A Novel Self‐protection Hydroquinone Electrochemical Sensor Based on Thermo‐sensitive Triblock Polymer PS‐PNIPAm‐PS

A novel self‐protection sensor was successfully constructed based on an interesting thermo‐sensitive triblock polymer PS‐PNIPAm‐PS. At low temperatures (<24 °C), the analyte was able to undergo the redox process at the modified electrode. However, the polymer shrunk and accumulated at high temperatures (>30 °C), which dramatically increased the electron transfer resistance (Rct) of the modified electrode and consequently blocked the occurrence of the redox reaction to protect the electrode from high temperatures and enhance its stability. Under optimized conditions, the proposed sensor showed a good detection range for hydroquinone (6×10^?7 to 2.35×10^?3 M) and a low LOD (490 nM). The sensor was also successfully applied for detecting hydroquinone in real samples. The present work may provide a novel method for electrode protection, high‐temperature alarm, high‐temperature protection of batteries and new sensors production.     

Impedimetric DNA‐Based Biosensor for Silver Ions Detection with Hemin/G‐Quadruplex Nanowire as Enhancer

A DNA‐based biosensor was reported for detection of silver ions (Ag⁺) by electrochemical impedance spectroscopy (EIS) with [Fe(CN)₆]^4?/3? as redox probe and hybridization chain reaction (HCR) induced hemin/G‐quadruplex nanowire as enhanced label. In the present of target Ag⁺, Ag⁺ interacted with cytosine‐cytosine (C? C) mismatch to form the stable C? Ag⁺? C complex with the aim of immobilizing the primer DNA on electrode, which thus triggered the HCR to form inert hemin/G‐quadruplex nanowire with an amplified EIS signal. As a result, the DNA biosensor showed a high sensitivity with the concentration range spanning from 0.1 nM to 100 µM and a detection limit of 0.05 nM.     

Electrochemical Properties of an Osmium(II) Copolymer Film and Its Electrocatalytic Ability Towards the Oxidation of Ascorbic Acid in Acidic and Neutral pH

Copolymerization of an osmium(II) functionalized pyrrole moiety, osmium‐bis‐N,N'‐(2,2′‐bipyridyl)‐N‐(pyridine‐4‐ylmethyl‐(8‐pyrrole‐1yl–octyl)‐amine)chloride ( I ) with 3‐methylthiophene was carried out. The resulting conducting polymer film exhibited a clear redox couple associated with the Os^3+/2+ response and the familiar conducting polymer backbone signature. The effect of film thickness upon the redox properties of the copolymer was investigated in organic electrolyte solutions. Scanning electron micrographs (SEM) along with energy dispersive X‐ray (EDX) spectra of the copolymerized films were undertaken, both after formation and redox cycling in neutral buffer solution. These clearly show that electrolyte is incorporated into the polymer film upon redox cycling through the Os^3+/2+ redox system. The Os^3+/2+ response associated with the copolymer was seen to be significantly altered in the presence of ascorbic acid both in acidic and neutral pH buffer solutions. This pointed to an electrocatalytic reaction between the ascorbic acid and the Os³⁺ form of the copolymer. Under acidic conditions the copolymer film exhibited a sensitivity of 1.76 (±0.05) μA/mM with a limit of detection (LOD) of 1.45 μM for ascorbic acid. Under neutral pH conditions the copolymer exhibited a sensitivity of 19.26 (±1.05) μA/mM with a limit of detection (LOD) of 1.28 μM for ascorbic acid.     

Impedimetric Aptasensor for Thrombin Recognition Based on CD Support

We report an aptamer biosensing array for thrombin detection by measuring the electrochemical impedance upon aptamer‐protein formation at the surface of CD‐trodes (GCDTs) in the presence of the redox couple [Fe(CN)₆]^3?/4?. GCDTs are fabricated from recordable compact discs that contain a fine gold layer. The biosensor is constructed by self‐assembling of a thiol‐modified thrombin binding aptamer (TBA) onto a GCDT surface. The sensor reveals good ligand specificity, recognition in a wide range of thrombin concentrations from 20 nM to 1 µM with a limit of detection of 5 nM.     

