Heat-Induced Dry Hydrolysis of Sodium Borohydride/Oxalic Acid Dihydrate Composite for Hydrogen Production.

The generation of hydrogen, free of poisonous gas, combined with a lightweight proton-exchange membrane fuel cell can expand the use of hydrogen energy from conventional ground transportation vehicles and power stations to a variety of flying vehicles and wearable devices for civilian and military purposes. Herein, a hydrogen fuel composite composed of sodium borohydride (SB) and oxalic acid dihydrate (OA·2H2O) is introduced. The SB/OA·2H2O composite was easily decomposed to generate pure hydrogen at a trigger temperature of 50 °C, at which the water molecules of the OA·2H2O component were effectively liberated, inducing hydrolysis of the SB component to produce hydrogen gas. This dry hydrolysis-based hydrogen generation using the SB/OA·2H2O composite has the merits of rapidly generating hydrogen (i.e., 0.4 g of the composite can be fully decomposed within a minute at low temperatures), free of poisonous gas, in approximately 5 wt % yield (the theoretical maximum value).

Enhanced Stability and Amplified Signal Output of Single-Wall Carbon Nanotube-Based NH3-Sensitive Electrode after Dual Plasma Treatment.

Pristine nanomaterials are normally prepared using finely controlled fabrication processes. Because no imperfect nanostructure remains, they cannot be used directly as electrode substrates of functional devices. This is because perfectly organized nanostructures or nanomaterials commonly require posttreatment to generate intentionally, the kinds of desirable defects inside or on their surfaces that enable effective functionalization. Plasma treatment is an easier, simpler and more widely used way (relative to other methods) to modify a variety of nanomaterials, although plasma-functionalized nano surfaces commonly have a short lifetime. We present herein a dual plasma treatment (DPT) that significantly enhances the degree and lifetime of plasma-induced surface functional groups on single-walled carbon nanotubes (SWCNTs). The DPT process consists of two individually optimized oxygen-plasma treatments. The DPT-modified SWCNT functioned as a sensing material for ammonia gas for more than a month. It also provided more than three times the degree of functionality for amplified signal output than with a single-plasma-treated SWCNT electrode.

A Micromachined Metal Oxide Composite Dual Gas Sensor System for Principal Component Analysis-Based Multi-Monitoring of Noxious Gas Mixtures.

Microelectronic gas-sensor devices were developed for the detection of carbon monoxide (CO), nitrogen dioxides (NO2), ammonia (NH3) and formaldehyde (HCHO), and their gas-sensing characteristics in six different binary gas systems were examined using pattern-recognition methods. Four nanosized gas-sensing materials for these target gases, i.e., Pd-SnO2 for CO, In2O3 for NOX, Ru-WO3 for NH3, and SnO2-ZnO for HCHO, were synthesized using a sol-gel method, and sensor devices were fabricated using a microsensor platform. Principal component analysis of the experimental data from the microelectromechanical systems gas-sensor arrays under exposure to single gases and their mixtures indicated that identification of each individual gas in the mixture was successful. Additionally, the gas-sensing behavior toward the mixed gas indicated that the traditional adsorption and desorption mechanism of the n-type metal oxide semiconductor (MOS) governs the sensing mechanism of the mixed gas systems.

A Fully Integrated Paper-Microfluidic Electrochemical Device for Simultaneous Analysis of Physiologic Blood Ions.

A fully integrated paper microfluidic electrochemical device equipped with three different cation permeable films is developed to determine blood ions (Cl-, Na⁺, K⁺, and Ca2+) at a time. These blood ions that are normally dissolved in the real human blood stream are essential for cell metabolisms and homeostasis in the human body. Abnormal concentration of blood ions causes many serious disorders. The optimized microfluidic device working without any external power source can directly and effectively separate human blood components, and subsequently detect a specific blood ion with minimized interference. The measured sensitivity to Cl-, K⁺, Na⁺, and Ca2+ are -47.71, 45.97, 51.06, and 19.46 in mV decade-1, respectively. Potentiometric responses of the microfluidic devices to blood serum samples are in the normal ranges of each cation, and comparable with responses from the commercial blood ion analyzer Abbott i-Stat.

