Green Bio-Assisted Synthesis, Characterization and Biological Evaluation of Biocompatible ZnO NPs Synthesized from Different Tissues of Milk Thistle (Silybum marianum)

Abstract

The purpose of the current study was green synthesis of ZnO-nanoparticles (NPs) from different tissues of Silybum marianum (L.) Gaernt. (i.e., seeds, wild plant, in vitro derived plantlets and callus cultures) followed by extensive characterization and evaluation of their biological potency. ZnO-NPs thus synthesized were subjected to characterization using standard techniques such as XRD, FTIR and SEM. Thermal stability of synthesized NPs was also evaluated using thermo-gravimetric analysis. Highly stable crystalline NPs with size ranging between 30.8 and 46.0 nm were obtained from different tissues of S. marianum. These NPs have revealed a wide range of biological applications showing antioxidant, moderate α-amylase inhibitor, antibacterial and cytotoxic potencies. The highest antibacterial activity (20 ± 0.98 mm) was shown by seed extract-mediated ZnO NPs against Staphylococcus aureus (ATCC-6538). Seed extract-mediated ZnO NPs also showed the most potent antioxidant activity (27.7 ± 0.9 µgAAE/mg, 23.8 ± 0.7 µgAAE/mg and 12.7 ± 1.9% total antioxidant capacity (TAC), total reducing power (TRP) and DPPH-free radical scavenging assay (FRSA), respectively). All of the synthesized ZnO NPs also showed cytotoxic activity against the hepato-cellular carcinoma (HepG2) human cells. Interestingly, these ZnO NPs were also highly biocompatible, as evidenced by the brine shrimp lethality and human red blood cells hemolytic assays. Among all of the NPs synthesized and used, the effect of seed extract-mediated NPs was found to be most promising for future applications.

Keywords: Nanoparticles (NPs); Silybum marianum; Zinc Oxide (ZnO); characterization; cytotoxic assay; green synthesis; in vitro plantlets.

Figure 1

X-ray diffraction analysis of (a) wild plant extract mediated ZnO nanoparticles (NPs) (W-ZNPs), (b) in vitro derived plantlets extract mediated ZnO NPs (P-ZNPs), (c) callus extract mediated ZnO NPs (C-ZNPs) and (d) seed extract mediated ZnO NPs (S-ZNPs).

Figure 2

SEM images of (a) W-ZNPs, (b) P-ZNPs, (c) C-ZNPs and (d) S-ZNPs.

Figure 3

FTIR spectral analysis of (a) W-ZNPs, (b) P-ZNPs, (c) C-ZNPs and (d) S-ZNPs.

Figure 4

Thermal stability of ZnO NPs at different temperatures. The experiment was carried out in triplicate. The values given in figure are mean ± standard deviation of the original data.

Figure 5

NPs activity against (a) S. aureus, (b) K. pneumonia, (c) P. aeruginosa. The experiments were carried out in triplicate. The values given in Table 1, expressed as mean ± standard deviation of the original data.

Figure 6

Total antioxidant capacity (TAC) (a), total reducing power (TRP) (b) and DPPH-free radical scavenging assay (FRSA) (c) potential of the biosynthesized ZnO NPs. The experiments were carried out in triplicate. The values given in figure are mean ± standard deviation of the original data.

Figure 7

ZnO NPs induced % inhibition of α-amylase. The experiments were carried out in triplicate. The values given in figure are mean ± standard deviation of the original data.

Figure 8

Characteristic pictures of non-treated (a) and treated (b) NPs activity against HepG2 cell line.

Figure 9

Compatibility of the synthesized ZnO NPs against human red blood cells. The experiments were carried out in triplicates. The values given in figure are mean ± standard deviation of the original data.