For the first time, different morphologies of zinc oxide (ZnO) superstructures are synthesized by a simple and environmental friendly route using Nerium oleander leaf extract as fuel. Powder X-ray diffraction, scanning electron microscopy, UV−visible spectroscopy, and photoluminescence studies are performed to ascertain the formation and characterization of ZnO. X-ray diffraction confirmed the crystalline nature of the compound with hexagonal Wurtzite structure. When the concentration of the leaf extract is varied, different morphologies are formed. ZnO are tested for antifungal using soybean seed-borne fungi by food-poison method and antibacterial activity against bacterial human pathogens by a broth microplate dilution method using 96-well plates. Among the screened soybean seed-borne fungi, Fusarium equisiti was found to be more susceptible, which was followed by Macrophomina phaseolina for ZnO nanoparticles (NPs) prepared using 0.2188 mol/dm 3 N. oleander leaf extract. It was observed that NPs exhibited pronounced antifungal activity in a dose-dependent manner with a relatively high percentage of mycelial inhibition. ZnO obtained with the concentration of 0.2188 mol/dm 3 leaf extract showed both minimum inhibitory concentration and minimum bactericidal concentration effectiveness compared to other synthesized compounds. It is observed that the samples with small crystallite size show greater antibacterial activity than those of larger crystallite size. Further, we found that crystallite size and morphology significantly affects the antibacterial activity of ZnO. Prepared compounds showed significant inhibition against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeurginosa. Among the tested bacteria, P. aeurginosa is more susceptible and E. coli is the least effective against bacterial pathogens. The antibacterial activities of the as-formed ZnO are preliminarily studied against Gram-positive (B. subtilis and S. aureus) and Gram-negative (E. coli and P. aeruginosa) bacteria and are found to be dependent on the shape of the nanostructures.

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In this paper, a robust and simple biogenic route has been developed to synthesize self-assembled ZnO superstructures in short intervals of time using naturally available aloe vera plant gel and zinc nitrate as starting materials. The stabilization of zinc ions with polysaccharides wrapped chains along with the support of proteins, lipids and physterols of aloe vera gel followed by combustion derives the ZnO superstructures. The obtained ZnO superstructures show a hexagonal crystal phase and exhibit a semiconducting behavior with the energy band gap varies from 2.92 to 3.08 eV. The aloe vera gel derived ZnO superstructures exhibit unique and strong orange-red emission centered at 600 nm. The better structural, morphological and photoluminescence results are obtained for ZnO prepared with 16.6% W/V of zinc nitrate with aloe vera content compared to other concentrations of aloe vera. The prepared compounds are tested for antimalassezial activity against Malassezia furfur, dermatologically prevalent yeast, and were found to have minimum inhibitory concentration (MIC) values ranging from 8 to 125 μg/mL. Fluorescence microscopic analysis revealed that yeast cells treated with ZnO superstructures have the chromatin as orange instead of green, showcasing the cell aggregation suggests that ZnO superstructures have an immense potential as an antifungal agent. Hence, the explored method of preparation shows high efficient ZnO superstructures derived from the aloe vera plant gel have potential applications in the medical, biomedical and cosmetic industries.

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