Biosynthesis, characterization, and antibacterial activity of ZnO nanoaggregates using aqueous extract from Anacardium occidentale leaf: comparative study of different precursors

Abstract

Background Various parts of Anacardium occidentale plant possess curative qualities like antidiabetic, anti-inflammatory, antibacterial, antifungal, and antioxidant. Aqueous extract of this plant leaf was used in biosynthesizing zinc oxide (ZnO) nanoaggregates using two precursors of zinc salt (zinc acetate dihydrate [Zn(CH3COO)2∙2H2O] and zinc chloride [ZnCl2]). The synthesized ZnO samples were used in a comparative study to investigate the antibacterial activity against selected Gram-positive and Gram-negative microbes [Staphylococcus aureus, Exiguobacterium aquaticum (Gram +ve) and Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii (Gram −ve)]. The synthesized ZnO nanoaggregates from the two precursors were characterized using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive x-ray spectroscopy (EDX) techniques. Results Micrographs of SEM and TEM confirmed nanoparticles agglomerated into aggregates. While spherical nanoaggregates were identified in samples prepared from Zn(CH3COO)2∙2H2O, flake-like structures were identified in samples synthesized from ZnCl2. Particle size determined by TEM was 107.03 ± 1.54 nm and 206.58 ± 1.86 nm for zinc acetate dihydrate and zinc chloride precursors respectively. ZnO nanoaggregate synthesized using zinc acetate as precursor gave higher antibacterial activity than its counterpart, zinc chloride with K. pneumonia recording the highest inhibition zone of 2.08 ± 0.03 mm (67.53%) whereas S. aureus recorded the least inhibition zone of 1.06 ± 0.14 mm (34.75%) for ZnO nanoaggregate from zinc chloride precursor. Also, antibacterial activity increases with increasing concentration of the extract in general. However, A. baumannii, E. aquaticum, and K. pneumoniae did not follow the continuity trend with regards to the 250 ppm and 500 ppm concentrations. Conclusion Biosynthesis of ZnO nanoaggregates using aqueous extract of A. occidentale leaf from zinc acetate dihydrate and zinc chloride as precursors was successful with the formation of nanospheres and nanoflakes. The study suggested that A. occidentale sp. could be an alternative source for the production of ZnO nanoparticles and are efficient antibacterial compounds against both Gram +ve and Gram −ve microbes with its promising effect against infectious bacteria.

Recent Advances in Plant-Mediated Zinc Oxide Nanoparticles with Their Significant Biomedical Properties

“…Zinc oxide (ZnO) nanoparticles (NPs) were created utilizing thyme leaf extract using a green technique, according to ST Karam et al The formation of the nanoparticles were spherical in shape with an average size in the range of 39.4–51.86 nm [ 51 ]. In a study conducted by Droepenu et al, Anacardium occidentale leaf extract was used to produce ZnO NPs with two precursors of zinc salt (zinc acetate dihydrate and zinc chloride) and evaluated against Acinetobacter baumannii , Escherichia coli , Staphylococcus aureus , and Exiguobacterium aquaticum [ 52 ]. Zinc nitrate hexahydrate was used as a precursor to producing ZnO nanoparticles from the Vitex negundo plant, which demonstrated bacterial inhibition against pathogenic gram-positive and gram negative bacteria [ 53 ].…”

New Green Approaches in Nanoparticles Synthesis: An Overview

“…The use of zinc chloride has led to the synthesis of ZnO nanorods that were 167 nm in length and 68 nm in width. However, both samples faced aggregation [ 148 ]. The ZnO NPs synthesized from zinc sulphate had a nanorod morphology and an average size of 30 nm when Justicia adhatoda leaf extract was used.…”

Green Synthesis of Metal and Metal Oxide Nanoparticles Using Different Plants’ Parts for Antimicrobial Activity and Anticancer Activity: A Review Article

“…Sambucus ebulus-mediated ZnO nanoparticles explain efficient antioxidant and antibacterial activity [86]. Droepenu, Eric Kwabena, et al reported the biosynthesis of ZnO nanoparticles using Anacardium occidentale and tested against S. aureus (ZOI = 1.06 ± 0.14 mm), E. aquaticum (ZOI = 1.99 ± 0.11 mm), K. pneumoniae (ZOI = 2.08 ± 0.03 mm), E. coli (ZOI = 1.49 ± 0.09 mm), and A. baumanii (ZOI = 2.99 ± 0.01 mm) [87].…”