Sustainable green synthesis of zinc oxide nanoparticles utilizing Zingiber officinale peel aqueous extract, characterization, and determination of its anticancer and antimicrobial potential

Abstract

This study demonstrates the green synthesis, characterization, and biomedical applications of zinc oxide nanoparticles (ZnONPs) using Zingiber officinale (Z. officinale) (ginger) peel extract. Green synthesis offers advantages over conventional methods, including environmental friendliness, cost-effectiveness, and enhanced biocompatibility. Ultraviolet-Visible (UV-Vis) spectroscopy confirmed ZnONPs formation with a peak at 364 nm. Fourier-Transform Infrared (FTIR) spectroscopy analysis revealed characteristic peaks indicating functional groups involved in nanoparticle formation. Scanning Electron Microscope (SEM) analysis showed spherical/agglomerated nanoparticles, and Energy-Dispersive X-ray Spectroscopy (EDS) confirmed 77.7% zinc oxide by mass%. The X-ray Diffraction (XRD) indicated an average particle size of 24.67 nm with distinct crystal orientations. Phytochemical analysis detected alkaloids, saponins, and steroids in the extract. Optimal synthesis occurred at 50-60°C and pH 10, yielding stable ZnONPs. The ZnONPs exhibited significant antibacterial activity against Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis), Bacillus cereus (B. cereus), Escherichia coli (E.coli), Zymomonas mobilis (Z. mobilis), and Pseudomonas aeruginosa (P. aeruginosa), as well as antifungal activity against Candida albicans (C. albicans). The in vitro cytotoxicity study on M.D. Anderson - Metastatic Breast - 231 (MDA-MB-231) breast cancer cells showed a dose-dependent reduction in cell viability [Half-maximal Inhibitory Concentration (IC50) = 82.13 µg/mL] with notable morphological changes at higher concentrations. The ZnONPs synthesized from ginger peel extract are innovative, environmentally friendly, and economical. Our findings show that biologically generated ZnONPs are effective antibacterial and antifungal agents against several pathogens. This research uniquely demonstrates the potential of ginger peel, a commonly discarded agro-waste, as a sustainable source for ZnONPs synthesis, highlighting its biotechnological and medicinal applications. The novelty of this study lies in the green synthesis approach using ginger peel and the comprehensive evaluation of its antimicrobial and anticancer properties. Further in-depth studies and optimization are needed to validate their therapeutic efficacy and safety.

Fig 1. General description and characteristics of Zingiber officinale.

Fig 2. Different steps involved in the synthesis of zinc oxide nanoparticles from Zingiber officinale peel extract.

Fig 3. Ultraviolet-Visible (UV-Vis) absorption spectrum of zinc oxide nanoparticles (ZnONPs) synthesized using ginger peel extract.

This figure shows the UV-Vis spectrum of biosynthesized ZnONPs, with a prominent absorption peak at 364 nm. This peak corresponds to the characteristic absorption edge and bandgap energy of ZnONPs, which are key indicators of their optical properties. The presence of this peak confirms the successful formation of ZnONPs and reflects their nanoscale dimensions.

Fig 4. Fourier Transform Infrared (FTIR) spectrum of zinc oxide nanoparticles (ZnONPs) synthesized using ginger peel extract.

This figure displays the FTIR spectrum used to identify functional groups involved in the formation and stabilization of ZnONPs. The spectrum shows characteristic absorption bands at 3393 cm ⁻ ¹ (O–H stretching in alcohols and phenols), 2920 cm ⁻ ¹ (C–H stretching in alkanes or methyl groups), 1637 cm ⁻ ¹ (C = O stretching in ketones, esters, or aldehydes), and 1552 cm ⁻ ¹ (N–H bending in primary amines or amides). Additional peaks include 1407 cm ⁻ ¹ (C–H bending in methyl groups), 1019 cm ⁻ ¹ (C–O stretching in ethers or secondary alcohols), 800 cm ⁻ ¹ (aromatic C–H out-of-plane bending), and 643 cm ⁻ ¹ (C–H bending in substituted benzene rings or alkenes). These functional groups originate from bioactive compounds in the ginger peel extract and play a role in reducing and stabilizing the nanoparticles. The presence of Zn–O bonds is confirmed by peaks in the 400–700 cm ⁻ ¹ region and at 1018 cm ⁻ ¹, validating the formation of ZnONPs.

