A methyl parathion electrochemical sensor based on Nano-TiO2, graphene composite film modified electrode

A methyl parathion electrochemical sensor based on nano-TiO₂ and graphene composite film modified glassy carbon electrode has been developed. The electrochemical behavior of MP at the sensor was investigated by cyclic voltammetry and linear sweep voltammetry. Scanning electron microscopy was used to characterize the surface morphology of nano-TiO₂ and graphene composite film. Compared with a bare glassy carbon electrode or a mono-film modified electrode, the redox peak currents of methyl parathion on the composite film modified electrode improved greatly, indicating that the sensor showed good catalytic effects. The optimal experimental condition was obtained. The results indicated that the linear sweep voltammetry responses of methyl parathion, in pH 5.2 acetate buffer solution with open-circuit accumulation for 2 min, were linear with concentrations of methyl parathion in two ranges of 0.002～5 μM and 5～100 μM. The linear equations were i_Pc(μA) = 0.0136 + 4.965c_MP(μM) (R₁² = 0.9911) and i_Pc(μA) = 21.87 + 0.8206c_MP(μM) (R₂² = 0.9914), respectively. The detection limit was 1.0 nM (S/N = 3). The sensor exhibited high sensitivity and good reproducibility as well as certain anti-interference ability. It was applied to the determination of residual MP in fresh apple sample with the recovery of 92%～102%. The result was satisfactory.     

Selective voltammetric determination of norepinephrine in the presence of acetaminophen and tryptophan on the surface of a modified carbon nanotube paste electrode

A new electrochemical sensor for the determination of norepinephrine (NE), acetaminophen (AC) and tryptophan (TRP) is described. The sensor is based on carbon paste electrode (CPE) modified with 5-mino-3′,4′-dimethyl-biphenyl-2-ol (5ADB) and takes the advantages of carbon nanotubes (CNTs), which makes the modified electrode highly sensitive for the electrochemical detection of these compounds. Under the optimum pH of 7.0, the oxidation of NE occurs at a potential about 170 mV less positive than that of the unmodified CPE. Also, square wave voltammetry (SWV) was used for the simultaneous determination of NE, AC and TRP at the modified electrode.     

Detection of organophosphate pesticide using polyaniline and carbon nanotubes composite based on acetylcholinesterase inhibition

Acetylcholinesterase (AChE) activity may be useful biomarker for detecting of organophosphate pesticides (OP). Thus a sensitive biosensor for quantitative determination of OP based on AChE biomonitoring was developed. Multi-walled carbon nanotube (MWCNT)/polyaniline (PANI) composite film was prepared by electrochemical polymerization. The immobilized AChE catalyzed the hydrolysis of acetylthiocholine chloride to produce thiocholine, which engendered an irreversible oxidation peak. The enzyme activity was monitored by measuring the oxidation current of thiocholine and further detection of OP. The developed sensor provided a new promising tool for pesticide analysis and assay of enzyme activity.     

Multiwalled Carbon Nanotubes Modified Electrode as a Sensor for Adsorptive Stripping Voltammetric Determination of Hydrochlorothiazide

The study of electrochemical behavior and determination of hydrochlorothiazide, a thiazide diuretic and antihypertensive drug, on multiwalled carbon nanotubes (MCNTs) modified glassy carbon electrode (GCE) is described by adsorptive stripping voltammetry in open circuit potential. The cyclic voltammetric results indicate that MCNTs remarkably enhance the oxidation of hydrochlorothiazide in wide pH range of 2.0–9.5, which is leading to considerable improvement of anodic peak current for hydrochlorothiazide, and allow the development of a highly sensitive voltammetric sensor for determination of hydrochlorothiazide in pharmaceutical and urine samples. Electrochemical studies by alpha-Fe$_{2}$O $_{3}$ nanoparticles modified carbon paste electrode show these oxides have no electrocatalytic effect for hydrochlorothiazide oxidation and support iron oxide impurities in the MCNTs are not active sites in sensing of hydrochlorothiazide. Under optimized conditions, the oxidation peak have two linear dynamic range of 2.0–20.0 nM and 0.2–100.0 $mu$M with experimental detection limit of 0.8 nM and a precision of $≪hbox{4}hbox{%}$ (RSD for 8 analysis).      

