Fe2O3-decorated boron/nitrogen-co-doped carbon nanosheets as an electrochemical sensing platform for ultrasensitive determination of paraquat in natural water

Boron/nitrogen-co-doped carbon (BCN) nanosheets decorated with Fe₂O₃ nanocrystals (Fe₂O₃–BCN) were cast on a glassy carbon electrode (GCE) and applied as an electrochemical sensor to effectively detect paraquat (PQ), a toxic herbicide, in aqueous environments. A linear experiment performed using square wave voltammetry (SWV) under optimized experimental conditions produced a decent linear relationship and a low detection limit (LOD) of 2.74 nmol/L (S/N = 3). Repeatability, reproducibility, stability, and interference experiments confirmed that the Fe₂O₃–BCN/GCE system exhibited decent electrochemical sensing performance for PQ molecules. Notably, the designed sensor showed high selectivity and a decent linear relationship with PQ concentration in natural water samples. To the best of our knowledge, this is the first study on the preparation of Fe₂O₃–BCN nanosheets for PQ detection. The proposed sensor can be employed as an effective alternative tool for distinguishing and processing PQ.     

Hollow Fe2O3/Co3O4 microcubes derived from metal-organic framework for enhanced sensing performance towards acetone

In this work, hollow Fe₂O₃/Co₃O₄ microcubes have been successfully synthesized through a hydrothermal method followed by an annealing process using metal-organic framework of Prussian blue as a soft template. The morphologies, microstructures, surface area and element compositions have been carefully characterized by a series of techniques. Meanwhile, compared with that of pure Fe₂O₃ and Co₃O₄, the gas sensor based on the hollow microcubes exhibits enhanced sensing performances towards acetone, e.g., a higher response of 21.2 and a shorter response time of 5 s towards 20 ppm acetone at a relatively low working temperature of 200 °C. Moreover, the hollow microcubes-based gas sensor still shows perfect long-term stability, excellent repeatability and the ability of sub-ppm level detection, which provides a possibility for its application in real life. The enhanced gas sensing performances can be attributed to the hollow structure with a high surface area and the formed p-n heterojunctions within the microcubes.     

Core/shell microcapsules consisting of Fe3O4 microparticles coated with nitrogen-doped mesoporous carbon for voltammetric sensing of hydrogen peroxide

The authors describe the preparation of core/shell composites consisting of Fe₃O₄ microparticles coated with nitrogen-doped mesoporous carbon. Synthesis was accomplished by simultaneous reduction of template α-Fe₂O₃ and pyrolysis of a nitrogen-containing poly(ionic liquids). The mesoporous composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffractometry and adsorption/desorption isotherms. The characterizations prove successful formation of an Fe₃O₄ core and an outer shell (coating) consisting of nitrogen-doped mesoporous carbon. The material was placed on a glassy carbon electrode and synergistic catalytic effect of of N-doping, the mesoporous, core/shell structure and two types of active sites properties between Fe₃O₄ core and nitrogen-doped mesoporous carbon shell is shown to result in superior electrochemical activity towards the reduction of hydrogen peroxide. Figures of merit include (a) a sensitivity of 77.1 μA mM⁻¹ cm⁻²; (b) a linear response over the 50 μM to 33 mM H₂O₂ concentration range, (c) a 5.9 μM detection limit of (at an S/N ratio of 3), and (d) a low working voltage of −0.4 V (vs. saturated calomel electrode) which makes the method more selective.

Electrochemical method for H₂O₂ detection based on Fe₃O₄@nitrogen-doped mesoporous carbon microcapsules core/shell composites (Fe₃O₄@NMCMs), prepared by the polymerization of the ionic liquids (1-Allyl-3-ethylimidazolium tetrafluoroborate, [AEIm]BF₄) monomer (PILs) on the surface of α-Fe₂O₃ nano-peanuts and then pyrolysis.

