Glassy carbon electrode modified with electrodeposited cobalt oxide nanostructure shows an excell... more Glassy carbon electrode modified with electrodeposited cobalt oxide nanostructure shows an excellent electrocatalytic activity toward insulin oxidation at a wide pH range. Cyclic voltammetry, hydrodynamic amperometry, and flow injection analysis (FIA) were used for insulin determination at a picomolar and higher-concentration range. Amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear range, 100 pM–15 nM; sensitivity of 83.9 nA nM−1 and detection limit 10 pM. FIA yielded the calibration curve with sensitivity and detection limit of 2.0 nA nM−1 and 25 pM, respectively. Furthermore, the RSD of repetitive FIA for 200 pM insulin (n = 13) is 2%. In addition, the interference effect of electroactive existing species (lactic acid, cholesterol, ascorbic acid, uric acid, and glucose) was eliminated by covering the surface of the modified electrode with nafion film. Fast response time, signal stability, high sensitivity, low cost, and ease of preparation are the advantages of the proposed insulin sensor.
Iridium oxide (IrOx) films formed electrochemically on the surface boron doped diamond electrode ... more Iridium oxide (IrOx) films formed electrochemically on the surface boron doped diamond electrode by potential cycling in the range −0.2 to 1.2 V from a saturated solution of alkaline iridium(III) solution. A strongly adherent deposit of iridium oxide is formed after 5–10 potential scans. The properties, stability and electrochemical behavior of iridium oxide layers were investigated by atomic force microscopy and cyclic voltammetry. The boron doped diamond (BDD) electrode modified with electrodeposition of a thin film, exhibited an excellent catalytic activity for oxidation of Hg(I) over a wide pH range. The modified electrode shows excellent analytical performance for Hg(I) amperometric detection. The detection limit, sensitivity, response time and dynamic concentration ranges are 3.2 nM, 77 nA μM−1, 100 ms and 5 nM–5 μM. These analytical parameters compare favorably with those obtained with modern analytical techniques and recently published electrochemical methods.
A simple procedure was developed for the preparation of glassy carbon electrodes modified with si... more A simple procedure was developed for the preparation of glassy carbon electrodes modified with single wall carbon nanotubes (SWCNTs) and multilayers of SiΜο12Ο404−-[Ru(bpy)(tpy)Cl]+(byp; bipyridine, tpy; terpyridine). Layer-by-layer deposition technique was used for the multilayer formation of SiΜο12Ο404−-[Ru(bpy)(tpy)Cl]+ onto SWCNTs films. Based on the strong electrostatic attraction of oppositely charged species a Ru-complex/poly oxometalate hybrid film strongly and irreversibly adsorbed on the glassy carbon electrode modified with single walled carbon nanotubes. The multilayer assembly exhibited good stability and excellent electrochemical reversibility for both redox systems in the pH range1–7. It was found that up to fifteen monolayers could be deposited onto a carbon nanotube film with well defined redox behavior. The modified electrode shows excellent electrocatalytic activity towards sulfite oxidation. Due to synergistic effect between SWCNTs and oppositely charged species the repeated alternate adsorption of anions and cations by this simple dipping method leads to molecular sandwiches with interesting redox activity and remarkable stability.
For the first time silicon carbide nanoparticles (SiC) was used for electrode modification and el... more For the first time silicon carbide nanoparticles (SiC) was used for electrode modification and electrocatalytic oxidation of insulin. In comparison to bare glassy carbon (GC) electrode, the oxidation of insulin at GC electrode modified with SiC nanoparticles occurred at reduced overpotentials. The modified electrode was applied for insulin detection using cyclic voltammetry, differential pulse voltammetry (DPV) and flow injection analysis (FIA). Flow injection amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear dynamic range up to 600 pM, sensitivity of 710 pA pM−1 cm−2 and detection limit of 3.3 pM. In addition interference effect of the electroactive existing species (uric acid, glucose, lactic acid, l-cysteine and cholesterol) was diminished and for ascorbic acid eliminated by covering the surface of modified electrode with nafion film. This electrode shows many advantages as an insulin sensor such as simple preparation method without using any specific electron transfer mediator or specific reagent, high sensitivity, excellent catalytic activity, short response time, long term stability and remarkable antifouling property toward insulin and its oxidation product. Sensitivity, detection limit and antifouling properties of this insulin sensor are better than all of the reports in the literature for insulin detection at physiological pH solutions.
The electrochemical properties of aqueous thionin (an electroactive water soluble dye) of pH 1–12... more The electrochemical properties of aqueous thionin (an electroactive water soluble dye) of pH 1–12 were investigated by cyclic voltammetry at a boron doped diamond(BDD) electrode. A well defined reversible redox couple was observed in acidic, neutral and alkaline solutions. The standard potential and kinetic parameters for thionin were obtained by fitting experimental cyclic voltammograms to those generated by the DigiSim program. The electrogenerated reduced form of thionin has been used as an efficient organic catalyst for the reduction of Cr(VI) at a BDD electrode immersed in aqueous media. The cyclic voltammetry measurements indicate that an electrocatalytic process occurs, where electrochemically generated thionin reduced species (Leucothionin) is oxidized by Cr(VI) back to the parent thionin species via a EC' reaction mechanism. The determination of catalytic rate constant (Kcat) was accomplished again by fitting experimental cyclic voltammograms with simulated ones.
A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single-w... more A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single-walled carbon nanotubes (SWCNTs) and polyoxometalate. With immersing SWCNTs modified GC electrode in silicon polyoxomolybdate (α-SiMo12O404−) solution (direct deposition) for a short period of time (2–10 s) oxoanion adsorbed strongly and irreversibly on SWCNTs. Cyclic voltammograms of the α-SiMo12O404− incorporated-SWCNTs indicates three well-defined and reversible redox couples with surface confined characteristic at wide pH range (1–7). The surface coverage (Γ) of α-SiMo12O404− immobilized on SWCNTs was 2.14 (±0.11)×10−9 mol cm−2 indicating high loading ability of SWCNTs for polyoxometalate. The charge transfer rate constant (ks) of three redox couples of adsorbed α-SiMo12O404− were 9.20 (±0.20), 8.02 (±0.20), and 3.70 (±0.10) s−1, respectively, indicate great facilitation of the electron transfer between α-SiMo12O404− and CNTs. In this research the attractive mechanical and electrical characteristics of CNTs and unique properties and reactivity of polyoxometalates were combined. The modified electrode in buffer solution containing Sb(III) shows a new redox system at 0.38 V in pH 1. The voltammetric peak current increased with increasing Sb(III) concentration. The differential pulse voltammetry (DPV) technique was used for detection micromolar concentration of antimony. Furthermore, the interference effects various electroactive compounds on voltammetric response of Sb(III) were negligible. Finally the ability of the modified electrode for antimony detection in real samples was evaluated.
