Preparation and characterization of Prussian blue nanowire array and bioapplication for glucose biosensing

Prussian blue nanowire array (PBNWA) was prepared via electrochemical deposition with polycarbonate membrane template for effective modification of glassy carbon electrode. The PBNWA electrode thus obtained was demonstrated to have high-catalytic activity for the electrochemical reduction of hydrogen peroxide in neutral media. This enabled the PBNWA electrode to show rapid response to H₂O₂ at a low potential of −0.1 V over a wide range of concentrations from 1 × 10⁻⁷ M to 5 × 10⁻² M with a high sensitivity of 183 μA mM⁻¹ cm⁻². Such a low-working potential also substantially improved the selectivity of the PBNWA electrode against most electroactive species such as ascorbic acid and uric acid in physiological media. A detection limit of 5 × 10⁻⁸ M was obtained using the PBNWA electrode for H₂O₂, which compared favorably with most electroanalysis procedures for H₂O₂. A biosensor toward glucose was then constructed with the PBNWA electrode as the basic electrode by crosslinking glucose oxidase (GOx). The glucose biosensor allowed rapid, selective and sensitive determination of glucose at −0.1 V. The amperometric response exhibited a linear correlation to glucose concentration through an expanded range from 2 × 10⁻⁶ M to 1 × 10⁻² M, and the response time and detection limit were determined to be 3 s and 1 μM, respectively.     

Prussian Blue electrodeposited on MWNTs-PANI hybrid composites for H2O2 detection

A Prussian Blue (PB)/polyaniline (PANI)/multi-walled carbon nanotubes (MWNTs) composite film was fabricated by step-by-step electrodeposition on glassy carbon electrode (GCE). The electrode prepared exhibits enhanced electrocatalytic behavior and good stability for detection of H₂O₂ at an applied potential of 0.0 V. The effects of MWNTs thickness, electrodeposition time of PANI and rotating rate on the current response of the composite modified electrode toward H₂O₂ were optimized to obtain the maximal sensitivity. A linear range from 8 × 10⁻⁹ to 5 × 10⁻⁶ M for H₂O₂ detection has been observed at the PB/PANI/MWNTs modified GCE with a correlation coefficient of 0.997. The detection limit is 5 × 10⁻⁹ M on signal-to-noise ratio of 3. To the best of our knowledge, this is the lowest detection limit for H₂O₂ detection. The electrode also shows high sensitivity (526.43 μA μM⁻¹ cm⁻²) for H₂O₂ detection which is more than three orders of magnitude higher than the reported.     

A novel bimediator amperometric sensor for electrocatalytic oxidation of gallic acid and reduction of hydrogen peroxide

A novel bimediator amperometric sensor is fabricated for the first time by surface modification of graphite electrode with thionine (TH) and nickel hexacyanoferrate (NiHCF). The electrochemical behavior of the TH/NiHCF bimediator modified electrode was characterized by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The TH/NiHCF bimediator modified electrode exhibited a pair of distinct redox peaks for NiHCF and TH with formal potentials of 0.33 V and −0.27 V vs. SCE at a scan rate of 50 mV s⁻¹ in 0.1 M NaNO₃ and 0.1 M NH₄NO₃ respectively. The electrocatalytic activity of the bimediator modified electrode towards oxidation of gallic acid with NiHCF and reduction of hydrogen peroxide with TH was evaluated and it was observed that the modified electrode showed an electrocatalytic activity towards the oxidation of gallic acid in the concentration range of 4.99 × 10⁻⁶–1.20 × 10⁻³ M with a detection limit of 1.66 × 10⁻⁶ M (S/N = 3) and reduction of H₂O₂ in the concentration range of 1.67 × 10⁻⁶–1.11 × 10⁻³ M with a detection limit of 5.57 × 10⁻⁷ M (S/N = 3). The bimediator modified electrode was found to exhibit good stability and reproducibility.     

