Development of structure-specific electrochemical sensor and its application for polyamines determination

A novel structure-specific electrochemical sensing scheme to monitor analyte, independent of its oxidation potential, is described. Molecules with multidentate chelating sites that can form stable five- or six-membered ring complexes with cupric ions are appropriate for this approach. In the copper-based electrode, potential-accelerating complex formation behavior is observed, and an apparent oxidation current is induced to regenerate the oxide layer until reaching its maximum steady state. In this unique electroanalytical method, a suitable potential is utilized to increase the coordination number of the metal electrode surface rather than direct oxidation of the analyte. The experimental results show that the signal sensitivity depends primarily on the pK_a of the chelating sites and the solution pH. Several aliphatic amines were studied with this simple approach, and the detection limits for spermidine (SPD; 0.19 μM) and spermine (SPM; 0.14 μM) at a low oxidation potential (0.25 V vs. Ag/AgCl) were obtained. A higher operating potential was used to improve the sensitivity for putrescine (PUT) and cadaverine (CAD). The detection limit was improved to 0.05, 0.06, 0.11 and 0.27 μM for SPD, SPM, PUT and CAD, respectively, without surface fouling (less than 3% with RSD). The feasibility of its clinical application is demonstrated by integrating this sensor with high-performance liquid chromatography (HPLC).     

Boron-doped diamond electrochemical sensor for sensitive determination of nicotine in tobacco products and anti-smoking pharmaceuticals

A sensitive, selective and reliable electrochemical method for the determination of nicotine using differential pulse voltammetry on a bare boron-doped diamond electrode has been developed. Nicotine yielded a single oxidation peak at a highly positive potential of + 1.45 V (vs. Ag/AgCl/3 M KCl) in Britton–Robinson buffer solution at pH 8. The influence of supporting electrolyte, pH and scan rate on the current response of NIC was investigated. At optimized experimental conditions, a linear relation between peak current and concentration of nicotine was found for the range from 0.5 to 200 μM (0.08–32.9 mg L^− 1) with a detection limit of 0.3 μM (0.05 mg L^− 1) and a good repeatability (relative standard deviation of 2.1% at 25 μM concentration level, n = 10) was achieved without any electrode surface modification. The practical usefulness of the developed procedure was successfully demonstrated with the determination of nicotine in tobacco products and anti-smoking pharmaceuticals with results similar to those obtained by a high-performance liquid chromatography and to the contents declared by the manufacturer, respectively. Prior to analysis, the sample pretreatment includes only sonication and/or simple liquid–liquid extraction. The proposed sensor represents an effective electrochemical tool and a promising alternative for quality control analysis of products in tobacco and pharmaceutical industry.     

Mesoporous semiconducting oxides for gas sensor application

A fabrication procedure of thermally stable mesoporous SnO₂ and TiO₂ powders has been overviewed along with their gas-sensing properties. Treatment of an as-prepared composite material of a supramolecule surfactant and SnO₂, i.e. a self-assembly of the surfactant fringed with a SnO₂ thin wall, with phosphoric acid enabled us to fabricate thermally stable ordered mesoporous SnO₂ powder having a d₁₀₀ value of 3.2 nm, a crystallite size of 2.0 nm and a large specific surface area of 305 m² g⁻¹ even after calcination at 600 °C for 5 h. A thick film sensor fabricated with the ordered mesoporous SnO₂ powder exhibited higher sensing performance than that fabricated with SnO₂ powder prepared by a conventional method and therefore having a lower specific surface area. Surface modification of the conventional SnO₂ powder with a mesoporous SnO₂ layer was also found to be effective for improving the sensing properties. Mesoporous TiO₂ powder could be prepared by employing a modified sol-gel method with Ti(NO₃)₄ and polyethylene glycol having different molecular weights. Higher sensitivity was achieved with a disc-type sensor fabricated with mesoporous TiO₂ powder, in comparison with one fabricated with commercially available TiO₂ powder in the same form, but its sensing properties needed to be further modified.     

