CuO Crystalline Modified Glassy Carbon Electrodes for Anodic Amperometric Determination of Hydrogen Peroxide

As an alternative selection of electrocatalytic surface modifier, the electrochemically generated copper oxides is re‐ investigated by using cyclic voltammetry (CV), scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). Interesting phenomena have been found, which indicate that the electrodeposition from the Cu²⁺ solution under cyclic voltammetric conditions can generate a transparent Cu(OH)₂ crystalline on the surface of glassy carbon electrodes, and this crystalline can be further transferred to a novel cubic opaque CuO crystalline of about 300 nm in size by second step of cyclic voltammetry in pH 12 NaOH solution. The final electrode (denoted as nano‐CuO/GCE) can catalyze the oxidation (as well as the reduction) of H₂O₂ in basic solutions. It shows pH dependent three‐part catalytic mechanism in the range from pH 7 to pH 14. In 0.10 mol/L NaOH solution, the amperometric response at 0.15 V (vs. SCE) can give a current sensitivity as high as 139 mA/(mol·L^?1) in the rage of 5.0×10^?7?6.0×10^?4 mol/L with a lower detection limit (s/n=3) of 2.5×10^?8 mol/L, and a current sensitivity of 78.4 mA/(mol·L^?1) in the rage of 6.0×10^?4–2.0×10^?3 mol/L. This electrode also has excellent reproducibility and stability. The mechanisms for the two steps of preparation and the catalytic reactions are proposed. The nano‐CuO crystalline modified electrode may have more applications in the field of electrochemical sensing.     

Voltammetric Determination of Dopamine in Human Serum and Urine at a Glassy Carbon Electrode Modified by Cysteic Acid Based on Electrochemical Oxidation of L ‐cysteine

Abstract

The voltammetric behavior of dopamine was studied at a glassy carbon electrode modified by cysteic acid, based on electrochemical oxidation of L ‐cysteine. The modified electrode showed strong electrocatalytic activity towards dopamine and good selectivity. In a phosphate buffer solution (pH 7.4), the anodic peak current obtain from the differential pulse voltammetry of dopamine was linearly dependent on its concentration in the range of 5×10^?9 to 4.0×10^?6mol · L^?1, with a detection limit of 2×10^?9mol · L^?1. The low‐cost modified electrode had been applied to the determination of dopamine in human serum and urine samples with satisfactory results.     

Direct Electron Transfer of Glucose Oxidase and Glucose Biosensor Based on Nano-structural Attapulgite Clay Matrix

The direct electrochemistry of glucose oxidase (GOD) was achieved based on the immobilization of GOD on a natural nano‐structural attapulgite (ATP) clay film modified glassy carbon (GC) electrode. The immobilized GOD displayed a pair of well‐defined quasi‐reversible redox peaks with a formal potential (E^0′) of ?457.5 mV (vs. SCE) in 0.1 mol·L^?1 pH 7.0 phosphate buffer solution. The peak current was linearly dependent on the scan rate, indicating that the direct electrochemistry of GOD in that case was a surface‐controlled process. The immobilized glucose oxidase could retain bioactivity and catalyze the oxidation of glucose in the presence of ferrocene monocarboxylic acid (FMCA) as a mediator with the apparent Michaelis‐Menten constant K^app_m of 1.16 mmol·L^?1. The electrocatalytic response showed a linear dependence on the glucose concentration ranging widely from 5.0×10^?6 to 6.0×10^?4 mol·L^?1 (with correlation coefficient of 0.9960). This work demonstrated that the nano‐structural attapulgite clay was a good candidate material for the direct electrochemistry of the redox‐active enzyme and the construction of the related enzyme biosensors. The proposed biosensors were applied to determine the glucose in blood and urine samples with satisfactory results.     

