Electrochemical co-reduction synthesis of graphene/nano-gold composites and its application to electrochemical glucose biosensor

Recent advances in biological molecule detection based on a three-dimensional graphene structure

Graphene has become an attractive material in the field of electrochemical detection owing to its unique electrical properties. Although the simple stacking structures of two-dimensional (2D) graphene sheets can provide excellent detection properties, a macroscopic three-dimensional (3D) structure needs to be constructed to enhance its functional properties. Graphene with a 3D structure has elegant functions, unlike graphene with a 2D structure. These properties include a large specific surface area, easy loading of nanomaterials with electrocatalytic and redox functions, and so on. Herein, we outline the preparation methods (self-assembly, chemical vapor deposition, templates, and 3D printing) for 3D graphene structures for obtaining excellent detection performance and applications in detecting biological molecules, bacteria, and cells. Furthermore, this review focuses on the improvement of the detection performance and enhancement of the applicability of graphene-based electrochemical sensors. We hope that this article will provide a reference for the future development of electrochemical sensors based on 3D graphene composites.

Noninvasive glucose monitoring using portable GOx-Based biosensing system

Wearable biosensors have gained huge interest due to their potential for real-time physiological information. The development of a non-invasive blood glucose device is of great interests for health monitoring in reducing the diabetes incidence. Here, we report a sandwich-structured biosensor that is designed for glucose levels detection by using sweat as the means of monitoring. The Prussian blue nanoparticles (PBNPs) and carboxylated carbon nanotubes (MWCNT-COOH) were self-assembled on the electrode to improve the electrochemical performance and as the sensor unit, glucose oxidase (GOx) was immobilized by chitosan (CS) as the reaction catalysis unit, and finally encapsulated with Nafion to ensure a stable performance. As a result, the GOx/PBNPs/MWCNT-COOH sensor displays a low detection limit (7.0 μM), high sensitivity (11.87 μA mM-1 cm-2), and excellent interference resistance for a full sweat glucose application range (0.0-1.0 mM) for both healthy individuals and diabetic patients. Additionally, the glucose sensor exhibits stable stability for two weeks and can be successfully applied to screen-printed carbon electrodes (SPCE), demonstrating its great potential for personalized medical detection and chronic disease management.

Dual-Gate Organic Thin-Film Transistor and Multiplexer Chips for the Next Generation of Flexible EG-ISFET Sensor Chips

Ion-sensitive field-effect transistors (ISFETs) are used as elementary devices to build many types of chemical sensors and biosensors. Organic thin-film transistor (OTFT) ISFETs use either small molecules or polymers as semiconductors together with an additive manufacturing process of much lower cost than standard silicon sensors and have the additional advantage of being environmentally friendly. OTFT ISFETs' drawbacks include limited sensitivity and higher variability. In this paper, we propose a novel design technique for integrating extended-gate OTFT ISFETs (OTFT EG-ISFETs) together with dual-gate OTFT multiplexers (MUXs) made in the same process. The achieved results show that our OTFT ISFET sensors are of the state of the art of the literature. Our microsystem architecture enables switching between the different ISFETs implemented in the chip. In the case of sensors with the same gain, we have a fault-tolerant architecture since we are able to replace the faulty sensor with a fault-free one on the chip. For a chip including sensors with different gains, an external processor can select the sensor with the required sensitivity.

In-situ synthesis of Pt nanoparticles/reduced graphene oxide/cellulose nanohybrid for nonenzymatic glucose sensing

In recent years, nanocellulose-based bioinorganic nanohybrids have been exploited in numerous applications due to their unique nanostructure, excellent catalytic properties, and good biocompatibility. To the best of our knowledge, this is the first report on the simple and effective synthesis of graphene/cellulose (RGO/CNC) matrix-supported platinum nanoparticles (Pt NPs) for nonenzymatic electrochemical glucose sensing. The Pt/RGO/CNC nanohybrid presented a porous network structure, in which Pt NPs, RGO, and CNCs were integrated well. Here, cellulose nanocrystals act as a biocompatible framework for wrapped RGO and monodispersed Pt nanoparticles, effectively preventing the restacking of graphene during reduction. The superior glucose sensing performance of Pt/RGO/CNC modified glass carbon electrode (GCE) was achieved with a linear concentration range from 0.005 to 8.5 mM and a low detection limit of 2.1 μM. Moreover, the Pt/RGO/CNC/GCE showed remarkable sensitivity, selectivity, durability, and reproducibility. The obtained results indicate that the CNCs-based bioinorganic nanohybrids could be a promising electrode material in electrochemical biosensors.

