Selective Determination of Dopamine on a Boron‐Doped Diamond Electrode Modified with Gold Nanoparticle/Polyelectrolyte‐coated Polystyrene Colloids

Negatively charged gold nanoparticles (AuNPs) and a polyelectrolyte (PE) have been assembled alternately on a polystyrene (PS) colloid by a layer‐by‐layer (LBL) self‐assembly technique to form three‐dimensional (Au/PAH)₄/(PSS/PAH)₄ multilayer‐coated PS spheres (Au/PE/PS multilayer spheres). The Au/PE/PS multilayer spheres have been used to modify a boron‐doped diamond (BDD) electrode. Cyclic voltammetry is utilized to investigate the properties of the modified electrode in a 1.0 M KCl solution that contains 5.0 × 10^?3 M K₃Fe(CN)₆, and the result shows a dramatically decreased redox activity compared with the bare BDD electrode. The electrochemical behaviors of dopamine (DA) and ascorbic acid (AA) on the bare and modified BDD electrode are studied. The cyclic voltammetric studies indicate that the negatively charged, three‐dimensional Au/PE/PS multilayer sphere‐modified electrodes show high electrocatalytic activity and promote the oxidation of DA, whereas they inhibit the electrochemical reaction of AA, and can effectively be used to determine DA in the presence of AA with good selectivity. The detection limit of DA is 0.8 × 10^?6 M in a linear range from 5 × 10^?6 to 100 × 10^?6 M in the presence of 1 × 10^?3 M AA.     

Gold‐Cluster Sensors Formed Electrochemically at Boron‐Doped‐Diamond Electrodes: Detection of Dopamine in the Presence of Ascorbic Acid and Thiols

Gold clusters have been electrodeposited on a boron‐doped diamond (BDD) electrode by scanning the potential from 0.7 V to 0.0 V (vs. 3 M KCl‐Ag/AgCl reference) in a solution of 0.5 mM KAuCl₄ and 1.0 M KCl. The cluster‐modified diamond (Au/BDD) electrode has been used to investigate the oxidative properties of dopamine (DA) and ascorbate (AA). The modified diamond electrode shows a higher activity for DA oxidation than AA; the oxidation potential of DA shifted to a less‐positive potential (0.11 V) than that of AA, which oxidized at 0.26 V, and DA possesses a much higher peak current than that of AA. The reversibility of the electrode reaction with DA is significantly improved at the Au/BDD electrode, which results in a large increase in the square‐wave voltammetric peak current, with a detection limit of 0.1 μM in the presence of a large excess of AA. The Au/BDD electrode shows excellent sensitivity and good selectivity for DA detection. A self‐assembled monolayer (SAM) of mercaptoacetic acid on the Au clusters was used to provide an antifouling effect as the negative CO₂^– groups repulse negative ascorbate and attract positive dopamine in pH 7.4 buffer. After pre‐absorption, the SAM/Au/BDD electrode could detect 1.0 nM DA in a linear range from 10 nM to 10 μM in the presence of 10^–4 M AA.     

Carbon Electrodes Modified with TiO2/Metal Nanoparticles and Their Application for the Detection of Trinitrotoluene

The preparation of modified, catalytically active, functional carbon electrodes and their application to the electrochemical reduction of trinitrotoluene (TNT) is reported. Modification of the electrodes is performed with composites of nanometer‐sized, mesoporous titanium dioxide, which acts as a support containing inserted/deposited nanoparticles of ruthenium, platinum, or gold. These composites are prepared by a novel sonochemical synthesis using simple and low‐cost precursors. Cyclic voltammetry shows that 2,4,6‐trinitrotoluene can be reduced on thus‐modified carbon‐paper electrodes at potentials of around –0.5 V (vs. Ag/AgCl/Cl^–) in aqueous solutions. Unexpectedly, carbon‐paper electrodes modified with the TiO₂/nano‐Pt composites demonstrate a remarkable electrochemical activity toward the reduction of trinitrotoluene. A significant finding is that the two electrode processes—the reduction of TNT and of oxygen—are quite well separated in potential on the modified carbon‐paper electrodes because of selective electrochemical activity of the TiO₂/nano‐Pt and TiO₂/nano‐Au composites. TiO₂/nano‐Ru composites are found to be much less electrochemically active for the detection of TNT compared to the previous two. It was also established that the titanium dioxide support of TiO₂/nano‐Pt composites plays a specific role for facilitating the TNT‐ and oxygen‐reduction processes.     

