A sensitive biosensor for cyanide detection using modified glassy carbon electrode with reduced graphene oxide and immobilization of horseradish peroxidase

Cyanide is a highly poisonous and hazardous substance which may release into the environment from natural sources or industrial effluent; therefore, cyanide detection is a fundamental step to prevent environmental pollution and secure health and safety. In this study, we prepared a sensitive amperometric inhibition biosensor for cyanide detection by immobilization of horseradish peroxidase (HRP) enzyme and reduced graphene oxide (rGO) on the surface of glassy carbon electrode (GCE). To do so, we performed the amperometric measurement by modified GCE to test its efficiency in detecting cyanide. The optimum conditions of pH equal to 7.5, −100 mV applied potential, 0.7 μM mediator concentration, and 0.5 mM substrate concentration were found. Then, experiments were performed at different boundary conditions in a range of 0.1 to 10 μM cyanide concentration at optimal conditions and a low detection limit of 0.01 μM was obtained. Also, the possible mechanism of inhibition was analyzed based on the Michalis–Menten equation and non-competitive inhibition was observed. Due to high sensitivity, low detection limit, and low cost, this biosensor is proposed as a useful method for cyanide determination in real samples.     

Reduced graphene oxide reinforced PET/PBT nanocomposites: Compatibilization and characterization

This research work focused on the effects of different compatibilizers on the properties of reduced graphene oxide (rGO) reinforced poly(ethylene terephthalate) (PET)/poly(butylene terephthalate) (PBT) nanocomposites. The samples were prepared via melt compounding and injection molding methods. The Joncryl and glycidyl isooctyl polyhedral oligomeric silsesquioxane (GPOSS) were used as compatibilizers at different loading levels (0.5%-4%). The structural, thermal, mechanical, morphological, and electrical properties of the nanocomposites were investigated. The Fourier transform infrared analysis results revealed that no significant interaction was observed when GPOSS was added. On the other hand, there were more obvious changes in the peaks of the nanocomposite containing Joncryl. The thermal results showed that the compatibilizer addition caused small changes while rGO addition did not considerably affect the thermal stability of blend. The glass transition temperature of the nanocomposite significantly decreased with the addition of GPOSS. The tensile test indicated that compatibilizers improved the mechanical performance of PET/PBT/rGO nanocomposite.     

Heteroatom-doped reduced graphene oxide/polyaniline nanocomposites with improved n-type thermoelectric performance

Polyaniline (PANI) is a potential candidate for n-type thermoelectric (TE) materials owing to its intrinsic electrical conductivity, low thermal conductivity, and facile synthesis techniques. However, its low Seebeck coefficient and power factor have limited its widespread usage. In this study, nitrogen-doped, and sulfur-nitrogen co-doped reduced graphene oxide (rGO) were used for tuning the TE properties of PANI. Doped rGO and PANI/doped-rGO nanocomposites were prepared via hydrothermal technique and chemical oxidative polymerization respectively and thereafter characterized. The TE properties of the nanocomposites were also studied and an optimized Seebeck coefficient, power factor and zT value of −1.75 mV K⁻¹, 95 μW m⁻¹ K⁻² and 0.06, respectively were reported for the PANI nanocomposite containing 1 wt% sulfur-nitrogen co-doped rGO. These results suggest that PANI/heteroatom-doped rGO can serve as promising candidates for n-type based TE applications.     

Application of conducting poly(aniline‐co‐pyrrole) film to cholesterol biosensor

Cholesterol oxidase (ChOx) has been covalently immobilized onto poly(aniline‐co‐pyrrole), electrochemically deposited onto indium‐tin‐oxide (ITO) glass plates, using glutaraldehyde as a crosslinker. These poly (An‐co‐Py)/ChOx films have been characterized using UV–visible spectroscopy fourier transform infrared spectroscopy, scanning electron microscopy, and photometric and amperometric techniques, respectively. The poly(An‐co‐Py)/ChOx bioelectrodes have been utilized for cholesterol estimation in the range of 1–10 mM. The ChOx activity in poly(An‐co‐Py)/ChOx bioelectrode has been found to be the highest at pH 7.0 at 25°C. The sensitivity and stability of poly(An‐co‐Py)/ChOx bioelectrode have been experimentally determined as 93.35 μA/mM and 10 weeks at 4°C, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

A highly sensitive electrochemical biosensor based on zinc oxide nanotetrapods for L-lactic acid detection