Ultrahigh Energy and Power Densities of d-MXene-Based Symmetric Supercapacitors

Here, rational design electrodes are fabricated by mixing MXene with an aqueous solution of chloroauric acid (HAuCl₄). In order to prevent MXene from self-restacking, the groups of -OH on the surface of Ti₃C₂T_x nanosheets underwent a one-step simultaneous self-reduction from AuCl₄-, generating spaces for rapid ion transit. Additionally, by using this procedure, MXene's surface oxidation can be decreased while preserving its physio-chemical properties. The interlayered MX/Au NPs that have been obtained are combined into a conducting network structure that offers more active electrochemical sites and improved mass transfer at the electrode-electrolyte interface, both of which promote quick electron transfer during electrochemical reactions and excellent structural durability. The Ti₃C₂T_x-AuNPs film thus demonstrated a rate performance that was preferable to that of pure Ti₃C₂T_x film. According to the results of the characterization, the AuNPs effectively adorn the MXene nanosheets. Due to the renowned pseudocapacitance charge storage mechanism, MXene-based electrode materials also work well as supercapacitors in sulfuric acid, which is why MXene AuNPs electrodes have been tested in 3 M and 1 M H₂SO₄. The symmetric supercapacitors made of MXene and AuNPs have shown exceptional specific capacitance of 696.67 Fg^-1 at 5 mVs^-1 in 3 M H₂SO₄ electrolyte, and they can sustain 90% of their original capacitance for 5000 cycles. The highest energy and power density of this device, which operates within a 1.2 V potential window, are 138.4 Wh kg^-1 and 2076 W kg^-1, respectively. These findings offer a productive method for creating high-performance metal oxide-based symmetric capacitors and a straightforward, workable approach for improving MXene-based electrode designs, which can be applied to other electro-chemical systems that are ion transport-restricted, such as metal ion batteries and catalysis.

Development and Practical Application of Glucose Biosensor Based on Dendritic Gold Nanostructures Modified by Conducting Polymers

In this study, graphite rod (GR) electrodes were electrochemically modified by dendritic gold nanostructures (DGNs) followed by immobilization of glucose oxidase (GOx) in the presence of mediator phenazine methosulfate (PMS). Modified with polyaniline (PANI) or polypyrrole (Ppy), GOx/DGNs/GR electrodes were used in glucose biosensor design. Different electrochemical methods were applied for the registration of glucose concentration, and constant potential amperometry (CPA) was chosen as the best one. PANI and Ppy layers synthesized enzymatically on the GOx/DGNs/GR electrodes extended the linear glucose determination range, the width of which depended on the duration of PANI- and Ppy-layers formation. Enzymatically formed polypyrrole was determined as the most suitable polymer for the modification and formation of the glucose biosensor instead of polyaniline, because it was 1.35 times more sensitive and had a 2.57 times lower limit of detection (LOD). The developed glucose biosensor based on the Ppy/GOx/DGNs/GR electrode was characterized by appropriate sensitivity (59.4 μA mM⁻¹ cm⁻²), low LOD (0.070 mmol L⁻¹), wide linear glucose determination range (up to 19.9 mmol L⁻¹), good repeatability (8.01%), and appropriate storage stability (33 days). The performance of the developed glucose biosensor was tested in biological samples and beverages.

Voltammetric determination of palmitic acid by electrode modified with reduced graphene oxide

Palm oil is one of the most produced and traded vegetable oils in the world recently. The quality of palm oil is very important to be examined and one of the quality indices is free fatty acid (FFA) content. Thus, in this study, an electrochemical technique for the determination of FFA as alternative to conventional method (titration method) has been explored. The electrochemical method was developed based on electrochemically reduced graphene oxide (rGO) deposited onto screen printed carbon electrode (SPCE) via drop-casting technique. The modified electrode was characterized by physico-chemical and electrochemical methods, respectively. The voltammetric behaviour of 2-methyl-1,4-naphthaquinone (VK₃) in the presence of palmitic acid at the modified electrode was investigated in an acetonitrile/water (3:1) mixture containing 2.5 M lithium perchlorate (LiClO₄). The electrochemical detection of palmitic acid was based on the voltammetric reduction of VK₃ to form corresponding hydroquinone which is proportional to the concentration of palmitic acid. Under optimum condition, the developed method showed a good linear relationship in the concentration ranging from 0.192 mM to 0.833 mM with the detection limit of 0.079 mM. The developed sensor illustrates high sensitivity and rapid detection towards determination of FFA content in palm oil.

