Glass Carbon Electrode Research Articles

Monoclinic WO3 nanosheets-carbon nanotubes nanocomposite based electrochemical sensor for sensitive detection of bisphenol A

• WO 3 -CNT nanocomposite was hydrothermally prepared and used as a novel sensing material. • WO 3 -CNT/GCE has enhanced electro-oxidation peak current and reduced potential for BPA. • Improved surface area, good electron transfer and reproducibility of the sensor. • WO 3 -CNT/GCE sensor for BPA has two linear ranges with low detection limit (16.3 nM) • Admirable performance of the sensor for the practical applicability in real samples. A novel and sensitive electrochemical sensor based on monoclinic tungsten trioxide (WO 3 ) nanosheets-carbon nanotubes nanocomposite (WO 3 -CNT) modified glass carbon electrode (GCE) is developed for the direct detection of endocrine disruptor bisphenol A (BPA) in textile sample for the first time. The electrochemical behavior of BPA on the resultant WO 3 -CNT/GCE sensor is investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronocoulometry (CC). Under the optimized conditions, the proposed sensor can be adopted to the quantification of BPA using differential pulse voltammetry (DPV), and the electro-oxidation peak current is proportional to the BPA concentration in the range of 0.03–3.0 μM and 3.0–100 μM with a correlation coefficient of 0.9993 and 0.9992, respectively. Moreover, the proposed sensor with a detection limit of 16.3 nM (S/N = 3) exhibits good reproducibility, selectivity and stability, and can be successfully applied to detect the BPA concentrations in real samples (textile, plastic and tap water) with satisfactory recovery (99.4%-110.1%). The present strategy on the hybridization of CNTs and WO 3 enables more opportunities for the electrochemical detection of BPA in the practical applications.

Hetero MOF‐on‐MOF‐derived carbon nanotube interconnected nitrogen‐doped carbon‐encapsulated FeNi/FeF2 for efficient oxygen evolution reaction

AbstractHeterostructures derived from metal–organic frameworks (MOFs) with multicomponent synergism are significant in the energy conversion and catalysis reactions. Herein, we demonstrated such an efficient catalyst with the structure of self‐catalyzed nitrogen‐doped carbon nanotube interconnected FeNi/FeF2 derived from hetero‐zeolite imidazolate frameworks 8 (ZIF‐8) on Fe2Ni MIL (MIL represents Materials of Institut Lavoisier) for oxygen evolution reaction. The obtained catalyst showed efficient synergism of the multicomponents, high polarity, more active sites exposure, increased intrinsic activity, and improved conductivity and stability by a carbon interconnected and confined structure as revealed by the spectroscopic analysis and electrochemical measurements. It required an overpotential of only ca. 240 mV (no iR correction) to reach the current density of 10 mA cm−2 in a KOH solution when loaded on an inert glass carbon electrode, much better than similar kinds of catalysts. The improved catalytic performance can be well correlated to the structural transformation step by step from different MOFs to their derivatives by subsequent carbonation and fluorination. Because of the above‐mentioned structural advantages, good catalysis performance of high activity and stability, faster catalytic kinetics, and facile active phase formation were observed compared to those of other similar materials. This work offers a new platform of derivatives from hetero MOF‐on‐MOF for catalysis reactions.

Anti-biofouling Ti3C2TX MXene-holey graphene modified electrode for dopamine sensing in complex biological fluids

