Graphene-modified Electrode Research Articles

Characterizing Graphene-modified Electrodes for Interfacing with Arduino®-based Devices.

Portable low-cost platform and sensing systems for identification and quantitative measurement are in high demand for various environmental monitoring applications, especially in field work. Quantifying parameters in the field requires both minimal sample handling and a device capable of performing measurements with high sensitivity and stability. Furthermore, the one-device-fits-all concept is useful for continuous monitoring of multiple parameters. Miniaturization of devices can be achieved by introducing graphene as part of the transducer in an electrochemical sensor. In this project, we characterize graphene deposition methods on glassy-carbon electrodes (GCEs) with the goal of interfacing with an Arduino-based user-friendly microcontroller. We found that a galvanostatic electrochemical method yields the highest peak current of 10 mA, promising a highly sensitive electrochemical sensor. An Atlas Scientific™ printed circuit board (PCB) was connected to an Arduino® microcontroller using a multi-circuit connection that can be interfaced with graphene-based electrochemical sensors for environmental monitoring.

Multiplexed electrochemical immunosensing of obesity-related hormones at grafted graphene-modified electrodes

An electrochemical immunosensor was prepared for the simultaneous determination of two hormones, ghrelin (GHRL) and peptide YY (PYY), which play important roles in the regulation of hunger and saciety. Dual screen-printed carbon electrodes modified with reduced graphene oxide (rGO) were used as scaffolds for the immobilization of the corresponding capture antibodies. Grafting of the diazonium salt of 4-aminobenzoic acid (4-ABA) on the modified electrode surfaces allowed covalent immobilization of antibodies. Competitive immunoassays were employed and the affinity reactions were monitored by differential pulse voltammetry upon addition of 1-naphthyl phosphate. Under the optimized working conditions, linear current vs. log [hormone] plots extending between 10−3 and 100ng/mL GHRL (r2=0.990), and 10−4 and 10ng/mL PYY (r2=0.992) were obtained. These ranges are adequate for the determination of both hormones at clinical levels in serum and saliva. An excellent analytical performance in terms of detection limit, reproducibility of the measurements, storage stability and selectivity against other proteins was achieved. The usefulness of the approach was demonstrated by its application to spiked human serum and saliva.

Biofuel Cell Based on Carbon Fiber Electrodes Functionalized with Graphene Nanosheets

Carbon fiber electrodes were electrochemically modified with graphene nanosheets in situ deposited in the 3D-structure, characterized by field emission scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman scattering methods. The graphene-modified electrodes were further functionalized with PQQ-dependent glucose dehydrogenase and laccase and used for assembling a biofuel cell operating in the presence of oxygen and glucose “fuel”. The paper represents novel approach to the production of graphene-functionalized electrodes and their use in biofuel cells, potentially applicable in implantable bioelectronics devices.

A cost-effective disposable graphene-modified electrode decorated with alternating layers of Au NPs for the simultaneous detection of dopamine and uric acid in human urine

A disposable electrode based on a highly sensitive and readily fabricated arrangement of alternating AuNP and graphene layers was introduced for the simultaneous determination of dopamine and uric acid.

Rapid Prototyping of a High Sensitivity Graphene Based Glucose Sensor Strip.

A rapid prototyping of an inexpensive, disposable graphene and copper nanocomposite sensor strip using polymeric flexible substrate for highly sensitive and selective nonenzymatic glucose detection has been developed and tested for direct oxidization of glucose. The CuNPs were electrochemically deposited on to the graphene sheets to improve electron transfer rates and to enhance electrocatalytic activity toward glucose. The graphene based electrode with CuNPs demonstrated a high degree of sensitivity (1101.3±56 μA/mM.cm2), excellent selectivity (without an interference with Ascorbic Acid, Uric Acid, Dopamine, and Acetaminophen), good stability with a linear response to glucose ranging from 0.1 mM to 0.6 mM concentration, and detection limits of 0.025 mM to 0.9 mM. Characterization of the electrodes was performed by scanning electron microscopy (FESEM and SEM). The electrochemical properties of the modified graphene electrodes were inspected by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry.