Electrocatalytic Oxidation of Nitrite at Gold Nanoparticle-polypyrrole Nanowire Modified Glassy Carbon Electrode

A novel chemically modified electrode based on the dispersion of gold nanoparticles on polypyrrole nanowires has been developed to investigate the oxidation behavior of nitrite using cyclic voltammetry, differential pulse voltammetry and chronoamperometry techniques. The diffusion coefficient (D), electron transfer coefficient (α) and charge transfer rate constant (k) for the oxidation of nitrite were determined. The modified electrode exhibited high electrocatalytic activity toward the oxidation of nitrite. The catalytic peak current was found to be linear with nitrite concentrations in the range of 8.0×10^?7?2.5×10^?3 mol·L^?1 with a detection limit of 1.0×10^?7 mol·L^?1 (s/n=3). The proposed method was successfully applied to the detection of nitrite in water samples with obtained satisfactory results. Additionally, the sensor also showed excellent sensitivity, anti‐interference ability, reproducibility and stability properties.     

(4-Ferrocenylethyne) phenylamine on Graphene as the Signal Amplificator to Determinate Dopamine and Acetaminophen Simultaneously

A novel (4‐ferrocenylethyne) phenylamine functionalized graphene sheets (FEPA‐GR), coupling with chitosan (CS) were used as a signal amplification platform for simultaneous and sensitive determination of dopamine (DA) and acetaminophen (AC). In this work, FEPA used as electron transfer mediator can be immobilized on GR surface via strong π‐π stacking interaction between the conjugate chain of FEPA and GR, which effectively prevents FEPA electron mediator leaking from the electrode surface and amplified the signal. Transmission electron microscopy, FT‐IR spectroscopy, UV‐vis spectroscopy and electrochemical experiments results are all demonstrated the strong π‐π stacking interaction between FEPA and GR. The resulted biosensor exhibited a fast response, remarkable electrocatalytic activity, perfect anti‐interference ability and good stability for simultaneous detection of DA and AC. Under the optimum conditions, the oxidation peak currents of DA and AC were linearly correlated to their concentrations in the range of 2.0–135.0 µmol·L^?1 and 0.3–80.0 µmol·L^?1, respectively. The lower detection limits for DA and AC were 0.30 and 0.05 µmol·L^?1, respectively. The feasibility of the proposed method was validated by successfully applied to the simultaneous determination of DA and AC in serum samples with the standard addition method.     

Simultaneous Detection of Dopamine and Uric Acid under Coexistence of Ascorbic Acid with DNA/Pt Nanocluster Modified Electrode

A novel biosensor by electrochemically codeposited Pt nanoclusters and DNA film was constructed and applied to detection of dopamine (DA) and uric acid (UA) in the presence of high concentration ascorbic acid (AA). Scanning electron microscopy and X‐ray photoelectron spectroscopy were used for characterization. This electrode was successfully used to resolve the overlapping voltammetric response of DA, UA and AA into three well‐defined peaks with a large anodic peak difference (ΔE_pa) of about 184 mV for DA and 324 mV for UA. The catalytic peak current obtained from differential pulse voltammetry was linearly dependent on the DA concentration from 1.1× 10^?7 to 3.8×10^?5 mol·L^?1 with a detection limit of 3.6×10^?8 mol·L^?1 (S/N=3) and on the UA concentration from 3.0×10^?7 to 5.7×10^?5 mol·L^?1 with a detection limit of 1.0×10^?7 mol·L^?1 with coexistence of 1.0×10^?3 mol·L^?1 AA. The modified electrode shows good sensitivity and selectivity.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin Based on Nafion‐Room Temperature Ionic Liquids‐Multiwalled Carbon Nanotubes Composite Film