Dispersed Conducting Polymer Nanocomposites with Glucose Oxidase and Gold Nanoparticles for the Design of Enzymatic Glucose Biosensors

Biosensors for the determination of glucose concentration have a great significance in clinical diagnosis, and in the food and pharmaceutics industries. In this research, short-chain polyaniline (PANI) and polypyrrole (Ppy)-based nanocomposites with glucose oxidase (GOx) and 6 nm diameter AuNPs (AuNPs_{(6 nm)}) were deposited on the graphite rod (GR) electrode followed by the immobilization of GOx. Optimal conditions for the modification of GR electrodes by conducting polymer-based nanocomposites and GOx were elaborated. The electrodes were investigated by cyclic voltammetry and constant potential amperometry in the presence of the redox mediator phenazine methosulfate (PMS). The improved enzymatic biosensors based on GR/PANI-AuNPs_{(6 nm)}-GOx/GOx and GR/Ppy-AuNPs_{(6 nm)}-GOx/GOx electrodes were characterized by high sensitivity (65.4 and 55.4 μA mM⁻¹ cm⁻²), low limit of detection (0.070 and 0.071 mmol L⁻¹), wide linear range (up to 16.5 mmol L⁻¹), good repeatability (RSD 4.67 and 5.89%), and appropriate stability (half-life period (τ_1/2) was 22 and 17 days, respectively). The excellent anti-interference ability to ascorbic and uric acids and successful practical application for glucose determination in serum samples was presented for GR/PANI-AuNPs_{(6 nm)}-GOx/GOx electrode.

Formation and Electrochemical Evaluation of Polyaniline and Polypyrrole Nanocomposites Based on Glucose Oxidase and Gold Nanostructures

Nanocomposites based on two conducting polymers, polyaniline (PANI) and polypyrrole (Ppy), with embedded glucose oxidase (GOx) and 6 nm size gold nanoparticles (AuNPs_(6nm)) or gold-nanoclusters formed from chloroaurate ions (AuCl₄⁻), were synthesized by enzyme-assisted polymerization. Charge (electron) transfer in systems based on PANI/AuNPs_(6nm)-GOx, PANI/AuNPs_(AuCl4⁻₎-GOx, Ppy/AuNPs_(6nm)-GOx and Ppy/AuNPs_(AuCl4⁻₎-GOx nanocomposites was investigated. Cyclic voltammetry (CV)-based investigations showed that the reported polymer nanocomposites are able to facilitate electron transfer from enzyme to the graphite rod (GR) electrode. Significantly higher anodic current and well-defined red-ox peaks were observed at a scan rate of 0.10 V s⁻¹. Logarithmic function of anodic current (log I_pa), which was determined by CV-based experiments performed with glucose, was proportional to the logarithmic function of a scan rate (log v) in the range of 0.699–2.48 mV s⁻¹, and it indicates that diffusion-controlled electrochemical processes were limiting the kinetics of the analytical signal. The most efficient nanocomposite structure for the design of the reported glucose biosensor was based on two-day formed Ppy/AuNPs_(AuCl4⁻₎-GOx nanocomposites. GR/Ppy/AuNPs_(AuCl4⁻₎-GOx was characterized by the linear dependence of the analytical signal on glucose concentration in the range from 0.1 to 0.70 mmol L⁻¹, the sensitivity of 4.31 mA mM cm⁻², the limit of detection of 0.10 mmol L⁻¹ and the half-life period of 19 days.