Iridium oxide nanoparticles are grown on a glassy carbon electrode by electrodepositing method. T... more Iridium oxide nanoparticles are grown on a glassy carbon electrode by electrodepositing method. The electrochemical behavior and electrocatalytic activity of modified electrode towards reduction of iodate and periodate are studied. The reductions of both ions occur at the unusual positive peak potential of 0.7 V vs. reference electrode. The modified electrode is employed successfully for iodate and periodates detection using cyclic voltammetry, hydrodynamic amperometry and flow injection analysis (FIA). In the performed experiments, flow injection amperometric determination of iodate and periodate yielded calibration curves with the following characteristics: linear dynamic range up to 100 and 80 μM, sensitivity of 140.9 and 150.6 nA μM−1 and detection limits of 5 and 36 nM, respectively. The repeatability of the modified electrode for 21 injections of 1.5 μM of iodate solution is 1.5%. The interference effects of NO2−, NO3−, ClO3−, BrO3−, ClO4−, SO42−, Cu2+, Zn2+, Mn2+, Mg2+, Cd2+, Ca2+, Na+, K+, NH4+ and K+, CH3COO− and glucose were negligible at the concentration ratio of more than 1000. The obtained attractive analytical performance together with high selectivity and simplicity of the proposed method provide an effective and e novel modified electrode to develop an iodate and periodate sensor. Sensitivity, selectivity, the liner concentration range and the detection limit of the developed sensor are all much better than all known similar sensors in the literature for iodate and periodate determination.
Electrodeposited cobalt oxide (CoOx) nanomaterials are not only used for immobilization of choles... more Electrodeposited cobalt oxide (CoOx) nanomaterials are not only used for immobilization of cholesterol oxidase (ChOx) but also as electron transfer mediator for oxidation of H2O2 generated in the enzymatic reaction. Voltammetry and flow injection analysis (FIA) were used for determination of cholesterol. FIA determination of cholesterol with biosensors yielded a calibration curve with the following characteristics: linear range up to 50 μM, sensitivity of 43.5 nA μM−1 cm−2 and detection limit of 4.2 μM. The apparent Michaelis-Menten constant and the response time of the biosensor are 0.49 mM and 15 s, respectively. This biosensor also exhibits good stability, reproducibility and long life time.
A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotu... more A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes and Ruthenium (III) complexes. First, 25 μl of dimethyl sulfoxide–carbon nanotubes solutions (0.4 mg/ml) was cast on the surface of the glassy carbon electrode and dried in air to form a carbon nanotube film at the electrode surface. Then, the glassy carbon/carbon nanotube-modified electrode was immersed into a Ruthenium (III) complex solution (direct deposition) for a short period of time (10–20 s for multiwalled carbon nanotubes and 20–40 s for single-walled carbon nanotubes). The cyclic voltammograms of the modified electrode in aqueous solution shows a pair of well-defined, stable, and nearly reversible redox couple, Ru(III)/Ru(II), with surface-confined characteristics. The attractive mechanical and electrical characteristics of carbon nanostructures and unique properties and reactivity of Ru complexes are combined. The transfer coefficient (α), heterogeneous electron transfer rate constants (k s), and surface concentrations (Γ) for the glassy carbon/single-walled carbon nanotubes/Ru(III) complex-, glassy carbon/multiwalled carbon nanotubes/Ru(III) complex-, and glassy carbon/Ru(III) complex-modified electrodes were calculated using the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time, and high sensitivity toward the reduction of nicotinamide adenine dinucleotide in phosphate buffer solutions at a pH range of 4–8. The catalytic cathodic current depends on the nicotinamide adenine dinucleotide concentration. In the presence of alcohol dehydrogenase, the modified electrode exhibited a response to addition of acetaldehyde. Therefore, the main product of nicotinamide adenine dinucleotide electroreduction at the Ru(III) complex/carbon nanotube-modified electrode was the enzymatically active NADH. The purposed sensor can be used for acetaldehyde determination.
Zinc oxide (ZnOx) nanoparticles electrodeposited on the surface of glassy carbon (GC) electrode b... more Zinc oxide (ZnOx) nanoparticles electrodeposited on the surface of glassy carbon (GC) electrode by applying potential step (−0.8 V for 120 s) from a zinc acetate solution with 50 °C. Then, potential cycling was used for oxidation of guanine and producing an electroactive redox couple which strongly and irreversibly adsorbed on the ZnOx nanoparticles/modified electrode. Modified electrode shows a pair of well-defined nearly reversible and surface-controlled redox couple (Eo′=0.28 VEo′=0.28 V in pH 7 buffer solution), at pH range 2–12. The surface coverage (Γ) and heterogeneous electron transfer rate constant (ks) of adsorbed redox couple were about 9.5 × 10−9 mol cm−2 and 3.18(±0.20) s−1, respectively, indicating the high loading ability of ZnOx nanoparticles toward guanine oxidation product and great facilitation of the electron transfer between redox couple and ZnOx nanoparticles. The modified electrode exhibited excellent electrocatalytic activity toward l-cysteine oxidation. The kcat for l-cysteine oxidation was found to be 4.20(±0.20) × 103 M−1 s−1. The catalytic oxidation current allows the amperometric detection of l-cysteine at potential of 0.5 V with detection limit of 50 nM, linear response up to 20 μM and sensitivity of 215.4 nA μ A−1 cm−2.
A sol-gel technique was used for fabrication of a renewable carbon composite electrode (CCE) modi... more A sol-gel technique was used for fabrication of a renewable carbon composite electrode (CCE) modified with nickel powder. This modified electrode shows excellent catalytic activity for the oxidation of insulin in alkaline solutions. The nickel powder was then oxidized to form a nickel oxide film electrode, which was used as an amperometric detector for hydrodynamic amperometry and flow injection analysis of insulin. It was found that the calibration curve was linear up to 30 microM with a detection limit of 40 pM under the optimized conditions for hydrodynamic amperometry using a rotating disk modified CCE. Flow injection amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear dynamic range of 15-1000 pM, sensitivity of 8659.23 pA pM-1 cm-2, and detection limit of 2 pM. This electrode shows many advantages as an insulin sensor such as simple preparation method without using any specific electron-transfer mediator or specific reagent, high sensitivity, excellent catalytic activity, short response time, long-term stability, and remarkable antifouling property toward insulin and its oxidation product. Sensitivity, detection limit, and antifouling properties of this insulin sensor are better than all of the reports in the literature. Additionally, it is promising for monitoring insulin in chromatographic effluents.
