Hydrogen peroxide biosensor based on gold nanoparticles/thionine/gold nanoparticles/multi-walled carbon nanotubes-chitosans composite film-modified electrode

In this paper, an amperometric electrochemical biosensor for the detection of hydrogen peroxide (H₂O₂), based on gold nanoparticles (GNPs)/thionine (Thi)/GNPs/multi-walled carbon nanotubes (MWCNTs)-chitosans (Chits) composite film was developed. MWCNTs-Chits homogeneous composite was first dispersed in acetic acid solution and then the GNPs were in situ synthesized at the composite. The mixture was dripped on the glassy carbon electrode (GCE) and then the Thi was deposited by electropolymerization by Au-S or Au-N covalent bond effect and electrostatic adsorption effect as an electron transfer mediator. Finally, the mixture of GNPs and horseradish peroxidase (HRP) was assembled onto the modified electrode by covalent bond. The electrochemical behavior of the modified electrode was investigated by scanning electron microscope, cyclic voltammetry and chronoamperometry. This study introduces the in situ-synthesized GNPs on the other surface of the modified materials in H₂O₂ detection. The linear response range of the biosensor to H₂O₂ concentration was from 5 × 10⁻⁷ mol L⁻¹ to 1.5 × 10⁻³ mol L⁻¹ with a detection limit of 3.75 × 10⁻⁸ mol L⁻¹ (based on S/N = 3).     

Study on the electrochemical behavior of vanadium nitride as a promising supercapacitor material

Vanadium nitride (VN) powder was synthesized by calcining V₂O₅ xerogel in a furnace under an anhydrous NH₃ atmosphere at 400 °C. The structure and surface morphology of the obtained VN powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The supercapacitive behavior of VN in 1 M KOH electrolyte was studied by means of cyclic voltammetry (CV), constant current charge-discharge cycling (CD) and electrochemical impedance spectroscopy (EIS). The XRD result indicates that the obtained VN belongs to the cubic crystal system (Fm3m [2 2 5]) with unit-cell parameter 4.15 Å. SEM images show the homogeneous surface of the obtained VN. The CV diagrams illustrate the existence of fast and reversible redox reactions on the surface of VN electrode. The specific capacitance of VN is 161 F g⁻¹ at 30 mV s⁻¹. Furthermore, the specific capacitance remains 70% of the original value when the scan rate increases from 30 to 300 mV s⁻¹. CD experiments show that VN is suitable for CD at high current density, and the slow and irreversible faradic reactions exist during the charge-discharge process of the VN electrode. The experimental results indicate that VN is a promising electrode material for electrochemical supercapacitors.     

Preparation and electrochemical characterization of cobalt-manganese oxide as electrode materials for electrochemical capacitors

Cobalt-manganese oxide materials (CMOs) were prepared by chemical method and heat treated at 150, 400, 600, 800 and 1000 °C, respectively. The physical and electrochemical properties of the materials were characterized. The heat treatment process leads to the removal of water molecules adsorbed on the surface of CMO particles (below 400 °C) and the progressive reduction of Mn and Co ions from Mn⁴⁺ and Co³⁺ to Mn³⁺/Mn²⁺ and Co²⁺, respectively (440-1000 °C). CMOs obtained by treatment below 800 °C have poor crystallinity and a highly crystallized tetragonal phase by treatment at 1000 °C. The ratio of Mn and Co in CMOs is found by EDX analysis to be about 2:1. The electrochemical testing results indicate that the high crystallization of CMO is disadvantageous for the energy storage as electrode material of electrochemical capacitors. However, for CMOs with poor crystallinity, relatively high specific capacitances can be obtained. The incorporation of protons and ions into the CMO's lattice during electrochemical charge/discharge process leads to the distortion of crystal lattice and improvement of crystallinity of CMO. The XRD patterns show that negative electrode (NE) and positive electrode (PE) have tetragonal (Co, Mn)(Mn, Co)₂O₄ phase.     

