Amperometric Biosensors Based on Platinum Nanowires

Abstract

Platinum nanowires (PtNW) were prepared by an electrodeposition strategy using nanopore alumina template. The nanowires prepared were dispersed in chitosan (CHIT) solution and stably immobilized onto the surface of glassy carbon electrode (GCE). The electrochemical behavior of PtNW‐modified electrode and its application to the electrocatalytic reduction of hydrogen peroxide (H₂O₂) are investigated. The modified electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. As an application example, the glucose oxidase was immobilized onto the surface of PtNW‐modified electrode through cross‐linking by glutaric dialdehyde. The detection of glucose was performed in phosphate buffer at –0.2 V. The resulting glucose biosensor exhibited a short response time (<8 s), with a linear range of 10^?5?10^?2 M and detection limit of 5×10^?6 M.     

Electrocatalytic oxidation of some biologically important compounds at conducting polymer electrodes modified by metal complexes

Conducting poly(3-methylthiophene) electrodes were electrochemically prepared. The resulting polymer films were modified with an inorganic complex, ferrocene. The incorporation of the ferrocene/ferrocenium moiety into the polymer film resulted in enhanced charge transfer towards the oxidation of some organic molecules of biological interest. The electrochemical response of the complex-containing polymer electrode was compared to that of the unmodified polymer electrode and that of the substrate. Apparent diffusion coefficients of the redox species were estimated from the cyclic voltammetric data for different biological molecules at the ferrocene-containing polymer electrode. Infra-red spectroscopic measurements for the “as-grown” films revealed the presence of the inorganic complex within the polymer. The modified polymer electrode showed noticeable enhancement for the charge transfer across the film interface and can be used as an electrochemical sensor for biological compounds. Received: 3 June 1997 / Accepted: 7 July 1997     

Study on Preferential Solvation of Water by Electrochemical Method

The preferential solvation of water plays an important role in ferrocene research which is a subject of current interest. Voltammetric investigations were carried out for Au electrode in acetonitrile/water, showing preferential solvation of water. In our work, the preferential solvation of water in acetonitrile/water was studied by electrochemical methods including cyclic volitammetry, electrochemical impedance spectra and double‐step chronoamperometry. Ferrocenemethanol (FcCH₂OH) molecules as a solute spontaneously adsorb on the electrode surface in anhydrous acetonitrile, resulting from acetonitrile molecules tend to form an acetonitrile solvent layer on the surface of the electrode and acetonitrile solvent layer has a lower energy barrier than the aqueous solvent layer, which has been obtained by modeling solvation. The solvent strongly influences electrochemical behavior of solute. Once there is an amount of water in acetonitrile solvent, FcCH₂OH that adsorbed on the electrode surface desorb. This is because water preferentially solvate with FcCH₂OH in term of intermolecular forces between solvent and solute. Moreover, hydrogen bond between water molecules and FcCH₂OH molecules is stronger than dipole‐dipole interaction between acetonitrile molecules and FcCH₂OH molecules in solvation effect. Through electrochemical behavior of FcCH₂OH changing, preferential solvation of water is analyzed by electrochemical methods.     

Preparation, characterization, and application of electrodes modified with electropolymerized one-dimensional Magnus' green salts: Pt(NH3)4 · PtCl4 and Pt(NH3)4 · PtCl6

We report the modification of various electrode surfaces with electropolymerized Magnus' green salts, [Pt(NH₃)₄ · PtCl₄] _n and [Pt(NH₃)₄ · PtCl₆] _n . The modified electrodes were prepared by cyclic scanning of the electrode potential in an aqueous solution containing Pt(NH₃)₄ ²⁺ and PtCl₄ ²⁻ or PtCl₆ ²⁻ and the supporting electrolyte. The conditions for the film deposition were studied in detail. Several surface analytical techniques, including micro-Raman scattering and X-ray diffraction, were employed to characterize the modifier film. The electrochemical behavior of the modified electrode was studied in detail and the modified electrodes display very good electrocatalytic activity in the oxidation of ascorbic acid, hydrogen peroxide, thiosulfate, and especially nitric oxide. Received: 22 April 1999 / Accepted: 30 June 1999     

