Amperometric biosensors for glucose based on carbon paste modified electrodes

The modification of carbon-paste electrodes by incorporation of the enzyme glucose oxidase (GOD) is described. The resulting probes can be operated as amperometric glucose sensors in the presence or absence of a mediator (1,1'-dimethylferrocene) mixed into the paste. Extended linear calibration ranges have been obtained up to 90 and 5OmM glucose respectively. The electrode responses were rapid, reaching steady-state values within 30-40 sec. Advantages of using a GOD-paste formulation are suggested. Plasma glucose assays were correlated with spectrophotometric determinations based on glucose oxidase (y = 1.07x - 0.16, r = 0.973, n = 17).     

Bioelectrochemical studies on catalase modified glassy carbon paste electrodes

The enzyme catalase (EC: 1.11.1.6) has been covalently coupled onto the surface of glassy carbon (GC) powder matrix using a 16 atom spacer arm. The enzyme coupled powder was made into a paste electrode that was used to study the electrochemical properties. Standard electrochemical techniques like cyclic voltammetry, differential pulse voltammetry and flow injection analysis studies were carried out using this paste electrode. The cyclic voltammogram of the modified paste exhibited a clear increase in the reduction peak at −180 mV in the presence of hydrogen peroxide. The potential at which maximum Faradaic activity was observed was determined using differential pulse voltammetry, which showed a clear peak at −100 mV. This potential was used to monitor the response of the electrode to varying substrate concentrations using a home made setup for flow injection analysis. A linear increase in the current values in the range 0.1–1 mM hydrogen peroxide concentration was observed in our system.     

Dopamine sensor based on a glassy carbon electrode modified with a reduced graphene oxide and palladium nanoparticles composite

We report on a sensitive electrochemical sensor for dopamine (DA) based on a glassy carbon electrode that was modified with a nanocomposite containing electrochemically reduced graphene oxide (RGO) and palladium nanoparticles (Pd-NPs). The composite was characterized by scanning electron microscopy, energy dispersive spectroscopy, and electrochemical impendence spectroscopy. The electrode can oxidize DA at lower potential (234 mV vs Ag/AgCl) than electrodes modified with RGO or Pd-NPs only. The response of the sensor to DA is linear in the 1–150 μM concentration range, and the detection limit is 0.233 μM. The sensor was applied to the determination of DA in commercial DA injection solutions.

A novel electrochemiluminescence glucose biosensor based on platinum nanoflowers/graphene oxide/glucose oxidase modified glassy carbon electrode

A novel electrochemiluminescence (ECL) biosensor based on platinum nanoflowers (PtNFs)/graphene oxide (GO)/glucose oxidase (GODx) was discovered for glucose detection. PtNFs/GO was synthesized using a nontoxic, rapid, one-pot and template-free method and characterized by transmission electron microscopy (TEM) and high-resolution TEM techniques. The as-prepared PtNFs/GO with clean surface and multiporous structure was used to assemble GODx to form a glucose biosensor. Based on ECL results, the PtNFs/GO/GODx film-modified electrode displayed a high electrocatalytic activity towards the oxidation of glucose, which generated hydrogen peroxide (H₂O₂) to react with the luminol radicals thus enhanced the luminol ECL. Under the optimized conditions, two linear regions of ECL intensity to glucose concentration were valid in the range from 5 to 80 μmol/L (r?=?0.9957) and 80 to 1,000 μmol/L (r?=?0.9909) with a detection limit (S/N?=?3) of 2.8 μmol/L. In order to verify the reliability, the thus-fabricated biosensor was applied to determine the glucose concentration in glucose injection, glucose functional drink, and blood serum. The results indicated that the proposed biosensor presented good characteristics in terms of high sensitivity and good reproducibility for glucose determination, promising the applicability of this sensor in practical analysis.     

Mediated amperometric biosensors for lactic acid based on carbon paste electrodes modified with baker's yeast Saccharomyces cerevisiae

Carbon paste electrodes modified with baker's yeast Saccharomyces cerevisiae (a source of flavocytochrome b(2)) were investigated as amperometric biosensors for lactic acid. Phenazine methosulphate was used as a mediator. The optimal operational conditions of the electrodes were: an operating potential 0.0 V, solution pH 7.2, concentration of phenazine methosulphate in solution 0.2 mM. A linear range in the dependence of the current responses on the concentration of lactic acid was up to 1 mM. The suitability of the electrodes for determination of lactic acid in milk and dairy products such as kefir and yoghurt was tested. The yeast cells in the paste remained viable at least for 1 month.     

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.

