Simplifying the evaluation of graphene modified electrode performance using rotating disk electrode voltammetry

Graphene modified electrodes have been fabricated by electrodeposition from an aqueous graphene oxide solution onto conducting Pt, Au, glassy carbon, and indium tin dioxide substrates. Detailed investigations of the electrochemistry of the [Ru(NH(3))(6)](3+/2+) and [Fe(CN)(6)](3-/4-) and hydroquinone and uric acid oxidation processes have been undertaken at glassy carbon and graphene modified glassy carbon electrodes using transient cyclic voltammetry at a stationary electrode and near steady-state voltammetry at a rotating disk electrode. Comparisons of the data with simulation suggest that the transient voltammetric characteristics at graphene modified electrodes contain a significant contribution from thin layer and surface confined processes. Consequently, interpretations based solely on mass transport by semi-infinite linear diffusion may result in incorrect conclusions on the activity of the graphene modified electrode. In contrast, steady-state voltammetry at a rotating disk electrode affords a much simpler method for the evaluation of the performance of graphene modified electrode since the relative importance of the thin layer and surface confined processes are substantially diminished and mass transport is dominated by convection. Application of the rotated electrode approach with carbon nanotube modified electrodes also should lead to simplification of data analysis in this environment.     

Electrochemical Determination of Dopamine Using a Poly(3,4-Ethylenedioxythiophene)-Reduced Graphene Oxide-Modified Glassy Carbon Electrode

Poly(3,4-ethylenedioxythiophene) was deposited on a reduced graphene oxide-decorated glassy carbon electrode through an electrochemical polymerization. The resulting glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was applied as an electrochemical biosensor for the determination of dopamine in the presence of ascorbic acid and uric acid. The material deposited on glassy carbon electrode was investigated in terms of morphology and structural analysis. The comparison of electrochemical behavior of the glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode with the glassy carbon electrode-graphene oxide, glassy carbon electrode-reduced graphene oxide, and glassy carbon electrode-poly(3,4-ethylenedioxythiophene) electrodes exhibited high electrocatalytic activity for dopamine detection. Electrochemical kinetic parameters of glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene), including the charge transfer coefficient α (0.49) and electron transfer rate constant k_s (1.04), were determined and discussed. The glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was studied for the determination of dopamine by differential pulse voltammetry and exhibited a linear range from 19.6 to 122.8?µM with a sensitivity of 3.27?µA?µM^?1?cm^?2 and a detection limit of 1.92?µM. The developed biosensor exhibited good selectivity toward dopamine with high reproducibility and stability.     

Selective Electrochemical Determination of Salicylic Acid in Wheat Using Molecular Imprinted Polymers

Salicylic acid is a phytohormone, playing crucial roles in signal transduction, crop growth, and development, and defense to environmental challenges. In this study, a highly selective electrochemical sensor was designed and used to determine salicylic acid using molecularly imprinted polymers for recognition. The electrochemical sensor was fabricated via stepwise modification of gold nanoparticle–graphene–chitosan and molecularly imprinted polymers on a glassy carbon electrode. With electrochemical deposition, a gold nanoparticle–graphene–chitosan film was deposited on the glassy carbon electrode and enhanced the sensitivity. Molecularly imprinted polymers with adsorbed template salicylic acid were added to the surface of the modified electrode. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the modified electrodes. Salicylic acid in wheat was quantified by the sensor using the molecularly imprinted polymer/gold nanoparticle–graphene–chitosan/glassy carbon electrode. Concentrations of salicylic acid from 5?×?10^?10 to 5?×?10^?5?mol?L^?1 were determined showing that the developed sensor was suitable for the analysis of food.     

Electrocatalytic Activity of Immobilized Co(II) on Porous Graphene Aerogels

The highly‐porous graphene aerogel (GA) with BET surface area of 810 m² g^?1 and three‐dimensional structure has been successfully fabricated using the hydrothermal technique. The modified glassy carbon electrode was then prepared by casting the graphene aerogel solution followed by immersing the GA/GCE in Co⁺² solution. The results showed that graphene aerogels improved the adsorption ability of the Co (II) ions. The electrocatalysis of oxygen evolution reaction (OER) at the Co‐GA modified glassy carbon elec‐ trode (Co‐GA/GCE) has been investigated using linear sweep voltammetry (LSV) in alkaline solution. The OER was noticeably enhanced at Co‐GA/GCE, representing a negative shift in the LSV curve at the Co‐GA/GCE compared to that obtained at the bare GCE. The high electrocatalytic activity, good reproducibility and low cost of proposed electrode provides desired characteristics of a potential candi‐ date in the industrial water electrolysis process.     

