Functionalization of graphene with Prussian blue and its application for amperometric sensing of H2O2

As a two-dimensional carbon material with high surface area and conductivity, graphene shows great promise for designing composite nanomaterials to achieve high-performance electrochemical devices. In this work, we prepared graphene-based nanocomposite material by electrochemically depositing Prussian blue (PB) nanoparticles on the surface of graphene. Fourier transform infrared spectra, SEM, and cyclic voltammetry were used to characterize the successful immobilization of PB. Compared with PB films and graphene sheets, the PB–graphene composite films showed the largest current response to the reduction of H₂O₂, probably due to the synergistic effects between graphene sheets and PB nanoparticles. Therefore, a fast and highly sensitive amperometric sensor for H₂O₂ was obtained with a detection sensitivity of 1.6 μA μM^?1 H₂O₂ per cm² and a linear response range of 50～5,000 μM. The detection limit of H₂O₂ was 20 nM at a signal-to-noise ratio of 3. These obtained results are much better than those reported for carbon nanotubes-based amperometric sensors.     

Electrochemical Sensors Based on Au Nanoparticles Decorated Pyrene-Reduced Graphene Oxide for Hydrazine, 4-Nitrophenol and Hg2+ Detection in Water

Monitoring hazardous chemical compounds such as hydrazine (N₂H₄), 4-nitrophenol (4-NP) and Hg²⁺ in natural water resources is a crucial issue due to their toxic effects on human health and catastrophic impact on the environment. Electrochemical nanostructured platforms integrating hybrid nanocomposites based on graphene derivatives and inorganic nanoparticles (NPs) are of great interest for such a purpose. In this work, disposable screen-printed carbon electrodes (SPCEs) have been modified with a hybrid nanocomposite formed by reduced graphene oxide (RGO), functionalized by 1-pyrene carboxylic acid (PCA), and decorated by colloidal Au NPs. These hybrid platforms have been tested for the electrocatalytic detection of N₂H₄ and 4-NP by differential pulse voltammetry and have been modified with an electropolymerized film of Hg²⁺ ions imprinted polycurcumin for the electroanalytical detection of Hg²⁺ by DPV. LODs, lower and in line with the lowest ones reported for state-of-the-art electrochemical sensors, integrating similar Au-graphene < nanocomposites, have been estimated. Additionally, good repeatability, reproducibility, and storage stability have been assessed, as well as a high selectivity in the presence of a 100-fold higher concentration of interfering species. The applicability of the proposed platforms for the detection of the compounds in real complex matrices, such as tap and river water samples, has been effectively demonstrated.     

CC Bonding of Graphene Oxide on 4‐Aminophenyl Modified Gold Electrodes towards Simultaneous Detection of Heavy Metal Ions

This paper studied the electrochemical sensors based on C? C bonding of graphene oxide (GO) on π‐conjugated aromatic group modified gold electrodes for simultaneous detection of heavy metal ions. For comparison, another sensing interface Au‐Ph‐NH‐CO‐GO, in which GO was modified to Au‐Ph‐NH₂ interfaces by amide bonding. On the basis of the principle of heavy metal ions complexation with oxygenated species on GO, the fabricated sensing interfaces were used for the simultaneous determination of Pb²⁺, Cu²⁺ and Hg²⁺. The performance of two sensing interfaces for simultaneous detection of three metal ions was compared. Au‐Ph‐GO sensing interface demonstrated higher sensitivity and better repeatability than Au‐Ph‐NH‐CO‐GO sensing interface.     

Graphene Quantum Dots‐based Electrochemical Biosensor for Catecholamine Neurotransmitters Detection

An useful electrochemical sensing approach was developed for epinephrine (EP) detection based on graphene quantum dots (GQDs) and laccase modified glassy carbon electrodes (GC). The miniature GC biosensor was designed and constructed via the immobilization of laccase in an electroactive layer of the electrode coated with carbon nanoparticles. This sensing arrangement utilized the catalytic oxidation of EP to epinephrine quinone. The detection process was based on the oxidation of catecholamine in the presence of the enzyme – laccase. With the optimized conditions, the analytical performance demonstrated a high degree of sensitivity −2.9 μA mM⁻¹ cm⁻², selectivity in a broad linear range (1–120×10⁻⁶ M) with detection limit of 83 nM. Moreover, the method was successfully applied for EP determination in labeled pharmacological samples.     

