Self-assembled Electrode Research Articles

Self-Assembled Au Electrode for Direct Electrochemistry of Horseradish Peroxidase and Detection of Hydrogen Peroxide

The H2O2 biosensor was prepared by continuous processes: 2,3-dimercaptosuccinic acid (DMSA) self-assembly monolayers gold nanoparticles (AuNPs) film by electrodepositioncovalent immobilization of horseradish peroxidase (HRP). In pH 7.2 phosphoric buffer solution (PBS), the HRP-AuNPs-DMSA-Au electrode exhibited a pair of well-defined cyclic voltammetric peaks in H2O2 solution, and the oxidation peak is about +0.4V versus saturated calomel electrode (SCE). The resulting substrates were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The biosensor exhibited remarkable sensitivity towards H2O2 and a wide dynamic range of 2-800 μM. The electrode retained 90% of its initial activity after 30 days of storage at 4°C.

Layer-by-Layer Self-Assembled Carbon Nanotube Electrode for Microbial Fuel Cells Application

Anodic material is usually a limiting factor in power generation in microbial fuel cell (MFC). A meditatorless two-chambered MFC was constructed using new type of carbon nanotube (CNT)-based electrode architecture by layer-by-layer (LBL) self-assembly to increase power density. Multi-walled carbon nanotube (MWNT) and polyeletrolyte polyethyleneimine (PEI) were employed to modify carbon paper (CP) electrode utilizing a LBL self-assembly technique, and the electrochemical properties and performance of the modified electrode as an anode in MFC were investigated. The CNT-based LBL self-assembled electrode showed a better electrochemical performance than that of unmodified CP electrode. The self-assembled MWNT/PEI onto CP produced the maximum power density of 480 mW/m2, which was 48% larger than that of the plain CP anode. The CNT-based LBL self-assembled electrode therefore offers good prospects for application in MFCs.

Highly Transparent Conductive Sheet by Self-assembled Silver Network Electrodes with Antireflective Coating via Roll-to-Roll Process

A highly transparent conductive film was fabricated using self-assembled silver electrodes with anti-reflection (AR) film. The micro pore diameter of sliver nanoparticles (ca 50～60nm in diameter) network electrodes expanded to size of 200-300 μm by the increase of air voids with evaporated water. The transmittance of the silver network electrode increased was drastically increased by the optical interference from the AR film on the surface and it showed a maximal value 84％ (sheet resistance: 8.0 Ω/□). The surface resistance of silver network electrodes films did not change even after coating with the AR films because thickness of AR films (ca 100～200 nm) are extremely thin compared with the diameter of the silver wire (ca 3 μm). High performance transparent conductive film for electric and optical devic was successfully fabricated by roll to roll layer-by-layer (LBL) process.

A nano-structured Ni(II)–chelidamic acid modified gold nanoparticle self-assembled electrode for electrocatalytic oxidation and determination of methanol

A nano-structured Ni(II)–chelidamic acid (2,6-dicarboxy-4-hydroxypyridine) film was electrodeposited on a gold nanoparticle–cysteine–gold electrode. The morphology of Ni(II)–chelidamic acid gold nanoparticle self‐assembled electrode was investigated by scanning electron microscopy (SEM). Electrocatalytic oxidation of methanol on the surface of modified electrode was studied by cyclic voltammetry and chronoamperometry methods. The hydrodynamic amperometry at a rotating modified electrode at constant potential versus reference electrode was used for detection of methanol. Under optimized conditions the calibration plots are linear in the concentration range 0–50mM with a detection limit of 15μM. The formed matrix in our work possessed a 3D porous network structure with a large effective surface area, high catalytic activity and behaved like microelectrode ensembles. The modified electrode indicated reproducible behavior and a high level stability during the experiments, making it particularly suitable for analytical purposes.

Optical immunosensor using carbon nanotubes coated with a photovoltaic polymer

In this work, an on-chip optical immunosensor using an individually assembled carbon nanotube (CNT) coated with a photovoltaic polymer has been proposed, developed, characterized, and applied for the detection of cardiac biomarkers. An individual CNT was self-assembled on a nickel (Ni)-patterned electrode by magnetically attracting the residual iron catalyst at one end of the CNT. After the CNT self-assembled electrode was prepared, it was coated with a photovoltaic polymer to implement a CNT photodetector. Under an incident light, the photovoltaic polymer generated electrons that changed the conductivity of the CNT. The CNT photodetector was finally insulated with parylene to prevent interruptions of charged molecules in a sample solution, such as non-specifically bound proteins and various ions. Chemiluminescent immunoassay was directly performed on the CNT photodetector for an on-chip detection of cardiac troponin T (cTnT) with a detection limit of 12pg/mL. High sensitivity and reliable selectivity have been achieved through the use of on-chip measurement of chemiluminescent light by the CNT photodetector. As a result, the developed device is envisaged as a new platform for optical immunosensing using the individually self-assembled CNT for point-of-care (POC) clinical diagnostics.

