Antimicrobial Synergistic Effect Between Ag and Zn in Ag-ZnO·mSiO2 Silicate Composite with High Specific Surface Area

Antimicrobial materials are widely used for inhibition of microorganisms in the environment. It has been established that bacterial growth can be restrained by silver nanoparticles. Combining these with other antimicrobial agents, such as ZnO, may increase the antimicrobial activity and the use of carrier substrate makes the material easier to handle. In the paper, we present an antimicrobial nanocomposite based on silver nanoparticles nucleated in general silicate nanostructure ZnO·mSiO₂. First, we prepared the silicate fine net nanostructure ZnO·mSiO₂ with zinc content up to 30 wt% by precipitation of sodium water glass in zinc acetate solution. Silver nanoparticles were then formed within the material by photoreduction of AgNO₃ on photoactive ZnO. This resulted into an Ag-ZnO·mSiO₂ composite with silica gel-like morphology and the specific surface area of 250 m²/g. The composite, alongside with pure AgNO₃ and clear ZnO·mSiO₂, were successfully tested for antimicrobial activity on both gram-positive and gram-negative bacterial strains and yeast Candida albicans. With respect to the silver content, the minimal inhibition concentration of Ag-ZnO·mSiO₂ was worse than AgNO₃ only for gram-negative strains. Moreover, we found a positive synergistic antimicrobial effect between Ag and Zn agents. These properties create an efficient and easily applicable antimicrobial material in the form of powder.

Environmentally sustainable route to SiO2@Au-Ag nanocomposites for biomedical and catalytic applications

A facile, sustainable, operationally simple and mild method for the synthesis of SiO2@Au-Ag nanocomposites (NCs) using Nephrolepis cordifolia tuber extract is described and its catalytic, antibacterial and cytotoxic properties were investigated. The fabricated SiO2@Au-Ag NCs were well characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) to determine the optical activity, size and morphology, elemental composition, functional groups present, crystallinity, thermal stability and chemical state respectively. The obtained SiO2@Au-Ag NCs exhibited spherical shape SiO2 decorated with Au and Ag nanoparticles. The diameter of the SiO2 nanoparticles ranges from 200-246 with average 3 nm diameter of Au and Ag NPs. Synthetic utility of this protocol has been demonstrated by exploring its effective catalytic activities for the solvent-free amidation of carboxylic acid with a primary amine with excellent yields. Moreover, the synthesized nanocomposite exhibited as noticeable antibacterial effect against Gram negative and Gram positive bacteria and better bio-compatibility against human keratinocytes. Thus, additive free SiO2@Au-Ag NCs display the potential for catalysis and biomedical applications.

Luminescent Silver-Purine Double Helicate: Synthesis, Self-Assembly and Antibacterial Action

The synthesis, self-assembly and antibacterial activity of a luminescent silver-purine double helicate is reported. The structure of the newly synthesized silver-supported helicate [C₃₆ H₂₄ N₁₆ O₄ Cl₅ Ag₁ ] was unambiguously characterized by single-crystal X-ray crystallography. It exhibited a bright bluish-green emission (λ_max =460 nm), when excited with 380 nm light. Microscopic investigations showed that the complex has a propensity to self-assemble into nanospheres. The antibacterial activity of this silver-containing helicate was studied against both Gram-positive and Gram-negative bacteria. MIC (minimal inhibitory concentration) values showed that the complex is very active against Gram-negative bacteria. Further internalization of the silver complex into E. coli bacteria was mapped with the help of microscopic techniques. These results are significant as silver was recently found to enhance antibiotic action against Gram-negative bacteria, raising hope in countering severe bacterial infections.

A hybrid antioxidizing and antibacterial material based on Ag-La2O3 nanocomposites

The Ag-La2O3 hybrid nanoparticles were prepared by loading Ag nanoparticles on the surface of the La2O3 nanorods. The synthesis was a one-step process where sodium borohydride was used as a reducing agent to convert silver ions into silver nanoparticles, which were further deposited on the La2O3 nanorods. Moreover, they were found evenly dispersed upon the surface of La2O3 supports. The as-prepared Ag-La2O3 nanocomposites showed anti-oxidizing and significant antibacterial effect in vitro. Using the results from transmission electron microscope (TEM), the plausible mechanism was also proposed to explain the inhibition of bacterial growth. The present strategy can be potentially extended to develop drug-labels and other antibacterial agents.