Buckling Structured Stretchable Pseudocapacitor Yarn.

Cable-type stretchable electrochemical pseudocapacitors based on multi-walled carbon nanotube (MWCNT) sheets and two different metal oxide nanopowders (NP), i.e., MnO2 and RuO2 are developed using a newly-devised dry painting method to mechanically fix the NP to the elastic rubber-based MWCNT electrode substrate, resulting in a porous buckling structured pseudocapacitor yarn. Highly stretchable stylene-ethylene/butylene-stylene (SEBS) is used as the supporting elastomeric core for wrapping with the MWCNT sheets and the electroactive NP. The dry painting can successfully deposit NP on the soft SEBS surface, which is normally an unfavorable substrate for coating alien materials. The resulting yarn-type pseudocapacitor, composed of eight-layered MWCNT sheets, three-layered RuO2, and two-layered MnO2, showing a diameter of approximately 400 µm with a porous buckling structure, records a specific capacitance of 25 F g-1. After being stretched by 200% in strain with no sacrifice of the porous buckling structure, the cable-type stretchable electrochemical pseudocapacitor yarn retains its electrical capacity, and is potentially applicable to energy storage devices for wearable electronics.

Fully Automated Field-Deployable Bioaerosol Monitoring System Using Carbon Nanotube-Based Biosensors.

Much progress has been made in the field of automated monitoring systems of airborne pathogens. However, they still lack the robustness and stability necessary for field deployment. Here, we demonstrate a bioaerosol automonitoring instrument (BAMI) specifically designed for the in situ capturing and continuous monitoring of airborne fungal particles. This was possible by developing highly sensitive and selective fungi sensors based on two-channel carbon nanotube field-effect transistors (CNT-FETs), followed by integration with a bioaerosol sampler, a Peltier cooler for receptor lifetime enhancement, and a pumping assembly for fluidic control. These four main components collectively cooperated with each other to enable the real-time monitoring of fungi. The two-channel CNT-FETs can detect two different fungal species simultaneously. The Peltier cooler effectively lowers the working temperature of the sensor device, resulting in extended sensor lifetime and receptor stability. The system performance was verified in both laboratory conditions and real residential areas. The system response was in accordance with reported fungal species distribution in the environment. Our system is versatile enough that it can be easily modified for the monitoring of other airborne pathogens. We expect that our system will expedite the development of hand-held and portable systems for airborne bioaerosol monitoring.

Evaluation of Surface Cleaning Procedures in Terms of Gas Sensing Properties of Spray-Deposited CNT Film: Thermal- and O2 Plasma Treatments.

The effect of cleaning the surface of single-walled carbon nanotube (SWNT) networks by thermal and the O2 plasma treatments is presented in terms of NH3 gas sensing characteristics. The goal of this work is to determine the relationship between the physicochemical properties of the cleaned surface (including the chemical composition, crystal structure, hydrophilicity, and impurity content) and the sensitivity of the SWNT network films to NH3 gas. The SWNT networks are spray-deposited on pre-patterned Pt electrodes, and are further functionalized by heating on a programmable hot plate or by O2 plasma treatment in a laboratory-prepared plasma chamber. Cyclic voltammetry was employed to semi-quantitatively evaluate each surface state of various plasma-treated SWNT-based electrodes. The results show that O2 plasma treatment can more effectively modify the SWNT network surface than thermal cleaning, and can provide a better conductive network surface due to the larger number of carbonyl/carboxyl groups, enabling a faster electron transfer rate, even though both the thermal cleaning and the O2 plasma cleaning methods can eliminate the organic solvent residues from the network surface. The NH3 sensors based on the O2 plasma-treated SWNT network exhibit higher sensitivity, shorter response time, and better recovery of the initial resistance than those prepared employing the thermally-cleaned SWNT networks.

