Abstract
Triangular silver nanoplates were prepared by using the seeding growth approach with the presence of citrate-stabilized silver seeds and a mixture of gelatin–chitosan as the protecting agent. By understanding the critical role of reaction components, the synthesis process was improved to prepare the triangular nanoplates with high yield and efficiency. Different morphologies of silver nanostructures, such as triangular nanoplates, hexagonal nanoprisms, or nanodisks, can be obtained by changing experimental parameters, including precursor AgNO3 volume, gelatin–chitosan concentration ratios, and the pH conditions. The edge lengths of triangular silver nanoplates were successfully controlled, primarily through the addition of silver nitrate under appropriate condition. As-prepared triangular silver nanoplates were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), UV-Vis, Fourier transform infrared spectroscopy (FT-IR), and X-Ray diffraction (XRD). Silver nanoplates had an average edge length of 65–80 nm depending on experimental conditions and exhibited a surface plasma resonance absorbance peak at 340, 450, and 700 nm. The specific interactions of gelatin and chitosan with triangular AgNPs were demonstrated by FT-IR. Based on the characterization, the growth mechanism of triangular silver nanoplates was theoretically proposed regarding the twinned crystal of the initial nanoparticle seeds and the crystal face-blocking role of the gelatin–chitosan mixture. Moreover, the antibacterial activity of triangular silver nanoplates was considerably improved in comparison with that of spherical shape when tested against Gram-positive and Gram-negative bacteria species, with 6.0 ug/mL of triangular silver nanoplates as the MBC (Minimum bactericidal concentration) for Escherichia coli and Vibrio cholera, and 8.0 ug/mL as the MBC for Staphylococcus aureus and Pseudomonas aeruginosa. The MIC (Minimum inhibitory concentration) of triangular Ag nanoplates was 4.0 ug/mL for E. coli, V. cholera, S. aureus, and P. aeruginosa.
Highlights
Nanoscale materials have been extensively studied with respect to their potential applications and synthesis procedures [1,2,3,4,5,6,7]
3.0 × 10−4 M, 20 mL of trisodium citrate (TSC) 5.0 × 10−4 M, 60 μL solution of NaBH4 0.1 M), (b) the inset of the size distribution of formed seeds, (c) UV-Vis spectra of triangular AgNPs synthesized distribution of formed seeds, (c) UV-Vis spectra of triangular AgNPs synthesized by different volumes of AgNO3 0.01 M, 6.0 mL mixed solution of gelatin (0.2%, w/v)-chitosan (0.06%, w/v), (d) the inset of the snipped tips and edge length of a silver nanoplate theme, and (e) digital photographs of the samples at different volumes of AgNO3 0.01 M
The formation of triangular AgNPs in colloidal dispersion can be identified through the appearance of the surface plasmon resonance (SPR) peaks at the positions of about 340, 450, and 650 nm, which attributed to the out-of-plane quadrupole, in-plane quadrupole, and in-plane dipole resonances of triangular silver nanoplates, respectively [16,41]
Summary
Nanoscale materials have been extensively studied with respect to their potential applications and synthesis procedures [1,2,3,4,5,6,7]. With the presence of chitosan as a cationic natural polymer, under a suitable pH value [31,32], the formed triangular AgNPs could effectively interact with the negatively charged membranes of organisms to release higher concentration of ion Ag+ , thereby improving the bactericidal properties of the formed nanoparticles This mechanism was elaborated by the study of Sukdeb et al where coagulation of nanoparticles, caused by the charge neutralized interaction, was proposed to bring about synergistic effects of silver nanoparticles and cationic protecting agent on negative charge cells [13]. Antibacterial activities of the synthesized triangular AgNPs were evaluated against various species of bacteria, including Staphylococcus aureus, Escherichia coli, Vibrio cholerae, and Pseudomonas aeruginosa
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