Graphene-modified Electrode Research Articles

Electrochemical detection of dopamine using water-soluble sulfonated graphene

In the present study, a biosensor was prepared using the water-soluble sulfonated graphene with the aim of achieving the selective and sensitive determination of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). The aromatic π–π stacking and electrostatic attraction between positively charged DA and negatively charged sulfonated graphene can accelerate the electron transfer whereas weakening AA and UA oxidation on the sulfonated graphene-modified electrode. Fourier transform infrared spectra (FTIR), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to characterize the successful synthesis of sulfonated graphene sheets. Differential pulse voltammetry was used for electrochemical detection, the separation of the oxidation peak potentials for AA-DA, DA-UA and UA-AA was about 227mV, 125mV and 352mV, which allowed selectively determining DA. A broad linear range, low detection limit, along with good ability to suppress the background current from large excess ascorbic acid (AA) and uric acid (UA) were obtained. The as-prepared sulfonated graphene sheets exhibited superior performance over conventional negatively charged Nafion films, such as flexible film thickness, unique nanostructure, excellent anti-interference ability, high sensitivity and selectivity. The proposed method was used to detect DA in real hydrochloride injection sample, human urine and serum samples with satisfactory recovery results.

Graphene‐Based Electrochemical Sensors

Graphene, one kind of emerging carbon nanomaterial, has attracted increasing attention recently. Due to its fascinating physical and electrochemical properties, graphene as a promising electrode material has been widely used in electrochemical sensing applications. In this review, different approaches for the fabrication of graphene and the preparation of graphene-modified electrodes for electrochemical sensors are introduced. Moreover, recent research results on different graphene-based materials as an electrochemical platform for the detection of various biomolecules and chemicals are reviewed and compared. More electrochemical studies on this novel material should show up in the near future.

Graphene-modified electrode. Determination of hydrogen peroxide at high concentrations

A gold electrode partially coated by graphene multilayer is developed and tested with respect to high concentrations of hydrogen peroxide. The effective use of conventional electrode materials for the determination of such an analyte by anodic oxidation or cathodic reduction is prevented by the occurrence of adsorptions fouling the electrode surface. This prevents reliable and repeatable voltammetric curves for being recorded and serious problems arise in quantitative analysis via amperometry. The gold-graphene electrode is shown to be effective in quantitative evaluation, by cathodic reduction, of hydrogen peroxide at concentration levels that are of interest in an industrial. Acid, neutral, and basic pH values have been tested through correct adjustment of a Britton Robinson buffer. The experiments have been performed both by cyclic voltammetry and with amperometry at constant potential in unstirred solution. The latter technique has been employed in drawing a calibration linear plot. In particular, the performances of the developed electrode system have been compared with those of both pure gold and pure graphene electrode materials. The bi-component electrode was more sensitive; co-catalytic action by the combination of the two components is hypothesised. The system is stable over many potential cycles, as checked by surface-enhanced Raman spectra recorded over time.

Electrochemical Determination of Ranitidine Hydrochloride in Pharmaceutical Formulations and Biological Fluids at Graphene Modified Electrode

Electrochemical Determination of Ranitidine Hydrochloride in Pharmaceutical Formulations and Biological Fluids at Graphene Modified Electrode

Determination of Trace Cadmium and Lead in Water Based on Graphene-modified Platinum Electrode Sensor

Graphene,grow on platinum electrode(prepared with the method of micro-electromechanical system) with CVD,was used in combination with in situ plated bismuth film electrode for fabricating the enhanced electrochemical sensing platform to determine trace cadmium(Cd2+) and lead(Pb2+) by differential pulse anodic stripping voltammetry(DPASV).The sensor is three-electronic system that consisted of graphene-modified platinum(G/Pt) working electrode,Ag/AgCl reference electrode and platinum wire auxiliary electrode.The experiment result showed that the sensor performed well in simultaneously detecting Cd2+ and Pb2+.The linear calibration curves ranged from 0.05 mg/L to 10 mg/L for Cd2+ and 0.03 mg/L to 5 mg/L for Pb2+.The detection limits were estimated to be around 10 μg/L for Cd2+and Pb2+.This method is simple,safe,fast and good reproducibility,and can be used for rapid detection of Cd and Pb in wastewater,surface water and domestic water.

