A novel sensor based on electrochemical polymerization of diglycolic acid for determination of acetaminophen

Diglycolic acid (DA) polymer was coated on glassy carbon (GC) electrode by cyclic voltammetry (CV) technique for the first time. The electrochemical performances of the modified electrode were investigated by CV and electrochemical impedance (EIS). The obtained electrode showed an excellent electrocatalytic activity for the oxidation of acetaminophen (ACOP). A couple of well-defined reversible electrochemical redox peaks were observed on the ploy(DA)/GC electrode in ACOP solution. Compared with bare GC electrode, the oxidation peak potential of ACOP on ploy(DA)/GC electrode moved from 0.289 V to 0.220 V. Meanwhile, the oxidation peak current was much higher on the modified electrode than that on the bare GC electrode, indicating DA polymer modified electrode possessed excellent performance for the oxidation of ACOP. This kind of capability of the modified electrode can be enlisted for the highly sensitive and selective determination of ACOP. Under the optimized conditions, a wide linear range from 2 × 10(-8) to 5.0 × 10(-4)M with a correlation coefficient 0.9995 was obtained. The detection limit was 6.7 × 10(-9)M (at the ratio of signal to noise, S/N=3:1). The modified electrode also exhibited very good stability and reproducibility for the detection of ACOP. The established method was applied to the determination of ACOP in samples. An average recovery of 100.1% was achieved. These results indicated that this method was reliable for determining ACOP.     

Amperometric detection of insulin at renewable sol-gel derived carbon ceramic electrode modified with nickel powder and potassium octacyanomolybdate(IV)

A renewable three-dimensional chemically modified carbon ceramic electrode (CCE) containing nickel powder and K4[Mo(CN)8] was constructed by sol-gel technique. The electrochemical properties and stability of modified electrode was evaluated by cyclic voltammetry in pH range 4-10. The redox couple of [Mo(CN)8] (4-/3-) was shown both as a solute in electrolyte solution and as a component of a carbon based conducting composite electrode. The apparent electron transfer rate constant (ks) and transfer coefficient (alpha) were determined by cyclic voltammetry and they were about 17.1 and 0.57 s(-1), respectively. The catalytic activity of the modified CCE toward insulin oxidation was investigated at pH range of 3-8 by cyclic votammetry. The modified electrode showed excellent electrocatalytic activity toward insulin electroxidation at physiological pH value. The modified electrode was used for insulin detection chronoamperometrically at pH 7. Under optimized condition in amperometry method, the concentration calibration range, detection limit and sensitivity were 0.5-500 nM, 0.45 nM and 6140 nA/microM, respectively. Flow injection amperometric determination of insulin at pH 7.4, at this modified electrode yielded a calibration curve with the following characteristics, linear dynamic range 100-500 pM; sensitivity 8.1 nA/nM and detection limit 40 pM (based on S/N = 3). The inherent stability at wide pH range, high sensitivity, low detection limit, low cost and ease of preparation are of advantageous of this insulin sensor. This sensor indicates great promise for monitory insulin in chromatographic effluents.     

Deep oxidation of glucose in enzymatic fuel cells through a synthetic enzymatic pathway containing a cascade of two thermostable dehydrogenases

A sensitive glutamate biosensor is prepared based on glutamate dehydrogenase/vertically aligned carbon nanotubes (GLDH, VACNTs). Vertically aligned carbon nanotubes were grown on a silicon substrate by direct current plasma enhanced chemical vapor deposition (DC-PECVD) method. The electrochemical behavior of the synthesized VACNTs was investigated by cyclic voltammetry and electrochemical impedance spectroscopic methods. Glutamate dehydrogenase covalently attached on tip of VACNTs. The electrochemical performance of the electrode for detection of glutamate was investigated by cyclic and differential pulse voltammetry. Differential pulse voltammetric determinations of glutamate are performed in mediator-less condition and also, in the presence of 1 and 5 μM thionine as electron mediator. The linear calibration curve of the concentration of glutamate versus peak current is investigated in a wide range of 0.1-500 μM. The mediator-less biosensor has a low detection limit of 57 nM and two linear ranges of 0.1-20 μM with a sensitivity of 0.976 mA mM(-1) cm(-2) and 20-300 μM with a sensitivity of 0.182 mA mM(-1) cm(-2). In the presence of 1 μM thionine as an electron mediator, the prepared biosensor shows a low detection limit of 68 nM and two linear ranges of 0.1-20 with a calibration sensitivity of 1.17 mA mM(-1) cm(-2) and 20-500 μM with a sensitivity of 0.153 mA mM(-1) cm(-2). The effects of the other biological compounds on the voltammetric behavior of the prepared biosensor and its response stability are investigated. The results are demonstrated that the GLDH/VACNTs electrode even without electron mediator is a suitable basic electrode for detection of glutamate.     