A robust and effective composite film combined the benefits of Nafion, room temperature ionic liquid (RTIL) and multi‐wall carbon nanotubes (MWNTs) was prepared. Hemoglobin (Hb) was successfully immobilized on glassy carbon electrode surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Hb were investigated in detail. A pair of well‐defined and quasi‐reversible redox peaks of Hb was obtained in 0.10 mol·L^?1 pH 7.0 phosphate buffer solution (PBS), indicating that the Nafion‐RTIL‐MWNTs film showed an obvious promotion for the direct electron transfer between Hb and the underlying electrode. The immobilized Hb exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis current was linear to H₂O₂ concentration in the range of 2.0×10^?6 to 2.5×10^?4 mol·L^?1, with a detection limit of 8.0×10^?7 mol·L^?1 (S/N=3). The apparent Michaelis‐Menten constant (K_m^app) was calculated to be 0.34 mmol·L^?1. Moreover, the modified electrode displayed a good stability and reproducibility. Based on the composite film, a third‐generation reagentless biosensor could be constructed for the determination of H₂O₂.     

Synergistic Effect of Graphene and Multiwalled Carbon Nanotubes on a Glassy Carbon Electrode for Simultaneous Determination of Uric Acid and Dopamine in the Presence of Ascorbic Acid

A poly(diallyldimethylammonium chloride)-graphene-multiwalled carbon nanotube modified glassy carbon electrode was fabricated and evaluated by cyclic voltammetry and differential pulse voltammetry. The modified electrode offered high sensitivity, selectivity, excellent long-term stability, and electrocatalytic activity for uric acid and dopamine. This sensor showed wide linear dynamic ranges of 5.0 to 350.0 µmol L^?1 for uric acid and 10.0 to 400.0 µmol L^?1 for dopamine in the presence of 500 µmol L^?1 ascorbic acid. The limits of detection were 0.13 for uric acid and 0.55 µmol L^?1 for dopamine. This functionalized electrode has potential application in bioanalysis and biomedicine.     

Fabrication of a Sensitive Electrochemical Biosensor for Detection of DNA Hybridization Based on Gold Nanoparticles/CuO Nanospindles Modified Glassy Carbon Electrode

In this work, a sensitive electrochemical DNA biosensor for the detection of sequence‐specific target DNA was reported. Firstly, CuO nanospindles (CuO NS) were immobilized on the surface of a glassy carbon electrode (GCE). Subsequently, gold nanoparticles (Au NPs) were introduced to the surface of CuO NS by the electrochemical deposition mode. Probe DNA with SH (HS‐DNA) at the 5′‐phosphate end was covalently immobilized on the surface of the Au NPs through Au? S bond. Scanning electron microscopy (SEM) was used to elucidate the morphology of the assembled film, and electrochemical impedance spectroscopy technique (EIS) was used to investigate the DNA sensor assembly process. Hybridization detection of DNA was performed with differential pulse voltammetry (DPV) and the methylene blue (MB) was hybridization indicator. Under the optimal conditions, the decline of reduction peak current of MB (ΔI) was linear with the logarithm of the concentration of complementary DNA from 1.0×10^?13 to 1.0×10^?6 mol·L^?1 with a detection limit of 3.5×10^?14 mol·L^?1 (S/N=3). In addition, this DNA biosensor has good selectivity, and even can distinguish single‐mismatched target DNA.     

Electrocatalysis Oxidation of GMP Based on Layered Double Hydroxide Functionalized with Anionic Surfactant and Room Temperature Ionic Liquid Modified Glassy Carbon Electrode

The electrocatalysis oxidation of guanosine‐5′‐monophosphate (GMP) was investigated on Mg‐Al layered double hydroxide (LDH) functionalized with sodium dodecyl sulfate (SDS) and room temperature ionic liquid (RTIL) modified glass carbon electrode (GCE). The cyclic voltammogram of GMP on the modified electrode (RTIL/ LDH‐SDS/GCE) exhibited a well defined anodic peak at 1.091 V in 0.2 mol·L^?1 pH 4.4 acetate buffer solution. The GMP oxidation was enhanced in the presence of anionic surfactant in the ?lms. The results suggest that the surfactant molecules intercalate the LDH layers to preconcentrate GMP molecules and the RTIL showed good ionic conductivity. The experimental parameters were optimized, the kinetic parameters were investigated and the probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to GMP concentration in the range from 5.0×10^?7 to 1.0×10^?4 mol·L^?1 with the correlation coefficient of 0.9987 and the detection limit was 1.0×10^?7 mol·L^?1. The RTIL/LDH‐SDS/GCE showed a good electrochemical response to the oxidation of GMP and would be developed into a new biosensor.     