Detection of cancer cells using a peptidenanotube–folic acid modified graphene electrode

This article describes the preparation of a graphene electrode modified with a new conjugate of peptide nanotubes and folic acid for the selective detection of human cervical cancer cells over-expressing folate receptors. The functionalization of peptide nanotubes with folic acid was confirmed by fluorescence microscopy and atomic force microscopy. The peptide nanotube-folic acid modified graphene electrode was characterized by scanning electron microscopy and cyclic voltammetry. The modification of the graphene electrode with peptide nanotube-folic acid led to an increase in the current signal. The human cervical cancer cells were bound to the modified electrode through the folic acid-folate receptor interaction. Cyclic voltammograms in the presence of [Fe(CN)(6)](3-/4-) as a redox species demonstrated that the binding of the folate receptor from human cervical cancer cells to the peptide nanotube-folic acid modified electrode lowered the electron transfer resulting in a decrease in the measured current. A detection limit of 250 human cervical cancer cells per mL was obtained. Control experiments confirmed that the peptide nanotube-folic acid electrode specifically recognized folate receptors. The modified electrode described here opens up new possibilities for future applications in early stage diagnoses of diseases where cells over-express folate receptors, such as in cancer or leishmaniasis disease.

A voltammetric sensor based on graphene-modified electrode for the determination of trace amounts of l-dopa in mouse brain extract and pharmaceuticals

l-Dopa is the intermediate precursor of the neurotransmitter dopamine. Unlike dopamine, l-dopa easily enters the central nervous system. l-Dopa, as one of the catecholamines, is widely used as a source of dopamine in the treatment of most patients with Parkinson’s disease and epilepsy. Graphene (GR) is ideally suited for implementation in electrochemical applications due to its reported large electrical conductivity, large surface area, unique heterogeneous electron transfer rate, and low production costs. This work reports the synthesis of GR using a modified Brodie method and its application for the electrochemical determination of l-dopa in real samples. Electrochemical measurements were performed at glassy carbon electrode modified with graphene (GR/GCE) via drop casting method. Cyclic voltammograms of l-dopa at GR/GCE showed an increased current intensity compared with GCE. All the measurements were done in phosphate buffer solution 0.1 M (pH 6.2) and the oxidation peak was observed at 0.27 V vs. Ag/AgCl. The effect of scan rate showed that oxidation of l-dopa on GR/GCE was surface controlled. The oxidation peak current of l-dopa gradually increased with increasing accumulation time from 0 to 300 s and accumulation potential from 0.0 to 0.3 V and reached the maximum current response at 240 s and 0.2 V for the accumulation time and accumulation potential, respectively. Voltammetric peak currents showed a linear response for l-dopa concentration in the range of 0.04 to 79 μM and a detection limit of 0.022 μM (22 nM). The relative standard deviation for five determinations of 50 μM l-dopa was 0.52 %.

Chitosan-modified graphene electrodes for DNA mutation analysis

Graphene has remarkable electrochemical properties that make it an ideal material for constructing bio-sensors. Herein, we report on a chitosan-modified graphene platform for the electrochemical detection of changes in DNA sequences. For this purpose, graphene synthesized chemically and characterized by Raman spectroscopy and Transmission electron microscopy, was covalently modified with positively charged chitosan to facilitate the immobilization of a single-stranded DNA ‘capture’ oligonucleotide. The covalent attachment of chitosan to graphene was confirmed by FT-IR spectroscopy and then the capture DNA was immobilized on to the chitosan modified graphene electrode. Then, the target DNA (complementary or mismatched ‘mutant’ DNA) was applied to the electrode and cyclic voltammetry was performed. The results of the voltammetric experiments indicate that the chitosan modified graphene electrodes immobilized with ssDNA+complementary DNA exhibit a significantly higher magnitude of redox peak current than the chitosan modified graphene electrodes immobilized with the non-complementary mutant DNAs. Together, these results demonstrate that the chitosan-graphene platform provides a rapid, stable and sensitive detection of mismatched DNA and has the potential to be used for point-of-care diagnostic tests for specific DNA mutations associated with disease conditions.