Functionalized graphene foam as electrode for improved electrochemical storage

We report on a non-covalent functionalization of graphene foam (GF) synthesized via chemical vapour deposition (CVD). The GF was treated with pyrene carboxylic acid (PCA) which acted as a source of oxygen and/or hydroxyl groups attached to the surface of the graphene foam for its electrochemical performance improvement. The modified graphene surface enabled a high pseudocapacitive effect on the GF. A specific capacitance of 133.3 F g^?1, power density ～ 145.3 kW kg^?1 and energy density ～ 4.7 W h kg^?1 were achieved based on the functionalized foam in 6 M KOH aqueous electrolyte. The results suggest that non-covalent functionalization might be an effective approach to overcome the restacking problem associated with graphene electrodes and also signify the importance of surface functionalities in graphene-based electrode materials.     

Diazonium salts: Stable monolayers on gold electrodes for sensing applications

The modification of gold electrodes with 4-carboxyphenyl diazonium salts to form stable layers for sensing applications is reported. Electrochemical reduction of 4-carboxyphenyl diazonium salts on gold electrodes yielded more stable layers than alkanethiol self-assembled monolayers in terms of extremes of electrode potential, sonication and with time. The application of the 4-carboxyphenyl modified electrodes for electrochemical sensing, which typically requires short chain alkanethiols on gold electrodes, is demonstrated via the covalent attachment of oligopeptides for the selective detection of Cu²⁺, Cd²⁺ and Pb²⁺. The diazonium salt/peptide modified gold electrodes not only had greater stability but also performed with lowest detected concentration to alkanethiol/peptide modified electrodes and with far greater sensitivity than the metal ion sensors when diazonium salt/peptide modified similar glassy carbon electrodes were employed.     

Electrochemical DNA sensors based on the use of gold nanoparticles: a review on recent developments

Electrochemical DNA sensors represent a simple, accurate and economical platform for DNA detection. Gold nanoparticles are known to be efficient labels in electrochemical sensors and to be viable materials to modify the surface of electrodes thereby to enhance the detection limit of the sensor. For surface modification, gold nanoparticles are used in combination with nanomaterials like graphene, graphene oxide, or carbon nanotubes to improve electrochemical performance in general. This review (with 116 refs.) mainly covers the advances made in recent years in the use of gold nanoparticles in DNA sensing. It is divided into the following main sections: (a) An introduction covers aspects of electrochemical sensing of DNA and of appropriate nanomaterials in general. (b) The use of gold nanoparticles in DNA is specifically addressed next, with subsections on AuNPs acting as electrochemical labels, electron transfer mediators, signal amplifiers, carriers of electroactive molecules, catalysts, immobilization platforms, on silver enhancement strategies, on AuNPs modified with carbonaceous materials (such as graphenes and nanotubes), and on multiple amplification schemes. The review concludes with a discussion of current challenges and trends in terms of highly sensitive DNA based sensing using AuNPs.

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Graphical abstract The review describes the state of the art in the use of gold nanoparticles in the electrochemical DNA sensors and contains sections on the use of AuNPs as labels, signal amplifiers, carriers of electroactive molecules, catalyst, immobilization platform, and on silver enhancement and multiple amplification strategies.

     

氮掺杂碳层包覆金属钴颗粒与氮掺杂石墨烯纳米复合材料作为高容量锂离子电池负极材料

合成了一种石墨烯基纳米复合材料即：由氮掺杂碳层包覆的金属钴纳米颗粒,充分分散于氮掺杂的石墨烯表面。这种纳米复合材料进一步提高了石墨烯的导电性,增加了石墨烯的储锂容量。该材料被用作锂离子电池负极材料,在性能测试中展现了良好的循环性能,在以100 mA·g^-1的电流密度循环200圈后,放电容量高达950.1 mAh·g^-1,库伦效率约为98%。     

氮掺杂碳层包覆金属钴颗粒与氮掺杂石墨烯纳米复合材料作为高容量锂离子电池负极材料

合成了一种石墨烯基纳米复合材料即：由氮掺杂碳层包覆的金属钴纳米颗粒,充分分散于氮掺杂的石墨烯表面。这种纳米复合材料进一步提高了石墨烯的导电性,增加了石墨烯的储锂容量。该材料被用作锂离子电池负极材料,在性能测试中展现了良好的循环性能,在以100 mA·g^-1的电流密度循环200圈后,放电容量高达950.1 mAh·g^-1,库伦效率约为98%。     

