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Le Thi Thanh, 2017. Green synthesis of Gold nanoparticles using Cassia alata Linn. leaf extract and evaluation of their Antimicrobial activities. MSc. Thesis Abstract.
Thứ hai, 25-09-2017 | 13:10:20

Advisers: Rajkumar H. Garampalli and Shobha Jagannath, DOS in Botany, University of Mysore, India.


Nanomaterials are materials at nanoscale as between 0.1 and 100 nanometer(1nm = 10-9 m), which have large surface area, orientation, and physical properties, appropriate to be used in medicinal sciences, physics and chemistry. The use of gold nanoparticles in biological studies was first introduced by Faulk and Taylor (1971). Currently, it was applied in biochemistry, microbiology, immunology, cytology, plant physiology, morphology, etc. Gold nanoparticles had been found inducing toxicity in plants and improving seed germination, the number of leaves, plant height, chlorophyll content, sugar content, helping increasing crop yielding.


The green synthesis of gold nanoparticles was carried out using leaf extract of Cassia alata plant. The aqueous extract was added in to precursor chloroauric acid (HAuCl4.3H2O) and incubated in dark condition at room temperature. The reaction of synthesis was indicated firstly by the change in color into dark purple. The UV-Visible spectroscopy analysis was done after two hours of incubation to confirm the formation of gold nanoparticles. Different concentrations of precursor and different ratios of plant extract resulted different UV-Vis spectra recorded with the peaks of gold surface plasmon resonance (SPR) were found between 530 and 560 nm. The chloroauric acid precursor 1mM and ratio 9:1 into Cassia alata leaf extract showed the clearly performance in color change, and peak of SPR appeared at 549 nm was the suitable for synthesis of gold nanoparticles using for further study of characteristic and evaluation of antimicrobial activities. The scanning electron microscopy (SEM) analysis and X-Ray diffraction (XRD) were done as resulting the synthesized gold nanoparticles were found to be spherical in shape and 12.3 nm in size. Energy dispersive X-ray spectroscopy (EDS) was study in the range from 4000 to 400 cm-1 for the elements analysis of synthesized nanoparticles. Gold nanoparticles contributed 80.70 % of weight and 28.03 % of atom in sample along with the presences of other atoms such as carbon, oxygen, chlorine and sodium. The Fourier transforms infrared (FT-IR) spectroscopy was used for analysis of biomolecules in plant extract which responsible for the reduction of gold ions and formation of gold nanoparticles. The presences of different groups were found, including O─H stretching of phenols (band at 3232 cm-1), tertiary amine salts (band at 2325 cm-1), C≡C stretching of monosubstituted alkynes (band at 2115 cm-1) and C─OH stretching of secondary alcohols (band at 1015 cm-1) which acted as capping agents involved in reduction of Au+ to Au0 nanoparticles.


Antimicrobial activities including antifungal and antibacterial activities were measured using well diffusion method. In the assay of antifungal, the gold nanoparticles (1mg/mL) showed inhibition zones around 10 mm in diameter on Aspergillus flavus, 9 mm on Fusarium oxysporum and 10 mm on Didymella bryoniae. The antifungal activity of synthesized gold nanoparticles was found to be not significant compared to fungicide in this study. In the antibacterial assay, activity of synthesized gold nanoparticles was studied on three bacteria strains: Bacillus subtilis, Xanthomonas campestris and Escherichia coli which showed the zones of inhibition at 13 mm, 14 mm and 13 mm, respectively. The results showed that gold nanoparticles were more active than antibiotic (no inhibition zone found) against Bacillus subtilis, and gold nanoparticles did not show the significant activity on Escherichia coli and Xanthomonas campestris compared to antibiotic.

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