Syntheses,Properties and Electrochemical Activity of Carbon Microtubes Modified with Amino Groups

Amine‐modified carbon micro/sub‐microtubes that encapsulate magnetite cores have been synthesized by decomposing a ferrocene/hexabromobenzene mixture in the presence of ammonia under solvothermal conditions at 250 °C for 24 h in a one‐step process. The as‐prepared carbon microstructures (NH₂‐ME‐CMTs) were 90–2000 nm in diameter and from tens to hundreds of micrometers in length that could be tuned in various solvents. The surface of the carbon microtubes can be modified with amino groups by the synthetic process, as confirmed by infra‐red (IR) spectroscopy and X‐ray photoelectron spectroscopy (XPS). Ammonia in the reaction system plays a key role in the formation of the microtube morphology and was the source of the surface functionalization groups. Fluorescent fluorescein isothiocyanate (FITC) was selected as a model compound and successively attached to the amino groups of the carbon microtubes. This result confirms the reactivity of the amino groups on the surface of the carbon microtubes. The inner magnetite cores were removed after immersion in 1 M HCl solution at room temperature over two months, and hollow carbon microtubes (NH₂‐H‐CMTs) were obtained. The magnetite‐encapsulated carbon microtubes and the hollow carbon microtubes were coated on gold electrodes to prepare carbon microtube‐modified gold electrodes. The two electrodes have been used to investigate the oxidative properties of dopamine (DA) and ascorbic acid (AA). Different from the magnetite‐encapsulated microtube‐modified electrode, the hollow microtube‐modified electrode can be utilized in the selective detection of DA in the presence of a large excess of AA. The electrochemical behaviour of DA and AA on the hollow carbon microtubes modified with amino groups is similar to that on carbon nanotubes. This result suggests that the one‐step synthesis method will not change the electrochemical properties or break the backbone structure of the carbon microtubes.     

Manipulating the Sensitivity and Selectivity of OECT‐Based Biosensors via the Surface Engineering of Carbon Cloth Gate Electrodes

Organic electrochemical transistors (OECTs) provide the opportunity to fabricate flexible biosensors with high sensitivity. However, there are currently very few methods to improve the selectivity of OECT sensors. In this work, nitrogen/oxygen‐codoped carbon cloths (NOCCs) are prepared by the carbonization of polyaniline‐wrapped carbon cloths at 750 °C under different atmospheres. The resulting NOCC electrodes exhibit different electrochemical sensing behaviors toward ascorbic acid (AA) and dopamine (DA), enabling the fabrication of OECT sensors with high sensitivity and selectivity that are comparable to the state‐of‐the‐art OECT sensors for AA and DA. The structural characterization and theoretical calculation reveal that the electrochemical sensing behaviors of the NOCC electrodes are closely related to their surface compositions, providing an unprecedented strategy for the design of flexible OECT sensors with high sensitivity and selectivity.     

合成扫速对聚苯胺电极电容性能的影响

采用循环伏安法在不锈钢网上合成了导电聚苯胺(PANI)。研究了合成扫速分别为5,10,20,50,100 mV/s时聚苯胺电极的性能。结果表明,扫速为5 mV/s时生成的聚苯胺膜孔隙最小,比表面积最大,电阻最小,具有最好的电容性能,在0.1 A/g和1 A/g充放电电流密度下,其比容量分别达860 F/g和485 F/g。     