An amperometric biosensor based on zinc oxide (ZnO) nanotetrapods was designed to detect L-lactic acid. The lactate oxidase was immobilized on the surface of ZnO nanotetrapods by electrostatic adsorption. Unlike traditional detectors, the special four-leg individual ZnO nanostructure, as an adsorption layer, provides multiterminal charge transfer channels. Furthermore, a large amount of ZnO tetrapods are randomly stacked to form a three-dimensional network naturally that facilitates the exchange of electrons and ions in the phosphate buffer solution. Utilizing amperometric response measurements, the prepared ZnO nanotetrapod L-lactic acid biosensor displayed a detection limit of 1.2 μM, a low apparent Michaelis-Menten constant of 0.58 mM, a high sensitivity of 28.0 μA cm(-2) mM(-1) and a good linear relationship in the range of 3.6 μM-0.6 mM for the L-lactic acid detection. This study shows that the biosensor based on ZnO tetrapod nanostructures is highly sensitive and able to respond rapidly in detecting lactic acid.     

Preparation of manganese monoxide@reduced graphene oxide nanocomposites with superior electrochemical performances for lithium-ion batteries

Manganese monoxide (MnO) nanowire@reduced graphene oxide (rGO) nanocomposites are synthesized using a simple hydrothermal method combined with a calcination process. The structural and morphological characterization of the composites indicates that the MnO nanowires homogeneously anchor on both sides of the cross-linked rGO. The nanocomposites exhibit a high surface area of 126.5?m² g^?1. When employed as an anode material for lithium-ion batteries, the nanocomposites exhibit a reversible capacity of 1195 mAh g^?1 at a current density of 0.1?A?g^?1, with a high charge-discharge efficiency of 99.2% after 150 cycles. The three-dimensional architecture of the present materials exhibits high porosity and electron conductivity, significantly shortening the diffusion path of lithium ions and accelerating their reaction with the electrolyte, which greatly improves the lithium-ion storage properties. These excellent electrochemical performances make the composite a promising electrode material for lithium-ion batteries.     

PAN/氧化石墨烯纳米复合材料的热性能研究

采用原位聚合的方法制备了聚丙烯腈(PAN)/氧化石墨烯(GO)纳米复合材料;利用红外光谱和紫外光谱表征了试样的组成及组分间的相互作用;使用扫描电镜和透射电镜对试样的微观形貌进行观察;从单体转化率和聚合液的黏度变化研究了GO对丙烯腈自由基聚合的影响;用热分析仪分析了GO对PAN热稳定化过程的影响。结果表明:复合体系聚合至13 h时,与空白试样(PAN)相比,聚合液的黏度和单体转化率分别降低了1.3%和2.9%,说明在聚合前期GO对自由基聚合起到一定的阻聚作用;GO的厚度由聚合前的3～4 nm剥离到聚合后的1 nm,表明GO在原位聚合过程中以单层形式分散在PAN基体中;PAN与GO之间存在较强的π-π相互作用,这种相互作用抑制了PAN在热稳定化过程中的环化反应。     

Synthesis of polythiophene/graphene oxide composites by interfacial polymerization and evaluation of their electrical and electrochemical properties

We report a new method for the synthesis of polythiophene (PTh)/graphene oxide (GO) nanocomposites by interfacial polymerization. Polymerization occurred at the interface of two immiscible solvents, i.e. n‐hexane containing thiophene and nitromethane containing GO and an initiator. Characterizations were done using Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and electrochemical and electrical conductivity measurements. Spectroscopic analyses showed successful incorporation of GO in the PTh matrix. Morphological analysis revealed good dispersion of GO sheets in the polymer matrix. The PTh/GO composites showed marked improvements in thermal stability and electrical conductivity (2.7 × 10^?4 S cm^?1) compared to pure PTh. The composites exhibited excellent electrochemical reversibility compared to pure PTh at a scan rate of 0.1 V s^?1. The composites were stable even up to 100 electrochemical cycles, indicating good cycle performance. The specific capacitance of the composites was calculated using cyclic voltammetry and was found to be 99 F g^?1. © 2014 Society of Chemical Industry     

Ultrasound–assisted synthesis and characterization of polymethyl methacrylate/reduced graphene oxide nanocomposites

This article reports ultrasound–assisted synthesis of polymethyl methacrylate (PMMA)/reduced graphene oxide (RGO) nanocomposites by in situ emulsion polymerization coupled with in situ reduction of graphene oxide. The thermal degradation kinetics of the nanocomposites was also assessed with Criado and Coats‐Redfern methods. Intense microconvection generated by ultrasound and cavitation results in uniform dispersion of RGO in the polymer matrix, which imparts markedly higher physical properties to resulting nanocomposites at low (≤1.0 wt %) RGO loadings, as compared to nanocomposites synthesized with mechanical stirring. Some important properties of the PMMA/RGO nanocomposites synthesized with sonication (with various RGO loadings) are: glass transition temperature (0.4 wt %) = 124.5°C, tensile strength (0.4 wt %) = 40.4 MPa, electrical conductivity (1.0 wt %) = 2 × 10^?7 S/cm, electromagnetic interference shielding effectiveness (1.0 wt %) = 3.3 dB. Predominant thermal degradation mechanism of nanocomposites (1.0 wt % RGO) is 1D diffusion with activation energy of 111.3 kJ/mol. © 2017 American Institute of Chemical Engineers AIChE J, 64: 673–687, 2018     