The electrochemical preparation of FAD/ZnO with hemoglobin film-modified electrodes and their electroanalytical properties

Flavin adenine dinucleotide (FAD)-modified zinc oxide self-assembly films were prepared using repeated cyclic voltammetry. The electrochemical reaction of the hemoglobin with the FAD/ZnO self-assembly film-modified electrodes and their electrocatalytic properties were investigated. This paper describes the successful loading of the electrochemically active molecules of hemoglobin and FAD along with ZnO by electrochemical method. In addition to the cyclic voltammetry, an electrochemical quartz crystal microbalance was used to study the growth mechanism and the properties of the films. The FAD/zinc oxide films exhibited a single redox couple, which corresponded to the FAD redox couple. The electrocatalytic properties of the O2, H2O2, trichloroacetic acid and SO(3)2- were studied by the FAD/zinc oxide films in the absence or in the presence of hemoglobin. The electrocatalytic reduction current had been developed from the cathodic peak of the FAD/zinc oxide redox couple. The electrocatalytic process involved an interaction of hemoglobin and FAD/GC film-modified electrode to increase the electrocatalytic reduction current. The electrocatalytic reduction of O2 using the FAD/zinc oxide films was investigated by cyclic voltammetry and rotating ring-disk electrode methods.     

Screening of potential substrates or inhibitors of cytochrome P450 17A1 (CYP17A1) by electrochemical methods

The electrochemical redox reactions of the recombinant form of human cytochrome P450 17A1 (CYP17A1) were investigated. The hemoprotein was immobilized on the electrode modified with a biocompatible nanocomposite material based on the membrane-like synthetic surfactant didodecyldimethylammonium bromide (DDAB) and gold nanoparticles. Analytical characteristics of DDAB/Au/CYP17A1 electrodes were investigated using cyclic voltammetry, square wave voltammetry, and differential pulse voltammetry. Analysis of electrochemical behavior of cytochrome P450 17A1 was performed in the presence of a natural substrate, pregnenolone (1), known inhibitor, ketoconazole (2), and in the presence of synthetic derivatives of pregnenolone: acetyl pregnenolone (3), cyclopregnenolone (4), and tetrabromo-pregnenolone (5). Ketoconazole, the azole inhibitor of cytochromes P450, blocked catalytic current in the presence of the substrate, pregnenolone (1). Compounds 3–5 did not demonstrate substrate properties towards the electrode/CYP17A1 system. Compound 3 did not influence catalytic activity with pregnenolone, whereas compounds 4 and 5 demonstrated some inhibitory activity. Thus, electrochemical redox reactions of CYP17A1 may serve as an adequate substitution of the reconstituted system, which requires additional redox partners for manifestation of catalytic activity of hemoproteins of the cytochrome P450 superfamily.     

Electrochemical immunosensor for casein based on gold nanoparticles and poly(L-Arginine)/multi-walled carbon nanotubes composite film functionalized interface

In this paper, a novel electrochemical immunosensor for the determination of casein based on gold nanoparticles and poly(L-Arginine)/multi-walled carbon nanotubes (P-L-Arg/MWCNTs) composite film was proposed. The P-L-Arg/MWCNTs composite film was used to modify glassy carbon electrode (GCE) to fabricate P-L-Arg/MWCNTs/GCE through electropolymerization of L-Arginine on MWCNTs/GCE. Gold nanoparticles were adsorbed on the modified electrode to immobilize the casein antibody and to construct the immunosensor. The stepwise assembly process of the immunosensor was characterized by cyclic voltammetry and differential pulse voltammetry. Results demonstrated that the peak currents of [Fe(CN)(6)](3-/4-) redox pair decreased due to the formation of antibody-antigen complex on the modified electrode. The optimization of the adsorption time of gold nanoparticles, the pH of supporting electrolyte and the incubation time were investigated in details. Under optimal conditions, the peak currents obtained by DPV decreased linearly with the increasing casein concentrations in the range from 1 × 10(-7) to 1 × 10(-5) g mL(-1) with a linear coefficiency of 0.993. This electrochemical immunoassay has a low detection limit of 5 × 10(-8) g mL(-1) and was successfully applied to the determination of casein in cheese samples.     

