Electrochemical detection in paper-based analytical devices using microwire electrodes

Microwire electrodes are presented as an alternative to screen-printed electrodes for detection in electrochemical paper-based analytical devices (ePADs). Compared to carbon ink electrodes, microwire electrodes offer lower resistance and a significant increase in current density relative to carbon ink electrodes. Various microwire compositions and diameters, including 30 μm Pt, 25 μm Au, 18 μm Pt with 8% W, and 15 μm Pt with 20% Ir, were tested and compared to theoretically predicted behavior. The measured current in static solution was below predicted levels for cylindrical microelectrodes but greater than levels predicted for hemi-cylindrical electrodes most likely as a result of the proximity of the electrode to the paper surface. Furthermore, the current response was indicative of semi-thin layer behavior, likely due to the confined solution volume in the paper. After electrode characterization, a device was developed for the non-enzymatic detection of glucose, fructose, and sucrose using a Cu electrode in alkaline solution. The limits of detection for glucose, fructose, and sucrose were 270 nM, 340 nM, and 430 nM, respectively, which are significantly below sugar concentrations found in sweetened beverages or glucose levels in serum.     

苯甲酸在疏水性复合电极上的电化学还原行为

以铜片和锌片为基材,复合电镀制得Cu-PTFE(聚四氟乙烯)和Zn-PTFE疏水性复合电极,并将复合电极应用于苯甲酸的电化学还原行为研究。测定了复合电极在电解液中的Tafel极化曲线、循环伏安、电极稳定性和交流阻抗等电化学参数。结果表明,在苯甲酸电还原制备苯甲醛中,Cu-PTFE复合电极相对于Zn-PTFE复合电极具有较高的催化活性,其电还原产率分别为88.4%和79.2%,因此,Cu-PTFE复合电极有望成为苯甲酸电化学还原制备苯甲醛的电极材料。电化学行为的研究结果显示,苯甲酸在疏水性复合电极上的电还原过程可能只受电子迁移过程控制。     

Electrochemical Behavior and Voltammetric Determination of Curcumin at Electrochemically Reduced Graphene Oxide Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of curcumin by using a electrochemically reduced graphene oxide (ERGO) modified glass carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The electrochemical behaviors of curcumin at ERGO/GCE were investigated by cyclic voltammetry, suggesting that the ERGO/GCE exhibits excellent electrocatalytic activity towards curcumin, compared with bare GCE and GO/GCE electrodes. The electrochemical reaction mechanisms of curcumin, demethoxycurcumin and bisdemethoxycurcumin at the ERGO/GCE were also investigated and discussed systematically. Under physiological condition, the modified electrode showed linear voltammetric response from 0.2 μM to 60.0 μM for curcumin, with the detection limit of 0.1 μm. This work demonstrates that the graphene‐modified electrode is a promising strategy for electrochemical determination of biological important phenolic compounds.     

Preparation,Characterization, and Electrocatalytic Properties of Cobalt Oxide and Cobalt Hexacyanoferrate Hybrid Films

Polynuclear mixed‐valent films of cobalt oxide and cobalt hexacyanoferrate (CoOCoHCF) have been deposited on electrode surfaces from a solution of Co²⁺ and Fe(CN)₆^3? ions by repetitive potential cycling method. Simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance measurements demonstrate the steady growth of modified film. The effect of type of monovalent cations as well as acidity of the supporting electrolyte on film growth and redox behavior of resulting film was investigated. In pure supporting electrolyte, electrochemical responses of modified electrode resemble with that of a surface immobilized redox couple. The hybrid film electrodes showed electrocatalytic activity toward oxidation of NADH, hydrazine and hydroxylamine. The feasibility of using our modified electrodes for analytical application was also explored.     