An electrochemical sensor based on gold nanoparticles-functionalized reduced graphene oxide screen printed electrode for the detection of pyocyanin biomarker in Pseudomonas aeruginosa infection

Multidrug resistant Pseudomonas aeruginosa (P. aeruginosa) is known to be a problematic bacterium for being a major cause of opportunistic and nosocomial infections. In this study, reduced graphene oxide decorated with gold nanoparticles (AuNPs/rGO) was utilized as a new sensing material for a fast and direct electrochemical detection of pyocyanin as a biomarker of P. aeruginosa infections. Under optimal condition, the developed electrochemical pyocyanin sensor exhibited a good linear range for the determination of pyocyanin in phosphate-buffered saline (PBS), human saliva and urine at a clinically relevant concentration range of 1-100 μM, achieving a detection limit of 0.27 μM, 1.34 μM, and 2.3 μM, respectively. Our developed sensor demonstrated good selectivity towards pyocyanin in the presence of interfering molecule such as ascorbic acid, uric acid, NADH, glucose, and acetylsalicylic acid, which are commonly found in human fluids. Furthermore, the developed sensor was able to discriminate the signal with and without the presence of pyocyanin directly in P. aeruginosa culture. This proposed technique demonstrates its potential application in monitoring the presence of P. aeruginosa infection in patients.

Development of an enzymatic biosensor to determine eugenol in dental samples

A GCE/CRGO-βCD's/ADA-SPE/AuNPs biosensor was successfully developed to determine eugenol in dental samples. The optimal conditions to construct the biosensor were obtained from an experimental design based on the response surfaces methodology. The GCE/CRGO-βCD/ADA-SPE/AuNPs biosensor exhibited a very good analytical performance for the quantification of eugenol. Thus, it shows a linear range between 1.3 × 10^-8 and 1 × 10^-5 mol L^-1, with a sensitivity of (5.3 ± 0.3) x 10^-3 A mol^-1 L. The limits of detection and quantification were 4 × 10^-9 mol L^-1 and 1.3 × 10^-8 mol L^-1, respectively. Biosensors had an intraday and inter day reproducibility of 5% and 8%, respectively. The repeatability was of 3%, and the stability was 21 days (a decrease of 30% in current responses was observed after the fourth week). Recovery studies were performed in order to validate the proposed method. Recovery percentages were between 94 and 108%. A value of the apparent Michaellis-Menten constant, K_M^app, of 3.1 × 10^-6 mol L^-1 was obtained using both Lineweaver-Burk and Eadi-Hofstee methods.

A Study on Technology Competition of Graphene Biomedical Technology Based on Patent Analysis

Graphene, with high biocompatibility, physiological solubility and stability, has been reported as an emerging material for biomedical applications such as biosensors, drug delivery, and tissue engineering. Recently, identifying the technological competition (TC) of graphene biomedical technology has received worldwide attention from stakeholders. However, few studies have attached great importance to review the TC of this field by the analysis of patents. The main objective of this study is to develop a new and comprehensive method to investigate TC in a given technology field by conducting a patent review and then employing a patent roadmap to dig out the technology opportunity. The effectiveness of the approach is verified with the case study on graphene biomedical technology. Compared to previous research, this study makes the following important contributions. First, this study provides a new and systematic framework for the dynamic analysis of TC in a given technology field. It also extends the research perspectives of TC for industry, assignees, and technology, employs a patent roadmap to dig out technology opportunities, and enables stakeholders to understand TC from a dynamic perspective. Second, this study integrates patent analysis with a patent roadmap that has not appeared in existing methodologies of patent review. Third, it first introduces indicators (e.g., high value patent and competition position of top assignees) to the previous patent roadmap and provides a new methodology for patent roadmaps from a country level and assignee level. Finally, this study provides useful information for stakeholders interested in graphene biomedical technology, helps them to find new technology opportunities in this field, encourages them to determine the direction of future research, and has important significance for its application to diverse other emerging technologies.

A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters.

Synergic effect of plasmonic gold nanoparticles and graphene oxide on the performance of glucose sensing

A highly sensitive Au–GO hybrid nanostructure based non-enzymatic glucose biosensor is fabricated and exhibits superior sensitivity of 84.53 μA mM⁻¹ cm⁻². The biosensor also has applications for the detection of glucose in human blood serum, food samples and drinks.

