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Microstructural, spectroscopic, and antibacterial properties of silver-based hybrid nanostructures biosynthesized using extracts of coriander leaves and seeds

View Article: PubMed Central - PubMed

ABSTRACT

Coriander leaves and seeds have been highly appreciated since ancient times, not only due to their pleasant flavors but also due to their inhibitory activity on food degradation and their beneficial properties for health, both ascribed to their strong antioxidant activity. Recently, it has been shown that coriander leaf extracts can mediate the synthesis of metallic nanoparticles through oxidation/reduction reactions. In the present study, extracts of coriander leaves and seeds have been used as reaction media for the wet chemical synthesis of ultrafine silver nanoparticles and nanoparticle clusters, with urchin- and tree-like shapes, coated by biomolecules (mainly, proteins and polyphenols). In this greener route of nanostructure preparation, the active biocompounds of coriander simultaneously play the roles of reducing and stabilizing agents. The morphological and microstructural studies of the resulting biosynthesized silver nanostructures revealed that the nanostructures prepared with a small concentration of the precursor Ag salt (AgNO3 =5 mM) exhibit an ultrafine size and a narrow size distribution, whereas particles synthesized with high concentrations of the precursor Ag salt (AgNO3 =0.5 M) are polydisperse and formation of supramolecular structures occurs. Fourier transform infrared and Raman spectroscopy studies indicated that the bioreduction of the Ag− ions takes place through their interactions with free amines, carboxylate ions, and hydroxyl groups. As a consequence of such interactions, residues of proteins and polyphenols cap the biosynthesized Ag nanoparticles providing them a hybrid core/shell structure. In addition, these biosynthesized Ag nanomaterials exhibited size-dependent plasmon extinction bands and enhanced bactericidal activities against both Gram-positive and Gram-negative bacteria, displaying minimal inhibitory Ag concentrations lower than typical values reported in the literature for Ag nanoparticles, probably due to the synergy of the bactericidal activities of the Ag nanoparticle cores and their capping ligands.

No MeSH data available.


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TEM studies of sample L-0.5M.Notes: (A) TEM micrograph. The inset shows the SAED pattern of the area shown in the micrograph. The orange numbers are Miller indexes and indicate the crystallographic planes associated to the observed diffraction rings. (B) Histogram of the particle diameter distribution. (C) TEM image of a nanoparticle aggregate with a branched structure. The inset shows a high magnification TEM micrograph of a branch of this aggregate. (D) EDS spectrum of the supramolecular structure observed in panel C. The traces of Cu correspond to the copper TEM grid. The trace of C is probably partially related to the presence of organic material adsorbed by the Ag nanoparticles from the coriander extract and the carbon present in the coating of the TEM grid. (E) SAED pattern of the branch of the nanoparticle aggregate highlighted by an orange circle in panel C. The numbers and / symbol – indicate Miller indexes associated to crystallographic planes; orange numbers are related to forbidden reflections and white ones to reflections expected according Bragg’s law; [ ] indicates a crystallografic direction, in this case, the zone axis.Abbreviations: TEM, transmission electron microscope; SAED, selected-area electron diffraction; L-0.5M, final colloid obtained using coriander leaf extract and 0.5 M AgNO3; EDS, energy dispersive spectrometry; ZA, zone axis; Ag, silver; Cu, copper; C, carbon.
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f3-ijn-11-4787: TEM studies of sample L-0.5M.Notes: (A) TEM micrograph. The inset shows the SAED pattern of the area shown in the micrograph. The orange numbers are Miller indexes and indicate the crystallographic planes associated to the observed diffraction rings. (B) Histogram of the particle diameter distribution. (C) TEM image of a nanoparticle aggregate with a branched structure. The inset shows a high magnification TEM micrograph of a branch of this aggregate. (D) EDS spectrum of the supramolecular structure observed in panel C. The traces of Cu correspond to the copper TEM grid. The trace of C is probably partially related to the presence of organic material adsorbed by the Ag nanoparticles from the coriander extract and the carbon present in the coating of the TEM grid. (E) SAED pattern of the branch of the nanoparticle aggregate highlighted by an orange circle in panel C. The numbers and / symbol – indicate Miller indexes associated to crystallographic planes; orange numbers are related to forbidden reflections and white ones to reflections expected according Bragg’s law; [ ] indicates a crystallografic direction, in this case, the zone axis.Abbreviations: TEM, transmission electron microscope; SAED, selected-area electron diffraction; L-0.5M, final colloid obtained using coriander leaf extract and 0.5 M AgNO3; EDS, energy dispersive spectrometry; ZA, zone axis; Ag, silver; Cu, copper; C, carbon.