A new amperometric glucose biosensor based on platinum nanoparticles/polymerized ionic liquid-carbon nanotubes nanocomposites

A new amperometric glucose biosensor has been developed based on platinum (Pt) nanoparticles/polymerized ionic liquid-carbon nanotubes (CNTs) nanocomposites (PtNPs/PIL-CNTs). The CNTs was functionalized with polymerized ionic liquid (PIL) through directly polymerization of the ionic liquid, 1-vinyl-3-ethylimidazolium tetrafluoroborate ([VEIM]BF₄), on carbon nanotubes and then used as the support for the highly dispersed Pt nanoparticles. The electrochemical performance of the PtNPs/PIL-CNTs modified glassy carbon (PtNPs/PIL-CNTs/GC) electrode has been investigated by typical electrochemical methods. The PtNPs/PIL-CNTs/GC electrode shows high electrocatalytic activity towards the oxidation of hydrogen peroxide. Taking glucose oxidase (GOD) as the model, the resulting amperometric glucose biosensor shows good analytical characteristics, such as a high sensitivity (28.28 μA mM⁻¹ cm⁻²), wide linear range (up to 12 mM) and low detection limit (10 μM).     

Properties and structural characterization of oxide starch/chitosan/graphene oxide biodegradable nanocomposites

Novel chitosan (CS)/oxidized starch (OST)/graphene oxide (GO) nanocomposites (COST/GO‐n) films are prepared in a casting and solvent evaporation method. Fourier transform infrared spectroscopy, X‐ray diffractions, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, tensile testing, and moisture uptake are used to study the structure and properties of these nanocomposites. To indicate the effect of carboxyl groups of OST, some results of the properties of CS/starch/GO nanocomposite (CST/GO‐n) were selected for control experimentation. Compared with the control CST/GO‐n series, COST/GO‐n films, which have the same component ration showed higher tensile strength (σ_b) and lower elongation at break (ε_b). Additionally, in the COST/GO‐n series, the σ_b increased with an increase of GO loading. However, higher proportion of GO could result in aggregations of GO nanosheets and deterioration of the film properties. Compared with the COST/GO‐0, the values of σ_b and water resistance of the COST/GO‐4 containing 2.0 wt % of GO were improved by 57.7 and 20.1%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Potassium-doped carbon nanotubes toward the direct electrochemistry of cholesterol oxidase and its application in highly sensitive cholesterol biosensor

We demonstrate herein a newly developed serum total cholesterol biosensor by using the direct electron transfer of cholesterol oxidase (ChOx), which is based on the immobilization of cholesterol oxidase and cholesterol esterase (ChEt) on potassium-doped multi-walled carbon nanotubes (KMWNTs) modified electrodes. The KMWNTs accelerate the electron transfer from electrode surface to the immobilized ChOx, achieving the direct electrochemistry of ChOx and maintaining its bioactivity. As a new platform in cholesterol analysis, the resulting electrode (ChOx/KMWNTs/GCE) exhibits a sensitive response to free cholesterol, with a linear range of 0.050–16.0 μmol L⁻¹ and a detection limit of 5.0 nmol L⁻¹ (S/N = 3). Coimmobilization of ChEt and ChOx (ChEt/ChOx/KMWNTs/GCE) allows the determination of both free cholesterol and esterified cholesterol. The resulting biosensor shows the same linear range of 0.050–16.0 μmol L⁻¹ for free cholesterol and cholesteryl oleate, with the detection limit of 10.0 and 12.0 nmol L⁻¹ (S/N = 3), respectively. The concentrations of total (free and esterified) cholesterol in human serum samples, determined by using the techniques developed in the present study, are in good agreement with those determined by the well-established techniques using the spectrophotometry.     

