Biogenic Synthesis of MnO2 Nanoparticles With Leaf Extract of Viola betonicifolia for Enhanced Antioxidant, Antimicrobial, Cytotoxic, and Biocompatible Applications

Abstract

In this study, we propose to synthesize NPs using plant extract containing active biomedical components, with the goal of obtaining NPs that inherit the biomedical activities of the plant. Herein, we report the synthesis of manganese dioxide nanoparticles (VBLE-MnO₂ NPs) using the leaves extract of Viola betonicifolia, in which the biological active plant's secondary metabolites function as both reducing and capping agents. The synthesized NPs were successfully characterized with different spectroscopic techniques. The antibacterial, antifungal, and biofilm inhibition properties of the synthesized VBLE-MnO₂ NPs were further explored against a variety of bacteria (Gram-positive and Gram-negative) and mycological species. Additionally, their antioxidant ability against linoleic acid peroxidation inhibition, cytobiocompatibility with hMSC cells, and cytotoxicity against MCF-7 cells were investigated compared to leaves extract and chemically synthesized manganese dioxide NPs (CH-MnO₂ NPs). The results were demonstrated that the synthesized VBLE-MnO₂ NPs presented excellent antibacterial, antifungal, and biofilm inhibition performance against all the tested microbial species compared to plant leaves extract and CH-MnO₂ NPs. Moreover, they also exhibited significant antioxidant potential, which was comparable to the external standard (ascorbic acid); however, it was higher than plant leaves extract and CH-MnO₂ NPs. Furthermore, the synthesized CH-MnO₂ NPs displayed good cytobiocompatibility with hMSC cells compared to CH-MnO₂ NPs. The enhanced antioxidant, antibacterial, antifungal, and biofilm inhibition efficacy as compared to CH-MnO₂ NPs might be attributed to the synergistic effect of the VBLE-MnO₂ NPs' physical properties and the adsorbed biologically active phytomolecules from the leaves extract of V. betonicifolia on their surface. Thus, our study establishes a novel ecologically acceptable route for nanomaterials' fabrication with increased and/or extra medicinal functions derived from their herbal origins.

Keywords: MnO2 NPs; antimicrobial; antioxidant; biofilm inhibition; cytotoxic.

Figure 1

Schematic demonstration and possible synthesis mechanism for the green synthesized VBLE-MnO₂ NPs with the leaves extract of Viola betonicifolia.

Figure 2

(A) XRD pattern, (B) TEM image, (C) size distribution, and (D) EDX pattern for the green synthesized VBLE-MnO₂ NPs.

Figure 3

Antibacterial activity of VBLE-MnO₂ NPs in terms of (A) log₁₀ reduction and (B) % killing efficiency of bacterial strains in comparison with leaves extract of Viola betonicifolia and CH-MnO₂ NPs. (C) Representative images of control and treated S. aureus and K. pneumonia with VBLE-MnO₂.

Figure 4

CLSM images of untreated [control (A,C)] and treated (B,D) bacteria with synthesized VBLE-MnO₂ NPs. Red represents dead bacterial cells.

Figure 5

CLSM images of ROS generation in untreated (control) and treated bacteria with hydrogen peroxide (H₂O₂) and synthesized VBLE-MnO₂.

Figure 6

Comparison of (A) Gram-positive and (B) Gram-negative bacterial cell wall. (C) Proposed antibacterial mechanism of green synthesized VBLE-MnO₂ NPs.

Figure 7

Antifungal activity of VBLE-MnO₂ NPs in terms of (A) log₁₀ reduction and (B) % killing efficiency of fungal strains in comparison with leaves extract of V. betonicifolia and CH-MnO₂ NPs.

Figure 8

Biofilm inhibition performance of the synthesized VBLE-MnO₂ NPs against the (A) bacterial and (B) fungal strains in comparison with V. betonicifolia leaves extract and CH-MnO₂ NPs.

Figure 9

(A) Cytotoxic potential in terms of cell viability percentage against MCF-7 carcinoma cells treated with V. betonicifolia leaves extract, CH-MnO₂ NPs, and VBLE-MnO₂ NPs. Linear plot and regression coefficient between the cell viability % of the MCF-7 carcinoma cells with different concentrations of (B) V. betonicifolia leaves extract, (C) CH-MnO₂ NPs, and (D) VBLE-MnO₂ NPs.

Figure 10

CLSM images of the live and dead MCF-7 cancer cells stained with Hoechst 33342 and PI dye before (A) control and after treatment with (B) plant extract, (C) CH-MnO₂ NPs, and (D) VBLE-MnO₂ NPs.

Figure 11

(A) Antioxidant activity of the newly synthesized VBLE-MnO₂ NPs in comparison with V. betonicifolia leaves extract, CH-MnO₂ NPs, and external standard (Ascorbic acid). (B,C) Biocompatibility analysis of the newly synthesized VBLE-MnO₂ NPs with hMSC cells compared to the leaves extract of V. betonicifolia and CH-MnO₂ NPs.