In this scholarly study, silver nanoparticles (Ag NPs) coated with catechol-conjugated
In this scholarly study, silver nanoparticles (Ag NPs) coated with catechol-conjugated chitosan (CSS) were prepared using green methods. by conjugation of catechol to chitosan, which was confirmed by NMR, FT-IR, and XRD9. As demonstrated in Fig.?2a, the aromatic protons featured in catechol were successfully detected in the 1H NMR spectrum of CSS. Fig.?2b shows the FT-IR spectrum for CS and CCS. The CSS spectrum shows several fresh absorption peaks at 1289, 820, and 780?cm?1, related to SB 431542 pontent inhibitor the characteristic absorption peaks of phenolic constructions14. The characteristic absorption peak (CNH2 group) at 1590?cm?1 decreased dramatically SB 431542 pontent inhibitor and the absorption maximum (amide type II) at 1530?cm?1 increased in intensity, revealing the amino organizations on chitosan reacted with the catechol to form amide15. XRD analysis was carried out to further investigate the phase structural changes from CS to CCS. As demonstrated in Fig.?2c, XRD pattern analysis of CS shows two peaks at 12 and 21 related to the hydrated crystals and anhydrous crystals, respectively. Therein, the impressive maximum at 21 is definitely attributed to strong hydrogen bonds within or between the molecules of CS16. As demonstrated in the XRD pattern analysis of CSS, the maximum at 21 was weakened dramatically, revealing a partial breakage of the hydrogen bonds. The results indicated that catechol conjugation would significantly decrease the rigidity of chitosan backbones, which contribute to the significantly enhanced water-solubility of CSS. Like a reducing and stabilizing agent, CSS was added to a metallic nitrate aqueous remedy to prepare the CSS-Ag NPs. A schematic of the green synthesis process is demonstrated in Fig.?1. Open in a separate window Number 2 Characterization of CSS. (a) 1H NMR spectrum of CSS, (b) FT-IR spectrum of CS and CSS, (c) XRD analysis of CS and CSS. Number?3a shows the UV-vis spectrum and corresponding optical picture of the synthesized CSS-Ag NP remedy. A characteristic sterling silver surface plasmon resonance (SPR) absorption band was observed at 408?nm, indicating a successful SB 431542 pontent inhibitor formation of silver nanoparticles without aggregation8. The transparent yellow of the CSS-Ag NP solution also confirmed the UV-vis result. Open in a separate window Figure 3 Dispersion property of CSS-Ag NPs solution. (a) UV-vis spectrum and optical photo of CSS-Ag NPs solution, (b) size distribution of CSS-Ag NPs measured by DLS, and insert shows a TEM image of CSS-Ag NPs, (c) TEM image of CSS-Ag NPs, (d) size distribution of CSS-Ag NPs measured by TEM. Figure?3bCd shows the size distribution of CSS-Ag NPs measured by TEM and DLS. The TEM image indicates that the CSS-Ag NPs were spherical with a narrow size distribution, which coincided with the DLS result. The hydrodynamic diameter of the CSS-Ag NPs evaluated by DLS was 48.9??3.15?nm. The average size of the CSS-Ag NPs obtained from the TEM images was 44.2??5.2?nm. Antibacterial activities of CSS-Ag NPs In our prior study, the minimum inhibitory concentration (MIC) of CSS-Ag NPs was measured to characterize the antibacterial activity, which was Rabbit Polyclonal to BVES defined as the lowest concentration sufficient to prevent bacterial growth17. If we want to further investigate how CSS-Ag NPs can kill bacteria, we need to coculture the bacteria with a minimum bactericidal concentration of nanoparticles SB 431542 pontent inhibitor to make sure all cells are killed. Therefore, the minimum bactericidal concentrations (MBCs) of CSS-Ag NPs were measured by counting colony-forming units (CFUs). As shown in Fig.?4, no viable colony remained on the agar plate after exposure to CSS-Ag NPs at low concentration, indicating that the cells were killed. This demonstrated that CSS-Ag NPs exhibited remarkable antibacterial activities at very low dosages, with an MBC of 14?g/mL against and 25?g/mL against S. aureus. Open in a separate window Figure 4 Images of CFU counting. (a,b) Untreated E. coil and S. aureus; (c) E. coil treated with CSS-Ag NPs (14?g/ml, silver concentration); (d) S. aureus treated with CSS-Ag NPs (25?g/ml, silver concentration). Ultrastructural changes of the bacteria after exposure to CSS-Ag NPs Interestingly, the MBC values revealed that the CSS-Ag NPs exhibited an increased toxicity.