Functionalization of graphene with electrodeposited Prussian blue towards amperometric sensing application

Prussian blue (PB) was grown compactly on graphene matrix by electrochemical deposition. The as-prepared PB-graphene modified glassy carbon electrode (PB-graphene/GCE) showed excellent electrocatalytic activity towards both the reduction of hydrogen peroxide and the oxidation of hydrazine, which could be attributed to the remarkable synergistic effect of graphene and PB. The PB-graphene/GCE showed sensitive response to H₂O₂ with a wide linear range of 10-1440 μM at 0.0 V, and to hydrazine with a wide linear range of 10-3000 μM at 0.35 V. The detection limit was 3 μM and 7 μM, respectively, and both of them had rapid response within 5 s to reach 95% steady state response. The wide linear range, good selectivity and long-time stability of the PB-graphene/GCE make it possible for the practical amperometric detection of hydrogen peroxide and hydrazine.     

Facile Synthesis of Graphene/Cobalt Oxide Nanohexagons for the Selective Detection of Dopamine

This work presents a simple green approach for the chemical synthesis of cobalt oxide nano hexagons (Co₃O₄ NHs) with an average size of 160±40 nm incorporated graphene nanosheets (GR). The techniques used to confirm the formation of GR−Co₃O₄ NHs are transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX), and X‐ray diffraction spectroscopy (XRD). The dopamine (DA) sensor was fabricated by drop casting GR−Co₃O₄ NHs on the pre‐cleaned glassy carbon electrode (GCE). GR−Co₃O₄ modified GCE displayed a sensitive and selective electrochemical determination of DA compared to only GR and Co₃O₄ NHs modified GCE. Our fabricated sensor showed a wide linear range from 0.2 to 3443 μM with low limit of detection (84 nM) towards the determination of DA. The sensitivity of our fabricated sensor was calculated to be 108 μA mM⁻¹ cm⁻². As well, a significant storage stability, repeatability and reproducibility were attained by GR−Co₃O₄ NHs modified GCE. Human urine samples were targeted for the demonstration of practicality of our sensor.     

Preparation of Co3O4/graphene Oxide Composites by a Depositing‐decompostion Method and its Application for Electrochemical Determination of Glucose

Co₃O₄/graphene oxide (GO) nanocomposites were successfully prepared by a depositing‐decomposition method. The as‐prepared samples were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Cyclic voltammetry (CV) was used to evaluate the electrochemical response of a glass carbon electrode (GCE) modified with Co₃O₄/GO nanocomposite towards glucose. Compared with the Co₃O₄/GCE, the Co₃O₄/GO/GCE exihibits higher electrocatalytic activity due to the synergistic effects of electrocatalytic ability of Co₃O₄ and large surface of GO. The Co₃O₄/GO/GCE was applied for glucose detection in alkaline solution. The linear current response range of glucose on Co₃O₄/GO/GCE covered the range from 9 × 10^?5 to 6.03 × 10^?3 M, with a detection limit of 5.2 × 10^?7 M (S/N = 3).     

Facile Synthesis of Reduced Graphene Oxide-octahedral Mn3O4 Nanocomposites as a Platform for the Electrochemical Determination of Metronidazole and Sulfamonomethoxine

A facile synthesis strategy of reduced graphene oxide (RGO)-octahedral Mn₃O₄ (oct-Mn₃O₄) nanocomposites using in situ one-pot hydrothermal reaction was reported. The RGO-oct-Mn₃O₄ nanocomposites were drop-casted onto the surface of glassy carbon electrode (GCE) to obtain RGO-oct-Mn₃O₄/GCE. DPV results revealed that the performance of RGO-oct-Mn₃O₄/GCE towards metronidazole displayed a linear ranging from 0.1 to 9.5 μM with a detection limit of 0.037 μM. For sulfamonomethoxine, it exhibited a linear ranging from 1 to 95 μM with a detection limit of 0.27 μM. Moreover, the proposed sensor had good anti-interference capability, high stability, satisfactory reproducibility, and was successfully applied in real samples.     