Study of the electrochemical behavior of isorhamnetin on a glassy carbon electrode and its application

The electrochemical behavior of isorhamnetin (ISO) at a glassy carbon electrode was studied in a phosphate buffer solution (PBS) of pH 4.0 by cyclic voltammetry (CV) and differential pulse voltammetric method (DPV). A well-defined redox wave of ISO involving one electrons and one proton appeared. The electrode reaction is a reactant weak adsorption-controlled process with a charge transfer coefficient (α) of 0.586. Based on the understanding of the electrochemical process of ISO at the glassy carbon electrode, analysis of ISO can be realized. Under optimal conditions, the oxidation peak current showed linear dependence on the concentration of ISO in the range of 1.0 × 10⁻⁸ to 4.0 × 10⁻⁷ M and 1.0 × 10⁻⁶ to 1.0 × 10⁻⁵ M. The detection limit is 5.0 × 10⁻⁹ M. This method has been successfully applied to the detection of ISO in tablets.     

A novel amperometric sensor for the detection of difenidol hydrochloride based on the modification of Ru(bpy)3 on a glassy carbon electrode

An amperometric sensor for the detection of difenidol, a tertiary amine-containing analyte, was proposed. Ruthenium(II) tris(bipyridine)/multi-walled carbon nanotubes/Nafion composite film was suggested to modify the glassy carbon electrode. The modified electrode was shown to be an excellent amperometric sensor for the detection of difenidol hydrochloride. The linear range is from 1.0 × 10⁻⁶ to 3.3 × 10⁻⁵ M with a correlation coefficient of 0.998. The limit of detection was 5 × 10⁻⁷ M, which was obtained through experimental determination based on a signal-to-noise ratio of three. The sensor was employed to the determination of the active ingredients in the tablets containing difenidol hydrochloride.     

Carbon paste electrode modified with silver thimerosal for the potentiometric flow injection analysis of silver(I)

The utility of carbon paste electrode modified with silver ethylmercurythiosalicylate (silver thimerosal) in both static mode and flow injection analysis (FIA) is demonstrated. The electrode was fully characterized in terms of composition, response time, thermal stability, usable pH and ionic strength ranges. It has been shown that diisononyl phthalate (DINP) acts as more suitable solvent mediator for preparation of the electrode, which exhibits linear response range to Ag(I) extending from 5.0 × 10⁻⁷ to 1.0 × 10⁻³ M with detection limit of 2.5 × 10⁻⁷ M and Nernstian slope of 59.3 ± 1.0 mV/decade. The proposed chemically modified carbon paste electrode shows a very good selectivity for Ag(I) over a wide variety of metal ions and successfully used for the determination of the silver content of silver sulphadiazine (burning cream) and developed radiological films. The electrode was also used as an indicator electrode in the potentiometric titration of thiopental and thimerosal with AgNO₃.     

Bienzymatic amperometric biosensor for glucose based on polypyrrole/ceramic carbon as electrode material

A novel amperometric biosensor utilizing two enzymes, glucose oxidase (GOD) and horseradish peroxidase (HRP), was developed for the cathodic detection of glucose. The glucose biosensor was constructed by electrochemical formation of a polypyrrole (PPy) membrane in the presence of GOD on the surface of a HRP-modified sol-gel derived-mediated ceramic carbon electrode. Ferrocenecarboxylic acid (FCA) was used as mediator to transfer electron between enzyme and electrode. In the hetero-bilayer configuration of electrode, all enzymes were well immobilized in electrode matrices and showed favorable enzymatic activities. The amperometric detection of glucose was carried out at +0.16 V (versus saturated calomel reference electrode (SCE)) in 0.1 M phosphate buffer solution (pH 6.9) with a linear response range between 8.0×10⁻⁵ and 1.3×10⁻³ M glucose. The biosensor showed a good suppression of interference in the amperometric detection.     

Carbon nanotube composite coated platinum electrode for detection of Cr(III) in real samples

This paper demonstrates the application of composite multi-walled carbon nanotube (MWNT) polyvinylchloride (MWNT-PVC) based on 1,5-diphenylcarbazide as chromium ionophore in potentiometric measurement. The sensor shows a good Nernstian slope of 19.52 ± 0.40 mV/decade in a wide linear range concentration of 6.3 × 10⁻⁸ to 1.0 × 10⁻² M for Cr(NO₃)₃. The detection limit of this electrode was found to be 3.2 × 10⁻⁸ M of Cr(NO₃)₃ and is applicable in a pH range of 3.0-6.8. It has a short response time of about 10 s. This chromium electrode has a good selectivity over 16 various metal ions. The practical analytical utility of this electrode was demonstrated by measurement of Cr(III) in drinking water and mineral water samples without any serious preliminary pre-treatment and chromium in multivitamin.     