     

Synthesis of Fe3O4, Fe2O3, Ag/Fe3O4 and Ag/Fe2O3 nanoparticles and their electrocatalytic properties

Two important iron oxides:Fe3O4 and Fe2O3,as well as Fe3O4 and Fe2O3 nanoparticles mingling with Ag were successfully synthesized via a hydrothermal procedure.The samples were confirmed and characterized by X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).The morphology of the samples was observed by transmission electron microscopy(TEM).The results indicated Fe3O4,Fe2O3,Ag/Fe3O4 and Ag/Fe2O3 samples all were nanoparticles with smaller sizes.The samples were modified on a glassy carbon electrode and their elctrocatalytic properties for p-nitrophenol in a basic solution were investigated.The results revealed all the samples showed enhanced catalytic performances by comparison with a bare glassy carbon electrode.Furthermore,p-nitrophenol could be reduced at a lower peak potential or a higher peak current on a glassy carbon electrode modified with Ag/Fe3O4 or Ag/Fe2O3 composite nanoparticles.     

A novel hydrogen peroxide sensor based on Ag nanoparticles electrodeposited on DNA-networks modified glassy carbon electrode

A novel strategy to fabricate hydrogen peroxide (H₂O₂) sensor was developed by electrodepositing Ag nanoparticles (NPs) on a glassy carbon electrode modified with three-dimensional DNA networks. The result of electrochemical experiments showed that such constructed sensor had a favorable catalytic ability to reduction of H₂O₂. The well catalytic activity of the sensor was ascribed to the DNA networks that facilitated the formation and homogenous distribution of small Ag NPs. The resulted sensor achieved 95% of the steady-state current within 2 s and had a 1.7 μM detection limit of H₂O₂.     

A lead(II) sensor based on a glassy carbon electrode modified with Fe3O4 nanospheres and carbon nanotubes

We have developed a highly sensitive and selective sensor for lead(II) ions. A glassy carbon electrode was modified with Fe₃O₄ nanospheres and multi-walled carbon nanotubes, and this material was characterized by scanning electron microscopy and X-ray diffraction. The electrode displays good electrochemical activity toward Pb(II) and gives anodic and cathodic peaks with potentials at ?496 mV and ?638 mV (vs. Ag/AgCl) in pH?6.0 solution. The sensor exhibits a sensitive and fairly selective response to Pb(II) ion, with a linear range between 20 pM and 1.6 nM, and a detection limit as low as 6.0 pM (at a signal-to noise ratio of 3). The sensor was successfully applied to monitor Pb(II) in spiked water samples.

Nafion covered core–shell structured Fe3O4@graphene nanospheres modified electrode for highly selective detection of dopamine

Nafion covered core–shell structured Fe₃O₄@graphene nanospheres (GNs) modified glassy carbon electrode (GCE) was successfully prepared and used for selective detection dopamine. Firstly, the characterizations of hydro-thermal synthesized Fe₃O₄@GNs were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Then Fe₃O₄@GNs/Nafion modified electrode exhibited excellent electrocatalytic activity toward the oxidations of dopamine (DA). The interference test showed that the coexisted ascorbic acid (AA) and uric acid (UA) had no electrochemical interference toward DA. Under the optimum conditions, the broad linear relationship was obtained in the experimental concentration from 0.020 μM to 130.0 μM with the detection limit (S/N = 3) of 0.007 μM. Furthermore, the core–shell structured Fe₃O₄@GNs/Nafion/GCE was applied to the determination of DA in real samples and satisfactory results were got, which could provide a promising platform to develop excellent biosensor for detecting DA.     

Porous cuprous oxide microcubes for non-enzymatic amperometric hydrogen peroxide and glucose sensing

Using porous cuprous oxide (Cu₂O) microcubes, a simple non-enzymatic amperometric sensor for the detection of H₂O₂ and glucose has been fabricated. Cyclic voltammetry (CV) revealed that porous Cu₂O microcubes exhibited a direct electrocatalytic activity for the reduction of H₂O₂ in phosphate buffer solution and the oxidation of glucose in an alkaline medium. The non-enzymatic amperometric sensor used in the detection of H₂O₂ with detection limit of 1.5 × 10^?6 M over wide linear detection ranges up to 1.5 mM and with a high sensitivity of 50.6 μA/mM. This non-enzymatic voltammetric sensor was further utilized in detection of glucose with a detection limit of 8.0 × 10^?7 M, a linear detection range up to 500 μM and with a sensitivity of ?70.8 μA/mM.     