Nanocrystalline bioactive TiO2–chitosan impedimetric immunosensor for ochratoxin-A

Fourier transform infrared (FT-IR) and UV-visible spectroscopy were used to optimize TiO₂ concentration in chitosan (CS) to develop a sensitive CS/TiO₂ bioactive electrode. Electrochemical impedance spectroscopy (EIS) used to measure electro-activity of these bioactive electrodes associated with enhance oligosaccharide containing –CO groups from degradation of CS molecules. This matrix has free –NH₂ and –OH functional groups due to higher probability of hydrogen and covalent bonding between –OH group in CS molecules with Ti–O–Ti which supported immobilization of rabbit antibodies (IgGs) and proteins. Ochratoxin A (OTA) was detected and showed a linear response up to 10 ng/mL with CS/TiO₂ bio-electrode. The OTA detection sensitivity of 7.5 mM TiO₂ added CS bioactive electrode was four times higher than only CS.     

Hydrogen peroxide biosensor based on the immobilization of horseradish peroxidase on ��-Al2O3 nanoparticles/chitosan film-modified electrode

An amperometric biosensor based on horseradish peroxidase (HRP) and ??-Al₂O₃/chitosan composite film at a glassy carbon electrode has been developed. Hydrogen peroxide (H₂O₂) was detected with the aid of ferrocene monocarboxylic acid mediator to transfer electrons between the electrode and HRP. The morphology and composition of the modified electrode were characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and amperometry. The effects of HRP concentration, the applied potential, and the pH values of the buffer solution on the response of the sensor were investigated for optimum analytical performance. The proposed biosensor showed high sensitivity (0.249?A M^?1?cm^?2) and a fast response (<5?s) to H₂O₂ with the detection limit of 0.07???M. The linear response range of the enzyme electrode to H₂O₂ concentration was from 0.5 to 700???M with a correlation coefficient of 0.9998. The apparent Michaelis-Menten constant of the biosensor was calculated to be 0.818?mM, exhibiting a high enzymatic activity and affinity for H₂O₂.     

The Effect of Ionic Liquid Covalent Bonding to Sol‐Gel Processed Film on Ion Accumulation and Transfer

Accumulation of electroactive anions into a silicate film with covalently bonded room temperature ionic liquid film deposited on an indium tin oxide electrode was studied and compared with an electrode modified with an unconfined room temperature ionic liquid. A thin film containing imidazolium cationic groups was obtained by sol‐gel processing of the ionic liquid precursor 1‐methyl‐3‐(3‐trimethoxysilylpropyl)imidazolium bis(trifluoromethylsulfonyl)imide together with tetramethylorthosilicate on the electrode surface. Profilometry shows that the obtained film is not smooth and its approximate thickness is above 1 μm. It is to some extent permeable for a neutral redox probe – 1,1′‐ferrocene dimethanol. However, it acts as a sponge for electroactive ions like Fe(CN)₆^3?, Fe(CN)₆^4? and IrCl₆^3?. This effect can be traced by cyclic voltammetry down to a concentration equal to 10^?7 mol dm^?3. Some accumulation of the redox active ions also occurs at the electrode modified with the ionic liquid precursor, but the voltammetric signal is significantly smaller compare with the bare electrode. The electrochemical oxidation of the redox liquid t‐butyloferrocene deposited on silicate confined ionic liquid film is followed by the expulsion of the electrogenerated cation into an aqueous solution. On the other hand, the voltammetry obtained with the electrode modified with t‐butyloferrocene solution in the ionic liquid precursor exhibits anion sensitive voltammetry. This is explained by anion insertion into the unconfined ionic liquid deposit following t‐butylferricinium cation formation.     

