Electrochemical determination of NADH using a glassy carbon electrode modified with Fe3O4 nanoparticles and poly-2,6-pyridinedicarboxylic acid, and its application to the determination of antioxidant capacity

We have prepared a glassy carbon electrode modified with poly-2,6-pyridinedicarboxylic acid and with magnetic Fe₃O₄ nanoparticles. This modification enhances the effective surface area and the electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) in addition to providing positively charged groups for electrostatic assembly of the phosphate group of NADH. The modified electrode responds linearly to NADH in the range from 5?×?10^?8 to 2.5?×?10^?5?M and gives a lower detection limit of 1?×?10^?8?M. It displays satisfactory selectivity and reproducibility. The sensor was applied to rapid screening of plant extracts for their antioxidant properties.

Novel glucose biosensor based on a glassy carbon electrode modified with hollow gold nanoparticles and glucose oxidase

A novel glucose biosensor is presented as that based on a glassy carbon electrode modified with hollow gold nanoparticles (HGNs) and glucose oxidase. The sensor exhibits a better differential pulse voltammetric response towards glucose than the one based on conventional gold nanoparticles of the same size. This is attributed to the good biological conductivity and biocompatibility of HGNs. Under the optimal conditions, the sensor displays a linear range from 2.0?×?10^?6 to 4.6?×?10^?5?M of glucose, with a detection limit of 1.6?×?10^?6?M (S/N?=?3). Good reproducibility, stability and no interference make this biosensor applicable to the determination of glucose in samples such as sports drinks.

Iodide-induced adsorption of lead(II) ion on a glassy carbon electrode modified with ferroferric oxide nanoparticles

Spherical Fe₃O₄ nanoparticles (NPs) were prepared by hydrothermal synthesis and characterized by scanning electron microscopy and X-ray diffraction. A glassy carbon electrode was modified with such NPs to result in a sensor for Pb(II) that is based on the strong inducing adsorption ability of iodide. The electrode gives a pair of well-defined redox peaks for Pb(II) in pH 5.0 buffer containing 10 mM concentrations of potassium iodide, with anodic and cathodic peak potentials at ?487 mV and ?622 mV (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.10 to 44 nM, and the detection limit is 40 pM at an SNR of 3. The sensor exhibits high selectivity and reproducibility.

Synthesis of multi-branched gold nanoparticles by reduction of tetrachloroauric acid with Tris base, and their application to SERS and cellular imaging

A biosensor for hydrogen peroxide was constructed by immobilizing horseradish peroxidase on chitosan-wrapped NiFe₂O₄ nanoparticles on a glassy carbon electrode (GCE). The electron mediator carboxyferrocene was also immobilized on the surface of the GCE. UV?Cvis spectra, Fourier transform IR spectra, scanning electron microscopy, and electrochemical impedance spectra were acquired to characterize the biosensor. The experimental conditions were studied and optimized. The biosensor responds linearly to H₂O₂ in the range from 1.0?×?10^?5 to 2.0?×?10^?3?M and with a detection limit of 2.0?×?10^?6?M (at S/N?=?3).

Preparation of an amperometric sensor for norfloxacin based on molecularly imprinted grafting photopolymerization

A sensitive amperometric sensor for norfloxacin (NF) was introduced. The receptor layer was prepared by molecularly imprinted photopolymerization of acrylamide and trimethylolpropane trimethacrylate on the surface of a gold electrode. The binding mechanism of the molecularly imprinted polymer was explored by ultraviolet (UV) and infrared (IR) spectroscopy. The chemosensor was characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance (EI), and scanning electron microscopy (SEM). The electrode prepared by photopolymerization has a better recognition ability to template molecules than that of electropolymerization and NIP. Some parameters affecting sensor response were optimized. Norfloxacin was detected by measurements of an amperometric i–t curve. The linear relationships between current and logarithmic concentration are obtained from 1.0?×?10^?9 to 1.0?×?10^?3?mol?L^?1. The detection limit of the sensor was 1.0?×?10^?10?mol?L^?1. The proposed method is sensitive, simple, and cheap, and is applied to detect NF in human urine successfully.

