Phyto-fabrication of Cobalt Oxide Nanoparticles from Ocimum Gratissimum L. Leaf and Flower Extracts and their Antimicrobial Activities

Abstract

Background: Phyto-fabrication of nanoparticles has gained attention in recent times owing to its simple mode, cost-effective and eco-friendly nature. Objective: Hence, the present study aimed to synthesize cobalt oxide nanoparticles from methanol extracts of Ocimum gratissimum flower and leaf and to evaluate their antimicrobial action towards pathogenic bacteria and fungi. Methods: Phyto-fabrication of Cobalt nanoparticles (CoONPs) was achieved using cobalt chloride hydrate solution as a precursor. Characterization of fabricated CoONPs was performed using Ultra Violet-Visible spectrometry (UV-Vis), X-ray diffractometer (XRD), and Fourier Transform-Infrared spectroscopy (FTIR). The antimicrobial property was tested against two bacteria (Staphylococcus aureus and Escherichia coli) and two fungi (Cryptococcus albidus and Candida globasa) by agar disc diffusion technique and by measurement of Minimum Inhibitory Concentration (MIC). Results: Initial confirmation of CoONPs synthesis was observed by the colour change from light pink to reddish pink. Further, the UV-Vis spectrophotometry validated the CoONPs synthesis with a peak at 509 nm. The XRD authenticated the crystal nature of CoONPs synthesized using flower extract at 2θ angles with an average size of 54.9 nm and CoONPs fabricated using leaf extract at 2θ angles with an average size of 55.02 nm. The FTIR spectroscopy confirmed the functional groups present in plant extracts, which are believed to reduce and stabilize CoONPs. The findings of antibacterial activity showed that CoONPs synthesized using leaf showed a higher inhibition zone against E. coli (20.00 ± 2.00 mm) than S. aureus. Relating to fungi, the CoONPs fabricated using flower extract displayed significantly the highest activity against C. albidus (28.67±0.57 mm) and C. globasa (25.0 ± 0.00 mm). The lowest MIC was observed against S. aureus (MIC 7.5 µg/ml). For fungi, the smallest MIC was found against C. albidus (MIC 2.5 μg/ml). Conclusion: The current research established the efficacy of the phytochemical constituents of leaf and flower extracts of O. gratissimum for the enhancement of the effectiveness of CoONPs against both the tested bacteria and fungi.