With the development of new methods for the medical diagnosis, electrochemical sensors have attracted increasing attention. However, biofouling on the surface of the sensor significantly decreases sensor performance, thereby limiting the application of electrochemical sensors in complex biological fluids. Given the urgent need for anti-biofouling electrodes, a sensor based on a glass carbon electrode (GCE) modified with Ti3C2TX MXene and electrochemically reduced holey graphene (ERHG) was fabricated and demonstrated to have excellent electrochemical performance and anti-biofouling properties. ERHG provides abundant surface-active sites and imparts stability by hindering the agglomeration and oxidation of MXene. Furthermore, the excellent conductivity and hydrophilicity of MXene result in a high electron transfer rate and strong hydrophilicity. The MXene-ERHG/GCE sensor can detect dopamine with a wide linear range (0.2–125 μM) and a low detection limit of 0.044 μM in phosphate-buffer saline solution. Importantly, the hydrophilicity of MXene-ERHG reduces non-specific protein adsorption on the electrode surface, providing resistance to biofouling. After immersion in bovine serum albumin for 30 min, MXene-ERHG/GCE retained 85.90% of its initial peak current value, much higher than that of ERHG/GCE (17.75%). The MXene-ERHG/GCE sensor also showed good sensitivity for dopamine detection in serum and artificial cerebrospinal fluid (aCSF) containing bovine serum albumin. Moreover, MXene-ERHG/GCE exhibited excellent reproducibility and long-term stability in aCSF. The results demonstrate that MXene-ERHG/GCE has excellent anti-biofouling performance, and shows potential as an electrode material for application in biosensing.

Synthesis of core-shell structured metal oxide@covalent organic framework composites as a novel electrochemical platform for dopamine sensing

In this work, a novel core-shell structured CuO@TAPB-DMTP-COF composites were synthesized by encapsulating CuO nanorods into TAPB-DMTP-COF host matrix. The structural properties of the composites were revealed by X-ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), and Transmission electron microscopy (TEM). Subsequently, the CuO@TAPB-DMTP-COF composites were immobilized on the glass carbon electrode (GCE) surface to fabricate an electrochemical sensor for dopamine detection. CuO functions as a highly catalytic active substance to accelerate the charge transfer rate of the reaction, while TAPB-DMTP-COF with a large electroactive surface area enhances the adsorption ability of the modified electrode toward the target molecules. The main parameters during the analytical procedure were investigated in detail, and the analytical performance was improved significantly due to the synergistic effects of CuO and TAPB-DMTP-COF. Under the optimal conditions, the dopamine peak responses are linear in a wide range from 0.07 to 800 μM, and the detection limit is as low as 0.023 μM. Furthermore, the dopamine sensor also exhibits good repeatability, stability, and accurate detection ability in actual samples. This study will expand the application of organic porous material based composites in ultra-sensitive electrochemical bioanalysis.

A facile electrochemical sensor based on green synthesis of Cs/Ce-MOF for detection of tryptophan in human serum

A facile electrochemical sensor for tryptophan detection was designed and constructed by using Cs/Ce-MOF modified glass carbon electrode. The synthesis strategy of Cs/Ce-MOF composite not only greatly saved both energy and time costs, but also prevented the aggregation of Ce-MOF. The electrochemical sensor possessed excellent performance with wide linear range (0.25–331 μM) and a low limit of detection (0.14 μM), which is due to the good film-forming ability, permeability and rich accessible active sites. Additionally, the as-prepared electrochemical sensor has good selectivity, reproducibility, repeatability, stability and potential application in real samples.

Electrochemical Biosensor Using Nitrogen-Doped Graphene/Au Nanoparticles/DNAzyme for Ca2+ Determination.

An electrochemical biosensor for detecting Ca2+ concentration was proposed using glass carbon electrodes (GCEs) modified with nitrogen-doped graphene (NGR), gold nanoparticles (AuNPs) and DNAzyme. The resistance signal was amplified through two methods: electrochemical reduction of AuNPs on the NGR surface to increase the specific surface area of the electrode and strengthen the adsorption of DNAzyme; and increasement of the DNAzyme base sequence. The process of electrode modification was characterized by scanning electron microscopy, Raman spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Experimental parameters’ influence, such as the deposition time of gold nanoparticles and the detection time, were assessed by electrochemical methods. The linear ranges of the electrochemical biosensor were in the range from 5 × 10−6 to 5 × 10−5 and 5 × 10−5 to 4 × 10−4 M, with a detection limit of 3.8 × 10−6 M. The concentration of Ca2+ in the serum of dairy cows was determined by the biosensor with satisfactory results, which could be potentially used to diagnose subclinical hypocalcemia.