Electroless Deposition of Thionin onto Glassy Carbon Electrode Modified with Single Wall and Multiwall Carbon Nanotubes: Improvement of the Electrochemical Reversibility and Stability

A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes (CNTs) and thionin. Abrasive immobilization of CNTs on a GC electrode was achieved by gently rubbing the electrode surface on a filter paper supporting carbon nanotubes, then immersing the GC/CNTs‐modified electrode into a thionin solution (electroless deposition) for a short period of time (5–50 s for MWCNTs and 5–120 s for SWCNTs ). Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple with surface confined characteristic at wide pH range 2–12. The electrochemical reversibility and stability of modified electrode prepared with incorporation of thionin into CNTs film was compared with usual methods for attachment of thionin to electrode surfaces such as electropolymerization and adsorption on the surface of preanodized electrodes. The formal potential of redox couple (E°′) shifts linearly toward the negative direction with increasing solution pH. The surface coverage of thionin immobilized on CNTs glassy carbon electrode was approximately 1.95×10^?10 mol cm^?2 and 3.2×10^?10 mol cm^?2 for MWCNTs and SWCNTs, respectively. The transfer coefficient (α) was calculated to be 0.3 and 0.35 and heterogeneous electron transfer rate constants (K_s) were 65 s^?1 and 55 s^?1 for MWCNTs/thionin and SWCNTs/thionin‐modified GC electrodes, respectively. The results clearly show a great facilitation of the electron transfer between thionin and CNTs adsorbed on the electrode surface. Excellent electrochemical reversibility of redox couple, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this procedure for modification of electrodes.     

多巴胺在聚亚甲基蓝/石墨烯修饰电极上的电化学行为研究

利用电聚合方法在石墨烯修饰的玻碳电极表面制备了聚亚甲基蓝/石墨烯修饰电极(PMB/GH/GCE)。采用循环伏安法(CV)和差分脉冲伏安法(DPV)研究了多巴胺(DA)和抗坏血酸(AA)在该修饰电极上的电化学行为。在pH 6.9的磷酸盐缓冲溶液中,DA和AA分别在0.208 V和-0.108 V处产生灵敏的氧化峰,与其在聚亚甲基蓝和石墨烯单层修饰电极上的电化学行为相比,两者的峰电流明显增加,峰电位差达316 mV。研究表明,电聚合方法使亚甲基蓝牢固地非共价修饰到石墨烯上,并产生协同增效作用,较好地提高了电极的灵敏度和分子识别性能,有利于在大量AA存在下实现对DA的选择性测定。在1.00×10-3mol/L AA的存在下,DA的差分脉冲伏安法峰电流与其浓度在1.00×10-7～5.00×10-3mol/L范围内呈良好的线性关系,检出限达1.00×10-8mol/L。将该方法用于盐酸多巴胺注射液的测定,结果满意。     

Electrochemical study of single wall carbon nanotubes/graphene/ferritin composite for biofuel cell applications

A single wall carbon nanotubes (SWNTs)/graphene/ferritin/GOx layer on a glassy carbon electrode (GCE) acting as a biofuel cell anode was fabricated using a SWNTs/graphene/ferritin composite as an electron transfer mediator from the enzyme to the electrode. In the presence of glucose, the SWNTs/graphene/ferritin/GOx composite showed a higher current response than SWNTs/graphene/GOx composite and the electrocatalytic oxidation of glucose on the anode increased linearly with increasing concentration of glucose. The highly distributed SWNTs/graphene/ferritin composite acts as a platform for enzyme immobilization resulted in an enhanced electrocatalytic activity towards glucose. The SWNTs/graphene/ferritin composite showed an enhanced electron transfer from enzyme to the electrode; therefore, SWNTs/graphene/ferritin/GOx composite can be used as an anode in biofuel cells.     