Voltammetric determination of adenosine and guanosine using fullerene-C60-modified glassy carbon electrode

A fullerene-C₆₀-modified glassy carbon electrode (GCE) is used for the simultaneous determination of adenosine and guanosine by differential pulse voltammetry. Compared to a bare glassy carbon electrode, the modified electrode exhibits an apparent shift of the oxidation potentials in the cathodic direction and a marked enhancement in the voltammetric peak current response for both the biomolecules. Linear calibration curves are obtained over the concentration range 0.5 μM-1.0 mM in 0.1 M phosphate buffer solution at pH 7.2 with a detection limit of 3.02 × 10⁻⁷ M and 1.45 × 10⁻⁷ M for individual determination of adenosine and guanosine, respectively. The interference studies showed that the fullerene-C₆₀-modified glassy carbon electrode exhibited excellent selectivity in the presence of hypoxanthine, xanthine, uric acid and ascorbic acid. The proposed procedure was successfully applied to detect adenosine and guanosine in human blood plasma and urine, without any preliminary pre-treatment.     

Improved potentiometric response of solid-contact lanthanum (III) selective electrode

For the first time, the analytical application of integrate ionophore-transducer material based on magnetic graphene hybrids and 2,2-dithiodipyridine (DTDP) in solid-contact lanthanum (III) selective electrode is reported. The attachment of Fe₃O₄ nanoparticles (NPs) to graphene oxide (GO) for magnetic graphene hybrid is achieved by covalent bonding, and the universal problem, Fe₃O₄ NPs may easily leach out from the graphene during application, is successfully solved by the method above. The proposed electrode exhibits an excellent near-Nernstian response to lanthanum (III) ranging from 1.0 × 10⁻⁹ to 1.0 × 10⁻³ M with a slope of 17.81 mV/dec. Moreover, the excellent performance on fairly good selectivity, wide applicable pH range (3.0^_8.0), fast response time (10 s) and long life time (2 months) reveal the superiority of the electrode. Most importantly, we have made a great improvement in the detection limit (2.75 × 10⁻¹⁰ M), which brings new dawn to the real-time detection of lanthanum (III) using ion selective electrode.     

Organically nanoporous silica gel based on carbon paste electrode for potentiometric detection of trace Cr(III)

A new ion-selective electrode (ISE) for the detection of trace chromium(III) was designed by using 2-acetylpyridine and nanoporous silica gel (APNSG)-functionalized carbon paste electrode (CPE). The presence of APNSG acted as not only a paste binder, but also a reactive material. With 7.5 wt% APNSG proportions, the developed electrode exhibited wide dynamic range of 1.0 × 10⁻⁸ to 1.0 × 10⁻³ M toward Cr(III) with a detection limit of 8.0 × 10⁻⁹ M and a Nernstian slope of 19.8 ± 0.2 mV decade⁻¹. The as-prepared electrode displayed rapid response (∼55 s), long-time stability, and high sensitivity. Moreover, the potentiometric responses could be carried out with wide pH range of 1.5-5.0. In addition, the content of Cr(III) in food samples, e.g. coffee and tea leaves, has been assayed by the developed electrode, atomic absorption spectrophotometer (AAS) and atomic emission spectrometer (ICP-AES), respectively, and consistent results were obtained. Importantly, the response mechanism of the proposed electrode was investigated by using AC impedance and UV-vis spectroscopy.     

Immobilization of [Cu(bpy)2]Br2 complex onto a glassy carbon electrode modified with α-SiMo12O40 and single walled carbon nanotubes: Application to nanomolar detection of hydrogen peroxide and bromate

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.     

Electrocatalytic reduction of nitrite at polypyrrole nanowire-platinum nanocluster modified glassy carbon electrode

Pt nanoclusters were deposited in polypyrrole (PPy) nanowires by cyclic voltammetry method, fabricating a PPy-Pt nanocomposite on glassy carbon electrode (PPy-Pt/GCE). The electrocatalytic reduction of nitrite at PPy-Pt/GCE has been investigated using 0.5 M H₂SO₄ solution. The sensor exhibited excellent electrocatalytic activity toward nitrite reduction. In acidic medium, the cyclic voltammetry at 20 mV s^− 1 gave a nitrite reduction peak at − 0.124 V with 0.566 μA μM^− 1 current sensitivity in the range of 5.0 × 10^− 7-1.0 × 10^− 3 M. The detection limit was 1.5 × 10^− 7 M (s/n = 3). The proposed method was successfully applied in the detection of nitrite in real water samples and obtained satisfactory results. The PPy-Pt composite modified electrode had good storage stability, reproducibility and anti-interference ability.     