A study of the electrochemical behavior of an oxadiazole derivative electrodeposited on multi-wall carbon nanotube-modified electrode and its application as a hydrazine sensor

In this study, an oxadiazole multi-wall carbon nanotube-modified glassy carbon electrode (OMWCNT−GCE) was used as a highly sensitive electrochemical sensor for hydrazine determination. The surface charge transfer rate constant, k _s, and the charge transfer coefficient, α, for electron transfer between GCE and electrodeposited oxadiazole were calculated as 19.4 ± 0.5 s⁻¹ and 0.51, respectively at pH = 7.0. The obtained results indicate that hydrazine peak potential at OMWCNT−GCE shifted for 14, 109, and 136 mV to negative values as compared with oxadiazole-modified GCE, MWCNT−GCE, and activated GCE surface, respectively. The electron transfer coefficient, α, and the heterogeneous rate constant, k′, for the oxidation of hydrazine at OMWCNT−GCE were also determined by cyclic voltammetry measurements. Two linear dynamic ranges of 0.6 to 10.0 μM and 10.0 to 400.0 μM and detection limit of 0.17 μM for hydrazine determination were evaluated using differential pulse voltammetry. In addition, OMWCNT−GCE was shown to be successfully applied to determine hydrazine in various water samples.

     

Electrochemical Behavior and Voltammetric Determination of Curcumin at Electrochemically Reduced Graphene Oxide Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of curcumin by using a electrochemically reduced graphene oxide (ERGO) modified glass carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The electrochemical behaviors of curcumin at ERGO/GCE were investigated by cyclic voltammetry, suggesting that the ERGO/GCE exhibits excellent electrocatalytic activity towards curcumin, compared with bare GCE and GO/GCE electrodes. The electrochemical reaction mechanisms of curcumin, demethoxycurcumin and bisdemethoxycurcumin at the ERGO/GCE were also investigated and discussed systematically. Under physiological condition, the modified electrode showed linear voltammetric response from 0.2 μM to 60.0 μM for curcumin, with the detection limit of 0.1 μm. This work demonstrates that the graphene‐modified electrode is a promising strategy for electrochemical determination of biological important phenolic compounds.     

Electrode Modification through Click Chemistry Using Ni and Co Alkyne Phthalocyanines for Electrocatalytic Detection of Hydrazine

This work reports on the development of sensors for the detection of hydrazine using glassy carbon electrodes (GCE) modified with phthalocyanines through click chemistry. Tetrakis(5‐hexyn‐oxy) cobalt(II) phthalocyanine (complex 2 ) and tetrakis(5‐hexyn‐oxy) nickel(II) phthalocyanine (complex 3 ) were employed as electrode modifiers for hydrazine detection. The GCE was first grafted via the in situ diazotization of a diazonium salt, rendering the GCE surface layered with azide groups. From this point, the 1, 3‐dipolar cycloaddition reaction, catalysed by a copper catalyst was utilised to “click” the phthalocyanines to the surface of the grafted GCE. The modified electrodes were characterized by scanning electrochemical microscopy, X‐ray photoelectron spectroscopy and cyclic voltammetry. The electrografted CoP 2 ‐clicked‐GCE and NiP 3 ‐clicked‐GCE exhibited electrocatalytic activity towards the detection of hydrazine. The limit of detection (LoD) for the CoPc‐GCE was 6.09 μM, while the NiPc‐GCE had a LoD of 8.69 μM. The sensitivity was 51.32 μA mM⁻¹ for the CoPc‐GCE and 111.2 μA mM⁻¹ for the NiPc‐GCE.     

