Anh-Tuan Le

Silver nanoparticles: synthesis, properties, toxicology, applications and perspectives

In recent years the outbreak of re-emerging and emerging infectious diseases has been a significant burden on global economies and public health. The growth of population and urbanization along with poor water supply and environmental hygiene are the main reasons for the increase in outbreak of infectious pathogens. Transmission of infectious pathogens to the community has caused outbreaks of diseases such as influenza (A/H5N1), diarrhea (Escherichia coli), cholera (Vibrio cholera), etc throughout the world. The comprehensive treatments of environments containing infectious pathogens using advanced disinfectant nanomaterials have been proposed for prevention of the outbreaks. Among these nanomaterials, silver nanoparticles (Ag-NPs) with unique properties of high antimicrobial activity have attracted much interest from scientists and technologists to develop nanosilver-based disinfectant products. This article aims to review the synthesis routes and antimicrobial effects of Ag-NPs against various pathogens including bacteria, fungi and virus. Toxicology considerations of Ag-NPs to humans and ecology are discussed in detail. Some current applications of Ag-NPs in water-, air- and surface- disinfection are described. Finally, future prospects of Ag-NPs for treatment and prevention of currently emerging infections are discussed.

Powerful colloidal silver nanoparticles for the prevention of gastrointestinal bacterial infections

In this work we have demonstrated a powerful disinfectant ability of colloidal silver nanoparticles (NPs) for the prevention of gastrointestinal bacterial infections. The silver NPs colloid was synthesized by a UV-enhanced chemical precipitation. Two gastrointestinal bacterial strains of Escherichia coli (ATCC 43888-O157:k-:H7) and Vibrio cholerae (O1) were used to verify the antibacterial activity of the as-prepared silver NPs colloid by means of surface disinfection assay in agar plates and turbidity assay in liquid media. Transmission electron microscopy was also employed to analyze the ultrastructural changes of bacterial cells caused by silver NPs. Noticeably, our silver NPs colloid displayed a highly effective bactericidal effect against two tested gastrointestinal bacterial strains at a silver concentration as low as 3mgl 1 . More importantly, the silver NPs colloid showed an enhancement of antibacterial activity and long-lasting disinfectant effect as compared to conventional chloramin B (5%) disinfection agent. These advantages of the as-prepared colloidal silver NPs make them very promising for environmental treatments contaminated with gastrointestinal bacteria and other infectious pathogens. Moreover, the powerful disinfectant activity of silver-containing materials can also help in controlling and preventing further outbreak of diseases.

Decoration of silver nanoparticles on multiwalled carbon nanotubes: antibacterial mechanism and ultrastructural analysis

Recently, development of carbon nanocomposites composed of carbon nanostructures and metal nanoparticles has attracted much interests because of their large potential for technological applications such as catalyst, sensor, biomedicine, and disinfection. In this work, we established a simple chemistry method to synthesize multiwalled carbon nanotubes (MWCNTs) decorated with silver nanoparticles (Ag-NPs) using amodified photochemical reaction (Tollens process). The formation and interaction of Ag-NPs with functionalized groups on the surface of MWCNTs were analyzed by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy. The average size of Ag-NPs on the MWCNTs was approximately ∼7nm with nearly uniform size distribution. Antibacterial effect of Ag-MWCNTs nanocomposites was evaluated against two pathogenic bacteria including Gram-negative Escherichia Coli and Gram-positive Staphylococcus aureus bacteria. Interaction and bactericidal mechanism of Ag-MWCNTs with tested bacteria was studied by adapting the electron microscopy. Analysis on ultrastructural changes of bacterial cells indicates that antibacterial actionmechanism of Ag-MWCNTs is physical interaction with cellmembrane, the large formation of cell-Ag-MWCNTs aggregates, and faster destructibility of cell membrane and disruption of membrane function, hence resulting in cells death.

Enhanced magnetic anisotropy and heating efficiency in multi-functional manganese ferrite/graphene oxide nanostructures.