还原氧化石墨烯/金纳米修饰电极在新冠病毒检测中的应用

研究使用电化学沉积法在丝网印刷碳电极表面制备了还原氧化石墨烯和金纳米颗粒,构建了一种用于新冠病毒检测的石墨烯电化学传感器。通过扫描电子显微镜(SEM)和相应的电化学方法对纳米复合材料在电极表面的成功修饰进行了表征分析。并采用差分脉冲伏安法对传感器的性能进行检测,实验构建的电化学传感器具有良好的灵敏度,该传感器检线性范围为10_-10^-10_-6^mol/L,具有良好的重复性和特异性。     

A glassy carbon electrode modified with a film composed of cobalt oxide nanoparticles and graphene for electrochemical sensing of H2O2

We have prepared a graphene-based hybrid nanomaterial by electrochemical deposition of cobalt oxide nanoparticles (CoO_xNPs) on the surface of electrochemically reduced graphene oxide deposited on a glassy carbon electrode (GCE). Scanning electron microscopy and cyclic voltammetry were used to characterize the immobilized nanoparticles. Electrochemical determination of H₂O₂ is demonstrated with the modified GCE at pH 7. Compared to GCEs modified with CoO_xNPs or graphene sheets only, the new electrode displays larger oxidative current response to H₂O₂, probably due to the synergistic effects between the graphene sheets and the CoO_xNPs. The sensor responds to H₂O₂ with a sensitivity of 148.6 μA mM^?1 cm^?2 and a linear response range from 5 μM to 1 mM. The detection limit is 0.2 μM at a signal to noise ratio (SNR) of three. The method was successfully applied to the determination of H₂O₂ in hydrogen peroxide samples.

Graphene Paper Decorated with a 2D Array of Dendritic Platinum Nanoparticles for Ultrasensitive Electrochemical Detection of Dopamine Secreted by Live Cells

To circumvent the bottlenecks of non‐flexibility, low sensitivity, and narrow workable detection range of conventional biosensors for biological molecule detection (e.g., dopamine (DA) secreted by living cells), a new hybrid flexible electrochemical biosensor has been created by decorating closely packed dendritic Pt nanoparticles (NPs) on freestanding graphene paper. This innovative structural integration of ultrathin graphene paper and uniform 2D arrays of dendritic NPs by tailored wet chemical synthesis has been achieved by a modular strategy through a facile and delicately controlled oil–water interfacial assembly method, whereby the uniform distribution of catalytic dendritic NPs on the graphene paper is maximized. In this way, the performance is improved by several orders of magnitude. The developed hybrid electrode shows a high sensitivity of 2 μA cm^?2 μm ^?1, up to about 33 times higher than those of conventional sensors, a low detection limit of 5 nm, and a wide linear range of 87 nm to 100 μm . These combined features enable the ultrasensitive detection of DA released from pheochromocytoma (PC 12) cells. The unique features of this flexible sensor can be attributed to the well‐tailored uniform 2D array of dendritic Pt NPs and the modular electrode assembly at the oil–water interface. Its excellent performance holds much promise for the future development of optimized flexible electrochemical sensors for a diverse range of electroactive molecules to better serve society.     

Electrochemical metal-ion sensor based on a cobalt phthalocyanine complex captured in Nafion® on a glassy carbon electrode

This article describes an electrochemical metal-ion sensor based on a cobalt phthalocyanine (CoPc) complex and determination of its sensor activity for some transition metal ions. Ag⁺ and Hg²⁺, among several transition metal ions, coordinate to the sulfur donors of CoPc and alter the electrochemical responses of CoPc in solution, indicating possible application of the complex as Ag⁺ and Hg²⁺ sensor. For practical application, CoPc was encapsulated into a polymeric cation exchange membrane, Nafion, on a glassy carbon electrode and used as an electrochemical coordination element. This composite electrode was potentiometrically optimized and potentiometrically and amperometrically characterized as transition metal-ion sensors with respect to reproducibility, repeatability, stability, selectivity, linear concentration range, and sensitivity. A µmol?dm^?3 sensitivity of the CoPc-based sensor indicates its possible practical application for the determination of Ag⁺ and Hg⁺² in waste water samples.     

