Spherical Particles of Zirconia-Titania of Hexagonal Structure from a Neutral Amine Route

Through the sol–gel process, using the so-called neutral amine route, spherical particles of 1:1 zirconia–titania were synthesized from zirconium(IV) and titanium(IV) butoxides as well as 1,12-diaminododecane as precursor species. The obtained product exhibited a hexagonal structure, as determinated by X-ray diffraction data. The obtained material was also characterized by thermogravimetry, differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, and surface area measurements. Despite the release of template molecules on heating, the spherical morphology was retained up to about 1200°C, at which the disruption of the spheres took place.     

Effects of Adsorbed Polyaniline on Redox Process on MoO3 Surface

The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press.     

Quartz crystal microbalance immunosensor for the detection of antibodies to double-stranded DNA

We report the development of a novel quartz crystal microbalance immunosensor with the simultaneous measurement of resonance frequency and motional resistance for the detection of antibodies to double-stranded DNA (dsDNA). The immobilization of poly(l-lysine) and subsequent complexation with DNA resulted in formation of a sensitive dsDNA-containing nanofilm on the surface of a gold electrode. Atomic force microscopy has been applied for the characterization of a poly(l-lysine)–DNA film. After the blocking with bovine serum albumin, the immunosensor in flow-injection mode was used to detect the antibodies to dsDNA in purified protein solutions of antibodies to dsDNA and to single-stranded DNA, monoclonal human immunoglobulin G, DNase I and in blood serum of patients with bronchial asthma and systemic lupus erythematosus. Experimental results indicate high sensitivity and selectivity of the immunosensor. In memoriam Prof. Victor G. Vinter     

Tubule Nanoclay‐Organic Heterostructures for Biomedical Applications

Natural halloysite nanotubes (HNTs) show unique hollow structure, high aspect ratio and adsorption ability, good biocompatibility, and low toxicity, which allow for various biomedical applications in the diagnosis and treatment of diseases. Here, advances in self‐assembly of halloysite for cell capturing and bacterial proliferation, coating on biological surfaces and related drug delivery, bone regeneration, bioscaffolds, and cell labeling are summarized. The in vivo toxicity of these clay nanotubes is discussed. Halloysite allows for 10–20% drug loading and can extend the delivery time to 10–100 h. These drug‐loaded nanotubes are doped into the polymer scaffolds to release the loaded drugs. The rough surfaces fabricated by self‐assembly of the clay nanotubes enhance the interactions with tumor cells, and the cell capture efficacy is significantly improved. Since halloysite has no toxicity toward microorganisms, the bacteria composed within these nanotubes can be explored in oil/water emulsion for petroleum spilling bioremediation. Coating of living cells with halloysite can control the cell growth and is not harmful to their viability. Quantum dots immobilized on halloysite were employed for cell labeling and imaging. The concluding academic results combined with the abundant availability of these natural nanotubes promise halloysite applications in personal healthcare and environmental remediation.     

Interfacing multicellular organisms with polyelectrolyte shells and nanoparticles: a Caenorhabtidis elegans study

We report the surface modification of microscopic live multicellular nematodes Caenorhabtidis elegans with polyelectrolyte multilayers (pure and doped with 20 nm gold nanoparticles) and the direct magnetic functionalization of nematodes with biocompatible magnetic nanoparticles. Magnetically functionalized "ironoxideclad" nematodes can be effectively separated and moved using an external magnetic field. The surface-functionalized nematodes preserve their viability and reproduction.     

Clay nanotube encapsulation for functional biocomposites

Natural halloysite clay nanotubes with 50 nm outer- and 15 nm inner- diameters are described as miniature vehicles for sustained release of drugs and proteins. The release time may be adjusted from 10 to 200 h with the tube surface polymeric coating. An explanation of sustained release through locking electrical potential at the nanotube ends is suggested. These biocompatible ceramic tubes may be also used for architectural construction of nanoshells on microbes through alternation with polycations to enhance the intrinsic properties of biological cells. Halloysite nanotubes (pristine or drug-loaded) are well mixable with polar and low-polar polymers allowing for functional biocomposites with enhanced mechanical strength, adhesivity and slow release of drugs or other chemical agents. Halloysite is nontoxic abundantly available from natural deposit material which does not require exfoliation or other complicated energy consuming processing.     