DNA Electrochemical Biosensor Based on Au Nanoparticles Self-Assembled Au Electrode

A novel electrochemical DNA biosensor system based on Au nanoparticles (AuNPs) modified Au electrode and anthraquinone-2,6-disulfonic acid (AQDS) as hybridization indicator was presented in this paper. AuNPs with different particle sizes were prepared from gold chloride by reduction, and self-assembled on Au electrode (AuNPs/Au electrode) by cysteamine as linker. Then, 5’ end –SH modified DNA (HS-DNA) as nucleotide probes were self-assembled onto the surface of AuNPs modified Au electrode (HS-DNA/AuNPs/Au electrode), and the HS-DNA/AuNPs/Au electrode could detect target DNA (completely complementary with HS-DNA). Because AuNPs were on Au electrode, the surface of Au electrode was increased. Therefore, this would result in the increase of electrochemical signal and increase the sensitivity of biosensor. If a completely complementary single stranded DNA (ssDNA) as target existed in the detection system, the cathodic peak current (△Ip) of AuNPs modified Au electrode was increased about 3 times than the HS-DNA/AuNPs/Au electrode because of the hybridization between HS-DNA and complementary DNA target and the formation of double stranded DNA (dsDNA), and if the target was a mismatching base-pair with HS-DNA, the electrochemical signal of electrode would have no obviously change. These results showed that this DNA biosensor system based on AuNPs self-assembled Au electrode had an excellent sensitivity with a complete complementary DNA sequence.

A nano-structured Ni(II)–ACDA modified gold nanoparticle self-assembled electrode for electrocatalytic oxidation and determination of tryptophan

A nano-structured Ni (II)/ACDA (2-amino-1-cyclopentene-1-dithiocarboxylic acid) film was electrodeposited on a gold nanoparticle–cysteine–gold electrode. The formation of Ni (II)/ACDA film and electrocatalytic oxidation of tryptophan on the surface of the modified electrode were investigated with cyclic voltammetric and chronoamperometric techniques. The hydrodynamic amperometry at rotating modified electrode was used for determination of tryptophan in the range of 0.085–43.0 μmol l −1. The detection limit was found to be 23 nmol l −1. The rate constant, transfer coefficient for the catalytic reaction and the diffusion coefficient of tryptophan in the solution were found to be 9.1 × 10 2 M −1 S −1, 0.52 and 1.09 × 10 −5 cm 2 s −1 respectively. It is worth noting that the as formed matrix in our work possesses a 3D porous network structure with a large effective surface area and high catalytic activity and behaves like microelectrode ensembles. The modified electrode indicated reproducible behavior and a high level stability during the experiments, making it particularly suitable for the analytical purposes.

Hydrogen peroxide sensor based on Prussian blue electrodeposited on (3-mercaptopropyl)-trimethoxysilane polymer-modified gold electrode

A hydrogen peroxide (H(2)O(2)) sensor was developed by electrodepositing Prussian blue (PB) on a gold electrode modified with (3-mercaptopropyl)-trimethoxysilane (MPS) polymer. The characterization of the self-assembled electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The results of electrochemical experiments showed that such constructed sensor had a favorable catalytic ability to reduce H(2)O(2). The MPS film on the modified gold electrode greatly enhanced the pH-adaptive range of PB. Large surface-to-volume ratio property of double-layer 2d-network MPS-modified PB electrode enabled stable and highly sensitive performance of the non-enzymatic H(2)O(2) sensor. The linear range of H(2)O(2) determined is from 2.0×10(-6) to 2.0×10(-4) mol L(-1) with a correlation coefficient of 0.9991 and a detection limit for H(2)O(2) of 1.8×10(-6) mol L(-1). The influences of the potentially interfering substances on the determination of H(2)O(2) were investigated. This modified electrode exhibits a good selectivity and high sensitivity with satisfactory results.