A novel catechin electrochemical sensor based on a two-dimensional MOFs material derivative Zn doped carbon nanosheets and multi-walled carbon nanotubes composite film

In this paper, the precursor ZIF-8/NaCl composite material was successfully synthesized by the in-situ synthesis method, and the two-dimensional zinc doped carbon nanosheets (Zn CNs) were obtained after heat treatment of the precursor. Zn CNs were electrodeposited on carboxylated carbon nanotubes (MWCNTs-COOH) modified glass carbon electrode (GCE) to construct an electrochemical sensor for catechins. The materials are characterized using scanning electron microscope, X-ray photoelectron spectroscopy, and nitrogen adsorption-desorption isotherm. Zn CNs/MWCNTs-COOH composite provide the sensor with excellent electrochemical and electrocatalytic performance. Therefore, the sensor has a wide detection range (30.0–738 nM) and a low detection limit (LOD = 10.0 nM) for catechins. The effectiveness of the sensor was also verified in actual sample detection with good stability and accuracy. This study may provide a feasible solution for the detection of catechin.

Construct α-FeOOH-Reduced Graphene Oxide Aerogel as a Carrier for Glucose Oxidase Electrode.

A promising α-FeOOH-reduced graphene oxide aerogel (FeOOH-GA) has been prepared for the assembly of an enzyme electrode. The α-FeOOH-reduced graphene oxide aerogel was characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The results reveal that graphene oxide is reduced by Fe2+ ion and α-FeOOH nanorods anchored on the reduced graphene oxide sheet through the Fe-O-C bond. Analyses using scanning electron microscopy and the Brunauer–Emmett–Teller method show that FeOOH-GA displays a various and interconnected pore structure. The FeOOH-GA was used as a support material on the glass carbon electrode (GCE) for glucose oxidase (GOD). Electrochemistry properties and bioelectrocatalytic activities of Nafion/GOD/FeOOH-GA/GCE were achieved from cyclic voltammetry and electrochemical impedance spectroscopy. The results show that Nafion/GOD/FeOOH-GA/GCE maintains outstanding catalytic activity and electrochemical properties. The FeOOH-GA could immobilize GOD through the hydrophobicity of the reduced graphene oxide and hydroxide radical of α-FeOOH. Appropriate α-FeOOH and diversified pore structure are beneficial for electron transfer, enzyme electrode storage, and interfacial electron transfer rate. All results indicated that the α-FeOOH-reduced graphene oxide aerogel as a carrier could effectively immobilize the tested enzyme.

Amplified electrochemical determination of niclosamide in food based on carbon nanohorn@MWCNT composite.

In this work, carbon nanohorn (CNH)-decorated multi-walled carbon nanotube (MWCNT) (CNH@MWCNT) composite was prepared and used to modify glass carbon electrode (GCE) as sensitive electrochemical sensor for niclosamide (NA) determination. Herein, the decoration of CNHs induces higher dispersibility for MWCNTs, and endows the composite with better conductivity, larger surface area, and higher catalytic activity, which leads to significantly enhanced electrochemical behavior toward NA oxidation. The parameters such as mass ratios of CNHs and MWCHTs, the amount of composite materials, the accumulation time, and the solution pH are systematically optimized. Under optimized conditions, the developed electrochemical sensor exhibits a low detection limit of 2.0nM with a wide linear range of 7.0nM-10.0µM and high anti-interference ability. In addition, the sensor displays good stability, repeatability, and reproducibility. The feasibility of the assay was verified by testing NA in brown rice and rice field water samples.