Preparation of Graphene-modified Electrode and Voltammetric Determination of Acetaminophen

A glassy carbon electrode was modified with graphene by casting.The modified electrode showed an excellent electrocatalytical effect on the oxidation of acetaminophen(ACOP).The voltammetric behavior and electrochemical analysis method of ACOP were studied on the modified electrode.The effect of pH value on the response of ACOP was studied in phosphate buffer solution(PBS).The results showed that the redox peak potential of ACOP shifted negatively with increasing pH value,and a pair of well-defined redox waves were obtained in PBS of pH=6.0.The oxidation peak currents of ACOP increased linearly with the concentration,in the range of 6.00×10-7~4.00×10-5 mol/L,the linear regression equation was ipa(A)=3.00c+1.21×10-5,with correlation coefficient 0.9940.The detection limit(S/N=3) was 5.00×10-8 mol/L.The graphene modified electrode showed a good sensitivity,selectivity and stability.It was applied to the ACOP tablets analysis.

Zeolite A functionalized with copper nanoparticles and graphene oxide for simultaneous electrochemical determination of dopamine and ascorbic acid

A novel Cu-zeolite A/graphene modified glassy carbon electrode for the simultaneous electrochemical determination of dopamine (DA) and ascorbic acid (AA) has been described. The Cu-zeolite A/graphene composites were prepared using Cu2+ functionalized zeolite A and graphene oxide as the precursor, and subsequently reduced by chemical agents. The composites were characterized by X-ray diffraction, Fourier transform infrared spectra and scanning electron microscopy. Based on the Cu-zeolite A/graphene-modified electrode, the potential difference between the oxidation peaks of DA and AA was over 200mV, which was adequate for the simultaneous electrochemical determination of DA and AA. Also the proposed Cu-zeolite/graphene-modified electrode showed higher electrocatalytic performance than zeolite/graphene electrode or graphene-modified electrode. The electrocatalytic oxidation currents of DA and AA were linearly related to the corresponding concentration in the range of 1.0×10−7–1.9×10−5M for DA and 2.0×10−5–2.0×10−4M for AA. Detection limits (<!-- no-mfc -->S/N<!-- /no-mfc -->=3) were estimated to be 4.1×10−8M for DA and 1.1×10−5M for AA, respectively.

A glucose biosensor based on direct electrochemistry of glucose oxidase immobilized onto platinum nanoparticles modified graphene electrode

The platinum nanoparticles were adsorbed on graphene oxide sheets and played an important role in catalytic reduction of graphene oxide with hydrazine, leading to the formation of graphene-Pt nanoparticles. Because of their good electronic properties, biocompatibility and high surface area, graphene-Pt based composites achieved the direct electron transfer of redox enzyme and maintained their bioactivity well. The graphene-Pt nanocomposites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED). The amperometric biosensor fabricated by depositing glucose oxidase over Nafion-solubilized graphene-Pt electrode retained its biocatalytic activity and has offered fast and sensitive glucose quantification.

Electrochemical ascorbic acid/hydroquinone detection on graphene electrode and the electro-active site study

In this article, graphite oxide (GO) and graphene have been prepared by chemical method and applied to modify electrodes in electrochemical detection of hydroquinone and ascorbic acid (AA). It is confirmed that the as-prepared GO- and graphene-modified electrodes own good electro-sensitivity for detecting hydroquinone and AA by cyclic voltammogram measurements. The detection limit of hydroquinone on graphene electrode was 3.8 × 10−7 mol L−1 (S/N = 3). Graphene has lowered the over-potential of hydroquinone and improved its electrochemical reversibility. The redox process of hydroquinone is more prone to be diffusion-controlled, as shown by the relationship between anodic peak currents and scan rate results. Different from hydroquinone detecting, both GO- and graphene-modified electrodes have favourable oxidation peaks in detecting AA, as the oxygen content sites on GO and graphene have been tested to be the electro-active sites for AA detecting. The redox process of AA on GO- and graphene-modified electrodes is more prone to be absorption-controlled. The results presented in this article demonstrate that GO and graphene have a good prospect in the making of an AA sensor device.

