Direct electrochemistry of cytochrome c immobilized on a novel macroporous gold film coated with a self-assembled 11-mercaptoundecanoic acid monolayer

We have successfully constructed a novel gold film with open interconnected macroporous walls of nanoparticles by combining the hydrogen bubble dynamic template synthesis with galvanic replacement reaction. After modified by a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (MUA), the three-dimensionally (3D) interconnected macroporous Au film has been used as a biocompatible substrate for the immobilization of cytochrome c. The morphology, structure and electrochemical features of the modified and unmodified macroporous Au films were characterized by field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results reveal that the resultant films had a large electroactive surface area for high protein loading, enhanced electron transfer of cytochrome c, retained electrochemical activity, good stability and repeatability. And the excellent electrochemical behaviors could be attributed to the hierarchical structure of the macroporous Au film constructed by nanoparticles.     

Modification of a glassy carbon surface with amine-terminated dendrimers and its application to electrocatalytic hydrazine oxidation

Amine-terminated polyamidoamine (PAMAM) dendrimers were immobilized on glassy carbon electrodes (GCEs) via electrochemical oxidation of the terminal amine groups of dendrimers. The electrochemical immobilization of dendrimers was confirmed by cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The immobilized dendrimer films were robust and behaved as charge-selective electrochemical gates for oppositely charged redox molecules. The immobilization approach was applied to assemble Au dendrimer-encapsulated nanoparticles (Au DENs, dia. 1.5 ± 0.3 nm) on GCEs, and the resulting Au DEN films showed electrocatalytic activity to hydrazine oxidation.     

Anodization of Au thin film on Al in oxalic acid

An Au thin film, which was sputter-deposited on an Al substrate, was potentiostatically anodized in oxalic acid. The Au film was first anodized and a spongelike nanoporous film grew down to the interface between Au and Al. Then, the Al was anodized and a very thin and fine nanoporous alumina film was formed underneath the nanoporous Au. Under the same anodization conditions, the current density for Al was ~ 40 μA cm^− 2, less than 1% of that for Au (~ 30 mA cm^− 2). The growth rates of the nanoporous films were ~ 0.7 nm/min for Al and 26 nm/min for Au, indicating that the growth rate of nanoporous alumina was less than 3% of that of nanoporous Au. Al is suitable as the substrate for preparing nanoporous Au films because the electrochemical reactions of both the electrolyte and the substrate are significantly suppressed when the nanopores penetrate Au and the electrolyte reaches the substrate.     

Controllable growth of gold nanowires and nanoactuators via high-frequency AC electrodeposition

An electrochemical deposition method using high-frequency alternating current (AC) signal is reported here for the in situ synthesis and assembly of Au nanowires and nanoactuators on microelectrodes without using any masks or templates. High conductivity of 3.79 ± 0.14 × 10⁷ Ω^− 1 m^− 1 is achieved on the Au nanowires assembled between electrodes. Au nanoactuators with expansion ratio of more than 500% can be fabricated at higher frequency. The actuators can act as claws to grab SiO₂ nanoparticles in a water solution when driven by an alternating electric field. Disconnected nanowires and nanoparticles which self-aligned around the electrodes were also obtained at lower gold ion concentration, indicating a different current transfer mode in AC electrodeposition.     

Fabrication and properties of three-dimensional macroporous Sn–Ni alloy electrodes of high preferential (1 1 0) orientation for lithium ion batteries

One of the most important problems in utilizing Sn-based intermetallic compound anodes is its poor cyclability due to mechanical fatigue caused by volume change during lithium insertion and extraction processes. To overcome this problem, a new facile procedure to prepare three-dimensional (3D) macroporous materials of Sn–Ni alloy by using colloidal crystal template method is presented. The structural and electrochemical characteristics of 3D macroporous Sn–Ni alloy were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), galvanostatic cycling. When used as a negative electrode for a rechargeable lithium battery, the 3D macroporous Sn–Ni alloy electrode delivered a reversible capacity of 536.1 mAh g⁻¹ up to 75th cycles.     

Hierarchically ordered porous nickel oxide array film with enhanced electrochemical properties for lithium ion batteries

Hierarchically ordered porous nickel oxide array film was prepared by electrodeposition through monolayer polystyrene spheres template. The as-prepared film had a highly porous structure of interconnected macrobowls array possessing nanopores. As anode material for lithium ion batteries, the porous array NiO film exhibited weaker polarization, higher coulombic efficiency and better cycling performance in comparison with the dense NiO film. After 50 cycles, the discharge capacity of porous array NiO film was 518 mAh g^? 1 at 1 C rate, higher than that of the dense NiO film (287 mAh g^? 1). The enhancement of the electrochemical properties was due to the unique hierarchical porous architecture, which provided fast ion/electron transfer and alleviated the structure degradation during the cycling process.     