Electrodeposition of Silver Nanoparticles on MWCNT Film Electrodes for Hydrogen Peroxide Sensing

Silver （Ag） nanoparticles were directly electrodeposited on multi-walled carbon nanotubes （MWCNT） in AgNO3/LiNO3 containing EDTA （ethylenediaminetetraacetic acid）. The structure and nature of the resulting Ag/MWNT composite were characterized by field emission scanning electron microscopy （FE-SEM）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）, and the distribution shape of Ag nanoparticles was found to be dependent on the presence of EDTA. The modified electrode showed excellent electrocatalytic activity to redox reaction of hydrogen peroxide and the mechanism of hydrogen peroxide was partly reversible procession with oxidation and reduction peaks at 0.77 and -0.83 V, respectively. The oxidation and reduction peak currents were linearly related to hydrogen peroxide concentration in the range of 1×10^-6-3×10^-4 and 1 ×10^-8-7× 10^-4 mol·L^-1 with correlation coefficients of 0.996 and 0.986, and 3s-detection limit of 9 × 10^-7 and 7 × 10^-9 mol·L^-1.     

A New Amperometric Biosensor Based on HRP/Nano-Au/L-Cysteine/Poly（o-Aminobenzoic acid）-Membrane-Modified Platinum Electrode for the Determination of Hydrogen Peroxide

The third generation amperometric biosensor for the determination of hydrogen peroxide （H2O2） has been described. For the fabrication of biosensor, o-aminobenzoic acid （oABA） was first electropolymerized on the surface of platinum （Pt） electrode as an electrostatic repulsion layer to reject interferences. Horseradish peroxidase （HRP） absorbed by nano-scaled particulate gold （nano-Au） was immobilized on the electrode modified with polymerized o-aminobenzoic acid （poABA） with L-cysteine as a linker to prepare a biosensor for the detection of H2O2. Amperometric detection of H2O2 was realized at a potential of ＋20 mV versus SCE. The resulting biosensor exhibited fast response, excellent reproducibility and sensibility, expanded linear range and low interferences. Temperature and pH dependence and stability of the sensor were investigated. The optimal sensor gave a linear response in the range of 2.99×10^-6 to 3.55×10^-3 mol·L^-1 to H2O2 with a sensibility of 0.0177 A·L^-1·mol^-1 and a detection limit （S/N = 3） of 4.3×10^-7 mol·L^-1. The biosensor demonstrated a 95% response within less than 10 s.     

金属离子对氯过氧化物酶在25℃到55℃激活作用以及机理的研究

基于氯过氧化物酶（CPO）的卤化活性分析,发现某些碱土金属（Ca2+, Mg2+）和过渡金属（Co2+, Ni2+）对CPO具有明显的激活及稳定化作用。例如25 ºC时与CPO在纯缓冲溶液中相比,在75 μmol·L-1 Ca2+,90 μmol·L-1 Mg2+,90 μmol·L-1 Ni2+及105 μmol·L-1 Co2+存在时CPO可分别获得1.33,1.37,1.34 及1.27倍的最大相对活性。而在55 ºC,没有金属离子存在时,CPO 30分钟后仅能保留40%的活性,但在Ca2+,Mg2+离子的介质中,CPO的活性可分别保留81% 和 75%。推测这是由于金属离子结合在CPO活性中心周围的酸-碱催化位点Glu183, His105 and Asp106上,通过底物浓集和诱导有利构象来激活CPO. 同时动力学研究表明金属离子对CPO的激活归因于催化效率（kcat）的提高,以及CPO对底物亲和性及选择性的改善。     