Molecular imprinting polymer electrosensor based on gold nanoparticles for theophylline recognition and determination

An electrochemical sensor for theophylline (ThPh) was prepared by electropolymerizing o-phenylenediamine on a glassy carbon electrode in the presence of ThPh via cyclic voltammetry, followed by deposition of gold nanoparticles using a potentiostatic method. The effects of pH, ratio between template molecule and monomer, number of cycles for electropolymerization, and of the solution for extraction were optimized. The current of the electro-active model system hexacyanoferrate(III) and hexacyanoferrate(IV) decreased linearly with successive addition of ThPh in the concentration range between 4.0?×?10^?7?~?1.5?×?10^?5 mol·L^?1 and 2.4?×?10^?4?~?3.4?×?10^?3 mol·L^?1, with a detection limit of 1.0?×?10^?7 mol·L^?1. The sensor has an excellent recognition capability for ThPh compared to structurally related molecules, can be regenerated and is stable.

Ultrasensitive determination of hydrazine using a glassy carbon electrode modified with Pyrocatechol Violet electrodeposited on single walled carbon nanotubes

A glassy carbon electrode (GCE) was modified with pyrocatechol violet (PCV) that was electrodeposited on single walled carbon nanotubes (SWCNTs) via continuous cycling between 0 and 0.9 V (vs. SCE). The resulting electrode exhibits excellent electrocatalytic activity towards the oxidation of hydrazine at 0.3 V. The apparent surface coverage of the electrode is at least 24 times higher (2.7?×?10^?10 mol cm^?2) than that obtained with a bare GCE (1.1?×?10^?11 mol cm^?2). This is attributed to a remarkably strong synergistic effect between the acid-pretreated SWCNTs and the electrodeposited PCV coating. Response is fast (2 s) and sensitive (281 mA M^?1 cm^?2). Other features include a wide linear range (150 nM to 0.4 mM) and a low detection limit (150 nM at an SNR of 3). The sensor has been successfully applied to the determination of hydrazine in water and cigarette samples with good accuracy and precision. In addition, the morphology and the wetting properties of the coating were studied by scanning electromicroscopy and contact angle measurements.

Biocompatible and label-free amperometric immunosensor for hepatitis B surface antigen using a sensing film composed of poly(allylamine)-branched ferrocene and gold nanoparticles

An amperometric immunosensor has been developed for sensitive determination of hepatitis B surface antigen as a model protein. A glassy carbon electrode was modified with an assembly of positively charged poly(allylamine)-branched ferrocene (PAA-Fc) and negatively charged gold nanoparticles (Au NPs). The formation of PAA-Fc effectively avoids the leakage of Fc, retains its electrochemical activity, and enhances the conductivity of the composite. The adsorption of Au NPs onto the PAA-Fc matrix provides sites for the immobilization of the antigen and a favorable micro-environment to maintain its activity. The morphologies and electrochemistry of the sensing film were investigated via scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Factors influencing the performance of the immunosensor were studied in detail. The concentration of the antigen can be quantitated (by measuring the decrease of the amperometric response resulting from the specific binding between antigen and antibody) in the range between 0.1 and 150?ng?mL^?C1, with a detection limit of 40?pg?mL^?C1 (S/N = 3). The method is economical, efficient, and potentially attractive for clinical immunoassays.