Electrochemical Monitoring of the Early Events of Hydrogen Peroxide Production by Mitochondria

Mitochondria consume oxygen in the respiratory chain and convert redox energy into ATP. As a side process, they produce reactive oxygen species (ROS), whose physiological activities are still not understood. However, current analytical methods cannot be used to monitor mitochondrial ROS quantitatively and unambiguously. We have developed electrochemical biosensors based on peroxidase‐redox polymer‐modified electrodes, providing selective detection of H₂O₂ with nanomolar sensitivity, linear response over five concentration decades, and fast response time. The release of H₂O₂ by mitochondria was then monitored under phosphorylating or inhibited respiration conditions. We report the detection of two concomitant regimes of H₂O₂ release: large fluxes (hundreds of nM ) under complex III inhibition, and bursts of a few nM immediately following mitochondria activation. These unprecedented bursts of H₂O₂ are assigned to the role of mitochondria as the hub of redox signaling in cells.     

The Signal Amplification in Electrochemical Detection of Chloramphenicol Using Sulfonated Polyaniline‐chitosan Composite as Redox Capacitor

In this work, a novel redox capacitor was designed for signal amplification in electrochemical detection. It was fabricated by co‐electrodeposition of a conducting polymer, sulfonated polyaniline (SPAN) and chitosan on a glass carbon electrode, and its function was evaluated for being a localized source to transfer electron between FcCOOH (Fc) and Ru(NH₃)₆Cl₃ in solution via redox cycling. Furthermore, the electrochemical detection of chloramphenicol, a broad‐spectrum antibiotic was performed using the redox capacitor in the presence of Fc. A significant amplification in cathodic current response of chloramphenicol was obtained through a continuous redox‐cycling reaction. The performance of the amplifying signal responded linearly to chloramphenicol in a concentration range of 0.05 to 50.0 μmol L⁻¹ with a low detection limit of 0.01 μmol L⁻¹. The proposed approach exhibited good reproducibility and stability, and could be used for detection of chloramphenicol in eye drops by standard addition method with the recoveries from 96.5 % to 103.0 %.     

Ion‐selective Electrodes with 3D Nanostructured Conducting Polymer Solid Contact

Until now both ion‐to‐electron transducers as well as large surface area nanostructured conducting materials were successfully used as solid contacts for polymer‐based ion‐selective electrodes. We were interested to explore the combination of these two approaches by fabricating ordered electrically conducting polymer (ECP) nanostructures using 3D nanosphere lithography and electrosynthesis to provide a high surface area and capacitive interface for solid contact ion‐selective electrodes (SC‐ISEs). For these studies we used poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT(PSS)) films with 750 nm diameter interconnected pores as the intermediate layer between a glassy carbon electrode and a Ag⁺ ‐selective polymeric membrane. We also investigated the feasibility of loading the voids created in the polymer film with a lipophilic redox mediator (1,1’‐dimethylferrocene) to provide the respective ISEs with well‐defined/controllable E⁰ values. These expectations were fulfilled as the standard deviation of E⁰ values were reduced with almost an order of magnitude for 3D nanostructured SC‐ISEs filled with the redox mediator as compared to their redox mediator‐free analogs. The detrimental effect of the redox mediator extraction into the plasticized PVC‐based ion‐selective membrane (ISM) was efficiently suppressed by replacing the PVC‐based ISMs with a low diffusivity silicone rubber matrix.     

Enzyme activity control by responsive redoxpolymers

A new thermoresponsive poly-N-isopropylacrylamide (PNIPAM)-ferrocene polymer was synthesized and characterized. PNIPAMFoxy bears additional oxirane groups which were used for attachment by a self-assembly process on a cysteamine-modified gold electrode to create a thin hydrophilic film. The new redox polymer enabled electrical communication between the cofactor pyrrolinoquinoline quinone (PQQ) of soluble glucose dehydrogenase (sGDH) and the electrode for sensitive detection of this enzyme as a prospective protein label. The temperature influence on the redox polymer/enzyme complex was investigated. An inverse temperature response behavior of surface bound PNIPAMFoxy compared to the soluble polymer was found and is discussed in detail. The highest efficiency of mediated electron transfer for the immobilized PNIPAMFoxy with sGDH was observed at 24 degrees C, which was twice as high as that of its soluble counterpart. A steady-state electrooxidation current densitiy of 4.5 microA.cm-2 was observed in the presence of 10 nM sGDH and 5 mM glucose. A detection limit of 0.5 nM of soluble PQQ-sGDH was obtained.     

