Silver–zinc oxide nanocomposite antiseptic from the extract of Bidens pilosa

Abstract

Silver nanoparticles (Ag-NPs), zinc oxide (ZnO-NPs) and zinc oxide–silver (ZnO–Ag-NPs) were biosynthesized based on the rich matrix of alkaloids, flavones, tannins capping/stabilizing agents present in Bidens pilosa extract. Different plant parts-root, leaf and seed ware used to prepare the plant extract for synthesis. Also, zinc and silver nitrate salts were used as precursor materials. The surface plasmon peaks (SPR) based on the UV–Vis results for the Ag-NPs, ZnO-NPs were located between 408–411 and 365–450 nm respectively. The SPR peaks for the Ag–ZnO-NPs occurred at 300–450 nm indicating both blue and red shifts. The Ag–ZnO-NPs SPR shifts were associated with possible nanoparticle size reduction and change in dielectric constant of the synthesis medium. Raman measurement peaks at 356, 484, 1350, 1578, 2435 cm−1 associated with OH, –C==C–, –C–O, S=O, =C–H moieties indicated successful capping. Nanoparticle yield was temperature dependent and optimal yield could not be tied to a particular plant part as source of extract. Tunneling electron microscope results showed Ag-NPs and ZnO-NPs were globular/spherical with a diameter range of 2–20 nm. Interestingly, ZnO-NPs TEM displayed isolated miniaturized globular nanoparticles (< 2 nm) which then joined up to form a large donut shaped structure indicating different formation mechanisms for the nanoparticles. XRD results showed the Ag-NPs, ZnO-NPs and the Ag–ZnO-NPs particles were crystalline in nature. The high signal/noise in XRD originated from possible crystalline biomaterials in the extracts. Energy dispersive spectroscopy (EDS) elemental composition results confirmed successful formation of the nanoparticles. Anti-Microbial activity of the synthesized Ag-NPs, ZnO-NPs and ZnO–Ag-NPs were studied against gram negative bacteria Escherichia coli (E. coli), gram positive bacteria Staphylococcus aureus and fungus Candida albicans. Different ZnO: Ag-NPs nanocomposite ratios were used to test for antimicrobial activity. Optimal antimicrobial activity was attained at Ag-NPs:ZnO-NPs ratio of 4:1 which also displayed the least minimum inhibition concentration (MIC) and therefore was used as the active ingredient in formulating a hand sanitizing antiseptic. The formulated antiseptic exhibited good antimicrobial activity.