Controlled reversible assembly of gold nanoparticles as a new colorimetric and sensitive detection of glucose-6-phosphate dehydrogenase deficiency.

Recently, several studies have examined possible applications of nanoparticles for the development of electronic and optical sensors. The plasmon absorbance of gold nanoparticles has been used extensively to study biomolecular processes, including nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate-dependent enzymatic reactions. In this report, we describe the development of gold nanoparticles as a new colorimetric and sensitive detection method of glucose-6-phosphate dehydrogenase deficiency by means of controlled reversible assembly of gold nanoparticles. 3-nm polyvinylpyrrolidone/N,N'-dimethylaminopyridine-stabilized gold nanoparticles were synthesized, characterized and applied for an in vitro activity assay of 11 recombinant human glucose-6-phosphate dehydrogenase variants. Differences in the activity of the glucose-6-phosphate dehydrogenase variants from different deficiency classes were readily detected using the synthesized gold nanoparticles. The developed method can be easily distinguished with color change by naked eye for the detection of glucose-6-phosphate dehydrogenase deficiency. Moreover, we are the first to propose the segregation mechanism of polyvinylpyrrolidone/N,N'-dimethylaminopyridine-stabilized gold nanoparticles by reduced nicotinamide adenine dinucleotide phosphate. The method enables visual detection of glucose-6-phosphate dehydrogenase deficiency, which could be further developed for diagnostic testing of glucose-6-phosphate dehydrogenase deficiency.

Asymmetric Modification of Carbon Nanotube Arrays with Thermoresponsive Hydrogel for Controlled Delivery.

In this work, bipolar electrochemistry is used to perform wireless indirect electrodeposition of two different polymer coatings on both sides of carbon nanotube arrays. Using a thermoresponsive hydrogel on one side and an inert insoluble polymer on the other side, it is possible to generate, in a single step, a nanoporous reservoir with Janus character closed on one side by a thermoresponsive membrane. The thermoresponsive polymer, poly(N-isopropylacrylamide) (pNIPAM), is generated by the local reduction of persulfate ions, which initiates radical polymerization of NIPAM. Electrophoretic paint (EP) is chosen as an inert polymer. It is deposited by precipitation because of a local decrease in pH during water oxidation. Both polymers can be deposited simultaneously on opposite sides of the bipolar electrode during the application of the electric field, yielding a double-modified Janus object. Moreover, the length and thickness of the polymer layers can be controlled by varying the electric field and the deposition time. This concept is applied to vertically aligned carbon nanotube arrays (VACNTs), trapped inside an anodic aluminum oxide membrane, which can further be used as a smart reservoir for chemical storage and release. A fluorescent dye is loaded in the VACNTs and its release is studied as a function of temperature. Low temperature, when the hydrogel layer is in the swollen state, allows diffusion of the molecule. Dye release occurs on the hydrogel-modified side of the VACNTs. At high temperatures, when the hydrogel layer is in the collapsed state, dye release is blocked because of the impermeability of the pNIPAM layer. This concept paves the way toward the design of advanced devices in the fields of drug storage and directed delivery.

Anisotropic Metal Deposition on TiO2 Particles by Electric-Field-Induced Charge Separation.

Deposition of metals on TiO2 semiconductor particles (M-TiO2 ) results in hybrid Janus objects combining the properties of both materials. One of the techniques proposed to generate Janus particles is bipolar electrochemistry (BPE). The concept can be applied in a straightforward way for the site-selective modification of conducting particles, but is much less obvious to use for semiconductors. Herein we report the bulk synthesis of anisotropic M-TiO2 particles based on the synergy of BPE and photochemistry, allowing the intrinsic limitations, when they are used separately, to be overcome. When applying electric fields during irradiation, electrons and holes can be efficiently separated, thus breaking the symmetry of particles by modifying them selectively and in a wireless way on one side with either gold or platinum. Such hybrid materials are an important first step towards high-performance designer catalyst particles, for example for photosplitting of water.

A novel method for dengue virus detection and antibody screening using a graphene-polymer based electrochemical biosensor.

Dengue fever is a major disease that kills many people in the developing world every year. During early infection, a patient displays a high temperature without other signs. After this stage, and without proper treatment, serious damage to internal organs can happen, which occasionally leads to death. A rapid technique for the early detection of dengue virus (DENV) could reduce the number of fatalities. This study presents a new technique for the detection, classification and antibody screening of DENV based on electrochemical impedance spectroscopy (EIS). We found that the charge transfer resistance (Rct) of a gold electrode coated with graphene oxide reinforced polymer was influenced by virus type and quantity exposed on the surface. Molecular recognition capability established during the GO-polymer composite preparation was used to explain this observation. The linear dependence of Rct versus virus concentrations ranged from 1 to 2×103pfu/mL DENV with a 0.12 pfu/mL detection limit.