Determination of Sulfite in Hair Waving Products Using Oxygen‐Incorporated Gold‐Modified Screen‐Printed Electrodes

An electrodeposition oxygen‐incorporated gold‐modified screen‐printed carbon electrode (AuOSPE) was fabricated to determine the sulfite content in hair waving products. The AuOSPE showed an electrocatalytic current for sulfite at +0.4 V (vs. Ag/AgCl). Compared with a gold screen‐printed electrode (AuSPE), the AuOSPE showed a higher electrocatalytic current. The increase in the electrocatalytic current was ascribed to the increase of the oxygen incorporated with gold atom on AuOSPE. The AuOSPE coupled with a flow injection analysis (FIA) system showed excellent oxidation current for sulfite in a 0.1 mol L^?1 phosphate buffer solution (PBS), pH 6.0. The linear working range for determining the sulfite content was 0.05 to 1200 mg L^?1 (0.625 µmol L^?1 to 15.00 mmol L^?1) with a calculated detection limit of 0.03 mg L^?1 (0.375 µmol L^?1) (DL, S/N=3). Relative standard deviations (RSD) of 3.03 %, 2.30 % and 4.26 % were calculated for consecutive injections (n=12) of 20, 300 and 900 mg L^?1 sulfite, respectively. The amount of sulfite in two hair waving products was determined by the proposed method and a standard iodometric method. The recoveries ranged from 96.18 % to 105.61 %. The AuOSPE showed high sensitivity, selectivity, stability and reproducibility for sulfite.     

Nanoporous Pt Catalyst Modified by Sn Electrodeposition for Electrochemical Oxidation of Formaldehyde

A nanoporous Pt particles‐modified Ti (nanoPt/Ti) electrode was prepared through a simple hydrothermal method using aqueous H₂PtCl₆ as a precursor and formaldehyde as a reduction agent. The nanoPt/Ti electrode was then modified with limited amounts of tin particles generated by cyclic potential scans in the range of ?0.20 to 0.50 V in a 0.01 mol·L^?1 SnCl₂ solution, to synthesize a Sn‐modified nanoporous Pt catalyst (Sn/nanoPt/Ti). Electroactivity of the nanoPt/Ti and Sn/nanoPt/Ti electrodes towards formaldehyde oxidation in a 0.5 mol·L^?1 H₂SO₄ solution was evaluated by cyclic voltammetry and chronoamperometry. Electrooxidation of formaldehyde on the nanoPt/Ti electrode takes place at a potential of 0.45 V and then presents high anodic current densities due to the large real surface area of the nanoPt/Ti electrode. The formaldehyde oxidation rate is dramatically increased on the Sn/nanoPt/Ti electrode at the most negative potentials, where anodic formaldehyde oxidation is completely suppressed on the nanoPt/Ti electrode. Chronoamperogramms (CA) of the Sn/nanoPt/Ti electrode display stable and large quasi‐steady state current densities at more negative potential steps. Amperometric data obtained at a potential step of 100 mV show a linear dependence of the current density for formaldehyde oxidation upon formaldehyde concentration in the range of 0.003 to 0.1 mol·L^?1 with a sensitivity of 59.29 mA·cm^?2 (mol·L^?1)^?1. A detection limit of 0.506 mmol·L^?1 formaldehyde was found. The superior electroactivity of the Sn/nanoPt/Ti electrode for formaldehyde oxidation can be illustrated by a so‐called bifunctional mechanism which is involved in the oxidation of poisoning adsorbed CO species via the surface reaction with OH adsorbed on neighboring Sn sites.     