A promising nanocomposite material composed of MnFe2O4 (MFO) nanoparticles of ∼17 nm diameter deposited onto graphene oxide (GO) nanosheets was successfully synthesized using a modified co-precipitation method. X-ray diffraction, transmission electron microscopy, and selected area electron diffraction confirmed the quality of the synthesized samples. Fourier transform infrared measurements and analysis evidenced that the MFO nanoparticles were attached to the GO surface. Magnetic measurements and analysis using the modified Langevin model evidenced the superparamagnetic characteristic of both the bare MFO nanoparticles and the MFO-GO nanocomposite at room temperature, and an appreciable increase of the effective anisotropy for the MFO-GO sample. Magnetic hyperthermia experiments performed by both calorimetric and ac magnetometry methods indicated that relative to the bare MFO nanoparticles, the heating efficiency of the MFO-GO nanocomposite was similar at low ac fields (0-300 Oe) but became progressively larger with increasing ac fields (>300 Oe). This has been related to the higher effective anisotropy of the MFO-GO nanocomposite. In comparison with the bare MFO nanoparticles, a smaller reduction in the heating efficiency was observed in the MFO-GO composites when embedded in agar or when their concentration was increased, indicating that the GO helped minimize the physical rotation and aggregation of the MFO nanoparticles. These findings can be of practical importance in exploiting this type of nanocomposite for advanced hyperthermia. Magnetoimpedance-based biodetection studies also indicated that the MFO-GO nanocomposite could be used as a promising magnetic biomarker in biosensing applications.

Microstructure and Magnetic Properties of Au-doped Finemet-type Alloy

In this report, we demonstrate a comprehensive analysis of the effects of Au addition on the microstructure and magnetic properties of Fe 73.5 Si 13.5 B 9 Nb₃Au₁ Finemet-type alloy. It was found that the as-quenched alloys were the amorphous state and turned into nanocrystalline state under heat treatments. The DSC analysis indicates that the sharply exothermal peak corresponding to the crystallization of the α-Fe(Si) was observed at 547- 579℃ depending on the heating rates, which is little higher than that of original Finemet (542-570℃, respectively). Besides, the thermomagnetic result confirmed that the full substitution of Cu by Au with the single phase structure in the M(T) curve along cooling cycle. Ultrasoft magnetic properties of the nanocrystallized samples were significantly enhanced by the proper annealing such as the increase of permeability and the decrease of the coercivity. The optimum annealing condition was found at the annealing temperature of 540℃ and the increase of the annealing time up to 90 min.

Cytotoxicity and antiviral activity of electrochemical - synthesized silver nanoparticles against poliovirus.

Silver nanoparticles (AgNPs) have been proven to have noticeable cytotoxicity in vitro and antiviral activity against some types of enveloped viruses. This paper presents the cytotoxicity and antiviral activity of pure AgNPs synthesized by the electrochemical method, towards cell culture and poliovirus (a non-enveloped virus). Prepared AgNPs were characterized by ultraviolet-visible spectroscopy, energy-dispersive X-ray spectroscopy and transmission electron microscopy. Before incubation with poliovirus, different concentrations of AgNPs were added to human rhabdomyosarcoma (RD) cell monolayers seeded in 96 well plates for testing their cytotoxicity. The in vitro cytotoxicity and anti-poliovirus activity of AgNPs were daily assessed for cytopathic effect (CPE) through inverted light microscopy. CPE in the tested wells was determined in comparison with those in wells of negative and positive control. Structure analysis showed that AgNPs were formed with a quasi-spherical shape with mean size about 7.1nm and high purity. No CPE of RD cells was seen in wells at the time point of 48h post-incubation with AgNPs at concentration up to 100ppm. The anti-poliovirus activity of AgNPs was determined at 3.13ppm corresponding to the viral concentration of 1TCID50 (Tissue Culture Infective Dose) after 30min, and 10TCID50 after 60min, the cell viability was found up to 98% at 48h post-infection, with no CPE found. Whereas, a strong CPE of RD cells was found at 48h post-infection with the mixture of AgNPs and poliovirus at concentration of 100TCID50, and in wells of positive controls. With mentioned advantages, electrochemical-synthesized AgNPs are promising candidate for advanced biomedical and disinfection applications.

Photochemical synthesis of highly bactericidal silver nanoparticles

In this work we describe an experimental technique that makes it possible to obtain highly bactericidal silver nanoparticles (NPs). Synthesis was carried out using nontoxic reagents, and the technique consisted of reducing silver by glucose via UV irradiation in the presence of oleic or myristic acids as stabilizers. The size of the NPs fell in the range of 4–18 nm, and the average diameter was about 7 ± 1 nm (oleic acid) and 4 ± 1 nm (myristic acid). Unlike previous reports, where the Tollens reaction was used only with the assistance of thermal activation, we conducted the UV reduction of a silver nitrate solution, glucose, and the stabilizer at room temperature for the first time. The minimum inhibition concentration of nanosized silver against a gram-negative Escherichia coli was 1 μg/ml. Thus, the activity of the NPs appeared to be considerably higher than that of nanosilver samples that are currently known.