Electrochemical recognition for sugars on the chitosan-poly(diallyldimethylammonium chloride)-nano-Prussian blue/nano-Au/4-mercaptophenylboronic acid modified glassy carbon electrode

A new amperometric biosensor for the detection of sugars was prepared. A glassy carbon electrode was modified with Prussian blue (PB) nanoparticles protected by chitosan (CS) and poly(diallyldimethylammonium chloride) (PDDA), and then gold nanoparticles were assembled onto the electrode followed by the assembly of 4-mercaptophenylboronic acid (MPBA) onto the surface of gold nanoparticles through a sulfur-Au bond to fabricate a self-assembled biosensor. The PB nanoparticles protected by CS and PDDA were characterized using transmission electron microscopy and UV-vis absorption spectroscopy. The characterization of the self-assembled electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The pKa values of the MPBA monolayer before and after combining with sugars were determined. The fabricated electrode exhibited excellent performances for determining D(+)-glucose, D(+)-mannose, and D(-)-fructose on the basis of the change in i(p) of the Fe(CN)6(3-/4-) ion in the presence of sugars.

Ternary Self-Assembly of Ordered Metal Oxide−Graphene Nanocomposites for Electrochemical Energy Storage

Surfactant or polymer directed self-assembly has been widely investigated to prepare nanostructured metal oxides, semiconductors, and polymers, but this approach is mostly limited to two-phase materials, organic/inorganic hybrids, and nanoparticle or polymer-based nanocomposites. Self-assembled nanostructures from more complex, multiscale, and multiphase building blocks have been investigated with limited success. Here, we demonstrate a ternary self-assembly approach using graphene as fundamental building blocks to construct ordered metal oxide-graphene nanocomposites. A new class of layered nanocomposites is formed containing stable, ordered alternating layers of nanocrystalline metal oxides with graphene or graphene stacks. Alternatively, the graphene or graphene stacks can be incorporated into liquid-crystal-templated nanoporous structures to form high surface area, conductive networks. The self-assembly method can also be used to fabricate free-standing, flexible metal oxide-graphene nanocomposite films and electrodes. We have investigated the Li-ion insertion properties of the self-assembled electrodes for energy storage and show that the SnO2-graphene nanocomposite films can achieve near theoretical specific energy density without significant charge/discharge degradation.

A novel layer-by-layer self-assembled carbon nanotube-based anode: Preparation, characterization, and application in microbial fuel cell

To exploit the outstanding ability of carbon nanotubes to facilitate electron transfer in a microbial fuel cell (MFC) system, multi-wall carbon nanotube (MWNT) and polyeletrolyte polyethyleneimine (PEI) were employed to modify carbon paper (TP) electrode utilizing a layer-by-layer (LBL) assemble technique for the first time, and the performance of the modified electrode as an anode in MFC was investigated. This modification strategy ensured a relatively high content of MWNTs within the polymer matrix. IR and cyclic voltammetry (CV) demonstrated the uniform formation of a polyethyleneimine/MWNT multilayer composite on the TP surface. The SEM profiles presented a three-dimensional MWNTs interwoven network surface structure with a large accessible surface area. Electrochemical impedance spectroscopy (EIS) measurements confirmed that the existence of polyelectrolyte/MWNT multilayers decreased the interfacial charge transfer resistance from 1163 to 258 Ω. With the modified anode, the MFC produced a higher power density with 20% enhancement comparing to the bare TP anode. The MWNT-based LBL self-assembled electrode is promising for the electricity production by MFC.

Lithium Ion Electro-Insertion and Spectroelectrochemical Properties of Films from Hexaniobate

Layer-by-layer (LbL) films from K2Nb6O172− and polyallylamine (PAH) and dip-coating films of H2K2Nb6O17 were prepared on a fluorine-doped tin−oxide (FTO)-coated glass. The atomic force microscopy (AFM) images were carried out for morphological characterization of both materials. The real surface area and the roughness factor were determined on the basis of pseudocapacitive processes involved in the electroreduction/electrooxidation of gold layers deposited on these films. Next, lithium ion insertion into these materials was examined by means of electrochemical and spectroelectrochemical measurements. More specifically, cyclic voltammetry and current pulses under visible light beams were used to investigate mass transport and chromogenic properties. The lithium ion diffusion coefficient (DLi) within the LbL matrix is significantly higher than that within the dip-coating film, ensuring high storage capacity of lithium ions in the self-assembled electrode. Contrary to the LbL film, the potentiodynamic profil...

2,3-Dimercaptosuccinic acid self-assembled gold electrode for the simultaneous determination of epinephrine and dopamine

Simultaneous determination of epinephrine (EP) and dopamine (DA) at 2,3-dimercaptosuccinic acid (DMSA) modified electrode was studied. The oxidation peaks of the mixture of EP and DA appeared at the same potential, but the cathodic peak currents were only linear to the concentration of DA, whereas the anodic peak currents were equal to the sum of individual anodic peak currents of EP and DA. Therefore, a novel electrochemical method for the simultaneous determination of EP and DA at a DMSA modified electrode (DMSA/Au electrode) by cyclic voltammetry was established. The DMSA self-assembled electrode showed good sensitivity, selectivity and stability and could be used to determine DA and EP, simultaneously, in the real application with satisfactory results.