3,4,9,10‐Perylenetetracarboxylic Acid/Hemin Nanocomposites Act as Redox Probes and Electrocatalysts for Constructing a Pseudobienzyme‐Channeling Amplified Electrochemical Aptasensor

A simple wet‐chemical strategy for the synthesis of 3,4,9,10‐perylenetetracarboxylic acid (PTCA)/hemin nanocomposites through π–π interactions is demonstrated. Significantly, the hemin successfully conciliates PTCA redox activity with a pair of well‐defined redox peaks and intrinsic peroxidase‐like activity, which provides potential application of the PTCA self‐derived redox activity as redox probes. Additionally, PTCA/hemin nanocomposites exhibit a good membrane‐forming property, which not only avoids the conventional fussy process for redox probe immobilization, but also reduces the participation of the membrane materials that act as a barrier of electron transfer. On the basis of these unique properties, a pseudobienzyme‐channeling amplified electrochemical aptasensor is developed that is coupled with glucose oxidase (GOx) for thrombin detection by using PTCA/hemin nanocomposites as redox probes and electrocatalysts. With the addition of glucose to the electrolytic cell, the GOx on the aptasensor surface bioelectrocatalyzed the reduction of glucose to produce H₂O₂, which in turn was electrocatalyzed by the PTCA/hemin nanocomposites. Cascade schemes, in which an enzyme is catalytically linked to another enzyme, can produce signal amplification and therefore increase the biosensor sensitivity. As a result, a linear relationship for thrombin from 0.005 to 20 nM and a detection limit of 0.001 nM were obtained.     

木犀草素在离子液体修饰电极上的电催化氧化及其测定

用1-丁基-3-甲基咪唑六氟磷酸盐([BMIM]PF₆)疏水性离子液体修饰玻碳电极,在0.2 mol/L磷酸盐缓冲溶液(pH为4.0～8.0)中,运用循环伏安法（CV）和差示脉冲溶出伏安法(DPSV)研究了木犀草素在修饰电极上的电化学行为,建立了测定木犀草素含量的新方法。 实验结果表明,该修饰电极上木犀草素氧化、还原峰电位均负移,峰电流增大。 在-0.2～0.7 V电位区间,pH=7.0的磷酸盐缓冲溶液体系中,木犀草素在修饰电极表面发生的是受吸附控制的准可逆等电子等质子电极反应,电子转移系数α=0.5,吸附量为4.6×10-10 mol/cm²;木犀草素氧化峰电流与其浓度在1.0×10^-10～1.6×10^-8 mol/L范围内呈良好的线性关系,检出限达到3.2×10^-11 mol/L,回收率为98.7%～102.0%;该法操作简单、快速、灵敏、准确;可用于野菊花中类黄酮的测定。     

Electroenzymatic Nitrogen Fixation Using a MoFe Protein System Immobilized in an Organic Redox Polymer

We report an organic redox‐polymer‐based electroenzymatic nitrogen fixation system using a metal‐free redox polymer, namely neutral‐red‐modified poly(glycidyl methacrylate‐co‐methylmethacrylate‐co‐poly(ethyleneglycol)methacrylate) with a low redox potential of ?0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N₃^?, NO₂^? and N₂ to NH₃ catalyzed by the MoFe protein via the polymer‐bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH₃ nmol MoFe^?1 h^?1 from N₂ reduction. ¹⁵N₂ labeling experiments and NMR analysis were performed to confirm biosynthetic N₂ reduction to NH₃.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin Immobilized in a Polymeric Ionic Liquid Film

A polymer film based on polymeric ionic liquid, which was poly(1‐vinyl‐3‐butylimidazolium chloride) (poly(ViBuIm⁺Cl^?)for short), was firstly used as matrix to immobilize hemoglobin (Hb). FTIR and UV‐vis spectra demonstrated that the native structure of Hb was well preserved after entrapped into the polymer film. The Hb immobilized in the poly(ViBuIm⁺Cl^?) film showed a fast direct electron transfer for the Hb‐Fe^III/Fe^II redox couple. Based on the direct electron transfer of the immobilized Hb, polyvinyl alcohol (PVA)/Hb/poly(ViBuIm⁺Cl^?)/GC electrode displayed good sensitivity and wide linear range for the detection of H₂O₂. The linear range of the PVA/Hb/poly(ViBuIm⁺Cl^?)/GC electrode to H₂O₂ is from 3.5 to 224 μM with a limit of detection of 1.17 μM. Such an avenue, which integrated polymeric ionic liquid and redox protein via a simple method, may provide a novel and efficient platform for the fabrication of biosensors, biofuel cells and other bioelectrochemical devices.     