Aptamer-functionalized nanoparticles for surface immobilization-free electrochemical detection of cortisol in a microfluidic device

Monitoring the periodic diurnal variations in cortisol from small volume samples of serum or saliva is of great interest, due to the regulatory role of cortisol within various physiological functions and stress symptoms. Current detection assays are immunologically based and require cumbersome antibody immobilization chemistries, thereby limiting the assay versatility, kinetics, and reproducibility. We present a quantitative aptamer-based detection methodology for cortisol that does not require target labeling, capture probe immobilization on the detection surface or wash steps prior to readout. Using a recognition system of aptamer functionalized gold nanoparticles pre-bound with electro-active triamcinolone, the cortisol level is detected based on its competitive binding to the aptamer by following signal from the displaced triamcinolone using square wave voltammetry at patterned graphene-modified electrodes in a microfluidic or nanoslit device. Due to the 3D analyte diffusion profile at the aptamer interface and the ability to enhance the surface area for cortisol capture, this assay shows signal linearity over a five-log analyte concentration range (10μg/mL to 30pg/mL) and exhibits rapid binding kinetics with cortisol versus other glucocorticoids, as apparent from the absence of interferences from estradiol, testosterone and progesterone. The assay is carried out within the biologically relevant range for glucocorticoids in serum and saliva matrices, and benchmarked versus ELISA and radioimmunoassays. Based on absence of cumbersome surface immobilization and wash steps for carrying out this assay, its quantitative signal characteristics and its ability to resist interferences from other glucocorticoids, we envision its application towards routine monitoring of cortisol within bio-fluids.

Graphene decorated microelectrodes for simultaneous detection of ascorbic, dopamine, and folic acids by means of chemical vapor deposition

In this paper, high quality and large area graphene layers were synthesized using thermal chemical vapour deposition on copper foil substrates. We use graphene incorporated electrodes to measure simultaneously ascorbic acid, dopamine and folic acid. Cyclic voltammetry and differential pulse voltammetry methods were used to evaluate electrochemical behaviour of the grown graphene layers. The graphene-modified electrode shows large electrochemical potential difference compared to bare gold electrodes with higher current responses. Also our fabricated electrodes configuration can be used easily for microfluidic analysis.

Study on Determination of Sudan Red I with Graphene-modified Heat Glassy Carbon Electrode (GR/HGCE)

Study on Determination of Sudan Red I with Graphene-modified Heat Glassy Carbon Electrode (GR/HGCE)

Preparation and characterization of “clickable” polyaniline derivatives on graphene modified electrodes

The electrochemical polymerization of 2- and 3-ethynylaniline and copolymers with aniline was investigated. It is found that 3-ethynylaniline is more reactive than 2-ethynylaniline and, in the presence of aniline it electropolymerizes. The effect of the electrode material on the electropolymerization of 3-ethynylaniline and its copolymers with aniline was studied and graphene-modified electrodes show very good performance for the formation of a PANI-like polymer, as demonstrated by FTIR and Raman measurements. The graphene layer thickness also appears to influence the polymerization, the best results obtained for the thinnest films used. Finally, copolymers of aniline and 3-ethynylaniline were chemically prepared at room temperature. These copolymers display PANI-like structure with alkyne grafted groups and showed good electrochemical response, slightly different to that of the parent PANI with lower electrical conductivity. Preliminary tests indicate that the PANI derivative can be successfully clicked to poly(ethylene glycol) by a thiol-yne click reaction.

Intrinsic electrochemical performance and precise control of surface porosity of graphene-modified electrodes using the drop-casting technique

Graphenes have for a long time been shown to exhibit enhanced electrochemical sensing and fast heterogeneous electron transfers, but the nature of such improved electrochemistry is disputed due to its inherent porosity. Adsorption and thin layer effects may additionally contribute to the observed behaviour. Furthermore, overall extents of the impact from these factors are typically unclear. Towards a practical solution to this issue, we show that electrode porosity can be adequately controlled close to the case of an ideal planar electrode. With increased mass loadings, the apparent porosity can still be precisely controlled by performing multiple drop-casts from less concentrated dispersions. Thus with application of such experimental practices, the drop-casting technique remains a reliable option for nanomaterial electrode preparation.

Electrodeposition of reduced graphene oxide on a Pt electrode and its use as amperometric sensor in microchip electrophoresis.

