A Novel Enzymatic Glucose Biosensor and Nonenzymatic Hydrogen Peroxide Sensor Based on (3‐Aminopropyl) Triethoxysilane Functionalized Reduced Graphene Oxide

In the present study, a novel enzymatic glucose biosensor using glucose oxidase (GOx) immobilized into (3‐aminopropyl) triethoxysilane (APTES) functionalized reduced graphene oxide (rGO‐APTES) and hydrogen peroxide sensor based on rGO‐APTES modified glassy carbon (GC) electrode were fabricated. Nafion (Nf) was used as a protective membrane. For the characterization of the composites, Fourier transform infrared spectroscopy (FTIR), X‐ray powder diffractometer (XRD), and transmission electron microscopy (TEM) were used. The electrochemical properties of the modified electrodes were investigated using electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry. The resulting Nf/rGO‐APTES/GOx/GC and Nf/rGO‐APTES/GC composites showed good electrocatalytical activity toward glucose and H₂O₂, respectively. The Nf/rGO‐APTES/GC electrode exhibited a linear range of H₂O₂ concentration from 0.05 to 15.25 mM with a detection limit (LOD) of 0.017 mM and sensitivity of 124.87 μA mM⁻¹ cm⁻². The Nf/rGO‐APTES/GOx/GC electrode showed a linear range of glucose from 0.02 to 4.340 mM with a LOD of 9 μM and sensitivity of 75.26 μA mM⁻¹ cm⁻². Also, the sensor and biosensor had notable selectivity, repeatability, reproducibility, and storage stability.     

A Sensitive Sensor Based on CuTSPc and Reduced Graphene Oxide for Simultaneous Determination of the BHA and TBHQ Antioxidants in Biodiesel Samples

A novel and sensitive electrochemical sensor was developed for the simultaneous determination of the butylated hydroxyanisole (BHA) and tert‐butylhydroquinone (TBHQ) antioxidants in biodiesel samples employing the differential pulse voltammetry (DPV). In this sense, a glassy carbon electrode (GCE) modified with copper (II) tetrasulfonated phthatocyanine immobilized on reduced graphene oxide (CuTSPc/rGO) allowed the detection of BHA and TBHQ at potentials lower than those observed at unmodified electrodes. The sensor was characterized by cyclic voltammetry (CV) and linear scan voltammetry (LSV). After optimization of the experimental parameters, the analytical curves for simultaneous determination of BHA and TBHQ by DPV technique demonstrated an excellent linear response from 0.1 to 500 µmol L^?1 with detection limit of 0.045 µmol L^?1 for TBHQ and 0.036 µmol L^?1 for BHA. Finally, the proposed method was successfully applied in the simultaneous determination of BHA and TBHQ in six biodiesel samples, and the results obtained were found to be similar to those obtained using the HPLC method with agreement at 95 % confidence level.     

Evaluation of Reduced Graphene Oxide Modified with Antimony and Copper Nanoparticles for Levofloxacin Oxidation

This work presents, for the first time, the oxidation mechanism of levofloxacin combining electrochemical experiments and molecular modelling techniques. Levofloxacin is one of the most widely used antibiotics in the world. The detection of this antibiotic is important, because it cannot be fully assimilated by the human organism, therefore levofloxacin is considerate a hazardous pollutant for environment. Sensors based on reduced graphene oxide (rGO) modified with antimony and copper nanoparticles (NPs) were synthesized, characterized and evaluated for the electrochemical detection of the levofloxacin. The morphological and electrochemical characterization of the composites confirmed that the rGO was modified with the metallic nanoparticles. Molecular modelling studies were performed applying Density Functional Theory (DFT) approach, which indicated that the mechanism of levofloxacin oxidation is given by the loss of two electrons: one from N14 atom and other from C13 atom of the levofloxacin molecule. The glassy carbon electrode (GCE) modified with the SbNPs/rGO and CuNPs/rGO composites were evaluated for the determination of levofloxacin using differential pulse voltammetry (DPV) and achieved detection limit of 4.1×10⁻⁸ mol L⁻¹ and 1.7×10⁻⁸ mol L⁻¹, respectively, presenting as alternative composites to be used in the analysis of antibiotics.     