Real-time detection of chlorine gas using Ni/Si shell/core nanowires.

We demonstrate the selective adsorption of Ni/Si shell/core nanowires (Ni-Si NWs) with a Ni outer shell and a Si inner core on molecularly patterned substrates and their application to sensors for the detection of chlorine gas, a toxic halogen gas. The molecularly patterned substrates consisted of polar SiO2 regions and nonpolar regions of self-assembled monolayers of octadecyltrichlorosilane (OTS). The NWs showed selective adsorption on the polar SiO2 regions, avoiding assembly on the nonpolar OTS regions. Utilizing these assembled Ni-Si NWs, we demonstrate a sensor for the detection of chlorine gas. The utilization of Ni-Si NWs resulted in a much larger sensor response of approximately 23% to 5 ppm of chlorine gas compared to bare Ni NWs, due to the increased surface-to-volume ratio of the Ni-Si shell/core structure. We expect that our sensor will be utilized in the future for the real-time detection of halogen gases including chlorine with high sensitivity and fast response.

Label-free electrochemical detection of the human adenovirus 40/41 fiber gene.

A nanoporous silicon-based label-free DNA biosensor was fabricated to monitor rapidly enteric adenovirus types 40 and 41, a leading cause of viral gastroenteritis in children. Nanoporous silicon (NPS) was formed by an anodic etching process in a mixture solution containing hydrofluoric acid and ethanol. The polypyrrole (PPy) film was directly electropolymerized on The NPS substrate. Twenty-five base pairs of probe DNA (pDNA), derived from the fiber gene, was electrochemically doped on the PPy-coated NPS substrate. The conductivity change due to the immobilized pDNA and hybridized target DNA (tDNA) was expressed as an arbitrary factor, γ, which is a normalized numerical term used for the selective quantification of the tDNA. γ was inversely proportional to the concentration of complementary tDNA, but independent of the non-complementary tDNA. The sensitivity slope for detecting tDNAc was -1.54 µM(-1), based on the factor γ in the range of 0.4 to 1.0 µM of tDNA. The surface roughness was characterized using atomic force microscopy.

Electrochemical serotonin monitoring of poly(ethylenedioxythiophene):poly(sodium 4-styrenesulfonate)-modified fluorine-doped tin oxide by predeposition of self-assembled 4-pyridylporphyrin.

A 5,10,15,20-tetrakis(4-pyridyl)-21H,23H-porphyrin (TPyP)-modified self-assembled functional layer was prepared on a fluorine-doped tin oxide (FTO) substrate. We employed a bifunctional molecule, 3-iodopropionate (3IP), to covalently bind TPyP to the FTO substrate. The 3IP-monolayered FTO and the TPyP-3IP-bilayered FTO electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and Fourier transform-infrared spectroscopy. Compared to conventional electropolymerized poly(ethylenedioxythiophene):poly(sodium 4-styrenesulfonate) (PEDOT:PSS) film on bare FTO, the PEDOT:PSS film on the TPyP-3IP-bilayered FTO showed better sensitivity and selectivity in monitoring serotonin in the presence of high concentrations of interfering agents such as ascorbic acid, urea, D-(+)-glucose, epinephrine, and L-3,4-dihydroxyphenylalanine. Both PEDOT:PSS films on the bare FTO and the TPyP-3IP-bilayered FTO showed electrocatalytic effects in serotonin detection, and only the TPyP-3IP-based PEDOT:PSS film acted as a pH resistant buffer layer in the selective detection of serotonin.

Covalent attachment of biomacromolecules to plasma-patterned and functionalized carbon nanotube-based devices for electrochemical biosensing.