This report describes the development and application of a novel graphene-modified electrode to be used as amperometric sensor in microchip electrophoresis (ME) devices. The modified electrode was achieved based on electroreduction of graphene oxide on an integrated Pt working electrode of a commercial ME device. The surface modification was characterized by SEM and cyclic voltammetry techniques. The results indicated that graphene sheets were successfully deposited exhibiting higher surface conductivity and greater electrode sensitivity. The performance of the modified electrode for the amperometric detection on ME devices has been demonstrated by the separation and detection of an anionic mixture containing iodide and ascorbate. The graphene-modified electrode provided significantly higher sensitivity (896.7 vs. 210.9 pA/μM for iodide and 217.8 vs. 127.8 pA/μM for ascorbate), better separation efficiencies (3400 vs. 700 plates/m for iodide and 10000 vs. 2400 plates/m for ascorbate), enhanced peak resolutions (1.6 vs. 1.0), and LODs (1.5 vs. 5.3 μM for iodide and 3.1 vs. 7.3 μM for ascorbate) in comparison with the unmodified Pt electrode. The proposed amperometric sensor was successfully applied for the analysis of ascorbic acid (through its anionic form) in a commercial medicine sample, and the results achieved were in agreement with the value provided by the supplier. Based on the data here presented, the modified graphene electrode shows great promise for ME applications.

In-situ synthesis of reduced graphene oxide modified lithium vanadium phosphate for high-rate lithium-ion batteries via microwave irradiation

We report a simple and rapid method to synthesize graphene-modified Li3V2(PO4)3 as cathode material for lithium-ion batteries via microwave irradiation. By treating graphene oxide and the precursor of Li3V2(PO4)3 in a commercial microwave oven, both reduced graphene oxide and Li3V2(PO4)3 could be simultaneously synthesized within 5min. The structure, morphology and electrochemical performances of as-synthesized graphene-modified Li3V2(PO4)3 are investigated systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, charge/discharge tests, electrochemical impedance spectra (EIS) and cyclic voltammetry (CV). The XRD result indicates that single-phase graphene-modified Li3V2(PO4)3 with monoclinic structure can be obtained. Both SEM and TEM images show that Li3V2(PO4)3 nanocrystals are embedded in the reduced graphene oxide sheets which could provide an easy path for the electrons and Li-ions during the cycling process. Compared with the pristine Li3V2(PO4)3 electrode, graphene-modified Li3V2(PO4)3 exhibits a better high-rate ability and cyclic stability. These superior electrochemical performances are attributed to the good conductivity of reduced graphene oxide which enhances the electrons and Li-ions transport on the surface of Li3V2(PO4)3. Thus, this simple and rapid method could be promising to synthesize graphene-modified electrode materials.

Graphene frameworks synthetized with Na2CO3 as a renewable water-soluble substrate and their high rate capability for supercapacitors

Substrates are normally required in the chemical synthesis of graphene to enhance its formation. However, removing substrates in the post purification stage is difficult, during which harsh reagents are used and the substrates are usually consumed undesirably. In this paper, we report that universal sodium carbonate (Na2CO3) particles can effectively promote the construction of well-structured graphene frameworks based on a quick thermal decomposition of fumaric acids. Notably, the Na2CO3 particles are easily separated from graphene through a simple and green method, namely, washing with water at room temperature. Together with the reused characteristic of the recovered Na2CO3 particles, this approach is undoubtedly beneficial to the low-cost and clean synthesis of graphene. Benefiting from the framework structure, the as-synthesized graphene exhibits excellent performance in the supercapacitor. The specific capacitance of the GFs-modified electrode was calculated to be 242 F g−1 at 0.5 A g−1, which was almost twice that of the RGO-modified electrode (134 F g−1). More importantly, the GFs-modified electrode maintained 92.6% retention of its initial specific capacitance (from current density of 0.5 to 16 A g−1), which was much higher than that of 2D graphene-modified electrode.