Electrochemical analysis of methylparathion pesticide by a gemini surfactant-intercalated clay-modified electrode

In this study, an hybrid material obtained by the intercalation of a gemini surfactant between the layers of smectite-type clay, was fully characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and N₂ adsorption-desorption experiments (BET method). To ascertain the intercalation process of the starting clay by the dimeric surfactant, the permselectivity and ion exchange properties of the organoclay were investigated by ion exchange voltammetry using [Fe(CN)₆]³⁻ and [Ru(NH₃)₆]³⁺ as redox probes, by the means of a clay film-modified electrode. Due to its organophilic character, the surfactant-intercalated complex was evaluated as electrode modifier for the accumulation of methylparathion (MP) pesticide. The electroanalytical procedure involves two steps: preconcentration under open-circuit followed by voltammetric detection by square wave voltammetry: the peak current obtained (after 5 min preconcentration in 4 × 10⁻⁵ mol L⁻¹ MP) on a glassy carbon electrode coated by a thin film of the modified clay was more than five times higher than that exhibited by the same substrate covered by a film of the pristine clay. This opens the way to the development of a sensitive method for the detection of the pesticide. Many parameters that can affect the stripping response (surfactant loading of the hybrid material, film composition, pH of the detection medium, preconcentration time, electrolysis potential and duration as well as some other instrumental parameters) were systematically investigated to optimize the sensitivity of the organoclay-modified electrode. After optimization, a linear calibration curve for MP was obtained in the concentration range from 4 × 10⁻⁷ to 8.5 × 10⁻⁶ mol L⁻¹ in acetate buffer (pH 5), with a detection limit of 7 × 10⁻⁸ mol L⁻¹ (signal-to-noise ratio equal to 3). The interference effect of various inorganic ions likely to influence the stripping determination of the pesticide was also examined, and the described method was applied to spring water analysis.     

Seed-mediated synthesis of copper nanoparticles on carbon nanotubes and their application in nonenzymatic glucose biosensors

In this paper, for the first time, Cu nanoparticles (CuNPs) were prepared by seed-mediated growth method with Au nanoparticles (AuNPs) playing the role of seeds. Carbon nanotubes (CNTs) and AuNPs were first dropped on the surface of glassy carbon (GC) electrode, and then the electrode was immersed into growth solution that contained CuSO₄ and hydrazine. CuNPs were successfully grown on the surface of the CNTs. The modified electrode showed a very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium, which was utilized as the basis of the fabrication of a nonenzymatic biosensor for electrochemical detection of glucose. The biosensor can be applied to the quantification of glucose with a linear range covering from 1.0 × 10⁻⁷ to 5 × 10⁻³ M and a low detection limit of 3 × 10⁻⁸ M. Furthermore, the experiment results also showed that the biosensor exhibited good reproducibility and long-term stability, as well as high selectivity with no interference from other oxidable species.     

A selective modified carbon paste electrode for determination of cyanide using tetra-3,4-pyridinoporphyrazinatocobalt(II)

A chemically modified carbon paste electrode with 3,4-tetra pyridinoporphirazinatocobalt(II) (Co(3,4 tppa) was applied to the determination of free cyanide ion. The electrode has a linear range between 1.5 × 10⁻⁵ M and 1.0 × 10⁻² M with a Nernstian slope of 60 ± 1.5 mV/decade and its detection limit is 9 × 10⁻⁶ M. The response time of electrode is 5 min. The proposed electrode was applied successfully for the determination of cyanide in commercially available spring water. Some anions, such as SCN⁻, I⁻, Cl⁻, Br⁻ and oxalate that are usually serious interfering species for most of cyanide selective electrodes, did not have any interfering effect for this proposed electrode.     