A simple procedure has been used for preparation of modified glassy carbon electrode with carbon ... more A simple procedure has been used for preparation of modified glassy carbon electrode with carbon nanotubes and copper complex. Copper complex [Cu(bpy)2]Br2 was immobilized onto glassy carbon (GC) electrode modified with silicomolybdate, α-SiMo12O404− and single walled carbon nanotubes (SWCNTs). Copper complex and silicomolybdate irreversibly and strongly adsorbed onto GC electrode modified with CNTs. Electrostatic interactions between polyoxometalates (POMs) anions and Cu-complex, cations mentioned as an effective method for fabrication of three-dimensional structures. The modified electrode shows three reversible redox couples for polyoxometalate and one redox couple for Cu-complex at wide range of pH values. The electrochemical behavior, stability and electron transfer kinetics of the adsorbed redox couples were investigated using cyclic voltammetry. Due to electrostatic interaction, copper complex immobilized onto GC/CNTs/α-SiMo12O404− electrode shows more stable voltammetric response compared to GC/CNTs/Cu-complex modified electrode. In comparison to GC/CNTs/Cu-complex the GC/CNTs/α-SiMo12O404− modified electrodes shows excellent electrocatalytic activity toward reduction H2O2 and BrO3− at more reduced overpotential. The catalytic rate constants for catalytic reduction hydrogen peroxide and bromate were 4.5(±0.2) × 103 M−1 s−1 and 3.0(±0.10) × 103 M−1 s−1, respectively. The hydrodynamic amperommetry technique at 0.08 V was used for detection of nanomolar concentration of hydrogen peroxide and bromate. Detection limit, sensitivity and linear concentration range proposed sensor for bromate and hydrogen peroxide detection were 1.1 nM and 6.7 nA nM−1, 10 nM–20 μM, 1 nM, 5.5 nA nM−1 and 10 nM–18 μM, respectively.
Single-walled carbon nanotubes(SWCNTs) were dispersed into DMSO, and a SWCNTs-film coated glassy ... more Single-walled carbon nanotubes(SWCNTs) were dispersed into DMSO, and a SWCNTs-film coated glassy carbon electrode was achieved via evaporating the solvent. The results indicated that CNT modified glassy carbon electrode exhibited efficiently electrocatalytic reduction for ranitidine and metronidazole with relatively high sensitivity, stability and life time. Under conditions of cyclic voltammetry, the potential for reduction of selected analytes is lowered by approximately 150 mV and current is enhanced significantly (7 times) in comparison to the bare glassy carbon electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for these analytes determinations by hydrodynamic amperometry. Under optimized condition in amperometric method the concentration calibration range, detection limit and sensitivity were about, 0.1–200 μM, detection limit (S/N=3) 6.3×10−8 mol L−1 and sensitivity 40 nA/μM for metronidazole and 0.3–270 μM 7.73×10−8 mol L−1 and 25 nA/μM for ranitidine. In addition, the ability of the modified electrode for simultaneous determination of ranitidine and metronidazole was evaluated. The proposed method was successfully applied to ranitidine and metronidazole determination in tablets. The analytical performance of this sensor has been evaluated for detection of these analytes in serum as a real sample.
Potential cycling was used for oxidation of NAD+ and producing an electroactive redox couple whic... more Potential cycling was used for oxidation of NAD+ and producing an electroactive redox couple which strongly adsorbed on the electrode surface modified with single walled carbon nanotubes (SWCNTs). Modified electrode shows a pair of well defined and nearly reversible redox peaks at pH range 1–13 and the response showed a surface-controlled electrode process. The surface coverage and heterogeneous electron transfer rate constant (ks) of adsorbed redox couple onto CNTs films were about 6.32×10−10 mol cm−2 and 2.0 (±0.20) s−1, respectively, indicating the high loading ability of CNTs toward the oxidation product of NAD+ (2,8-dihydroxy adenine dinucleotide) and great facilitation of the electron transfer between redox couple and CNTs immobilized onto electrode surface. The modified electrode exhibited excellent electrocatalytic activity for H2O2 reduction at reduced overpotential. The catalytic rate constant for H2O2 reduction was found to be 2.22(±0.20)×104 M−1 s−1. The catalytic reduction current allows the amperometric detection of H2O2 at an applied potential of −0.25 V vs. Ag/AgCl with a detection limit of 10 pM and linear response up to 100 nM and resulting analytical sensitivity 747.6 nA/pM. The remarkably low detection limit (10 pM) is the lowest value ever reported for direct H2O2 determination on the electrodes at pH 7. The modified electrode can be used for monitoring H2O2 without the need for an enzyme or enzyme mimic. The proposed method for rapid amperometric detection of H2O2 is low cost and high throughput. Furthermore, the sensor can be used to any detection scheme that uses enzymatically generated H2O2 as a reactive product in biological systems.
In this research a novel osmium complex was used as electrocatalyst for electroreduction of oxyge... more In this research a novel osmium complex was used as electrocatalyst for electroreduction of oxygen and H2O2 in physiological pH solutions. Electroless deposition at a short period of time (60 s), was used for strong and irreversible adsorption of 1,4,8,12-tetraazacyclotetradecane osmium(III) chloride (Os(III)LCl2) ClO4 onto single-walled carbon nanotubes (SWCNTs) modified GC electrode. The modified electrode shows a pair of well defined and reversible redox couple, Os(IV)/Os(III) at wide pH range (1–8). The glucose biosensor was fabricated by covering a thin film of glucose oxidase onto CNTs/Os-complex modified electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The fabricated biosensor shows high sensitivity, 826.3 nA μM−1cm−2, low detection limit, 56 nM, fast response time <3 s and wide calibration range 1.0 μM–1.0 mM. The biosensor has been successfully applied to determination of glucose in human plasma. Because of relative low applied potential, the interference from electroactive existing species was minimized, which improved the selectivity of the biosensor. The apparent Michaelis-Menten constant of GOx on the nanocomposite, 0.91 mM, exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. Excellent electrochemical reversibility, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this glucose biosensor.
