In situ fabrication of ultrathin porous alumina and its application for nanopatterning Au nanocrystals on the surface of ion-sensitive field-effect transistors

In situ fabrication in a single step of thin films of alumina exhibiting a thickness of less than 100 nm and nanopores with a highly regular diameter distribution in order to pattern nanostructures over field-effect devices is a critical issue and has not previously been demonstrated. Here we report the fabrication in situ of 50 nm thick ultrathin nanoporous alumina membranes with a regular pore size directly over metal-free gate ion-sensitive field-effect transistors. Depositing thin films of aluminum by an electron beam at a relatively low rate of deposition on top of chips containing the transistors and using a conventional single-step anodization process permits the production of a well-adhering nanoporous ultrathin layer of alumina on the surface of the devices. The anodization process does not substantially affect the electrical properties of the transistors. The small thickness and pore size of ultrathin alumina membranes allow them to be sequentially employed as masks for patterning Au nanocrystals grown by an electroless approach directly on the top of the transistors. The patterning process using a wet chemical approach enables the size of the patterned crystals to be controlled not only by the dimensions of the pores of alumina, but also by the concentration of the reactants employed. Surface modification of these nanocrystals with alkanethiol molecules demonstrates that the electrostatic charge of the functional groups of the molecules can modulate the electrical characteristics of the transistors. These results represent substantial progress towards the development of novel nanostructured arrays on top of field-effect devices that can be applied for chemical sensing or non-volatile memories.

Modulation of gut microbiota by antibiotics improves insulin signalling in high-fat fed mice

AIMS/HYPOTHESIS

A high-fat dietary intake induces obesity and subclinical inflammation, which play important roles in insulin resistance. Recent studies have suggested that increased concentrations of circulating lipopolysaccharide (LPS), promoted by changes in intestinal permeability, may have a pivotal role in insulin resistance. Thus, we investigated the effect of gut microbiota modulation on insulin resistance and macrophage infiltration.

METHODS

Swiss mice were submitted to a high-fat diet with antibiotics or pair-feeding for 8 weeks. Metagenome analyses were performed on DNA samples from mouse faeces. Blood was collected to determine levels of glucose, insulin, LPS, cytokines and acetate. Liver, muscle and adipose tissue proteins were analysed by western blotting. In addition, liver and adipose tissue were analysed, blinded, using histology and immunohistochemistry.

RESULTS

Antibiotic treatment greatly modified the gut microbiota, reducing levels of Bacteroidetes and Firmicutes, overall bacterial count and circulating LPS levels. This modulation reduced levels of fasting glucose, insulin, TNF-α and IL-6; reduced activation of toll-like receptor 4 (TLR4), c-Jun N-terminal kinase (JNK), inhibitor of κ light polypeptide gene enhancer in B cells, kinase β (IKKβ) and phosphorylated IRS-1 Ser307; and consequently improved glucose tolerance and insulin tolerance and action in metabolically active tissues. In addition, there was an increase in portal levels of circulating acetate, which probably contributed to an increase in 5'-AMP-activated protein kinase (AMPK) phosphorylation in mice. We observed a striking reduction in crown-like structures (CLS) and F4/80(+) macrophage cells in the adipose tissue of antibiotic-treated mice.

CONCLUSIONS/INTERPRETATION

These results suggest that modulation of gut microbiota in obesity can improve insulin signalling and glucose tolerance by reducing circulating LPS levels and inflammatory signalling. Modulation also appears to increase levels of circulating acetate, which activates AMPK and finally leads to reduced macrophage infiltration.

The effects of dimensionality on electrochemical sensors based on carbon nanotubes and metallic nanowires

Electrochemistry based unidimensional nanoelectrodes, such as carbon nanotubes and metallic nanowires, is now a reality that is leaving the academy and reaching a broad range of high-tech companies around the world. The intrinsic properties of electron-electron interactions, sizes and geometries significantly differentiate those nanostructures from conventional macroelectrodes or electrodes with sizes in a millimetric range. The inherent properties as well as the configuration of carbon nanotubes and metallic nanowires as electrochemical sensors are the main focus of this review. Applications and some future trends on developing of a clear pathway for assembly and integration of these into functional materials, are summarized as well.

Surface plasmon resonance immunosensor for early diagnosis of Asian rust on soybean leaves

Soybean rust (Asian rust) is a disease that occurs in soy cultures, negatively affecting pod formation and final grain weight and reducing value and product quality. Early identification of fungus in the plants prevents severe farming losses and spread to neighboring cultures. In this paper, a fast response sensor was developed based on surface plasmon resonance to detect Asian rust in soybean leaf extract at early stages of the disease. The antibody anti-Phakopsora pachyrhizi (pathogen) was covalently immobilized on a gold substrate via a self-assembled monolayer (SAM) of thiols using cysteamine-coupling chemistry. This immunosensor presented a linear response range for the antigen from 3.5 to 28.0 microg mL(-1) (r(2)=0.996). The effects of the antibody amount and the surface blocking to minimize non-specific adsorption on immunosensor response were evaluated. These studies provide new perspectives on using SPR technology for the development of a highly sensitive sensor for agricultural applications.