Fe3O4 Nanorods-RGO-ionic Liquid Nanocomposite Based Electrochemical Sensor for Aflatoxin B1 in Ground Paprika

A novel and sensitive method for the determination of aflatoxin B1 (AFA−B1) in ground paprika using a methyltrioctylammonium chloride ionic liquid (IL), iron oxide nanorods (Fe₃O₄ nanorods) and reduced graphene oxide (RGO) fabricated glassy carbon electrode (GCE) was developed. The synthesized nanoparticles, nanocomposites and modified electrode surfaces were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA/DSC) and x-ray diffraction (XRD) analyses. Moreover, the electrochemical performance of the developed sensor was determined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The obtained results demonstrate that the sensitivity of AFA−B1 is significantly enhanced on RGO-Fe₃O₄ nanorods-IL-GCE in comparison with bare GCE, RGO-GCE and RGO-Fe₃O₄ nanorods-GCE. The redox peak currents of AFA−B1 exhibited good linear relationship with its concentration in the range from 0.02 to 0.33 ng mL⁻¹ with detection limit of (LOD) 0.03 ng mL⁻¹ and limit of quantification (LOQ) 0.36 ng mL⁻¹ respectively (S/N=3). In addition, the fabricated electrode showed good stability and reproducibility. The proposed technique was effectively applied to identify the AFA−B1 in real ground paprika samples with acceptable results.     

Pt‐Pd Bimetallic Nanoparticles Decorated Nanoporous Graphene as a Catalytic Amplification Platform for Electrochemical Detection of Xanthine

The nanoporous graphene papers (NGPs) was prepared by the hard‐template method. The Pt−Pd modified NGPs hybrid was prepared by the self‐assembly method. Then a glassy carbon electrode (GCE) modified with Pt−Pd bimetallic nanoparticles‐functionalized nanoporous graphene composite has been prepared for the electrochemical determination of Xanthine (XA). The Pt−Pd/NGPs hybrid was characterized by transmission electron microscopy, scanning electron microscope and X‐ray diffraction. The electrochemical behavior of XA on Pt−Pd/NGPs/GCE was investigated by cyclic voltammetry and amperometric i‐t. The Pt−Pd/NGPs modified electrode exhibited remarkably electrocatalytic activity towards the oxidation reaction of XA in phosphate buffer solution (pH=5.5). Under the optimal conditions, the determination of XA was accomplished by using amperometric i‐t, the linear response range from 1.0×10⁻⁵∼1.2×10⁻⁴ M. The detection limit was 3.0×10⁻⁶ M (S/N=3). The proposed modified electrode showed good sensitivity, selectivity, and stability with applied to determine XA in human urine.     

Synthesis and characterisation of Ag-nanoparticles immobilised on ordered mesoporous carbon as an efficient sensing platform: application to electrocatalytic determination of hydrazine

In this study, a new strategy for the preparation of a modified glassy carbon electrode (GCE) based on a novel nano-sensing layer for the electrocatalytic oxidation of hydrazine was suggested. The suggested nano-sensing layer was prepared with the immobilisation of silver nanoparticles (AgNPs) on ordered mesoporous carbon. The morphology and properties of the prepared nanocomposite on the surface of GCE were characterised by scanning electron microscopy, transmission electron microscopy, N₂ adsorption-desorption, X-ray powder diffraction and electrochemical impedance spectroscopy. The electrochemical response characteristics of the modified electrode towards the target analyte were investigated by cyclic voltammetry. Under optimal experimental conditions, the suggested modified GCE showed excellent catalytic activity towards the electro-oxidation of hydrazine (pH = 7.5) with a significant increase in anodic peak currents in comparison with the unmodified GCE. By differential pulse voltammetry and amperometric methods, the suggested sensor demonstrated wide dynamic concentration ranges of 0.08–33.8 µM and 0.01–128 µM with the detection limit (S/N = 3) of 0.027 and 0.003 µM for hydrazine, respectively. The suggested hydrazine sensor was successfully applied for the highly sensitive determination of hydrazine in different real samples with satisfactory results.     