Cyclic voltammetry has been used for modification of glassy carbon (GC) electrode with cobalt oxi... more Cyclic voltammetry has been used for modification of glassy carbon (GC) electrode with cobalt oxide (CoOx) nanoparticles and flavin adenine dinucleotide (FAD) film. Electrodeposited cobalt oxide may be a promising material for FAD immobilization owing to its high biocompatibility and large surface. The adsorbed FAD film is stable and electrochemically active in aqueous solution. The FAD films assembled on cobalt oxide exhibited a pair of well defined, stable and nearly reversible CV peaks at wide pH range. The formal potential of adsorbed FAD onto cobalt oxide nanoparticles film, E0′ vs. Ag/AgCl reference electrode is −0.44 V in pH 7 buffer solution was similar to dissolved FAD and changed linearly with a slope of 46 mV/pH in the pH range 4–12. The surface coverage and heterogeneous electron transfer rate constant (ks) of FAD immobilized on CoOx film glassy carbon electrode are 1.47 × 10−9 mol cm−2 and 0.85 ± 0.1 s−1, indicating the high loading ability of the CoOx nanoparticles and great facilitation of the electron transfer between FAD and CoOx nanoparticles. Cobalt oxide/FAD composite modified GC electrode shows excellent catalytic activity for nitrite reduction at reduced overpotential. Furthermore, FAD/CoOx rotating disk electrode modified GC electrode shows good analytical performance for amperometric determination nitrite. Under optimized condition of the amperometry method the concentration calibration range, detection limit and sensitivity are 1–30 μΜ, 0.20 μM and 10.5 nA/μM, respectively. Finally the kinetics of the catalytic reaction between nitrite anion and reduced FAD was characterized, using cyclic voltammetry and a value of 2.08 (±0.3) × 103 M−1 s−1 was obtained for the rate constant.
A two-step sol–gel technique was used here to prepare a carbon ceramic electrode modified with na... more A two-step sol–gel technique was used here to prepare a carbon ceramic electrode modified with nafion and [Ru(bpy)(tpy)Cl]PF6. This involves two steps: first, forming a bulk-modified carbon ceramic electrode with nafion, and then immersing the electrode into a Ru-complex solution (electroless deposition) for a short period of time (5–25 s). Cyclic voltammograms of the resulting surface-modified carbon ceramic electrode show stable and a well-defined redox couple due to Ru(II)/Ru(III) system with surface-confined characteristic. l-Cysteine (CySH) has been chosen as a model to elucidate the electrocatalytic ability of Ru-complex nafion sol–gel composite electrode. Not only the modified electrode shows excellent catalytic activity toward l-cysteine electrooxidation in pH range 3–9, but the antifouling effect of nafion film also increases the reproducibility of results in comparison with CCE modified with homogeneous mixing of graphite powder and Ru-complex (one step sol–gel method). Under the optimized conditions in amperometry method, the concentration calibration range, detection limit and sensitivity were 0.1–100 μM, 20 nM and 50 nA/μM, respectively. The advantages of this modified electrode are good reproducibility, excellent catalytic activity, simplicity of preparation and especially its antifouling properties towards l-cysteine and its oxidation products. Additionally, it is promising as a detector in flow system or chromatography systems.
The sol–gel technique was used to fabricate nickel powder carbon composite electrode (CCE). The n... more The sol–gel technique was used to fabricate nickel powder carbon composite electrode (CCE). The nickel powder successfully used to deposit NiOx thin film on conductive carbon ceramic electrode for large surface area catalytic application. Repetitive cycling in potential range −0.2 to 1.0 V was used to form of a thin nickel oxide film on the surface carbon composite electrode. The thin film exhibits an excellent electro-catalytic activity for oxidation of SO32−, S2O42−, S2O32−, S4O62− and S2− in alkaline pH range 10–14. Optimum pH values for detection of all sulfur derivatives is 13 and catalytic rate constants are in range 2.4 × 103–8.9 × 103 M−1 s−1. The hydrodynamic amperometry at rotating modified CCE at constant potential versus reference electrode was used for detection of sulfur derivatives. Under optimized conditions the calibration plots are linear in the concentration range 10 μM–15 mM and detection limit 1.2–34 μM and 0.53–7.58 nA/μM (sensitivity) for electrode surface area 0.0314 cm2. The nickel powder doped modified carbon ceramic electrode shows good reproducibility, a short response time (2.0 s), remarkable long term stability, less expense, simplicity of preparation, good chemical and mechanical stability, and especially good surface renewability by simple mechanical polishing and repetitive potential cycling. This sensor can be used into the design of a simple and cheap chromatographic amperometry detector for analysis of sulfur derivatives.
Cyclic voltammetry at potential range − 1.1 to 0.5 V from aqueous buffer solution (pH 7) containi... more Cyclic voltammetry at potential range − 1.1 to 0.5 V from aqueous buffer solution (pH 7) containing CoCl2 produced a well defined cobalt oxide (CoOx) nanoparticles deposited on the surface of glassy carbon electrode. The morphology of the modified surface and cobalt oxide formation was examined with SEM and cyclic voltammetry techniques. Hemoglobin (Hb) was successfully immobilized in cobalt-oxide nanoparticles modified glassy carbon electrode. Immobilization of hemoglobin onto cobalt oxide nanoparticles have been investigated by cyclic voltammetry and UV–visible spectroscopy. The entrapped protein can take direct electron transfer in cobalt-oxide film. A pair of well defined, quasi-reversible cyclic voltammetric peaks at about − 0.08 V vs. SCE (pH 7), characteristic of heme redox couple (Fe(III)/Fe(II)) of hemoglobin, and the response showed surface controlled electrode process. The dependence of formal potential (E0′) on the solution pH (56 mV pH− 1) indicated that the direct electron transfer reaction of hemoglobin was a one-electron transfer coupled with a one proton transfer reaction process. The average surface coverage of Hb immobilized on the cobalt oxide nanoparticles was about 5.2536 × 10− 11 mol cm− 2, indicating high loading ability of nanoparticles for hemoglobin entrapment. The heterogeneous electron transfer rate constant (ks) was 1.43 s− 1, indicating great of facilitation of the electron transfer between Hb and electrodeposited cobalt oxide nanoparticles. Modified electrode exhibits a remarkable electrocatalytic activity for the reduction of hydrogen peroxide and oxygen. The Michaels–Menten constant Km of 0.38 mM, indicating that the Hb immobilized onto cobalt oxide film retained its peroxidases activity. The biosensor exhibited a fast amperometric response < 5 s, a linear response over a wide concentration range 5 μM to 700 μM and a low detection limit 0.5 μM. According to the direct electron transfer property and enhanced activity of Hb in cobalt oxide film, a third generation reagentless biosensor without using any electron transfer mediator or specific reagent can be constructed for determination of hydrogen peroxide in anaerobic solutions.