Coral reef-like zinc niobate nanostructures decorated functionalized carbon nanofiber as electrode modifier for detection of oxidative stress biomarker: 3-nitro-L-tyrosine

Oxidative stress can transform immunologic disorders to malignancy by enhancing the effect of pathogenic factors associated with adverse health problems. Biomarkers generated during oxidative stress are essential in assessing the in vivo condition of the cell for evaluating health and diagnosing the disease at an early stage, prognosis, benign and effectual drug development, and testing the drug efficacy. 3-Nitro-L-tyrosine is an oxidative stress biomarker produced from L-tyrosine through nitration mediated by active metabolites. Thus, precise detection of 3-NO₂-Tyr in the biological medium is significantly important to monitor the cell environment. Consequently, a novel electrochemical sensing platform had been designed using ZnNb₂O₆ nanostructures anchored f-CNF as a glassy carbon electrode modifier. The crystalline and structural features, morphology, and elemental composition of ZnNb₂O₆/f-CNF nanocomposite were keenly verified. The synchronic activation of ZnNb₂O₆/f-CNF nanocomposite for effective detection of 3-NO₂-Tyr is mainly due to the synergic effect between its counterparts. Accordingly, the fabricated sensor possesses a remarkably low limit of detection (0.021 μM) with a good linear range, and sensitivity is noted to be 7.745 μA/μM?cm?². The consistency of this sensor was evinced through real-time monitoring of 3-NO₂-Tyr in urine and saliva samples which is beneficial in monitoring the pathological situation.     

A novel electrochemical sensor based on magnetic core@shell molecularly imprinted nanocomposite (Fe3O4@graphene oxide@MIP) for sensitive and selective determination of anticancer drug capecitabine

Capecitabine, known as an anti-cancer drug, despite clinical evidence in the general society of patients, the absence of specific data from the perception of increased toxic effects in older people and randomized trials, can be harmful to the body. So, its measurement is essential. A novel electrochemical sensor was fabricated based on glassy carbon electrode (GCE) decorated by molecularly imprinted polymer (MIP)-coated magnetic nanocomposite of iron (II, III) oxide @graphene oxide (Fe₃O₄@GO) for the detection of capecitabine. The MIP was deposited on the surface of core@shell nanocomposite by non-covalent imprinting process. Fe₃O₄@GO@MIP composite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) techniques. The electrochemical performance of proposed sensor was investigated by cyclic and square wave voltammetry techniques. Several parameters such as the electrochemical behavior of the modified electrodes, the type and pH value of supporting electrolyte and scan rates were studied. Under the optimized conditions, the linear range and detection limit were obtained 1.0–100.0 nM and 0.324 nM, respectively. The proposed electrode was successfully applied to the quantification of capecitabine in health human plasma and pharmaceutical samples.     

Detection of Dexamethasone Sodium Phosphate in Blood Plasma: Application of Hematite in Electrochemical Sensors

We studied sensor application of a graphene oxide and hematite (α‐Fe₂O₃/GO) composite electrode well‐characterized by the SEM and XRD. Through differential pulse voltammetry (DPV), oxidation of dexamethasone sodium phosphate (DSP) was studied at the surface of a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) and the α‐Fe₂O₃/GO composite. The values of the transfer coefficient (α) and the diffusion coefficient (D) of DSP were 0.5961 and 4.71×10^?5 cm² s^?1 respectively. In the linear range of 0.1–50 μM, the detection limit (DL) was 0.076 μM. In the second step, a GCE was modified with α‐Fe₂O₃/GO composite and the DSP measurement step was repeated to analyzed and compare the effects of hematite nanoparticles present on graphene oxide surfaces. According to the results, α and D were 0.52 and 2.406×10^?4 cm² s^?1 respectively and the DL was 0.046 μM in the linear range of 0.1–10.0 μM. The sensor is simple, inexpensive and uses blood serum.     

Direct electrochemical sensing of ο-phenylendiamine based on perovskite-type nanomaterial LaNiTiO3–Fe3O4

An electrochemical sensor is developed in this work based on the new perovskite-type nanomaterial LaNiTiO₃–Fe₃O₄ for sensitive determination of o-phenylenediamine (OPD). As-synthesized materials and the surface of as-fabricated electrochemical sensor are characterized by X-ray diffraction, atomic force microscope, and electrochemical impedance spectroscopy, respectively. The results of characterizations depict that the sample is of nanoscaled complex oxides consisting of perovskite structure and spinel structure, and has good conductive properties. The construction and experimental conditions of the electrochemical sensor are also optimized. The electrochemical properties of OPD at glassy carbon electrode modified with LaNiTiO₃–Fe₃O₄ are investigated in alkaline solution (NaOH). The new electrochemical sensor exhibits high electrocatalytic activity and stability in NaOH, and a promotion of electrochemical oxidation of OPD at low potentials can be obviously observed. A wide linear range is obtained from 1.0?×?10^?6 to 7.0?×?10^?3 M with a relative low detection limit of 0.15 μM (S/N?=?3) under optimal conditions. Furthermore, the sensor exhibits reliable results for the determination of OPD in commercial samples.     