Voltammetric sensor for general purpose organohalide detection at picogram per liter concentrations based on a simple collector-generator method

With the aim of producing a general purpose sensor for environmental analysis, we describe a simple and sensitive method for organohalide detection, based on an electrochemical collector-generator process. The sensor consists of four coplanar electrodes contacting a solution volume of 300 microL, containing organohalide. At the first working electrode (a Zn/PTFE composite), the analyte is electrolyzed to liberate halide ions. At the second working electrode (Ag), the halide ions are detected by cathodic stripping voltammetry. Using a preconcentration time of 600 s, with differential pulse voltammetry for stripping, the responses to 1-chloropropane, chloroform, carbon tetrachloride, iodoethane, and bromoethane can be plotted on a common calibration curve, with a detection limit of 0.1 nM (1.3 pg L(-1) or less depending on the organohalide). To the best of our knowledge, this is the lowest reported organohalide detection limit by an electrochemical method and is so far the only general purpose electrochemical method sensitive enough for regulatory requirements. The sensor response was invariant for approximately 40 measurements. Analysis of tap water, spiked with chloroform or carbon tetrachloride, gave recoveries within 1.0-2.6% of the recoveries by the standard GC method.     

Electrochemical oxidation of oxalic acid at highly boron-doped diamond electrodes

Electrochemical oxidation of oxalic acid has been investigated at bare, highly boron-doped diamond electrodes. Cyclic voltammetry and flow injection analysis with amperometric detection were used to study the electrochemical reaction. Hydrogen-terminated diamonds exhibited well-defined peaks of oxalic acid oxidation in a wide pH range. A good linear response was observed for a concentration range from 50 nM to 10 microM, with an estimated detection limit of approximately 0.5 nM (S/N = 3). In contrast, oxygen-terminated diamonds showed no response for oxalic acid oxidation inside the potential window, indicating that surface termination contributed highly to the control of the oxidation reaction. An investigation with glassy carbon electrodes was conducted to confirm the surface termination effect on oxalic acid oxidation. Although a hydrogen-terminated glassy carbon electrode showed an enhancement of signal-to-background ratio in comparison with untreated glassy carbon, less stability of the current responses was observed than that at hydrogen-terminated diamond.     

Iridium-based electrocatalytic systems for the determination of insulin

Two electrochemical catalytic systems for the determination of insulin were developed. The homogeneous system was based on the oxidation of insulin by chloro complexes of iridium(IV). Kinetic studies revealed that the aquation of iridium complexes activated them toward the oxidation of insulin in acidic solutions; e.g., the rate constant was equal to 25, 900, and 8,400 L mol(-1) s(-1) for the oxidation of insulin by the IrCl62-, Ir(H2O)CI5-, and Ir(H2O)2Cl4 complexes, respectively. The inertness of the iridium complexes argued for the outer-sphere mechanism of the homogeneous oxidation reaction. Electroplating of aquated iridium complexes on the glassy carbon electrode resulted in the formation of the iridium oxide (IrOx) surface film, which was used in the heterogeneous detection system for insulin. The catalytic activity of the IrOx film toward insulin oxidation was ascribed to a combination of electron-transfer mediation and oxygen transfer which was related to the acid/base chemistry of the film. The IrOx film electrode was used as an amperometric detector for flow injection analysis of insulin in pH 7.40 phosphate buffer. Linear least-squares calibration curves over the range 0.05-0.50 microM (five points) had slopes of 35.2 +/- 0.4 nA microM(-1) and correlation coefficients of 0.999. The detection limit for insulin was 20 nM using the criterion of a signal of 3 times the peak-to-peak noise. The advantageous properties of the detector based on the IrOx film are its inherent stability at physiological pH, high catalytic activity toward insulin oxidation, and simplicity of preparation.     