Voltammetric sensor for caffeine based on a glassy carbon electrode modified with Nafion and graphene oxide

A facile, one-step and template-free method has been developed for the electrodeposition of well-dispersed platinum nanoparticles (Pt-NPs) on a glassy carbon electrode. The effects of various inorganic anions and overpotential on the morphologies and dimensions of the final products were investigated. The resulting Pt-NPs show high electrocatalytic activity towards methanol oxidation and are less easily poisoned by carbon monoxide.

Sensing of picric acid with a glassy carbon electrode modified with CuS nanoparticles deposited on nitrogen-doped reduced graphene oxide

We describe the preparation of a nanohybrid consisting of nitrogen doped reduced graphene oxide and CuS nanoparticles (N-rGO/CuS) by in-situ microwave irradiation at weight ratios of 25/75, 50/50, and 75/25. The resulting nanohybrids were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, FTIR, spectroscopy, scanning electron and transmission electron microscopy, electrochemically by cyclic voltammetry and electrochemical impedance analysis. It is shown that the CuS nanoparticles are evenly decorated onto the N-rGO surface. The nanohybrids was placed on glassy carbon electrode (GCE) where they showed electro-reductive activity towards picric acid, typically at working voltages between ?0.2 and ?0.8 V (vs. SCE). Effects of pH value and scan rate were evaluated, and it is shown that two electrons are involved in electro-reduction. The detection limits of the GCE modified with various N-rGO/CuS hybrids (with 25/75, 50/50, and 75/25 wt%) are 6.2, 3.2, and 0.069 μM respectively. The method demonstrates its applicability in sensing of picric acid with good reproducibility.

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Graphical abstract Nitrogen doped reduced graphene oxide nanohybrids was synthesized for the detection of picric acid. A straightforward and preconcentration free analysis of picric acid was successfully demonstrated at nanomolar levels using the nanohybrids.

     

A glassy carbon electrode modified with carbon nanotubes and reduced graphene oxide decorated with platinum-gold nanoparticles for voltammetric aptasensing of urea

This article reports on a novel aptamer-based platform for the quantitation of urea by using an aptamer with high affinity and selectivity for urea. The surface of a glassy carbon electrode (GCE) was modified by drop casting a cocktail consisting of carbon nanotubes and reduced graphene oxide (rGO) decorated with platinum-gold nanoparticles. The urea aptamer was then immobilized on the nanocomposite via covalent conjugation. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to trace the modification of the GCE. Binding of urea caused the aptamer to be folded, and this result in an inhibition of the interfacial charge transfer rate when using hexacyanoferrate as an electrochemical redox probe. The change in redox current was quantified by differential pulse voltammetry, typically at a working voltage of 0.22 V vs. Ag/AgCl. The assay has a 1.9 pM detection limit, and the response is linear up to 150 nM concentration of urea. The superior selectivity and affinity of aptamer-modified GCE makes it a most useful tool for analysis of urea present in very low concentrations.

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Graphical abstract Schematic representation of different steps of aptasensor fabrication.

     

Glucose biosensors based on the immobilization of copper oxide and glucose oxidase within a carbon paste matrix

The performance of amperometric glucose biosensors based on the dispersion of glucose oxidase (GOx) and copper oxide within a classical carbon (graphite) paste composite is reported in this work. Copper oxide promotes an excellent electrocatalytic activity towards the oxidation and reduction of hydrogen peroxide, allowing a large decrease in the oxidation and reduction overpotentials, as well as an important enhancement of the corresponding currents. Therefore, it is possible to perform the glucose biosensing at low potentials where there is no interference even in large excess of ascorbic acid, uric acid or acetaminophen. The influence of the copper oxide and glucose oxidase content in the paste on the analytical performance of the bioelectrode is discussed. The resulting biosensor shows a fast response, a linear relationship between current and glucose concentration up to 1.35 × 10⁻² M (2.43 g L⁻¹) and a detection limit of 2.0 × 10⁻⁵ M. The effect of the presence of the enzyme in the composite material on the dispersion of the copper oxide particles is also discussed.     

Nonenzymatic glucose sensor based on glassy carbon electrode modified with a nanocomposite composed of nickel hydroxide and graphene

We report on a nonenzymatic glucose sensor based on a glassy carbon electrode that was electrochemically modified with a nanocomposite prepared from nickel hydroxide and graphene. Scanning electron microscopy revealed that the nickel hydroxide in the nanocomposite was present in the form of a nanostructure of three-dimensional spheres that were assembled by many densely arranged nanosheets. The electrocatalytic activity of the electrode toward the oxidation of glucose was investigated by chronoamperometry. The current response was linearly related to the glucose concentration in the range from 1 to 10?μM, with a sensitivity of 494?μA?mM^–1?cm^–2 and a correlation coefficient of 0.9990, and a second range (from 10 to 1000?μM with a sensitivity of 328?μA?mM^–1?cm^–2 and a correlation coefficient of 0.9990). The detection limit was 0.6?μM at a signal-to-noise ratio of 3, and the response time was as short as 2?s.