Fig 5. Scanning Electron Microscopy (SEM) images of zinc oxide nanoparticles (ZnONPs) synthesized using ginger peel extract.

This figure presents SEM micrographs of ZnONPs captured at magnifications of (a) 2000 × , (b) 5000 × , (c) 15,000 × , and (d) 30,000 × . The images reveal the surface morphology and size distribution of the nanoparticles. The ZnONPs appear predominantly spherical, with some degree of agglomeration, indicating the presence of both individual nanoparticles and larger aggregates.

Fig 6. Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) analysis of zinc oxide nanoparticles (ZnONPs) synthesized using ginger peel extract.

This figure shows the SEM-EDS image used to analyze the surface morphology and elemental composition of the synthesized ZnONPs. The EDS spectrum reveals prominent peaks corresponding to zinc (Zn), oxygen (O), and carbon (C), confirming the successful formation of ZnONPs. The quantitative analysis indicates that approximately 43.76% of the sample is composed of zinc oxide, validating the synthesis process. The presence of Zn and O aligns with expected ZnONPs composition, while carbon may originate from the plant extract used in the green synthesis.

Fig 7. The X-ray Diffraction (XRD) pattern of ZnONPs, displaying distinct diffraction peaks corresponding to the spherical structure at 2θ values of 31.73°, 34.38°, 36.21°, 47.50°, 56.54°, 62.74°, and 68.92°, which correspond to specific lattice planes including (100), (002), (101), (102), (110), (103), (200), (112), (201), (004), (202), and (104).

These peaks match the standard Zinc oxide pattern reported by the Joint Committee on Powder Diffraction Standards (JCPDS No. 36-1451), confirming the crystalline nature and phase purity of the nanoparticles.

Fig 8. Ultraviolet-Visible (UV-Vis) spectral analysis illustrating the effect of temperature and pH on the ZnONPs.

Peaks in the spectra represent Surface Plasmon Resonance (SPR), which correlates with nanoparticle size and dispersion. Optimal synthesis occurred at 50–60°C and pH 10, yielding stable ZnONPs with desirable optical properties.

Fig 9. Percentage of cell viability of MDA-MB-231 breast cancer cells treated by ZnONPs.

The cell viability decreased with increasing concentration of ZnONPs.

Fig 10. Representative micrographs showing morphological changes in breast cancer cells (MDA-MB-231) following treatment with biogenic zinc oxide nanoparticles (ZnONPs).

This figure illustrates the cellular morphology of MDA-MB-231 cells after exposure to ZnONPs. Cells were treated with increasing concentrations of ZnONPs: 20, 40, 60, 80, and 100 µg/mL. The micrograph for 20 µg/mL is not included due to negligible morphological changes and technical constraints during imaging. Observable changes include cell shrinkage, elongation, detachment, and loss of turgidity, which are indicative of cytotoxic effects and reduced cell viability.

Fig 11. Zingiber officinale synthesized zinc oxide nanoparticles (ZnONPs) showed significant antibacterial activity against Escherichia coli.

Data presented as mean ± SEM (n = 3). Statistical significance at ***p < 0.001 compared to Zinc oxide (ZnO).

Fig 12. Antimicrobial activity of tested compounds against various bacterial strains.

(a) Escherichia coli (ATCC no 25922), (b)Pseudomonas aeruginosa (ATCC no 27853), (c) Bacillus subtilis (ATCC no 122264), (d) Zymomonas mobilis (ATCC no 31821) and (e) Staphylococcus aureus (ATCC no 25923). ATCC = American Type Culture Collection; STD = Standard antibiotic; PE = Plant extract; ZnO = Zinc oxide.

Fig 13. Antifungal activity depicting the zone of inhibition (ZOI).

The ZOI measured 12 mm, indicating significant antifungal activity. STD- standard drug fluconazole; Zn- Zinc Acetate; GE-Ginger peel extract; ZnONPs -Zinc oxide nanoparticles.