Electrodeposition⁻Assisted Assembled Multilayer Films of Gold Nanoparticles and Glucose Oxidase onto Polypyrrole-Reduced Graphene Oxide Matrix and Their Electrocatalytic Activity toward Glucose

The study reports a facile and eco-friendly approach for nanomaterial synthesis and enzyme immobilization. A corresponding glucose biosensor was fabricated by immobilizing the gold nanoparticles (AuNPs) and glucose oxidase (GOD) multilayer films onto the polypyrrole (PPy)/reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) via the electrodeposition and self-assembly. PPy and graphene oxide were first coated on the surface of a bare GCE by the electrodeposition. Then, AuNPs and GOD were alternately immobilized onto PPy-RGO/GCE electrode using the electrodeposition of AuNPs and self-assembly of GOD to obtain AuNPs-GOD multilayer films. The resulting PPy-RGO-(AuNPs-GOD)_n/GCE biosensors were used to characterize and assess their electrocatalytic activity toward glucose using cyclic voltammetry and amperometry. The response current increased with the increased number of AuNPs-GOD layers, and the biosensor based on four layers of AuNPs-GOD showed the best performance. The PPy-RGO-(AuNPs-GOD)₄/GCE electrode can detect glucose in a linear range from 0.2 mM to 8 mM with a good sensitivity of 0.89 μA/mM, and a detection limit of 5.6 μM (S/N = 3). This study presents a promising eco-friendly biosensor platform with advantages of electrodeposition and self-assembly, and would be helpful for the future design of more complex electrochemical detection systems.

Nanocomposite Platform Based on EDTA Modified Ppy/SWNTs for the Sensing of Pb(II) Ions by Electrochemical Method

Heavy metal ions are considered as one of the major water pollutants, revealing health hazards as well as threat to the ecosystem. Therefore, investigation of most versatile materials for the sensitive and selective detection of heavy metal ions is need of the hour. Proposed work emphasizes the synthesis of conducting polymer and carbon nanotube nanocomposite modified with chelating ligand for the detection of heavy metal ions. Carbon nanotubes are having well known features such as tuneable conductivity, low density, good charge transport ability, and current carrying capacity. Conducting polymers are the most reliable materials for sensing applications due to their environmental stability and tuning of conductivity by doping and de-doping. Formation of nanocomposite of these two idealistic materials is advantageous over the individual material, which can help to tackle the individual limitations of these materials and can form versatile materials with ideal chemical and electrical properties. Chelating ligands are the most favorable materials due to their ability of complex formation with metal ions. The present work possesses a sensing platform based on conducting polymer and carbon nanotube nanocomposite, which is stable in various aqueous media and possess good charge transfer ability. Chelating ligands played an important role in the increased selectivity toward metal ions. Moreover, in present investigation Ethylenediaminetetraacetic acid (EDTA) functionalized polypyrrole (Ppy) and single walled carbon nanotubes (SWNTs) nanocomposite was successfully synthesized by electrochemical method on stainless steel electrode (SSE). The electrochemical detection of Pb(II) ions using EDTA-Ppy/SWNTs nanocomposite was done from aqueous media. Cyclic voltammetry technique was utilized for the electrochemical synthesis of Ppy/SWNTs nanocomposite. Ppy/SWNTs nanocomposite was further modified with EDTA using dip coating technique at room temperature. The EDTA-Ppy/SWNTs modified stainless steel electrode (SSE) exhibited good sensitivity and selectivity toward heavy metal ions [Pb(II)]. Detection limit achieved for Pb(II) ions was 0.07 μM.

Controlling enzyme function through immobilisation on graphene, graphene derivatives and other two dimensional nanomaterials

Controlling enzyme function through immobilisation on graphene, graphene derivatives and other two dimensional nanomaterials.