Glassy carbon electrode modified with electrodeposited cobalt oxide nanostructure shows an excell... more Glassy carbon electrode modified with electrodeposited cobalt oxide nanostructure shows an excellent electrocatalytic activity toward insulin oxidation at a wide pH range. Cyclic voltammetry, hydrodynamic amperometry, and flow injection analysis (FIA) were used for insulin determination at a picomolar and higher-concentration range. Amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear range, 100 pM–15 nM; sensitivity of 83.9 nA nM−1 and detection limit 10 pM. FIA yielded the calibration curve with sensitivity and detection limit of 2.0 nA nM−1 and 25 pM, respectively. Furthermore, the RSD of repetitive FIA for 200 pM insulin (n = 13) is 2%. In addition, the interference effect of electroactive existing species (lactic acid, cholesterol, ascorbic acid, uric acid, and glucose) was eliminated by covering the surface of the modified electrode with nafion film. Fast response time, signal stability, high sensitivity, low cost, and ease of preparation are the advantages of the proposed insulin sensor.
Iridium oxide (IrOx) films formed electrochemically on the surface boron doped diamond electrode ... more Iridium oxide (IrOx) films formed electrochemically on the surface boron doped diamond electrode by potential cycling in the range −0.2 to 1.2 V from a saturated solution of alkaline iridium(III) solution. A strongly adherent deposit of iridium oxide is formed after 5–10 potential scans. The properties, stability and electrochemical behavior of iridium oxide layers were investigated by atomic force microscopy and cyclic voltammetry. The boron doped diamond (BDD) electrode modified with electrodeposition of a thin film, exhibited an excellent catalytic activity for oxidation of Hg(I) over a wide pH range. The modified electrode shows excellent analytical performance for Hg(I) amperometric detection. The detection limit, sensitivity, response time and dynamic concentration ranges are 3.2 nM, 77 nA μM−1, 100 ms and 5 nM–5 μM. These analytical parameters compare favorably with those obtained with modern analytical techniques and recently published electrochemical methods.
A simple procedure was developed for the preparation of glassy carbon electrodes modified with si... more A simple procedure was developed for the preparation of glassy carbon electrodes modified with single wall carbon nanotubes (SWCNTs) and multilayers of SiΜο12Ο404−-[Ru(bpy)(tpy)Cl]+(byp; bipyridine, tpy; terpyridine). Layer-by-layer deposition technique was used for the multilayer formation of SiΜο12Ο404−-[Ru(bpy)(tpy)Cl]+ onto SWCNTs films. Based on the strong electrostatic attraction of oppositely charged species a Ru-complex/poly oxometalate hybrid film strongly and irreversibly adsorbed on the glassy carbon electrode modified with single walled carbon nanotubes. The multilayer assembly exhibited good stability and excellent electrochemical reversibility for both redox systems in the pH range1–7. It was found that up to fifteen monolayers could be deposited onto a carbon nanotube film with well defined redox behavior. The modified electrode shows excellent electrocatalytic activity towards sulfite oxidation. Due to synergistic effect between SWCNTs and oppositely charged species the repeated alternate adsorption of anions and cations by this simple dipping method leads to molecular sandwiches with interesting redox activity and remarkable stability.
For the first time silicon carbide nanoparticles (SiC) was used for electrode modification and el... more For the first time silicon carbide nanoparticles (SiC) was used for electrode modification and electrocatalytic oxidation of insulin. In comparison to bare glassy carbon (GC) electrode, the oxidation of insulin at GC electrode modified with SiC nanoparticles occurred at reduced overpotentials. The modified electrode was applied for insulin detection using cyclic voltammetry, differential pulse voltammetry (DPV) and flow injection analysis (FIA). Flow injection amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear dynamic range up to 600 pM, sensitivity of 710 pA pM−1 cm−2 and detection limit of 3.3 pM. In addition interference effect of the electroactive existing species (uric acid, glucose, lactic acid, l-cysteine and cholesterol) was diminished and for ascorbic acid eliminated by covering the surface of modified electrode with nafion film. This electrode shows many advantages as an insulin sensor such as simple preparation method without using any specific electron transfer mediator or specific reagent, high sensitivity, excellent catalytic activity, short response time, long term stability and remarkable antifouling property toward insulin and its oxidation product. Sensitivity, detection limit and antifouling properties of this insulin sensor are better than all of the reports in the literature for insulin detection at physiological pH solutions.
The electrochemical properties of aqueous thionin (an electroactive water soluble dye) of pH 1–12... more The electrochemical properties of aqueous thionin (an electroactive water soluble dye) of pH 1–12 were investigated by cyclic voltammetry at a boron doped diamond(BDD) electrode. A well defined reversible redox couple was observed in acidic, neutral and alkaline solutions. The standard potential and kinetic parameters for thionin were obtained by fitting experimental cyclic voltammograms to those generated by the DigiSim program. The electrogenerated reduced form of thionin has been used as an efficient organic catalyst for the reduction of Cr(VI) at a BDD electrode immersed in aqueous media. The cyclic voltammetry measurements indicate that an electrocatalytic process occurs, where electrochemically generated thionin reduced species (Leucothionin) is oxidized by Cr(VI) back to the parent thionin species via a EC' reaction mechanism. The determination of catalytic rate constant (Kcat) was accomplished again by fitting experimental cyclic voltammograms with simulated ones.
A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single-w... more A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single-walled carbon nanotubes (SWCNTs) and polyoxometalate. With immersing SWCNTs modified GC electrode in silicon polyoxomolybdate (α-SiMo12O404−) solution (direct deposition) for a short period of time (2–10 s) oxoanion adsorbed strongly and irreversibly on SWCNTs. Cyclic voltammograms of the α-SiMo12O404− incorporated-SWCNTs indicates three well-defined and reversible redox couples with surface confined characteristic at wide pH range (1–7). The surface coverage (Γ) of α-SiMo12O404− immobilized on SWCNTs was 2.14 (±0.11)×10−9 mol cm−2 indicating high loading ability of SWCNTs for polyoxometalate. The charge transfer rate constant (ks) of three redox couples of adsorbed α-SiMo12O404− were 9.20 (±0.20), 8.02 (±0.20), and 3.70 (±0.10) s−1, respectively, indicate great facilitation of the electron transfer between α-SiMo12O404− and CNTs. In this research the attractive mechanical and electrical characteristics of CNTs and unique properties and reactivity of polyoxometalates were combined. The modified electrode in buffer solution containing Sb(III) shows a new redox system at 0.38 V in pH 1. The voltammetric peak current increased with increasing Sb(III) concentration. The differential pulse voltammetry (DPV) technique was used for detection micromolar concentration of antimony. Furthermore, the interference effects various electroactive compounds on voltammetric response of Sb(III) were negligible. Finally the ability of the modified electrode for antimony detection in real samples was evaluated.
