Phytosynthesis and Characterization of Silver Nanoparticles from Antigonon leptopus: Assessment of Antibacterial and Cytotoxic Properties

Abstract

Background: Silver nanoparticles (AgNPs) show promises as antimicrobial biomaterials with use for combating multidrug-resistant microorganisms, and they are widely used in healthcare, medicine, and food industries. However, traditional physicochemical synthesis methods often require harsh conditions and toxic reagents, generating harmful waste. The synthesis of AgNPs using plant-derived bioactive compounds offers an eco-friendly alternative to conventional methods. Methods: In this study, a bio-green approach was employed to synthesize AgNPs using ethanolic extracts from Antigonon leptopus leaves (EXT-AL). The synthesis was optimized under different pH conditions (5.5, 8.0, 10.0) and EXT-AL concentrations (10-200 μg/mL). Antibacterial activity was evaluated against Escherichia coli and Staphylococcus aureus, and cytotoxicity was assessed in HeLa, CaCo-2, T731-GFP, and HaCaT cell lines. Results: UV-Vis spectroscopy confirmed nanoparticle formation, with a surface plasmon resonance peak at 410 nm. Alkaline conditions (pH 10.0) favored the formation of smaller, spherical AgNPs. Characterization by DLS, TEM, and AFM revealed uniform nanoparticles with a hydrodynamic diameter of 93.48 ± 1.88 nm and a zeta potential of -37.80 ± 1.28 mV. The AgNPs remained stable in Milli-Q water but tended to aggregate in PBS, DMEM, and MHB media. Antibacterial assays demonstrated significant bactericidal activity against Escherichia coli and Staphylococcus aureus at 3.9 μg/mL (Ag⁺ equivalent). Cytotoxicity tests showed no toxicity to HeLa, T731-GFP, CaCo-2, or HaCaT cells at concentrations ≥ 7.8 μg/mL after 24 h. Conclusions: These findings highlight Antigonon leptopus extract as a sustainable and cost-effective resource for AgNPs synthesis, with strong antimicrobial properties and potential biomedical applications.

Keywords: Antigonon leptopus; antibacterial activity; cytotoxic properties; phytosynthesis; silver nanoparticles.

Figure 1

UV-Vis absorption spectra of AgNPs synthesized in various pH conditions: 5.5 (A), 8.0 (B), and 10.0 (C), at different concentrations of Antigonon leptopus ethanolic extract.

Figure 2

Transmission electron microscopy (TEM) micrograph of AgNPs synthesized at a 100 µg/mL concentration of EXT-AL (A), size distribution of AgNPs as determined by TEM with Gaussian fitting curves (blue, green, and red represent the average distribution particle size) (B), atomic force microscopy (AFM) 2-D topography of AgNPs at 100 µg/mL concentration of EXT-AL (C), and the height profile along the white line in image C (D).

Figure 3

(A) UV–Vis spectral evolution of the synthesized AgNPs over 24 h. The color change from black to blue indicates the time progression during nanoparticle formation, with black lines representing early time points and blue lines representing later stages. The inset graph shows the increase in absorbance at 410 nm over time, confirming the formation of AgNP colloids. (B) Linear plot of ln((A_∞ − A_t)/(A_∞ − A₀)) versus time, used to determine the apparent rate constant of the reaction. The red line represents the linear regression fit (R² = 0.995).

Figure 4

Circular and single-crystal diffraction pattern (A) and X-ray diffraction pattern (B) of the synthesized AgNPs.

Figure 5

Normalized FTIR spectra of EXT-AL (black line) and synthesized AgNPs (red line).

Figure 6

TGA and DTG plots of EXT-AL (A) and synthesized AgNPs (B).

Figure 7

Colloidal stability of AgNPs over 10 days in different dispersion media. (A) Hydrodynamic diameter and (B) zeta potential measured in: Milli-Q water (black squares), PBS at pH 7.2 (red circles), PBS at pH 5.5 (blue upward triangles), DMEM (magenta downward triangles), and Mueller–Hinton Broth (MHB, green diamonds).

Figure 8

Effect of EXT-AL (A) and AgNPs (B) on the viability of S. aureus and E. coli. Represented statistical differences between groups are denoted by ns for p < 0.1234, ** for p < 0.002, *** for p < 0.0002, and **** for p < 0.0001.

Figure 9

Growth kinetics of S. aureus (A) and E. coli (B) in the presence of varying concentrations of AgNPs (0.975–31.2 µg/mL), monitored by optical density at 620 nm over 48 h.

Figure 10

Cellular viability at different AgNPs-100 μg/mL concentrations against HeLa, T731-GFP, CaCo-2, and HaCaT. Represented statistical differences between groups are shown by ns for p < 0.1234, * for p < 0.033, *** for p < 0.0002, and **** for p < 0.0001.