Synthesis of silver nanoparticles was achieved by mixing a 3 mM silver nitrate solution with the plant extract, and the synthesized silver nanoparticles were characterized by X-ray diffraction and scanning electron microscopy. The antioxidant activities of the extracts and the synthesized silver nanoparticles were evaluated by the DPPH scavenging assay, while the in vitro antimicrobial activities were evaluated using the agar disc diffusion method against selected bacterial and fungal strains. The results of the phytochemical analysis indicated the presence of alkaloids, saponins, flavonoids, terpenoids, tannins, phenolics, steroids, and glycosides. The results of the antioxidant activity evaluation of AgNPs, methanol extract, chloroform extract, and n-hexane extract showed that they possess remarkable antioxidant activities. The antioxidant activity analysis also indicated that percentage inhibition and IC50 were dose-dependent. Synthesized silver nanoparticles showed the highest antioxidant activity with an IC50 value of 78 μg/mL, while the methanol extract gave an IC50 value of 170 μg/mL. The results of the antimicrobial activity evaluation showed that the plant extract and the synthesized silver nanoparticles exhibited antimicrobial activities. The highest zone of inhibition observed was 16.33±1.155 mm for synthesized silver nanoparticles and 15.33±1.155 mm for the plant extract. The lowest zone of inhibition observed was 9.67±0.577 mm for synthesized silver nanoparticles and 7.33±0.577 mm for the plant extract. Generally, the plant extracts and synthesized silver nanoparticles exhibited strong antioxidant and antimicrobial activities. Further studies should be conducted on the phytochemical constituents, antioxidant, and antimicrobial activities of this plant.