Iridium oxide nanoparticles are grown on a glassy carbon electrode by electrodepositing method. T... more Iridium oxide nanoparticles are grown on a glassy carbon electrode by electrodepositing method. The electrochemical behavior and electrocatalytic activity of modified electrode towards reduction of iodate and periodate are studied. The reductions of both ions occur at the unusual positive peak potential of 0.7 V vs. reference electrode. The modified electrode is employed successfully for iodate and periodates detection using cyclic voltammetry, hydrodynamic amperometry and flow injection analysis (FIA). In the performed experiments, flow injection amperometric determination of iodate and periodate yielded calibration curves with the following characteristics: linear dynamic range up to 100 and 80 μM, sensitivity of 140.9 and 150.6 nA μM−1 and detection limits of 5 and 36 nM, respectively. The repeatability of the modified electrode for 21 injections of 1.5 μM of iodate solution is 1.5%. The interference effects of NO2−, NO3−, ClO3−, BrO3−, ClO4−, SO42−, Cu2+, Zn2+, Mn2+, Mg2+, Cd2+, Ca2+, Na+, K+, NH4+ and K+, CH3COO− and glucose were negligible at the concentration ratio of more than 1000. The obtained attractive analytical performance together with high selectivity and simplicity of the proposed method provide an effective and e novel modified electrode to develop an iodate and periodate sensor. Sensitivity, selectivity, the liner concentration range and the detection limit of the developed sensor are all much better than all known similar sensors in the literature for iodate and periodate determination.
Electrodeposited cobalt oxide (CoOx) nanomaterials are not only used for immobilization of choles... more Electrodeposited cobalt oxide (CoOx) nanomaterials are not only used for immobilization of cholesterol oxidase (ChOx) but also as electron transfer mediator for oxidation of H2O2 generated in the enzymatic reaction. Voltammetry and flow injection analysis (FIA) were used for determination of cholesterol. FIA determination of cholesterol with biosensors yielded a calibration curve with the following characteristics: linear range up to 50 μM, sensitivity of 43.5 nA μM−1 cm−2 and detection limit of 4.2 μM. The apparent Michaelis-Menten constant and the response time of the biosensor are 0.49 mM and 15 s, respectively. This biosensor also exhibits good stability, reproducibility and long life time.
A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotu... more A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes and Ruthenium (III) complexes. First, 25 μl of dimethyl sulfoxide–carbon nanotubes solutions (0.4 mg/ml) was cast on the surface of the glassy carbon electrode and dried in air to form a carbon nanotube film at the electrode surface. Then, the glassy carbon/carbon nanotube-modified electrode was immersed into a Ruthenium (III) complex solution (direct deposition) for a short period of time (10–20 s for multiwalled carbon nanotubes and 20–40 s for single-walled carbon nanotubes). The cyclic voltammograms of the modified electrode in aqueous solution shows a pair of well-defined, stable, and nearly reversible redox couple, Ru(III)/Ru(II), with surface-confined characteristics. The attractive mechanical and electrical characteristics of carbon nanostructures and unique properties and reactivity of Ru complexes are combined. The transfer coefficient (α), heterogeneous electron transfer rate constants (k s), and surface concentrations (Γ) for the glassy carbon/single-walled carbon nanotubes/Ru(III) complex-, glassy carbon/multiwalled carbon nanotubes/Ru(III) complex-, and glassy carbon/Ru(III) complex-modified electrodes were calculated using the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time, and high sensitivity toward the reduction of nicotinamide adenine dinucleotide in phosphate buffer solutions at a pH range of 4–8. The catalytic cathodic current depends on the nicotinamide adenine dinucleotide concentration. In the presence of alcohol dehydrogenase, the modified electrode exhibited a response to addition of acetaldehyde. Therefore, the main product of nicotinamide adenine dinucleotide electroreduction at the Ru(III) complex/carbon nanotube-modified electrode was the enzymatically active NADH. The purposed sensor can be used for acetaldehyde determination.
Zinc oxide (ZnOx) nanoparticles electrodeposited on the surface of glassy carbon (GC) electrode b... more Zinc oxide (ZnOx) nanoparticles electrodeposited on the surface of glassy carbon (GC) electrode by applying potential step (−0.8 V for 120 s) from a zinc acetate solution with 50 °C. Then, potential cycling was used for oxidation of guanine and producing an electroactive redox couple which strongly and irreversibly adsorbed on the ZnOx nanoparticles/modified electrode. Modified electrode shows a pair of well-defined nearly reversible and surface-controlled redox couple (Eo′=0.28 VEo′=0.28 V in pH 7 buffer solution), at pH range 2–12. The surface coverage (Γ) and heterogeneous electron transfer rate constant (ks) of adsorbed redox couple were about 9.5 × 10−9 mol cm−2 and 3.18(±0.20) s−1, respectively, indicating the high loading ability of ZnOx nanoparticles toward guanine oxidation product and great facilitation of the electron transfer between redox couple and ZnOx nanoparticles. The modified electrode exhibited excellent electrocatalytic activity toward l-cysteine oxidation. The kcat for l-cysteine oxidation was found to be 4.20(±0.20) × 103 M−1 s−1. The catalytic oxidation current allows the amperometric detection of l-cysteine at potential of 0.5 V with detection limit of 50 nM, linear response up to 20 μM and sensitivity of 215.4 nA μ A−1 cm−2.
A sol-gel technique was used for fabrication of a renewable carbon composite electrode (CCE) modi... more A sol-gel technique was used for fabrication of a renewable carbon composite electrode (CCE) modified with nickel powder. This modified electrode shows excellent catalytic activity for the oxidation of insulin in alkaline solutions. The nickel powder was then oxidized to form a nickel oxide film electrode, which was used as an amperometric detector for hydrodynamic amperometry and flow injection analysis of insulin. It was found that the calibration curve was linear up to 30 microM with a detection limit of 40 pM under the optimized conditions for hydrodynamic amperometry using a rotating disk modified CCE. Flow injection amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear dynamic range of 15-1000 pM, sensitivity of 8659.23 pA pM-1 cm-2, and detection limit of 2 pM. This electrode shows many advantages as an insulin sensor such as simple preparation method without using any specific electron-transfer mediator or specific reagent, high sensitivity, excellent catalytic activity, short response time, long-term stability, and remarkable antifouling property toward insulin and its oxidation product. Sensitivity, detection limit, and antifouling properties of this insulin sensor are better than all of the reports in the literature. Additionally, it is promising for monitoring insulin in chromatographic effluents.