Self-assembly of a silver nanoparticles modified electrode and its electrocatalysis on neutral red

Silver nanoparticles (AgNP) were synthesized with NaBH4 as reducing agent and oleate as stabilizer. AgNP and L-cysteine (L-cys) were co-deposited on a gold electrode surface to fabricate the AgNP/L-cys modified electrode (AgNP/L-cys/Au). First, we prepared the L-cysteine self-assembled film modified gold electrode through S-Au bond, then it was rinsed into the Ag colloid solution to prepare the Ag nanoparticles/L-cysteine modified electrode through interaction of the silver surface and the carboxylate and amino groups of L-cysteine. After the self-assembled electrode was prepared, the electrochemical behavior of the modified electrode was investigated. The electrochemical response of neutral red (NR) on the modified electrode was investigated. The electrochemical response of cyclic voltammetry and determination by differential pulse voltammetry of neutral red on the modified electrode were reported. We also observed that the modified electrode catalyzes the redox process of neutral red, which provided another way of applying Ag nanoparticles in composite neutral red-AgNP films.

Electrochemical Biosensors in Nonaqueous Solutions and Their Applications

This review first describes the invention of functional interfaces to promote biochemical redox reactions between substrates in dipolar aprotic solvents and enzymes or related compounds immobilized at the interface. The interfaces contain hydrophilic polymer membranes, a gold nanoparticle self-assembled electrode constructed by using rigid rod dithiols, and binary self-assembled monolayers composed of amino and carboxyl terminal groups. Other topics covered are: the electrochemical characterization of the hydrophilic polymer membrane; the development of biosensors to obtain reaction parameters of enzymatic and of electrochemical kinetics; and applications to the study of materials involved in metabolism.

Trapping of Charge Carriers in Colloidal Particles of Self-Assembled Films from TiO2 and Poly(vinyl sulfonic acid)

Self-assembled electrodes consisting of TiO(2) nanoparticles and poly(vinyl sulfonic acid) (PVS) were prepared by the layer-by-layer (LbL) technique. The electrostatic interaction between the TiO(2) nanoparticles and PVS allowed the growth of visually uniform multilayers of the composite, with high control of the thickness and nanoarchitecture. The electrochemical and chromogenic properties of these TiO(2)/PVS films were examined in an electrolytic solution of 0.5 M LiClO(4)/propylene carbonate. The presence of two intercalation sites was noted during the positive potential scan, and they were attributed to different mobilities of charge carriers. Several charge/discharge cycles demonstrated the trapping of charge carriers in the TiO(2) sites. The absorbance change associated with the oxidation of the trapping sites was attributed to electronic transitions involving energy states in the gap band formed due to the strong distortion of the TiO(2) host. Using the quadratic logistic equation (QLE), it was possible to analyze the electronic intervalence transfer from Ti(3+) to Ti(4+). Using the parameters obtained from this fitting, the amount of trapping sites in the LbL film was also determined. Electrochemical impedance spectroscopy (EIS) data gave the time constant associated with diffusion and the trapping sites. The diffusion coefficient of lithium ions changed from ca. 4.5 x 10(-13) cm(2) s(-1) to 3.0 x 10(-14) cm(2) s(-1) for all the potential range applied, indicating that PVS did not hinder the ionic transport within the LbL film. Finally, on the basis of the spectroelectrochemical data and scanning electron micrographs, the trapping effects were attributed to the colloidal particles of Li(0.55)TiO(2).

Electrogenerated chemiluminescence of luminol in neutral and alkaline aqueous solutions on a silver nanoparticle self‐assembled gold electrode