Self-assembly of ultra-small gold nanoparticles on an indium tin oxide electrode for the enzyme-free detection of hydrogen peroxide

A novel enzyme-free electrochemical sensor for H₂O₂ was fabricated by modifying an indium tin oxide (ITO) support with (3-aminopropyl) trimethoxysilane to yield an interface for the assembly of colloidal gold. Gold nanoparticles (AuNPs) were then immobilized on the substrate via self-assembly. Atomic force microscopy showed the presence of a monolayer of well-dispersed AuNPs with an average size of ~4 nm. The electrochemical behavior of the resultant AuNP/ITO-modified electrode and its response to hydrogen peroxide were studied by cyclic voltammetry. This non-enzymatic and mediator-free electrode exhibits a linear response in the range from 3.0?×?10^?5 M to 1.0?×?10^?3 M (M?=?mol?·?L^?1) with a correlation coefficient of 0.999. The limit of detection is as low as 10 nM (for S/N?=?3). The sensor is stable, gives well reproducible results, and is deemed to represent a promising tool for electrochemical sensing.

A solid state Cr(VI) ion-selective electrode based on polypyrrole

We report on a graphite electrode onto which polypyrrole was electrodeposited and then doped with chromate ion. This electrode can serve as a Cr(VI)-selective solid-state electrode. Electropolymerization of pyrrole was performed potentiostatically at 0.80?V (vs. SCE) using battery graphite as the working electrode in a solution containing 0.10?M of pyrrole and 20?mM of chromate. A platinum wire was used as an auxiliary electrode. The new electrode displays high selectivity, a very wide dynamic range, a sufficiently fast response time and a good shelf lifetime. It shows a linear Nernstian response over 1.0?×?10^?6 to 1.0?×?10^?1?M concentration range (with a slope of 26.55?±?0.20?mV per log of concentration). The detection limit is 0.5?μM, and the pH optimum is 7.0.

Nonenzymatic hydrogen peroxide sensor based on a glassy carbon electrode modified with electrospun PdO-NiO composite nanofibers

A glassy carbon electrode was modified with PdO-NiO composite nanofibers (PdO-NiO-NFs) and applied to the electrocatalytic reduction of hydrogen peroxide (H₂O₂). The PdO-NiO-NFs were synthesized by electrospinning and subsequent thermal treatment, and then characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Factors such as the composition and fraction of nanofibers, and of the applied potential were also studied. The sensor exhibits high sensitivity for H₂O₂ (583.43 μA?·?mM^?1?·?cm^?2), a wide linear range (from 5.0 μM to 19 mM), a low detection limit (2.94 μM at an SNR of 3), good long term stability, and is resistant to fouling.

Ultra-sensitive electrochemical DNA biosensor based on signal amplification using gold nanoparticles modified with molybdenum disulfide,graphene and horseradish peroxidase

We have developed an ultra-sensitive electrochemical DNA biosensor by assembling probe ssDNA on a glassy carbon electrode modified with a composite made from molybdenum disulfide, graphene, chitosan and gold nanoparticles. A thiol-tagged DNA strand coupled to horseradish peroxidase conjugated to AuNP served as a tracer. The nanocomposite on the surface acts as relatively good electrical conductor for accelerating the electron transfer, while the enzyme tagged gold nanoparticles provide signal amplification. Hybridization with the target DNA was studied by measuring the electrochemical signal response of horseradish peroxidase using differential pulse voltammetry. The calibration plot is linear in the 5.0?×?10^?14 and 5.0?×?10^?9 M concentration range, and the limit of detection is 2.2?×?10^?15 M. The biosensor displays high selectivity and can differentiate between single-base mismatched and three-base mismatched sequences of DNA. The approach is deemed to provide a sensitive and reliable tool for highly specific detection of DNA.

Electrochemical investigation of a glassy carbon electrode modified with carbon nanotubes decorated with (poly)crystalline gold