Use of Capillary Electrophoresis to Study the Binding Interaction of Aptamers with Wild-Type, K103N, and Double Mutant (K103N/Y181C) HIV-1 RT : Studying the Binding Interaction of Wild-Type, K103N, and Double Mutant (K103N/Y181C) HIV-1 RT with Aptamers by Performing the Capillary Electrophoresis.

A number of nucleic acid aptamers with high affinities to human immunodeficiency virus reverse transcriptase (HIV-1 RT) are currently known. They can potentially be developed as broad-spectrum antiviral drugs, but there is little known about their binding interaction with mutant HIV-1 RT. Therefore, we utilized non-equilibrium capillary electrophoresis of equilibrium mixture (NECEEM) to study the interaction of three HIV-1 RTs (wild type, K103N, and double mutant (K103N/Y181C)) with RT1t49 and RT12 aptamers. This approach was used to study and evaluate the K d values of these molecules. The results showed that the K d values of the tested aptamers were lower than that of the DNA substrate. The results also pointed out that RT1t49 could bind with all HIV-1 RTs and compete with the DNA substrate at the active site. Moreover, we studied the binding stoichiometry of HIV-1 RT using aptamers as probes. The findings showed evidence of two binding stoichiometries with HIV-1 RT and the RT12 aptamer but only one binding stoichiometry for RT1t49. In addition, RT1t49 could bind specifically with the wild-type, K103N, and double mutants in Escherichia coli lysate. This result also indicated that the aptamer could detect HIV-1 RT in the presence of E. coli lysate.

Wireless Synthesis and Activation of Electrochemiluminescent Thermoresponsive Janus Objects Using Bipolar Electrochemistry.

In this work, bipolar electrochemistry (BPE) is used as a dual wireless tool to generate and to activate a thermoresponsive electrochemiluminescent (ECL) Janus object. For the first time, BPE allows regioselective growth of a poly(N-isopropylacrylamide) (pNIPAM) hydrogel film on one side of a carbon fiber. It is achieved thanks to the local reduction of persulfate ions, which initiate radical polymerization of NIPAM. By controlling the electric field and the time of the bipolar electrochemical reactions, we are able to control the length and the thickness of the deposit. The resulting pNIPAM film is found to be swollen in water at room temperature and collapsed when heated above 32 °C. We further incorporated a covalently attached ruthenium complex luminophore, Ru(bpy)32+, in the hydrogel film. In the second time, BPE is used to activate remotely the electrogenerated chemiluminescence (ECL) of the Ru(bpy)32+ moieties in the film. We take advantage of the film responsiveness to amplify the ECL signal. Upon collapse of the film, the ECL signal, which is sensitive to the distance between adjacent Ru(bpy)32+ centers, is strongly amplified. It is therefore shown that BPE is a versatile tool to generate highly sophisticated materials based on responsive polymers, which could lead to sensitive sensors.

Asymmetric synthesis using chiral-encoded metal.

The synthesis of chiral compounds is of crucial importance in many areas of society and science, including medicine, biology, chemistry, biotechnology and agriculture. Thus, there is a fundamental interest in developing new approaches for the selective production of enantiomers. Here we report the use of mesoporous metal structures with encoded geometric chiral information for inducing asymmetry in the electrochemical synthesis of mandelic acid as a model molecule. The chiral-encoded mesoporous metal, obtained by the electrochemical reduction of platinum salts in the presence of a liquid crystal phase and the chiral template molecule, perfectly retains the chiral information after removal of the template. Starting from a prochiral compound we demonstrate enantiomeric excess of the (R)-enantiomer when using (R)-imprinted electrodes and vice versa for the (S)-imprinted ones. Moreover, changing the amount of chiral cavities in the material allows tuning the enantioselectivity.

Reaction mechanism of methanol to formaldehyde over Fe- and FeO-modified graphene.

We employed periodic DFT calculations (PBE-D2) to investigate the catalytic conversion of methanol over graphene embedded with Fe and FeO. Two possible pathways of dehydrogenation to formaldehyde and dehydration to dimethyl ether (DME) over these catalysts were examined. Both processes are initiated with the activation of methanol over the catalytic center through O-H cleavage. As a result, a methoxo-containing intermediate is formed. Subsequently, H-transfer from the methoxy to the adjacent ligand leads to the formation of formaldehyde. Conversely, the activation of the second methanol over the intermediate gives DME and H2O. Over Fe/graphene, the dehydration process is kinetically and thermodynamically preferable. Unlike Fe/graphene, FeO/graphene is predicted to be an efficient catalyst for the dehydrogenation process. Oxidative dehydrogenation over FeO/graphene takes place through two steps with free energy barriers of 5.7 and 10.2 kcal mol(-1).

Site-selective synthesis of Janus-type metal-organic framework composites.