Single-wall carbon nanotube-based proton exchange membrane assembly for hydrogen fuel cells

A membrane electrode assembly (MEA) for hydrogen fuel cells has been fabricated using single-walled carbon nanotubes (SWCNTs) support and platinum catalyst. Films of SWCNTs and commercial platinum (Pt) black were sequentially cast on a carbon fiber electrode (CFE) using a simple electrophoretic deposition procedure. Scanning electron microscopy and Raman spectroscopy showed that the nanotubes and the platinum retained their nanostructure morphology on the carbon fiber surface. Electrochemical impedance spectroscopy (EIS) revealed that the carbon nanotube-based electrodes exhibited an order of magnitude lower charge-transfer reaction resistance (R(ct)) for the hydrogen evolution reaction (HER) than did the commercial carbon black (CB)-based electrodes. The proton exchange membrane (PEM) assembly fabricated using the CFE/SWCNT/Pt electrodes was evaluated using a fuel cell testing unit operating with H(2) and O(2) as input fuels at 25 and 60 degrees C. The maximum power density obtained using CFE/SWCNT/Pt electrodes as both the anode and the cathode was approximately 20% better than that using the CFE/CB/Pt electrodes.     

Development of a Glucose Biosensor Using Advanced Electrode Modified by Nanohybrid Composing Chemically Modified Graphene and Ionic Liquid

Nanohybrids of chemically modified graphene (CMG) and ionic liquid (IL) were prepared by sonication to modify the electrode. The modified CMG‐IL electrodes showed a higher current and smaller peak‐to‐peak potential separation than a bare electrode due to the promoted electron transfer rate. Furthermore, the glucose oxidase (GOx) immobilized on the modified electrode displayed direct electron transfer rate and symmetrical redox potentials with a linear relationship at different scan rates. The fabricated GOx/CMG‐IL electrodes were developed selective glucose biosensor with respect to a sensitivity of 0.64 μA mM^?1, detection limit of 0.376 mM, and response time of <5 s.     

CeO<Subscript>2</Subscript> nanoparticle-modified electrode as a novel electrochemical interface in the quantification of Zn<Superscript>2+ </Superscript>ions at trace level: application to real sample analysis

A simple strategy has been proposed to quantify Zn²⁺ ions using CeO₂ nanoparticle-modified glassy carbon electrode. The CeO₂ nanoparticles were prepared by sucrose-nitrate decomposition method, and it was characterized by X-ray diffraction (XRD), FT-IR, TEM, and surface area analyzer. The synthesized CeO₂ nanoparticles were used as modifier molecules as a thin film on glassy carbon electrode (GCE) in the trace level quantification of Zn²⁺ by using cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) techniques. The fabricated sensor exhibited a good analytical response towards Zn²⁺ ions. The modified electrode showed a wide linearity in the concentration range 20–380 μg L^?1 with a limit of detection 0.36 μg L^?1. The proposed electrochemical sensor was successfully applied to trace level Zn²⁺ quantification from real sample matrices.     

石墨烯修饰玻碳电极测定邻苯二酚

制备了用于测定邻苯二酚(CAT)的石墨烯修饰电极,并应用循环伏安法研究了CAT在该修饰电极上的电化学行为;用差分脉冲伏安法研究了测试底液的pH值对该修饰电极性能的影响,结果表明,此修饰电极在含不同浓度CAT的PBS溶液(pH=7.0)中测定,响应电流与CAT浓度在5.0×10-8～5.6×10-4mol/L范围内有良好的线性关系,相关系数r=0.9919,检出限为6.68×10-9mol/L(S/N=3)。与其它几种修饰电极相比,石墨烯修饰电极制备简单、响应时间快、操作简便,稳定性和重现性良好,有应用价值。     

Evaluation of Ionic Liquids Based on Amino Acid Anions for Use in Liquid‐junction Free Reference Electrodes

In this paper we report on the novel polymeric membranes for the liquid junction‐free reference electrodes. The membranes contain the ionic liquids (ILs) based on the amino acid anions, namely valine‐, leucine‐, lysine‐ and histidine‐anions, and 1‐butyl‐3‐methylimidazolium cation. Addition of the ILs, and especially of the valine‐based one, to the polymeric plasticized membranes allows significant stabilization of the electrode potential and makes it insensitive to the solution composition. A simple criterion based on the calculated lipophilicities of the cation and anion of the IL is proposed for a priori estimation of its applicability for potential stabilization. The addition of the IL as a microcomponent is found to be advantageous over plasticizing the membrane with the IL due to better potential stability, higher dissociation degree and mobility of the species. The resistance of the novel reference membranes can be tuned by addition of the lipophilic membrane electrolytes, e. g. ETH500. The applicability of the developed reference electrodes is verified in the potentiometric calibration of the indicator K⁺‐ and Ca²⁺‐selective electrodes. Implementation of the amino acid‐based ionic liquids with low environmental toxicity can make a significant contribution to the development of nature‐friendly potentiometry.     