Enhanced oxidation of estrone at multi-wall carbon nanotubes film electrode: direct evidence for the advantage of carbon nanotubes over other carbonaceous materials

The electrochemical behaviors of estrone at various carbonaceous nanomaterials-dihexadecyl hydrogen phosphate (DHP) composite films coated glassy carbon electrodes were investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronocoulometry (CC) and electrochemical impedance spectroscopy (EIS). Comparing with the composite films of acetylene black (AB) and carbon nanofiber (CNF), multi-wall carbon nanotubes (MWCNTs)-DHP film showed the best electrochemical performance towards the oxidation of estrone, reflected by the significantly enhanced oxidation current in the voltammograms as well as the apparently reduced charge transfer resistance in EIS. Studies on the active surface area, the surface coverage and EIS suggested that the apparently improved electrochemical responses of estrone at MWCNTs should arise from their large surface area, good conductivity and the ability to facilitate the charge transfer process. The reaction mechanisms of estrone oxidation at the three composite films were also discussed, which were expected to follow a process involved the total loss of two electrons and two protons.     

Electrochemical oxidation of histamine and serotonin at highly boron-doped diamond electrodes

The electrochemistry of histamine and serotonin in neutral aqueous media (pH 7.2) was investigated using polycrystalline, boron-doped diamond thin-film electrodes. Cyclic voltammetry, hydrodynamic voltammetry, and flow injection analysis (FIA) with amperometric detection were used to study the oxidation reactions. Comparison experiments were carried out using polished glassy carbon (GC) electrodes. At diamond electrodes, highly reproducible and well-defined cyclic voltammograms were obtained for histamine with a peak potential at 1.40 V vs SCE. The voltammetric signal-to-background ratios obtained at diamond were 1 order of magnitude higher than those obtained for GC electrodes at and above 100 microM analyte concentrations. A linear dynamic range of 3-4 orders of magnitude and a detection limit of 1 microM were observed in the voltammetric measurements. Well-defined sweep rate-dependent voltammograms were also obtained for 5-hydroxytryptamine (5-HT). The characteristics of the voltammogram indicated lack of adsorption of its oxidation products on the surface. No fouling or deactivation of the electrode was observed within the experimental time of several hours. A detection limit of 0.5 microM (signal-to-noise ratio 13.8) for histamine was obtained by use of the FIA technique with a diamond electrode. A remarkably low detection limit (10 nM) was obtained for 5-HT on diamond by the same method. Diamond electrodes exhibited a linear dynamic range from 10 nM to 100 microM for 5-HT determination and a range of 0.5-100 microM for histamine determination. The FIA response was very reproducible from film to film, and the response variability was below 7% at the actual detection limits.     

纳米TiO2/还原石墨烯复合修饰电极用于食品中 柠檬黄的检测

为了检测食品中柠檬黄的含量,利用滴涂法和电化学还原法制备纳米TiO_2/还原石墨烯复合修饰玻碳电极(TiO_2-Er GO/GCE)。采用透射电子显微镜和X射线粉末衍射仪对TiO_2和TiO_2-GO两种修饰电极材料进行表征;通过循环伏安法观察了柠檬黄在不同电极上的电化学行为,并对检测条件如p H值、富集电位、富集时间进行了优化。实验结果表明:TiO_2-Er GO/GCE增大了电极的电化学活性面积,提高了柠檬黄的电化学氧化响应;最优的检测条件为p H值为3.7、富集电位为-0.20 V、富集时间为180 s;在最优的检测条件下,采用线性扫描伏安法检测柠檬黄的线性范围为2.0×10-8~2.0×10-5 mol/L,检测限为8.0×10-9 mol/L(信噪比为3)。     

Simultaneous determination of serotonin and dopamine at the PEDOP/MWCNTs-Pd nanoparticle modified glassy carbon electrode