Highly Ordered Platinum‐Nanotubule Arrays for Amperometric Glucose Sensing

Direct glucose sensing on highly ordered platinum‐nanotubule array electrodes (NTAEs) is systematically investigated. The NTAEs are fabricated by electrochemical deposition of platinum in a 3‐aminopropyltrimethoxysilane‐modified anodic alumina membrane. Their structures and morphologies are then characterized using X‐ray diffraction and scanning electron microscopy, respectively. Electrochemical results show that NTAEs with different real surface areas could be achieved by controlling the deposition time or by using anodic alumina membranes with different pore size. Electrochemical responses of the as‐synthesized NTAEs to glucose in a solutions of either 0.5 M H₂SO₄, or phosphate‐buffered saline (PBS, pH 7.4) containing 0.1 M KCl are discussed. Based on the different electrochemical reaction mechanisms of glucose and interferents such as p‐acetamedophenol and ascorbic acid, their high roughness factor makes NTAEs sensitive, selective, and stable enough to be a kind of biosensor for the non‐enzymatic detection of glucose. Such a glucose sensor allows the determination of glucose in the linear range 2–14 mM, with a sensitivity of 0.1 μA cm^–2 mM^–1 (correlation coefficient 0.999), and a detection limit of 1.0 μM glucose, with neglectable interference from physiological levels of 0.1 mM p‐acetamedophenol, 0.1 mM ascorbic acid, and 0.02 mM uric acid.     

Microscopic and Nanoscopic Three‐Phase‐Boundaries of Platinum Thin‐Film Electrodes on YSZ Electrolyte

Agglomerated Pt thin films have been proposed as electrodes for electrochemical devices like micro‐solid oxide fuel cells (μ‐SOFCs) operating at low temperatures. However, comprehensive studies elucidating the interplay between agglomeration state and electrochemical properties are lacking. In this contribution the electrochemical performance of agglomerated and “dense” Pt thin film electrodes on yttria‐stabilized‐zirconia (YSZ) is correlated with their microstructural characteristics. Besides the microscopically measurable triple‐phase‐boundary (tpb) where Pt, YSZ and air are in contact, a considerable contribution of “nanoscopic” tpbs to the electrode conductivity resulting from oxygen permeable grain boundaries is identified. It is demonstrated that “dense” Pt thin films are excellent electrodes provided their grain size and thickness are in the nanometer range. The results disprove the prevailing idea that the performance of Pt thin film electrodes results from microscopic and geometrically measurable tpbs only.     

Thin‐Film Electrodes: Microscopic and Nanoscopic Three‐Phase‐Boundaries of Platinum Thin Film Electrodes on YSZ Electrolyte (Adv. Funct. Mater. 3/2011)

Agglomerated Pt thin films have been proposed as electrodes for electrochemical devices like micro‐solid oxide fuel cells (μ‐SOFCs) operating at low temperatures. However, comprehensive studies elucidating the interplay between agglomeration state and electrochemical properties are lacking. In this contribution the electrochemical performance of agglomerated and “dense” Pt thin film electrodes on yttria‐stabilized‐zirconia (YSZ) is correlated with their microstructural characteristics. Besides the microscopically measurable triple‐phase‐boundary (tpb) where Pt, YSZ and air are in contact, a considerable contribution of “nanoscopic” tpbs to the electrode conductivity resulting from oxygen permeable grain boundaries is identified. It is demonstrated that “dense” Pt thin films are excellent electrodes provided their grain size and thickness are in the nanometer range. The results disprove the prevailing idea that the performance of Pt thin film electrodes results from microscopic and geometrically measurable tpbs only.     

One‐Pot Preparation of Polymer–Enzyme–Metallic Nanoparticle Composite Films for High‐Performance Biosensing of Glucose and Galactose

New polymer–enzyme–metallic nanoparticle composite films with a high‐load and a high‐activity of immobilized enzymes and obvious electrocatalysis/nano‐enhancement effects for biosensing of glucose and galactose are designed and prepared by a one‐pot chemical pre‐synthesis/electropolymerization (CPSE) protocol. Dopamine (DA) as a reductant and a monomer, glucose oxidase (GOx) or galactose oxidase (GaOx) as the enzyme, and HAuCl₄ or H₂PtCl₆ as an oxidant to trigger DA polymerization and the source of metallic nanoparticles, are mixed to yield polymeric bionanocomposites (PBNCs), which are then anchored on the electrode by electropolymerization of the remaining DA monomer. The prepared PBNC material has good biocompatibility, a highly uniform dispersion of the nanoparticles with a narrow size distribution, and high load/activity of the immobilized enzymes, as verified by transmission/scanning electron microscopy and electrochemical quartz crystal microbalance. The thus‐prepared enzyme electrodes show a largely improved amperometric biosensing performance, e.g., a very high detection sensitivity (99 or 129 µA cm^?2 mM ^?1 for glucose for Pt PBNCs on bare or platinized Au), a sub‐micromolar limit of detection for glucose, and an excellent durability, in comparison with those based on conventional procedures. Also, the PBNC‐based enzyme electrodes work well in the second‐generation biosensing mode. The proposed one‐pot CPSE protocol may be extended to the preparation of many other functionalized PBNCs for wide applications.     