Multiwalled carbon nanotubes with nanosized sputtered gold were used to modify a glassy carbon electrode (GCE). The substrate was characterized by scanning electron microscopy (SEM), X-ray diffraction, cyclic voltammetry and amperometry. SEM micrographs indicated an uniform coverage of the carbon nanotubes with nanosized (poly)crystalline gold. Cyclic voltammetry reveals that peak separation of the unmodified GCE in the presence of 1?mM ferricyanide is 131?mV, but 60?mV only for the modified GCE. In addition, the oxidation of NADH (1?mmol?L^?1 solution) begins at negative potentials (around ?100?mV vs. Ag/AgCl), and the anodic peak potential (corresponding to the irreversible oxidation of NADH) is found at +94?mV. The effect of pH on the electrocatalytic activity was studied in the range from 5.4 to 8.0. The relationship between the anodic peak potential and the pH indicated a variation of ?33.5?mV/pH which is in agreement with a two-electron and one-proton reaction mechanism. Amperometry, performed at either ?50 or +50?mV vs. an Ag/AgCl reference electrode, indicates that the modified electrode is a viable amperometric sensor for NADH. At a working potential of +50?mV, the response to NADH is linear in the concentration range from 1 to 100???mol?L^?1, with an RSD of 6% (n?=?4).

Iron nanoparticles decorated graphene-multiwalled carbon nanotubes nanocomposite-modified glassy carbon electrode for the sensitive determination of nitrite

In the present work, we described the preparation of iron nanoparticles decorated graphene-multiwalled carbon nanotubes nanocomposite (GR-MWCNTs/FeNPs) modified glassy carbon electrode (GCE) and its application for the sensitive determination of nitrite. First, GR-MWCNTs/FeNPs nanocomposite has been prepared by a simple solution-based approach via chemical reduction and then it was characterized. Afterwards, GR-MWCNTs/FeNPs/GCE was prepared and employed for the electrocatalysis of nitrite. Electrocatalytic oxidation of nitrite at the GR-MWCNTs/FeNPs/GCE has been significantly improved in terms of both reduction in overpotential and increase in peak current. Therefore, the modified electrode was employed for amperometric determination of nitrite which exhibited excellent analytical parameters with wide linear range of 1?×?10^?7 M to 1.68?×?10^?3 M and very low detection limit of 75.6 (±1.3)?nM. The proposed sensor selectively detects nitrite even in the presence of high concentration of common ions and biological interferrants. Good recoveries achieved for the determination of nitrite in various water samples reveal the promising practicality of the sensor. In addition, the sensor displays an acceptable repeatability and reproducibility along with appreciable storage and excellent operational stabilities.

Amperometric nonenzymatic glucose sensor based on a glassy carbon electrode modified with a nanocomposite made from nickel(II) hydroxide nanoplates and carbon nanofibers

We report on a highly sensitive and selective nonenzymatic glucose sensor based on a glassy carbon electrode modified with a composite prepared from nickel(II) hydroxide nanoplates and carbon nanofibers. The nanocomposite was characterized by scanning electron microscopy and powder X-ray diffraction. Electrodes modified with pure Ni(OH)₂ and with the nanocomposite were characterized by electrochemical impedance spectroscopy. Cyclic voltammetric and amperometric methods were used to investigate the catalytic properties of the modified electrodes for glucose electrooxidation in strongly alkaline solution. The sensor exhibits a wide linear range (from 0.001 to 1.2 mM), a low detection limit (0.76 μM), fast response time (< 5 s), high sensitivity (1038.6 μA?·?mM^?1?·?cm^?2), good reproducibility, and long operational stability. Application of the nonenzymatic sensor for monitoring glucose in real samples was also demonstrated.

Sensor for lead(II) ion based on a glassy carbon electrode modified with double-stranded DNA and ferric oxide nanoparticles

Shuttle-like Fe₂O₃ nanoparticles (NPs) were prepared by microwave-assisted synthesis and characterized by scanning electron microscopy and X-ray diffraction. The NPs were immobilized on a glassy carbon electrode and then covered with dsDNA. The resulting electrode gives a pair of well-defined redox peaks for Pb(II) at pH 6.0, with anodic and cathodic peak potentials occurring at ?0.50?V and ?0.75?V (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.12 to 40?nM, and the detection limit is 0.1?nM at a signal-to-noise ratio of 3. The sensor exhibits high selectivity and reproducibility.