Electron-transfer mediation on poly-aryl dendrimer-modified electrodes

Electrochemical properties of a dendrimer-modified electrode that was prepared by immobilization of ferrocenyl-terminated dendrimers on a poly-phenyl acetate anchoring layer were investigated in CH₂Cl₂. The anchoring layer was made by electro-grafting of the corresponding diazonium salt on a glassy carbon surface. The method allows the fabrication of a robust interface where the properties of the dendrimers are well-preserved. Moreover, the control of the layer properties as the permeation of molecules from the solution to the surface could be tuned up from only limited to totally blocked through the electrochemical conditions used during the electro-grafting of the anchoring layer. Detailed investigations performed with cyclic voltammetry and on different types of layers show that the modified electrode catalyses the oxidation of redox substrates. The process depends on the standard potential of the redox couple compared to that of the adsorbed dendrimer molecules. Experiments indicate that the electron exchange with molecules in solution takes place mainly at the dendrimer film–solution interface as the dendrimers inside the film permit the charge-transfer through the modified film to the carbon substrate. The interest of using robust electrode dendrimer relies on the possibility of large structural variations allowing the careful introduction of specific properties in the layer.     

Label-Free Detection of DNA Hybridization Based on MnO2 Nanoparticles

Abstract

Nano-MnO₂/chitosan composite film modified glassy carbon electrode (MnO₂/CHIT/GCE) was fabricated and a DNA probe was immobilized on the electrode surface. The immobilization and hybridization events of DNA were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was applied to the label-free detection of the target DNA. The human immunodeficiency virus (HIV) gene fragment was successfully detected by this DNA electrochemical sensor. The dynamic detection range was from 2.0 × 10^?11 to 2.0 × 10^?6 mol/L, with a detection limit of 1.0 × 10^?12 mol/L.     

Trans-membrane electron transfer in red blood cells immobilized in a chitosan film on a glassy carbon electrode

We have studied the trans-membrane electron transfer in human red blood cells (RBCs) immobilized in a chitosan film on a glassy carbon electrode (GCE). Electron transfer results from the presence of hemoglobin (Hb) in the RBCs. The electron transfer rate (k _s) of Hb in RBCs is 0.42 s^?1, and <1.13 s^?1 for Hb directly immobilized in the chitosan film. Only Hb molecules in RBCs that are closest to the plasma membrane and the surface of the electrode can undergo electron transfer to the electrode. The immobilized RBCs displayed sensitive electrocatalytic response to oxygen and hydrogen peroxide. It is believed that this cellular biosensor is of potential significance in studies on the physiological status of RBCs based on observing their electron transfer on the modified electrode.

Microelectrode Electrochemistry in Microemulsion Systems

Abstract

In this paper, we demonstrate the microelectrode electrochemistry of a simple electroactive probe (ferrocene) in SDS/n‐C₄H₉OH/H₂O microemulsion systems. The oxidation of ferrocene within the microemulsion environment was carried out at a Pt microelectrode using a three‐electrode assembly with a Pt wire acting as an auxiliary electrode and an Ag wire as the pseudo‐reference electrode. Excellent Nernstian electrochemical responses were observed. The well‐defined reversible electrochemical responses facilitated the measurement of the self‐diffusion coefficient of microemulsion droplets and introduced the possibility of probing the structural changes of microemulsion systems.     

Electrochemical Characterization of the Self-Assembled Monolayer of 8-Mercaptoquinoline on Polycrystalline Gold Electrode

Self-assembled monolayer of 8-mercaptoquinoline (MQ) on the surface of gold from MQ dilute ethanolic solutions is investigated by electrochemical methods. Some aqueous redox probes, such as ferrocene carboxylic acid and Fe(CN)₆ ^4–/3– can sufficiently diffuse into the monolayer because significant diffusion-limited current peaks are observed when the redox reactions take place, showing that the monolayer is very loosely packed or dominated by defects. However, the study on the electron transfer of other aqueous probes, such as Cu²⁺ and Ru(NH₃)₆ ^3+/2+, confirm that the monolayer can block the electron transfer on the gold electrode surface rather effectively for its low ratio of pinhole defects. These studies show that the MQ monolayer on the electrode can provide an excellent barrier for penetration of some probes but cannot resist the penetration of other probes effectively. The unusual properties of the self-assembled monolayers are attributed to the entity of the very large heterocyclic moiety.     

