A sensitive determination of estrogens with a Pt nano-clusters/multi-walled carbon nanotubes modified glassy carbon electrode

On the top of a multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (MWNTs/GCE), Pt nanoclusters were electrochemically deposited, fabricating a Pt/MWNTs composite modified electrode, Pt/MWNTs/GCE. X-ray photoelectron spectroscopy, powder X-ray diffraction and field emission scanning electron microscope were used for the surface characterization of the electrode, and demonstrated the formation and distribution of Pt clusters of Pt nanoparticles of 8.4 nm in averaged size in the MWNTs matrix. The preliminary study found that this composite modified electrode has strong electrocatalytic activity toward the oxidation of estrogens involving estradiol, estrone and estriol. The voltammetric behavior of estrogens on this electrode was investigated by cyclic voltammetry, linear sweep voltammetry and square-wave voltammetry. In comparison with the MWNTs/GCE or a Pt nanoparticles modified GCE prepared in the similar way, this composite modified electrode exhibited much higher current sensitivity and catalytic activity. This electrode is also stable. The linear range of square-wave voltammetric determination was 5.0 x 10(-7)-1.5 x 10(-5)mol/L for estradiol, 2.0 x 10(-6)-5.0 x 10(-5)mol/L for estrone, and 1.0 x 10(-6)-7.5 x 10(-5)mol/L for estriol. Under an assumption that the concentration ratio of estradiol:estrone:estriol is 2:2:1, the real sample of blood serums was tested for the determination using this electrode. Satisfactory result was obtained with averaged recovery of 105%.     

Selective detection of uric acid in the presence of ascorbic acid at physiological pH by using a beta-cyclodextrin modified copolymer of sulfanilic acid and N-acetylaniline

A beta-cyclodextrin (CD) modified copolymer membrane of sulfanilic acid (p-ASA) and N-acetylaniline (SPNAANI) on glassy carbon electrode (GCE) was prepared and used to determine uric acid (UA) in the presence of a large excess of ascorbic acid (AA) by differential pulse voltammetry (DPV). The properties of the copolymer were characterized by X-ray photoelectron spectra (XPS) and Raman spectroscopy. The oxidation peaks of AA and UA were well separated at the composite membrane modified electrode in phosphate buffer solution (PBS, pH 7.4). A linear relationship between the peak current and the concentration of UA was obtained in the range from 1.0 x 10(-5) to 3.5 x 10(-4)mol L(-1), and the detection limit was 2.7 x 10(-6)mol L(-1) at a signal-to-noise ratio of 3. Two hundred and fifty-fold excess of AA did not interfere with the determination of UA. The application of the prepared electrode was demonstrated by measuring UA in human serum samples without any pretreatment, and the results were comparatively in agreement with the spectrometric clinical assay method.     

Electrochemical behaviors of diethylstilbestrol and its application in pharmacokinetics

The electrochemical behaviors of diethylstilbestrol (DES) at a glassy carbon electrode were investigated by cyclic voltammetry, linear sweep voltammetry, and differential pulse voltammetry (DPV). Based on these, a sensitive and selective DPV method was developed for determination of DES. The linear response range of DES is 1.0 x 10(-4)-2.0 x 10(-6) mol/L and the detection limit was 8.0 x 10(-8) mol/L. The developed method has been used for the pharmacokinetics of DES in rabbit blood plasma.     

Preparation of novel mercury-doped silver nanoparticles film glassy carbon electrode and its application for electrochemical biosensor

