XRD Analysis Results
The XRD pattern presented in Figure (4) is a testament to the crystalline nature of the gold nanoparticles synthesized through an environmentally benign process. The distinct peaks corresponding to the Miller indices (111), (200), (220), and (311) are indicative of a well-defined face-centered cubic (FCC) crystalline structure, which is characteristic of elemental gold [29]. The specific 2θ angles of 38.04°, 44.5°, 64°, and 77.7° align perfectly with the standard reference, confirming the high crystallinity of the nanoparticles.
The absence of any superfluous diffraction peaks is a clear indicator of the high purity of the gold nanoparticles. This suggests that the synthesis process, aided by the Halpeh plant extract, is not only effective in reducing the gold ions to their nanoparticle form but also in preventing the formation of impurities or by-products.
The calculated average size of 22.8 nm for the gold nanoparticle crystals, derived from the Debye-Scherrer equation, points to a uniform and controlled nanoparticle formation. This size is ideal for a multitude of applications, ranging from medical to electronic, due to its potential for high surface area and reactivity.
Moreover, the calculated d-spacing of approximately 2.5 nm for the (111) plane further corroborates the FCC structure and is consistent with the expected values for gold nanoparticles. The ICDD (International Centre for Diffraction Data) reference number PDF (Powder Diffraction File) # 04-0784 serves as a benchmark for comparing and validating the crystal structure, ensuring that the synthesized nanoparticles conform to the recognized standards for gold.
The successful synthesis of gold nanoparticles using the Halpeh plant extract highlights the precision of the green synthesis approach. These nanoparticles, with their confirmed structure and high purity, hold promise for diverse functional applications.
TEM Analysis Results
Figure (7) illustrates the TEM analysis of the gold nanoparticles synthesized using the Halpeh plant extract, demonstrating their spherical shape with diameters less than 50 nanometers. Figures (8), which presents a histogram of the size distribution of the gold nanoparticles, indicates an average diameter of 22.89 nm.
The TEM images provide valuable insights into the uniformity and quality of the nanoparticles. The spherical morphology is advantageous for many applications due to its symmetrical properties and even distribution of surface area. The size distribution histogram further confirms the consistency in nanoparticle size, which is crucial for reproducibility in industrial and research applications. The sub-50 nm size range of these nanoparticles makes them suitable for high-precision tasks, including targeted drug delivery and sensing applications, where small size and large surface area are beneficial. Differences in sample preparation and imaging techniques contribute to discrepancies in nanoparticle size measurements between TEM and SEM [31].
The results of the antimicrobial activity of the aqueous and methanolic extracts of the Halpeh plant and the synthesized gold nanoparticles
This research focused on the antibacterial and antifungal effects of extracts and synthesized gold nanoparticles, and their comparative efficacy against three antibiotics: ampicillin, gentamicin, and clotrimazole. The study found that these extracts and nanoparticles demonstrated a commendable ability to inhibit the growth of the tested pathogenic microorganisms, suggesting their potential as alternative antimicrobial agents.
As per the data presented in Figure (9) and Table (2), the synthesized gold nanoparticles exhibited significantly superior antibacterial and antifungal activity compared to the aqueous and methanolic extracts. This was particularly evident in the case of the gram-negative bacteria Escherichia coli and the fungus Aspergillus niger, where the zones of inhibition were notably larger (18mm and 20mm respectively) [32].
This enhanced antimicrobial effect of the gold nanoparticles could potentially be attributed to their combination with the extract of the medicinal plant Halpeh. This suggests that the integration of traditional medicinal plant extracts with modern nanotechnology could lead to more potent antimicrobial treatments.
Furthermore, the study inferred from the data that the synthesized nanoparticles were effective against all tested microbes. This is a significant finding as it highlights the broad-spectrum antimicrobial activity of the nanoparticles. In contrast, each of the antibiotics was found to be ineffective against some of the microbes. This underscores the potential of these nanoparticles as a more effective antimicrobial agent, capable of overcoming the limitations of traditional antibiotics.
Table (2): Results of the antimicrobial activity of the aqueous and methanolic extracts of the Halpeh plant and synthesized gold nanoparticles compared with antibiotics.
Microorganism | The diameter of the growth inhibition zone (mm) |
Biosynthesized Au NPs | Aqueous Extract | Methanolic Extract | Ampicillin | Gentamicin | Clotrimazole |
Escherichia coli | 18 | 6 | 14 | 26 | 28 | - |
Salmonella Typhimurium | 16 | 6 | 11 | 27 | 29 | - |
Staphylococcus aureus | 14 | 8 | 13 | 25 | 26 | - |
Bacillus cereus | 15 | 7 | 12 | 27 | 27 | - |
Aspergillus niger | 20 | 10 | 15 | - | - | 30 |
Candida albicans | 19 | 9 | 13 | - | - | 28 |
The Effects of Gold Nanoparticles on Phytochemical Compounds in Halpeh Plant Extract
After extracting the essence from the Halpeh plant using a Cloninger apparatus, the results of analyzing the plant essence through gas chromatography-mass spectrometry (GC-MS) are presented in Table (3). Various concentrations of gold nanoparticles (0, 10, 20, 40, 60, and 80 ppm) have significantly impacted the yield and composition of the plant essence. Specifically, the changes in Halpeh plant essence yield were 1.10, 0.118, 0.125, 0.133, 0.151 and 0.113% for the respective concentrations.