Fast and Simple Preparation of a Sensor Based on Electrochemically Reduced Graphene Oxide (rGO) for the Determination of Zopiclone in Pharmaceutical Dosage by Square Wave Adsorptive Stripping Voltammetry (SWAdSV)

The interactions of zopiclone with electrochemically reduced graphene oxide (rGO) modified electrode were examined. A comparison of GC/rGO and glassy carbon electrode (GC) by electrochemical impedance spectroscopy and scanning electrochemical microscopy (SECM) shows that the modified surface is much less conductive than GC. The role of rGO is to act as a site of specific adsorption of the analyte. Molecular dynamics showed that the monoanionic form of zopiclone presents more interactions with defects of rGO. The analytical methodology allowed obtaining a linearity of 10–130 μg L⁻¹, with a limit of detection of 2.14 μg L⁻¹ using SWAdSV at pH 10.0.     

Competitive Host-guest Electrochemical Detection of Ivermectin Drug Using a β-Cyclodextrin/Graphene-based Electrode

The present study describes the novel development and application of an ivermectin (IVM) sensing electrochemical platform based on reduced graphene oxide (rGO) and the macrocyclic host β-cyclodextrin (β-CD) molecule. The sensing method was based in the host-guest characteristics of β-CD and competitive interaction between the target analyte and the methylene blue (MB) redox probe. Differential pulse voltammetry (DPV) was employed for the detection of IVM and a linear response between 0.5 and 40.0 μmol L⁻¹ with a limit of detection of 0.25 μmol L⁻¹ was obtained using the glassy carbon (GC)/rGO/β-CD electrode. The sensing platform was successfully applied for the detection of IVM in tap water samples, which may expand the applications of β-CD towards the analysis of other chemical species.     

Voltammetric Determination of Sophoridine Based on Gold Nanoparticles/L‐cysteine/ Graphene Modified Glassy Carbon Electrode

A new strategy to make the electrochemical sensor was presented, through combining gold nanoparticles (GNPs) with reduced graphene oxide (rGO) via L‐cysteine (L‐cys) as crosslinker. The resulting electrodes were characterized by scanning electron microscopy (SEM) and electrochemical methods. And it was applied to develop a high‐sensitive electrochemical sensor for determination of sophoridine. Compared with the bare GCE and reduced graphene oxide modified electrode, the resulting electrodes exhibited excellent response toward the oxidation of sophoridine by significantly enhancing the oxidation peak currents and decreasing the overpotential of sophoridine. Under the selected conditions, there exist the linear relation between the oxidation peak currents and sophoridine concentration in the range of 1.0 x 10^‐6～1.0 x 10^‐4 mol L^‐1, with detection limit of 4.0 x 10^‐7 mol L^‐1. At the same time, the method can be successfully applied to the quantitative determination of sophoridine in injection samples and its result is satisfactory.     

Simultaneous Electrochemical Determination of Hydroquinone and Bisphenol A using a Carbon Paste Electrode Modified with Silver Nanoparticles

In this paper, a rapid and sensitive modified electrode for the simultaneous determination of hydroquinone (HQ) and bisphenol A (BPA) is proposed. The simultaneous determination of these two compounds is extremely important since they can coexist in the same sample and are very harmful to plants, animals and the environment in general. A carbon paste electrode (CPE) was modified with silver nanoparticles (nAg) and polyvinylpyrrolidone (PVP). The PVP was used as a reducing and stabilizing agent of nAg from silver nitrate in aqueous media. The nAg‐PVP composite obtained was characterized by transmission electron microscopy and UV‐vis spectroscopy. The electrochemical behavior of HQ and BPA at the nAg‐PVP/CPE was investigated in 0.1 mol L⁻¹ B−R buffer (pH 6.0) using cyclic voltammetry (CV) and square wave voltammetry (SWV). The results indicate that the electrochemical responses are improved significantly with the use of the modified electrode. The calibration curves obtained by SWV, under the optimized conditions, showed linear ranges of 0.09–2.00 μmol L⁻¹ for HQ (limit of detection 0.088 μmol L⁻¹) and 0.04–1.00 μmol L⁻¹ for BPA (limit of detection 0.025 μmol L⁻¹). The modified electrode was successfully applied in the analysis of water samples and the results were comparable to those obtained using UV‐vis spectroscopy.     

Ionic liquid-functionalized graphene as modifier for electrochemical and electrocatalytic improvement: comparison of different carbon electrodes

Electrochemical activities of typically electrochemical targets at three kinds of modified carbon electrodes, i.e. carbon ionic liquid electrode (CILE), graphene/carbon paste electrode (CPE), and ionic liquid-functionalized graphene (IL-graphene)/CPE, were compared in detail. The redox processes of the probes at IL-graphene/CPE were faster than those at CILE and graphene/CPE from cyclic voltammetry. An electrochemical method for the simultaneous determination of guanine and adenine was described with detection limits of 6.5 × 10⁻⁸ mol L⁻¹ (guanine) and 3.2 × 10⁻⁸ mol L⁻¹ (adenine). Single A → G mutation of sequence-specific DNA could be discriminated by the IL-graphene/CPE.     