Electrochemical determination of dopamine (DA) and serotonin (5-HT) have been studied at a modified glassy carbon electrode (GCE) in 0.1 M phosphate buffer solution (PBS) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at pH 7.4, all over the interfering biomolecule ascorbic acid (AA). The GCE was modified by palladium-functionalized, multi-walled carbon nanotubes (MWCNTs-Pd) with electrochemical deposition of poly 3,4-ethylenedioxy pyrrole (PEDOP), denoted as PEDOP/MWCNTs-Pd/GCE, and investigated by SEM and EIS experiments. The highly electrocatalytic activity of the modified electrode toward 5-HT and DA was demonstrated from the sensitive and well-separated voltammetric experiment. The oxidation peaks found were 0.165 and 0.355 mV for DA and 5-HT, respectively. The composite film shows a significant accumulation effects on two species, as well as the mutual interference among the analytes. This biosensor was best in response compared to other modified electrodes made in the same lab. The lowest detection limits were found to be 5.0 x 10(-9) and 1.0 x 10(-8) for 5-HT and DA, respectively. The respective linear ranges were determined as 1.0 x 10(-7) to 2.0 x 10(-4) and 1.0 x 10(-7) to 2.0 x 10(-4) for 5-HT and DA.     

MnO2纳米棒-还原石墨烯复合修饰玻碳电极用于苋菜红的检测

利用电化学还原法制备MnO₂纳米棒-还原石墨烯复合修饰电极（MnO₂ NRs-ErGO/GCE）用于苋菜红的检测。采用SEM和XRD分别对修饰电极材料进行微观形貌和成分结构表征。通过循环伏安法考察了苋菜红在裸电极、ErGO/GCE和MnO₂ NRs-ErGO/GCE上的电化学行为,并对测定条件如pH值、富集电位、富集时间进行了优化。结果表明,MnO₂ NRs-ErGO增大了GCE电化学活性面积,提高了苋菜红的电化学氧化响应。在最优的检测条件下,MnO₂ NRs-ErGO/GCE线性扫描伏安法检测苋菜红线性范围为2.0×10^-8~1.0×10^-5 mol/L和1.0×10^-5~4.0×10^-4 mol/L,检测限为1.0×10^-8 mol/L。MnO₂ NRs-ErGO/GCE用于真实饮料样品检测,获得满意结果。     

Electrochemical detection of thiols with a coenzyme pyrroloquinoline quinone modified electrode

A modified electrode sensor for the detection of thiols is described. The sensor was constructed by incorporation of the coenzyme pyrroloquinoline quinone (PQQ) into a polypyrrole (PPy) film on a glassy carbon electrode substrate by the electropolymerization of pyrrole in the presence of PQQ. The electrochemical properties of entrapped PQQ in the PPy film were influenced by the applied potential during electropolymerization and by film thickness, both of which were optimized to yield a stable and reproducible response for entrapped PQQ. The PQQ/ PPy sensor was utilized for the amperometric detection of cysteine, homocysteine, penicillamine, N-acetylcysteine, and glutathione. The response for each thiol in pH 8.42 borate buffer was found to be linear with detection limits (S/N = 3) ranging from 13.2 microM for glutathione to 63.7 nM for cysteine with sensitivities of 0.023 nA/microM and 4.71 nA/microM, respectively. The response and detection limits were found to be sensitive to the nature of the thiol and the solution pH. Furthermore, in the presence of dopamine, ascorbic acid, or uric acid, the pH-dependent redox potential of the PQQ catalyst allows tuning of the detection potential to enhance the selectivity for thiols over these potential electroactive interferences.     