An amperometric sensor for hydrazine based on nano-copper oxide modified electrode

A sensitive hydrazine sensor has been fabricated using copper oxide nanoparticles modified glassy carbon electrode (GCE) to form nano-copper oxide/GCE. The nano-copper oxide was electrodeposited on the surface of GCE in CuCl₂ solution at −0.4 V and was characterized by Scanning electron microscopy and X-ray diffraction. The prepared modified electrode showed a good electrocatalytic activity toward oxidation of hydrazine. The electrochemical behavior of hydrazine on nano-copper oxide/GCE was explored. The oxidative current increased linearly with improving concentration of hydrazine on nano-copper oxide/GCE from 0.1 to 600 μM and detection limit for hydrazine was evaluated to be 0.03 μM at a signal-to-noise ratio of 3. The oxidation mechanism of hydrazine on the nano-copper oxide/GCE was also discussed. The fabricated sensor could be used to determine hydrazine in real water.     

A graphene-based electrochemical sensor for sensitive determination of caffeine

An electrochemical sensor based on the electrocatalytic activity of graphene (Gr) for sensitive detection of caffeine is presented. The electrochemical behaviors of caffeine on Nafion-Gr modified glassy carbon electrode (Nafion-Gr/GCE) were investigated by cyclic voltammetry and differential pulse voltammetry. The results showed that the Nafion-Gr/GCE exhibited excellent electrocatalytic activity to caffeine. Caffeine can be effectively accumulated at Nafion-Gr/GCE and produce a sensitive anodic peak. Such electrocatalytic behavior of Gr is attributed to its unique physical and chemical properties, e.g., subtle electronic characteristics and strong adsorptive capability. This electrochemical sensor shows an excellent performance for detecting caffeine with a detection limit of 1.2×10(-7) M (S/N=3), a reproducibility of 5.2% relative standard deviation, and a satisfied recovery from 98.6% to 102.0%. The sensor shows great promise for simple and sensitive determination of caffeine.     

Synthesis of graphene oxide nanosheet: A novel glucose sensor based on nickel-graphene oxide composite film

The graphene oxide (GO) nanosheets were produced by chemical conversion of graphite, and were characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR). An electrochemical sensor based on Ni/graphene (GR) composite film was developed by incorporating Ni²⁺ into the graphene oxide film modified glassy carbon electrode (Ni/GO/GCE) through the electrostatic interactions with negatively charged graphene oxide. The Ni²⁺/graphene modified glassy carbon electrode (Ni/GR/GCE) was prepared by cyclic voltammetric scanning of Ni/GO/GCE in the potential range from ?1.5 to 0.2 V at 50 mV s^?1 for 5 cycles. The electrochemical activity of Ni/GR/GCE was illustrated in 0.10 M NaOH using cyclic voltammetry. The Ni/GR/GCE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple. The introduction of conductive graphene not only greatly facilitates the electron transfer of Ni²⁺, but also dramatically improves the long-term stability of the sensor by providing the electrostatic interactions. Ni/GR/GCE also shows good electrocatalytic activity toward the oxidation of glucose. The Ni/GR/GCE gives a good linear range over 10 to 2700 μM with a detection limit of 5 μM towards the determination of glucose by amperometry. This sensor keeps over 85% activity towards 0.1 mM glucose after being stored in air for a month, respectively. Furthermore, the modified sensor was successfully applied to the sensitive determination of glucose in blood samples.     

In situ Electroreduction of Graphene Oxide: Increased Sensitivity for the Determination of NADH

A novel and useful method to catalyze the electro‐oxidation of nicotinamide adenine dinucleotide (NADH) over a glassy carbon electrode (GCE) modified with graphene oxide (GO) is presented. Based on the presence of oxygen moieties in GO, which can be easily reduced, an in situ electrochemical generation of reduced graphene oxide (denoted as erGO) applying a sufficient negative potential. A potential of ?1.000 V was selected to generate the erGO/GCE as a pretreatment potential before the detection of NADH. The in situ generated erGO/GCE system produces a decrease in the overpotential of NADH oxidation from +0.720 V to +0.230 V compared with GCE. The process also produced an important increase in current signals. The modified electrode was characterized by scanning electron (SEM) and electrochemical microscopies (SECM), cyclic voltammetry and by Raman spectroscopy. Amperometric detection of NADH via this straightforward electrocatalytic method provides a wide linear range between 10 and 100 μM, a lower detection limit of 0.36 μM and an excellent sensitivity of (1.47±0.09) μA mM^?1.     