A novel process to prepare porous membranes comprising SnO2 nanoparticles and P(MMA-AN) as polymer electrolyte

We have successfully developed a new process to prepare porous poly(methyl methacrylate-co-acrylonitrile) (P(MMA-AN)) copolymer based gel electrolyte. The porous structure in the polymer matrix is achieved by adding SnO₂ nanoparticles which are mostly used as gas sensor materials. The quasi-aromatic solvent, NMP, has an electron-repulsion effect with the space charge layer on the surface of SnO₂ nanoparticles and forms a special gas–liquid phase interface. Once the cast polymer solution is stored at an elevated temperature to evaporate the solvent, gas–liquid phase separation happens and spherical pores are obtained. The ionic conductivity at room temperature of the prepared gel polymer electrolyte based on the porous membrane is as high as 1.54 × 10⁻³ S cm⁻¹ with the electrochemical stability up to 5.10 V (vs. Li/Li⁺). This method presents another promising way to prepare porous polymer electrolyte for practical use.     

A lotus root-like porous nanocomposite polymer electrolyte

A lotus root-like porous nanocomposite polymer electrolyte (NCPE) based on poly(vinylidene difluoride-co-hexafluoropropylene) [P(VDF-HFP)] copolymer and TiO₂ nanoparticles was easily prepared by a non-solvent induced phase separation (NIPS) process. The formation mechanism of the lotus root-like porous structure is explained by a qualitative ternary phase diagram. The resulting NCPE had a high ionic conductivity up to 1.21 × 10⁻³ S cm⁻¹ at room temperature, and exhibited a high electrochemical stability potential of 5.52 V (vs. Li/Li⁺), lithium ion transference number of 0.65 and 22.89 kJ mol⁻¹ for the apparent activation energy for transportation of ions. It is of great potential application in polymer lithium ion batteries.     

Surface-enhanced Raman studies of bradykinin using colloidal gold

In this paper, bradykinin (BK), an endogenous peptide hormone, which is involved in a number of physiological and pathophysiological processes was deposited onto the colloidal Au nanoparticles. The surface-enhanced Raman spectroscopy (SERS) was used to determine the adsorption mode of BK under different environmental conditions, including: excitation wavelengths (514.5 nm and 785.0 nm), pH of aqueous sol solutions (from pH = 3 to pH = 11), and size of the colloidal nanoparticles (10, 20, and 50 nm). The metal surface plasmon of the colloidal suspended Au nanoparticles was examined by ultraviolet-visible (UV–vis) spectroscopy. The results showed that the C-terminal part of BK plays a crucial role in the adsorption process onto the colloidal suspended Au particles. The Phe^5/8 and Arg⁹ residues of BK mainly participate in the interactions with the colloidal Au nanoparticles. At acidic pH of the solution (pH = 3), the BK COO⁻ terminal group through the both oxygen atoms strongly binds to the Au nanoparticles. The Phe⁵/Phe⁸ rings adopt tilted orientation with respect to the colloidal Au nanoparticles with diameters of 10 and 20 nm. As the particle size increases to 50 nm, the flat orientation of the Phe ring(s) with respect to the Au nanoparticles is observed.     

Photoelectrochemical determination of inorganic mercury ions based on energy transfer between CdS quantum dots and Au nanoparticles

A novel photoelectrochemical (PEC) sensor for mercury ions (Hg^2 +) was fabricated based on the energy transfer (ET) between CdS quantum dots (QDs) and Au nanoparticles (NPs) with the formation of T–Hg^2 +–T pairs. In the presence of Hg^2 + ions, a T-rich single-strand (ss) DNA labeled with Au NPs could hybridize with another T-rich ssDNA anchored on the CdS QDs modified electrode, through T–Hg^2 +–T interactions, rendering the Au NPs in close proximity with the CdS QDs and hence the photocurrent decrease due to the ET between the CdS QDs and the Au NPs. Under the optimal condition, the photocurrent decrease was proportional to the Hg^2 + concentration, ranging from 3.0 × 10^− 9 to 1.0 × 10^− 7 M, with the detection limit of 6.0 × 10^− 10 M.     