Sandwich electrochemical thrombin assay using a glassy carbon electrode modified with nitrogen- and sulfur-doped graphene oxide and gold nanoparticles

Graphene oxide doped with nitrogen and sulfur was decorated with gold nanoparticles (AuNP-SN-GO) and applied as a substrate to modify a glassy carbon electrode (GCE). An aptamer against the model protein thrombin was self-assembled on the modified GCE which then was exposed to thrombin. Following aptamer-thrombin interaction, biotin-labeled DNA and aptamer 2 are immobilized on another AuNP-SN-GO hybrid and then are reacted with the thrombin/AuNP-SN-GO/GCE to form a sandwich. The enzyme label horseradish peroxidase (HRP) was then attached to the electrode by biotin–avidin interaction. HRP catalyzes the oxidation of hydroquinone by hydrogen peroxide. This generates a strong electrochemical signal that increases linearly with the logarithm of thrombin concentration in the range from 1.0?×?10^?13 M to 1.0?×?10^?8 M with a detection limit of 2.5?×?10^?14 M (S/N?=?3). The assay is highly selective. It provides a promising strategy for signal amplification. In our perception, it has a large potential for sensitive and selective detection of analytes for which appropriate aptamers are available.

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Graphic abstract A sandwich-type electrochemical aptasensor is fabricated for detection of thrombin using a glassy carbon electrode modified with nitrogen- and sulfur-doped graphene oxide and gold nanoparticles.

     

Electrocatalytic O2 reduction at glassy carbon electrodes modified with dendrimer-encapsulated Pt nanoparticles

Platinum dendrimer-encapsulated nanoparticles (DENs) were prepared within fourth-generation, hydroxyl-terminated, poly(amidoamine) dendrimers and immobilized on glassy carbon electrodes using an electrochemical coupling strategy. X-ray photoelectron spectroscopy, electron microscopy, and electrochemical experiments confirmed that the Pt DENs were about 1.4 nm in diameter and that they remained within the dendrimer following surface immobilization. The resulting Pt DEN films were electrocatalytically active for the oxygen reduction reaction. The films were also robust, surviving up to 50 consecutive cyclic voltammograms and sonication.     

A sensitive and selective nitrite sensor based on a glassy carbon electrode modified with gold nanoparticles and sulfonated graphene

We describe a highly sensitive and selective amperometric sensor for the determination of nitrite. A glassy carbon electrode was modified with a composite made from gold nanoparticles (AuNPs) and sulfonated graphene (SG). The modified electrode displays excellent electrocatalytic activity in terms of nitrite oxidation by giving much higher peak currents (at even lower oxidation overpotential) than those found for the bare electrode, the AuNPs-modified electrode, and the SG-modified electrode. The sensor has a linear response in the 10 μM to 3.96 mM concentration range, a very good detection sensitivity (45.44 μA mM^?1), and a lower detection limit of 0.2 μM of nitrite. Most common ions and many environmental organic pollutants do not interfere. The sensor was successfully applied to the determination of nitrite in water samples, and the results were found to be consistent with the values obtained by spectrophotometry.

Amperometric nonenzymatic determination of glucose via a glassy carbon electrode modified with nickel hydroxide and N-doped reduced graphene oxide

The authors describe a nonenzymatic glucose sensor that was obtained by electrochemical deposition and oxidization of metallic nickel on the surface of nitrogen-doped reduced graphene oxide (N-RGO) placed on a glassy carbon electrode (GCE). An analysis of the morphology and chemical structure indicated the composite to possess a well-defined vermicular Ni(OH)₂ nanorods combined with N-RGO. The electrochemical performance of the modified GCE with respect to the detection of glucose in 0.1 M NaOH was investigated by cyclic voltammetry and amperometry. The wrinkle and protuberance of N-RGO for loading of nanostructured Ni(OH)₂ are found to increase electrical conductivity, surface area, electrocatalytical activity and stability. The modified GCE displays a high electrocatalytic activity towards the oxidation of glucose in 0.1 M NaOH solution. The lower detection limit is 0.12 μM at an applied potential of +0.45 V (vs Ag/AgCl) (S/N=3), and the sensitivity is 3214 μA mM^?1 cm^?2. The modified GCE possesses long-term stability, good reproducibility and high selectivity over fructose, sucrose and lactose.

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Graphical abstract The composite of vermicular Ni(OH)₂ nanorods combined with N-doped reduced graphene oxide is a viable catalyst for non-enzymatic electrochemical sensing of glucose.