Au-TiO2/Chit modified sensor for electrochemical detection of trace organophosphates insecticides

In this paper, Au–TiO₂/Chit modified electrode was prepared with Au–TiO₂ nanocomposite (Au–TiO₂) and Chitosan (Chit) as a conjunct. The Au–TiO₂ nanocomposite and the films were characterized by electrochemical and spectroscopy methods. A set of experimental conditions was also optimized for the film's fabrication. The electrochemical and electrocatalytic behaviors of Au–TiO₂/Chit modified electrode to trace organophosphates (OPs) insecticides such as parathion were discussed in this work. By differential pulse voltammetry (DPV) measurement, the current responses of Au–TiO₂/Chit modified electrode were linear with parathion concentration ranging from 1.0 ng/ml to 7.0 × 10³ ng/ml with the detection limit of 0.5 ng/ml. In order to evaluate the performance of the detection system, we also examined the real samples successfully in this work. It exhibited a sensitive, rapid and easy-to-use method for the fast determination of trace OPs insecticides.     

Self-assembly of TiO2/polypyrrole nanocomposite ultrathin films and application for an NH3 gas sensor

TiO₂/polypyrrole (PPy) nanocomposite ultrathin films for NH₃ gas detection were fabricated by the in situ self-assembly technique. The films were characterized by UV–Vis absorption, FT–IR spectroscopy, and atomic force microscopy (AFM). The electrical properties of TiO₂/PPy ultrathin film NH₃ gas sensors, such as sensitivity, selectivity, reproducibility, and stability were investigated at room temperature in air as well as in N₂. The results showed that the optimum gas-sensing characteristics of TiO₂/PPy ultrathin film were obtained in the presence of 0.1?wt% colloidal TiO₂ for 20-min deposition. Compared with pure PPy thin-film sensors, the TiO₂/PPy film gas sensor has a shorter response/recovery time. It was also found that both humidity and temperature had an effect on the operation of the TiO₂/PPy film gas sensor at low NH₃ concentrations.     

A novel sensor based on multi-walled carbon nanotubes and boron-doped double-layer molecularly imprinted membrane for the analysis of SCZ in pharmaceutical and biological samples

ABSTRACT

A molecularly imprinted electrochemical sensor for the rapid detection of the anti-parasitic drug Secnidazole (SCZ) is reported. In this work, the build electrochemical sensor was based on a carbon paste electrode (CPE) modified with multi-wall carbon nanotubes (MWCNTs) and boron-embedded duplex molecularly imprinted composite membranes (B-DMICMs), that significantly increased the efficiency of the sensor for the detection of template molecule SCZ. Density functional theory (DFT) was employed to study the interactions between the template and monomers to select appropriate functional monomers for rational design of the B-DMICMs.The optimal experimental conditions were optimised for the factors affecting the performance of the sensor. Under the optimal conditions, the reduction peak currents of SCZ by differential pulse voltammetry increased linearly with SCZ concentration in the range from 3.0 × 10^?4 to 1.0 × 1.0^?6 mol L^?1 and 1.0 × 1.0^?6 to 1.91 × 10^?8 mol L^?1 with a detection limit of 1.72 × 10^?8 mol L^?1 for secnidazole, which is significantly lower than those in the currently used methods and in previous reports. This method offers low cost, sensitive and effective determination of SCZ and can potentially be used for detection of SCZ in pharmaceutical and biological samples with good precision and accuracy.     

Direct electrochemistry and electrocatalysis of hemoglobin on chitosan-room temperature ionic liquid-TiO(2)-graphene nanocomposite film modified electrode

TiO₂-graphene nanocomposite was prepared by hydrolysis of titanium isopropoxide in colloidal suspension of graphene oxide and in situ hydrothermal treatment. The direct electrochemistry and electrocatalysis of hemoglobin in room temperature ionic liquid 1-Butyl-3-methylimidazolium hexafluorophosphate, chitosan and TiO₂-graphene nanocomposite modified glassy carbon electrode were investigated. The biosensor was examined by using UV-vis spectroscopy, scanning electron microscopy and electrochemical methods. The results indicated that hemoglobin remained its bioactivity on the modified electrode, showing a couple of well-defined and quasi-reversible redox peaks, corresponding to hemoglobin Fe^III/Fe^II couple. The kinetic parameters for the electrode reaction, such as the formal potential (E^o'), the electron transfer rate constant (k_s), the apparent coverage (Γ), and Michaelis–Menten constant (K_m) were evaluated. The biosensor showed good electrochemical responses to the reduction of H₂O₂ in the ranges of 1–1170 μM. The detection limit was 0.3 μM (S/N = 3). The properties of this composite film, together with the bioelectrochemical catalytic activity, could make them useful in the development of bioelectronic devices, and investigation of electrochemistry of other heme proteins at functional interface.     