Highly sensitive methanol chemical sensor based on undoped silver oxide nanoparticles prepared by a solution method

We have prepared silver oxide nanoparticles (NPs) by a simple solution method using reducing agents in alkaline medium. The resulting NPs were characterized by UV–vis and FT-IR spectroscopy, X-ray powder diffraction, and field-emission scanning electron microscopy. They were deposited on a glassy carbon electrode to give a sensor with a fast response towards methanol in liquid phase. The sensor also displays good sensitivity and long-term stability, and enhanced electrochemical response. The calibration plot is linear (r ²?=?0.8294) over the 0.12?mM to 0.12?M methanol concentration range. The sensitivity is ~2.65?μAcm^?2?mM^?1, and the detection limit is 36.0?μM (at a SNR of 3). We also discuss possible future prospective uses of this metal oxide semiconductor nanomaterial in terms of chemical sensing.

A glassy carbon electrode modified with a film composed of cobalt oxide nanoparticles and graphene for electrochemical sensing of H2O2

We have prepared a graphene-based hybrid nanomaterial by electrochemical deposition of cobalt oxide nanoparticles (CoO_xNPs) on the surface of electrochemically reduced graphene oxide deposited on a glassy carbon electrode (GCE). Scanning electron microscopy and cyclic voltammetry were used to characterize the immobilized nanoparticles. Electrochemical determination of H₂O₂ is demonstrated with the modified GCE at pH 7. Compared to GCEs modified with CoO_xNPs or graphene sheets only, the new electrode displays larger oxidative current response to H₂O₂, probably due to the synergistic effects between the graphene sheets and the CoO_xNPs. The sensor responds to H₂O₂ with a sensitivity of 148.6 μA mM^?1 cm^?2 and a linear response range from 5 μM to 1 mM. The detection limit is 0.2 μM at a signal to noise ratio (SNR) of three. The method was successfully applied to the determination of H₂O₂ in hydrogen peroxide samples.

An enzymatic glucose biosensor based on a glassy carbon electrode modified with manganese dioxide nanowires

A glassy carbon electrode was modified with β-manganese dioxide (β-MnO₂), and glucose oxidase (GOx) was immobilized on its surface. The β-MnO₂ nanowires were prepared by a hydrothermal method and characterized by scanning electron microscopy and powder X-ray diffraction. They were then dispersed in Nafion solution and cast on the glassy carbon electrode (GCE) to form an electrode modified with β-MnO₂ nanowires that exhibits improved sensitivity toward hydrogen peroxide. If GOx is immobilized in the surface, the β-MnO₂ acts as a mediator, and Nafion as a polymer backbone. The fabrication process was characterized by electrochemical impedance spectroscopy, and the sensor and its materials were characterized by cyclic voltammetry and amperometry. The biosensor enables amperometric detection of glucose with a sensitivity of 38.2 μA?·?mM^?1?·?cm^?2, and a response time of?<?5 s. This study also demonstrates the feasibility of realizing inexpensive, reliable, and high-performance biosensors using MnO₂ nanowires.

The electrochemistry of uric acid at a gold electrode modified with L-cysteine, and its application to sensing uric urine

The electrochemistry of uric acid at a gold electrode modified with a self-assembled film of L-cysteine was studied by cyclic voltammetry and differential pulse voltammetry. Compared to the bare gold electrode, uric acid showed better electrochemical response in that the anodic peak current is stronger and the peak potential is negatively shifted by about 100 mV. The effects of experimental conditions on the oxidation of uric acid were tested and a calibration plot was established. The differential pulse response to uric acid is linear in the concentration range from 1.0?×?10^?6 to ~?1.0?×?10^?4 mol?L^?1 (r?=?0.9995) and from 1.0?×?10^?4 to ~?5.0?×?10^?4 mol?L^?1 (r?=?0.9990), the detection limit being 1.0?×?10^?7 mol?L^?1 (at S/N?=?3). The high sensitivity and good selectivity of the electrode was demonstrated by its practical application to the determination of uric acid in urine samples.