Mentions: An increase in the concentration of AgNO3 during biosynthesis with respect to the concentration of coriander leaf or seed extracts resulted in an increase in the degree of polydispersity of the resulting nanoparticles, owing to the occurrence of secondary particle growth by aggregation and coalescence, and probably by Ostwald ripening.25 In this manner, a broad and asymmetric size distribution was found for sample L-0.5M (Figure 3A and B). However, most particles of this sample (~90%) displayed diameters smaller than 10 nm, and ~45% exhibited sizes smaller than 5 nm. This is an interesting characteristic of this sample because previous results have indicated that the Ag nanoparticles of sizes smaller than 10 nm exhibit potent antibacterial26 and catalytic27 activities. On the other hand, the biggest particles (with sizes of tens of nanometers) tended to coalesce into elongated particles, whose surface served as preferential sites for nanoparticle aggregation (shown in the inset of Figure 3C), forming supramolecular branched structures (Figure 3C shows a typical TEM image of these structures). EDS analysis of these nanoparticle aggregates corroborated that their principal component is Ag (Figure 3D). Figure 3E shows a SAED pattern of a branch of the particle aggregate shown in Figure 3C. In this pattern, bright spots that can be indexed to the (111) zone axis of the metallic silver are observed, suggesting that the aggregation of the Ag nanoparticles occurs by a spontaneous oriented attachment, as it has been reported in other nanoparticle systems.28,29 Interestingly, some of the diffraction spots are associated to 1/3(224) forbidden reflections, which are usually observed in very thin nanostructures of fcc metals with (111) stacking faults.13,17,30


Microstructural, spectroscopic, and antibacterial properties of silver-based hybrid nanostructures biosynthesized using extracts of coriander leaves and seeds
TEM studies of sample L-0.5M.Notes: (A) TEM micrograph. The inset shows the SAED pattern of the area shown in the micrograph. The orange numbers are Miller indexes and indicate the crystallographic planes associated to the observed diffraction rings. (B) Histogram of the particle diameter distribution. (C) TEM image of a nanoparticle aggregate with a branched structure. The inset shows a high magnification TEM micrograph of a branch of this aggregate. (D) EDS spectrum of the supramolecular structure observed in panel C. The traces of Cu correspond to the copper TEM grid. The trace of C is probably partially related to the presence of organic material adsorbed by the Ag nanoparticles from the coriander extract and the carbon present in the coating of the TEM grid. (E) SAED pattern of the branch of the nanoparticle aggregate highlighted by an orange circle in panel C. The numbers and / symbol – indicate Miller indexes associated to crystallographic planes; orange numbers are related to forbidden reflections and white ones to reflections expected according Bragg’s law; [ ] indicates a crystallografic direction, in this case, the zone axis.Abbreviations: TEM, transmission electron microscope; SAED, selected-area electron diffraction; L-0.5M, final colloid obtained using coriander leaf extract and 0.5 M AgNO3; EDS, energy dispersive spectrometry; ZA, zone axis; Ag, silver; Cu, copper; C, carbon.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036574&req=5