Lotus seedpods biochar decorated molybdenum disulfide for portable, flexible, outdoor and inexpensive sensing of hyperin

Biomass waste, a good candidate for advanced carbon materials for sustainable electrodes, is receiving more and more attention for high value-added materials because of its promising contribution to economic growth and sustainable development. We proposed a green co-hydrothermal approach to prepare lotus seedpods biochar (BC) decorated molybdenum disulfide (MoS2) from waste lotus seedpods and precursors of MoS2, and a portable, flexible, outdoor and inexpensive sensing platform for hyperin on the integrated flexible three-electrode using U-disk potentiostat with smartphone was successfully developed. Structure and properties of MoS2-BC were characterized, it was proved that BC improves microstructure and morphology, electronic conductivity, electrode stability and electrocatalytic properties of MoS2. Attributing to these impressive features, the detection signal of hyperin was significantly amplified by the MoS2-BC modified glass carbon electrode (GCE) in detection range of 0.01–21 μΜ with detection limit (LOD) of 5 nM. It was worth mentioning that the MoS2-BC modified screen-printed electrode (SPE) performs hyperin detection in range of 100 nM - 3 μM with LOD 50 nM (S/N = 3). The practicability of the proposed method confirmed that the portable, on-site, low-cost, and outdoor detection of hyperin was feasible and practical in comparison with traditional both electrochemical sensing and HPLC methods.

Structure evolution from Fe2Ni MIL MOF to carbon confined O-doped FeNi/FeF2 via partial fluorination for improved oxygen evolution reaction

Carbon confined active phase plays a significant role in the novel catalyst materials development and fabrication. Herein, we demonstrate such a catalyst material in the form of carbon confined iron-nickel alloy/iron fluoride doped by oxygen (C/O-FeNi/FeF2) derived from the Fe2Ni MIL MOF via facile carbonization and fluorination for efficient oxygen evolution reaction (OER) in the water-splitting reaction. The structural transformation from the Fe2Ni MIL MOF to the C/O-FeNi/FeF2 is demonstrated by the spectroscopic analysis and correlated to their electrochemical catalytic performance. Because of some combined merits resulting from the carbon confined active phase, increased polarity, strong electronic effect and efficient synergism of metal and metal fluoride for the facile active phase reconstruction in this hybrid system, this catalyst exhibits many good characteristics for electrochemical measurements in terms of improved conductivity, high intrinsic activity and stability, fast catalytic kinetics, increase surface area and rapid charge transfer ability. Specifically, the C/O-FeNi/FeF2 catalysts have a low overpotential of ca. 250 mV when loaded on a glass carbon electrode to offer the current density of 10 mA cm−2 in the alkaline electrolyte for OER; and no obvious performance decay is observed in the long-term stability test conducted at different potentials. The current results will be instructive for novel carbon confined catalyst and MOF derived catalyst design and fabrication in the energy catalysis reaction.

A facile electrochemical method for rapid determination of 3-chloropropane-1,2-diol in soy sauce based on nanoporous gold capped with molecularly imprinted polymer

3-monochloropropane-1,2-diol (3-MCPD) is a well-known heat-produced food contaminant, which has been reported to be carcinogenic, nephrotoxic, and reproductively toxic. In this study, a facile electrochemical sensor based on nanoporous gold (NPG) capped with molecularly imprinted polymer (MIP) was constructed for the rapid and selective determination of 3-monochloropropane-1,2-diol (3-MCPD). Firstly, NPG was fabricated on the electrode through coating the glass carbon electrode (GCE) surface with NPG film to provide an ideal substrate for polymerization of the MIP membrane and improve the electrocatalysis activity of the sensor. Then, the MIP membrane was constructed on the NPG surface via self-assembly by electropolymerization to realize selective recognition of target 3-MCPD molecules. As a consequence of the combined effect of NPG and MIP, the optimized molecularly imprinted polymer/nanoporous gold/glassy carbon electrode (MIP/NPG/GCE) sensor exhibited outstanding analytical performance towards 3-MCPD with a much wider linear range from 10 −16 to 10 −7 mol/L and fairly low detection limit of 3.5 × 10 −17 mol/L (S/N = 3). Meanwhile, the constructed electrochemical sensor presented outstanding specificity, anti-interference capability, and reproducibility. In order to demonstrate practical applicability, the MIP/NPG/GCE was applied for the detection of 3-MCPD in real soy sauce and satisfactory results were obtained with recovery rates ranging from 105.90% to 107.52%. • An electrochemical sensor was prepared for detecting 3-MCPD using NPG and MIP. • NPG improved the electrocatalysis activity of the sensor. • The structure of NPG provided an ideal substrate for polymerization of MIP film. • The MIP film self-assembled on NPG realized selective recognition of 3-MCPD. • The fabricated sensor showed outstanding analytical performance towards 3-MCPD.