Recycling Chocolate Aluminum Wrapping Foil as to Create Electrochemical Metal Strip Electrodes

The development of low-cost electrode devices from conductive materials has recently attracted considerable attention as a sustainable means to replace the existing commercially available electrodes. In this study, two different electrode surfaces (surfaces 1 and 2, denoted as S1 and S2) were fabricated from chocolate wrapping aluminum foils. Energy dispersive X-Ray (EDX) and field emission scanning electron microscopy (FESEM) were used to investigate the elemental composition and surface morphology of the prepared electrodes. Meanwhile, cyclic voltammetry (CV), chronoamperometry, electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV) were used to assess the electrical conductivities and the electrochemical activities of the prepared electrodes. It was found that the fabricated electrode strips, particularly the S1 electrode, showed good electrochemical responses and conductivity properties in phosphate buffer (PB) solutions. Interestingly, both of the electrodes can respond to the ruthenium hexamine (Ruhex) redox species. The fundamental results presented from this study indicate that this electrode material can be an inexpensive alternative for the electrode substrate. Overall, our findings indicate that electrodes made from chocolate wrapping materials have promise as electrochemical sensors and can be utilized in various applications.     

基于电化学重氮还原的碳膜电极表面修饰及功函调控

基于高温裂解光刻胶制备的碳薄膜(PPF)是一种新型的性能优异的碳基电极. 为了拓展其在功能器件中的应用, 利用电化学重氮还原法在PPF电极表面生长了三氟甲基苯胺重氮盐(CF₃-PD)和对氨基苯甲醚重氮盐(OCH₃-PD)两种组分的混合膜. 通过调节两组分溶液在混合膜中的摩尔浓度比例, 实现了对PPF电极功函的可控调节. 紫外光电子能谱(UPS)和开尔文探针显微镜(KPFM)对修饰前后PPF电极功函(?)的表征表明, 随着混合溶液中CF₃-PD组分的摩尔分数从0增至100%, PPF电极的?(4.75 eV)从4.5 eV梯度增至5.14 eV. 研究结果实现了可在一定范围内“定制”PPF电极功函, 为碳膜电极在分子光电器件中的应用奠定了基础.     

邻碘苯甲酸电还原脱碘的原位红外光谱研究

采用循环伏安法研究了邻碘苯甲酸在NaOH溶液中的电化学还原反应,与Pt和Ti等电极相比,Ag和Cu电极对邻碘苯甲酸具有较好的电还原活性,还原电位向正电位方向移动.通过原位红外光谱技术研究了邻碘苯甲酸在Ag和Cu电极上的电还原机理.结果表明,在电位高于-800 mV时,邻碘苯甲酸在Ag电极表面先形成吸附中间态R…I…Ag,而在Cu电极表面以负离子形式存在.随着电位的进一步负移,邻碘苯甲酸在Ag和Cu电极上均发生脱碘加氢反应,经还原得到最终产物苯甲酸.     

可检测有机磷农药残留的丝网印刷酶电极

制备了用于有机磷农药检测的电化学生物酶电极, 并从工作电极上修饰物的选择、测定电压的确定、生物酶电极预活化时间的选定、测定时间的选定、温度的影响、pH值的影响、底物浓度的影响、固定方法的选择、固定酶时温度和时间的影响等多方面对丝网印刷的生物酶电极进行了较为全面的研究, 应用经过优化的生物酶电极对有机磷农药乙基对氧磷进行了检测. 结果表明: 抑制率与乙基对氧磷浓度的常用对数在1.00×10^－7～1.00×10^－5 g•mL^－1范围内成线性关系, 线性回归方程为A/%＝267.2＋37.20lg[c/(g•mL^－1)], 相关系数r＝0.9882. 当信噪比为3时, 检出限为2.10 ng•mL^－1, 低于国家标准所要求的最低残留量.     

Behavior of Glassy Carbon Paste Electrode in Flowing Methanolic Solutions

Carbon paste electrodes are often used for electrochemical determinations, but their application in media with high content of organic solvents, particularly in HPLC, is limited by their low stability. The work presented here examines the effect of a moving methanol‐containing solution on a glassy carbon paste electrode by studying its electrochemical behavior in relation to the period of contact and methanol content in the solution. In combination with microscopic observation of the paste surface it can be concluded that the electrode is affected by the methanolic solution and the surface roughness increases, resulting in the stable state compatible with measurements in highly methanolic solutions.     