A Novel Electrogenerated Chemiluminescence (ECL) Sensor Based on Ru(bpy)32+‐Doped Titania Nanoparticles Dispersed in Nafion on Glassy Carbon Electrode

A novel electrogenerated chemiluminescence (ECL) sensor based on Ru(bpy)₃²⁺‐doped titania (RuDT) nanoparticles dispersed in a perfluorosulfonated ionomer (Nafion) on a glassy carbon electrode (GCE) was developed in this paper. The electroactive component‐Ru(bpy)₃²⁺ was entrapped within the titania nanoparticles by the inverse microemulsion polymerization process that produced spherical sensors in the size region of 38±3 nm. The RuDT nanoparticles were characterized by electrochemical, transmission electron and scanning microscopy technology. The Ru(bpy)₃²⁺ encapsulation interior of the titania nanoparticles maintains its ECL efficiency and also reduces Ru(bpy)₃²⁺ leaching from the titania matrix when immersed in water due to the electrostatic interaction. This is the first attempt to prepare the RuDT nanoparticles and extend the application of electroactive component‐doped nanoparticles into the field of ECL. Since a large amount of Ru(bpy)₃²⁺ was immobilized three‐dimensionally on the electrode, the Ru(bpy)₃²⁺ ECL signal could be enhanced greatly, which finally resulted in the increased sensitivity. The ECL analytical performance of this ECL sensor for tripropylamine (TPA) was investigated in detail. This sensor shows a detection limit of 1 nmol/L for TPA. Furthermore, the present ECL sensor displays outstanding long‐term stability.     

A review: Influence of divalent,trivalent, rare earth and additives ions on Ni–Cu–Zn ferrites

From several decades, researchers were fabricated the materials like ferrites, perovskites, ceramic, metal oxides, chalcogenides, etc. and investigated its properties for numerous useful applications. Among all the materials, ferrites are more useful in technological and industrial application purpose. In modern era of technology, ferrites in the form of a nano scales are be the soul of electronic and electrical components. Due to the noticeable versatile properties like high resistivity, moderate permeability, low dielectric loss and moderate sensitivity researcher's shifts their theoretical and technological point of view from other materials to ferrites. The scientists from chemistry, physics, material science and metallurgy are trying to achieve the desirable electric, magnetic, optical and sensing properties of nanoferrites by optimizing its parameters like chemical composition, synthesis methods, addition of impurity, sintering conditions etc. In this review we investigated an influence of substitution or doping of divalent (Ni²⁺, Cu²⁺, Zn²⁺, Mn²⁺, Mg²⁺ etc.), trivalent (Cr³⁺, Al³⁺, In³⁺, WO³⁺ etc.), rare earth (La³⁺, Sm³⁺, Y³⁺, Nd³⁺, Dy³⁺, Tb³⁺, Tm³⁺ etc.) metal ions and addition of additive (MnO₂, SiO₂, TiO₂, BaTiO₃, PbO, V₂O₅ etc.) in Ni–Cu–Zn ferrites. Researchers successfully transforms the Ni–Cu–Zn properties in a way that, industrialists utilized it for various applicative products such as in Li-Ion battery, super capacitors, EM filters, magnetic recording media, micro-inductors, biofuel production, gas sensors, humidity sensors etc. In nutshell, review is a complete combination of preparation methods, impact of divalent, trivalent, rare earth and additives on Ni–Cu–Zn nanoferrite with its useful applications.     

Oligonucleotides-based biosensors with high sensitivity and selectivity for mercury using electrochemical impedance spectroscopy

A novel electrochemical biosensor with high sensitivity and selectivity for mercuric ion detection, based on DNA self-assembly electrode, is designed. Thiol functionalized poly-T oligonucleotides were used as gold electrode modifier through formation of Au–S bond between DNA and gold electrode. In presence of Hg²⁺ ions, the specific coordination between Hg²⁺ and thymine bases can change parallel ss-DNA from linear to hairpin structures, which can cause the release of partial DNA molecules from the surface of the electrode. The density of DNA on the surface of electrode correlated with the concentration of mercury in the solution and can be monitored by electrochemical impedance spectroscopy. The limit of detection of this method is pM level of mercuric ions which is far below the upper limit of Hg²⁺ mandated by United States Environmental Protection Agency (EPA), 2 ppb (10 nM). In addition, this method showed excellent selectivity. A series of divalent metal ions, including Ni²⁺, Co²⁺, Mg²⁺, Zn²⁺, Ba²⁺ and Cd²⁺, have little interference with the detection of Hg²⁺.     

Mn,B, N co-doped graphene quantum dots for fluorescence sensing and biological imaging