Effect of detonation nanodiamonds on the electrocatalytic activity of asymmetric cobalt phthalocyanine: Covalent versus non-covalent linking

We report on the effect of detonation nanodiamonds (DNDs) on electrocatalytic properties of an asymmetrically substituted cobalt phthalocyanine (CoPc). The incorporation of DNDs onto cobalt phthalocyanine enhances its electrochemical behaviour. An asymmetrical CoPc alone, when π-π stacked (CoPc-DNDs(ππ)) or covalently linked (CoPc@DNDs) to DNDs is used to modify a glassy carbon electrode (GCE) for the electrocatalytic detection of hydrazine. In addition, the GCE was modified by sequentially adding CoPc and DNDs onto its surface, represented as GCE/CoPc-DNDs(seq) when CoPc is placed before DNDs on the electrode and GCE/DNDs-CoPc(seq) when DNDs are placed before CoPc, where seq represents sequential. The obtained catalytic rate for the detection of hydrazine on GCE/CoPc@DNDs was 9.3×10⁴ M⁻¹.s⁻¹ with a limit of detection as 0.33 μM. GCE/CoPc@DNDs gave better electrocatalytic activities when compared to its counterparts.     

Rapid and Sensitive Determination of Dinotefuran Residue Based on Electrochemical Enhancement of β‐cyclodextrin‐Graphene Composite

A rapid method for sensitive voltammetric determination of dinotefuran residue was reported. The proposed method was based on the electrocatalytic reduction of dinotefuran on β‐cyclodextrin‐graphene composite modified glassy carbon electrode (β‐CD‐rGO/GCE), giving rise to a higher reduction signal to dinotefuran relative to the bare (GCE) and graphene modified electrode (rGO/GCE). Moreover, a further signal enhancement was observed when the modified electrode incubated in solution at low temperature (0 °C) for a short time. The reduction mechanism and binding affinity were also discussed. The external standard calibration curve was obtained from linear sweep voltammetry in the range of 0.5 to 16.0 μM with a detection limit of 0.10 μM. In addition to optimization of pretreatment, this electrochemical method has been applied to the dinotefuran residue determination in millet samples with the detection limit of 0.01 mg kg^?1 and compared with an high performance liquid chromatography method. The proposed electrode and analysis methods were proven to be sensitive, accurate and rapid under the used conditions.     

A glassy carbon electrode modified with poly(anthranilic acid), poly(diphenylamine sulfonate) and CuO nano-particles for the sensitive determination of hydrogen peroxide

We report on a modified glassy carbon electrode (GCE) for sensing hydrogen peroxide (H₂O₂). It was constructed by consecutive electrochemical deposition of poly(anthranilic acid) and poly(diphenylamine sulfonate) on the GCE, followed by the deposition of copper oxide (CuO). The morphology and electrochemistry of the modified electrode was characterized by atomic force microscopy, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. The catalytic performance of the sensor was studied with the use of differential pulse voltammetry under optimized conditions. This sensor displayed significantly better electrocatalytic activity for the reduction of H₂O₂ in comparison to a GCE without or with modification with CuO or polymer films alone. The response to H₂O₂ is linear in the range between 0.005 to ~11 mM, and the detection limit is 0.18 μM (at an S/N of 3).

Graphene Nanocomposites Based Electrochemical Sensing Platform for Simultaneous Detection of Multi-drugs

Three reduced graphene oxide nanocomposites were employed to achieve the simultaneous electrochemical determination of multi-drugs including acetaminophen (ACTM), carbendazim (CB) and ciprofloxacin (CFX). All nanocomposite modified electrodes showed improved current responses for three drugs. Notably cauliflower-like platinum nanoparticles decorated reduced graphene oxide modified electrode (or Pt−RGO/GCE) exhibited the best performance in terms of electrochemical stability. Using Pt−RGO/GCE, the linear detect ranges of 30–120 μM, 25–115 μM and 10–25 μM, and detection limit values of 3.49, 2.96, and 1.53 μM were achieved for ACTM, CB and CFX respectively. The electrode was further used for the successful determination of above drugs in tap and river water using differential pulse voltammetry. From the obtained results, we believe that Pt-RGO/GCE is highly promising for the fabrication of robust electrochemical sensors for simultaneously determining ACTM, CB and CFX or similar types of drugs in the future.     