Enhancement of solar cell efficiency using perovskite dyes deposited via a two-step process

This study examined the effect of different thick-compact-TiO2 blocking layers (c-TiO2) and mesoporous-TiO2 layers (m-TiO2) on the efficiency of perovskite cells. Anatase c-TiO2 layers with different thicknesses were in situ deposited onto a FTO/glass substrate at a temperature of 400 °C via nano-cluster deposition (NCD). The 80 nm-thick c-TiO2 layers were deposited with good step-coverage on the rough-FTO surface, and were in situ crystallized via an anatase phase. The perovskite cells with 80 nm-thick c-TiO2 and 600 nm-thick-m-TiO2 layers showed the highest photovoltaic parameters: JSC of 21.0 mA cm−2, VOC of 0.89 V, FF of 62%, and efficiency (η) of 11.5%. For enhancement of the cell efficiency, solar cells with bi-layer perovskite dyes were deposited via a two-step process onto the m-TiO2 layer (200 nm)/TiO2 blocking layers (80 nm) and showed VOC and FF values of approximately 1.06 and 64%, respectively, with a maximum photo-conversion efficiency of approximately 14.2%.

Functional manganese ferrite/graphene oxide nanocomposites: effects of graphene oxide on the adsorption mechanisms of organic MB dye and inorganic As(V) ions from aqueous solution

In this study, manganese ferrite-graphene oxide (MFO-GO) nanocomposites were prepared via a co-precipitation reaction of Fe3+ and Mn2+ ions in a GO suspension. The effects of graphene oxide on the physicochemical characteristics, magnetic properties and adsorption activities of the MFO-GO nanocomposites were studied. Methylene blue (MB) and arsenic(V) were used in this study as model water pollutants. With an increase in the GO content in the range of 10 wt% to 50 wt%, the removal efficiency for both MB dye and arsenic(V) ions was improved. Our adsorption data revealed that the adsorption behavior of MB dye showed good agreement with the Langmuir isotherm model and pseudo-second-order equation, whereas the Freundlich isotherm model was more suitable for simulating the adsorption process of arsenic(V) ions on the MFO-GO nanocomposites. In addition, an important role of the GO content in the adsorption mechanisms of both MB dye and arsenic(V) ions was found, in which GO nanosheets play a key role in the mechanisms of electrostatic/ionic interactions, oxygen-containing groups and π–π conjugation in the case of the adsorption of MB dye, whereas the role of the GO content is mainly related to the mechanism of electrostatic/ionic interactions in the case of the adsorption of arsenic(V). Graphene oxide has the functions of increasing the number of active binding sites comprising oxygen-containing functional groups, reducing the agglomeration of MFO nanoparticles, increasing the number of adsorption sites, and improving the electrostatic/ionic interactions between adsorbents and adsorbates in order to enhance the adsorption performance of cationic organic dyes and/or heavy metal anions from aqueous solutions.

Microstructure and Chemo-Physical Characterizations of Functional Graphene Oxide-Iron Oxide-Silver Ternary Nanocomposite Synthesized by One-Pot Hydrothermal Method

In this work, a functional graphene oxide-iron oxide-silver (GO-Fe3O4-Ag) ternary nanocomposite was synthesized by using one-pot hydrothermal treatments of mixture solutions of silver nitrate (AgNO3), ferrous chloride tetrahydrate (FeCl2 4H2O), polyvinylpyrrolidone (PVP), graphene oxide (GO), and ammonium hydroxide solution (NH4OH). The systematic effects of synthesis conditions on the microstructure and formation of binary and ternary composite systems were studied. Importantly, high-crystalline GO-Fe3O4-Ag ternary nanomaterials with average sizes of Fe3O4 particles ~16 nm and of Ag particles ~20 nm were obtained at optimized conditions (125 °C, 2.5 mM of AgNO3 and 5 mL of NH4OH). Magnetic analysis indicated that the saturated magnetization value of Fe3O4-Ag binary composite sample (~73.1 emu/g) was improved as compared with pure Fe3O4 nanoparticles (~60.6 emu/g), while this of GO-Fe3O4-Ag ternary composite sample was about 57.3 emu/g. With exhibited advantages of low-cost, high purity and short synthesis time, the hydrothermal-synthesized GO-Fe3O4-Ag ternary nanocomposite can be a promising candidate for advanced environmental catalyst and biomedical applications.