Amperometric sensor for glutathione reductase activity determination in erythrocyte hemolysate

The development of an amperometric sensor for glutathione reductase (GR) activity in erythrocyte hemolysate to contribute to oxidative stress evaluation is presented. In this assay, the reduced form of glutathione, the product of the GR reaction, reacts with 5,5(')-dithiobis(2-nitrobenzoic acid), producing GSTNB, which is easily reduced in the electrode surface. The current was recorded during 180 s after the sample addition, applying a potential of -300 mV. The sensor presented a suitable sensitivity, a good operational range, and precision. The effects of pH variations and specific uncompetitive inhibitor (safranin-O) in the enzyme activity were also evaluated. The GR activity determination in human erythrocyte hemolysate using this method has provided results that are statistically equal to those obtained by the classical spectrophotometric method, with 95% of confidence. The advantages of this method are the saved time, reagents, and samples and the possibility of its use in the field.

Remediation and toxicity removal from Kraft E1 paper mill effluent by ozonization

The degradation of Kraft E1 pulp mill effluent was studied by four different ozonization oxidation systems (O3/pH3, O3/pH11, O3/pH11/H2O2, O3/pH11/UV). The investigation was focused on the reduction of total organic carbon (TOC), total phenols, color and acute toxicity (monitoring by inhibition of Escherichia coli respiration). For a reaction time of 90 minutes, the O3/pH11/UV was the most effective process for decoloration (45%). The O3/pH11/H2O2, O3/pH11/UV and O3/pH11 processes showed the best results for total phenols reduction (approximately/= 90%). None of the studied processes showed a significant TOC reduction. The O3/pH11/UV and O3/pH11 processes were effective for the acute toxicity reduction. Different kinetic parameters were also determined in order to quantify the reactivity of the effluent towards the applied oxidation systems.

Influence of gamma irradiation on a natural source of peroxidase and its effect in the reagentless amperometric biosensor for hydrogen peroxide

Peroxidase was extracted from a natural source (turnip) and irradiated with 60Co (0.1 kGy). It was then used in the construction of biosensors for hydrogen peroxide determination, in order to study the effect of the gamma irradiation on the performance of the biosensors. The biosensors were constructed using two immobilization procedures: cross-linking with glutaraldehyde and covalent binding through carbodiimide. The biosensor prepared using covalent binding through carbodiimide showed a higher sensitivity for H2O2. A good enhancement in stability and sensitivity was obtained for the biosensors from irradiated material, when compared to biosensors prepared with non-irradiated enzyme. However, the initial linear response range (1.0 to 10.0 mmol dm-3) and response time (0.5 s) were equal with or without irradiation.

Development of an amperometric biosensor based on glutathione peroxidase immobilized in a carbodiimide matrix for the analysis of reduced glutathione from serum

The development of an amperometric biosensor for the reduced glutathione determination in serum is described. The biosensor is based on glutathione peroxidase (GSH-Px, EC 1.11.1.9) immobilized onto a pyrolytic graphite-working electrode using carbodiimide as enzymatic condensing reagent. This resulted in an amperometric biosensor with good sensitivity and stability. The reduced glutathione (GSH) was enzymatically converted to glutathione disulfide (GSSG) in the presence of hydroperoxide, which was monitored amperometrically by its electrooxidation at +0.65 V vs. SCE (saturated calomel electrode). Glutathione measurement was carried out by maintaining the ratio between GSH and hydrogen peroxide at 2:1 (25 degrees C). The amperometric response of the biosensor was linearly proportional to the GSH concentration between 1.9x10(-5) and 1.4x10(-4) mol/l, in 0.1 mol/l phosphate buffer (pH=7.8), containing 0.1 mol/l KCl and 0.5 mmol/l Na(2)H(2)EDTA, as the supporting electrolyte. In presence of interfering compounds, the recoveries ranged between 97.2% and 110.7%. The biosensor useful lifetime was at least 2 months when it was evaluated after continuous use. Serum samples analyzed by this biosensor showed a good correlation with the results from the spectrophotometric method (Ellman's reagent) used as reference, presenting relative deviations lower than 7.0%. The low apparent Michaelis-Menten constant value, K(M)(app)=1.6 mmol/l, demonstrated that GSH-Px immobilized on pyrolytic graphite exhibited a high affinity to GSH, without loss of enzymatic activity.

Electrochemical properties of Doyle catalyst immobilized on carbon paste in the presence of DNA

The electrochemical behaviour of Doyle catalyst, dirhodium(II) tetrakis [methyl-2-oxopyrrolidine-5(S)-carboxylate] (Rh2(5S-MEPY)4), immobilised in graphite powder was evaluated preparing the carbon paste electrode, as well as its electrochemical properties in the presence (DCDE) and absence (DCE) of DNA. In both cases, one redox couple at 0.35 V vs. SCE in 0.5 mol l(-1) KCl solution at pH 7 and 10 mV s(-1) was observed. The resolution of the peak current in the voltammetric studies and other electrochemical properties were improved when the Doyle catalyst was immobilised in the presence of DNA. The estimated rate constants were of 17 and 26 s(-1) for a scan rate of 1 V s(-1) for DCE and DCDE, respectively. Furthermore, the interaction between rhodium carboxylates and electrolytes become more evident, suggesting a good hydrophilic and conductor character of this biopolymer.