Carbon nanotube-based electrochemical sensor for the determination of halobetasol propionate, a topical corticosteroid

Electrocatalytic reduction of halobetasol propionate (HBP) at single-walled carbon nanotube (SWCNT) modified edge plane pyrolytic graphite electrode (EPPGE) was performed by square wave voltammetry and cyclic voltammerty in phosphate buffer of pH 7.2. The surface morphology of SWCNT/EPPGE was characterized by field emission scanning electron microscopy. The enhanced peak current (i _p) and lower reduction peak potential (E _p) at modified electrode as compared to bare electrode were obvious evidences for the electrocatalytic ability of SWCNT toward the reduction of HBP. The cathodic peak current varied linearly with concentration of HBP in the range 0.02 to 1 mM with sensitivity of 2.432 μA mM⁻¹ and detection limit (3σ/slope) of 10 μM. The product of electrochemical reduction of HBP was characterized using FT-IR and ¹H-NMR spectroscopic techniques. A tentative mechanism for the formation of product was suggested and it was found that reduction of >C=O occurred at position three. The proposed methodology was successfully applied to the detection of HBP in pharmaceutical preparations.     

Novel bismuth/multi-walled carbon nanotubes-based electrochemical sensor for the determination of neuroprotective drug cilostazol

A very sensitive electrochemical sensor has been developed by modification of glassy carbon electrode (GCE) with nanoparticles of bismuth (III) oxide (Bi₂O₃) and multi-walled carbon nanotubes (MWCNTs). The sensor was applied for the determination of cilostazol, cyclic nucleotide phosphodiesterase inhibitors in pharmaceutical formulation and human plasma. The voltammetric responses were compared with those obtained at bare GCE under optimum conditions. The cyclic and square-wave voltammograms of cilostazol showed 3.3 and 4.9 times enhancement in the oxidation peak current at MWCNTs–Bi₂O₃/GCE as compared to a bare GCE. Bi₂O₃–MWCNTs/GCE showed a linear response for cilostazol in standard solution over the concentration range of 0.8–13 μg mL⁻¹ with the detection limit 0.76 μg mL⁻¹, whereas human plasma over the concentration range 0.8–12.5 μg mL⁻¹ with the detection limit 0.66 μg mL⁻¹.     

镍锰氧化物复合电化学传感器对抗坏血酸的检测

基于镍锰氧化物复合物对抗坏血酸具有催化氧化作用,因此利用镍锰氧化物复合物修饰玻碳电极构建抗坏血酸快速检测的电化学传感器。通过一步水热合成法制备了镍锰基氧化物复合材料。并利用电子显微镜(SEM)、能量色散X射线能谱(EDS)、X射线衍射(XRD)以及傅里叶红外光谱(FT-IR)对材料的形貌、元素组成以及结构进行表征。结果表明该材料为外表带有孔隙的球型结构,衍射峰索引为Mn2O3(JCPDS编号41-1442)、NiMnO3(JCPDS号48-1330)且Mn-O官能团与Ni-O官能团均存在。采用滴涂法将复合材料修饰于电极表面,用循环伏安法(CV)、差分脉冲伏安法(DPV)测试了抗坏血酸在镍锰氧化物复合物电极上的电化学行为,并对其进行了分析,在pH=4的乙酸缓冲溶液条件下,滴涂量为10μL,抗坏血酸的浓度在0.4～7600 μmol/L时与氧化峰电流值呈线性关系,线性方程为Ip=0.0039 x(mmol/L)+11.643,R2=0.9900,检出限为0.023 μmol/L。该传感器实际应用于果汁饮料中抗坏血酸的含量的测定,加标回收率为95.5%～103.12%,表明它在食品分析等方面具有良好的应用前景。     

钼酸盐的制备及其光催化性能研究进展

综述了近些年不同钼酸盐材料的典型制备方法,分析了不同钼酸盐材料在可见光催化降解等方面的性能特点。详细总结了钼酸盐在光催化反应机理方面的研究进展,并在此基础上总结了钼酸盐光催化性能的改进方法。阐述了钼酸盐光催化剂的优势与缺点,试图为高性能钼酸盐催化剂的研究提供基础参考。     

铅笔芯电化学传感器研究进展

详细介绍了铅笔芯电极作为碳基电极,具有成本低、易变形、易于使用、广泛的商业可用性等优点而受到广泛关注,应用于环境样品中不经过浓缩提纯的无机和有机污染物的低检测限灵敏检测。并介绍了裸铅笔芯电极制备、预处理及化学修饰后电极特性。在此基础上,提出了铅笔芯作为电化学传感器在研究和应用方面需要克服的问题,并对铅笔芯电极未来研究方向进行了展望。     