Macroporous Co3O4 platelets with excellent rate capability as anodes for lithium ion batteries

This paper reports the microwave-assisted synthesis of Co₃O₄ nanomaterials with different morphologies including nanoparticles, rod-like nanoclusters and macroporous platelets. The new macroporous platelet-like Co₃O₄ morphology was found to be the best suitable for reversible lithium storage properties. It displayed superior cycling performances than nanoparticles and rod-like nanoclusters. More interestingly, excellent high rate capabilities (811 mAh g^?1 at 1780 mA g^?1 and 746 mAh g^?1 at 4450 mA g^?1) were observed for macroporous Co₃O₄ platelet. The good electrochemical performance could be attributed to the unique macroporous platelet structure of Co₃O₄ materials.     

Gold nanoparticles decorated carbon fiber mat as a novel sensing platform for sensitive detection of Hg(II)

The three-dimensional fibril-like carbon fiber mat electrode (CFME) decorated with Au nanoparticles (AuNPs) was employed to construct Hg(II) sensing platform for the first time. The highly porous feature of CFME combining the high affinity of AuNPs for mercury endowed the sensing platform with high sensitivity and good reproducibility. Under optimal conditions, the prepared AuNPs/CFME was capable of sensing Hg(II) with a detection limit of 0.1 μg L^− 1 (S/N = 3) using differential pulse anodic stripping voltammetry (DPASV). Finally, the AuNPs/CFME was successfully demonstrated for the determination of Hg(II) in real water samples with satisfactory results.     

Electro-reduction of cuprous chloride powder to copper nanoparticles in an ionic liquid

Cyclic voltammetry of the CuCl powder in a cavity microelectrode revealed direct electro-reduction in solid state in 1-butyl-3-methylimidazolium hexafluorophosphate. Potentiostatic electrolysis of the salt powder (attached to a current collector) in the ionic liquid produced Cu nanoparticles as confirmed by X-ray diffraction, energy dispersive X-ray analysis, scanning and transmission electron microscopy. The particle size decreased down to 10 nm when the electrode potential was shifted from −0.9 V to −1.8 V (versus Ag/Ag⁺). The electro-reduction and the nanoparticle formation mechanisms were investigated in the ionic liquid and also in aqueous 0.1 mol L⁻¹ KClO₄ in which larger Cu particles were obtained.     

Synthesis of Au/C and Au/Pani for anode electrodes in glucose microfluidic fuel cell

Gold nanoparticles have been prepared by two methods: chemical (ex-situ, Au/C) by two phase protocol, and electrochemical (in-situ, Au/Pani) by electroreduction of gold ions on a polyaniline film and compared as anode catalysts in a glucose microfluidic fuel cell. In this paper the structural characteristics and electrocatalytic properties were investigated by X-ray diffraction and electrochemical measurements. The catalytic behavior of both anodes was tested in a microfluidic fuel cell with a reference electrode incorporated, by means of linear sweep voltammetry (LSV), showing a cathodic shift in the glucose oxidation peak for Au/Pani. Results show a higher power density (0.5 mW cm^? 2) for Au/C anode compared with an already reported value, where a glucose microfluidic fuel cell was used in similar conditions.     

Synthesis of highly active nanostructured PtRu electrocatalyst with three-dimensional mesoporous silica template

Nanostructured PtRu material has been successively synthesized via chemical co-reduction of hexachloroplatinic acid and ruthenium trichloride using three-dimensional (3D) hexagonal mesoporous SBA-12 silica as a solid template, and has been studied as an electrocatalyst toward methanol electro-oxidation. The ordered nanostructure of the PtRu particles has been disclosed by transmission electron micrographs and is characterized by regular pores of ca. 3.0 ± 0.3 nm in diameter separated by walls of ca. 3.0 ± 0.3 nm thick. X-ray diffraction and energy dispersive X-ray spectroscope studies indicate that the PtRu material comprises of complicated phases rather than a single alloy phase of Pt and Ru. The specific electrochemical surface area of the nanostructured powder measured using both CO and underpotential deposited Cu stripping techniques is 74–78 m² g^–1, higher than that of unsupported precious metal catalysts prepared using standard techniques. The combination of high surface area and periodic nanostructure of the templated PtRu makes it an interesting promising fuel cell electrocatalyst. This has been demonstrated by the high activity of the templated PtRu towards the methanol electrooxidation. Therefore the solid template route based on 3D mesoporous silica with controlled pore size and high pore interconnectivity provides an interesting alternative to produce promising high-surface-area electrode materials.     