Sensitive Voltammetric Determination of Bisphenol A Based on a Glassy Carbon Electrode Modified with Copper Oxide‐Zinc Oxide Decorated on Graphene Oxide

A highly sensitive and selective chemical sensor was prepared based on metallic copper‐copper oxides and zinc oxide decorated graphene oxide modified glassy carbon electrode (Cu?Zn/GO/GCE) through an easily electrochemical method for the quantification of bisphenol A (BPA). The composite electrode was characterized via scanning electron microscopy (SEM), X‐Ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of BPA in Britton‐Robinson (BR) buffer solution (pH 7.1) was examined using cyclic voltammetry (CV). Under optimized conditions, the square wave voltammetry (SWV) response of Cu?Zn/GO/GCE towards BPA indicates two linear relationships within concentrations (3.0 nmol L^?1?0.1 μmol L^?1 and 0.35 μmol L^?1?20.0 μmol L^?) and has a low detection limit (0.88 nmol L^?1). The proposed electrochemical sensor based on Cu?Zn/GO/GCE is both time and cost effective, has good reproducibility, high selectivity as well as stability for BPA determination. The developed composite electrode was used to detect BPA in various samples including baby feeding bottle, pacifier, water bottle and food storage container and satisfactory results were obtained with high recoveries.     

Evaluation of graphene oxide and reduced graphene oxide in the immobilization of laccase enzyme and its application in the determination of dopamine

Bioelectrodes were developed based on a simple deposition of graphene oxide (GO) or reduced graphed oxide (rGO) and laccase (Lac) on a glassy carbon (GC) electrode surface. The morphology and electrochemical behavior of the biosensors were characterized by scanning electron microscopy and cyclic voltammetry. These results demonstrated that only rGO was successfully applied for the immobilization of the laccase enzyme, improving the analytical signal for the determination of dopamine. The GC/rGO/Lac biosensor was applied to the detection of dopamine in synthetic urine and plasmatic serum samples, achieving a detection limit of 91.0 nmol L^?1.     

基于还原石墨烯/纳米银复合材料的电化学传感器测定双酚A

石墨烯特有的褶皱层状结构以及银纳米粒子良好的催化性能,使其在电化学方面具有良好的应用潜能.本研究以柠檬酸钠为还原剂,通过水热反应原位制备出还原石墨烯/纳米银复合材料(rGO/AgNPs),用于修饰玻碳电极,研究了双酚A的电化学行为.循环伏安法(CV)和方波伏安法(SWV)的实验结果表明,双酚A可以在rGO/AgNPs修饰电极表面发生快速的氧化还原反应,基于此实现了对双酚A的高灵敏检测.在最优条件下,双酚A的氧化峰电流与其浓度在0.1~40.0μmol/L范围内呈良好的线性关系(r2=0.996),检出限为50.7 nmol/L(S/N=3).将其用于实际环境和塑料样品中双酚A的检测,回收率为91.7%~102.9%.     

Electroanalytical Determination of Cd(II) and Pb(II) in Bivalve Mollusks using Electrochemically Reduced Graphene Oxide‐based Electrode

An electrochemical sensor for the simultaneous determination of Cd(II) and Pb(II) by square wave anodic stripping voltammetry (SWASV) in bivalve mollusks using a glassy carbon electrode modified with electrochemically reduced graphene oxide has been developed. The modified surface was characterized by cyclic voltammetry, high resolution scanning electron microscopy (HR‐SEM), and Raman spectroscopy. The optimum conditions were optimized and a linear range was observed from 15–105 μg L^?1 with a limits of detection of 15 μg L^?1 for Cd(II) and Pb(II). The methodology was validated and applied in different samples of commercial bivalve mollusks with satisfactory results. The high conductivity and greater surface area of the modifying agent improves the preconcentration capacity of the electrochemical sensor, allowing to develop a simple, rapid and sensitive analysis in the detection of lead and cadmium in marine resources.     