Graphene Quantum Dots‐based Electrochemical Biosensor for Catecholamine Neurotransmitters Detection

An useful electrochemical sensing approach was developed for epinephrine (EP) detection based on graphene quantum dots (GQDs) and laccase modified glassy carbon electrodes (GC). The miniature GC biosensor was designed and constructed via the immobilization of laccase in an electroactive layer of the electrode coated with carbon nanoparticles. This sensing arrangement utilized the catalytic oxidation of EP to epinephrine quinone. The detection process was based on the oxidation of catecholamine in the presence of the enzyme – laccase. With the optimized conditions, the analytical performance demonstrated a high degree of sensitivity −2.9 μA mM⁻¹ cm⁻², selectivity in a broad linear range (1–120×10⁻⁶ M) with detection limit of 83 nM. Moreover, the method was successfully applied for EP determination in labeled pharmacological samples.     

Effect of Various Deposition Techniques,Electrode Materials and Posttreatment with Tetrabutylammonium and Tetrabutylphosphonium Salts on the Electrochemical Behavior and Stability of Various Prussian Blue Modified Electrodes

The effect of various deposition techniques, electrode materials and posttreatment with tetrabutylammonium and tetrabutylphosphonium salts on the electrochemical behavior and stability of various Prussian blue (PB) modified electrodes, namely PB modified glassy carbon electrodes, silicate‐film supported PB modified glassy carbon electrodes, PB‐doped silicate glassy carbon electrodes, PB modified carbon ceramic electrodes using electrochemical deposition and PB modified carbon ceramic electrodes using chemical deposition is reported. Cyclic voltammetry and amperometric measurements of hydrogen peroxide were performed in a flow injection system while the carrier phosphate buffer (pH 7.0) with a flow rate of 0.8 mL min^?1 was propelled into the electrochemical flow through cell housing the PB modified working electrode as well as an Ag|AgCl|0.1 M KCl reference and a Pt auxiliary electrode. The results showed that the deposition procedure, electrode material and posttreatment with additional chemicals can significantly alter the stability and electrochemical behavior of the PB film. Among the studied PB modified electrodes, those based on carbon ceramic electrodes modified with a film of electropolymerized PB showed the best electrochemical stability.     

Sensitive Determination of Acetaminophen in the Presence of Dopamine and Pyridoxine Facilitated by their Extent of Interaction with Single‐walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWCNTs) were immobilized on glassy carbon (GC) electrode by drop casting The resulting modified electrode (represented as GC/SWCNTs) efficiently oxidizes acetaminophen (AC), dopamine (DA) and pyridoxine (PY) by decreasing the respective oxidation potentials and increasing peak currents in comparison to bare GC electrode. The extent of lowering of overpotentials is in the order of AC>PY>DA, in agreement with the order of decrease in the HOMO‐LUMO energy gap (ΔE) of these analytes, as determined from Density Functional Theory (DFT) calculations. DFT calculations further reveal that due to the interaction of the analytes on the SWCNT(10,10) there is a negative charge density transfer (higher probability of electron transfer, lower ΔE value) to the frontier molecular orbitals of the analytes, which eases their oxidation. Since AC, DA and PY oxidize distinctly at distinct potential values, the present SWCNTs modified electrodes could be used to simultaneously determine them. Cyclic voltammetry, differential pulse voltammetry and amperometry techniques are utilized to understand the electrochemical characteristics of the analytes (AC, DA and PY) and subsequent sensing of them at the GC/SWCNTs electrode. The electrode is then applied to the determination of AC as a case study. Sensitivity, detection limit and linear calibration range for the AC are found to be 7.9 μA μM^?1 cm^?2, 1.1 μM and 2.0–100.0 μM, respectively. The increased electroactive surface area of the GC/SWCNTs increases the oxidation peak currents and hence increases the sensitivity of the determination.     

Simultaneous Determination of Ranitidine and Metronidazole at Glassy Carbon Electrode Modified with Single Wall Carbon Nanotubes

Single‐walled carbon nanotubes(SWCNTs) were dispersed into DMSO, and a SWCNTs‐film coated glassy carbon electrode was achieved via evaporating the solvent. The results indicated that CNT modified glassy carbon electrode exhibited efficiently electrocatalytic reduction for ranitidine and metronidazole with relatively high sensitivity, stability and life time. Under conditions of cyclic voltammetry, the potential for reduction of selected analytes is lowered by approximately 150 mV and current is enhanced significantly (7 times) in comparison to the bare glassy carbon electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for these analytes determinations by hydrodynamic amperometry. Under optimized condition in amperometric method the concentration calibration range, detection limit and sensitivity were about, 0.1–200 μM, detection limit (S/N=3) 6.3×10^?8 mol L^?1 and sensitivity 40 nA/μM for metronidazole and 0.3–270 μM 7.73×10^?8 mol L^?1 and 25 nA/μM for ranitidine. In addition, the ability of the modified electrode for simultaneous determination of ranitidine and metronidazole was evaluated. The proposed method was successfully applied to ranitidine and metronidazole determination in tablets. The analytical performance of this sensor has been evaluated for detection of these analytes in serum as a real sample.     