Herein, bipolar electrochemistry is applied in a straightforward way to the site-selective in situ synthesis of metal-organic framework (MOF) structures, which have attracted tremendous interest in recent years because of their significant application potential, ranging from sensing to gas storage and catalysis. The novelty of the presented work is that the deposit can be intentionally confined to a defined area of a substrate without using masks or templates. The intrinsic site-selectivity of bipolar electrochemistry makes it a method of choice to generate, in a highly controlled way, hybrid particles that may have different functionalities combined on the same particle. The wireless nature of electrodeposition allows the potential for mass production of such Janus-type objects.

Enantioselective recognition at mesoporous chiral metal surfaces.

Chirality is widespread in natural systems, and artificial reproduction of chiral recognition is a major scientific challenge, especially owing to various potential applications ranging from catalysis to sensing and separation science. In this context, molecular imprinting is a well-known approach for generating materials with enantioselective properties, and it has been successfully employed using polymers. However, it is particularly difficult to synthesize chiral metal matrices by this method. Here we report the fabrication of a chirally imprinted mesoporous metal, obtained by the electrochemical reduction of platinum salts in the presence of a liquid crystal phase and chiral template molecules. The porous platinum retains a chiral character after removal of the template molecules. A matrix obtained in this way exhibits a large active surface area due to its mesoporosity, and also shows a significant discrimination between two enantiomers, when they are probed using such materials as electrodes.

The conversion of CO2 and CH4 to acetic acid over the Au-exchanged ZSM-5 catalyst: a density functional theory study.

The direct conversion of methane and carbon dioxide to acetic acid is one of the most challenging research topics. Using the density functional theory (M06-L) the study reveals the catalytic activity of the Au(I)-ZSM-5 zeolite in this reaction. The Au(I)-ZSM-5 is represented by a 34T quantum cluster model. The activation of the C-H bond over the Au-ZSM-5 zeolite would readily take place via the homolytic σ-bond activation with an energy barrier of 10.5 kcal mol(-1), and subsequent proton transfer from the Au cation to the zeolitic oxygen, yielding the stable methyl-gold complex adsorbed on the zeolite Brønsted acid. The conversion of CO(2) on this bi-functional catalyst involves the Brønsted acid site playing a role in the protonation of CO(2) and the methyl-gold complex acting as a methylating agent. The activation energy of 52.9 kcal mol(-1) is predicted.

Structures, energetics and reaction mechanisms of nitrous oxide on transition-metal-doped and -undoped single-wall carbon nanotubes.

The catalytic activity of carbon nanotubes (CNTs) for the removal of greenhouse gases, like nitrous oxide (N(2)O), can be fine-tuned by metal doping. We modify the inert surfaces of CNTs with Sc, Ti and V transition metals in order to investigate their capability of converting N(2)O to N(2). The stable composite catalysts of Sc-, Ti- and V-doped (5,5)single-walled carbon nanotubes (SWCNTs), along with the unmodified one were investigated by periodic DFT calculations. Without metal doping, the N(2) O decomposition on the bare tube proceeds over a high energy barrier (54.3 kcal mol(-1)) which in the presence of active metals is reduced to 3.6, 8.0 and 10.2 kcal mol(-1) for V-, Ti- and Sc-doped (5,5)SWCNTs, respectively. The superior reactivity is a result of the facilitated electron transfer between the tube and N(2)O caused by the overlap between the d orbitals of the metal and the p orbitals of N(2)O.

Thermal stabilization of thin gold nanowires by surfactant-coating: a molecular dynamics study.

The thermal stabilization of thin gold nanowires with a diameter of about 2 nm by surfactants is investigated by means of classical molecular dynamics simulations. While the well-known melting point depression leads to a much lower melting of gold nanowires compared to bulk gold, coating the nanowires with surfactants can reverse this, given that the attractive interaction between surfactant molecules and gold atoms lies beyond a certain threshold. It is found that the melting process of coated nanowires is dominated by surface instability patterns, whereas the melting behaviour of gold nanowires in a vacuum is dominated by the greater mobility of atoms with lower coordination numbers that are located at edges and corners. The suppression of the melting by surfactants is explained by the isotropic pressure acting on the gold surface (due to the attractive interaction) which successfully suppresses large-amplitude thermal motions of the gold atoms.

Dissymmetric carbon nanotubes by bipolar electrochemistry.

Short carbon nanotubes have been modified selectively on one end with metal using a bulk technique based on bipolar electrochemistry. A stabilized suspension of nanotubes is introduced in a capillary containing an aqueous metal salt solution, and a high electric field is applied to orientate and polarize the individual tubes. During their transport through the capillary under sufficient polarization (30 kV), each nanotube is the site of water oxidation on one end and the site of metal ion reduction on the other end with the size of the formed metal cluster being proportional to the potential drop along the nanotube.