A simple procedure has been used for preparation of modified glassy carbon electrode with carbon ... more A simple procedure has been used for preparation of modified glassy carbon electrode with carbon nanotubes and copper complex. Copper complex [Cu(bpy)2]Br2 was immobilized onto glassy carbon (GC) electrode modified with silicomolybdate, α-SiMo12O404− and single walled carbon nanotubes (SWCNTs). Copper complex and silicomolybdate irreversibly and strongly adsorbed onto GC electrode modified with CNTs. Electrostatic interactions between polyoxometalates (POMs) anions and Cu-complex, cations mentioned as an effective method for fabrication of three-dimensional structures. The modified electrode shows three reversible redox couples for polyoxometalate and one redox couple for Cu-complex at wide range of pH values. The electrochemical behavior, stability and electron transfer kinetics of the adsorbed redox couples were investigated using cyclic voltammetry. Due to electrostatic interaction, copper complex immobilized onto GC/CNTs/α-SiMo12O404− electrode shows more stable voltammetric response compared to GC/CNTs/Cu-complex modified electrode. In comparison to GC/CNTs/Cu-complex the GC/CNTs/α-SiMo12O404− modified electrodes shows excellent electrocatalytic activity toward reduction H2O2 and BrO3− at more reduced overpotential. The catalytic rate constants for catalytic reduction hydrogen peroxide and bromate were 4.5(±0.2) × 103 M−1 s−1 and 3.0(±0.10) × 103 M−1 s−1, respectively. The hydrodynamic amperommetry technique at 0.08 V was used for detection of nanomolar concentration of hydrogen peroxide and bromate. Detection limit, sensitivity and linear concentration range proposed sensor for bromate and hydrogen peroxide detection were 1.1 nM and 6.7 nA nM−1, 10 nM–20 μM, 1 nM, 5.5 nA nM−1 and 10 nM–18 μM, respectively.
Single-walled carbon nanotubes(SWCNTs) were dispersed into DMSO, and a SWCNTs-film coated glassy ... more Single-walled carbon nanotubes(SWCNTs) were dispersed into DMSO, and a SWCNTs-film coated glassy carbon electrode was achieved via evaporating the solvent. The results indicated that CNT modified glassy carbon electrode exhibited efficiently electrocatalytic reduction for ranitidine and metronidazole with relatively high sensitivity, stability and life time. Under conditions of cyclic voltammetry, the potential for reduction of selected analytes is lowered by approximately 150 mV and current is enhanced significantly (7 times) in comparison to the bare glassy carbon electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for these analytes determinations by hydrodynamic amperometry. Under optimized condition in amperometric method the concentration calibration range, detection limit and sensitivity were about, 0.1–200 μM, detection limit (S/N=3) 6.3×10−8 mol L−1 and sensitivity 40 nA/μM for metronidazole and 0.3–270 μM 7.73×10−8 mol L−1 and 25 nA/μM for ranitidine. In addition, the ability of the modified electrode for simultaneous determination of ranitidine and metronidazole was evaluated. The proposed method was successfully applied to ranitidine and metronidazole determination in tablets. The analytical performance of this sensor has been evaluated for detection of these analytes in serum as a real sample.
Potential cycling was used for oxidation of NAD+ and producing an electroactive redox couple whic... more Potential cycling was used for oxidation of NAD+ and producing an electroactive redox couple which strongly adsorbed on the electrode surface modified with single walled carbon nanotubes (SWCNTs). Modified electrode shows a pair of well defined and nearly reversible redox peaks at pH range 1–13 and the response showed a surface-controlled electrode process. The surface coverage and heterogeneous electron transfer rate constant (ks) of adsorbed redox couple onto CNTs films were about 6.32×10−10 mol cm−2 and 2.0 (±0.20) s−1, respectively, indicating the high loading ability of CNTs toward the oxidation product of NAD+ (2,8-dihydroxy adenine dinucleotide) and great facilitation of the electron transfer between redox couple and CNTs immobilized onto electrode surface. The modified electrode exhibited excellent electrocatalytic activity for H2O2 reduction at reduced overpotential. The catalytic rate constant for H2O2 reduction was found to be 2.22(±0.20)×104 M−1 s−1. The catalytic reduction current allows the amperometric detection of H2O2 at an applied potential of −0.25 V vs. Ag/AgCl with a detection limit of 10 pM and linear response up to 100 nM and resulting analytical sensitivity 747.6 nA/pM. The remarkably low detection limit (10 pM) is the lowest value ever reported for direct H2O2 determination on the electrodes at pH 7. The modified electrode can be used for monitoring H2O2 without the need for an enzyme or enzyme mimic. The proposed method for rapid amperometric detection of H2O2 is low cost and high throughput. Furthermore, the sensor can be used to any detection scheme that uses enzymatically generated H2O2 as a reactive product in biological systems.
In this research a novel osmium complex was used as electrocatalyst for electroreduction of oxyge... more In this research a novel osmium complex was used as electrocatalyst for electroreduction of oxygen and H2O2 in physiological pH solutions. Electroless deposition at a short period of time (60 s), was used for strong and irreversible adsorption of 1,4,8,12-tetraazacyclotetradecane osmium(III) chloride (Os(III)LCl2) ClO4 onto single-walled carbon nanotubes (SWCNTs) modified GC electrode. The modified electrode shows a pair of well defined and reversible redox couple, Os(IV)/Os(III) at wide pH range (1–8). The glucose biosensor was fabricated by covering a thin film of glucose oxidase onto CNTs/Os-complex modified electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The fabricated biosensor shows high sensitivity, 826.3 nA μM−1cm−2, low detection limit, 56 nM, fast response time <3 s and wide calibration range 1.0 μM–1.0 mM. The biosensor has been successfully applied to determination of glucose in human plasma. Because of relative low applied potential, the interference from electroactive existing species was minimized, which improved the selectivity of the biosensor. The apparent Michaelis-Menten constant of GOx on the nanocomposite, 0.91 mM, exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. Excellent electrochemical reversibility, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this glucose biosensor.