Pt-Pb nanowire array electrode for enzyme-free glucose detection

Pt-Pb nanowire array was directly synthesized by electrochemical deposition of Pt-Pb alloy into the pores of microporous polycarbonate template and subsequent chemical etching of the template. The morphology and the composition of the Pt-Pb nanowires were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. Cyclic voltammetry (CV) was used to evaluate the electrochemical performance of the Pt-Pb nanowire array electrode (Pt-PbNAE). Direct glucose oxidation on Pt-PbNAE was investigated in detail by discussing the effect of the structure and materials of the electrode on electrocatalytic oxidation of glucose. As a result, we found that the Pt-PbNAE with a three-dimensional structure exhibited high electrocatalytic activity to glucose oxidation in neutral condition and could be used for the development of nonenzymatic glucose sensor. To effectively avoid the interference coming from ascorbic acid, a negative potential of -0.20V was chosen for glucose detection, and the sensitivity of the sensor to glucose oxidation was 11.25 microAmM(-1)cm(-2) with a linearity up to 11 mM, and a detection limit of 8 microM (signal-to-noise ratio of 3).     

Electrochemical imprinted sensor for determination of oleanic acid based on poly (sodium 4-styrenesulfonate-co-acrylic acid)-grafted multi-walled carbon nanotubes-chitosan and cobalt hexacyanoferrate nanoparticles

A novel sensitive and selective imprinted electrochemical sensor for the determination of oleanic acid was constructed on a carbon electrode by stepwise modification of functional multi-walled carbon nanotubes, cobalt hexacyanoferrate nanoparticles and a thin imprinted sol-gel film. The fabrication of a homogeneous porous poly (sodium 4-styrenesulfonate-co-acrylic acid)-grafted multi-walled carbon nanotubes/SiO(2)-chitosan nanocomposite film was conducted by controllable electrodeposition technology. The surface morphologies of the modified electrodes were characterized by scanning electron microscope. The performance of the imprinted sensor was investigated by cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy in detail. The imprinted sensor displayed high sensitivity and selectivity towards oleanic acid. A linear relationship between the sensor response signal and the logarithm of oleanic acid concentrations ranging from 1.0×10(-8) to 1.0×10(-3) mol L(-1) was obtained with a detection limit of 2.0×10(-9) mol L(-1). It was applied to the determination of oleanic acid in real capsule samples successfully.     

Direct electrochemistry of lactate dehydrogenase immobilized on silica sol-gel modified gold electrode and its application

The direct electrochemistry of lactate dehydrogenase (LDH) immobilized in silica sol-gel film on gold electrode was investigated, and an obvious cathodic peak at about -200 mV (versus SCE) was found for the first time. The LDH-modified electrode showed a surface controlled irreversible electrode process involving a one electron transfer reaction with the charge-transfer coefficient (alpha) of 0.79 and the apparent heterogeneous electron transfer rate constant (K(s)) of 3.2 s(-1). The activated voltammetric response and decreased charge-transfer resistance of Ru(NH(3))(6)(2+/3+) on the LDH-modified electrode provided further evidence. The surface morphologies of silica sol-gel and the LDH embedded in silica sol-gel film were characterized by SEM. A potential application of the LDH-modified electrode as a biosensor for determination of lactic acid was also investigated. The calibration range of lactic acid was from 2.0 x 10(-6) to 3.0 x 10(-5) mol L(-1) and the detection limit was 8.0 x 10(-7) mol L(-1) at a signal-to-noise ratio of 3. Finally, the effect of environmental pollutant resorcinol on the direct electrochemical behavior of LDH was studied. The experimental results of voltammetry indicated that the conformation of LDH molecule was altered by the interaction between LDH and resorcinol. The modified electrode can be applied as a biomarker to study the pollution effect in the environment.     

Direct electrochemistry of hemoglobin immobilized on gold electrode by Langmuir-Blodgett technique

In this research, we reported a novel method of forming hemoglobin (Hb)-linoleic acid (LA) Langmuir-Blodgett (LB) monolayer by spreading Hb solution directly onto the subphase covered with a layer of LA. This method is suitable for preparing electrochemical devices with protein-lipid LB film because almost no protein adsorbed on electrode surface before protein-lipid film transferred from air-water interface to electrode, which ensured better electrode activity. The compressibility of Hb-LA monolayer was used to character the phase transition during compression process. Optimal experimental conditions were obtained by analyzing pressure-time, pressure-area and pressure-compressibility curves. The direct electrochemistry of Hb, which was immobilized on Au electrode surface incorporated with LA layer by LB method, was investigated using cyclic voltammetry for the first time. The electrode modified with Hb-LA LB film holds high electrochemical activity and shows a fast direct electron transfer of Hb. Redox peak currents increased linearly with the increase of scan rate, indicating a surface-controlled electrode process. The electron transfer rate constant was 2.68+/-0.45 s-1. As a target of this research, this work provides a new way to prepare biomimetic film and biosensor.     