Dependence of intermediated noble metals on the optical and electrical properties of ITO/metal/ITO multilayers

Sn doped In₂O₃ (ITO) single layer and a sandwich structure of ITO/metal/ITO (IMI) multilayer films were deposited on a polycarbonate substrate using radio-frequency and direct-current magnetron sputtering process without substrate heating. The intermediated metal films in the IMI structure were Au and Cu films and the thickness of each layer in the IMI films was kept constant at 50 nm/10 nm/40 nm. In this study, the ITO/Au/ITO films show the lowest resistivity of 5.6 × 10⁻⁵ Ω cm.However the films show the lower optical transmission of 71% at 550 nm than that (81%) of as deposited ITO films. The ITO/Cu/ITO films show an optical transmittance of 54% and electrical resistivity of 1.5 × 10⁻⁴ Ω cm. Only the ITO/Au/ITO films showed the diffraction peaks in the XRD pattern. The figure of merit indicated that the ITO/Au/ITO films performed better in a transparent conducting electrode than in ITO single layer films and ITO/Cu/ITO films.     

Intercalation of lithium ions into bulk and powder highly oriented pyrolytic graphite

The electrochemical reactions of highly oriented pyrolytic graphite (HOPG) bulk and powder electrodes in 1 M LiPF₆ 1:1 EC/DMC solution were investigated and the results show that the intercalation reaction of lithium ion into HOPG electrode occurs only at the edge plane and SEI formation reaction on the basal plane is negligible in comparison with that on the edge plane. The active surface area of HOPG powder electrode could be deduced by comparing the peak area (consumed charge for SEI formation) at potential of 0.5 V on voltammograms with that of bulk HOPG edge electrode. The diffusion coefficients of lithium ion in HOPG bulk layers and in HOPG powder was for the first time measured by use of electrochemical impedance spectra and potential step chronamperameter methods. It was found that the diffusion coefficients of lithium in HOPG were in the range of 10⁻¹¹-10⁻¹² cm² s⁻¹ for the lithium-HOPG intercalation compounds at potentials from 0.2 (vs. Li/Li⁺) to 0.02 V, decreasing with the increase of lithium intercalation degree. A good agreement was obtained between the results from bulk and powder HOPG electrodes by electrochemical impedance spectra method.     

The luminescence and optoelectrical properties of ITO films prepared by a sputter type negative metal ion deposition

Transparent conducting indium tin oxide (ITO) thin films were prepared on glass substrates by a magnetron sputter type negative ion source which requires cesium (Cs) vapor injection for surface negative ionization on the ITO target surface. Although the film was prepared at 70 °C, it attained high optical transmittance, 88% and low resistivity, 2.03 × 10⁻⁴ Ω cm, at an optimized Cs partial pressure of P_Cs = 1.7 × 10⁻³ Pa. The as-deposited ITO films have a poly-crystalline structure with (2 1 1), (2 2 2), (4 0 0), (4 1 1) and (4 4 0) reflections.Also, ITO films prepared at P_Cs = 1.7 × 10⁻³ Pa were post-deposition vacuum annealed at 300 °C for 30 min. The films had a resistivity of 1.8 × 10⁻⁴ Ω cm and a transparency of 89.2%. The post-deposition vacuum annealed ITO film was used as an anode for a transparent organic light emitting diode (TOLED). A maximum luminance of 19,000 cd/m² was obtained.     

Electrochemical and surface characterisation of carbon-film-coated piezoelectric quartz crystals

The electrochemical properties of carbon films, of thickness between 200 and 500 nm, sputter-coated on gold- and platinum-coated 6 MHz piezoelectric quartz crystal oscillators, as new electrode materials have been investigated. Comparative studies under the same experimental conditions were performed on bulk electrodes. Cyclic voltammetry was carried out in 0.1 M KCl electrolyte solution, and kinetic parameters of the model redox systems Fe(CN)₆^3−/4− and [Ru(NH₃)₆]^3+/2+ as well as the electroactive area of the electrodes were obtained. Atomic force microscopy was used in order to examine the surface morphology of the films, and the properties of the carbon films and the electrode-solution interface were studied by electrochemical impedance spectroscopy. The results obtained demonstrate the feasibility of the preparation and development of nanometer thick carbon film modified quartz crystals. Such modified crystals should open up new opportunities for the investigation of electrode processes at carbon electrodes and for the application of electrochemical sensing associated with the EQCM.     