Electroconductive Polyaniline–Ag-ZnO Green Nanocomposite Material

Metal-conducting polyaniline (PANI)-based nanocomposite materials have attracted attention in various applications due to their synergism of electrical, mechanical, and optical properties of the initial components. Herein, metal-PANI nanocomposites, including silver nanoparticle-polyaniline (AgNP-PANI), zinc oxide nanoparticle-polyaniline (ZnONP-PANI), and silver-zinc oxide nanoparticle-polyaniline (Ag–ZnONP-PANI), were prepared using the two processes. Nanocomposite-based electrode platforms were prepared by depositing AgNPs, ZnONPs, or Ag–ZnONPs on a PANI modified glass carbon electrode (GCE) in the presence of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide/N-Hydroxysuccinimide (EDC/NHS, 1:2) as coupling agents. The incorporation of AgNPs, ZnONPs, and Ag–ZnONPs onto PANI was confirmed by UV-Vis spectrophotometry, which showed five absorbance bands at 216 nm, 412 nm, 464 nm, 550 nm, and 831 nm (i.e., transition of π-π*, π-polaron band transition, polaron-π* electronic transition, and AgNPs). The FTIR characteristic signatures of the nanocomposite materials exhibited stretching arising from C–H aromatic, C–O, and C–N stretching mode for benzenoid rings, and =C–H plane bending vibration formed during protonation. The CV voltammograms of the nanocomposite materials showed a quasi-reversible behavior with increased redox current response. Notably, AgNP–PANI–GCE electrode showed the highest conductivity, which was attributed the high conductivity of silver. The increase in peak currents exhibited by the composites shows that AgNPs and ZnONPs improve the electrical properties of PANI, and they could be potential candidates for electrochemical applications.

A label-free electrochemical aptasensor based on AuNPs-loaded zeolitic imidazolate framework-8 for sensitive determination of aflatoxin B1

In this study, an electrochemical aptasensor for sensitive detection of aflatoxin B1 (AFB1) was fabricated by electrodepositing gold nanoparticles (AuNPs) on the glass carbon electrode (GCE) modified with zeolitic imidazolate framework-8 (ZIF-8). The high specific surface area of AuNPs/ZIF-8 nanocomposite increased the aptamers loading on the electrode surface. When compared to other previously reported sensors, the developed aptasensor exhibited a wider linear range of 10.0 to 1.0 × 105 pg/mL with a lower limit of detection (LOD) of 1.82 pg/mL under the optimized conditions. Furthermore, the obtained results revealed that the constructed aptasensor exhibited outstanding selectivity, reproducibility and stability. Moreover, the aptasensor was successfully employed to detect the AFB1 in corn oil and peanut oil samples, with recoveries ranging from 93.49% to 106.9%, demonstrating the potential application value of this methodology.

Boosting the Electrochemical Performance of PI-5-CA/C-SWCNT Nanohybrid for Sensitive Detection of E. coli O157:H7 From the Real Sample.