Glucosamine conjugated iron oxide and graphene oxide nanohybrid for smart drug delivery

Smart drug delivery systems have attracted a lot of attention as one of the new treatment methods for cancer. In this study, a smart drug delivery system carrying anticancer drugs was obtained by the intelligent synthesis of glucosamine (GA)-functionalized graphene oxide (GO)-based iron oxide nanoparticles (Fe₃O₄@GO-GA) using Hummers and chemical co-precipitation processes. Nanohybrids have a high surface area (280.26 m²/g) and superparamagnetic behaviour (Ms = 26.017 emu/g), indicating a significant loading capacity (373.78 mg/mg) and efficiency (96.3%) for pharmaceutical loading. An adsorption study of conventional daunorubicin (DNR) on this carrier showed that the drug release is more prone to occur under acidic conditions (pH = 5.5), at moderately high temperatures (T = 40°C), and in the absence of smart carriers. The toxicity of the smart nanohybrids was examined using the sulphorhodamine B (SRB) assay in Michigan Cancer Foundation-7 (MCF-7) cell lines. The rate of death of cells exposed to smart drug-containing systems in comparison to the systems without GA shows that GA reduces the toxicity of Fe₃O₄@GO.     

Facile preparation of silver/reduced graphene oxide/chitosan colloid and application of the nanocomposite in antibacterial and catalytic activity

Reduced graphene oxide (RGO) decorated with silver nanoparticles (AgNPs) was synthesized by a facile solution‐based approach in chitosan (CS) solution. The morphology and elemental composition of as‐prepared Ag/RGO/CS colloid were characterized by SEM and energy dispersive X‐ray spectroscopy, respectively. TEM images show that most of the AgNPs are uniformly dispersed in the CS matrix while the other nanoparticles are decorated on the RGO nanosheets. XRD indicates that the interlayer distance of RGO is between 0.34 and 1.87 nm while the diameter of face‐centered cubic AgNPs is no more than 30 nm. Fourier transform infrared spectroscopy of the Ag/RGO/CS colloid confirms the formation of AgNPs and RGO. X‐ray photoelectron spectroscopy proves that both the Ag ? O bond and the C ? N bond exist in the nanocomposite. Antimicrobial assays were performed using the most common species of Gram bacteria. The inhibitory effect indicates that the incorporation of AgNPs and RGO significantly improves the antimicrobial activity of CS colloid. In addition, the nanocomposite colloid exhibits significant catalytic activity toward the reduction of 4‐nitrophenol by NaBH₄. © 2018 Society of Chemical Industry     

钇掺杂钛酸锂/石墨烯纳米复合材料的合成与电化学性能

以氧化石墨烯（GO）为基底，钛酸四丁酯、一水合氢氧化锂、六水合硝酸钇为原料，十六烷基三甲基溴化铵为表面活性剂，采用溶剂热法合成前驱体，在N2气氛保护下高温煅烧合成了钇掺杂钛酸锂/氧化石墨烯纳米复合材料。采用SEM、XRD、EDS、Raman对复合材料进行了形貌、结构和成分表征。将复合材料用作锂离子电池负极材料，采用循环伏安法、恒流充放电循环法研究了其电化学性能。结果表明，片状钛酸锂包覆在氧化石墨烯片上形成了钇掺杂钛酸锂/氧化石墨烯纳米复合材料。在100 mA/g的电流密度下，钇掺杂量为8%（以钛酸锂的物质的量为基准，下同）的纳米复合材料的首次放电比容量为145.5mA·h/g，经过100圈充放电循环后容量衰减几乎为0，经过200圈循环后容量衰减1.59%，经过300圈循环后容量衰减3.24%，与目前容量保持率只有80%左右的石墨负极相比有明显的改进。钇元素的掺杂和钛酸锂包覆氧化石墨烯形式的复合材料可以减小钛酸锂电极在充放电循环中的极化程度，从而改善了材料的循环性能。     

Superhydrophobic,mechanically flexible and recyclable reduced graphene oxide wrapped sponge for highly efficient oil/water separation

Water pollution has become an urgent issue for our modern society, and it is highly desirable to rapidly deal with the water pollution without secondary pollution. In this paper, we have prepared a reduced graphene oxide (RGO) wrapped sponge with superhydrophobicity and mechanically flexibility via a facile low-temperature thermal treatment method under a reducing atmosphere. The skeleton of this sponge is completely covered with RGO layers which are closely linked to the skeleton. This sponge has an abundant pore structure, high selectivity, good recyclability, low cost, and outstanding adsorption capacity for floating oil or heavy oil underwater. In addition, this sponge can maintain excellent adsorption performance for various oils and organic solvents over 50 cycles by squeezing, and exhibits extremely high separation efficiencies, up to 6 × 10⁶ and 3.6 × 10⁶ L·m^–3·h^–1 in non-turbulent and turbulent water/oil systems, respectively. This superhydrophobic adsorbent with attractive properties may find various applications, especially in large-scale removal of organic contaminants and oil spill cleanup.

