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Nanorods assembled 3D microspheres of TiO2/MnO2 were prepared via a simple one-pot hydrothermal approach. The resultant composite material exhibited remarkable electrocatalytic activity for hydrogen peroxide (H2O2) in comparison to each single component. The electrochemical sensor constructed with TiO2/MnO2 exhibited a linear relationship within the range 0.0001–5.6 mmol·L−1 for H2O2. The limit of detection (LOD) and sensitivity for H2O2 were 0.03 µmol·L−1 (S/N = 3) and 316.6 µA (mmol·L−1)−1 cm−2. Moreover, this sensor can be employed to detect trace amount of H2O2 in serum and urine samples successfully, supporting an insight and strategy for a more sensitive electrochemical sensor. [ABSTRACT FROM AUTHOR]

• Regulate ZnO microstructure by controlling concentration of hydroxide. • Prepare nanosheets cross-linked 3D ZnO. • Fabricate sensor to detect trace amount of NO 2 - in ham sausage and pickled vegetables. • Investigate catalytic mechanisms of cross-linked ZnO nanosheets for NO 2 -. A 3D cross-linked ZnO (cl-ZnO) nanosheets were prepared via a simple one-pot hydrothermal approach, and then characterized by a series of modern advanced technique including XRD, SEM, TEM and XPS. This nanomaterial was used to modify the glass carbon electrode (GCE), obtaining an electrochemical sensor (cl-ZnO/GCE) of which the electrochemical properties were studied using various electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The sensor exhibited remarkably enhanced electrocatalytic activity for nitrite ions (NO 2 -) in comparison to that of the commercially available ZnO-modified GCE. Two electrochemical techniques, including chronoamperometry (CA) and linear sweep voltammetry (LSV) were adopted to test the determination performance of the sensor for nitrite, it exhibited a good linear relationship within the range of 0.8 μmol·L-1 - 0.462 mmol·L-1 and 0.608 - 7.84 mmol·L-1 evaluated by CA, the limit of detection (LOD) and sensitivity for NO 2 - were 0.26 μmol·L-1 (S/ N = 3) and 824.6 µA (mmol·L-1)-1cm-2, respectively. For LSV, the two linearity responses of 0.95 μmol·L-1- 0.515 mmol·L-1 and 0.667 mmol·L-1- 5.41 mmol·L-1, high sensitivity of 1336.1 µA (mmol·L-1)-1cm-2 with low LOD of 0.32 μmol·L-1 were gained. This sensor can be employed to detect trace amount of NO 2 - in ham sausage and pickled vegetables successfully, supporting an insight and strategy for more sensitive nitrite electrochemical sensor. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Near-spherical ZnO/N-rGO nanocomposite was prepared by a facile hydrothermal method. • Systematic study of electrochemical sensing property of ns-ZnO/N-rGO for nitrite. • Sensor was used for detection of nitrite in ham sausage, pickle and tap water. • The electrochemical sensing mechanism of ns-ZnO/N-rGO for nitrite was explored. A hierarchical near-spherical ZnO (ns-ZnO)/Nitrogen-doped reduced graphene oxide (N-rGO) nanocomposite was synthesized via a facile hydro/solvo-thermal route. Then, a non-enzymatic nitrite electrochemical sensor (ns-ZnO/N-rGO/GCE) was obtained by modifying glassy carbon electrode (GCE) with the prepared nanocomposite. More adsorption sites and electro-catalytic active sites were provided at the electrode interface thanks to the formation of hierarchical structure, making the fabricated GCE possess a remarkable amperometric sensing property for nitrite. The limit of detection (LOD) was as low as 0.08 μM, and the detection range was as broad as 0.037 μM–5.9 mM. Furthermore, this sensor showed satisfactory recovery for nitrite in genuine samples including ham sausage, pickle and tap water, suggesting the potential practical application performance of ns-ZnO/N-rGO/GCE in the fields of food analysis and environmental monitoring. [ABSTRACT FROM AUTHOR]