分子印迹电化学传感器检测链霉素

为实现链霉素的快速、灵敏测定,将特异性强的分子印迹技术与检测灵敏度高的电化学检测方法结合,构建链霉素分子印迹电化学传感器。以链霉素为模板分子,吡咯为功能单体,利用电化学聚合方法制备分子印迹聚合物(MIP)膜。在最优化实验条件下,以铁氰化钾为探针,利用循环伏安法(CV)对链霉素进行定量测定及传感器性能研究。结果表明:传感器线性范围为5.00×10~(-8)～8.00×10~(-5)mol/L,最低检出限(LOD)为3.45×10~(-8)mol/L,为链霉素的测定提供了高效的方法。     

分子印迹电化学传感器的研究进展

分子印迹电化学传感器能特异性识别目标分子,在环境监测、药物检测、农药残留检测等诸多领域显示出良好的应用前景,受到越来越多的关注.本文综述了分子印迹电化学传感器制备中功能单体的选择、敏感膜的制备方法和电化学传感器的类型,分析了分子印迹电化学传感器研究中还存在的问题,并对其应用前景作了展望.     

Tailoring crystal facet microenvironments for simultaneous electrochemical ozone and hydrogen peroxide production

Developing a bifunctional electrocatalyst that can effectively produce O₃ and H₂O₂ is significant for the electrochemical synthesis of O₃ and H₂O₂ for the synergistic oxidative degradation of organic pollutants. In this study, SnO with various exposed facets was synthesized by tailoring the crystal facet microenvironment for oxygen intermediates adsorption for electrochemical ozone production (EOP) and two-electron oxygen reduction reaction (2e⁻ ORR). The Faraday efficiency of SnO-1 with a high (110) facet ratio for O₃ was 22.0%, while SnO-4 with a high (002) facet ratio achieved a selectivity of 93.6% for H₂O₂. The theoretical calculation indicates that their excellent performances originated from the strong adsorption of the (110) facet on O* and O₂* and the suitable adsorption and desorption strength of the (002) facet on OOH*, respectively. This study provides an attractive strategy for the development of a bifunctional electrocatalyst for advanced electrochemical oxidation by tailoring the crystal facet microenvironment.     

Potentiometric sensor for polyethoxylated nonionic surfactant determination

A new liquid membrane surfactant sensor based on a 1,3-didecyl-2-methylimidazolium-tetraphenylborate ion-exchange complex was tested in different ethoxylated nonionic surfactants (EONS) and polyethylene glycols. The sensor also responded to tetraphenylborate (slope = −56.1 ± 0.8 mV/decade of activity) in the 1 × 10⁻⁶ to 2 × 10⁻³ M concentration range.The selectivity performance of the sensor toward alkaline, alkaline earth, and heavy metal cations was investigated. The sensor exhibited a fast response (within a few seconds), when in solution with some metal cations, for a 10-fold concentration change of Triton X-100. Its main application is in indicating the end-point in a potentiometric titration of EONS using sodium tetraphenylborate as the titrant. Several pure and technical grade EONS and polyethylene glycols were successfully titrated. The sensor can be used for titrations within a pH range of 3-11.The resulting potentiometric titration curves revealed an analytically usable inflection for all investigations, enabling reliable equivalence point detection using the first derivative method.The sensor was also applied to the study of barium ion reaction stoichiometry and Triton X-100 pseudoionic complex formation, as well as its reaction with tetraphenylborate.     

聚L-丝氨酸/碳纳米管复合导电薄膜的制备及在多巴胺的电化学测定中的应用

研究了玻碳电极涂有碳纳米管后,基于功能化的带负电荷碳纳米管的羧基和氨基酸的—NH2质子化之间的静电吸附作用,制备聚L-丝氨酸/碳纳米管(PL-Ser/MWNTs)修饰电极的方法,并讨论了多巴胺(DA)在修饰电极上的电化学行为。试验发现多巴胺浓度在1.0×10-6~2.0×10-4mol/L范围内与其脉冲电流信号成线性关系,检出限2.0×10-7mol/L。修饰电极具有较好的稳定性能,应用于针剂中多巴胺含量的测定,结果满意。     

