Green Synthesis of Silver Nanoparticles Using Euphorbia wallichii Leaf Extract: Its Antibacterial Action against Citrus Canker Causal Agent and Antioxidant Potential

Abstract

Biologically synthesized silver nanoparticles are emerging as attractive alternatives to chemical pesticides due to the ease of their synthesis, safety and antimicrobial activities in lower possible concentrations. In the present study, we have synthesized silver nanoparticles (AgNPs) using the aqueous extract of the medicinal plant Euphorbia wallichii and tested them against the plant pathogenic bacterium Xanthomonas axonopodis, the causative agent of citrus canker, via an in vitro experiment. The synthesized silver nanoparticles were characterized by techniques such as UV-Vis spectroscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis and transmission electron microscopy. Moreover, the plant species were investigated for phenolics, flavonoids and antioxidant activity. The antioxidant potential of the extract was determined against a DPPH radical. The extract was also evaluated for phenolic compounds using the HPLC technique. The results confirmed the synthesis of centered cubic, spherical-shaped and crystalline nanoparticles by employing standard characterization techniques. A qualitative and quantitative phytochemical analysis revealed the presence of phenolics (41.52 mg GAE/g), flavonoids (14.2 mg QE/g) and other metabolites of medicinal importance. Different concentrations (1000 µg/mL to 15.62 µg/mL—2 fold dilutions) of AgNPs and plant extract (PE) alone, and both in combination (AgNPs-PE), exhibited a differential inhibition of X. axanopodis in a high throughput antibacterial assay. Overall, AgNPs-PE was superior in terms of displaying significant antibacterial activity, followed by AgNPs alone. An appreciable antioxidant potential was recorded as well. The observed antibacterial and antioxidant potential may be attributed to eight phenolic compounds identified in the extract. The Euphorbia wallichii leaf-extract-induced synthesized AgNPs exhibited strong antibacterial activity against X. axanopodis, which could be exploited as effective alternative preparations against citrus canker in planta in a controlled environment. In addition, as a good source of phenolic compounds, the plant could be further exploited for potent antioxidants.

Biosynthesized silver nanoparticles using Polygonatum geminiflorum efficiently control fusarium wilt disease of tomato

“…The solution turned brown due to reduction of silver ions in reaction mixture which indicated the formation of silver nanoparticles, and the result was compared with previously reported studies on green nanoparticles synthesis (Ali et al, 2016;Arif et al, 2022). Moreover, a characteristic surface plasmon resonance peak at 440 nm during UV-Vis analysis was observed which further confirmed the synthesis of nanoparticles.…”

“…These functional groups were likely responsible for synthesis of and providing capping layers to Ag nanoparticles. Therefore, the synthesized AgNPs were more stable and non-toxic as previously been discovered by Arif et al (2022) . The TEM analysis revealed spherical or round shaped monodispersed AgNPs that were not in direct contact because of the capping layers of secondary metabolites.…”

“…Results depicted rich phytochemical profile and significant antioxidant properties of the investigated plant extract which suggest its probable involvement as the major reducing compounds of silver ions. The solution turned brown due to reduction of silver ions in reaction mixture which indicated the formation of silver nanoparticles, and the result was compared with previously reported studies on green nanoparticles synthesis ( Ali et al, 2016 ; Arif et al, 2022 ). Moreover, a characteristic surface plasmon resonance peak at 440 nm during UV-Vis analysis was observed which further confirmed the synthesis of nanoparticles.…”

“…The reaction mixture was exposed to sunlight for 15 min and the color change was monitored following the reaction of both reactants. The mixture was incubated at room temperature and spectral readings were recorded at various time points until consistency in surface plasmon resonance was achieved after 48 h. The synthesized AgNPs were purified by following the protocol of Arif et al (2022) . Briefly, the samples were centrifuged at 15,000 rpm, the supernatants were discarded, and the pellets were dissolved in deionized distilled water by using ultrasonic sonicator.…”

Green synthesis of metronidazole or clindamycin-loaded hexagonal zinc oxide nanoparticles from Ziziphus extracts and its antibacterial activity

“…The leaves of this plant have been utilized as wound dressings, bronchial asthma, and fever remedies. Phytochemical analyses of the leaf extracts (aqueous and methanolic extract) were performed and revealed the presence of saponins, alkaloids, flavonoids, tannins, and polyphenols (Arif et al 2022). Current work was performed to evaluate the effect of "microbial catalyst" on the morphology of ZnO-NPs using the green synthesis technique.…”