A novel mercury-doped silver nanoparticles film glassy carbon (Ag/MFGC) electrode was prepared in this study. Electrochemical behaviors of cysteine on the Ag/MFGC electrode were investigated by electrochemical impedance spectroscopy and cyclic voltammetry (CV). The results indicated that cysteine could be strongly adsorbed on the surface of the Ag/MFGC electrode to form a thin layer. The doped electrode could catalyze the electrode reaction process of cysteine, and the cysteine displayed a pair of well-defined and nearly reversible CV peaks at the electrode in an acetate buffer solution (pH 5.0). The Ag/MFGC electrode was used for determination of cysteine by differential pulse voltammetry. The linear range was between 4.0x10(-7) and 1.3x10(-5) mol/L, with a detection limit of 1.0x10(-7) mol/L and a signal-to-noise ratio of 3. The relative standard deviation was 2.4% for seven successive determinations of 1.0x10(-5) mol/L cysteine. The determinations of cysteine in synthetic samples and urinal samples were carried out and satisfactory results were obtained. Amperometric application of the Ag/MFGC electrode as biosensors is proposed.     

Electrochemiluminescence determination of codeine or morphine with an organically modified silicate film immobilizing Ru(bpy)3(2+).

An ECL approach was developed for the determination of codeine or morphine based on tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)(3)(2+)) immobilized in organically modified silicates (ORMOSILs). Tetramethoxysilane (TMOS) and dimethyldimethoxysilane (DiMe-DiMOS) were selected as co-precursors for ORMOSILs, which were then immobilized on a surface of glassy carbon electrode (GCE) by a dip-coating process. Ru(bpy)(3)(2+) was immobilized in the ORMOSIL film via ion-association with poly(p-styrenesulphonate). The ORMOSIL-modified GCE presented good electrochemical and photochemical activities. In a flow system, the eluted codeine or morphine was oxidized on the modified GCE and reacted with immobilized Ru(bpy)(3)(2+) at a potential of +1.20 V (vs. Ag/AgCl). The modified electrode was used for the ECL determination of codeine or morphine and showed high sensitivity. The calibration curves were linear in the range 2 x 10(-8)-5 x 10(-5) mol/L for codeine and 1 x 10(-7)-3 x 10(-4) mol/L for morphine. The detection limit was 5 x 10(-9) mol/L for codeine and 3 x 10(-8) mol/L for morphine, at signal:noise ratio (S:N)=3. Both codeine and morphine showed reproducibility with RSD values <2.5% at 1.0 x 10(-6) mol/L. Furthermore, the modified electrode immobilized Ru(bpy)(3)(2+) was applied to the ECL determination of codeine or morphine in incitant samples.     

Nanostructured electrode based on multi-wall carbon nanotubes/Pt microparticles nanocomposite for electrochemical determination of thiols in rat striatum by high performance liquid chromatography separation

In this paper, multi-wall carbon nanotubes (MWNTs)/Pt microparticles nanocomposite was prepared by electrodepositing Pt microparticles onto the MWNTs matrix. The surface of glassy carbon electrode was modified with this kind of nanocomposite for measurement of thiols, such as L-cysteine (L-Cys) and glutathione (GSH). Compared with the MWNTs or Pt microparticles modified electrode, the nanocomposite modified electrode exhibited high sensitivity and good stability for detection of thiols. According to the results of experiments, the peak currents of L-Cys and GSH are linear with their concentrations and the detection limits (S/N=3) are 2.9 x 10(-8) mol/L and 4.5 x 10(-8) mol/L, respectively. Coupled with microdialysis, the method has been successfully applied to the determination of these two thiols in rat striatal microdialysates.     

Amperometric hydrogen peroxide biosensor based on the immobilization of HRP on nano-Au/Thi/poly (p-aminobenzene sulfonic acid)-modified glassy carbon electrode

A novel hydrogen peroxide biosensor was fabricated for the determination of H(2)O(2). The precursor film was first electropolymerized on the glassy carbon electrode with p-aminobenzene sulfonic acid (p-ABSA) by cyclic voltammetry (CV). Then thionine (Thi) was adsorbed to the film to form a composite membrane, which yielded an interface containing amine groups to assemble gold nanoparticles (nano-Au) layer for immobilization of horseradish peroxidase (HRP). The electrochemical characteristics of the biosensor were studied by CV and chronoamperometry. The factors influencing the performance of the resulting biosensor were studied in detail. The biosensor responded to H(2)O(2) in the linear range from 2.6 x 10(-6) mol/L to 8.8 x 10(-3) mol/L with a detection limit of 6.4 x 10(-7) mol/L. Moreover, the studied biosensor exhibited good accuracy and high sensitivity. The proposed method was economical and efficient, making it potentially attractive for the application to real sample analysis.     