The fluorescent and quantum yield (QY) of graphene quantum dots has been improved in recent years by doped atoms, which have good application prospects in fluorescence sensors and biological imaging. Here, a one-step hydrothermal synthesis method was used to synthesize manganese ions bonded with boron and nitrogen-doped graphene quantum dots (Mn-BN-GQDs). Compared with the boron and nitrogen co-doping graphene quantum dots (BN-GQDs), the fluorescence properties and quantum yield of Mn-BN-GQDs are significantly improved. Meanwhile, Mn-BN-GQDs exhibit low toxicity and good fluorescence imaging in living cells and has high selectivity to Fe³⁺ ions. Therefore, this experiment design Mn-BN-GQDs as a fluorescence sensor to detect Fe³⁺ ions, providing strong evidence for the advanced high sensitivity, selectivity and wide detection range of the Mn-BN-GQDs as a fluorescence sensor. These results indicate a dual linear relationship with good linear relationships in the 10–100 μM and 100–800 μM ranges, and limit of detection are 0.78 μM and 9.08 μM, respectively. Cellular imaging results demonstrate that Mn-BN-GQDs can be used as fluorescence sensors in biological imaging. Mn-BN-GQDs can be used for fluorescence sensing in biological imaging in combination with low toxicity, QY and quantum dot lifetime.     

Copper(II) ion sensor based on electropolymerized undoped conducting polymers

A solid state copper(II) ion sensor is reported based on the application of electropolymerized undoped (neutral) polycarbazole (PCz) and polyindole (PIn) modified electrodes. The new sensor shows high selectivity to Cu²⁺ ions with a detection limit of 10^–5 M. PCz and PIn are formed respectively by the anodic oxidation of 50 mM carbazole and 5 mM indole monomers in dichloromethane containing 0.1 M tetrabutylammonium perchlorate on a platinum electrode using a single compartment cell. Potentiostatic polymerization of both the monomers are carried out at 1.3 V and 1.0 V vs. Ag/AgCl, respectively. Perchlorate ions were electrochemically removed from the polymer films by applying – 0.2 V vs. Ag/AgCl. Polymer-coated electrodes are incubated in 1 M KCl solution for 8 h followed by incubation in distilled water for 2 h before using as a metal ion sensor. The undoped PCz and PIn electrodes were found to be highly selective and sensitive for Cu²⁺ ions with little selectivity for Pb²⁺ and negligible response towards Ag⁺, Hg²⁺, Cu⁺, Ni²⁺, Co²⁺, Fe²⁺, Fe³⁺ or Zn²⁺. Potentiometric responses for Cu²⁺ ions are recorded for both the sensor electrodes together with a double-junction Ag/AgCl reference electrode. Calibration curves for Cu²⁺ are reported for both ion sensors. The polymer-modified electrodes were found to be stable for several weeks. Electronic Publication     

Inherent Electrochemistry and Activation of Chemically Modified Graphenes for Electrochemical Applications

Graphene research is currently at the frontier of electrochemistry. Many different graphene‐based materials are employed by electrochemists as electrodes in sensing and in energy‐storage devices. Because the methods for their preparation are inherently different, graphene materials are expected to exhibit different electrochemical behaviors depending on the functionalities and density of defects present. Electrochemical treatment of these “chemically modified graphenes” (CMGs) represents an easy approach to alter surface functionalities and consequently tune the electrochemical performance. Herein, we report a preliminary electrochemical characterization of four common chemically modified graphenes, namely: graphene oxide, graphite oxide, chemically reduced graphene oxide, and thermally reduced graphene oxide. These CMGs were compared with graphite as a reference material. Cyclic voltammetry was used to ascertain the chemical functionalities present and to understand the potential ranges in which the materials were electroactive. Electrochemical treatment with either an oxidative or a reductive fixed potential were then carried out to activate these chemically modified graphenes. The effects of such electrochemical treatments on their electrocatalytic properties were then investigated by cyclic voltammetry in the presence of well‐known redox probes, such as [Fe(CN)₆]^4?/3?, Fe^3+/2+, [Ru(NH₃)₆]^2+/3+, and ascorbic acid. Thermally reduced graphene oxide exhibited the best electrochemical behavior amongst all of the CMGs, with the fastest rate of heterogeneous electron transfer (HET) and the lowest overpotentials. These findings will have far‐reaching consequences for the evaluation of different CMGs as electrode materials in electrochemical devices.     

Graphene-based Disposable Electrochemical Sensor for Chlorhexidine Determination

In this work, simple, reliable, eco-friendly, and quantitative electrochemical sensors were developed to detect chlorhexidine Digluconate (CHX) in a variety of dosage forms, including mouthwashes and intimate douches, as well as chlorhexidine in spiked human saliva. Without any sample pre-treatment or extraction processes, CHX was measured in colored aqueous formulations. Based on carbon screen-printed electrodes, two potentiometric sensors (sensors I and II), utilizing graphene nanocomposites (Gr-NC), were designed (SPEs). An ionophore, 2-hydroxypropyl-β-cyclodextrin, was doped into the Poly Vinyl Chloride (PVC) polymeric membrane to improve sensor selectivity.