Determination of l-histidine by modified carbon paste electrode using tetra-3,4-pyridinoporphirazinatocopper(II)

This paper describes a potentiometric method for determination of l-histidine (l-his) in aqueous media, using a carbon paste electrode modified with tetra-3,4-pyridinoporphirazinatocopper(II) (Cu (3,4tppa)). The electrode exhibits linear response to the logarithm of the concentration of l-histidine from 2.4 × 10⁻⁵ to 1.0 × 10⁻² M, with a response slope of −49.5 ± 1 mV and response time of about 1.5 min. The detection limit according to IUPAC recommendation was 2.0 × 10⁻⁵ M. The proposed electrode shows a good selectivity for l-his over a wide variety of anions. This chemically modified carbon paste electrode was successfully used for the determination of l-his in a synthetic serum and RANDOX control serum solutions.     

Cu nanoparticles incorporated polypyrrole modified GCE for sensitive simultaneous determination of dopamine and uric acid

Cu nanoparticles have been electrochemically incorporated polypyrrole film that was used for modification of the glassy carbon electrode surface. The performance of the electrode has been characterized by cyclic voltammetry and atomic force microscopy. The electrode has shown high electrocatalytic activity towards the oxidation of dopamine (DA) and uric acid (UA) simultaneously in a phosphate buffer solution (pH 7.00). The electrocatalytic oxidation currents of UA and DA were found linearly related to concentration over the range 1 × 10⁻⁹ to 1 × 10⁻⁵ M for UA and 1 × 10⁻⁹ to 1 × 10⁻⁷ M for DA using DPVs method. The detection limits were determined as 8 × 10⁻¹⁰ M (s/n = 3) for UA and 8.5 × 10⁻¹⁰ M (s/n = 3) for DA at a signal-to-noise ratio of 3.     

Amperometric detection of dopamine based on tyrosinase-SWNTs-Ppy composite electrode

A novel 3-dimensional single wall carbon nanotubes (SWNTs)-polypyrrole (Ppy) composite was prepared as an electrode by chemically polymerizing polypyrrole onto SWNTs using a LiClO₄ oxidant. This composite electrode was characterized by scanning electron microscopy (SEM) and cyclic voltammetry with 1 mM [Fe(CN)₆]⁻³/[Fe(CN)₆]⁻⁴. The SWNTs were thickly coated with chemically polymerized polypyrrole and the composite had many surface pores and crevices which could enhance mass transfer. The SWNTs-Ppy composite electrode showed a large specific surface area (30 m²/g) and a good reproducible current response, at about 100 times the peak current of a glassy carbon electrode (GCE). The diffusion coefficient was calculated to be 4.81 × 10⁻⁶ cm²/s. As a biosensor application, tyrosinase was immobilized on the functionalized SWNTs and tyrosinase-SWNTs-Ppy composite was prepared in the same manner. This tyrosinase-SWNT-Ppy composite electrode was used for amperometric detection of dopamine in the presence of ascorbic acid and showed high sensitivity (467 mA/M cm²) and lower detection limit (5 μM) compared to previous reports.     

Potentiometric stripping analysis of methyl and ethyl parathion employing carbon nanoparticles and halloysite nanoclay modified carbon paste electrode

Carbon nanoparticles (CNPs) and halloysite nanoclay (HNC) modified carbon paste electrode (HNC–CNP–CPE) was developed for the determination of methyl parathion (MP) and ethyl parathion (EP). The electrochemical behavior of these molecules was investigated employing cyclic voltammetry (CV), chronocoulometry (CC), electrochemical impedance spectroscopy (EIS) and potentiometric stripping analysis (PSA). After optimization of analytical conditions employing this electrode at pH 5.0 in acetate buffer (0.1 M), the peak currents were found to vary linearly with its concentration in the range of 1.55 × 10⁻⁹ to 3.67 × 10⁻⁶ M and 1.21 × 10⁻⁹ to 4.92 × 10⁻⁶ M for MP and EP, respectively. The detection limits (S/N = 3) of 4.70 × 10⁻¹⁰ M and 3.67 × 10⁻¹⁰ M were obtained for MP and EP, respectively, using PSA. The prepared modified electrode showed several advantages such as simple preparation method, high sensitivity, very low detection limits and excellent reproducibility. The proposed method was employed for the determination of MP and EP in fruits, vegetables, water and soil samples.