A new scheme of hybridization based on the Au(nano)-DNA modified glassy carbon electrode

DNA hybridization on the Au(nano)-DNA modified glassy carbon electrode (GCE) was investigated. The thiol modified probe oligonucleotides (SH-ssDNA) at the 5' phosphate end were assembled on the Au(nano)-DNA modified GCE surface. The electrochemical response of the probe immobilization and hybridization with target DNA was measured by differential pulse voltammetry (DPV) using methylene blue (MB) as the electroactive indicator. Gold nanoparticles can be dispersed effectively on the GCE surface in the presence of calf thymus DNA. Au(nano)-DNA modified GCE could greatly increase the active sites and enhance the response signal during immobilization and hybridization. The hybridization amount of target DNA could be greatly increased. The linear detection range of Au(nano)-DNA electrode for the complementary 21-mer oligonucleotide (cDNA) was achieved from 1.52 x 10(-10) to 4.05 x 10(-8) mol L(-1). The detection limit could reach the concentration of 10(-10) mol/L.     

Determination of midecamycin by capillary zone electrophoresis with electrochemical detection

Capillary zone electrophoresis was employed for the determination of midecamycin using an end-column amperometric detection with a carbon fiber micro-disk bundle electrode at a constant potential of +1.15 V vs. saturated calomel electrode. The optimum conditions of separation and detection are 1.00x10(-3) mol l(-1) Na(2)HPO(4)-3.49x10(-4) mol l(-1) NaOH (pH 11.4) for the buffer solution, 20 kV for the separation voltage, 5 kV and 5 s for the injection voltage and the injection time, respectively. The limit of detection is 5.0x10(-7) mol l(-1) or 0.41 fmol (S/N=3). The linear range of the calibration curve is 1.00x10(-6)-1.00x10(-3) mol l(-1). The relative standard deviation is 1.4% for the migration time and 4.9% for the electrophoretic peak current. The method could be applied to the determination of midecamycin in human urine. In this case, a separation voltage of 14 kV was used.     

Electrochemical investigations of the reaction mechanism and kinetics between NADH and redox-active (NC)2C6H3-NHOH/(NC)2C6H3-NO from 4-nitrophthalonitrile-(NC)2C6H3-NO2-modified electrode

A simple and sensitive method for the electrocatalytic detection of NADH on a carbon paste electrode modified with a redox-active (NC)(2)C(6)H(3)-NO/(NC)(2)C(6)H(3)-NHOH (NOPH/NHOHPH) electrogenerated in situ from 4-nitrophthalonitrile (4-NPHN) is presented. The electrode modified with 4-NPHN showed an efficient electrocatalytic activity towards the oxidation of NADH with activation overpotential of 0.12V vs. Ag/AgCl. The formation of an intermediate charge transfer complex is proposed for the charge transfer reaction between NADH and the 4-NPHN-resulting system. The second-order rate constant for electrocatalytic oxidation of NADH, kappa(obs), and the apparent Michaelis-Menten constant K(M), at pH 7.0 were evaluated with rotating disk electrode (RDE) experiments, giving 1.0x10(4)mol(-1)Ls(-1) and 2.7x10(-5)molL(-1), respectively. Employing the Koutecky-Levich approach indicated that the NADH oxidation reaction involves two electrons. The sensor provided a linear response range for NADH from 0.8 up to 8.5mumolL(-1) with sensitivity, detection, quantification limits and time response of 0.50muALmumol(-1), 0.25mumolL(-1), 0.82mumolL(-1) and 0.1s, respectively. The repeatability of the measurements with the same sensor and different sensors, evaluated in terms of relative standard deviation, were 4.1 and 5.0%, respectively, for n=10.     