Figure (10) illustrates the comparison of the composition percentages in the Halpeh plant essence under the influence of different concentrations of gold nanoparticles. The major constituents of the essence, such as geranyl acetate, showed the following percentages: 8.131, 6.147, 8.280, 12.418, and 5.629% with the highest percentage observed in the 60-ppm treatment. Regarding Citral (E), its percentages were 29.650, 16.044, 25.122, 8.748, 33.075 and 18.96%, with the highest percentage found in the 60-ppm treatment (33.075%). Citral (Z) had percentages of 22.437, 19.457, 17.394, 20.336, 23.281, and 13.130%, with the highest observed in the 60-ppm treatment (23.281%), although there was no significant difference compared to the 0-ppm treatment. Additionally, Piperitone had percentages of 6.912, 8.030, 9.003, 3.758, 4.725, and 3.733% with the highest percentage observed in the 20-ppm treatment (9.003%). This value showed a noticeable difference from the 0-ppm treatment, and in all cases, the 80-ppm treatment had lower compound percentages.
The percentage of Geraniol composition was 14.666, 9.818, 11.715, 8.747, 13.260, and 7.431% with the highest percentage in the 0-ppm treatment. As a result, the percentage of geraniol composition has relatively decreased under the influence of different concentrations of gold nanoparticles. Furthermore, the phytochemical compounds Phytol, Lianool, and cis-verbenol in the plant essence had percentages of 0.929, 2.310, and 1.919% respectively, in the 60-ppm treatment, which were higher than in other treatments.
In summary, gold nanoparticles can act as a catalyst, influencing the extraction of secondary compounds in Halpeh plant essence. Depending on the specific compound type, they may either enhance or reduce the synthesis of these secondary constituents.
Table (3): Composition Percentages of Halpeh Plant Essence Constituents Affected by Different Synthesized Gold Nanoparticle Concentrations
Compound Name | The Composition Percentage at the Concentration of 0 ppm | The Composition Percentage at the Concentration of 10 ppm | The Composition Percentage at the Concentration of 20 ppm | The Composition Percentage at the Concentration of 40 ppm | The Composition Percentage at the Concentration of 60 ppm | The Composition Percentage at the Concentration of 80 ppm |
Octan | 1.600 | 1.308 | 13.61 | 0.385 | - | 21.032 |
1-Octen-3-ol | 0.77 | 0.396 | 0.302 | 0.695 | 0.592 | - |
6-Methyl-5-hepten-2-one | 1.036 | 0.638 | 0.949 | 0.999 | 0.815 | 1.035 |
Decane | 1.15 | - | 4.57 | 0.645 | 0.595 | 7.436 |
2-Cyclohexen-1-one, 3-methyl | 0.713 | 0.322 | 0.344 | 0.537 | 0.467 | - |
Linalool | 0.783 | 0.524 | 0.443 | 0.529 | 0.929 | - |
Spiro[4.5]decan-7-one, 1,8-dimethyl-8,9-epoxy-4-isopropyl | 0.603 | 0.498 | 0.195 | - | - | - |
Linalool formate | 0.768 | - | - | 0.592 | 0.670 | - |
D(+)-10-Camphorsulfonyl chloride | 0.404 | - | - | 0.582 | 0.479 | - |
Gerinic acid | - | - | 0.986 | 3.133 | - | - |
Cis-Geranyl acetate | - | - | - | 2.201 | 0.616 | - |
Caryophyllene | - | - | 0.180 | - | - | 0.548 |
Cubebene | - | - | - | - | - | 1.099 |
Results of Investigating Antioxidant Properties and Reducing Power of Halpeh Plant Extract under Different Synthesized Gold Nanoparticle Treatments
The Half-Maximal Inhibitory Concentration (IC50) of Halpeh plant extract under various gold nanoparticle treatments with concentrations of 0, 10, 20, 40, 60, and 80 ppm is demonstrated in Figure (11) using the DPPH radical scavenging method. As observed in this figure, the IC50 values for the plant extract in different gold nanoparticle treatments 11.61, 10.48, 8.98, 9.94, and 12.67 µg/ml. Consequently, the antioxidant properties of the Halpeh plant extract increased in the 10, 20, 40, and 60 ppm treatments compared to the untreated sample (0 ppm). However, in the 80-ppm treatment, the antioxidant activity significantly decreased. Notably, in this test, the plant extract treated with gold nanoparticles at a concentration of 40- ppm exhibits the highest antioxidant properties with an IC50 value of 8.98 µg/ml relative to other treatments. The results indicate that the impact of gold nanoparticles on the antioxidant properties of Halpeh plant extract in the DPPH method is bidirectional. Up to a specific concentration, it enhances and stimulates the plant’s antioxidant properties.
The reducing power of Halpeh plant extract under treatment with synthesized gold nanoparticles at concentrations of 0, 10, 20, 40, 60, and 80 ppm is shown in Figure (12) based on the calibration curve obtained from the standard FeSO4.7H2O (FRAP method). The reducing power of the plant extract has increased in the 10, 20, 40, and 60 ppm treatments compared to the 0-ppm treatment, while it has decreased in the 80-ppm treatment. Specifically, in the 40 and 60 ppm treatments, the plant extract demonstrates the highest reducing power with 16.71 and 16.85 mMFe2+ /mg sample, respectively. These results indicate that the impact of gold nanoparticles on the reducing properties of the plant extract in the FRAP method is bidirectional, and up to a specific concentration, it enhances and stimulates the extract’s reducing power, confirming their antioxidant properties.