用稀土(镱)杂多酸盐/多壁碳纳米管修饰的玻碳电极测定亚硝酸根

将多壁碳纳米管分散在镱(Ⅲ)杂多酸盐溶液中,将上述获得的悬浊液滴涂在玻碳电极表面,制备了镱(Ⅲ)杂多酸盐/多壁碳纳米管修饰的玻碳电极(YbHS-MWCNT′s/GCE)。采用交流阻抗法对电极表面的性能进行了表征,采用循环伏安法对其电化学性能进行研究。研究发现,亚硝酸根在该修饰电极上出现一个氧化峰,氧化峰电位在-0.45V处,提出了用循环伏安法测定亚硝酸根的方法。亚硝酸根的浓度在5.0×10-6～1.0×10-4mol.L-1范围内,氧化峰电流与其浓度呈线性关系。修饰电极用于环境水样中亚硝酸根离子的测定,回收率在97.2%～98.0%之间。     

3D‐printed Metal Electrodes for Heavy Metals Detection by Anodic Stripping Voltammetry

Heavy metals, being one of the most toxic and hazardous pollutants in natural water, are of great public health concern. Much effort is still being devoted to the optimization of the electroanalytical methods and devices, particularly for the development of novel electrode materials in order to enhance selectivity and sensitivity for the analysis of heavy metals. The ability of 3D‐printing to fabricate objects with unique structures and functions enables infinite possibilities for the creation of custom‐made electrochemical devices. Here, stainless steel 3D‐printed electrodes (3D‐steel) have been tested for individual and simultaneous square wave anodic stripping analysis of Pb and Cd in aqueous solution. Electrodeposition methods have also been employed to modify the steel electrode surface by coating with a thin gold film (3D−Au) or a bismuth film (3D−Bi) to enhance the analytical performance. All 3D‐printed electrodes (3D‐steel, 3D−Au and 3D−Bi) have been tested against a conventionally employed glassy carbon electrode (GC) for comparison. The surface modified electrodes (3D−Au and 3D−Bi) outperformed the GC electrode demonstrating higher sensitivity over the studied concentration ranges of 50–300 and 50–500 ppb for Pb and Cd, respectively. Owing to the bismuth property of binary alloys formation with heavy metals, 3D−Bi electrode displayed well‐defined, reproducible signals with relatively low detection limits of 3.53 and 9.35 ppb for Pb and Cd, respectively. The voltammetric behaviour of 3D−Bi electrode in simultaneous detection of Pb and Cd, as well as in individual detection of Pb in tap water was also monitored. Overall, 3D‐printed electrodes exhibited promising qualities for further investigation on a more customizable electrode design.     

Application of silver electrode to the electrochemical studies of hemoglobin

Several aspects of the application of silver electrode to the electrochemical studies of hemoglobin have been discussed in this paper . The silver electrode could not only be used directly as the electrode for the electrochemical studies of hemoglobin, but also react with phenothiazine and benzimidazole to give stable and useful mediator-coated electrodes. In addition, the silver electrode could help sodium dodecyl sulfate to give full play to its promoting effect on the protein.     

IrO2电极在4-氯苯酚水溶液中的电化学活性

研究了在4-氯苯酚(简称氯酚)电化学稳定窗口内氯酚对Ti基IrO2电极在酸性水溶液中电化学活性的影响. 循环伏安(CV)与电化学阻抗谱(EIS)测试均显示, 几乎在整个氯酚的电化学稳定电位区间内, 氯酚对氧化物电极均起到活化作用. 以金属Ir电极为对比试样的测试结果却显示, 由于氯酚易于在金属表面吸附, 氯酚在其电化学稳定窗口内对金属电极的活性产生抑制作用. 基于氯酚对上述两类电极电化学行为影响的差异, 提出活性氧化物自身在上述电位区间内发生从低价态到高价态的转变, 进而用于氧化去除吸附在电极表面的有机分子, 可能是氯酚对IrO2电极造成活化的主要原因.     

扫描电化学显微镜直接电沉积法构建葡萄糖氧化酶微米点

利用自制的凹形电极在铂基底电极上直接构建了葡萄糖氧化酶微米点. 首先, 将电聚合和电化学刻蚀法相结合制备了凹形铂微米电极. 然后将此种电极作为参比及辅助电极, 基底铂电极作为工作电极, 利用葡萄糖氧化酶在合适的条件下(浓度、一定量Triton X-100存在、电极电位等)由于电极表面pH的降低可以在铂电极上电沉积这一特性, 将酶固定在铂基底电极上, 微修饰得到了具有活性的葡萄糖氧化酶微米点. 最终用扫描电子显微镜和扫描电化学显微镜对所得微米点进行了表征. 所得微米点直径约20 μm, 且具有催化活性. 该方法简便, 干扰因素较少.     