A novel nitric oxide biosensor based on electropolymerization poly(toluidine blue) film electrode and its application to nitric oxide released in liver homogenate

A novel poly(toluidine blue)-modified electrode has been constructed for the determination of nitric oxide in biological sample. The electrochemical behavior of poly(toluidine blue) film electrode and its electrocatalytic activity toward NO were studied in detail by cyclic voltammetry. Possible interferences were tested and evaluated after further coated with Nafion. The poly(toluidine blue) and Nafion composite film-modified electrode exhibits a good linear relationship over a NO concentration of 1.8 x 10(-7) to 8.6 x 10(-5)mol/L, and the detection limit is 1.8 x 10(-8)mol/L (S/N=3). NO release from the rat liver homogenate stimulated by l-arginine was studied, and the responses were decreased by the nitric oxide synthase inhibitor N(omega)-nitro-l-arginine.     

Rapid,fluorimetric-liquid chromatographic determination of malondialdehyde in biological samples

Capillary zone electrophoresis was employed for the determination of lactate using end-column amperometric detection at a carbon fiber bundle microdisk electrode. The optimum conditions of separation and detection are 3.6 x 10(-3) mol/l Na(2)HPO(4)-1.4 x 10(-3) mol/l NaH(2)PO (pH 7.2) for the buffer solution, 18 kV for the separation voltage and 1.60 V versus the saturated calomel electrode for the detection potential. The limit of detection is 7.6 x 10(-7) mol/l or 1.7 fmol (S/N=3) and the linear range is 1.7 x 10(-6)-8.2 x 10(-4) mol/l for the injection voltage of 6 kV and injection time of 5 s. The RSD is 1.8% for the migration time and 3.3% for the electrophoretic peak current. The method was applied to the determination of lactate in human saliva. The recovery of the method is between 95 and 109%.     

Simultaneous voltammetric measurement of ascorbic acid, epinephrine and uric acid at a glassy carbon electrode modified with caffeic acid

A stable electroactive thin film of poly(caffeic acid) has been deposited on the surface of a glassy carbon electrode by potentiostatic technique in an aqueous solution containing caffeic acid. Poly(caffeic acid) was used as a modified electrode for the detection of ascorbic acid (AA), epinephrine (EP), uric acid (UA) and their mixture by cyclic voltammetry. This modified electrode exhibits potent and persistent electron-mediating behavior followed by well-separated oxidation peaks towards AA, EP and UA with activation overpotential. For the ternary mixture containing AA, EP and UA, the three compounds can well separate from each other at the scan rate of 20 mVs(-1) with a potential difference of 156, 132 and 288 mV between AA and EP, EP and UA and AA and UA, respectively, which was large enough to determine AA, EP and UA individually and simultaneously. The catalytic peak current obtained, was linearly dependent on the AA, EP and UA concentrations in the range of 2.0 x 10(-5) to 1.0 x 10(-3) mol l(-1), 2.0 x 10(-6) to 8.0 x 10(-5) mol l(-1) and 5.0 x 10(-6) to 3.0 x 10(-4) mol l(-1), and the detection limits for AA, EP and UA were 7.0 x 10(-6), 2.0 x 10(-7) and 6.0 x 10(-7) mol l(-1), respectively. The modified electrode shows good sensitivity, selectivity and stability, and has been applied to the determination of EP in practical injection samples and that of EP, UA and AA simultaneously with satisfactory results.     

Determination of daunomycin at a novel COOH/indium tin oxide ion implantation-modified electrode

A novel COOH+ ion implantation-modified indium tin oxide (COOH/ITO) electrode was prepared for the first time and applied for determination of daunomycin (or daunorubicin [DNR]). The electrode showed higher catalytic activity than bare ITO electrode with good reproducibility and stability. The determination condition of linear voltammetry was optimized. A calibration curve was obtained over the range 2.0 x 10(-7) to 5.0 x 10(-6)mol/L, with a correlation coefficient of 0.9909 and a limit of detection of 1.0 x 10(-7)mol/L. The selectivity of the electrode was illustrated by determination of DNR in samples prepared of urine. X-ray photoelectron spectroscopy (XPS) analysis results showed that the implanted COOH+ maintained characteristics of organic group -COOH. A field emission-scanning electron microscope (FSEM) result showed that the implanted surface caused defects and partial dislocations and formed many active centers.     