Bio-electrocatalysis of NADH and ethanol based on graphene sheets modified electrodes

Characterization and application of graphene sheets modified glassy carbon electrodes (graphene/GC) have been presented for the electrochemical bio-sensing. A probe molecule, potassium ferricyanide is employed to study the electrochemical response at the graphene/GC electrode, which shows better electron transfer than graphite modified (graphite/GC) and bare glassy carbon (GC) electrodes. Based on the highly enhanced electrochemical activity of NADH, alcohol dehydrogenase (ADH) is immobilized on the graphene modified electrode and displays a more desirable analytical performance in the detection of ethanol, compared with graphite/GC or GC based bio-electrodes. It also exhibits good performance of ethanol detection in the real samples. From the results of electrochemical investigation, graphene sheets with a favorable electrochemical activity could be an advanced carbon electrode materials for the design of electrochemical sensors and biosensors.     

Electrochemical Properties of Hydroxyphenazine-Coated Electrodes

Glassy carbon and gold electrodes were coated with 1-hydroxyphenazine, and the electrochemical properties of these electrodes were tested using them as a rotating disc electrode to reduce Ru (bipy)₃³⁺, Fe³⁺, quinoxaline, O₂, and to oxidize Eu²⁺. The fixed redox couple can be reversibly reduced and oxidized, and acts as an intermediate medium for the electron transfer. For example the Ru(bipy)₃³⁺ (E_1/2= 1010 mV vs. SCE. (saturated calomel electrode) on a glassy carbon electrode in 1M H₂SO₄) is only reduced at 50 mV, whereas the oxidation of Eu²⁺ (E_1/2= ?460 mV vs. SCE. on a Hg-electrode in 1M HCl) takes place at ? 100 mV. The heterogeneous rate constant depends on the second order reaction between the attached coating and the redox couple in solution. Depending on this rate constant, selectivity of the electrode is observed.     

Demonstration of the advantages of using bamboo-like nanotubes for electrochemical biosensor applications compared with single walled carbon nanotubes

The modification of glassy carbon electrodes with random dispersions of nanotubes is currently the most popular approach to the preparation of carbon nanotube modified electrodes. The performance of glassy carbon electrodes modified with a random dispersion of bamboo type carbon nanotubes was compared with single walled carbon nanotubes modified glassy carbon electrodes and bare glassy carbon electrodes. The electrochemical performance of all three types for electrode were compared by investigating the electrochemistry with solution species and the oxidation of guanine and adenine bases of surface adsorbed DNA. The presence of edge planes of graphene at regular intervals along the walls of the bamboo nanotubes resulted in superior electrochemical performance relative to SWNT modified electrodes from two aspects. Firstly, with solution species the peak separation of the oxidation and reduction waves were smaller indicating more rapid rates of electron transfer. Secondly, a greater number of electroactive sites along the walls of the bamboo-carbon nanotubes (BCNTs) resulted in larger current signals and a broader dynamic range for the oxidation of DNA bases.     

An Immunosensor for Ultrasensitive Detection of 1‐Pyrenebutyric Acid with Enhanced Electrochemical Performance Based on a Graphene‐Ionic Liquid Doped Chitosan Film Modified Glassy Carbon Electrode

This paper describes a highly sensitive and label‐free electrochemical immunosensor for the detection of 1‐pyrenebutyric acid (PBA) which is based on a graphene (GS), chitosan (CS), and ionic liquid (IL) composite modified glassy carbon electrode (GS‐CS‐IL/GCE). The modification process was monitored by transmission electron microscopy (TEM) and cyclic voltammetry (CV). Due to the synergistic effects of GS, CS, and IL, the biosensor exhibits excellent selectivity to PBA. The current response of the proposed immunosensor decreases linearly at two concentration ranges from 0.01 to 5 and from 5 to 150 ng mL^?1 with a detection limit of 0.01 ng mL^?1.