Interface potential of calcium phosphate in simulated body fluid

Calcium phosphate ceramics are used in the substitution of injured or damaged bones. Nevertheless, the behaviour of these materials, and in particular, the mechanisms guiding their interface response in physiological environment is still unknown. This work describes the construction of hydroxyapatite and tricalcium phosphate electrodes used to determine the interface potential behaviour of these materials in a simulated body fluid, in a pH range corresponding to the variation observed in human body injuries, at ambient and physiological temperatures. These measurements are associated with the adsorption/desorption of ions from the materials. The results show that hydroxyapatite and tricalcium phosphate have similar behaviour in that they reach an interface potential equilibrium state faster when the solution pH is decreased and the temperature increased. This behaviour may be attributed to their ability to form a calcium-rich layer and is relevant to their quality as implantable materials.

Polishable and renewable DNA hybridization biosensors

Routine applications of DNA hybridization biosensors are often restricted by the need for regenerating the single-stranded (ss) probe for subsequent reuse. This note reports on a viable alternative to prolonged thermal or chemical regeneration schemes through the mechanical polishing of oligonucleotide-bulk-modified carbon composite electrodes. The surface of these biocomposite hybridization biosensors can be renewed rapidly and reproducibly by a simple extrusion/polishing protocol. The immobilized probe retains its hybridization activity on confinement in the interior of the carbon paste matrix, with the use of fresh surfaces erasing memory effects and restoring the original target response, to allow numerous hybridization/measurement cycles. We expect that such reusable nucleic acid modified composite electrodes can be designed for a wide variety of biosensing applications.

Study of NADH stability using ultraviolet-visible spectrophotometric analysis and factorial design

The chemical stability of nicotinamide adenine dinucleotide coenzyme (NADH/NAD+) and its derivatives (NADPH/NADP+) was investigated using changes in the UV-visible absorption spectra of these compounds. The spectra of cofactor (reduced form) were monitored at 340 nm wavelength in different buffers, showing a faster degradation in phosphate buffer. This was assigned to the adduct formation between phosphate and NADH (pyridine ring). The three-factor-two-level factorial design study evaluated the contributions: buffers (phosphate and Pipes 0.1 M), pH's (6.8 and 7.8), and temperature (25 and 30 degrees C). The freshly prepared aqueous solutions of coenzyme were analyzed after 40 min under the different conditions (eight assays in triplicate) of the experiment. The main observed effects of the NADH oxidation were, in increasing order, pH, temperature, and buffer without appreciable interactive effects. Therefore, it was verified that the better conditions for cofactor use were alkaline media employing Pipes buffer or its derivatives and low temperatures.

Use of Chemically Modified Silica with beta-Diketoamine Groups for Separation of alpha-Lactoalbumin from Bovine Milk Whey by Affinity Chromatography

Silica gel surface was chemically modified with beta-diketoamine groups by reacting the silanol from the silica surface with 3-aminopropyl-triethoxysilane and 3-bromopentanedione. With this material, copper ions were adsorbed from aqueous solutions. The chemical analysis of the silica-gel-immobilized acetylacetone provided a quantity of 0.67 mmol g-1 of organic groups attached to the support and 0.63 mmol g-1 of copper. This material was used as a stationary phase in IMAC (immobilized metal affinity chromatography), to separate alpha-lactoalbumin from bovine milk whey. The results showed an efficient separation in the chromatographic column. The possibility of reutilization of the stationary phase was also investigated.

Electrochemical Properties of

[Ru(edta)(H2O)]- is strongly adsorbed on a zirconium(IV) oxide-coated silica gel surface. The immobilized complex showed an electrochemical response due to the Ru(II)/Ru(III) redox couple. By substituting the coordinated water molecule in the adsorbed complex, the midpoint potentials shifted in the order (in mV) water, -290; thiocyanate, -200; pyridine, -180; 4-cyanopyridine, -80; and pyrazine, -50 vs SCE.

Study of the Adsorption of Some Amino Acids by Silica Chemically Modified with Aminobenzenesulfonic and Phosphate Groups

Two silica gels, one modified with aminobenzenesulfonic (SABS) groups and the other with phosphate (SZP) groups, were prepared to adsorb some amino acids. Chemical analysis of the modified silica gave 0.65 mmol g-1 aminobenzenesulfonic groups and 0.56 mmol g-1 phosphate groups. The maximum adsorption capacities for amino acids determined by batch experiments for SABS were 1.37, 0.67, 0.76, and 0.59 mmol g-1 for glycine, lysine, histidine, and leucine, respectively, and those for SZP were 0.75, 0.58, 0.44, and 0.75 mmol g-1 for glycine, lysine, histidine, and leucine, respectively. The adsorption capacity of SABS was significantly affected by the solution pH, showing a higher selectivity than SZP. The materials were very stable, allowing their use several times without changes in adsorption capacity.