Cyclic voltammetry has been used for modification of glassy carbon (GC) electrode with cobalt oxi... more Cyclic voltammetry has been used for modification of glassy carbon (GC) electrode with cobalt oxide (CoOx) nanoparticles and flavin adenine dinucleotide (FAD) film. Electrodeposited cobalt oxide may be a promising material for FAD immobilization owing to its high biocompatibility and large surface. The adsorbed FAD film is stable and electrochemically active in aqueous solution. The FAD films assembled on cobalt oxide exhibited a pair of well defined, stable and nearly reversible CV peaks at wide pH range. The formal potential of adsorbed FAD onto cobalt oxide nanoparticles film, E0′ vs. Ag/AgCl reference electrode is −0.44 V in pH 7 buffer solution was similar to dissolved FAD and changed linearly with a slope of 46 mV/pH in the pH range 4–12. The surface coverage and heterogeneous electron transfer rate constant (ks) of FAD immobilized on CoOx film glassy carbon electrode are 1.47 × 10−9 mol cm−2 and 0.85 ± 0.1 s−1, indicating the high loading ability of the CoOx nanoparticles and great facilitation of the electron transfer between FAD and CoOx nanoparticles. Cobalt oxide/FAD composite modified GC electrode shows excellent catalytic activity for nitrite reduction at reduced overpotential. Furthermore, FAD/CoOx rotating disk electrode modified GC electrode shows good analytical performance for amperometric determination nitrite. Under optimized condition of the amperometry method the concentration calibration range, detection limit and sensitivity are 1–30 μΜ, 0.20 μM and 10.5 nA/μM, respectively. Finally the kinetics of the catalytic reaction between nitrite anion and reduced FAD was characterized, using cyclic voltammetry and a value of 2.08 (±0.3) × 103 M−1 s−1 was obtained for the rate constant.
A two-step sol–gel technique was used here to prepare a carbon ceramic electrode modified with na... more A two-step sol–gel technique was used here to prepare a carbon ceramic electrode modified with nafion and [Ru(bpy)(tpy)Cl]PF6. This involves two steps: first, forming a bulk-modified carbon ceramic electrode with nafion, and then immersing the electrode into a Ru-complex solution (electroless deposition) for a short period of time (5–25 s). Cyclic voltammograms of the resulting surface-modified carbon ceramic electrode show stable and a well-defined redox couple due to Ru(II)/Ru(III) system with surface-confined characteristic. l-Cysteine (CySH) has been chosen as a model to elucidate the electrocatalytic ability of Ru-complex nafion sol–gel composite electrode. Not only the modified electrode shows excellent catalytic activity toward l-cysteine electrooxidation in pH range 3–9, but the antifouling effect of nafion film also increases the reproducibility of results in comparison with CCE modified with homogeneous mixing of graphite powder and Ru-complex (one step sol–gel method). Under the optimized conditions in amperometry method, the concentration calibration range, detection limit and sensitivity were 0.1–100 μM, 20 nM and 50 nA/μM, respectively. The advantages of this modified electrode are good reproducibility, excellent catalytic activity, simplicity of preparation and especially its antifouling properties towards l-cysteine and its oxidation products. Additionally, it is promising as a detector in flow system or chromatography systems.
The sol–gel technique was used to fabricate nickel powder carbon composite electrode (CCE). The n... more The sol–gel technique was used to fabricate nickel powder carbon composite electrode (CCE). The nickel powder successfully used to deposit NiOx thin film on conductive carbon ceramic electrode for large surface area catalytic application. Repetitive cycling in potential range −0.2 to 1.0 V was used to form of a thin nickel oxide film on the surface carbon composite electrode. The thin film exhibits an excellent electro-catalytic activity for oxidation of SO32−, S2O42−, S2O32−, S4O62− and S2− in alkaline pH range 10–14. Optimum pH values for detection of all sulfur derivatives is 13 and catalytic rate constants are in range 2.4 × 103–8.9 × 103 M−1 s−1. The hydrodynamic amperometry at rotating modified CCE at constant potential versus reference electrode was used for detection of sulfur derivatives. Under optimized conditions the calibration plots are linear in the concentration range 10 μM–15 mM and detection limit 1.2–34 μM and 0.53–7.58 nA/μM (sensitivity) for electrode surface area 0.0314 cm2. The nickel powder doped modified carbon ceramic electrode shows good reproducibility, a short response time (2.0 s), remarkable long term stability, less expense, simplicity of preparation, good chemical and mechanical stability, and especially good surface renewability by simple mechanical polishing and repetitive potential cycling. This sensor can be used into the design of a simple and cheap chromatographic amperometry detector for analysis of sulfur derivatives.
Cyclic voltammetry at potential range − 1.1 to 0.5 V from aqueous buffer solution (pH 7) containi... more Cyclic voltammetry at potential range − 1.1 to 0.5 V from aqueous buffer solution (pH 7) containing CoCl2 produced a well defined cobalt oxide (CoOx) nanoparticles deposited on the surface of glassy carbon electrode. The morphology of the modified surface and cobalt oxide formation was examined with SEM and cyclic voltammetry techniques. Hemoglobin (Hb) was successfully immobilized in cobalt-oxide nanoparticles modified glassy carbon electrode. Immobilization of hemoglobin onto cobalt oxide nanoparticles have been investigated by cyclic voltammetry and UV–visible spectroscopy. The entrapped protein can take direct electron transfer in cobalt-oxide film. A pair of well defined, quasi-reversible cyclic voltammetric peaks at about − 0.08 V vs. SCE (pH 7), characteristic of heme redox couple (Fe(III)/Fe(II)) of hemoglobin, and the response showed surface controlled electrode process. The dependence of formal potential (E0′) on the solution pH (56 mV pH− 1) indicated that the direct electron transfer reaction of hemoglobin was a one-electron transfer coupled with a one proton transfer reaction process. The average surface coverage of Hb immobilized on the cobalt oxide nanoparticles was about 5.2536 × 10− 11 mol cm− 2, indicating high loading ability of nanoparticles for hemoglobin entrapment. The heterogeneous electron transfer rate constant (ks) was 1.43 s− 1, indicating great of facilitation of the electron transfer between Hb and electrodeposited cobalt oxide nanoparticles. Modified electrode exhibits a remarkable electrocatalytic activity for the reduction of hydrogen peroxide and oxygen. The Michaels–Menten constant Km of 0.38 mM, indicating that the Hb immobilized onto cobalt oxide film retained its peroxidases activity. The biosensor exhibited a fast amperometric response < 5 s, a linear response over a wide concentration range 5 μM to 700 μM and a low detection limit 0.5 μM. According to the direct electron transfer property and enhanced activity of Hb in cobalt oxide film, a third generation reagentless biosensor without using any electron transfer mediator or specific reagent can be constructed for determination of hydrogen peroxide in anaerobic solutions.
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