[SiCu(H2O)W11O39]6-在玻碳电极上的多层组装及电催化性能

The electrochemical behavior of SiCu W11 heteropolyacide in acidic aqueous solution was studied. The effect of solution pH on the electrochemical behavior of SiCu W11 was discussed and the mechanism was suggested. New electrode was modified by muhilayer films composed of heteropolyanion (SiCu W11 and cationic polymer poly (diallyldimethylammonium chloride). Cyclic vohammetry showed the uniform growth of the film. The modified electrodes exhibited some special electrochemical properties in the films, different from those in homogeneous aqueous solutions. The effect of pH on the redox behavior of SiCu W11 in the films was discussed in details. The muhilayer film electrodes have an excellent electrocatalytic response to the reduction of BrO3^- and NO2^-.     

Individual and Simultaneous Voltammetric Determination of Cd(II), Cu(II) and Pb(II) Applying Amino Functionalized Fe3O4@Carbon Microspheres Modified Electrode

Amino‐functionalized Fe₃O₄@carbon microspheres (NH₂?Fe₃O₄@C) were prepared and the electrochemical sensor was constructed using NH₂?Fe₃O₄@C modified glassy carbon electrodes (GCE) to determine toxic heavy metals in aqueous solution. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the structure and phase of NH₂?Fe₃O₄@C. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results indicate that NH₂?Fe₃O₄@C modified GCE possesses large active area and excellent electron transfer. Under optimized electrochemical condition, Cd(II), Pb(II) and Cu(II) were determined using NH₂?Fe₃O₄@C modified GCE. The electrode through amino functionalization exhibits higher sensitivity and lower detection limit toward Cd(II) and Cu(II) due to the acid‐base pairing interaction between the electron‐rich ?NH₂ ligand and the electron‐deficient heavy metal ions. Compared with other similar results reported in the literature, the NH₂?Fe₃O₄@C modified electrode exhibits wider linear response range while with comparable lower detection limit. It also exhibits excellent stability, reproducibility and anti‐interference ability.     

In situ Ellipsometric Study of Redox Induced Orientation of a Short Chained Ferrocenylalkylthiol Monolayer Self-Assembled on Gold

The structural modifications accompanying the redox switching of a short ferrocene derivative [(C₅H₅)Fe(C₅H₄)CO(CH₂)₅SH] monolayer self-assembled on gold are investigated using ellipsometry. Average values for the complex refractive index and thickness of the monolayer are estimated from ex situ and in situ experiments. The changes in the optical parameters are monitored during potential cycling and between two potential values, where the ferrocene is in its either reduced or oxidized form. The optical changes point to an increase of 1 to 2 Å in the monolayer thickness as the ferrocene is oxidized to the ferricinium cation. The thickness variation is in very good agreement with the rotation of the ferrocene rings towards a more perpendicular position relative to the electrode surface. The changes in orientation are reversible when the potential is cycled. However, instability of the monolayer is observed when the modified electrode is polarized for a few minutes at potentials where the monolayer is oxidized and then returned to the reduced form. This instability is associated with the ferrocene moiety, since a loss of electroactivity is simultaneously detected by cyclic voltammetry.     

Carbon paste electrode modified by cobalt ions dispersed into poly (N-methylaniline) preparing in the presence of SDS: application in electrocatalytic oxidation of hydrogen peroxide

Conducting and stable poly (N-methylaniline) film was prepared by using the repeated potential cycling technique in aqueous solution containing N-methylaniline, sulfuric acid, and sodium dodecyl sulfate (SDS) at the surface of carbon paste electrode (CPE). The transition metal ions of Co(ІІ) were incorporated to the polymer by immersion of the modified electrode in 0.1 M cobalt chloride solution for 10 min. The electrochemical characterization of this modified electrode exhibits stable redox behavior of Co(ІІ)→Co(ІІІ) and formation of insoluble oxide/hydroxide cobalt species on the CPE surface. The modified electrode showed well-defined and stable redox couples in alkaline aqueous solution. The modified electrode showed excellent electrocatalytic activity for oxidation of hydrogen peroxide. The response of modified electrode toward the H₂O₂ oxidation was examined using cyclic voltammetry, differential pulse voltammetry, square wave voltammetry, and chronoamperometry. This modified electrode has many advantages such as simple preparation procedure, good reproducibility, and high catalytic activity toward the hydrogen peroxide oxidation. Such characteristics were explored for the specific determination of hydrogen peroxide in cosmetics product sample, giving results in excellent agreement with those obtained by standard method.     