Highly Efficient Electrochemiluminescence of Functionalized Tris(2,2′‐bipyridyl)ruthenium(II) and Selective Concentration Enrichment of Its Coreactants

An enhanced electrochemiluminescence (ECL) efficiency is obtained from the ruthenium complex tris(2,2′‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) by introduction of an ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMImBF₄). Upon addition of 1 % (v/v) BMImBF₄ to 0.1 mM Ru(bpy)₃²⁺ solution, a maximum increase in ECL intensity is obtained both at an indium tin oxide (ITO) electrode (15‐fold) and at a glassy carbon (GC) electrode (5‐ to 6‐fold). Furthermore, upon addition of 1 % (v/v) BMImBF₄ to 5 μM Ru(bpy)₃²⁺/100 mM co‐reactant systems at a GC electrode, IL adsorption occurs at the electrode surface, which results in a change of the polarity of the electrode surface. Such functionalization greatly improves the functions of both Ru(bpy)₃²⁺ and ionic liquids, as is demonstrated in the sensitive and selective concentration enrichment of the Ru(bpy)₃²⁺ co‐reactants.     

Optimized La0.6Sr0.4CoO3–δ Thin‐Film Electrodes with Extremely Fast Oxygen‐Reduction Kinetics

La_0.6Sr_0.4CoO_3–δ (LSC) thin‐film electrodes are prepared on yttria‐stabilized zirconia (YSZ) substrates by pulsed laser deposition at different deposition temperatures. The decrease of the film crystallinity, occurring when the deposition temperature is lowered, is accompanied by a strong increase of the electrochemical oxygen exchange rate of LSC. For more or less X‐ray diffraction (XRD)‐amorphous electrodes deposited between ca. 340 and 510 °C polarization resistances as low as 0.1 Ω cm² can be obtained at 600 °C. Such films also exhibit the best stability of the polarization resistance while electrodes deposited at higher temperatures show a strong and fast degradation of the electrochemical kinetics (thermal deactivation). Possible reasons for this behavior and consequences with respect to the preparation of high‐performance solid oxide fuel cell (SOFC) cathodes are discussed.     

High-Stability Platinum Nano-Electrocatalyst Synthesized by Cyclic Voltammetry for Oxygen Reduction Reaction

Cyclic voltammetry as a simple electrochemical deposition method was developed in order to prepare a platinum nano-electrocatalyst for oxygen reduction reaction (ORR) in low-temperature fuel cell systems. The morphology of the prepared platinum was evaluated by scanning electron microscopy and energy dispersive x-ray analysis. The effects of platinum concentration in electrodeposition solution and scan numbers of cyclic voltammetry (scan rate: 50 m V s^?1, between 1.489 and ??0.311 versus reversible hydrogen electrode) on the performance of prepared electrocatalysts for ORR were studied. The fabricated electrodes were evaluated by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The results revealed that the optimum conditions for the preparation of electrocatalysts were 2E?3 M H₂PtCl₆ and 30 scan numbers. The optimized electrode showed high stability after 1200 cycles.     

Conductive Mesocellular Silica–Carbon Nanocomposite Foams for Immobilization,Direct Electrochemistry,and Biosensing of Proteins