A Label-Free Amperometric Immunoassay for Thrombomodulin Using Graphene/Silver-Silver Oxide Nanoparticles as a Immobilization Matrix

A simple, sensitive, and label-free electrochemical immunosensor has been developed for the measurement of serum thrombomodulin (TM), an endothelial glycoprotein which is associated with the progression and metastasis of tumors. At first, the graphene nanosheets, which were dispersed in Nafion solution, were used to coat the bare gold electrode. Then, silver-silver oxide nanoparticles (Ag-Ag2O NPs) were immobilized on the graphene-modified electrode by a one-step electrochemical deposition method. Lastly, a thrombomodulin antibody (anti-TM) was attached via amido-Ag affinity. This strategy combines graphene/Ag-Ag2O NPs hybrid materials as an immobilization matrix and Ag-Ag2O NPs also as an electrochemical signal indication reagent. The main advantage of this strategy has two important aspects. One is the high stability and unique electronic properties of the graphene nanostructure. The other is the use of Ag-Ag2O NPs as the immobilization matrix and redox probes, thus avoiding the laborious labeling protein operation. Using this strategy, the concentration of TM in the range of 0.1 to 20 ng/mL was detected, with a detection limit of 31.5 pg/mL (at 3σ). The proposed methodology demonstrates that the nanocomposite film composed of graphene and Ag-Ag2O NPs is a potential for biosensor applications.

A LiF Nanoparticle‐Modified Graphene Electrode for High‐Power and High‐Energy Lithium Ion Batteries

AbstractSurface modification of carbon materials plays an important role in tailoring carbon surface chemistry to specify their electrochemical performance. Here, a surface modification strategy for graphene is proposed to produce LiF‐nanoparticle‐modified graphene as a high‐rate, large‐capacity pre‐lithiated electrode for high‐power and high‐energy lithium ion batteries. The LiF nanoparticles covering the active sites of the graphene surface provide an extra Li source and act as an effective solid electrolyte interphase (SEI) inhibiter to suppress LiFP6 electrolyte decomposition reactions, affect SEI components, and reduce their thickness. Consequently, the Li‐ion diffusion is greatly sped up and the thermodynamic stability of the electrode is significantly improved. This modified graphene electrode shows excellent rate capability and improved first‐cycle coulombic efficiency, cycling stability, and ultrahigh power and energy densities accessible during fast charge/discharge processes.

Self-Assembled Graphene for Determination of Catechol in Wastewater at Modified Glassy Carbon Electrode

Graphene-modified glassy carbon electrode was made by dropping. In phosphate-citric acid buffered saline, the modified electrode was shown to possess an excellent selective electrocatalytical effect on the redox of catechol, and further used to determine catechol in the presence of resorcin and hydroquinone by cyclic voltammetry. The oxidation peak currents Ipa showed a linear relationship with the concentrations (c) of catechol in the range of 2.97×10-7 mol•L-1~9.31×10-6 mol•L-1 and 9.31×10-6 mol•L-1~1.03×10-4 mol•L-1 with a correlation coefficient as follows: Ipa1(A)= -4.10×10-6-2.31c, R=0.Superscript text9971; Ipa2 (A) =-1.50×10-5-0.60c, R=0.9953, respectively, and the detection limit is 2.50×10-8 mol•L-1. The modified electrode is high sensitivity, selectivity, stability, and has been successfulSuperscript textly applied to analyzing catechol in wastewater.

Graphene-Modified Electrode for the Selective Determination of Uric Acid Under Coexistence of Dopamine and Ascorbic Acid

Graphene-Modified Electrode for the Selective Determination of Uric Acid Under Coexistence of Dopamine and Ascorbic Acid

Simultaneous determination of l-ascorbic acid, dopamine and uric acid with gold nanoparticles–β-cyclodextrin–graphene-modified electrode by square wave voltammetry

