Investigating the Possibility of Green Synthesis of Silver Nanoparticles Using Vaccinium arctostaphlyos Extract and Evaluating Its Antibacterial Properties

Abstract

Objective: Vaccinium genus plants have medicinal value, of which Vaccinium arctostaphylos (Caucasian whortleberry or Qare-Qat in the local language) is the only available species in Iran. Public tendency to use herbal remedies and natural products such as synthesized nanoparticles is increasing due to the proof of the destructive side effects of chemical drugs. Nanosilver products have been effective against more than 650 microbe types. This study was aimed at assessing the possibility of green synthesis of silver nanoparticles using Vaccinium arctostaphylos aqueous extract and at evaluating its antibacterial properties, as well.

Materials and methods: In order to synthesize silver nanoparticles, different volumes of Vaccinium arctostaphylos aqueous extract (3, 5, 10, 15, and 30 ml) were assessed with different silver nitrate solution concentrations (0.5, 1, 3, 5, and 10 mM) and different reaction time durations (1, 3, 5, 10, and 20 minutes) at room temperature using a rotary shaker with a speed of 150 rpm. Ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction analysis (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) were carried out. The antibacterial activity of the aqueous extract and the synthesized nanoparticles was evaluated, as well.

Results: Silver nanoparticle formation process was confirmed with XRD analysis, transmission electron microscopy (TEM), and FTIR spectroscopy. The UV-Vis spectroscopy of silver colloidal nanoparticles showed a surface plasmon resonance peak at 443 nm under optimal conditions (3 ml aqueous extract volume, 1 mM silver nitrate solution concentration, and 3 min reaction time under sunlight exposure). The reduction of silver ions to silver nanoparticles in solution was confirmed, as well. Based on X-ray diffraction analysis, the size of silver nanoparticles was in the range of 7-16 nm. TEM images showed an even distribution of silver nanoparticles, with a spherical shape. FTIR spectroscopy demonstrated the presence of different functional groups of oxygenated compounds such as carboxyl, hydroxyl, and nitrogenous groups. The antibacterial properties of the synthesized nanoparticles were confirmed.

Conclusion: The synthesized nanoparticles showed more antibacterial properties against gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) than gram-negative ones (Escherichia coli and Salmonella enteritidis).

Figure 1

Morphological characteristics of leaves and fruit of Vaccinium arctostaphylos L.

Figure 2

Color change of fruit extract (a) before and (b) after adding silver nitrate solution.

Figure 3

(a) UV-Vis spectrum under optimal conditions; (b) UV-Vis spectra of silver nanoparticles using different volumes of Vaccinium arctostaphylos aqueous extract (3, 5, 10, 15, and 30 ml), in the presence of 1 mM silver nitrate solution, sunlight catalyst, and time exposure of 3 minutes; (c) the effect of different AgNO₃ concentrations on silver nanoparticle synthesis using 3 ml of Vaccinium arctostaphylos aqueous extract; (d) the effect of reaction time on nanoparticle synthesis using Vaccinium arctostaphylos aqueous extract.

Figure 4

The effect of the presence and absence of 3-minute sunlight exposure on nanoparticle synthesis using Vaccinium arctostaphylos aqueous extract.

Figure 5

FTIR spectrum of silver nanoparticles synthesized under optimal conditions.

Figure 6

XRD spectrum of silver nanoparticles synthesized under optimal conditions.

Figure 7

TEM analysis of silver nanoparticles synthesized under optimal conditions.

Figure 8

Inhibition zone diameter of different concentrations of silver nitrate solution synthesized in Vaccinium arctostaphylos aqueous extract. Similar letters indicate no significant difference.

Figure 9

Disc diffusion test using 5 different concentrations of silver nitrate solution ((a) 10 mM; (b) 5 mM; (c) 3 mM; (d) 1 mM; (e) 0.5 mM). The aqueous extract of the plant was considered as the negative control, and gentamicin and streptomycin antibiotics were considered as the positive control.