High-performance electrochemical sensor based on electrodeposited iron oxide nanoparticle: catecholamine as analytical probe

In this paper, we report the synthesis and electrocatalytic activity of electrodeposited Fe₂O₃ nanoparticles modified on a glassy carbon electrode as highly sensitive sensors for determination of catecholamines. Results showed that the Fe₂O₃ nanoparticles on a glassy carbon electrode exhibit excellent catalytic activity toward catecholamines oxidation, including levodopa, dopamine, and epinephrine, resulting in a marked lowering in the peak potential and considerable improvement of the peak current as compared to the electrochemical activity at the bare glassy carbon electrode. The electrochemical characterizations of catecholamines were performed using cyclic voltammetry, chronoamperometry, and differential pulse voltammetry techniques. The electrocatalytic currents increase linearly with the levodopa, dopamine, and epinephrine concentrations in the ranges of 0.0625–1000, 0.25–1500, and 0.125–1000 µM, respectively, and the detection limits (3σ) were 24 ± 2, 14 ± 2, and 12 ± 2 nM, respectively.     

Ni0.1Co0.9Fe2O4-based electrochemical sensor for the detection of paracetamol

A novel electrochemical sensor based on nickel-doped cobalt ferrite nanoparticles (Ni_0.1Co_0.9Fe₂O₄)-modified glassy carbon electrode (NCF/GCE) was presented for the sensitive detection of paracetamol. Experimental conditions such as pH, applied potentials and concentration were investigated using cyclic voltammetric and chronoamperometric techniques. The modified electrode exhibited excellent catalytic response towards the oxidation of paracetamol with good reproducibility. The overpotential for oxidation of paracetamol is decreased, and the current response enhanced significantly on the modified electrode in comparison with that of bare electrode. Linear calibration curve is obtained over the range 2 μM to 8,000 μM having a detection limit of 11 nM. The modified electrode facilitated the simultaneous detection of paracetamol, ascorbic acid, and dopamine with good reproducibility.     

Three-dimensional porous reduced graphene oxide decorated with MoS2 quantum dots for electrochemical determination of hydrogen peroxide

Three-dimensional (3D) graphene-based nanomaterials have shown wide applications in electrochemical fields such as biosensors. In this study, we displayed a simple fabrication of 3D structural reduced graphene oxide (3D structural RGO) decorated with molybdenum disulfide quantum dots (MoS₂QDs) through a three-step reaction process. With its abundant raw materials, this strategy is economic and non-toxic. Various characterization techniques were utilized to characterize the morphologies of the synthesized MoS₂QDs, graphene oxide (GO), and 3D structural RGO-MoS₂QDs composites. Simultaneously, X-ray photoelectron spectroscopy was applied to characterize the structure and properties of composites. In order to understand the effects of the reaction period on the structure of 3D structural RGO-MoS₂QDs, a series of samples with various reaction periods were prepared for morphological characterization. Finally, the fabricated 3D structural RGO-MoS₂QDs composites were used to modify a glassy carbon electrode as an electrochemical non-enzymatic hydrogen peroxide (H₂O₂) sensor. The obtained results indicate that the fabricated electrochemical H₂O₂ sensor exhibits a wide detection range (0.01–5.57 mM), low detection limit (1.90 μM), good anti-interference performance, and long-time stability (18 days).     