A new electrochemical sensor for HO was constructed by depositing copper doped CuO nanosheets on a glassy carbon electrode (GCE). The morphology and composition of the modified electrode were characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The electrochemical properties of the electrode were studied using cyclic voltammetry and electrochemical impedance spectroscopy. The catalytic performance of the sensor was studied in 100 mM NaOH solution via differential pulse voltammetry and revealed the sensor to display significantly improved electrocatalytic activity with respect to the analysis of the HO in comparison to a plain GCE or a GCE modified with copper only. The response to HO at a working voltage of −0.46 V (vs. Ag/AgCl) is linear in the 0.003 - 8 mM concentration range, and the detection limit is 0.21 mM (at an S/N ratio of 3). Satisfactory results were obtained in the analysis of tap, rain and river waters spiked with HO. The analytical performance of this electrode compares favorably to the results obtained with other commonly used techniques for analysis of HO. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel stir bar-shaped ZnO (sb-ZnO)/nitrite-doped reduce grapheme oxide (N-rGO) nanocomposite (sb-ZnO/N-rGO) was facilely synthesized by using the hydrothermal route. Furthermore, a glassy carbon electrode (GCE) modified with the sb-ZnO/N-rGO nanocomposite was constructed and used as the non-enzymatic nitrite electrochemical sensor (sb-ZnO/N-rGO/GCE). Benefiting from the excellent catalytic activity to the electro-oxidation of nitrite as a result of the synergy of N-rGO and sb-ZnO, the modified electrode displayed a superior amperometric sensing performance toward nitrite detection including lower detection limit (LOD) of 0.13 μM, broad linearity range of 0.2 μM~1.2 mM and 1.5–7.8 mM, high sensitivity, rapid response, remarkable repeatability, outstanding durability, good storage stability and strong resistance against interfering substance. In addition, this sensor showed satisfying recovery between 96.0% and 103.0% to nitrite in practical application involved ham sausage, pickled vegetables as well as tap water. The as-synthesized sb-ZnO/N-rGO composite is a qualified candidate for fabricating nitrite electrochemical sensor, which would have promising application prospect in terms of food analysis and environmental monitoring. • stir bar-shaped ZnO/N-rGO nanocomposite was prepared by a facile hydrothermal method. • Systematic study of electrochemical sensing property of sb-ZnO/N-rGO for nitrite. • Sensor was used for detection of nitrite in ham sausage, pickle and tap water. • The electrochemical sensing mechanism of sb-ZnO/N-rGO for nitrite was explored. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • An expected near-spherical ZnO nanostructure was synthesized by using mixed solvent. • Cost-effective nitrite electrochemical sensor with excellent performance was obtained. • Successful application of ZnO/GCE for detecting nitrite in water, ham and pickle. • ZnO′s electrochemical sensing mechanism for detecting nitrite was studied. [ABSTRACT FROM AUTHOR]

We report on a modified glassy carbon electrode (GCE) for sensing hydrogen peroxide (HO). It was constructed by consecutive electrochemical deposition of poly(anthranilic acid) and poly(diphenylamine sulfonate) on the GCE, followed by the deposition of copper oxide (CuO). The morphology and electrochemistry of the modified electrode was characterized by atomic force microscopy, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. The catalytic performance of the sensor was studied with the use of differential pulse voltammetry under optimized conditions. This sensor displayed significantly better electrocatalytic activity for the reduction of HO in comparison to a GCE without or with modification with CuO or polymer films alone. The response to HO is linear in the range between 0.005 to ~11 mM, and the detection limit is 0.18 μM (at an S/N of 3). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel Prussian blue/copper-gold bimetallic nanoparticles hybrid film modified electrode was prepared by electrochemical deposition on a glassy carbon electrode (PB/Cu-AuNPs/GCE). Morphology and electrochemistry of this electrode were studied by UV-vis spectroscopy, scanning electron microscopy, X-ray diffraction, cyclic voltammetry and electrochemical impedance spectroscopy. The sensor showed significantly better electrocatalytic activity for the reduction of hydrogen peroxide in comparison with the single PB/GCE and PB/AuNPs/GCE. This was attributed to the synergistic effect of PB and Cu-Au bimetallic nanoparticles. Also, the sensor demonstrated an overall high level of performance for the analysis of H2O2 in the concentration range from 0.002 to 0.84 mM. [ABSTRACT FROM AUTHOR]

