Phytosynthesis of Nickel Oxide Nanoparticles and Their Antioxidant and Antibacterial Efficacy Studies

Abstract

Introduction: Multidrug-resistant (MDR) bacteria are widely acknowledged as a significant and pressing public health concern. Tribulus terrestris has been used as a health tonic in traditional medicine since ancient Vedic times. It was also utilized to synthesize small, well-dispersed metal nanoparticles (NPs). The biosynthesized nickel oxide nanoparticles (NiO-NPs) have a broad spectrum of biomedical uses.

Objective: The objective of the research was to utilize a green synthesis method to synthesize NiO-NPs using Tribulus terrestris, subsequently characterize, and this study aimed to assess the antioxidant and antibacterial effectiveness of these NPs against wound isolates that are resistant to multiple drugs.

Materials and methods: The synthesis of NiO-NPs was achieved through the titration method, which is a green synthesis approach, and it was characterized by using techniques such as ultraviolet-visible spectroscopy (UV), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and energy dispersive X-ray (EDX). The antioxidant activity of the NPs was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, and antibacterial activity was done using the agar well diffusion method. IBM SPSS Statistics for Windows, Version 21 (Released 2012; IBM Corp., Armonk, New York, United States) is used for statistical analysis.

Results: The biosynthesized NiO-NPs exhibited a color change from dark brown to dark green, indicating the successful reduction of the NPs. UV analysis peaks were observed at 310-350 nm, while FT-IR analysis showed the peaks at various wavelengths such as 629.31cm^-1 (halo compound; C-Br stretching), 957.80cm^-1(aromatic phosphates; P-O-C stretch), 1004.65cm^-1 (aliphatic phosphates; P-O-C stretch), 1094.93cm^-1 (organic siloxane or silicone; Si-O-Si), 1328.38cm^-1 (dialkyl/aryl sulfones), 1604.88cm^-1 (open-chain azo-N=N-), 2928.68cm^-1 (methylene C-H asym/sym stretch), 3268.65cm^-1 (normal polymeric "OH" stretch). The crystallinity of the NPs was determined to be 24.7%, while the remaining 75.6% exhibited an amorphous structure. The SEM image revealed a spherically agglomerated structure of the nano-ranged size NiO-NPs. The EDX analysis indicated the presence of elemental compositions Ni (7.4%), O (39.4%), and C (53.3%) in the biosynthesized NiO-NPs. These NPs demonstrated significant antibacterial activity against Pseudomonas aeruginosa and Klebsiella pneumoniae, moderate antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), and the lowest antibacterial activity against Enterococcus faecalis.

Conclusion: Our in vitro results demonstrate that the biosynthesized NiO-NPs exhibit significant antioxidant and antibacterial activity. These NPs can be used as a future antimicrobial medication, particularly against MDR clinical wound isolates of K. pneumoniae, P. aeruginosa, and MRSA.

Keywords: antibacterial activity; antioxidant; green synthesis; multidrug-resistant wound isolates; nickel oxide.

Figure 1. Tribulus terrestris-mediated synthesis of NiO-NPs by the titration method (green synthesis)

NiO-NPs: Nickel oxide nanoparticles (A) Tribulus terrestris extract before synthesis, (B) nickel oxide solution, (C) titration method, (D) after 24-hour incubation NiO-NP synthesis, (E) centrifuge and pellet collection, and (F) NiO-NPs powder form

Figure 2. UV-vis absorption spectrum of the NiO-NPs

UV-vis: UV-visible; NiO-NPs: nickel oxide nanoparticles (A) UV spectroscopy analysis-time 0 interval, (B) UV spectroscopy analysis-time 24-hour interval

Figure 3. Fourier transformed infrared spectra of the synthesized NiO-NPs

NiO-NPs: Nickel oxide nanoparticles

Figure 4. X-ray powder diffraction spectra of NiO-NPs

NiO-NPs: Nickel oxide nanoparticles

Figure 5. Scanning electron microscope images of the prepared NiO-NPs with different diameter distributions

NiO-NPs: Nickel oxide nanoparticles (A) 0.5 μm scale, (B) 100 nm scale

Figure 6. EDX images of biosynthesized NiO-NPs

NiO-NPs: Nickel oxide nanoparticles; EDX: energy dispersive X-ray

Figure 7. Antibacterial activity of NiO-NPs against the test organisms

NiO-NPs: Nickel oxide nanoparticles (A) Enterococcus faecalis, (B) Klebsiella pneumoniae, (C) Pseudomonas aeruginosa, (D) methicillin-resistant Staphylococcus aureus (MRSA)

Figure 8. Antioxidant activity (DPPH) of NiO-NPs compared with the standard L-ascorbic acid

DPPH: 2,2-diphenyl-1-picrylhydrazyl; NiO-NPs: nickel oxide nanoparticles