Electrochemical Behavior of Herbal Antitumor Drug Aloe‐Emodin at Carbon‐Coated Nickel Magnetic Nanoparticles Modified Glassy Carbon Electrode

The electrochemical behavior of aloe‐emodin (AE), an important herbal antitumor drug, was investigated at a carbon‐coated nickel magnetic nanoparticles modified glassy carbon electrode (CNN/GCE). A couple of well‐defined redox peaks was obtained. Some electrochemical parameters of AE at a CNN/GCE, such as the charge number, exchange current density, standard heterogeneous rate constant, were measured. The square wave voltammetry (SWV) response of AE was linear with the concentration over two concentration intervals viz. 6.24×10^?9?1.13×10^?6 M and 1.13×10^?6?1.23×10^?5 M, with a detection limit of 2.08 nM. A fast, simple and sensitive detection and analysis of AE was developed.     

A Nitrogen‐Rich 2D sp2‐Carbon‐Linked Conjugated Polymer Framework as a High‐Performance Cathode for Lithium‐Ion Batteries

A two‐dimensional (2D) sp²‐carbon‐linked conjugated polymer framework (2D CCP‐HATN) has a nitrogen‐doped skeleton, a periodical dual‐pore structure and high chemical stability. The polymer backbone consists of hexaazatrinaphthalene (HATN) and cyanovinylene units linked entirely by carbon–carbon double bonds. Profiting from the shape‐persistent framework of 2D CCP‐HATN integrated with the electrochemical redox‐active HATN and the robust sp² carbon‐carbon linkage, 2D CCP‐HATN hybridized with carbon nanotubes shows a high capacity of 116 mA h g^?1, with high utilization of its redox‐active sites and superb cycling stability (91 % after 1000 cycles) and rate capability (82 %, 1.0 A g^?1 vs. 0.1 A g^?1) as an organic cathode material for lithium‐ion batteries.     

Simultaneous Anodic Adsorptive Stripping Voltammetric Determination of Luteolin and 3‐Hydroxyflavone in Biological Fluids Using Renewable Pencil Graphite Electrodes

Simultaneous anodic adsorptive stripping voltammetry was applied for selective and sensitive electrochemical determination of the flavones luteolin (LU) and the basic flavone core 3‐hydroxyflavone (3HF) using a renewable pencil graphite electrode (PGE). The increased separation of the anodic peak potential of LU and 3HF on a PGE surface together with the increased sensitivity renders their simultaneous determination feasible by square wave anodic adsorptive stripping voltammetry (SWAASV). The electrochemical parameters such as surface concentration (Γ), electron transfer coefficient (α), and the standard rate constant (k_s) of both LU and 3HF at a PGE were calculated. For simultaneous detection of both compounds by synchronous change of the concentration of LU and 3HF, the detection limits were 1.34 nM and 5.15 nM, respectively. The proposed procedure was successfully applied for the simultaneous detection of LU and 3HF in human serum and urine samples with satisfactory results.     

A Nernstian Biosupercapacitor

We propose the very first “Nernstian biosupercapacitor”, a biodevice based on only one redox polymer: poly(vinyl imidazole‐co‐allylamine)[Os(bpy)₂Cl], and two biocatalysts. At the bioanode PQQ‐dependent glucose dehydrogenase reduces the Os³⁺ moieties at the polymer to Os²⁺ shifting the Nernst potential of the Os³⁺/Os²⁺ redox couple to negative values. Concomitantly, at the biocathode the reduction of O₂ by means of bilirubin oxidase embedded in the same redox polymer leads to the oxidation of Os²⁺ to Os³⁺ shifting the Nernst potential to higher values. Despite the use of just one redox polymer an open circuit voltage of more than 0.45 V was obtained during charging and the charge is stored in the redox polymer at both the bioanode and the biocathode. By connecting both electrodes via a predefined resistor a high power density is obtained for a short time exceeding the steady state power of a corresponding biofuel cell by a factor of 8.     