Selective Electrochemical Recognition of o-Phenylenediol by a Novel Calix[4]arene Derivative

A new type of calixarene-modified electrode has been prepared by directly coating the surface of a glassy carbon electrode with tetrahydrofuran solution containing 25,26,27,28-tetra-（3-amidino thiopropoxy）-5,11,17,23-tetratert-butylcalix[4]arene, and applied to the investigation of electrochemical behavior of phenylenediols. The results showed that the modified electrode could selectively recognize o-phenylenediol, making the over-potential of o-phenylenediol dropped and peak current increased greatly. The anodic peak current is proportional to the concentration of o-phenylenediol in the range of 1.0×10^-5-1.0×10^-4 mol·L^-1 with the detection limit （SIN=3） of 1.0×10^-7 mol·L^-1. The recognizing mechanism, including electrochemical process and binging sites, was also discussed using voltammetry.     

Fe_2O_3-Modified Hydrogen Storage Alloys as Electrocatalyst for Borohydride Oxidation

The effects of hot alkaline treatment and Fe₂O₃ modification of hydrogen storage alloy on the electrocatalytic activity for oxidation of borohydride have been investigated using linear sweep voltammetry. The performance of borohydride electrochemical oxidation was significantly influenced by the hot alkaline treatment and Fe₂O₃ modification of the hydrogen storage alloy. The results showed that the current density of the Fe₂O₃‐modified hot alkaline‐treated hydrogen storage alloy electrode containing 5 wt% Fe₂O₃ reached 125 mA·cm^?2 in 0.10 mol·L^?1 NaBH₄ and 2 mol·L^?1 NaOH solution at ?0.55 V vs. saturated Ag/AgCl, KCl electrode.     

Amperometric Nitric Oxide Sensor Based on Poly(Thionine)/Nafion‐Modified Electrode and Its Application in Monitoring Nitric Oxide Release from Rat Kidney

Abstract

A novel amperometric nitric oxide (NO) sensor based on a glassy carbon electrode modified with thionine and Nafion films has been developed. The oxidation peak current of NO increased significantly at the poly(thionine)/Nafion‐modified glassy carbon electrode (GCE), which can be used for the detection of NO. The oxidation peak current was linear with the concentration of nitric oxide over the range from 3.6×10^?7 to 6.8×10^?5 mol · L^?1, and the detection limit was 7.2×10^?8 mol · L^?1. This nitric oxide sensor showed high selectivity to nitric oxide determination, and some potential interference could be eliminated effectively. The nitric oxide sensor has been applied to monitor NO release from rat kidney stimulated by L‐arginine. The results indicated the applicability of the NO sensor to biomedical samples.     

Electrochemiluminescence of SDBS‐Ru(bpy)32+‐CPM System and Its Application

When the concentration of dodecyl benzene sulfonic acid sodium salt (SDBS) is 0.7 mmol·L^?1, the electrochemical and electrochemiluminescence (ECL) intensity of Ru(bpy)₃²⁺‐chlorpheniramine maleate (CPM) system at the Au electrode were studied. The results showed that compared with the absence of SDBS, enhancement of the ECL intensity was 14‐fold at Au electrode. Base on this, an ECL method was established for efficient and simple determination of CPM at Au electrode. Under the optimum experimental condition, the enhanced ECL intensities had good linear relationship with the concentration of CPM in the range of 1.0×10^?4–1.0×10^?7 mol·L^?1, and a linear regression equation was obtained as follows: I (counts)=48.805×10⁶c+394.03 (r=0.9975), the detection limit for CPM was 1.4×10^?8 mol·L^?1. The RSD for 5 times determinations of 1.0×10^?5 mol·L^?1 CPM was 3.2%. The results of recovery test were between 96.3%–102.5%, and the RSD of recovery test (n=5) was 2.7%. In addition, eleven kinds of tertiary amines‐Ru(bpy)₃²⁺ systems were investigated in the absence and presence of SDBS. The results showed that the enhancement of SDBS on ECL intensity of tertiary amines‐Ru(bpy)₃²⁺ systems was universal.