Electrochemical synthesis of Ag nanoparticles supported on glassy carbon electrode by means of p-isopropyl calix[6]arene matrix and its application for electrocatalytic reduction of H2O2

The silver nanoparticles were prepared on the glassy carbon (GC) electrode, modified with p-iso propyl calix[6]arene, by preconcentration of silver ions in open circuit potential and followed by electrochemical reduction of silver ions. The stepwise fabrication process of Ag nanoparticles was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The prepared Ag nanoparticles were deposited with an average size of 70 nm and a homogeneous distribution on the surface of electrode. The observed results indicated that the presence of calixarene layer on the electrode surface can control the particle size and prevent the agglomeratione and electrochemical deposition is a promising technique for preparation of nanoparticles due to its easy-to-use procedure and low cost of implementation. Cyclic voltammetry experiments showed that Ag nanoparticles had a good catalytic ability for the reduction of hydrogen peroxide (H₂O₂). The effects of p-isopropyl calix[6]arene concentration, applied potential for reduction of Ag⁺, number of calixarene layers and pH value on the electrocatalytic ability of Ag nanoparticles were investigated. The present modified electrode exhibited a linear range from 5.0 × 10⁻⁵ to 6.5 × 10⁻³ M and a detection limit 2.7 × 10⁻⁵ M of H₂O₂ (S/N = 3) using amperometric method.     

Pulsed Nd:YAG laser depositions of ITO and DLC films for OLED applications

Indium-tin oxide (ITO) films deposited on heated and non-heated glass substrates by a pulsed Nd:YAG laser at 355 nm and ∼2.5 J/cm² were used in the fabrication of simple organic light-emitting diodes (OLEDs), ITO/(PVK + Alq₃ + TPD)/Al. The ITO was deposited on heated glass substrates which possessed resistivity as low as ∼3 × 10⁻⁴ Ω cm, optical transmission as high as ∼92% and carrier concentration of about ∼5 × 10²⁰ cm⁻³, were comparable to the commercial ITO. Substrate heating transformed the ITO microstructure from amorphous to polycrystalline, as revealed by the XRD spectrum. While the polycrystalline ITO produced higher OLED brightness, it was still lower than that on the commercial ITO due to surface roughness. A DLC layer of ∼1.5 nm deposited on this ITO at laser fluence of >12.5 J/cm² improved its device brightness by suppressing the surface roughness effect.     

Synthesis and characterization of β-Ni(OH)2 up grown nanoflakes by SILAR method

In this paper we report a “bottom up” approach to synthesize β-Ni(OH)₂ nanoflakes using novel successive ionic layer adsorption and reaction (SILAR) method. Ni(OH)₂ thin films have been deposited on glass substrate using aqueous alkaline nickel chloride as nickel ion source and double distilled water maintained at 353 K temperature as hydroxyl ion source. The structural, surface morphological, optical and electrical properties of films are examined. The nanocrystallinity and β-phase of Ni(OH)₂ are confirmed by X-ray diffraction and FT-IR studies. Scanning electron microscope study revealed microporous and random distribution of well up grown interlocked nanoflakes. Optical absorption studies show wide optical band gap of 3.26 eV for β-Ni(OH)₂. The electrical properties revealed that β-Ni(OH)₂ has negative temperature coefficient of resistance with p-type semiconducting behaviour. The electrochemical property studied by cyclic voltametry in 2 M KOH electrolyte solution revealed pseudo capacitive behaviour, when β-Ni(OH)₂ thin film employed as working electrode in three electrode electrochemical cell with platinum as counter electrode and saturated calomel as reference electrode. The specific capacitance of 350 F g⁻¹ is obtained with nanoflake like morphology.     