An in-situ synthesis of novel V2O5/G-C3N4/PVA nanocomposite for enhanced electrocatalytic activity toward sensitive and selective sensing of folic acid in natural samples

This paper describes a highly sensitive and selective electrochemical sensing of folic acid (FA) using vanadium pentoxide decorated graphene carbon nitride covalently grafted polyvinyl alcohol modified GC electrode (V₂O₅/G-C₃N₄/PVA/GCE). The V₂O₅/G-C₃N₄/PVA nanocomposite was synthesized by an in-situ oxidative polymerization method and characterized by various techniques such as UV–visible, Raman, FE-SEM, XRD, FT-IR, EDX, HR-TEM, SAED, and electrochemical methods. The V₂O₅/G-C₃N₄/PVA nanocomposite modified GCE showed superior electrocatalytic activity towards the FA detection. The superior electrochemical activity of the catalyst is owing to good conductivity, high surface area and enhanced electron transfer efficiency of the nanocomposite. The amperometric (i-t) studies revealed that the V₂O₅/G-C₃N₄/PVA nanocomposite modified GCE performed well by attaining a linear response of FA from 0.01 to 60 µM with a lower detection limit 0.00174 µM and the sensitivity of 19.02 μA µM⁻¹ cm⁻². Meanwhile, the V₂O₅/G-C₃N₄/PVA nanocomposite modified GCE exhibited good selectivity, rapid and stable response towards FA. The proposed method has been successfully applied for the selective determination of FA in various real samples such as apple juice, green tea and tap water with samples with good recoveries.     

Viologen-terminated polyamidoamine (PAMAM) dendrimer encapsulated with gold nanoparticles for nonenzymatic determination of hydrogen peroxide

The development of an accurate and low-cost monitoring technique for hydrogen peroxide (H₂O₂) is a crucial demand in environment, food industry, medicine and biology. Herein, we report the design and synthesis of viologen terminated second (G2.0) and third generation (G3.0) poly(amidoamine) PAMAM dendrimers, followed by encapsulation with gold nanoparticles to form G2.0 and G3.0 Vio-PAMAM-AuNPs. The G2.0 and G3.0 Vio-PAMAM-AuNPs were deposited over glassy carbon electrode (GCE) to form G2.0 and G3.0 Vio-PAMAM-AuNPs/GCE modified electrodes, respectively. The electrochemical behavior of G2.0 and G3.0 Vio-PAMAM-AuNPs/GCEs were investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Both the G2.0 and G3.0 Vio-PAMAM-AuNPs/GCEs showed a pair of well-defined redox peaks in 0.1 M phosphate buffer corresponding to the redox behavior of viologen V²⁺?V^?+ radical. G3.0 Vio-PAMAM-AuNPs/GCE has shown a higher current response than that of the G2.0 Vio-PAMAM-AuNPs/GCE and further the G3.0 Vio-PAMAM-AuNPs/GCE demonstrated impressive electrocatalytic activity towards reduction of H₂O₂, based on which a nonenzymatic sensor for the detection of H₂O₂ has been developed. The developed nonenzymatic sensor has displayed excellent performance towards H₂O₂ detection in the broad linear range of 0.1 mM – 6.2 mM with a low detection limit of 27 μM and high sensitivity of 202.7 μA mM^?1 cm^?2. The G3.0 Vio-PAMAM-AuNPs/GCE modified electrode with its extensive dendritic structure creating tailored sanctuary to accommodate a large number of viologen mediator and AuNPs exhibited good operational and long term stability and further the quantification of H₂O₂ in real samples has been verified by standard addition method.