AgNP/Bi/Nafion‐modified Disposable Electrodes for Sensitive Zn(II), Cd(II), and Pb(II) Detection in Aerosol Samples

A new method for modifying electrodes with Ag nanoparticles (AgNPs) using electrospray deposition for sensitive, selective detection of Zn(II), Cd(II), and Pb(II) in aerosol samples when combined with Bismuth and Nafion coating and square‐wave anodic stripping voltammetry (SWASV) is reported. Carbon stencil‐printed electrodes (CSPEs) fabricated on a polyethylene transparency (PET) sheet were produced for an inexpensive, simple to fabricate, disposable sensor that can be used with the microliter sample volumes for analysis. Sensor performance was improved by modifying the electrode surface with electrospray‐deposited AgNPs. The use of electrospray deposition resulted in more uniform particle dispersion across the electrode surface when compared to drop‐casting. Using AgNP‐modified electrodes combined with Bi and Nafion, experimental detection limits (LODs) of 5.0, 0.5, and 0.1 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively, were achieved. The linear working ranges were 5.0–400.0 μg L⁻¹, 0.5–400.0 μg L⁻¹, and 0.1–500.0 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively. Interference studies showed Cu(II) was the only metal that interfered with this assay but inference could be eliminated with the addition of ferricyanide directly to the sample solution. This electrochemical sensor was applied for the simultaneous determination of Zn(II), Cd(II), and Pb(II) within source particulate matter (PM) samples collected on filters using an aerosol test chamber.     

Effect of Different Carbon Blacks on the Simultaneous Electroanalysis of Drugs as Water Contaminants Based on Screen‐printed Sensors

For the construction of the sensor, three different carbon black (CB) materials (VULCAN XC72R, BLACK PEARLS 4750 and CB N220) were explored as modifying nanomaterial. Firstly, the electrochemical activity of the each SPE modified was compared by cyclic voltammetry and electrochemical impedance spectroscopy technique, using [Fe(CN)₆]^3?/4? as redox couple. After demonstrating that electrodes modified with different types of CB were characterized by improved electrochemical performances when compared with bare electrodes, and among them, electrodes modified with CB BP4750 is characterised by slightly better electrochemical properties, this type of electrode was used for the development of the analytical method. By applying SWV technique in 0.2 mol L^?1 phosphate buffer (pH 3.0), the obtained analytical curves for ACP and LVF were found linearly from 4.0 to 80.0 μmol L^?1 and from 0.90 to 70.0 μmol L^?1 with limit of detection of 2.6 μmol L^?1 and 0.42 μmol L^?1 for ACP and LVF, respectively. Finally, the quantification of these drugs in river water was evaluated using the new here‐proposed sensor by recovery method in spiked samples, obtaining satisfactory recovery values. The results achieved demonstrated that the developed analytical tool is of great analytical interest being easy to use, cost‐effective, miniaturized, and thus suitable for low cost on site analysis.     

Nanocomposites of Sulfonic Polyaniline Nanoarrays on Graphene Nanosheets with an Improved Supercapacitor Performance

A new nanocomposite, poly(aniline‐co‐diphenylamine‐4‐sulfonic acid)/graphene (PANISP/rGO), was prepared by means of an in situ oxidation copolymerization of aniline (ANI) with diphenylamine‐4‐sulfonic acid (SP) in the presence of graphene oxide, followed by the chemical reduction of graphene oxide using hydrazine hydrate as a reductant. The morphology and structure of PANISP/rGO were characterized by field‐emission (FE) SEM, TEM, X‐ray photoelectron spectroscopy (XPS), Raman, FTIR, and UV/Vis spectra. The electrochemical performance was evaluated by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. The PANISP/rGO nanocomposite showed a nanosized structure, with sulfonic polyaniline nanoarrays coated homogeneously on the surface of graphene nanosheets. This special structure of the nanocomposite also facilitates the enhancement of the electrochemical performance of the electrodes. The PANISP/rGO nanocomposite exhibits a specific supercapacitance up to 1170 F g^?1 at the current density of 0.5 A g^?1. The as‐prepared electrodes show excellent supercapacitive performance because of the synergistic effects between graphene and the sulfonic polyaniline copolymer chains.     

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.     