Application of graphene-ionic liquid-chitosan composite-modified carbon molecular wire electrode for the sensitive determination of adenosine-5′-monophosphate

In this paper, a graphene (GR) ionic liquid (IL) 1-octyl-3-methylimidazolium hexafluorophosphate and chitosan composite-modified carbon molecular wire electrode (CMWE) was fabricated by a drop-casting method and further applied to the sensitive electrochemical detection of adenosine-5′-monophosphate (AMP). CMWE was prepared with diphenylacetylene (DPA) as the modifier and the binder. The properties of modified electrode were examined by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical behaviors of AMP was carefully investigated with enhanced responses appeared, which was due to the presence of GR-IL composite on the electrode surface with excellent electrocatalytic ability. A well-defined oxidation peak of AMP appeared at 1.314 V and the electrochemical parameters were calculated by electrochemical methods. Under the selected conditions, the oxidation peak current of AMP was proportional to its concentration in the range from 0.01 μM to 80.0 μM with the detection limit as 3.42 nM (3σ) by differential pulse voltammetry. The proposed method exhibited good selectivity and was applied to the detection of vidarabine monophosphate injection samples with satisfactory results.     

Electrochemiluminescence sensor based on partial sulfonation of polystyrene with carbon nanotubes

Herein, homogenously partial sulfonation of polystyrene (PSP) was performed. An effective electrochemiluminescence (ECL) sensor based on PSP with carbon nanotube (CNTs) composite film was developed. Cyclic voltammetry and electrochemical impendence spectroscopy were applied to characterize this composite film. The PSP was used as an immobilization matrix to entrap the ECL reagent Ru(bpy)3(2+) due to the electrostatic interactions between sulfonic acid groups and Ru(bpy)3(2+) cations. The introduction of CNTs into PSP acted not only as a conducting pathway to accelerate the electron transfer but also as a proper matrix to immobilize Ru(bpy)3(2+) on the electrode by hydrophobic interaction. Furthermore, the results indicated the ECL intensity produced at this composite film was over 3-fold compared with that of the pure PSP film due to the electrocatalytic activity of the CNTs. Such a sensor was verified by the sensitive determinations of 2-(dibutylamino)ethanol and tripropylamine.     

Ag/PANI/GCE电极的制备及对NO2-的电化学检测

亚硝酸盐是水中最常见的污染物之一,其检测长期以来一直是国内外研究的热点问题。制备了聚苯胺载银修饰玻碳电极(Ag/PANI/GCE)并将其应用于水中亚硝酸根的电化学检测。初步研究了亚硝酸根在电极表面的电化学行为的影响因素,并分析了所制备电极材料检测亚硝酸根的灵敏度、稳定性以及抗干扰性能。结果显示,所制备的Ag/PANI/GCE电极材料的电化学稳定性好,可以对水中的亚硝酸根浓度进行有效的检测,同时具有稳定性好、灵敏度较高、抗干扰性能强等优势,具有较高的研究价值和较好的应用前景。     

Selective determination of sucrose based on electropolymerized molecularly imprinted polymer modified multiwall carbon nanotubes/glassy carbon electrode

A novel and selective electrochemical sensor was successfully developed for the determination of sucrose by integrating electropolymerization of molecularly imprinted polymer with multiwall carbon nanotubes. The sensor was prepared by electropolymerizing of o-phenylenediamine in the presence of template, sucrose, on a multiwall carbon nanotube-modified glassy carbon electrode. The sensor preparation conditions including sucrose concentration, the number of CV cycles in the electropolymerization step, pH of incubation solution, extraction time of template from the imprinted film and the incubation time were optimized using response surface methodology (RSM). A mixture of acetonitrile/acetic acid was used to remove the template. Hexacyanoferrate(II) was used as a probe to characterize the sensor using electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. Capturing of sucrose by the modified electrode causes decreasing the response of the electrode to hexacyanoferrate(II). Calibration curve was obtained in the sucrose concentration range of 0.01–10.0 mmol L^? 1 with a limit of detection 3 μmol L^? 1. This sensor provides an efficient way for eliminating interferences from compounds with similar structures to sucrose. The sensor was successfully used to determine sucrose in sugar beet juices with satisfactory results.     