二茂铁与DNA作用的表面电化学研究

在研究碳纳米管电极上二茂铁电化学性质的基础上,应用二茂铁修饰电极和DNA修饰电极研究了二茂铁与小牛胸腺DNA的相互作用。结果表明,修饰电极上的二茂铁都呈现一对明显的氧化还原峰,二茂铁修饰电极与DNA的作用表现为氧化还原峰电流减小,与溶液中的两者作用情况类似,而DNA修饰电极与二茂铁的作用则表现为氧化还原峰电流增大。扫描电镜结果也证实了两种修饰电极上的二茂铁与DNA间的作用。此外,还讨论了二茂铁与DNA间的作用模式。     

聚苯胺薄膜修饰电极对抗坏血酸的电催化氧化

本文表明聚苯胺(PAn)薄膜修饰电极对水溶液中的抗坏血酸(AH_2)在较宽的pH范围和较宽的浓度范围内均有良好的电催化氧化作用, 为EC平行催化过程。利用旋转圆盘电极(RDE)进行了催化过程动力学分析, 求出了催化反应动力学参数。在抗坏血酸浓度10~(-2)～10~(-6) mol·L~(-1)范围内, 催化峰电流与AH_2浓度均成良好的线性关系, 且PAn薄膜修饰电极具有很好的稳定性, 有应用分析抗坏血酸的意义。     

Spectroscopic and Electrochemical Characterization of Iron(II) and 2,4-Dinitrotoluene

The objective of this work was the development of reliable methods to determine 2,4-dinitrotoluene, a precursor to explosives. A complex between Fe(II) ion and 2,4-dinitrotoluene was formed in solution and characterized by ultraviolet-visible absorption spectroscopy using Job’s plots and attenuated total reflection-Fourier transform infrared spectroscopy. Surface modification of glassy carbon electrodes were performed with iron nanoparticles via electrochemical reduction of iron(II). The modified electrode was employed for the determination of 2,4-dinitrotoluene. Scanning electron micrographs showed that the iron nanoparticles were incorporated on the surface of glassy carbon electrode. The electrochemical determination of 2,4-dinitrotoluene was performed by cyclic voltammetry using the modified electrode. The iron modified electrode produced larger reduction currents than the unmodified electrode for the same concentration of 2,4-dinitrotoluene. Concentrations of 2,4-dinitrotoluene as low as 10 parts per billion were determined using the modified electrode.     

铂、钌共修饰的氧化钛电极对甲醇的电催化氧化

燃料电池;铂、钌共修饰的氧化钛电极对甲醇的电催化氧化     

In Situ Renewal of Working Surfaces of Solid Indicator Electrodes and Their Use in Electroanalysis

The design of a device for the rapid regeneration of the indicator electrode surface in a test solution is discussed. The results of testing this device are presented. The device allows obtaining reproducible areas and properties of the surfaces of solid indicator electrodes by mechanically cutting 0.1–5-μm surface layers. The best reproducibility of these parameters is attained when a hexanite-R cutter is used. The serviceability of the cutter is more than 10⁵ cuts. The high-quality renewal of electrode surfaces is achieved by cutting a 4– 5-μm layer of metallic (Pt, Ag, Au, Cu, Cd, Zn, Co, Ni, etc.) electrodes and a 0.1–1.5-μm layer of graphite and graphite-based electrodes. Optimum tool angles of the cutter for all types of solid electrodes are selected. Long-term tests of the developed technique for the mechanical renewal of electrode surface confirm that the electrode surface area is well reproducible in the series of 10⁴ measurements of the analytical signal (RSD = 0.2–0.6%). Examples are given that point to the enhancement of the electrochemical activity of the surfaces of some electrodes renewed in situ in a solution without their exposure to air. It is shown that the mechanical regeneration of the electrode surface in the solution is the main condition for depositing metals under high-voltage (up to 1000 V) conditions for electroaccumulation. The advantages of the proposed technique are exemplified by determining the concentrations of cations, anions, and some organic substances by direct and stripping voltammetry. __________ Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 12, 2005, pp. 1284–1295. Original Russian Text Copyright ? 2005 by Skvortsova, Aleksandrova, Tarasova, Kiryushov, Zamyatin.