The interface between biomacromolecules and carbon nanotubes (CNTs) is of critical importance in developing effective techniques that provide CNTs with both biomolecular recognition and signal transduction through immobilization. However, the chemical inertness of CNT surfaces poses an obstacle to wider implementation of CNTs in bioanalytical applications. In this paper, we present a review of our recent research activities related to the covalent attachment of biomacromolecules to plasma-patterned and functionalized carbon nanotube films and their application to the fabrication of electrochemical biosensing devices. The SWCNT films were spray-deposited onto a miniaturized three-electrode system on a glass substrate and activated using highly purified atomic oxygen generated in radiofrequency plasma; this introduced oxygen-containing functional groups into the SWCNT surface without fatal loss of the original physicochemical properties of the CNTs. The carboxylated SWCNT electrodes were then selectively modified via amidation or esterification for covalent immobilization of the biomacromolecules. The plasma-treated SWCNT-based sensing electrode had an approximately six times larger effective area than the untreated SWCNT-based electrode, which significantly amplified the amperometric electrochemical signal. Finally, the efficacy of plasma-functionalized SWCNT (pf-SWCNT) as a biointerface was examined by immobilizing glucose oxidase, Legionella pneumophila ( L. pneumophila)-specific antibodies, L. pneumophila-originated DNAs, and thrombin-specific aptamers on the pf-SWCNT-based three-electrode devices. The pf-SWCNT films were found to support direct covalent immobilization of the above-listed biomacromolecules on the films and to thereby overcome the many drawbacks typically associated with simple physisorption. Thus, pf-SWCNT sensing electrodes on which biomacromolecules were covalently immobilized were found to be chemically stable and have a long lifetime.

A fully microfabricated carbon nanotube three-electrode system on glass substrate for miniaturized electrochemical biosensors.

We present an integration process to fabricate single-walled carbon nanotube (SWCNT) three-electrode systems on glass substrate for electrochemical biosensors. Key issues involve optimization of the SWCNT working electrode to achieve high sensitivity, developing an optimal Ag/AgCl reference electrode with good stability, and process development to integrate these electrodes. Multiple spray coatings of the SWCNT film on glass substrate enabled easier integration of the SWCNT film into an electrochemical three-electrode system. O2 plasma etching and subsequent activation of spray-coated SWCNT films were needed to pattern and functionalize the SWCNT working electrode films without serious damage to the SWCNTs, and to remove organic residues. The microfabricated three-electrode systems were characterized by microscopic and spectroscopic techniques, and the electrochemical properties were investigated using cyclic voltammetry and chrono-amperometry. The fully-integrated CNT three-electrode system showed an effective working electrode area about three times larger than its geometric surface area and an improved electrochemical activity for hydrogen peroxide decomposition. Finally, the effectiveness of miniaturized pf-SWCNT electrodes as biointerfaces was examined by applying them to immunosensors to detect Legionella(L) pneumophila, based on a direct sandwich enzyme-linked immunosorbent assay (ELISA) format with 3,3',5,5'-tetramethylbenzidine dihydrochloride/hydrogen peroxide(TMB/H2O2) as the substrate/mediator system. The lower detection limit of the pf-SWCNT-based immunosensors to L. pneumophila is about 1500 times lower than that of the standard ELISA assay.

Plasma-activated carbon nanotube-based high sensitivity immunosensors for monitoring Legionella pneumophila by direct detection of maltose binding protein peptidoglycan-associated lipoprotein (MBP-PAL).

Transferred multi-walled carbon nanotube (MWCNT)-modified platinum thin-film immunosensing electrode material was engineered on a glass substrate and fabricated a fully-integrated electrochemical three-electrode system for monitoring Legionella pneumophila. The transferred MWCNT film was treated with oxygen plasma to improve its electrochemical response and electrical conductivity. We voltammetrically characterized and optimized the electrochemical performance of the fabricated electrode for direct detection of Legionella pneumophila-specific peptidoglycan-associated lipoprotein (PAL) and maltose binding protein (MBP) peptidoglycan-associated lipoprotein (MBP-PAL) fusion. The latter, as an intermediate product to yield the former, has important roles in the growth and purification of PAL, which commercial enzyme-linked immunosorbent assay (ELISA) kits require as a target substrate. Consequently, direct electrochemical detection of MBP-PAL compared to PAL by square-wave voltammetry showed a greater than 50% increase in sensitivity with a lower detection limit of 5 pg mL(-1). We also investigated the affinity properties by determining kinetic parameters of the PAL and the MBP-PAL in relation to polyclonal antibodies immobilized on transferred MWCNT substrates using Michaelis-Menten assumptions and a Hanes-Woolf plot. This new method presented herein could save the time and effort for the separation and purification of PAL form MBP-PAL fusions that are required for performing ELISA-based immunoassay.