Electrochemical detection of selenium using glassy carbon electrode modified with reduced graphene oxide

In this work, a simple experimental procedure was reported for the electroanalytical determination of selenium (IV) using reduced graphene oxide (rGO) to modify glassy carbon electrode (GCE). The rGO was obtained by reduction of graphene oxide obtained via Hummer’s method. The synthesised rGO was characterised using X-ray diffraction, Raman spectroscopy, scanning electron microscope (SEM), energy-dispersive spectroscopy and transmission Electron microscopy (TEM). GCE was modified with rGO and the electrochemical properties of the bare and modified electrode were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The results obtained showed that the modified electrode exhibited more excellent electrochemical properties than the bare GCE. The optimum conditions for detection of selenium in water using square wave anodic stripping voltammetry were as follows: deposition potential ?500 mV, pH 1, pre-concentration time of 240 s and 0.1 M nitric acid was used as supporting electrolyte. The linear regression equation obtained was I (µA) = 0.8432C + 9.2359 and the detection limit was calculated to be 0.85 μg L^?1. However, Cu(II) and Cd(II) are the two cations that interfered in the analysis of selenium in water.

The sensor was also applied for real sample water analysis and the result obtained was affirmed with inductively coupled plasma optical emission spectroscopic method. It is believed that our proposed sensor hold promise for practical application.     

Synthesis of Ultrastable Ag Nanoplates/Polyethylenimine–Reduced Graphene Oxide and Its Application as a Versatile Electrochemical Sensor

Investigations on Ag nanostructures/reduced graphene oxide composites have been frequently reported, yet the morphology control of those loaded Ag nanocrystals is still challenging. We herein develop a facile method to grow triangular Ag nanoplates (AgP) on polyethylenimine‐modified reduced graphene oxide (AgP/PEI‐rGO). The AgP/PEI‐rGO hybrids show unexpected high stability against chloride ions (Cl^?) and hydrogen peroxide (H₂O₂), which is possibly due to the strong interaction between surface Ag atoms with the amine groups of PEI. In the chronoamperometry measurements for detecting H₂O₂, N₂H₄, and NaNO₂, the AgP/PEI‐rGO hybrid shows very wide linear ranges (usually 10^?6–10^?2 mol L^?1 for H₂O₂, N₂H₄, and NaNO₂) and low detection limits (down to ≈1×10^?7 mol L^?1), which demonstrate the promising electrochemical sensor applications of these metal/graphene hybrids with well‐defined morphologies and facets. In addition, this strategy could be extended to the deposition of other noble metals on rGO with controlled morphologies.     

Direct Electrochemical Determination of Glyphosate at Copper Phthalocyanine/Multiwalled Carbon Nanotube Film Electrodes

A copper phthalocyanine/multiwalled carbon nanotube film‐modified glassy carbon electrode has been used for the determination of the herbicide glyphosate (Gly) at ?50 mV vs. SCE by electrochemical oxidation using differential pulse voltammetry (DPV). Cyclic voltammetry and electrochemical impedance spectroscopy showed that Gly is adsorbed on the metallic centre of the copper phthalocyanine molecule, with formation of Gly‐copper ion complexes. An analytical method was developed using DPV in pH 7.4 phosphate buffer solution, without any pretreatment steps: Gly was determined in the concentration range of 0.83–9.90 μmol L^?1, with detection limit 12.2 nmol L^?1 (2.02 μg L^?1).     

Electrochemical Sensing of Flutamide Contained in Plasma and Urine Matrices Using NiFe2O4/rGO Nanocomposite,as an Efficient and Selective Electrocatalyst

In this article, we report on the synthesis and new employment of magnetic nickelferrite oxide nanoparticles decorated reduced graphene oxide (NiFe₂O₄/rGO) to electrochemically sensing of flutamide. The preparation of this electrocatalyst was first assessed using various analytical instrumental techniques including FT‐IR spectroscopy, X‐ray diffraction spectroscopy, energy‐dispersive X‐ray spectroscopy, and field emission scanning and transmission electron microscopy. Besides, its electrochemical performance was investigated utilizing some electrochemical methods such as cyclic and differential pulse voltammetry, and also electrochemical impedance spectroscopy. The findings of this research are especially relevant for sensing flutamide in aqueous and biological samples. At the optimized conditions, the electrochemical sensor showed a linear range of 0.24–40.0 μmol L^?1, the detection limit of 0.05 μmol L^?1 flutamide, calibration sensitivity of 1.016 μA/μmol L^?1, and repeatability and reproducibility of 1.7 % and 4.1 %, respectively. The selectivity of the method was investigated in the presence of ions, and species can generally exist in the biological medium. The resulting data of the present work represented that this type of magnetic nanocomposites is suitable for selective detection of flutamide in real samples of plasma and urine. The recoveries obtained for flutamide analyses represented lower than 5.0 percent of relative error in these real samples.