Ag nanoparticles decorated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/chitosan nanocomposite: synthesis,characterization and application toward electrochemical sensing of hydrogen peroxide

We studied a rapid, sensitive and selective amperometric sensor for determination of hydrogen peroxide by electrodeposited Ag NPs on a modified glassy carbon electrode (GCE). The modified GCE was constructed through a step by step modification of magnetic chitosan functional composite (Fe₃O₄–CH) and high-dispersed silver nanoparticles on the surface. The resulted Ag@Fe₃O₄–CH was characterized by various analytical methods including Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and cyclic voltammetry. The proposed sensor employed Ag@Fe₃O₄–CH/GCE as the working electrode with a linear current response to the hydrogen peroxide concentration in a wide range from 0.01 to 400 µM with a low limit of detection (LOD = 0.0038 µM, S/N = 3). The proposed sensor showed superior reproductivity, sensitivity and selectivity for the detection of hydrogen peroxide in environmental and clinical samples.     

Hydrothermal synthesis of reduced graphene sheets/Fe2O3 nanorods composites and their enhanced electrochemical performance for supercapacitors

Reduced graphene nanosheets/Fe₂O₃ nanorods (GNS/Fe₂O₃) composite has been fabricated by a hydrothermal route for supercapacitor electrode materials. The obtained GNS/Fe₂O₃ composite formed a uniform structure with the Fe₂O₃ nanorods grew on the graphene surface and/or filled between the graphene sheets. The electrochemical performances of the GNS/Fe₂O₃ hybrid supercapacitor were tested by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests in 6 M KOH electrolyte. Comparing with the pure Fe₂O₃ electrode, GNS/Fe₂O₃ composite electrode exhibits an enhanced specific capacitance of 320 F g⁻¹ at 10 mA cm⁻² and an excellent cycle-ability with capacity retention of about 97% after 500 cycles. The simple and cost-effective preparation technique of this composite with good capacitive behavior encourages its potential commercial application.     

A novel non-enzyme hydrogen peroxide sensor based on an electrode modified with carbon nanotube-wired CuO nanoflowers

We have prepared a novel sensor for hydrogen peroxide that is based on a glassy carbon electrode modified with a film containing multi-walled carbon nanotubes wired to CuO nanoflowers. The nanoflowers were characterized by X-ray powder diffraction, and the electrode was characterized by cyclic voltammetry (CV) and scanning electron microscopy. The response of the modified electrode towards hydrogen peroxide was investigated by CV and chronoamperometry and showed it to exhibit high electrocatalytic activity, with a linear range from 0.5?μM to 82?μM and a detection limit of 0.16?μM. The sensor also displays excellent selectivity and stability.

Sensor for lead(II) ion based on a glassy carbon electrode modified with double-stranded DNA and ferric oxide nanoparticles

Shuttle-like Fe₂O₃ nanoparticles (NPs) were prepared by microwave-assisted synthesis and characterized by scanning electron microscopy and X-ray diffraction. The NPs were immobilized on a glassy carbon electrode and then covered with dsDNA. The resulting electrode gives a pair of well-defined redox peaks for Pb(II) at pH 6.0, with anodic and cathodic peak potentials occurring at ?0.50?V and ?0.75?V (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.12 to 40?nM, and the detection limit is 0.1?nM at a signal-to-noise ratio of 3. The sensor exhibits high selectivity and reproducibility.

Synthesis,characterization and the electrocatalytic application of prussian blue/titanate nanotubes nanocomposite

A novel kind of nanocomposite, titanate nanotubes (TNTs) decorated by electroactive Prussian blue (PB), was fabricated by a simple chemical method. The as-prepared nanocomposite was characterized by XRD, XPS, TEM, FT-IR and Cyclic voltammetry (CV). Experimental results revealed that PB was adsorbed on the surface of TNTs, and the adsorption capacity of TNTs was stronger than that of anatase-type TiO₂ powder (TNP). The PB-TNTs nanocomposite was modified onto a glassy carbon electrode and the electrode showed excellent electroactivity. The modified electrode also exhibited outstanding electrocatalytic activity towards the reduction of hydrogen peroxide and can serve as an amperometric sensor for H₂O₂ detection. The sensor fabricated by casting Nafion (NF) above the PB-TNTs composite film (NF/PB-TNTs/GCE) showed two linear ranges of 2 × 10^?5–5 × 10^?4 M and 2 × 10^?3–7 × 10^?3 M, with a detection limit of 1 × 10^?6 M. Furthermore, PB-TNTs modified electrode with Nafion (NF/PB-TNTs/GCE) showed wider linear range and better stability compared with PB-TNTs modified electrode without Nafion (PB-TNTs/GCE) and PB modified electrode with Nafion (NF/PB/GCE).