Characterization of thin InP anodic oxide layers: Correlation of morphological investigations with chemical and electrical properties

Depending on the applied electrochemical parameters, various oxide films can be grown onto InP in aqueous media. In this work, two oxide layers have been grown in borate buffer solution at pH = 9 by applying a low (0.2 mA cm⁻²) or a high (30 mA cm⁻²) current density, but a similar coulometric charge. Capacitance–voltage measurements performed before and after the anodic processes have been made to investigate the electrical properties of new interfaces, while X-ray photoelectron spectroscopy (XPS) analysis and atomic force microscopy (AFM) observations were used to access to the chemical and topographic aspects of the two oxidized surfaces. It is demonstrated that AFM observations coupled with electrochemical and XPS measurements is a good probe for the study of thin oxide on InP. A correlation between the anodization parameters and the resulting electrical and morphological aspects of the anodic layers is clearly evidenced.     

Achieving high electrode specific capacitance with materials of low mass specific capacitance: Potentiostatically grown thick micro-nanoporous PEDOT films

Electrode materials for supercapacitors are at present commonly evaluated and selected by their mass specific capacitance (C_M, F g⁻¹). However, using only this parameter may be a misleading practice because the electrode capacitance also depends on kinetics, and may not increase simply by increasing material mass. It is therefore important to complement C_M by the practically accessible electrode specific capacitance (C_E, F cm⁻²) in material selection. Poly[3,4-ethylene-dioxythiophene] (PEDOT) has a mass specific capacitance lower than other common conducting polymers, e.g. polyaniline. However, as demonstrated in this communication, this polymer can be potentiostatically grown to very thick films (up to 0.5 mm) that were porous at both micro- and nanometer scales. Measured by both cyclic voltammetry and electrochemical impedance spectrometry, these thick PEDOT films exhibited electrode specific capacitance (C_E, F cm⁻²) increasing linearly with the film deposition charge, approaching 5 F cm⁻², which is currently the highest amongst all reported materials.     

Mesoporous silica thin film mechanized with a DNAzyme-based molecular switch for electrochemical biosensing

A novel electroanalytical strategy for copper and ascorbic acid detection was developed by using a nanostructured electrode surface mechanized with a DNAzyme-based molecular gate. This sensing interface was constructed by first electrodeposition of a mesoporous silica thin film on Au electrodes and further assembly of a Cu(II)-specific DNAzyme. The biosensing assay was based on the Cu(II) and ascorbic acid responsible activation of the DNAzyme, which acted as a molecular switch able to control the diffusion of the Fe(CN)₆^{3 −/4 −} electrochemical probe through the nanochannels of the mesoporous film.     

A study on solution deposited CuSCN thin films: Structural,electrochemical, optical properties

A cost-effective successive ionic layer adsorption and reaction (SILAR) method was used to deposit copper (I) thiocyanate (CuSCN) thin films on glass and steel substrates for this study. The deposited thin films were characterized for their structural, morphological, optical and electrochemical properties using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy and VersaSTAT potentiostat. A direct band gap of 3.88 eV and 3.6 eV with film thickness of 0.7 μm and 0.9 μm was obtained at 20 and 30 deposition cycles respectively. The band gap, microstrain, dislocation density and crystal size were observed to be thickness dependent. The specific capacitance of the CuSCN thin film electrode at 20 mV/s was 760 F g⁻¹ for deposition 20 cycles and 729 F g⁻¹ for deposition 30 cycles.     

Fabrication and electrochemical performance of nickel ferrite nanoparticles as anode material in lithium ion batteries

Nano-sized nickel ferrite (NiFe₂O₄) was prepared by hydrothermal method at low temperature. The crystalline phase, morphology and specific surface area (BET) of the resultant samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and nitrogen physical adsorption, respectively. The particle sizes of the resulting NiFe₂O₄ samples were in the range of 5–15 nm. The electrochemical performance of NiFe₂O₄ nanoparticles as the anodic material in lithium ion batteries was tested. It was found that the first discharge capacity of the anode made from NiFe₂O₄ nanoparticles could reach a very high value of 1314 mAh g⁻¹, while the discharge capacity decreased to 790.8 mAh g⁻¹ and 709.0 mAh g⁻¹ at a current density of 0.2 mA cm⁻² after 2 and 3 cycles, respectively. The BET surface area is up to 111.4 m² g⁻¹. The reaction mechanism between lithium and nickel ferrite was also discussed based on the results of cycle voltammetry (CV) experiments.