Graphene decorated with gold nanoparticles (AuNPs–β-CD–Gra) has been synthesized by in situ thermal reduction of graphene oxide and HAuCl4 with β-cyclodextrin (β-CD) under alkaline condition. The AuNPs–β-CD–Gra product was well characterized by infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. This material was used to fabricate an AuNPs–β-CD–Gra-modified glassy carbon electrode (GCE) which showed excellent electro-oxidation of l-ascorbic acid (AA), dopamine (DA) and uric acid (UA) in 0.10M NaH2PO4–HCl buffer solution (pH 2.0) by square wave voltammetry (SWV). Three well-resolved oxidation peaks of AA and DA and UA were obtained. The AuNPs–β-CD–Gra/GCE exhibits linear responses to AA, DA and UA in the ranges 30–2000, 0.5–150 and 0.5–60μM, respectively. The detection limits (based on S/N=3 and preconcentration time=3.0min) for AA, DA and UA are 10, 0.15 and 0.21μM, respectively. The AuNPs–β-CD–Gra/GCE has been successfully applied to determine UA in human urine with satisfactory results. Our work provides a simple, convenient and green route to synthesize AuNPs on Gra which is potentially useful in electroanalysis.

Electrochemical detection of dopamine using porphyrin-functionalized graphene

A new type of porphyrin-functionalized graphene was synthesized and used for highly selective and sensitive detection of dopamine (DA). The aromatic π–π stacking and electrostatic attraction between positively-charged dopamine and negatively-charged porphyrin-modified graphene can accelerate the electron transfer whereas weakening ascorbic acid (AA) and uric acid (UA) oxidation on the porphyrin-functionalized graphene-modified electrode. Differential pulse voltammetry was used for electrochemical detection, the separation of the oxidation peak potentials for AA-DA, DA-UA and UA-AA is about 188mV, 144mV and 332mV, which allows selectively determining DA. The detection limit of DA can be as low as 0.01μM. More importantly, the sensor we presented can detect DA in the presence of large excess of ascorbic acid and uric acid. With good sensitivity and selectivity, the present method was applied to the determination of DA in real hydrochloride injection sample, human urine and serum samples, respectively, and the results was satisfactory.

Electrochemical detection of dopamine in the presence of epinephrine, uric acid and ascorbic acid using a graphene-modified electrode

A sensitive and selective electrochemical method for the determination of dopamine (DA) in the presence of epinephrine (EP), uric acid (UA) and ascorbic acid (AA) was developed using a graphene-modified electrode. The electrochemical behaviour of DA at the modified electrode was studied by cyclic voltammetry. The results showed that the modified electrode exhibited excellent electrocatalytic activity towards the electrochemical oxidation of DA. When the reduction peak current of DA, in pH 7.0 phosphate buffer solution, was measured at a potential range of −0.1 to 0.6 V, no interference occurred from EP, UA and AA. The reduction peak current was linearly proportional to DA concentration from 2.50 × 10−6 to 1.00 × 10−4 mol L−1. The values of correlation coefficient and limit of detection for DA were 0.9984 and 5.00 × 10−7 mol L−1, respectively. The modified electrode shows excellent sensitivity, selectivity and stability for the voltammetric determination of DA in the presence of EP, UA and AA and was satisfactorily used for the determination of DA in pharmaceutical and biological samples.

Enhanced Cathodic Electrogenerated Chemiluminescence of Luminol at a Graphene Modified Electrode in Neutral Solution

Graphene oxide (GO) and electrochemically reduced graphene (ERG) modified glassy carbon electrodes (GCE) were prepared and characterized by FT-IR, scanning electron microscopy (SEM), and electrochemical techniques, respectively. Electrogenerated chemiluminescence (ECL) of luminol was studied on the modified electrodes in neutral phosphate buffer solution (PBS). Either at the GO modified electrode or at the ERG modified electrode, the anodic ECL emission of luminol was inhibited greatly and only one cathodic ECL peak was obtained. The intensity of the cathodic ECL emission at the ERG modified electrode increased 123 times compared with that of the GO modified electrode or the bare electrode, which is due to the strong adsorption of dissolved oxygen by ERG film. Several impact factors of luminol ECL, such as the electrochemical reduction potential, the duration of the applied reduction potential, the pH values, the supporting electrolytes, and the potential scan rate were studied and the mechanism of the cathodic luminol ECL emission on the ERG modified electrode was proposed.