Voltammetric characterization of a fully integrated, patterned single walled carbon nanotube three-electrode system on a glass substrate.

A single walled carbon nanotube (SWCNT)-based three-electrode system was fully integrated on glass substrates using a standard microfabrication process and electrochemically characterized using cyclic voltammetry. O(2) plasma functionalization of the SWCNT film working electrode for achieving high sensitivity was voltammetrically optimized with respect to the plasma power and treatment time. Chlorination of a Ag thin-film was done in an acidic solution for different dip times to form a thin-film Ag/AgCl reference electrode. The Nernstian behavior of as-prepared and seven-day-aged Ag/AgCl thin-film electrodes was investigated for seeking the optimum reference electrode with long-term stability and was compared to a commercial reference electrode. A quality control evaluation and a performance assessment of the fully integrated SWCNT-transferred sensing systems were performed using cyclic voltammetry. The proposed SWCNT-based three electrode device exhibited clear electrochemistry under voltammetric conditions, and is therefore a candidate for use in all electrochemical biosensors.

Electrochemical properties of a fully integrated, singlewalled carbon nanotube coplanar three-electrode system on glass substrate.

Fully integrated carbon nanotube-based three-electrode electrochemical systems were photolithographically prepared on glass substrates and electrochemically characterized. O(2) plasma treatment of the transferred single-walled carbon nanotube (SWCNT) film was voltammetrically optimized in terms of applied plasma power and the elapsed time. The patterned thin film Ag layer was chemically oxidized in an acidic solution for various dip times to form a chlorinated Ag layer. The Nernstian behavior of as-prepared and seven-day-aged Ag/AgCl thin-film electrodes was investigated for optimization, and the electrode's electrochemical attributes were compared to a commercial reference electrode. A quality control evaluation and a performance assessment of the fully integrated SWCNT-transferred sensing systems were performed using cyclic voltammetry. The proposed SWCNT-based three-electrode device exhibited clear electrochemistry under voltammetric conditions, and is therefore a candidate for use in all electrochemical biosensors.

Fibrillar superstructure formation of hemoglobin A and its conductive, photodynamic and photovoltaic effects.

The fabrication of biomaterials which serve as functional scaffolds exhibiting diversified effects has been valued. We report here a unique strategy to fibrillate hemoglobin A (HbA), which exhibits multiple photoelectrochemical properties, and a subsequent specific defibrillation procedure. A subtle structural rearrangement of the α/ß-subunits within the quaternary structure of HbA is responsible for the HbA fibril formation in the presence of 0.5% CHCl3. The narrow pH dependence of the suprastructure formation around pH 7.4 illustrates the highly sensitive nature of the structural alteration. The CHCl3-induced fibrils become disintegrated by ascorbic acid, indicating that the oxidation-reduction process of the iron within the heme moiety could be involved in stabilization of the fibrillar structures. The electron-transferring property of the iron allows the fibrils to exhibit not only their conductive behavior but also a photodynamic effect generating hydroxyl radicals in the presence of H(2)O(2) with light illumination. A photovoltaic effect is also demonstrated with the HbA fibrils, which generate an electric current on the fibril-coated microelectrode upon irradiation at 405nm. Taken together, the multiple effects of HbA fibrils and the selective fibrillation/defibrillation procedures could qualify the fibrils to be employed for various future applications in biotechnology, including bio-machine interfaces.

A comprehensive review of glucose biosensors based on nanostructured metal-oxides.