A composite prepared from covalent organic framework and gold nanoparticles for the electrochemical determination of enrofloxacin

A high conductivity composite based on covalent organic frameworks/gold nanoparticles (TAPB-PDA-COFs/AuNPs, TAPB: 3,5-tris(4-aminophenyl)benzene, PDA: p-phthalaldehyde) was prepared by a simple in-situ synthesized method and a novel electrochemical sensor based on TAPB-PDA-COFs/AuNPs was constructed for detection of Enrofloxacin (ENR). A variety of different characterization techniques including ultraviolet‐visible spectrophotometer (UV–vis), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the TAPB-PDA-COFs/AuNPs. ENR was detected by square wave stripping voltammetry (SWV) according to the relationship between the ENR concentration and the oxidation peak current. The result showed that TAPB-PDA-COFs/AuNPs was synthesized successfully. The electrochemical sensor showed two linear ranges in the range of 0.05–10 μmol L^?1 and 10–120 μmol L^?1 with the limit of detection of 0.041 μmol L^?1 (S/N = 3). The good recoveries (96.7–102.2%) and low RSDs (0.9–6.4%) indicated the possibility of using this sensor for actual sample detection. Therefore, TAPB-PDA-COFs/AuNPs-based electrochemical sensor showed good performance in detecting ENR, and would be a potential candidate for the development of fluoroquinolones determination.     

Development of piroxicam sensor based on molecular imprinted polymer-modified carbon paste electrode

A new voltammetric sensor for piroxicam measurement is introduced. A piroxicam-selective molecularly imprinted polymer (MIP) and a non-imprinted polymer (NIP) were synthesized in a non-covalent approach using methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linking monomer via a free radical polymerization and then was used for carbon paste (CP) electrode preparation. The MIP, embedded in the carbon paste electrode, functioned as a selective recognition element and pre-concentrator agent for piroxicam determination. The prepared electrode was used for piroxicam measurement via a three-step procedure including analyte extraction in the electrode, electrode washing and electrochemical measurement of piroxicam. The MIP–CP electrode showed good recognition ability in comparison to NIP–CP. Some parameters affecting sensor response were optimized. Under optimum conditions the oxidation peak current was proportional to piroxicam concentration over the range 2–190 and 190–2500 nM. The detection limit was found to be 0.5 nM. This sensor has been successfully applied for the determination of piroxicam in pharmaceutical formulations and serum samples.     

Poly(BCB)/Au-nanoparticles hybrid film modified electrode: Preparation, characterization and its application as a non-enzymatic sensor

We report electrochemical preparation and characterization of poly-brilliant cresyl blue (Poly(BCB))/gold nanoparticles (Au-NPs) modified electrode. The Poly(BCB)/Au-NPs modified electrode has been used as an electrochemical sensor for the detection of hydrogen peroxide (H₂O₂) at lower potential (− 0.2 V). The Poly(BCB)/Au-NPs film was characterized by scanning electron microscopy, Uv-visible spectroscopy (Uv-vis) and cyclic voltammetry. We have observed that, Au-NPs attached glassy carbon electrode (Au-NPs/GCE) significantly enhanced the polymerization of BCB compared to bare GCE. The Poly(BCB) film was irreversibly attached onto the Au-NPs modified electrode, the resulting hybrid film modified electrode was electrochemically active in the pH range from 2 to 11. Attachment of Poly(BCB)/Au-NPs hybrid film on the electrode surface was confirmed by Uv-vis spectra. In addition, electrocatalytic properties of the Poly(BCB)/Au-NPs/GCE towards reduction of H₂O₂ have been investigated, and it was found that the sensitivity, reduction potential as well as the corresponding detection limit were improved as compared to the voltammetric response of the Poly(BCB)/GCE and Au-NPs/GCE. Based on this study, a non-enzymatic electrochemical sensor for the determination of H₂O₂ has been reported. Moreover, analysis of commercial H₂O₂ samples was performed using the proposed method and satisfactory results were obtained.