Electrochemical Behavior of Gold Nanoparticles Generated In Situ on 3‐(1‐Imidazolyl)propyl‐silsesquioxane

Gold nanoparticles of different morphologies have been synthesized on a silica‐based organic‐inorganic hybrid material for catalytic applications. The gold nanoparticles formations proceed through in situ chemical reduction of the AuCl₄^? anions previously adsorbed on 3‐(1‐imidazolyl)propyl‐silsesquioxane, which plays the role of substrate and stabilizer. Two distinct reducing agents, sodium citrate and sodium borohydride, were employed to generate gold nanoparticles of different sizes. UV‐vis diffuse reflectance as well as transmission electron microscopy were employed to evaluate the particle’s morphology. Modified carbon paste electrodes were prepared from these materials and their electrochemical behavior investigated using potassium ferrocyanide and 4‐nitrophenol as redox model compounds. Both AuNPs‐modified electrodes decreased the overpotential of 4‐nitrophenol reduction by around 90 mV compared to the unmodified electrode as evidenced by cyclic voltammetry experiment. However, the smaller diameter particles (borohydride‐reduced) produced more significant catalytic effect as a consequence of their large surface area. Regarding the sensing parameters, the sensitivity is higher for the borohydride‐reduced AuNPs while the values of limit of detection are of the same order of magnitude. Thus, the detection limit and sensitivity are 70.0±0.6 nM and 187 µA/mM for the citrate‐reduced AuNPs; and 75.0±2.2 nM and 238 µA/mM for the borohydride‐reduced AuNPs.     

Cation‐Dependent Stabilization of Electrogenerated Naphthalene Diimide Dianions in Porous Polymer Thin Films and Their Application to Electrical Energy Storage

Porous polymer networks (PPNs) are attractive materials for capacitive energy storage because they offer high surface areas for increased double‐layer capacitance, open structures for rapid ion transport, and redox‐active moieties that enable faradaic (pseudocapacitive) energy storage. Here we demonstrate a new attractive feature of PPNs—the ability of their reduced forms (radical anions and dianions) to interact with small radii cations through synergistic interactions arising from densely packed redox‐active groups, only when prepared as thin films. When naphthalene diimides (NDIs) are incorporated into PPN films, the carbonyl groups of adjacent, electrochemically generated, NDI radical anions and dianions bind strongly to K⁺, Li⁺, and Mg²⁺, shifting the formal potentials of NDI’s second reduction by 120 and 460 mV for K⁺ and Li⁺‐based electrolytes, respectively. In the case of Mg²⁺, NDI’s two redox waves coalesce into a single two‐electron process with shifts of 240 and 710 mV, for the first and second reductions, respectively, increasing the energy density by over 20 % without changing the polymer backbone. In contrast, the formal reduction potentials of NDI derivatives in solution are identical for each electrolyte, and this effect has not been reported for NDI previously. This study illustrates the profound influence of the solid‐state structure of a polymer on its electrochemical response, which does not simply reflect the solution‐phase redox behavior of its monomers.     

Electrochemical Detection of Duplex DNA Using Intercalation‐Triggered Decomplexation of Ferrocene with β‐Cyclodextrin

The redox peak of ferrocenylnaphthalene diimide used as a threading intercalator shifted positively due to the formation of its complex with β‐cyclodextrin. This complex collapsed upon the addition of double‐stranded DNA, and its redox potential shifted negatively. This behavior was applied for the homogenous detection of a polymerase chain reaction (PCR) product from Porphyromonas gingivalis, which is important for the diagnosis of periodontal disease, and its quantitative detection was achieved with a detection limit of 2.7 nM.     

基于聚硫堇膜对DNA杂交的直接电化学检测

In this work, the application of a conducting polymer, poly（thionine）, modified electrode as matrix to DNA immobilization as well as transducer to label-free DNA hybridization detection was introduced. The electropolymerization of thionine onto electrode surface was carried out by a simple two-step method, which involved a preanodization of glassy carbon electrode at a constant positive potential in thionine solution following cyclic voltammetry scans in the solution. Electrochemical detection was performed by differential pulse voltammetry in the electroactivity potential domain of poly（thionine）. The resulting poly（thionine） modified electrode showed a good stability and electroactivity in aqueous media during a near neutral pH range. Additionally, the pendant amino groups on the poly（thionine） chains enabled poly（thionine） modified electrode to immobilize phosphate group terminated DNA probe via covalent linkage. Hybridization process induced a clear decrease in poly（thionine） redox current, which was corresponding to the decrease in poly（thionine） electroactivity after double stranded DNA was formed on the polymer film. The detection limit of this electrochemical DNA hybridization sensor was 1.0 × 10^-10mol/L. Compared with complementary sequence, the hybridization signal values of 1-base mismatched and 3-base mismatched samples were 63.9% and 9.2%, respectively.