A mesocellular silica–carbon nanocomposite foam (MSCF) is designed for the immobilization and biosensing of proteins. The as‐prepared MSCF has a highly ordered mesostructure, good biocompatibility, favorable conductivity and hydrophilicity, large surface area, and a narrow pore‐size distribution, as verified by transmission electron microscopy (TEM), IR spectroscopy, electrochemical impedance spectroscopy (EIS), nitrogen adsorption–desorption isotherms, pore size distribution plots, and water contact angle measurements. Using glucose oxidase (GOD) as a model, the MSCF is tested for immobilization of redox proteins and the design of electrochemical biosensors. GOD molecules immobilized in the mesopores of the MSCF show direct electrochemistry with a fast electron transfer rate (14.0 ± 1.7 s^–1) and good electrochemical performance. Based on a decrease of the electrocatalytic response of the reduced form of GOD to dissolved oxygen, the proposed biosensor exhibits a linear response to glucose concentrations ranging from 50 μM to 5.0 mM with a detection limit of 34 μM at an applied potential of –0.4 V. The biosensor shows good stability and selectivity and is able to exclude interference from ascorbic acid (AA) and uric acid (UA) species that always coexist with glucose in real samples. The nanocomposite foam provides a good matrix for protein immobilization and biosensor preparation.     

A Low‐Cost,Self‐Standing NiCo2O4@CNT/CNT Multilayer Electrode for Flexible Asymmetric Solid‐State Supercapacitors

The demand for a new generation of flexible, portable, and high‐capacity power sources increases rapidly with the development of advanced wearable electronic devices. Here we report a simple process for large‐scale fabrication of self‐standing composite film electrodes composed of NiCo₂O₄@carbon nanotube (CNT) for supercapacitors. Among all composite electrodes prepared, the one fired in air displays the best electrochemical behavior, achieving a specific capacitance of 1,590 F g^?1 at 0.5 A g^?1 while maintaining excellent stability. The NiCo₂O₄@CNT/CNT film electrodes are fabricated via stacking NiCo₂O₄@CNT and CNT alternately through vacuum filtration. Lightweight, flexible, and self‐standing film electrodes (≈24.3 µm thick) exhibit high volumetric capacitance of 873 F cm^?3 (with an areal mass of 2.5 mg cm^?2) at 0.5 A g^?1. An all‐solid‐state asymmetric supercapacitor consists of a composite film electrode and a treated carbon cloth electrode has not only high energy density (≈27.6 Wh kg^?1) at 0.55 kW kg^?1 (including the weight of the two electrodes) but also excellent cycling stability (retaining ≈95% of the initial capacitance after 5000 cycles), demonstrating the potential for practical application in wearable devices.     

Effect of Immobilized Nerve Growth Factor on Conductive Polymers: Electrical Properties and Cellular Response

The use of biologically active dopants in conductive polymers allows the polymer to be tailored for specific applications. The incorporation of nerve growth factor (NGF) as a co‐dopant in the electrochemical deposition of conductive polymers is evaluated for its ability to elicit specific biological interactions with neurons. The electrochemical properties of the NGF‐modified conducting polymers are studied by impedance spectroscopy and cyclic voltammetry. Impedance measurements at the neurobiologically important frequency of 1 kHz reveal that the minimum impedance of the NGF‐modified polypyrrole (PPy) film, 15 kΩ, is lower than the minimum impedance of peptide‐modified PPy film (360 kΩ). Similar results are found with NGF‐modified poly(3,4‐ethylene dioxythiophene) (PEDOT). The microstructure of the conductive polymer films is characterized by optical microscopy and electron microscopy and indicates that the NGF‐functionalized polymer surface topology is similar to that of the unmodified polymer film. Optical and fluorescence microscopy reveal that PC‐12 (rat pheochromacytoma) cells adhered to the NGF‐modified substrate and extended neurites on both PPy and PEDOT, indicating that the NGF in the polymer film is biologically active. Taken together these data indicate that the incorporation of NGF can modify the biological interactions of the electrode without compromising the conductive properties or the morphology of the polymeric film.     

Synthesis of Potassium‐Modified Graphene and Its Application in Nitrite‐Selective Sensing

Chemical modification with foreign atoms is a leading strategy to intrinsically modify the properties of host materials. Among them, potassium (K) modification plays a critical role in adjusting the electronic properties of carbon materials. Graphene, a true 2D carbon material, has shown fascinating applications in electrochemical sensing and biosensing. In this work, a facile and mild strategy to K‐modifying in graphene at room‐temperature is reported for the first time. X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectra, and cyclic voltammetry are used to characterize this K‐modified graphene. The K‐modified graphene is capable of acting as an electron transfer medium and more efficiently promotes charge transfer than unmodified graphene. A highly sensitive and stable amperometric sensor based on its excellent electrocatalytic activity toward the oxidation of NO₂^? is proposed. The sensor shows a linear range from 0.5 μM to 7.8 mM with a detection limit of 0.2 μM at a signal‐to‐noise ratio of 3. The modified electrode has excellent analytical performance and can be successfully applied in the determination of NO₂^? released from liver cancer and leukemia cells and shows good application potential in biological systems.     