Comparative Toxicity of Fly Ash: An In Vitro Study

Fly ash produced during coal combustion is one of the major sources of air and water pollution, but the data on the impact of micrometer-size fly ash particles on human cells is still incomplete. Fly ash samples were collected from several electric power stations in the United States (Rockdale, TX; Dolet Hill, Mansfield, LA; Rockport, IN; Muskogee, OK) and from a metallurgic plant located in the Russian Federation (Chelyabinsk Electro-Metallurgical Works OJSC). The particles were characterized using dynamic light scattering, atomic force, and hyperspectral microscopy. According to chemical composition, the fly ash studied was ferro-alumino-silicate mineral containing substantial quantities of Ca, Mg, and a negligible concentration of K, Na, Mn, and Sr. The toxicity of the fly ash microparticles was assessed in vitro using HeLa cells (human cervical cancer cells) and Jurkat cells (immortalized human T lymphocytes). Incubation of cells with different concentrations of fly ash resulted in a dose-dependent decrease in cell viability for all fly ash variants. The most prominent cytotoxic effect in HeLa cells was produced by the ash particles from Rockdale, while the least was produced by the fly ash from Chelyabinsk. In Jurkat cells, the lowest toxicity was observed for fly ash collected from Rockport, Dolet Hill and Muscogee plants. The fly ash from Rockdale and Chelyabinsk induced DNA damage in HeLa cells, as revealed by the single cell electrophoresis, and disrupted the normal nuclear morphology. The interaction of fly ash microparticles of different origins with cells was visualized using dark-field microscopy and hyperspectral imaging. The size of ash particles appeared to be an important determinant of their toxicity, and the smallest fly ash particles from Chelyabinsk turned out to be the most cytotoxic to Jukart cells and the most genotoxic to HeLa cells.     

Layer-by-layer coating of bacteria with noble metal nanoparticles for surface-enhanced Raman scattering

A simple layer-by-layer method to coat the bacterial cells with gold and silver nanoparticles (AuNPs and AgNPs) for the acquisition of surface-enhanced Raman scattering (SERS) spectra is reported. First, the bacteria cell wall is coated with poly (allylamine hydrochloride) (PAH), a positively charged polymer, and then with citrate reduced Au or AgNPs. In order to increase the stability of the coating, another layer of PAH is prepared on the surface. The SEM and AFM images indicate that the nanoparticles are in the form of both isolated and aggregated nanoparticles on the bacterial wall. The coating of bacterial cells with AgNPs or AuNPs not only serves for their preparation for SERS measurement but also helps to visualize the coated of bacterial cells under the ordinary white-light microscope objective due to efficient light-scattering properties of Au and AgNPs. A comparative study single versus aggregates of bacterial cells is also demonstrated for possible single bacterial detection with SERS. The two bacteria that differ in shape and cell wall biochemical structure, Escherichia coli and Staphylococcus cohnii, Gram-negative and -positive, respectively, are used as models. The preliminary results reveal that the approach could be used for single bacterial cell identification.     

Functional artificial free-standing yeast biofilms

Here we report fabrication of artificial free-standing yeast biofilms built using sacrificial calcium carbonate-coated templates and layer-by-layer assembly of extracellular matrix-mimicking polyelectrolyte multilayers. The free-standing biofilms are freely floating multilayered films of oppositely charged polyelectrolytes and live cells incorporated in the polyelectrolyte layers. Such biofilms were initially formed on glass substrates of circular and ribbon-like shapes coated with thin layers of calcium carbonate microparticles. The templates were then coated with cationic and anionic polyelectrolytes to produce a supporting multilayered thin film. Then the yeast alone or mixed with various micro- and nanoparticle inclusions was deposited onto the multilayer composite films and further coated with outer polyelectrolyte multilayers. To detach the biofilms from the glass substrates the calcium carbonate layer was chemically dissolved yielding free-standing composite biofilms. These artificial biofilms to a certain degree mimic the primitive multicellular and colonial species. We have demonstrated the added functionality of the free-standing artificial biofilms containing magnetic, latex and silver micro- and nanoparticles. We have also developed "symbiotic" multicellular biofilms containing yeast and bacteria. This approach for fabrication of free-standing artificial biofilms can be potentially helpful in development of artificial colonial microorganisms composed of several different unicellular species and an important tool for growing cell cultures free of supporting substrates.     

Ru/CdS Quantum Dots Templated on Clay Nanotubes as Visible-Light-Active Photocatalysts: Optimization of S/Cd Ratio and Ru Content

A nanoarchitectural approach based on in situ formation of quantum dots (QDs) within/outside clay nanotubes was developed. Efficient and stable photocatalysts active under visible light were achieved with ruthenium-doped cadmium sulfide QDs templated on the surface of azine-modified halloysite nanotubes. The catalytic activity was tested in the hydrogen evolution reaction in aqueous electrolyte solutions under visible light. Ru doping enhanced the photocatalytic activity of CdS QDs thanks to better light absorption and electron–hole pair separation due to formation of a metal/semiconductor heterojunction. The S/Cd ratio was the major factor for the formation of stable nanoparticles on the surface of the azine-modified clay. A quantum yield of 9.3 % was reached by using Ru/CdS/halloysite containing 5.2 wt % of Cd doped with 0.1 wt % of Ru and an S/Cd ratio of unity. In vivo and in vitro studies on the CdS/halloysite hybrid demonstrated the absence of toxic effects in eukaryotic cells and nematodes in short-term tests, and thus they are promising photosensitive materials for multiple applications.