Effect of TiO2-coating on structure and electrochemical performance of LiCo0.2Ni0.4Mn0.4O2

LiCo_0.2Ni_0.4Mn_0.4O₂, as the cathode material for lithium ion batteries, was modified by TiO₂-coating. The effect of TiO₂-coating on the structure and electrochemical performance of LiCo_0.2Ni_0.4Mn_0.4O₂ was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and galvanostatic charge-discharge tests. The results suggest that a small amount of TiO₂-coating does not change the crystalline structure, but considerably improves the electrochemical performance of LiCo_0.2Ni_0.4Mn_0.4O₂ in terms of capacity delivery and cyclability. XPS measurements confirm that the improved electrochemical performance is most possibly attributed to a decrease in interaction between the layered material and non-aqueous electrolyte during the charge-discharge processes. __________ Translated from Chinese Journal of Inorganic Chemistry, 2007, 23(5): 753–758 [译自: 无机化学学报]     

Sensitive electrochemical detection of bisphenol A with chitosan and urchinlike MnO2 microsphere modified carbon ionic liquid electrode

In this article, a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid N-hexylpyridinium hexafluorophosphate as the binder and the modifier. Then urchinlike MnO₂ microsphere and chitosan (CTS) was further casted on the CILE surface step-by-step to get a modified electrode that was denoted as CTS/MnO₂/CILE. Cyclic voltammetric studies indicated that bisphenol A (BPA) exhibited a well-defined oxidation peak at 0.486 V in 22.83 g L^?1 pH 8.0 Britton?Robinson buffer solution, which was attributed to the electro-oxidation of BPA on the modified electrode. The presence of urchinlike MnO₂ microsphere on the electrode surface could increase the oxidation peak current (I_pa) greatly, which may be due to the larger surface area that could adsorb more BPA on the electrode surface. Electrochemical parameters of BPA on the modified electrode were calculated with the electron transfer coefficient (α) as 0.66 and the apparent heterogeneous electron transfer rate constant (ks) as 0.50 s^?1. Under the optimal conditions, a linear relationship between the I_pa of BPA and its concentration was obtained in the range from 1.37 × 10^–1 mg L^?1 to 182.6 mg L^?1 with the detection limit as 7.31 × 10^–3 mg L^?1 (3σ). The CTS/MnO₂/CILE was applied to the detection of BPA content in different kinds of samples with satisfactory results.     

Immobilization and hybridization of DNA based on magnesium ion modified 2,6-pyridinedicarboxylic acid polymer and its application for label-free PAT gene fragment detection by electrochemical impedance spectroscopy

A new approach for a simple electrochemical detection of PAT gene fragment is described. Poly(2,6-pyridinedicarboxylic acid) (PDC) modified glassy carbon electrode (GCE) was prepared by potential scan electropolymerization in an aqueous solution. Mg2 ions were incorporated by immer-sion of the modified electrode in 0.5 mol/L aqueous solution of MgCl2 to complete the preparation of a generic "activated" electrode ready for binding the probe DNA. The ssDNA was linked to the conduct-ing polymer by forming a bidentate complex between the carboxyl groups on the polymer and the phosphate groups of DNA via Mg2 . DNA immobilization and hybridization were characterized with dif-ferential pulse voltammetry (DPV) by using methylene blue (MB) as indicator and electrochemical im-pedance spectroscopy (EIS). The EIS was of higher sensitivity for DNA detection as compared with voltammetric methods in our strategy. The electron transfer resistance (Ret) of the electrode surface in EIS in [Fe(CN)6]3-/4- solution increased after the immobilization of the DNA probe on the Mg/PDC/GCE electrode. The hybridization of the DNA probe with complementary DNA (cDNA) made Ret increase further. The difference between the Ret at ssDNA/Mg/PDC/GCE and that at hybridization DNA modified electrode (dsDNA/Mg/PDC/GCE) was applied to determine the specific sequence related to the target PAT gene with the dynamic range comprised between 1.0 × 10-9 and 1.0 × 10_5 mol/L. A detection limit of 3.4 × 10-10 mol/L of oligonucleotides can be estimated.     