Redox activity is an important indicator for evaluating electrochemical biosensors. In this work, we have successfully polymerized indole-5-carboxylic acid into poly-5-carboxyindole nanomaterials (PI-5-CA), using its superior redox activity, and introduced carboxylated single-walled carbon nanotubes (C-SWCNTs) to synthesize a composite material. Finally, a synthesized composite material was used for the modification of the glass carbon electrode to fabricate the PI-5-CA/C-SWCNTs/GCE-based immunosensor and was successfully applied for the sensitive detection of E. coli O157:H7. The fabricated immunosensor exhibited an outstanding electrocatalytic activity toward the detection of E. coli O157:H7 with a remarkably lowest limit of detection (2.5 CFU/ml, LOD = 3 SD/k, n = 3) and has a wide linear range from 2.98×101 to 2.98×107 CFU/ml. Inspired from the excellent results, the fabricated electrode was applied for the detection of bacteria from real samples (water samples) with a good recovery rate (98.13–107.69%) as well as an excellent stability and specificity. Owing to its simple preparation, excellent performance, and detection time within 30 min, our proposed immunosensor will open a new horizon in different fields for the sensitive detection of bacteria from real samples.

Engineering Electron-Rich Sites on CoSe2-x Nanosheets for the Enhanced Electroanalysis of As(III): A Study on the Electronic Structure via X-ray Absorption Fine Structure Spectroscopy and Density Functional Theory Calculation.

Vacancy and doping engineering are promising pathways to improve the electrocatalytic ability of nanomaterials for detecting heavy metal ions. However, the effects of the electronic structure and the local coordination on the catalytic performance are still ambiguous. Herein, cubic selenium vacancy-rich CoSe2 (c-CoSe2-x) and P-doped orthorhombic CoSe2-x (o-CoSe2-x|P) were designed via vacancy and doping engineering. An o-CoSe2-x|P-modified glass carbon electrode (o-CoSe2-x|P/GCE) acquired a high sensitivity of 1.11 μA ppb-1 toward As(III), which is about 40 times higher than that of c-CoSe2-x, outperforming most of the reported nanomaterial-modified glass carbon electrodes. Besides, o-CoSe2-x|P/GCE displayed good selectivity toward As(III) compared with other divalent heavy metal cations, which also exhibited excellent stability, repeatability, and practicality. X-ray absorption fine structure spectroscopy and density functional theory calculation demonstrate that electrons transferred from Co and Se to P sites through Co-P and Se-P bonds in o-CoSe2-x|P. P sites obtained plentiful electrons to form active centers, which also had a strong orbital coupling with As(III). In the detection process, As(III) was bonded with P and reduced by the electron-rich sites in o-CoSe2-x|P, thus acquiring a reinforced electrochemical sensitivity. This work provides an in-depth understanding of the influence of the intrinsic physicochemical properties of sensitive materials on the behavior of electroanalysis, thus offering a direct guideline for creating active sites on sensing interfaces.

Enhancing K2S2O8 electrochemiluminescence based on silver nanoparticles and zinc metal-organic framework composite (AgNPs@ZnMOF) for the determination of l-cysteine.

A silver nanoparticle-doped Zn(ii) metal–organic framework composite (AgNPs@ZnMOF) was investigated as an electrochemiluminescence (ECL) signal enhancer for potassium persulfate. First, ZnMOF was prepared by a one-step hydrothermal method, and then AgNPs@ZnMOF composite was obtained by depositing AgNPs on the surface and interior of ZnMOF. After the AgNPs@ZnMOF composite was modified on the glass carbon electrode (GCE), the cathode luminescence of potassium persulfate on bare GCE was enhanced by 8 times. A dual amplification mechanism provided by Zn(ii) and Ag nanoparticles in the AgNPs@ZnMOF composite has been validated by ECL spectra, fluorescence spectra, and electrochemical methods. The interaction between the sulfhydryl groups in l-cysteine (l-Cys) and AgNPs significantly affects the catalytic luminescence of the AgNPs@ZnMOF composite. Thus, a sensitive ECL method for the determination of l-Cys was developed based on the inhibition effect of l-Cys on the ECL signal within the linear range from 5.0 nM to 1.0 μM and the limit of detection was found to be 2 nM (S/N = 3). The established method has been successfully applied to the determination of l-Cys in human urine.

A novel temperature-responsive electrochemical sensing platform for reversible switch-sensitive detection of acetamidophenol.