NAD+-dependent dehydrogenase-based biosensors usually suffer from the low accuracy due to the interference of cofactors in the complex environment, such as fermentation samples. Herein, we demonstrate the example of an integrated biosensor device that can be applied for analyzing xylose fermentation samples. The device is composed of one chamber for the elimination of NAD+ and NADH in the fermentation broth and another chamber for the sample analysis. In the first chamber, a cyclic voltammetry method coupled with Ni foam as a working electrode was proven to be effective in removing NAD+ and NADH in the fermentation broth. In the other chamber, xylose dehydrogenase, as the recognition element, and diaphorase, used for the regeneration of bioactive NAD+ mediated by vitamin K 3 , were co-immobilized on the surface of the magnetic nanoparticles, which was further coated onto a magnetic glassy carbon electrode. The detection range of the constructed biosensor was from 0.5 to 10 g L−1 with a detection limit of 0.01 g L−1 at a signal-to-noise ratio of 3. Moreover, the biosensor achieved high selectivity, recovery, reproducibility, and good long-time stability when analyzing real xylose fermentation samples, suggesting its promising application potential. [Display omitted] • A new integrated biosensor device for analyzing xylose fermentation samples was developed. • A voltammetry-based method was developed to successfully remove NAD+ and NADH in fermentation broth samples. • A new, stable, reusable bioelectrode was developed and used to measure xylose in fermentation broth samples. [ABSTRACT FROM AUTHOR]

• Six ZnO materials with different morphology were synthesized by controlling solvent. • Practical application of stir bar-shaped ZnO/Nafion/GCE sensor for nitrite detection in water, ham, pickle. • A dependency between ZnO's sensing property and its morphology was revealed. • Study of ZnO's sensing mechanism for detecting nitrite. Excessive uptake of food or drinking water which is rich in nitrite has been demonstrated to be very hazardous to both the health of humans and animals, so it is of great significance to develop a reliable technique for low-concentration detection of nitrite. Herein, we reported the synthesized zinc oxide which is an excellent electrochemical material for the sensing of nitrite. Interestingly, the ZnO material exhibits a strong dependent relationship between the electrochemical sensing performance and its morphology controlled by the solvent employed in the solvo-thermal method. In particular, the stir-bar shaped ZnO nanorods, with a 40∼90 nm width and 50∼170 nm length, display significantly improved electrocatalytic performance to the electrochemical oxidation of nitrite which is benefited from the more reactive active sites based on the higher dispersion and smaller size. The sensor based on ZnO/Nafion modified glassy carbon electrode (ZnO/Nafion/GCE) shows a broad linear response within the range of 0.3 μM∼6.14 mM and 0.8 μM∼4.86 mM, respectively, for amperometry and linear sweep voltammetry (LSV), the corresponding limit of detection (LOD) were calculated to be 0.21 μM and 0.62 μM, respectively. Also the prepared sensor shows excellent sensitivity, reproducibility, stability and high anti-interference abilities. More importantly, the satisfactory recovery is obtained from ham sausage, pickle and running water, demonstrating the great application prospects of this sensor. In addition, the sensing mechanism of such ZnO sensing to nitrite is also discussed in detail. [ABSTRACT FROM AUTHOR]