f3-ijn-11-4787: TEM studies of sample L-0.5M.Notes: (A) TEM micrograph. The inset shows the SAED pattern of the area shown in the micrograph. The orange numbers are Miller indexes and indicate the crystallographic planes associated to the observed diffraction rings. (B) Histogram of the particle diameter distribution. (C) TEM image of a nanoparticle aggregate with a branched structure. The inset shows a high magnification TEM micrograph of a branch of this aggregate. (D) EDS spectrum of the supramolecular structure observed in panel C. The traces of Cu correspond to the copper TEM grid. The trace of C is probably partially related to the presence of organic material adsorbed by the Ag nanoparticles from the coriander extract and the carbon present in the coating of the TEM grid. (E) SAED pattern of the branch of the nanoparticle aggregate highlighted by an orange circle in panel C. The numbers and / symbol – indicate Miller indexes associated to crystallographic planes; orange numbers are related to forbidden reflections and white ones to reflections expected according Bragg’s law; [ ] indicates a crystallografic direction, in this case, the zone axis.Abbreviations: TEM, transmission electron microscope; SAED, selected-area electron diffraction; L-0.5M, final colloid obtained using coriander leaf extract and 0.5 M AgNO3; EDS, energy dispersive spectrometry; ZA, zone axis; Ag, silver; Cu, copper; C, carbon.
Mentions: An increase in the concentration of AgNO3 during biosynthesis with respect to the concentration of coriander leaf or seed extracts resulted in an increase in the degree of polydispersity of the resulting nanoparticles, owing to the occurrence of secondary particle growth by aggregation and coalescence, and probably by Ostwald ripening.25 In this manner, a broad and asymmetric size distribution was found for sample L-0.5M (Figure 3A and B). However, most particles of this sample (~90%) displayed diameters smaller than 10 nm, and ~45% exhibited sizes smaller than 5 nm. This is an interesting characteristic of this sample because previous results have indicated that the Ag nanoparticles of sizes smaller than 10 nm exhibit potent antibacterial26 and catalytic27 activities. On the other hand, the biggest particles (with sizes of tens of nanometers) tended to coalesce into elongated particles, whose surface served as preferential sites for nanoparticle aggregation (shown in the inset of Figure 3C), forming supramolecular branched structures (Figure 3C shows a typical TEM image of these structures). EDS analysis of these nanoparticle aggregates corroborated that their principal component is Ag (Figure 3D). Figure 3E shows a SAED pattern of a branch of the particle aggregate shown in Figure 3C. In this pattern, bright spots that can be indexed to the (111) zone axis of the metallic silver are observed, suggesting that the aggregation of the Ag nanoparticles occurs by a spontaneous oriented attachment, as it has been reported in other nanoparticle systems.28,29 Interestingly, some of the diffraction spots are associated to 1/3(224) forbidden reflections, which are usually observed in very thin nanostructures of fcc metals with (111) stacking faults.13,17,30

View Article: PubMed Central - PubMed

ABSTRACT

Coriander leaves and seeds have been highly appreciated since ancient times, not only due to their pleasant flavors but also due to their inhibitory activity on food degradation and their beneficial properties for health, both ascribed to their strong antioxidant activity. Recently, it has been shown that coriander leaf extracts can mediate the synthesis of metallic nanoparticles through oxidation/reduction reactions. In the present study, extracts of coriander leaves and seeds have been used as reaction media for the wet chemical synthesis of ultrafine silver nanoparticles and nanoparticle clusters, with urchin- and tree-like shapes, coated by biomolecules (mainly, proteins and polyphenols). In this greener route of nanostructure preparation, the active biocompounds of coriander simultaneously play the roles of reducing and stabilizing agents. The morphological and microstructural studies of the resulting biosynthesized silver nanostructures revealed that the nanostructures prepared with a small concentration of the precursor Ag salt (AgNO3 =5 mM) exhibit an ultrafine size and a narrow size distribution, whereas particles synthesized with high concentrations of the precursor Ag salt (AgNO3 =0.5 M) are polydisperse and formation of supramolecular structures occurs. Fourier transform infrared and Raman spectroscopy studies indicated that the bioreduction of the Ag− ions takes place through their interactions with free amines, carboxylate ions, and hydroxyl groups. As a consequence of such interactions, residues of proteins and polyphenols cap the biosynthesized Ag nanoparticles providing them a hybrid core/shell structure. In addition, these biosynthesized Ag nanomaterials exhibited size-dependent plasmon extinction bands and enhanced bactericidal activities against both Gram-positive and Gram-negative bacteria, displaying minimal inhibitory Ag concentrations lower than typical values reported in the literature for Ag nanoparticles, probably due to the synergy of the bactericidal activities of the Ag nanoparticle cores and their capping ligands.

No MeSH data available.


Related in: MedlinePlus