Colloidal gold as an electrochemical label of streptavidin-biotin interaction

A new electrochemical method to monitor biotin-streptavidin interaction, based on the use of colloidal gold as an electrochemical label, is investigated. Biotinylated albumin is adsorbed on the pretreated surface of a carbon paste electrode (CPE). This modified electrode is immersed in colloidal gold-streptavidin labelled solutions. Adsorptive voltammetry is used to monitor colloidal gold bound to streptavidin, obtaining a good reproducibility of the analytical signal (R.S.D. = 3.3%). A linear relationship between peak current and streptavidin concentration from 2.5 x 10(-9) to 2.5 x 10(-5) M is obtained when a sequential competitive assay between streptavidin and colloidal gold-labelled streptavidin is carried out. On the other hand, the adsorption of streptavidin on the electrode surface was performed, followed by the reaction with biotinylated albumin labelled with colloidal gold. In this way, a linear relationship between peak current and colloidal gold labelled biotinylated albumin concentration is achieved with a limit of detection of 7.3 x 10(9) gold particles per ml (5.29 x 10(-9) M in biotin).     

Preparation of thiolated polymeric nanocomposite for sensitive electroanalysis of dopamine

We report on the thiol-ene chemistry guided preparation of novel thiolated polymeric nanocomposite films of abundant anionic carboxylic groups for electrostatic enrichment and sensitive electroanalysis of cationic dopamine (DA) in neutral solution. Briefly, the thiol-ene nucleophilic reaction of a carboxylated thiol with oxidized polypyrrole (PPy), which was electrosynthesized on an Au electrode in the presence of solution-dispersed acidified multiwalled carbon nanotubes (MWCNTs), produced an a PPy-thiol-MWCNTs/Au electrode, and the PPy can be electrochemically overoxidized (OPPy) to form an OPPy-thiol-MWCNTs/Au electrode. The carboxylic groups of the polymeric nanocomposite film originate from the acidified MWCNTs, PPy-tethered carboxylated thiol, and OPPy. The carboxylated thiols examined are mercaptosuccinic acid (MSA) and thioglycolic acid, with β-mercaptoethanol as a control. Electrochemical quartz crystal microbalance, scanning electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy were used for film characterization and process monitoring. Under the optimized condition, the differential pulse voltammetry peak current of DA oxidation at OPPy-MSA-MWCNTs/Au electrode is linear with DA concentration from 1.00×10(-9) to 2.87×10(-6) mol L(-1), with a limit of detection of 0.4 nmol L(-1), good anti-interferent ability and stability.     

Development of a carbon nanotube paste electrode osmium polymer-mediated biosensor for determination of glucose in alcoholic beverages

This paper describes a new amperometric biosensor for glucose monitoring. The biosensor is based on the activity of glucose dehydrogenase (GDH) and diaphorase (DI) co-immobilized with NAD(+) into a carbon nanotube paste (CNTP) electrode modified with an osmium functionalized polymer. This mediator was demonstrated to shuttle the electron transfer between the immobilized diaphorase and the CNTP electrode, thus, showing a good electrocatalytic activity towards NADH oxidation at potentials around +0.2V versus Ag|AgCl, where interfering reactions are less prone to occur. The biosensor exhibits a detection limit of 10 micromol L(-1), linearity up to 8 x 10(-4) mol L(-1), a sensitivity of 13.4 microA cm(-2)mmol(-1)L(-1), a good reproducibility (R.S.D. 2.1%, n=6) and a stability of about 1 week when stored dry at 4 degrees C. Finally, the proposed biosensor was applied for the determination of glucose in different samples of sweet wine and validated with a commercial spectrophotometric enzymatic kit.     