A novel facile, quick, and temperature-controlled sensor was constructed based on a polystyrene-poly-N,N-diethyl acrylamide-polystyrene (PS-PDEAM)/carboxylated multi-walled carbon nanotube (MWCNT) composite modified glass carbon electrode. The sensor achieves acetaminophen (AP) reversibility through better temperature sensitivity. PS-PDEAM shrinks when the temperature exceeds its lower critical temperature (LCST). When AP molecules pass through the modified interface, the electron transfer rate is accelerated, and the sensor is turned on. In the off state, the electrochemical response of AP cannot be detected. Under ideal experimental conditions, for composite modified films, there is a wide detection range of AP between 1.5-85.1 μM and 85.1-235.1 μM, and the limit of detection of acetaminophen is as low as 0.57 μM (S/N = 3). This method has been successfully applied to the determination of AP in tablets, and shows high stability, good reproducibility and excellent anti-interference ability. The on-off sensor opens up a wide range of possibilities for the use of temperature-sensitive polymers in electro-catalysis, sensors, and environmental pollutant monitoring.

An ultrasensitive luteolin electrochemical sensor based on a glass carbon electrode modified using multi-walled carbon nanotube-supported hollow cobalt sulfide (CoSx) polyhedron/graphene quantum dot composites.

Luteolin (LU), belonging to the group of flavonoids with rich biological activities, has attracted considerable attention. Herein, a novel ultrasensitive LU electrochemical sensor based on hollow cobalt sulfide polyhedron-multi-walled carbon nanotube nanocomposites (CoSx-MWCNTs) and graphene quantum dots (GQDs) was proposed. The hollow CoSx polyhedrons derived from ZIF-67 showed excellent electrochemical sensing performance, which was attributed to the abundant surface active sites endowed by the special hollow structure. When detecting LU using the DPV model, the CoSx-MWCNTs/GQDs/GCE showed a linear range of 5 nM-2000 nM under optimal conditions, and the corresponding detection limit (LOD) was 1.2 nM (S/N = 3). In addition, the sensor exhibited satisfactory sensitivity and accuracy for detecting LU in real samples from Chrysanthemum extracts.

Non-enzymatic nitrite amperometric sensor fabricated with near-spherical ZnO nanomaterial

A unique near-spherical ZnO nanostructure was synthesized by using mixed solvents composed of polyethylene glycol-400 (PEG-400) and water at the volume ratio of 12:1 via the solvo-thermal method, and it possessed an ideal morphology with higher uniformity, better dispersion and small particle size. Such ZnO was employed to modify glass carbon electrode (GCE) for the construction of electrochemical sensor, i.e. near-spherical ZnO/GCE, whose nitrite sensing performance was evaluated by Chronoamperometry (CA) and Linear Sweep Voltammetry (LSV). In order to emphasis the superior sensing property and extensive suitability for different electrochemical detection techniques, the excellent but not the same nitrite detection performance obtained from CA and LSV was individually given in detail. This sensor based on CA showed broad linearity range of 0.6 μM–0.22 mM and 0.46 mM–5.5 mM, improved sensitivity of 0.785 μA μM−1 cm−2 accompanied with low LOD of 0.39 μM. With regard to LSV, wide linearity response of 1.9 μM–0.8 mM and 1.08 mM–5.9 mM, high sensitivity of 0.646 μA μM−1 cm−2 with LOD of 0.89 μM were obtained. Meanwhile, this sensor displayed outstanding repeatability with RSD of 2.96% (n = 4), high reproducibility with low RSD (1.72%–2.35%, n = 4), strong selectivity towards nitrite with the concentration set at one-tenth of the interfering substances, ideal stability with the peak current intensity above 90% of its initial value after storage for one month and acceptable recovery of 1.72–2.35% to actual samples including ham sausage, pickle and tap water. The near-spherical ZnO nanomaterial may be a preferred candidate for the fabrication of nitrite electrochemical sensor, which may exhibit a fascinating application in terms of food analysis and environmental monitoring.