Selection, Characterization, and Application of High Affinity Microcystin-Targeting Aptamers in a Graphene-Based Biosensing Platform

The development of successful biosensing platforms is highly dependent upon the biorecognition properties of the recognition receptor and the sensitivity of the transducer of the binding signal. The integration of the high affinity and specificity of DNA aptamers, and the unique properties of the carbon nanomaterial graphene, offers an excellent avenue for sensitive and selective biosensing architectures. In this work, novel microcystin-targeting DNA aptamers were successfully selected using systematic evolution of ligand by exponential enrichement (SELEX). Then, highly sensitive and selective aptasensor which utilizes an unlabeled aptamer noncovalently assembled on a graphene electrode for microcystin-LR detection was developed. Assembly of the DNA aptamer on the graphene-modified electrodes caused a marked drop in the square wave voltammetric reduction signal of the [Fe(CN)6]4−/3− redox couple. The presence of microcystin-LR, on the other hand, caused a dose-responsive increase in peak current, allowing the quantification of microcystin-LR through the measurement of peak current change. Under optimal conditions, the detection limit of the developed aptasensor was 1.9 pM in buffer, a concentration much lower than those offered by previously reported biosensors for microcystin-LR. The developed aptasensor also exhibited excellent selectivity for microcystin-LR with no detectable cross-reactivity to okadaic acid, microcystin-LA and -YR. Moreover, the proposed aptasensor has been applied for the analysis of spiked tap water and fish samples showing good recovery percentages. We also demonstrated in this work that the mechanism of the detection was based on the conformation change in part of the aptamer without complete release from the graphene surface. This novel, simple, high performance and low-cost detection platform would facilitate the routine monitoring of microcystin –LR in real samples.

A graphene-based electrochemical sensor for sensitive determination of cyanazine

An electrochemical sensor based on the electrocatalytic activity of graphene for sensitive detection of cyanazine (CZ) is presented. Graphene is ideally suited for electrochemical applications due to its large electrical conductivity, large surface area and unique heterogeneous electron transfer rate. Electrochemical measurements were performed at glassy carbon electrode (GCE) which was modified with graphene via drop-casting method. Cyclic voltammogram of ferri/ferrocyanide redox couple at graphene modified electrode showed an increased current intensity compared with glassy carbon and graphite modified electrode. The decrease of charge transfer resistance was also analyzed by electrochemical impedance spectroscopy. The morphology of the modified graphene electrode was characterized using scanning electron and atomic force microscopic techniques. Under the optimized experimental conditions, the proposed electrochemical sensor exhibited a rapid response to cyanazine with a linear calibration plot ranging from 0.55 to 1500 nM and a detection limit of 0.25 nM. The applicability of graphene/GCE for the determination of CZ in real samples such as tape water, river water and ground water, were checked by differential pulse voltammetry method.

Determination of Rutin by a Graphene-Modified Glassy Carbon Electrode

A reduced graphene oxide-modified glassy carbon electrode for sensitive detection of rutin is reported. The modified electrode was obtained by one-step electrochemical reduction of graphene oxide on the bare glassy carbon electrode. In the presence of graphene, an enhanced electrochemical response for rutin appeared with a pair of well-defined anodic and cathodic peaks in pH 3.0 phosphate buffer. Under the optimized conditions, the anodic peak currents exhibited a linear relationship with rutin concentration from 0.1 to 2.0 µM with a detection limit of 23.2 nM. The modified electrode was employed to the analysis of tablets (with satisfactory recovery of 19.96 mg/per tablet) and Flos Sophorae. The graphene-modified electrode exhibited high sensitivity, good stability, and selectivity for the determination of rutin.

An electrochemical sensor for the determination of phoxim based on a graphene modified electrode and molecularly imprinted polymer

The electrochemical impedance spectra of Fe(CN)63−/4− at NIP/graphene/GCE (a), MIP/GCE (b), the bare GCE (c), and MIP/graphene/GCE (d).

Electrochemical detection of cholesterol based on competitive host–guest recognition using a β-cyclodextrin/poly(N-acetylaniline)/graphene-modified electrode

Illustration of the strategy of the proposed electrochemical sensor based on the competitive host–guest interaction between β-CD and MB (signal probe)/cholesterol (target).

Graphene Modified Electrode for the Direct Electron Transfer of Bilirubin Oxidase

Graphene Modified Electrode for the Direct Electron Transfer of Bilirubin Oxidase

High photocurrent generation by photosystem I on artificial interfaces composed of π-system-modified graphene

We report on the development of graphene-nanobiohybrid light-harvesting electrodes consisting of photosystem I and π-system modified graphene electrodes.