Due to size- and shape-dependent properties, a shape-controlled synthesis of silver nanoparticles (AgNPs) is one of the research challenging topics for their production and potential applications. This work reported the simple eco-friendly syntheses of different shaped AgNPs controlled by the plasmid DNA content and light emitting diodes (LEDs) irradiation. The synthesized AgNPs appeared as yellow, orange and green colloidal AgNPs, which transmission electron microscope (TEM) images revealed their different shapes; spherical AgNPs, a mixture of spherical and hexagonal AgNPs, and a mixture of spherical, hexagonal and corner-truncated triangle AgNPs, respectively. The average sizes of spherical, hexagonal and corner-truncated triangle AgNPs in the green colloidal solution were 12.32 ± 2.22, 23.03 ± 6.62 and 15.84 ± 4.31 nm, respectively. The analyses of X-ray diffraction, selected area electron diffraction and high-resolution TEM indicated the crystalline nature of the synthesized particles as the face-centred cubic silver. All synthesized AgNPs exhibited antioxidant activities similarly, whereas the yellow colloidal AgNPs exhibited the strongest antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus as compared with the green and orange colloidal AgNPs.
Background: Synthesis of spherical silver nanoparticles is mostly reported but the use of DNA, especially short oligonucleotides, to mediate the production of anisotropic AgNPs is still questioned. Objective: This work aims to use 30-mer oligo(dA) and oligo(dC) (or A30 and C30) to assist the formation of anisotropic AgNPs under blue LED irradiation. Method: We reported a simple synthesis reaction containing AgNO3, A30 (or C30), and sodium borohydride, which were exposed to 460 nm LED light for 24 h. The obtained AgNPs were characterized and assayed for antioxidant and antibacterial activities. Results: With exposure to 460 nm LED light, A30 and C30 could mediate the transition from spherical to hexagonal shapes of AgNPs with average sizes of 16 18 nm. Analyses of X-ray diffraction and selected area electron diffraction indicated the face-centered cubic crystal structure of AgNPs. A30- and C30-AgNPs exhibited similar antioxidant activities; IC50 of 78.68 ± 0.83 and 73.91 ± 0.46 μg mL1, respectively. They also possessed antibacterial activities against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Scanning electron micrographs revealed surface pores and rupture of bacterial cells in response to AgNPs. Conclusion: Oligonucleotides of only 30 residues are shown to assist the generation of anisotropic AgNPs under activation of blue LED irradiation, in which the synthesized AgNPs still exhibited antioxidant and antibacterial activities, suggesting a simple method to synthesize non-spherical AgNPs using short-length DNA.
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