Simultaneous determination of 5-hydroxyindoleacetic acid and 5-hydroxytryptamine in urine samples from patients with acute appendicitis by liquid chromatography using poly(bromophenol blue) film modified electrode

The fabrication and application of a novel electrochemical detection (ED) system with a poly(bromophenol blue) (PBPB) film chemically modified electrode (CME) for high performance liquid chromatography (HPLC) were described. The electrochemical behaviors of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) at this CME were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the PBPB CME efficiently exhibited electrocatalytic effect on the current responses of 5-HT and 5-HIAA with relatively high sensitivity, stability and long life of activity. In HPLC-ED, the two analytes had good and stable current responses at the CME and their linear ranges were over four orders of magnitude (R> or =0.9992) with the detection limits being 0.25 nmol L(-1) for 5-HT and 0.50 nmol L(-1) for 5-HIAA. The application of this method for the determination of 5-HT and 5-HIAA in urine samples from patients with acute appendicitis (AA) was satisfactory.     

Syntheses of fully sulfonated polyaniline nano-networks and its application to the direct electrochemistry of cytochrome c

Fully sulfonated polyaniline nano-particles, nano-fibrils and nano-networks have been achieved for the first time by electrochemical homopolymerization of orthanilic acid using a three-step electrochemical deposition procedure in a mixed solvent of acetonitrile (ACN) and water. The diameter of the uniform nano-particles is about 60 nm, and the nano-fibrils can be organized in two-dimensional (2D) or three-dimensional (3D) non-periodic networks with good electrical contact. Average distance between contacts is about 850 and 600nm for a 2D and 3D system, respectively. The details of the poly(orthanilic acid) (POA) nano-structure were examined with a field emission scanning electron microscope (SEM). The structure and properties of POA were characterized with FTIR, UV-vis and electrochemical methods. The 3D POA nano-networks coated platinum electrode gave a direct electrochemical behavior of horse heart cytochrome c (Cyt c) immobilized on this electrode surface, a pair of well-defined redox waves with formal potential (E( degrees ')) of -0.032 V (versus Ag/AgCl) was achieved. The interaction between Cyt c and POA makes the formal potential shift negatively compared to that of Cyt c in solution. Spectrophotometric and electrochemical methods were used to investigate the interaction of Cyt c with POA. The immobilized Cyt c in the nano-networks POA film maintained its activity, showing a surface-controlled electrode process with the electron transfer rate constant (k(s)) of 21s(-1) and a of 0.53, and could be used for the electrocatalytic reduction of hydrogen peroxide. The quantitative determination of Cyt c by differential pulse voltammetry (DPV) using the fully sulfonated 3D POA nano-networks film coated platinum electrode was also studied.     

Characterization and electrocatalytic properties of Prussian blue electrochemically deposited on nano-Au/PAMAM dendrimer-modified gold electrode

Gold electrode was modified with 3-mercaptopropionic acid (MPA) and further reacted with poly(amidoamine) (PAMAM) dendrimer (generation 4.0) then attached the nano-Au to obtain films on which Prussian blue (PB) was electrochemically deposited to afford much wider pH adaptive range, much better electrochemical stability and excellent electrochemical response. The microstructure and electrochemical behavior of Au/MPA/PAMAM/nano-Au/PB electrode were investigated by scanning electron microscopy (SEM) and cyclic voltammetry. The electrochemical response of the Au/MPA/PAMAM/nano-Au/PB-modified electrode for the electrocatalytic reduction of hydrogen peroxide was investigated, and it was found that the sensitivity as well as the corresponding detection limits were improved as compared to the voltammetric response of a Au/PB-modified electrode and Au/MPA/PAMAM/PB electrode. Based on this, a new electrochemical sensor for determination of hydrogen peroxide has been developed.     

Electrochemical properties of cytochroms P450 using nanostructured electrodes: direct electron transfer and electro catalysis

The present study demonstrates direct electron transfer between cytochromes P450 2B4 (CYP2B4), P450 1A2 (CYP1A2), sterol 14alpha-demethylase (CYP51b1) on the one hand and screen-printed graphite electrodes, modified with gold nanoparticles and didodecyldimethylammonium bromide (DDAB) on the other. Electro detection of heme proteins was possible when 2-200 pmol P450/electrode were adsorbed on the surface of nanostructured electrochemical interfaces. Electron transfer, direct electrochemical reduction and interaction with P450 substrates (oxygen, benzphetamine, and lanosterol) and with P450 inhibitor (ketoconazole) were analyzed using cyclic voltammetry (CV), square wave voltammetry (SWV) differential pulse voltammetry (DPV), and amperometry.     