Preparation, characterization and application of a nanostructured composite: Octakis(cyanopropyldimethylsiloxy)octasilsesquioxane

Octakis(cyanopropyldimethylsiloxy)octasilsesquioxane was prepared and characterized by ¹³C, ²⁹Si NMR (MAS), SEM, FT-IR, XRD and thermogravimetric techniques. The four groups α, β, γ, κ (to the terminal silicon atom), associated with an acrylonitrile, were clearly seen in the ¹³C NMR (α-CH₂ at 17.9; β-CH₂ at 31.3; γ-CH₂ at 50.4; κ-CN at 59.0 ppm). The ²⁹Si NMR spectrum of the final product, exhibits only Q type silicon signal, ascribed to Q⁴ (−118.0 ppm). The presence of acrylonitrile substituted for octameric cube confers a relative change phase and thermal stability to the material. With regard to the applications for this new material, it was intended, in this case, to react with Na₂[Fe(CN)₅NH₃] by chemical substitution. This composite was incorporated into a carbon paste electrode and the electrochemical studies were performed by cyclic voltammetry. The cyclic voltammogram of the modified graphite paste electrode, showed one redox couples with formal potential () = 0.24 V versus SCE.     

Electrochemical properties of α-Fe2O3 /MWCNTs as anode materials for lithium-ion batteries

α-Fe₂O₃/MWCNTs composites were prepared by a simple hydrothermal process. The crystalline structure and the electrochemical performance of the as-synthesized samples were investigated. Results show that as anode materials for lithium-ion batteries, the α-Fe₂O₃/MWCNTs exhibit an initial discharge capacity of 1256 ± 5 mAh g⁻¹ and a stable specific discharge capacity of 430 ± 5 mAh g⁻¹ at ambient temperature, for up to 100 cycles with no noticeable capacity fading, while the initial discharge capacity of the bare Fe₂O₃ is 992.3 mAh g⁻¹, and the discharge capacity is 146.6 mAh g⁻¹ after 100 cycles. Moreover, the α-Fe₂O₃/MWCNTs composites also exhibit excellent rate performance.     

NbTi0.5Ni0.5O4 as anode compound material for SOFCs

NbTi_0.5Ni_0.5O₄ (NTNO) has been prepared using solid state synthesis and investigated as a potential anode material. The oxide form of NTNO has single phase rutile-type structure with tetragonal (P42/mnm) space group. The reduced form is a composite of nano-scaled particles of metallic Ni and Nb_1.33Ti_0.67O₄ phase. Reduced NTNO showed high electronic conductivity up to 280 S.cm^− 1 at 900 °C in reducing atmosphere, but suffers from low CTE equal to 3.78 10^− 6 K^− 1. Studies of NTNO as anode material were carried out in a three electrode - electrochemical half cell configuration under pure humidified H₂ at 900 °C using a 2 mm thick zirconia electrolyte and without any additional current collector material. The results show a reasonable series resistance (R_s) equal to 2.7 Ωcm² (about 50% higher than for metallic gold layers) indicating a good current collection performance for a 10 μm layer of material. The polarization resistance (R_p) was equal to 33 Ωcm² and is attributed to a poor density of three phase boundaries (TPB) and shortage of oxide ion conduction in the anode layer. The results show the potential of NTNO as an anode material, especially after optimization of the microstructure towards the increase of TPB length.     

Optical and electrochemical properties of ordered macroporous gold array on the ITO surface

The electrochemical and optical properties of transparent, two-dimensional macroporous gold film were investigated. Colloidal crystal templates were assembled onto indium-doped tin oxide (ITO) glass surface through vertical depositing method. Following gold electrodeposition, they were removed by dissolution with tetrahydrofuran (THF). The highly ordered macroporous gold array was achieved. It was characterized by scanning electron microscope (SEM) and ultraviolet visible (UV-vis) spectrophotometry. The optical transparency of the gold film was near 25% and fairly constant between 300 and 900 nm. The macroporous gold film electrode was mounted into a thin-layer transmission cell. The electrochemical response was evaluated by thin-layer cyclic voltammograms (CV) of the Fe (CN)₆³⁻/Fe (CN)₆⁴⁻ couple. Thin-layer cell exhibits good shape of waves and nearly symmetric cathodic and anodic waves. E⁰′ value and n of TMPD⁺/TMPD (TMPD is acronyms for N,N,N′,N′-tetramethyl-p-phenylenediamine, and TMPD⁺ is its mono-cation radical) couple were determined. Furthermore, results demonstrated electrolytic equilibrium was faster reached in macroporous gold film than ITO electrode.     