Nanotechnology has opened new and exhilarating opportunities for exploring glucose biosensing applications of the newly prepared nanostructured materials. Nanostructured metal-oxides have been extensively explored to develop biosensors with high sensitivity, fast response times, and stability for the determination of glucose by electrochemical oxidation. This article concentrates mainly on the development of different nanostructured metal-oxide [such as ZnO, Cu(I)/(II) oxides, MnO(2), TiO(2), CeO(2), SiO(2), ZrO(2,) and other metal-oxides] based glucose biosensors. Additionally, we devote our attention to the operating principles (i.e., potentiometric, amperometric, impedimetric and conductometric) of these nanostructured metal-oxide based glucose sensors. Finally, this review concludes with a personal prospective and some challenges of these nanoscaled sensors.

Electrochemical selective detection of dopamine on microbial carbohydrate-doped multiwall carbon nanotube-modified electrodes.

Microbial carbohydrate-doped multiwall carbon nanotube (MWNT)-modified electrodes were prepared for the purpose of determining if 4-(2-aminoethyl)benzene-1,2-diol (3,4-dihydroxyphenylalanine; dopamine) exists in the presence of 0.5 mM ascorbic acid, a representative interfering agent in neurotransmitter detection. The microbial carbohydrate dopants were alpha-cyclosophorohexadecaose (alpha-C16) from Xanthomonas oryzae and cyclic-(1 --> 2)-beta-d-glucan (Cys) from Rhizobium meliloti. The cyclic voltammetric responses showed that the highest sensitivity (5.8 x 10(-3) mA cm(-2) microM(-1)) is attained with the Cys-doped MWNT-modified ultra-trace carbon electrode, and that the alpha-C16-doped MWNT-modified glassy carbon electrode displays the best selectivity to dopamine (the approximate peak potential separation is 310 mV).

Electrochemical selectivity enhancement by using monosuccinyl beta-cyclodextrin as a dopant for multi-wall carbon nanotube-modified glassy carbon electrode in simultaneous determination of quercetin and rutin.

Monosuccinyl beta-cyclodextrin (succinyl-beta-CD) was synthesized and the selectivity to quercetin and rutin of the succinyl-beta-CD-modified, multi-wall carbon nanotube (MWNT)-coated, glassy carbon electrode [(succinyl-beta-CD + MWNT)/GCE] was investigated. (1)H NMR and MALDI-MS data confirmed molecular structure of the synthesized succinyl-beta-CD. As a dopant in carboxylated MWNT-modified electrode, succinyl-beta-CD clearly separated the peak potential (E(p)) of quercetin from that of rutin. The measured peak potential separation (DeltaE(p)) was 110 mV. More favorable complexation between succinyl-beta-CD and quercetin may enhance relative selectivity to quercetin of the (succinyl-beta-CD + MWNT)/GCE in quercetin-rutin mixture as compared to the beta-CD-modified GCE.

Performance enhancement of polyaniline-based polymeric wire biosensor.

We demonstrate here the performance enhancement of polyaniline-based biosensor using screen-printing technology and pulse mode measurement technique. Screen-printed silver electrodes were made on a nitrocellulose membrane and the distance between the two electrodes was approximately 550 microm. Resistance of the electrodes had an average of 1.4 Omega with a standard deviation of +/-0.4 Omega. The surface of nitrocellulose membrane was modified by glutaraldehyde to immobilize streptavidin. Biotinylated anti-mouse IgG was conjugated with polyaniline-coated magnetic nanoparticles. Formation of polyaniline-coated magnetic nanoparticles was confirmed by a transmission electron microscope image. The polyaniline was used as an electric signal transducer for the monitoring of the biospecific binding event. An electrical response induced by the streptavidin-biotin interaction was measured by pulse mode measurement. This measurement method reduced the resistance caused by interfacial capacitance. Dose-dependent resistance changes were also successfully analyzed by the pulse mode polymeric wire biosensor. Results showed that the pulse mode measurement technique enhanced the performance of the polyaniline-based polymeric wire biosensor by reducing the interfacial effects. This approach could be helpful in samples with high interfering background materials, such as food and clinical specimens.