Homogeneous and nanomolar detection of hydrazine by indigocarmine as a mediator at the surface of TiO2 nanoparticles modified carbon paste electrode

The homogeneous electrocatalytic oxidation of hydrazine（HZ） has been studied by indigocarmine（IND） as a mediator at the surface of TiO₂ nanoparticles modified carbon paste electrode（TNMCPE）.Cyclic voltammetry was used to study the electrochemical behavior of IND at different scan rates.The voltammetric response of the modified electrode was linear against the concentration of HZ in the ranges of 3.0×l0^-8-7.0×10⁶ mol/L with differential pulse voltammetry method.The detection limit（3σ） was determined as 27.3 nmol/L.To evaluate the applicability of the proposed method to real samples,the modified CPE was applied to the determination of HZ in water samples.     

Electrochemical determination of vitamin C in the presence of uric acid by a novel TiO2 nanoparticles modified carbon paste electrode

<正>The electrochemical behavior of vitamin C(ascorbic acid or AA) is investigated on the surface of a carbon-paste electrode modified with TiO_2 nanoparticles and 2,2'-(1,2 butanediylbis(nitriloethylidyne))-bis-hydroquinone(BBNBH).The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of AA,leading to remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction.This modified electrode exhibits well-separated oxidation peaks for AA and uric acid(UA).The modified electrode is successfully applied for the accurate determination of AA in pharmaceutical preparations.     

Electrochemical oxidation determination and voltammetric behaviour of 4-nitrophenol based on Cu2O nanoparticles modified glassy carbon electrode

Cu₂O nanoparticles (nano-Cu₂O) modified glassy carbon electrode (GCE) was fabricated and used to investigate the electrochemical behaviour of 4-nitrophenol (4-NP) by cyclic voltammetry (CV), chronoamperometry (CA), chronocoulometry (CC) and differential pulse voltammetry (DPV). Compared with GCE, a remarkable increase in oxidation peak current was observed. It indicates that nano-Cu₂O exhibits remarkable enhancement effect on the electrochemical oxidation of 4-NP. Under the optimised experimental conditions, the oxidation peak currents were propotional to 4-NP concentration in the range from 1.0?×?10^?6 to 4.0?×?10^?4?mol?L^?1 with a detection limit of 5.0?×?10^?7?mol?L^?1 (S/N?=?3). The fabricated electrode presented good repeatability, stability and anti-interference. Finally, the proposed method was applied to determine 4-NP in water samples. The recoveries for these samples were from 94.60% to 105.5%.     

Preparation of TiO<Subscript>2</Subscript>/activated carbon with Fe ions doping photocatalyst and its application to photocatalytic degradation of reactive brilliant red K2G

Titanium dioxide coated on activated carbon (AC) with Fe ions doping (Fe-TiO₂/AC) composite was prepared by an improved sol-gel method. The photocatalytic activities were tested by photocatalytic degradation of reactive brilliant red K2G in solution. The results show that in comparison with the agglomeration of pure TiO₂, the TiO₂ nanoparticles are well dispersed in the AC matrix, of which sizes are decreased with Fe ions doping. Additionally, the iron species on TiO₂ of composite are Fe₂O₃ and FeO, which do not affect the crystalline structures of TiO₂ nanoparticles. The AC matrix and iron doping content influence the fluorescence intensity of composite due to their effects on recombination probability of hole-electron pairs. Compared with TiO₂, 0.3% Fe-TiO₂, TiO₂/AC, 0.5% Fe-TiO₂/AC and 0.1% Fe-TiO₂/AC, the 0.3% Fe-TiO₂/AC shows the highest photoactivity with the complete mineralization of K2G for finite time due to the optimum Fe ions content and AC matrix. Furthermore, the kinetic constant (k = 0.0229 min⁻¹) of 0.3% Fe-TiO₂/AC composite is more than the sum of both TiO₂/AC (0.0154 min⁻¹) and 0.3% Fe-TiO₂ (0.0057 min⁻¹) because coexistence of the AC and Fe ions has an enlarging effect on improving the photoactivity of TiO₂. Supported by the Education Department Foundation of Hunan Province (Grant No. 08B063) and Science and Natural Science Foundation of Hunan Province (Grant No. 09JJ6101)     

An ion imprinted electrochemical sensor based on flower-like gold nanoparticles for the detection of trace arsenic(III) ions in water and food samples