Open image in new window

     

Electrochemical sensor-based gold nanoparticle/poly(aniline-co-o-toluidine)/graphene oxide nanocomposite modified electrode for hexavalent chromium detection: a real test sample

This paper presents the fabrication of poly(aniline-co-o-toluidine)/graphene oxide nanocomposite with a general abbreviation [PANI-co-PoT/GO_a–e] by well-known in-situ oxidative polymerization method with ultrasonic assistance. These materials were based on variable loading of GO when prepared. The chemical structures of the composite materials were confirmed by characterization technique. The FE-SEM and TEM micrographs were used to investigate the morphological features. Furthermore, FT-IR, XRD, TGA, and electrical conductivity measurements were utilized to estimate its complete performance. All nanocomposites showed CDT_max values in the range of 287.25–463.51 ºC which is significantly higher than that observed for pure copolymer (204.79 ºC). The main focus of this paper is to study the electroselective application using gold nanoparticle as a coating. A steady electroactive modified electrode [AuNPs/PANI-co-PoT/GO] was effectively prepared on a gold electrode (Au) surface using an electroadsorption process for the determination of Cr(VI). The electrochemical attitude of the modified sensor toward the reduction of Cr(VI) was studied by a square wave voltammetry (SWV) and a cyclic voltammetry (CV) technique. The AuNPs/PANI-co-PoT/GO modified electrode displayed a perfect electrochemical activity toward the reduction of Cr(VI). Using an SWV method, the modified electrode gave a linear response to Cr(VI) through the concentration range 5–500 µM with a limit of detection 0.0215 µM. The suggested sensor displayed good stability, sensitivity and selectivity and has exhibited potential for the detection of Cr(VI) in real samples.     

A sensitive DNA biosensor fabricated from gold nanoparticles, carbon nanotubes, and zinc oxide nanowires on a glassy carbon electrode

We outline here the fabrication of a sensitive electrochemical DNA biosensor for the detection of sequence-specific target DNA. Zinc oxide nanowires (ZnONWs) were first immobilized on the surface of a glassy carbon electrode. Multi-walled carbon nanotubes (MWCNTs) with carboxyl groups were then dropped onto the surface of the ZnONWs. Gold nanoparticles (AuNPs) were subsequently introduced to the surface of the MWNTs/ZnONWs by electrochemical deposition. A single-stranded DNA probe with a thiol group at the end (HS-ssDNA) was covalently immobilized on the surface of the AuNPs by forming an Au-S bond. Scanning electron microscopy (SEM) and cyclic voltammetry (CV) were used to investigate the film assembly process. Differential pulse voltammetry (DPV) was used to monitor DNA hybridization by measuring the electrochemical signals of [Ru(NH₃)₆]³⁺ bounding to double-stranded DNA (dsDNA). The incorporation of ZnONWs and MWCNTs in this sensor design significantly enhances the sensitivity and the selectivity. This DNA biosensor can detect the target DNA quantitatively in the range of 1.0 × 10⁻¹³ to 1.0 × 10⁻⁷ M, with a detection limit of 3.5 × 10⁻¹⁴ M (S/N = 3). In addition, the DNA biosensor exhibits excellent selectivity, even for single-mismatched DNA detection.     

DNA-templated synthesis of PtAu bimetallic nanoparticle/graphene nanocomposites and their application in glucose biosensor

In this paper, single-stranded DNA (ss-DNA) is demonstrated to functionalize graphene (GR) and to further guide the growth of PtAu bimetallic nanoparticles (PtAuNPs) on GR with high densities and dispersion. The obtained nanocomposites (PtAuNPs/ss-DNA/GR) were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDS), and electrochemical techniques. Then, an enzyme nanoassembly was prepared by self-assembling glucose oxidase (GOD) on PtAuNP/ss-DNA/GR nanocomposites (GOD/PtAuNPs/ss-DNA/GR). The nanocomposites provided a suitable microenvironment for GOD to retain its biological activity. The direct and reversible electron transfer process between the active site of GOD and the modified electrode was realized without any extra electron mediator. Thus, the prepared GOD/PtAuNP/ss-DNA/GR electrode was proposed as a biosensor for the quantification of glucose. The effects of pH, applied potential, and temperature on the performance of the biosensor were discussed in detail and were optimized. Under optimal conditions, the biosensor showed a linearity with glucose concentration in the range of 1.0 to 1,800 μM with a detection limit of 0.3 μM (S/N = 3). The results demonstrate that the developed approach provides a promising strategy to improve the sensitivity and enzyme activity of electrochemical biosensors.