Simultaneous determination of diclofenac and indomethacin using a sensitive electrochemical sensor based on multiwalled carbon nanotube and ionic liquid nanocomposite

Multiwalled carbon nanotube and ionic liquid-modified carbon ceramic electrode (MWCNT–IL|CCE) was employed for the simultaneous determination of diclofenac and indomethacin (IND). The measurements were carried out by differential pulse voltammetry method in optimal conditions. The prepared electrode showed appropriate voltammetric responses to DCF and IND with 0.225 V difference in the oxidation peak potentials, making fabricated electrode suitable for simultaneous determination of these compounds. The calibration curves were linear over a wide range of concentrations of each species including 0.05–50 μmol L^?1 for DCF and 1–50 μmol L^?1 for IND. Detection limits were found to be 18 and 260 nM for DCF and IND, respectively. The developed method having good stability and sensitivity was successfully applied for DCF and IND in commercial tablet as well as human blood plasma samples.     

Molecularly imprinted electrochemical sensor for the determination of ampicillin based on a gold nanoparticle and multiwalled carbon nanotube‐coated pt electrode

A novel molecularly imprinted electrochemical sensor was developed for the sensitive and selective determination of ampicillin (AMP). The sensor was prepared on a platinum electrode modified with multiwalled carbon nanotubes (MWCNTs), gold nanoparticles (AuNPs), and a thin film of molecularly imprinted polymers (MIPs). MWCNTs and AuNPs were introduced to enhance the sensor's electronic transmission and sensitivity. The molecularly imprinted polymer (MIP) was synthesized using AMP as the template molecule, methacrylic acid as functional monomer, and ethylene glycol maleic rosinate acrylate (EGMRA) as cross‐linker. The performance of the proposed imprinted sensor was investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The results showed that the imprinted film displayed a fast and sensitive response to AMP. Under optimal conditions, response peak current had a linear relationship with the concentration of AMP in the range of 1.0 × 10^?8 mol/L to 5.0 × 10^?6 mol/L and a detection limit of 1.0 × 10^?9 mol/L (S/N = 3). This imprinted sensor was used to detect AMP in food samples with recoveries of 91.4–105%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40613.     

Controllable synthesis of nitrogen-doped graphene and its effect on the simultaneous electrochemical determination of ascorbic acid,dopamine, and uric acid

A simple, low-cost method for fabricating nitrogen-doped graphene (NG) is demonstrated by combining the ultrafast thermal exfoliation and covalent transformation from the melamine (MA)–graphene oxide (GO) mixture. NGs prepared at 300, 600, and 900 °C were systematically characterized by X-ray photoelectron spectroscopy (XPS), in which pyridinic-N, pyrrolic-N and graphitic-N are the main nitrogen-doped structures in various ratios. These NGs possess large specific surface area and porous microstructures, confirmed by the N₂ adsorption–desorption isotherms. The NG-modified screen-printed carbon electrodes (SPCEs) were fabricated to detect ascorbic acid (AA), dopamine (DA) and uric acid (UA) simultaneously by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Due to the large specific surface area, mesoporous structures and nitrogen-doped sites, these NGs show highly electrochemical sensitivity for AA, DA and UA. Notably, the pyrrolic-N structure makes the negative shift in the oxidation peak potential of these biomolecules, showing the better catalytic activity than pyridinic-N and graphitic-N structures. The large surface area of NGs provides more nitrogen-doped sites to oxidize bio-compounds and enhances the corresponding currents. The good sensitivity of NG-modified SPCEs makes them become effective sensors for determining AA, DA and UA simultaneously. The discrimination to peak potential and current among these NGs can be observed.     

Method for simultaneous determination of sorption isotherms and diffusivity of cement-based materials

A method for simultaneous determination of the diffusion and sorption properties of cement-based materials is presented. It is a gravimetric method where one small specimen is exposed to stepwise changes in relative humidity while its mass is being measured. As sorption in cement-based materials is slow, the change in relative humidity to the next level is made before final equilibrium has been reached on the previous level. Approximate final (equilibrium) levels are found by extrapolation using an exponential equation, and a factor is applied to correct for the fact that the sorption step does not start at equilibrium conditions. A correction for external mass transfer resistance is also included. The method can be used in desorption as well as absorption mode. Measurements of two materials are presented and compared with the results obtained using conventional methods.