Amperometric glucose biosensor based on adsorption of glucose oxidase at platinum nanoparticle-modified carbon nanotube electrode

A new amperometric biosensor, based on adsorption of glucose oxidase (GOD) at the platinum nanoparticle-modified carbon nanotube (CNT) electrode, is presented in this article. CNTs were grown directly on the graphite substrate. The resulting GOD/Pt/CNT electrode was covered by a thin layer of Nafion to avoid the loss of GOD in determination and to improve the anti-interferent ability. The morphologies and electrochemical performance of the CNT, Pt/CNT, and Nafion/GOD/Pt/CNT electrodes have been investigated by scanning electron microscopy, cyclic voltammetry, and amperometric methods. The excellent electrocatalytic activity and special three-dimensional structure of the enzyme electrode result in good characteristics such as a large determination range (0.1-13.5mM), a short response time (within 5s), a large current density (1.176 mA cm(-2)), and high sensitivity (91mA M(-1)cm(-2)) and stability (73.5% remains after 22 days). In addition, effects of pH value, applied potential, electrode construction, and electroactive interferents on the amperometric response of the sensor were investigated and discussed. The reproducibility and applicability to whole blood analysis of the enzyme electrode were also evaluated.     

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.     

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.     

Voltammetric discrimination of mandelic acid enantiomers

We report a novel electrochemical biosensor for direct discrimination of d- and l-mandelic acid (d- and l-MA) in aqueous medium. The glassy carbon electrode (GCE) surface was modified with reduced graphene oxide (rGO) and γ-globulin (GLOB). Electrochemical characterization of the modified electrodes was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode surfaces were also characterized by scanning electron microscopy. Electrochemical response of the prepared electrode (GCE/rGO/GLOB) for discrimination of d- and l-MA enantiomers was investigated by cyclic voltammetry and was compared with bare GCE in the concentration range of 2 to 10 mM. Whereas the bare GCE showed no electrochemical response for the MA enantiomers, the GCE/rGO/GLOB electrode exhibited direct and selective discrimination with different oxidation potential values of 1.47 and 1.71 V and weak reduction peaks at potential values of −1.37 and −1.48 V, respectively. In addition, electrochemical performance of the modified electrode was investigated in mixed solution of d- and l-MA. The results show that the produced electrode can be used as electrochemical chiral biosensor for MA.     

Development of an electrochemical DNA biosensor with a high sensitivity of fM by dendritic gold nanostructure modified electrode

In this paper, dendritic gold nanostructure (DenAu) modified electrode was obtained by direct electrodeposition of planar electrode into 2.8 mM HAuCl(4) and 0.1 M H(2)SO(4) solution under a very negative potential of -1.5 V. Scanning electron microscopy was used to characterize the growth evolution of DenAu with time. The whole DNA biosensor fabrication process based on the DenAu modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy methods with the use of ferricyanide as an electrochemical redox indicator. The probe DNA immobilization and hybridization with target DNA on the modified electrode could be well distinguished by using methylene blue as an electrochemical hybridization indicator. The DenAu modified electrode could realize an ultra sensitivity of 1 fM toward complementary target DNA and a very wide dynamic detection range (from 1 fM to 1 nM).     

Electrochemical impedimetric immunosensor for insulin like growth factor-1 using specific monoclonal antibody-nanogold modified electrode

An electrochemical impedimetric immunosensor was developed for ultrasensitive determination of insulin-like growth factor-1 (IGF-1) based on immobilization of a specific monoclonal antibody on gold nanoparticles (GNPs) modified gold electrode. Self-assembly of colloidal gold nanoparticles on the gold electrode was conducted through the thiol groups of 1,6-hexanedithiol (HDT) monolayer as a cross linker. The redox reactions of [Fe(CN)(6)](4-)/[Fe(CN)(6)](3-) on the electrode surface was probed for studying the immobilization and determination processes, using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The interaction of antigen with grafted antibody recognition layer was carried out by soaking the modified electrode into antigen solution at 37°C for 3 h. The immunosensor showed linearity over 1.0-180.0 pg mL(-1) and the limit of detection was 0.15 pg mL(-1). The association constant between IGF-1 and immobilized antibody was calculated to be 9.17×10(11) M(-1). The proposed method is a useful tool for screening picogram amounts of IGF-1 in clinical laboratory as a diagnostic test.