The electrochemiluminescence (ECL) behaviour of luminol on a silver nanoparticle self-assembled gold electrode in neutral and alkaline solutions was investigated using conventional cyclic voltammetry (CV). The silver nanoparticle self-assembled gold electrode exhibited excellent ECL properties for the luminol ECL system. In neutral solutions, four ECL peaks (ECL-1-ECL-4) were observed at 0.73, 1.15, -0.46 and -1.35 V (vs. SCE), respectively. The intensities of these peaks were enhanced significantly compared with those on a bulk gold electrode and a gold nanoparticle self-assembled gold electrode. It was found that ECL-1 and ECL-2 on a silver nanoparticle-modified electrode were about 1000 and 1770 times stronger than those on a bare Au electrode and were about 17 and 15 times stronger than those on a gold nanoparticle-modified electrode, respectively. In alkaline solutions, four ECL peaks were also observed that were much stronger than those in neutral solutions, and ECL-1 and ECL-2 were enhanced by about three orders and one order of magnitude compared with those on a bare Au electrode and on a gold nanoparticle self-assembled electrode, respectively. Moreover, the silver nanoparticle-modified electrode exhibited good stability and reproducibility for luminol ECL. These peaks were found to depend on a number of factors, including silver nanoparticles on the surface of the modified electrode, potential scan direction, scan rate, scan range, the presence of O2 or N2, pH values, the concentrations of NaBr and luminol, and buffer solutions. The emitter of the ECL was confirmed as 3-aminophthalate by analysing the CL spectra. The surface state of the silver nanoparticle self-assembled electrode was characterized by scanning electron microscopy (SEM) and the interface property of the electrode was studied by electrochemical impedance spectroscopy (EIS). A mechanism for the formation of these ECL peaks is proposed. The results demonstrate that luminol has excellent ECL properties, such as strong ECL intensity and good reproducibility on a silver nanoparticle-modified gold electrode, in both neutral and alkaline solutions, which is of great potential in analytical applications.

Electrochemical Behavior of Dopamine at a Penicillamine Self‐Assembled Gold Electrode and its Analytical Application

The fabrication and electrochemical characteristics of penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The self-assembled electrode shows an obvious electrocatalytic activity for the oxidation of dopamine (DA). In phosphate buffer (pH 7.0), the peak current is proportional to the concentration of DA in the range of 8.0 x 10(-6) approximately 1.0 x 10(-3) M by the cyclic voltammetry methods with the detection limits of 4.5 x 10(-7) M. The PCA self-assembled monolayer modified gold electrode can be applied to the determination of DA in practical injection samples with simplicity, rapidness, and accurate results.

Fabrication and Electrocatalysis of Self-Assembly Directed Gold Nanoparticles Anchored Carbon Nanotubes Modified Electrode

A self-assembly directed approach was adopted to modify glassy carbon electrode (GC) with gold nanoparticles incorporation and the electrocatalytic performance of self-assembly modified electrode, GC/SA-Au-ME was critically evaluated for the oxidation of ascorbic acid (AA). The modification involves the dispersion of multi-wall carbon nanotube (MWNT) and an inclusion complex, beta-cyclodextrin-4-aminothiophenol on the surface of GC electrode in the presence of cetyltrimethylammonium bromide (CTAB). Gold nanoparticles were deposited into the self-assembled sites to fabricate the modified electrode, GC/SA-Au-ME. Another electrode (GC-Au-ME) was fabricated under similar conditions in the absence of CTAB. The electrocatalytic activity of the modified electrodes (GC/SA-Au-ME and GC-Au-ME) towards the oxidation of AA was critically compared. Cyclic voltammetry, chronoamperometry, and double potential chronoamperometry were used to evaluate the characteristics of the modified electrodes. The self-assembled electrode (GC/SA-Au-ME) shows excellent electrocatalytic activity over the other electrode, GC-Au-ME. Augmented current response, faster electron transfer kinetics (with a rate constant for electron transfer process as 3.25 x 10(4) cm3 mol(-1) s(-1)), linear range of response for the analyte (1-50 mM with an extended detection limit to 1 microM), better sensitivity, and selectivity were witnessed for the self-assembly directed modified electrode.

Electrochemical Behavior of Uric Acid and Epinephrine at a Meso-2,3-Dimercaptosuccinic Acid Self-Assembled Gold Electrode

A self-assembled electrode with a meso-2,3-dimercaptosuccinic acid (DMSA) monolayer has been characterized by electrochemical quartz crystal microbalance and complex impedance analysis, surface enhanced Raman spectroscopy and cyclic voltammetry. The self-assembled electrode was used for the simultaneous electrochemical detection of epinephrine (EP) and uric acid (UA) in phosphate buffer of pH 7.7. The simultaneous oxidation of EP and UA was performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and the signals for each method were well separated with a potential difference of over 330 mV and without interference by each other. The detection limit of EP is 5.4 × 10−8 mol L−1 by CV and 5.3 × 10−8 mol L−1 by DPV and that of UA is 8.4 × 10−8 mol L−1 by CV and 4.2 × 10−8 mol L−1 by DPV. The DMSA self-assembled electrode can be applied to the simultaneous determination of EP and UA.