Browsing by Author "Basu, Onita"

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Facile biosynthesis of Ag–ZnO nanocomposites using Launaea cornuta leaf extract and their antimicrobial activity
(Springer Nature, 2023-11-17) Makauki, Elizabeth; Mtavangu, Stanslaus; Basu, Onita; Rwiza, Mwemezi; Machunda, Revocatus
The quest to synthesize safe, non-hazardous Ag–ZnO nanoomposites (NCs) with improved physical and chemical properties has necessitated green synthesis approaches. In this research, Launaea cornuta leaf extract was proposed for the green synthesis of Ag–ZnO NCs, wherein the leaf extract was used as a reducing and capping agent. The antibacterial activity of the prepared nanoomposites was investigated against Escherichia coli and Staphylococcus aureus through the disc diffusion method. The influence of the synthesis temperature, pH, and precursor concentration on the synthesis of the Ag–ZnO NCs and antimicrobial efficacy were investigated. The nanoparticles were characterized by ATR-FTIR, XRD, UV–Vis, FESEM, and TEM. The FTIR results indicated the presence of secondary metabolites in Launaea cornuta which assisted the green synthesis of the nanoparticles. The XRD results confirmed the successful synthesis of crystalline Ag–ZnO NCs with an average particle size of 21.51 nm. The SEM and TEM images indicated the synthesized nanoparticles to be spherical in shape. The optimum synthesis conditions for Ag–ZnO NCs were at 70 °C, pH of 7, and 8% silver. Antibacterial activity results show Ag–ZnO NCs to have higher microbial inhibition on E. coli than on S. aureus with the zones of inhibition of 21 ± 1.08 and 19.67 ± 0.47 mm, respectively. Therefore, the results suggest that Launaea cornuta leaf extract can be used for the synthesis of Ag–ZnO NCs.
Launaea cornuta (wild lettuce) leaf extract: phytochemical analysis and synthesis of silver-zinc oxide nanocomposite
(IOP Science, 2024-10-11) Makauki, Elizabeth; Rwiza, Mwemezi; Basu, Onita
Access to quality drinking water is an essential human right and a fundamental aspect of human dignity, yet a challenge to many in developing countries. Over 2 billion people worldwide lack access to quality drinking water due to microbial contamination, among other factors. Silver-doped zinc oxide impregnated activated carbon nanocomposites, Ag-ZnO-AC NCs, a strong antimicrobial agent have been used at point-of-use to treat water treatment. Green synthesis of Ag-ZnO-AC NCs has played a vital role since it leads to the acquisition of non-toxic nanocomposites compared to chemical synthesis. In this study, Ag-ZnO-AC NCs were green-synthesized using Launaea cornuta leaf extract as a source of reducing and capping agents in place of synthetic chemicals. Antioxidants from Launaea cornuta (Wild Lettuce) leaves were extracted using 0, 50, and 100% EtOH solvents with different volumes and extraction circles. The highest phenolic (11044 ± 63 μg) and antioxidant (44112 ± 894 μg) contents were extracted using 50% EtOH and 20 ml of extract solvent with p < 0.05. The SEM and TEM images of the synthesized Ag-ZnO-AC NCs show the formation of highly porous AC with sheet-like structures and successful Ag-ZnO NCs impregnation within the pores and on the surface of the AC. Based on the inhibition zone, the antimicrobial activity of the Ag-ZnO AC NCs had significant results with 14.00 ± 0.37 for E. coli and 17.33 ± 0.36 mm for S. aureus, p < 0.05. These results confirm the significance of Launaea cornuta (Wild Lettuce) as a source of antioxidants that can be used as reducing and capping agents to synthesize Ag-ZnO-AC NCs.
Synergistic antimicrobial mechanisms of silver-doped zinc oxide for water treatment: a systematic review
(IWA Publishing, 2025-03-10) Makauki, Elizabeth; Machunda, Revocatus; Basu, Onita; Rwiza, Mwemezi
This systematic review provides an overview of the existing research on antimicrobial mechanisms of silver-doped zinc oxide nanocomposites (Ag/ZnO NCs). It reports the existing knowledge on the synergistic effect (relationship) between silver (Ag) and zinc oxide (ZnO) for its optimum application. The doping of Ag into the ZnO has been used to enhance its photocatalysis and antimicrobial performance by improving the generation of reactive oxygen species (ROS). The Ag/ZnO NCs’ microbial elimination can be done through generated ROS, metallic (Ag+ and Zn2+) ions, and direct attack by the nanoparticles (NPs). Unlike the summation of individual use outcomes, the antimicrobial results of Ag/ZnO create a synergetic effect. This brings the sustainable use of the materials by increasing their efficiency while lowering the amounts used. This article systematically reviews the antimicrobial mechanisms of Ag/ZnO against gram-negative and gram-positive bacteria. It further analyses the quantitative and qualitative synergism between Ag and ZnO when applied together as antimicrobial materials. This systematic review found Ag/ZnO as a potential microbial elimination agent. Many studies reported the chemical synthesis of Ag/ZnO, which might cause a yield of toxic nanomaterials. Further studies on biosynthesis are pivotal for the sustainable supply of safe, non-toxic materials aimed at drinking water treatment.