Synthesis of [Ru3(μ3-NPh)(Br)(CO)9] on self-assembled monolayers of di(3-aminopropyl)viologen/ITO surfaces and its application to photoelectrochemical cells

Triruthenium carbonyl clusters {[Ru₃(Br)(CO)₁₁]⁻ (denoted as Ru-1), [Ru₃(μ₂-Br)(CO)₁₀]⁻ (denoted as Ru-2), and [Ru₃(μ₃-NPh)(Br)(CO)₉]⁻ (denoted as Ru-3)} were synthesized on di(3-aminopropyl)viologen (DAPV)/indium tin oxide (ITO) using a surface reaction in a ruthenium (III) carbonyl [Ru₃(CO)₁₂] solution, and were applied to photoelectrochemical cells (PECs) at the molecular level. The formation of DAPV on ITO was realized in the form of self-assembled monolayers. Ru₃(CO)₁₂ then easily reacted with the Br⁻ of DAPV, and a mixture of Ru-1 and Ru-2 was formed on DAPV/ITO. Furthermore, Ru-3 was successfully anchored on DAPV/ITO by adding nitrosobenzene in order to react with Ru-2 on DAPV/ITO. The photocurrents of (Ru-1 and Ru-2)/DAPV/ITO and Ru-3/DAPV/ITO in PECs at the molecular level were 6.3 nA cm⁻² and 8.6 nA cm⁻², respectively. The quantum yield of Ru-3/DAPV/ITO was ∼0.8%. Time-resolved photoluminescence spectroscopy and emission spectroscopy were recorded to bring out the photoinduced charge transfer process from ruthenium clusters to DAPV.     

Preparation and characterization of nanocrystalline ITO thin films on glass and clay substrates by ion-beam sputter deposition method

Nanocrystalline indium tin oxide (ITO) thin films were prepared on clay-1 (Clay-TPP-LP-SA), clay-2 (Clay-TPP-SA) and glass substrates using ion-beam sputter deposition method. X-ray diffraction (XRD) patterns showed that the as-deposited ITO films on both clay-1 and clay-2 substrates were a mixture of amorphous and polycrystalline. But the as-deposited ITO films on glass substrates were polycrystalline. The surface morphologies of as-deposited ITO/glass has smooth surface; in contrast, ITO/clay-1 has rough surface. The surface roughnesses of ITO thin films on glass and clay-1 substrate were calculated as 4.3 and 83 nm, respectively. From the AFM and SEM analyses, the particle sizes of nanocrystalline ITO for a film thickness of 712 nm were calculated as 19.5 and 20 nm, respectively. Optical study showed that the optical transmittance of ITO/clay-2 was higher than that of ITO/clay-1. The sheet resistances of as-deposited ITO/clay-1 and ITO/clay-2 were calculated as 76.0 and 63.0 Ω/□, respectively. The figure of merit value for as-deposited ITO/clay-2 (12.70 × 10⁻³/Ω) was also higher than that of ITO/clay-1 (9.6 × 10⁻³/Ω), respectively. The flexibilities of ITO/clay-1 and ITO/clay-2 were evaluated as 13 and 12 mm, respectively. However, the ITO-coated clay-2 substrate showed much better optical and electrical properties as well as flexibility as compared to clay-1.     