A hollow urchin-like α-MnO2 material has been synthesized by a hydrothermal method starting from MnSO4·H2O and (NH4)2S2O8, and by using silver(I) as the catalyst. It has a hollow morphology with diameters of 5–6 μm and consists of densely aligned nanowires, with a 30–40 nm width and a 1.5 μm length. The diameter of the cavities and the thickness of the shell are about 1.2 μm and 300 nm, respectively. The material was placed on a glassy carbon electrode (GCE), and electrochemical experiments showed the respective sensor to possess good stability and reproducibility. The modified GCE displays response to both hydrogen peroxide (H2O2) and dopamine (DA) at working potentials of −0.40 V and +0.4 V, respectively (both versus SCE). H2O2 can be detected with an 80 nM detection limit, and DA with a 12 nM detection limit (at S/N = 3). Graphical abstract Schematic presentation of synthesis of a hollow urchin-like α-MnO2, which taking MnSO4.H2O and (NH4)2S2O8 as raw materials and was further used to construct an electrocatalytic sensor for hydrogen peroxide and dopamine with low detection limit, desirable selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

Co3O4/carbon hybrid hollow nanospheres (hs-Co3O4/C) with an empty cavity and a thin shell, were synthesized starting from the pectin and cobalt acetate via cross-linking deposition at room temperature and post-calcination. The hierarchical structure is constructed from the interconnected nanoparticles in the residual carbon matrix, and the carbon content can be adjusted by changing the calcination temperature. The gas sensor based on hs-Co3O4/C calcined at 300 °C in air shows high response towards 50 ppm of H2S (S = 95.5) and good selectivity at a low working temperature (92 °C). The detection limit is as low as 0.1 ppm. The non-enzymatic glassy carbon electrode based sensor constructed from the same material exhibits excellent electrocatalytic activity for H2O2 with the sensitivity of 405.8 μA∙mM∙cm−2 at 0.3 V (vs. SCE) in alkaline solution. The chronoamperometric response time is < 3 s and the detection limit (at S/N = 3) is 0.30 μM. The good sensing performances are attributed to the synergetic effect of unique hollow nanostructure and appropriate amount of carbon in the hybrid material. The porous nanostructure can increase the mass transfer efficiency, and the cross-linked nanoparticles with good crystallinity also improve the conductivity of materials. The presence of carbon enhances the charge transfer ability and increases the specific surface, thereby improving the sensor performance.Schematic illustration of the formation of hollow Co3O4 nanospheres composited with pectin-derived carbon. The material displays excellent selectivity for H2S gas and in non-enzymatic detection of dissolved H2O2. [ABSTRACT FROM AUTHOR]

[Display omitted] • WO 2 -Na x WO 3 /CSs composite was prepared by hydrothermal synthesis and calcination. • It was used to detect dopamine and shows low LOD and high sensitivity. • It also exhibits a good selectivity, admirable reproducibility and good stability. • It is successfully used for dopamine detection in mouse and bovine serum samples. WO 2 -Na x WO 3 nanoparticles modified carbon spheres (WO 2 -Na x WO 3 /CSs) composite has been successfully synthesized by simple hydrothermal synthesis and high temperature calcination, and highly selective detection of dopamine (DA) was performed. The existence of WO 2 -Na x WO 3 was confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectrum. Meanwhile, it can be seen from transmission electron microscopy (TEM) images that WO 2 -Na x WO 3 was modified on the surface of carbon spheres in the form of nanometer-scaled particles. Cyclic voltammetry (CV) showed that the glassy carbon electrode modified by WO 2 -Na x WO 3 /CSs composite had strong electrocatalytic activity for DA oxidation, and a non-enzyme DA electrochemical sensor based on this material was constructed. Under the best conditions, the differential pulse voltammetry (DPV) signals of proposed sensor linearly increased with the increase of DA concentration in the range of 0.004 ~ 15.4 μM and 15.4 ~ 106.4 μM, with high sensitivity of 19.335 μA·μM−1·cm−2 and 3.151 μA·μM−1·cm−2, respectively, and a low limit of detection (LOD) of 1.3 nM (S/N = 3) and a limit of quantification (LOQ) of 4.3 nM were obtained. Furthermore, the sensor had good selectivity and satisfactory reproducibility and good stability for DA detection (RSD = 2.50%). It was successfully used to detect DA in animal serums, its recovery rate was between 1.10% and 2.91%, showing potential practical application value. [ABSTRACT FROM AUTHOR]