Direct electrochemistry of hemoglobin on an ionic liquid carbon electrode modified with zinc tungstate nanorods

We have constructed a new electrochemical biosensor by immobilization of hemoglobin (Hb) and ZnWO₄ nanorods in a thin film of chitosan (CTS) on the surface of carbon ionic liquid electrode. UV–vis and FT-IR spectra reveal that Hb remains in its native conformation in the film. The modified electrode was characterized by scanning electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. A pair of well-defined redox peaks appears which indicates direct electron transfer from the electrode. The presence of CTS also warrants biocompatibility. The electron transfer coefficient and the apparent heterogeneous electron transfer rate constant were calculated to be 0.35 and 0.757 s^?1, respectively. The modified electrode displays good electrocatalytic activity for the reduction of trichloroacetic acid with the detection limit of 0.613 mmol L^?1 (3σ). The results extend the protein electrochemistry based on the use of ZnWO₄ nanorods.

Polymer-based bilayer interfaces for electrochemical rectification

In this paper, the electrochemical current rectification phenomenon exhibited at an electrochemical interface constituted by a glassy carbon electrode covered with a bilayer of polymer films is discussed. The authors have shown that Methylene Blue (MB) redox species can be confined to a very thin insulating polymer film formed from orthophenylene diamine. The poly(opd) film exhibited excellent blocking properties to redox molecules in solution. On the other hand, the insulating poly(opd) film trapped with MB could mediate electron transfer between the redox molecules in solution and the electrode. Further, a second polymeric layer (Nafion film) trapped with ferrocene redox species was formed as the outer layer over the inner poly (opd) film containing MB. This bilayer-modified electrode, due to the significant difference in the redox potentials of the MB and ferrocene species immobilized in the inner and outer layers, respectively, exhibits unidirectional current flow and the results of the voltammetric investigations on the modified electrodes are described in this communication.     

Solid-state electrochemiluminescence sensor through the electrodeposition of Ru(bpy)3/AuNPs/chitosan composite film onto electrode

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) has been successfully immobilized onto electrode through the electrodeposition of Ru(bpy)₃²⁺/AuNPs/chitosan composite film. In the experiments, chitosan solution was first mixed with Au nanoparticles (AuNPs) and Ru(bpy)₃²⁺. Then, during chronopotentiometry experiments in this mixed solution, a porous 3D network structured film containing Ru(bpy)₃²⁺, AuNPs and chitosan has been electrodeposited onto cathode due to the deposition of chitosan when pH value is over its pK_a (6.3). The applied current density is crucial to the film thickness and the amount of the entrapped Ru(bpy)₃²⁺. Additionally, these doping Ru(bpy)₃²⁺ in the composite film maintained their intrinsic electrochemical and electrochemiluminescence activities. Consequently, this Ru(bpy)₃²⁺/AuNPs/chitosan modified electrode has been used in ECL to detect tripropylamine, and the detection limit was 5 × 10⁻¹⁰ M.     

Sensitive Detection of NADH by Ferrocenylalkanethiol Functionalized Multiwall Carbon Nanotubes Electrodes

Abstract

The 6-ferrocenylhexanethiol (FcC₆SH) functionalized multiwall carbon nanotubes (MWNTs) modified glassy carbon electrode (FcC₆SH/MWNTs/GCE) was easily fabricated and used for the sensitive detection of NADH. Cyclic voltammetric and amperometric methods were used to study the behavior of NADH on the FcC₆SH/MWNTs/GCE. A broader linear response range to the NADH concentration from 5 µM to 1.5 mM with a correlation coefficient of 0.9982 was obtained. The detection limit was 0.54 µM. The synergetic effects of FcC₆SH and MWNTs make the modified electrode highly sensitive to NADH. In addition, the modified electrode can decrease the fouling of the electrode surface.