Effect of ultrasonic irradiation on structure and electrochemical properties of LiMn2O4 thin films cathode material for Li-ion micro-batteries

Two kinds of spinel LiMn₂O₄ thin film for lithium ion micro-batteries were successfully prepared on polycrystal Pt substrates by spin coating methods, which were carried out under ultrasonic irradiation (USG) and magnetic stirring (MSG), respectively. The microstructures and electrochemical performance of LiMn₂O₄ thin films were characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge-discharge measurements. It was found that the crystalline structure of USG samples grew better than that of the MSG samples. At the same time, higher discharge capacity and better cycle stability were obtained for the LiMn₂O₄ thin films of USG at the current density of 50 μAh/cm² between 3.0 and 4.3 V. The 1st discharge capacity was 57.8 μAh/cm²-μm for USG thin films and 51.7 μAh/cm²-μm for MSG thin films. After 50 cycles, 91.4% and 69% of discharge capacity could be retained respectively, indicating that ultrasonic irradiation condition during spin coating was more suitable for preparing spinel LiMn₂O₄ thin films with better electrode performance for lithium ion micro-batteries.     

Modification of multi-walled carbon nanotubes for electric double-layer capacitors: Tube opening and surface functionalization

Multi-walled carbon nanotubes (MWCNTs) obtained opening the closed ends and using surface functionalization by means of a combination of partial oxidation in air and chemical modifications are characterized systematically in 0.3 M H₂SO₄ between 0 and 1.0 V, and these nanotubes were planned to be used as electrode materials in electric double-layer capacitors (EDLCs). Opening of MWCNTs, clearly observed by means of transmission electron microscopy (TEM), can be easily achieved by the partial oxidation in air through a seven-step temperature program identified by thermogravimetric/differential thermal analyses (TG/DTA). An increase in 175% specific capacitance is obtained for the MWCNTs, partially oxidized in air and chemically modified in H₂SO₄+HNO₃. The temperature-programmed desorption (TPD) data showed that evolutions of CO and CO₂ are, respectively, promoted by the application of partial oxidation in air and chemical modification in H₂SO₄+HNO₃. The above increase in specific capacitance for modified MWCNTs is attributed to an obvious increase in the BET surface area (double-layer capacitance) and the density of oxygen-containing surface functional groups (pseudocapacitance).     

DNA hybridization and phosphinothricin acetyltransferase gene sequence detection based on zirconia/nanogold film modified electrode

This study reports a novel electrochemical DNA biosensor based on zirconia (ZrO₂) and gold nanoparticles (NG) film modified glassy carbon electrode (GCE). NG was electrodeposited onto the glassy carbon electrode at 1.5 V, and then zirconia thin film on the NG/GCE was fabricated by cyclic voltammetric method (CV) in an aqueous electrolyte of ZrOCl₂ and KCl at a scan rate of 20 mV/s. DNA probes were attached onto the ZrO₂/NG/GCE due to the strong binding of the phosphate group of DNA with the zirconia film and the excellent biocompatibility of nanogold with DNA. CV and electrochemical impedance spectroscopy (EIS) were used to characterize the modification of the electrode and the probe DNA immobilization. The electrochemical response of the DNA hybridization was measured by differential pulse voltammetry (DPV) using methylene blue (MB) as the electroactive indicator. After the hybridization of DNA probe (ssDNA) with the complementary DNA (cDNA), the cathodic peak current of MB decreased obviously. The difference of the cathodic peak currents of MB between before and after the hybridization of the probe DNA was used as the signal for the detection of the target DNA. The sequence-specific DNA of phosphinothricin acetyltransferase (PAT) gene in the transgenic plants was detected with a detection range from 1.0 × 10⁻¹⁰ to 1.0 × 10⁻⁶ mol/L, and a detection limit of 3.1 × 10⁻¹¹ mol/L.     

Formation mechanism of Si(1 0 0) surface morphology in alkaline fluoride solutions

Formation mechanism of Si(1 0 0) surface morphology in alkaline fluoride solutions was investigated both theoretically and experimentally. By analysis of Raman spectra of silicon wafer surfaces and three kinds of etching solutions (NaOH, NaOH/NH₄F, and NaOH/NH₄F/Na₂CO₃) with and without addition of Na₂SiO₃·9H₂O, no Si-F bond is formed, F⁻ and CO₃²⁻ ions accelerate the condensation of Si-OH groups. Based on experimental results, it is proposed that bare silicon and silicon oxide coexist at the wafer surface during etching process and silicon oxide of different structure, size, and site at the surface manufacture different surface morphology in alkaline fluoride solution.