A selective and sensitive electrode based on Au−S bonds between As(III) ion-imprinted polymer (IIP) and the flower-like gold nanoparticles (FL-AuNPs) had been rationally developed for detecting As(III) by using the square wave voltammetry (SWV) method. Under optimized measurement conditions, the prepared electrochemical sensor exhibited obvious detection performance of As(III) in the range of 0.009 μg/L–0.50 μg/L with a relatively low detection limit of 0.015 μg/L. Furthermore, the imprinted electrochemical sensor displayed good reusability, excellent specificity, and demonstrated high potential for environmental control with a recovery rate between 80.7 % and 113.3 %.     

B2O3/TiO2-ZrO2的结构表征及其与酸性和催化性能间的关系

采用XRD、N₂吸附、 ¹¹B MAS NMR、NH₃-TPD和催化性能评价等方法研究了B₂O₃/TiO₂-ZrO₂催化剂的结构、酸性及催化环己酮肟气相Beckmann重排反应性能间的关系。结果表明,催化剂中的B₂O₃同时以三配位的BO₃和四配位的BO₄结构单元存在;     

Facile fabrication of hydrophilic PAA-Ti/TiO2 nanocomposite for selective enrichment and detection of phosphopeptides from complex biological samples

Highly selective enrichment of trace phosphorylated proteins or peptides from complex biological samples is of profound significance for the discovery of disease biomarkers in biological systems. In this study, a novel affinity material has been synthesized to improve the enrichment specificity for phosphopeptides by using PAAS as coupling molecule. In the resulting materials, highly abundant titanium is available for selective enrichment of phosphopeptides, with plenty of carboxylate groups that can inhibit nonspecific adsorption. The enrichment results demonstrated that the hydrophilic PAA-Ti/TiO₂ composite possesses excellent selectivity for phosphopeptides even at a very low molar ratio of phosphopeptides/non-phosphopeptides (1:1000), extreme sensitivity (the detection limit was at the fmol level), and high recovery of phosphopeptides (as high as 78%). Moreover, the as-prepared nanocomposite provides effective enrichment of phosphopeptides from real samples (mouse liver), showing great potential in the detection of low-abundance phosphopeptides in biological samples.     

Fabrication of a new electrochemiluminescent sensor for fentanyl citrate based on glassy carbon microspheres and ionic liquid composite paste electrode

Due to the high performance of glassy carbon in the aspects of mechanical strength, electrical conductivity and high corrosion resistance, etc., glassy carbon has been widely used in the electrochemistry. A new form of glassy carbon, glassy carbon microsphere, was utilized to couple with ionic liquid in preparing a new electrochemiluminescent platform for Ru(bpy)₃Cl₂. Room temperature ionic liquid has been proposed to be very interesting and efficient pasting binder to replace the non conductive organic binders for the fabrication of composite paste electrode. Attributed to the special characteristics of glassy carbon microspheres and room temperature ionic liquid [N-octylpyridium tetrafluoroborate (OPFP)], this new electrochemiluminescent sensor exhibited excellent electrochemiluminescent performance in Ru(bpy)₃²⁺ solution. We first found that fentanyl citrate could increase the ECL of Ru(bpy)₃²⁺, hence an ECL approach was developed for the determination of fentanyl citrate based on this glassy carbon microspheres based electrochemiluminescent platform with high sensitivity. Under the optimized conditions, the enhanced electrochemiluminescent intensity versus fentanyl citrate concentration was linear in the range of 1.0 × 10⁻⁸ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 8.5 × 10⁻⁹ mol L⁻¹, and the relative standard deviation for 1.0 × 10⁻⁶ mol L⁻¹ fentanyl citrate was 1.90% (n = 10). This protocol has extended the application scopes of glassy carbon material and promoted the application of glassy carbon microspheres in electroanalysis.     