再生丝素固定的酶标免疫传感器的研究

所研究的酶标免疫传感器是采用再生丝素将待测抗原 (兔IgG)固定在石墨电极表面 ,选用抗体 (山羊抗兔IgG HRP)与其识别结合。利用H₂O₂ 将抗原抗体结合的电位响应信号放大采用直接电位法检测IgG的浓度。该传感器测定IgG的最低浓度可达 1.2×10^-10 mol/L ,标准曲线的线形范围在4.1×10^-7～1.2×10^-10 mol/L ,回归方程为: E=-1049+721g[IgG],响应时间为 15s。通过电泳的方法加速抗原抗体的识别结合 ,反应时间由原来的 90min缩短到 3 0min。这种以固定化抗原结合酶标抗体量的多少作为检测抗原标准的新型酶标免疫传感器 ,在临床检测、环境监测、HLA个人身份鉴定等领域都有着广阔的应用前景。     

Determination of lactate dehydrogenase in human erythrocytes by capillary electrophoresis with electrochemical detection

Capillary electrophoresis (CE) was employed to analyze lactate dehydrogenase (LDH) in human erythrocytes using an amperometric detector with a carbon fiber micro-disk bundle electrode. LDH activity was measured by determining the amount of NADH generated by LDH through a enzyme-catalyzed reaction between NAD(+) and lithium lactate. The factors influencing the enzyme-catalyzed reaction, separation and detection were examined and optimized. The following conditions were suitable for the determination of LDH: running buffer, 5.0 x 10(-2)mol/l Tris-HCl (pH 7.5); separation voltage, 20.0 kV; detection potential, 1.00 V (versus saturated calomel electrode (SCE)). The conditions of enzyme-catalyzed reaction were: reaction buffer, 5.0 x 10(-2)mol/l Tris-HCl (pH 9.3); substrates, 5.0 x 10(-2)mol/l lithium lactate and 5.0 x 10(-3)mol/l NAD(+); reaction time, 10 min. The concentration limit of detection (LOD) of the method was 0.017 U/ml at a signal-to-noise (S/N) ratio of 3, which corresponded to 1.10 x 10(-10)mol/l, and the mass LOD was 2 x 10(-20)mol. The linear dynamic range was 0.039-4.65 U/ml for the injection voltage of 5.0 kV and injection time of 10s. The relative standard deviation (R.S.D.) was 0.85% for the migration time and 1.8% for the electrophoretic peak area. The method was applied to determine LDH in human erythrocytes. The recovery of the method was between 98 and 101%.     

Liquid chromatography with amperometric detection using functionalized multi-wall carbon nanotube modified electrode for the determination of monoamine neurotransmitters and their metabolites

The fabrication and application of a novel electrochemical detection (ED) method with the functionalized multi-wall carbon nanotubes (MWNTs) chemically modified electrode (CME) for liquid chromatography (LC) were described. The electrochemical behaviors of dopamine (DA) and other monoamine neurotransmitters at the CME were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results indicated that the CME exhibited efficient electrocatalytic effects on the current responses of monoamine neurotransmitters and their metabolites with high sensitivity, high stability and long-life activity. In LC-ED, DA, norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) had good and stable current responses at the CME. The linear ranges of seven analytes were over four orders of magnitude and the detection limits were 2.5 x 10(-10) mol/l for DA, 2.5 x 10(-10) mol/l for NE, 5.0 x 10(-10) mol/l for MHPG, 3.0 x 10(-10) mol/l for DOPAC, 3.5 x 10(-10) mol/l for 5-HT, 6.0 x 10(-10) mol/l for 5-HIAA, 1.25 x 10(-9) mol/l for HVA. The application of this method coupled with microdialysis sampling for the determination of monoamine neurotransmitters and their metabolites in Parkinsonian patients' cerebrospinal fluid was satisfactory.