Electrochemical Synthesis of Polypyrrole, Reduced Graphene Oxide, and Gold Nanoparticles Composite and Its Application to Hydrogen Peroxide Biosensor

Here we report a facile eco-friendly one-step electrochemical approach for the fabrication of a polypyrrole (PPy), reduced graphene oxide (RGO), and gold nanoparticles (nanoAu) biocomposite on a glassy carbon electrode (GCE). The electrochemical behaviors of PPy–RGO–nanoAu and its application to electrochemical detection of hydrogen peroxide were investigated by cyclic voltammetry. Graphene oxide and pyrrole monomer were first mixed and casted on the surface of a cleaned GCE. After an electrochemical processing consisting of the electrooxidation of pyrrole monomer and simultaneous electroreduction of graphene oxide and auric ions (Au³⁺) in aqueous solution, a PPy–RGO–nanoAu biocomposite was synthesized on GCE. Each component of PPy–RGO–nanoAu is electroactive without non-electroactive substance. The obtained PPy–RGO–nanoAu/GCE exhibited high electrocatalytic activity toward hydrogen peroxide, which allows the detection of hydrogen peroxide at a negative potential of about −0.62 V vs. SCE. The amperometric responses of the biosensor displayed a sensitivity of 40 µA/mM, a linear range of 32 µM–2 mM, and a detection limit of 2.7 µM (signal-to-noise ratio = 3) with good stability and acceptable reproducibility and selectivity. The results clearly demonstrate the potential of the as-prepared PPy–RGO–nanoAu biocomposite for use as a highly electroactive matrix for an amperometric biosensor.

Graphene-Gold Nanoparticles Hybrid-Synthesis, Functionalization, and Application in a Electrochemical and Surface-Enhanced Raman Scattering Biosensor

Graphene is a single-atom-thick two-dimensional carbon nanosheet with outstanding chemical, electrical, material, optical, and physical properties due to its large surface area, high electron mobility, thermal conductivity, and stability. These extraordinary features of graphene make it a key component for different applications in the biosensing and imaging arena. However, the use of graphene alone is correlated with certain limitations, such as irreversible self-agglomerations, less colloidal stability, poor reliability/repeatability, and non-specificity. The addition of gold nanostructures (AuNS) with graphene produces the graphene-AuNS hybrid nanocomposite which minimizes the limitations as well as providing additional synergistic properties, that is, higher effective surface area, catalytic activity, electrical conductivity, water solubility, and biocompatibility. This review focuses on the fundamental features of graphene, the multidimensional synthesis, and multipurpose applications of graphene-Au nanocomposites. The paper highlights the graphene-gold nanoparticle (AuNP) as the platform substrate for the fabrication of electrochemical and surface-enhanced Raman scattering (SERS)-based biosensors in diverse applications as well as SERS-directed bio-imaging, which is considered as an emerging sector for monitoring stem cell differentiation, and detection and treatment of cancer.

Nanomaterials for biocatalyst immobilization – state of the art and future trends

Advantages, drawbacks and trends in nanomaterials for enzyme immobilization.

Significant improvement in the hydrogen storage capacity of a reduced graphene oxide/TiO2 nanocomposite by chemical bonding of Ti–O–C

A series of graphene-based nanocomposites with different TiO₂ contents have been prepared via a facile chemical method.

The applications of conductive nanomaterials in the biomedical field

As their name suggests, conductive nanomaterials (CNMs) are a type of functional materials, which not only have a high surface area to volume ratio, but also possess excellent conductivity. Thus far, CNMs have been widely used in biomedical applications, such as effectively transferring electrical signals, and providing a large surface area to adsorb proteins and induce cellular functions. Recent works propose further applications of CNMs in biosensors, tissue engineering, neural probes, and drug delivery. This review focuses on common types of CNMs and elaborates on their unique properties, which indicate that such CNMs have a potential to develop into a class of indispensable biomaterials for the diagnosis and therapy of human diseases.

Non-enzymatic electrochemical sensing platform based on metal complex immobilized carbon nanotubes for glucose determination

Nickel salophen (where salophen is N,N′-bis(salicylidene)-1,2-phenylenediamine) is immobilized on multiwall carbon nanotubes. This new material is utilized for electrocatalytic oxidization and sensitive determination of glucose in human blood samples.

A regular “signal attenuation” electrochemical aptasensor for highly sensitive detection of streptomycin

A novel aptasensor based on PCNRs and MWCNTs–CuO–AuNPs as the nanomatrix was constructed for the highly sensitive detection of streptomycin.

A green method to gold–graphene nanocomposite from cyclodextrin functionalized graphene for efficient non-enzymatic electrochemical sensing applications

Here, we report a new and green method of synthesis of gold nanoparticle functionalized graphene (Au–Gr) from β-cyclodextrin functionalized Gr (CD–Gr) with excellent electrochemical sensing properties.