Biomimetic Approach to Confer Redox Activity to Thin Chitosan Films

Electron transfer in biology occurs with individual or pairs of electrons, and is often mediated by catechol/o‐quinone redox couples. Here, a biomimetic polysaccharide‐catecholic film is fabricated in two steps. First, the stimuli‐responsive polysaccharide chitosan is electrodeposited as a permeable film. Next, the chitosan‐coated electrode is immersed in a solution containing catechol and the electrode is biased to anodically‐oxidize the catechol. The oxidation products covalently graft to the chitosan films as evidenced by electrochemical quartz crystal microbalance (EQCM) studies. Cyclic voltammetry (CV) measurements demonstrate that the catechol‐modified chitosan films are redox‐active although they are non‐conducting and cannot directly transfer electrons to the underlying electrode. The catechol‐modified chitosan films serve as a localized source or sink of electrons that can be transferred to soluble mediators (e.g., ferrocene dimethanol and Ru(NH₃) ₆Cl₃). This electron source/sink is finite, can be depleted, but can be repeatedly regenerated by brief (30 s) electrochemical treatments. Further, the catechol‐modified chitosan films can i) amplify currents associated with the soluble mediators, ii) partially‐rectify these currents in either oxidative or reductive directions (depending on the mediator), and iii) switch between regenerated‐ON and depleted‐OFF states. Physical models are proposed to explain these novel redox properties and possible precedents from nature are discussed.     

Bench‐Top Fabrication of Hierarchically Structured High‐Surface‐Area Electrodes

Fabrication of hierarchical materials, with highly optimized features from the millimeter to the nanometer scale, is crucial for applications in diverse areas including biosensing, energy storage, photovoltaics, and tissue engineering. In the past, complex material architectures have been achieved using a combination of top‐down and bottom‐up fabrication approaches. A remaining challenge, however, is the rapid, inexpensive, and simple fabrication of such materials systems using bench‐top prototyping methods. To address this challenge, the properties of hierarchically structured electrodes are developed and investigated by combining three bench‐top techniques: top‐down electrode patterning using vinyl masks created by a computer‐aided design (CAD)‐driven cutter, thin film micro/nanostructuring using a shrinkable polymer substrate, and tunable electrodeposition of conductive materials. By combining these methods, controllable electrode arrays are created with features in three distinct length scales: 40 μm to 1 mm, 50 nm to 10 μm, and 20 nm to 2 μm. The electrical and electrochemical properties of these electrodes are analyzed and it is demonstrated that they are excellent candidates for next generation low‐cost electrochemical and electronic devices.     

Reversible Electrochemically Triggered Delamination Blistering of Hydrogel Films on Micropatterned Electrodes

Stimuli responsive elastic instabilities provide opportunities for controlling the structures and properties of polymer surfaces, offering a range of potential applications. Here, a surface actuator based on a temperature and electrically responsive poly(N‐isopropyl acrylamide‐co‐sodium acrylate) hydrogel that undergoes a two‐step delamination and buckling instability triggered using micropatterned electrodes is described. The electrically actuated structures entail large out‐of‐plane displacements that take place on time‐scales of less than 1 s, in response to modest triggering voltages (?3–6 V). Alongside these experimental observations, finite element simulations are conducted to better understand the two‐step nature of the instability. In the first step, hydrogel films undergo delamination and formation of blisters, facilitated by electrochemical reduction of the thiol groups anchoring the film to the electrodes. Subsequently, at larger reducing potentials, the electrolytic current is sufficient to nucleate a gas bubble between the electrode and the gel, causing the delaminated region to adopt a straight‐sided blister shape. Finally, thermally induced deswelling of the gel allows the film to be returned to its flat state and readhered to the electrode, thereby allowing for repeated actuation.