Solid phase extraction and flame atomic absorption spectrometric determination of trace amounts of cadmium and lead in water and biological samples using modified TiO2 nanoparticles

A solid phase extraction procedure for the separation and preconcentration of trace amounts of Cd(II) and Pb(II) using the alizarin red S modified TiO₂ nanoparticles prior to their determination by flame atomic absorption spectrometry has been proposed. The influences of some analytical parameters such as pH, flow rates of sample and eluent, type and concentration of the eluent, and interfering ions on the recovery of Cd(II) and Pb(II) by the sorbent were investigated. The analytes were quantitatively sorbed from the aqueous solution at pH 5.5 onto a microcolumn packed with the sorbent and recovered with 2.0?mL of 1.5?mol?L^?1 hydrochloric acid. Under the optimum experimental conditions, the detection limits for Cd(II) and Pb(II) were 0.11 and 0.30?ng?mL^?1 and the relative standard deviations for ten replicate measurements of 5.0 and 50.0?ng?mL^?1 of Cd(II) and Pb(II) were 2.1 and 1.9%, respectively. A sample volume of 200?mL resulted in a preconcentration factor of 100. The method was successfully applied to the determination of Cd(II) and Pb(II) in water and biological samples, and accuracy was examined by the recovery experiments, independent analysis using electrothermal atomic absorption spectrometry, and analysis of a water standard reference material (SRM 1643e).     

Sensitively electrochemical detection of the DNA damage in situ by electro-Fenton reaction based on Fe@Fe2O3 core-shell nanonecklace and multi-walled carbon nanotube composite

An electrochemical biosensor for mimicking the metal-mediated DNA damage pathway in situ was presented. The Fenton reagents (H₂O₂ and iron ion) for the DNA damage were generated in situ with a constant rate from the sensing film. H₂O₂ and iron ion reacted further together to yield hydroxyl radical, which attacked DNA in the film. These courses of DNA damage were just like those happened in organism. The DNA damage was detected by monitoring the differential pulse voltammetric response of an electrochemical indicator, Co(phen)₃³⁺. Another electrochemical indicator, Ru(NH₃)₆³⁺, was also used for monitoring the DNA damage as a complementary means and the minimal detectable amount of DNA damage was 0.16 μg. The biosensor had good reproducibility. After this biosensor was used for 11 times, 90% of the first detection signal was obtained.     

Electrodeposition of dendritic gold/silver nanaoparticles on disposable screen‐printed carbon electrode and its application of 4‐mercaptopyridine in in situ electrochemical surface‐enhanced Raman scattering

Column electrodes pretreated through oxidation–reduction cycles were traditionally used in electrochemical surface‐enhanced Raman scattering (SERS). In this study, a disposable screen‐printed carbon electrode was introduced into in situ electrochemical SERS through the electrodeposition of dendritic gold/silver nanoparticles (Au/AgNPs) onto the surface of the carbon working electrode to induce the SERS enhancement effect on the electrode. Scanning electron microscopy images showed that dendritic Au/AgNPs nanostructures could be fabricated under appropriate electrodeposition conditions and could present a minimum SERS factor of 4.25 × 10⁵. Furthermore, the absorbed behavior of 4‐mercaptopyridine was investigated under different potentials. The adsorption configuration was inferred to transform from ‘vertical’ to ‘lying‐flat’. The proposed new electrode combined with a portable Raman spectrometer could be useful in the identifying products or intermediates during electrochemical synthesis or electrochemical catalysis in in situ electrochemical SERS. Copyright © 2016 John Wiley & Sons, Ltd.     

Fabrication and application of a new modified electrochemical sensor using nano-silica and a newly synthesized Schiff base for simultaneous determination of Cd,Cu and Hg ions in water and some foodstuff samples

A new chemically modified carbon paste electrode was constructed and used for rapid, simple, accurate, selective and highly sensitive simultaneous determination of cadmium, copper and mercury using square wave anodic stripping voltammetry (SWASV). The carbon paste electrode was modified by N,N′-bis(3-(2-thenylidenimino)propyl)piperazine coated silica nanoparticles. Compared with carbon paste electrode, the stripping peak currents had a significant increase at the modified electrode. Under the optimized conditions (deposition potential, −1.100 V vs. Ag/AgCl; deposition time, 60 s; resting time, 10 s; SW frequency, 25 Hz; pulse amplitude, 0.15 V; dc voltage step height, 4.4 mV), the detection limit was 0.3, 0.1 and 0.05 ng mL⁻¹ for the determination of Cd²⁺, Cu²⁺ and Hg²⁺, respectively. The complexation reaction of the ligand with several metal cations in methanol was studied and the stability constants of the complexes were obtained. The effects of different cations and anions on the simultaneous determination of metal ions were studied and it was found that the electrode is highly selective for the simultaneous determination of Cd²⁺, Cu²⁺ and Hg²⁺. Furthermore, the present method was applied to the determination of Cd²⁺, Cu²⁺ and Hg²⁺ in water and some foodstuff samples.