Green synthesis of bio-molecule encapsulated magnetic silver nanoparticles and their antibacterial activity

Silica-based silver nanocomposite 80S/Ag as Aggregatibacter actinomycetemcomitans inhibitor and its in vitro bioactivity

Background/purpose

As a commonly-found pathogen in periodontal disease, Aggregatibacter actinomycetemcomitans has been reported with several antibiotic resistance. Thus, to develop an alternative and protective therapy for A. actinomycetemcomitans infections is urgently needed in dentistry. In this study, we sought to synthesize a silica-based material to deliver silver nanoparticles for antibacterial purposes. Also, the bioactivities were examined via analyzing the formation of hydroxyapatite.

Materials and methods

The 80S/Ag powders were prepared by the evaporation-induced self-assembly method, with Si, Ca, P, and Ag composition ratios of 80, 15, 5, and 1/5/10 (mole percentage), respectively. The nitrogen adsorption-desorption isotherms, transmission electron microscope, selected area electron diffraction, and Fourier transform infrared spectroscopy were conducted for textural analyses. The disk diffusion test was carried out against A. actinomycetemcomitans strain ATCC 29523. In vitro bioactivity assessment involved soaking 80S/Ag membrane powders in acellular simulated body fluid.

Results

We successfully developed a material consisting of Si, Ca, P, and Ag, namely the 80S/Ag. In the antibacterial testing, the 80S/Ag demonstrated antibacterial activity against the commonly-found oral pathogen, A. actinomycetemcomitans, with a long-lasting effect for 168h. The formation of hydroxyapatite in simulated body fluid highlighted the characteristic of dentine remineralization for the 80S/Ag. The increased pH values after immersion in simulated body fluid would help neutralize the acidic oral environment.

Conclusion

Our results indicate that 80S/Ag possesses remarkable antibacterial properties, hydroxyapatite formation, and increased pH values after immersion in simulated body fluid, supporting the potential therapeutic application of 80S/Ag for treating periodontal disease.

Size controlled biosynthesis of silver nanoparticles using Ophiorrhiza mungos, Ophiorrhiza harrisiana and Ophiorrhiza rugosa aqueous leaf extract and their antimicrobial activity

In this work, the aqueous leaf extracts of three Ophiorrhiza genus species, namely Ophiorrhiza mungos (Om), Ophiorrhiza harrisiana (Oh) and Ophiorrhiza rugosa (Or), have been used as the reducing and capping agents to control the size of AgNPs, Om-AgNPs, Oh-AgNPs and Or-AgNPs, respectively and found to be an effective antimicrobial agent against a wide range of bacteria and fungi. The biosynthesized AgNPs were studied by UV-Visible spectrophotometer, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray, transmission electron microscopy (TEM) and Fourier transform infrared spectrometer (FTIR). The average particle sizes of Om-AgNPs, Oh-AgNPs and Or-AgNPs were measured as 17 nm, 22 nm and 26 nm, respectively, and observed to be spherical and face-centered cubic crystals. The antibacterial test of synthesized AgNPs was performed against Staphylococcus aureus, Bacillus cereus, Escherichia coli, and Vibrio cholerae where the maximum antibacterial activity was observed by reducing the nano-size and increasing the silver content of AgNPs. The antifungal effect of these three types of AgNPs on Penicillium notatum and Aspergillus niger was also evaluated and their growth with AgNPs concentrations of 450 μg/mL was inhibited up to 80-90% and 55-70%, respectively. The size-control synthesis of AgNPs using the Ophiorrhiza genus species is presented here for the first time where the synthesized AgNPs showed higher stability and antimicrobial activities. Therefore, this study might lead to synthesize AgNPs with different morphologies using plant extracts of the same genus but from different species and provide strong encouragement for future applications in treating infectious diseases.

Green synthesis of zinc oxide nanoparticles using Cocos nucifera leaf extract: characterization, antimicrobial, antioxidant and photocatalytic activity

Zinc oxide nanoparticles (ZnO NPs) have been successfully prepared using Cocos nucifera leaf extract and their antimicrobial, antioxidant and photocatalytic activity investigated. The structural, compositional and morphological properties of the NPs were recorded and studied systematically to confirm the synthesis. The aqueous suspension of NPs showed an ultraviolet-visible (UV-Vis) absorption maxima of 370 nm, indicating primarily its formation. X-ray diffraction analysis identified the NPs with a hexagonal wurtzite structure and an average particle size of 16.6 nm. Fourier transform infrared analysis identified some biomolecules and functional groups in the leaf extract as responsible for the encapsulation and stabilization of ZnO NPs. Energy-dispersive X-ray analysis showed the desired elemental compositions in the material. A flower-shaped morphology of ZnO NPs was observed by scanning electron microscopy, with a grain size of around 15 nm. The optical properties of the NPs were studied by UV-Vis spectroscopy, and the band gap was calculated as 3.37 eV. The prepared ZnO NPs have demonstrated antimicrobial activity against T. harzianum and S. aureus, with a zone of inhibition of 14 and 10 mm, respectively. The photocatalytic behaviour of ZnO NPs showed absorbance degradation at around 640 nm and it discoloured methylene blue dye after 1 h, with a degradation maximum of 84.29%. Thus, the prepared ZnO NPs could potentially be used in antibiotic development and pharmaceutical industries, and as photocatalysts.

In vitro cytotoxicity and antibiotic application of green route surface modified ferromagnetic TiO2 nanoparticles

The enormous numbers of applications of TiO₂ nanoparticles (NPs) cause concern about their risk to the environment and human health. Consequently, motivated by the necessity of searching for new sources of TiO₂ NPs of low cytotoxicity with antibacterial activity, we synthesized TiO₂ NPs by a green route using a solution of titanium(iv) isopropoxide as a precursor and an aqueous extract of Artocarpus heterophyllus leaf as a reducing and surface modifying agent. We investigated their structure, shape, size, and magnetic properties, and evaluated their antibiotic application and cytotoxicity. The synthesized TiO₂ NPs were applied against two Gram-negative bacteria (E. coli and S. typhimurium) and two Gram-positive bacteria (S. aureus and B. subtilis) to observe their antibacterial activity; and eventually clear zones of inhibition formed by the TiO₂ NPs were obtained. Moreover, after exposing the synthesized TiO₂ NPs to HeLa cells (carcinoma cells) and Vero cells (normal cells), no toxic effect was found up to a dose of 1000 mg L⁻¹, indicating the safe use of the samples up to at least 1000 mg L⁻¹. However, toxic effects on HeLa cells and Vero cells were observed at doses of 2000 mg L⁻¹ and 3000 mg L⁻¹, respectively. These results indicate the safe use of Artocarpus heterophyllus leaf extract mediated synthesized TiO₂ NPs in their potential applications.

Artocarpus heterophyllus leaf extract mediated green synthesized TiO₂ nanoparticles exhibit less toxicity with high antibacterial activity.