Direct electrochemical detection of glucose in human plasma on capillary electrophoresis microchips

We developed an electrochemical detector on a hybrid chip for the determination of glucose in human plasma. The microchip system described in this paper consists of a poly(dimethylsiloxane) (PDMS) layer containing separation and injection channels and an electrode plate. The copper microelectrode is fabricated by selective electroless deposition. The fabrication of the decoupler is performed by platinum electrochemical deposition on the metal film formed by electroless deposition. Factors influencing the performance, including detection potential, separation field strength, and buffer concentration, were studied. The electrodes exhibited good stability and durability in the analytical procedures. Under optimized detection conditions, glucose responded linearly from 10 microM to 1 mM. Finally, glucose in human plasma from three healthy individuals and two diabetics was successfully determined, giving a good prospect for a new clinical diagnostic instrument.     

Microchip Capillary Electrophoresis‐Electrochemistry with Rigid Graphite‐Epoxy Composite Detector

A new rigid graphite‐epoxy composite electrode for electrochemical detection in microchip electrophoresis is described. The end‐column wall‐jet detection design relying on tubular rigid composite working electrode shows favorably low noise level and high signal‐to‐noise ratio when compared to glassy carbon detector. The performance of rigid graphite‐epoxy composite detector was compared to glassy carbon detector using dopamine and catechol as model analytes. The various parameters of the microchip electrophoresis‐rigid graphite‐epoxy composite detector were optimized.     

Preparation of metal nanoband microelectrode on poly(dimethylsiloxane) for chip-based amperometric detection

We proposed herein a novel approach for fabricating nanoband microelectrodes for electrochemical detection on an electrophoresis microchip. The metal films were first obtained via region-selective electroless deposition of gold or copper films on PDMS substrates by selective region plasma oxidation through shadow masking. Both metal films show uniform surfaces with the thickness at the level of 100 nm. By casting another PDMS layer on the metal films, the cross section of the sandwich structures can be used as nanoband microelectrodes, which can be renewed just by cutting. These nanoband microelectrodes are successfully used as electrochemical detectors in microchip electrophoresis for the detection of amino acids, proteins and neurotransmitter molecules. Moreover, integrating an Au-Cu double-metal detector with a double-channel electrophoresis system, we can easily distinguish electroactive amino acids from that of non-electroactive amino acids.     

Nanoband electrode for high-performance in-channel amperometric detection in dual-channel microchip capillary electrophoresis

A nanoband electrode detector integrated with a dual-channel polydimethylsiloxane microchip is proposed for in-channel amperometric detection in microchip capillary electrophoresis. Gold nanoband electrodes, which were fabricated on SU-8 substrates with a 100-nm-width gold layer, were introduced into the dual-channel microchip to be an electrochemical detector. Due to the nano-sized width of the detector, the noise of the amperometric detection was significantly reduced, and a high separation resolution was achieved for monitoring the analytes. The detection sensitivity of the system was improved by high signal-to-noise ratio, and a low detection limit on microchip was obtained for p-aminophenol (2.09 nM). Because of the high resolution in measuring half-peak width, the plate number that is used to evaluate the separation efficiency was 1.5-fold higher than that using 50-μm-width electrochemical detector. The effect of sample injection time and data acquisition time on separation efficiency was investigated, and an attractive separation efficiency was achieved with a plate number up to 17,500.     

Quantitative determination of dopamine in single rat pheochromocytoma cells by microchip electrophoresis with only one high‐voltage power supply

We developed a method for the direct identification of dopamine in single cultured rat pheochromocytoma cells by capillary electrophoresis using an end‐channel carbon fiber nanoelectrode amperometric detector. The operation mode was designed to achieve single‐cell injection and lysis in microfluidic chip electrophoresis with only one high‐voltage power supply. The separation and detection conditions were optimized. Four catecholamines were baseline‐separated and determined with this system, and the cell density and liquid height of the reservoirs were accommodated for single cell loading, docking and analysis. The microchip capillary electrophoresis system was successfully applied to determine dopamine in single cultured rat pheochromocytoma cells.     

Microchip capillary electrophoresis with amperometric detection for rapid separation and detection of phenolic acids

A microchip capillary-electrophoresis protocol for rapid and effective measurements of food-related phenolic acids (including chlorogenic, gentisic, ferulic, and vanillic acids) is described. Relevant parameters of the chip separation and amperometric detection are examined and optimized. Under optimum conditions, the analytes could be separated and detected in a 15 mM borate buffer (pH 9.5, with 10% of methanol) within 300 s using a separation voltage of 2000 V and a detection voltage of +1.0 V. Linear calibration plots are observed for micromolar concentrations of the phenolic acid compounds. The negligible sample volumes used in the microchip procedure obviates surface fouling common to amperometric measurements of phenolic compounds. The new microchip protocol offers great promise for a wide range of food applications requiring fast measurements and negligible sample consumption. An application on a commercial red wine was performed with minimal sample preparation and promising results.     

In-channel modification of electrochemical detector for the detection of bio-targets on microchip

The coulometric efficiency (C_eff) of an amperometric detector integrated on PDMS/glass capillary electrophoresis microfluidic device (microchip) has been enhanced by in-channel electrochemical modification. In-channel electrochemical deposition of gold particles was performed in order to vertically increase the surface area of the Au sensing microelectrode. The roughness of the electrodes was characterized using scanning electron microscopy and profilometric analysis. The degree of electrode modification was also characterized by roughness factor determination. Separation processes including detection potential was optimized and the analytical performance of the microchip was tested using a mixture of dopamine (DA) and catechol (CA). The modified electrochemical detector provided well-resolved separation of DA and CA in less than 60 s with enhanced sensitivity; no peak broadening was observed. The limit of detection using in-channel modification of working electrode for DA and CA are 60 and 110 nM, respectively. Thus, in-channel electrochemical deposition of metallic particles should be used to enhance the C_eff of integrated amperometric detection of analytes with good redox properties in order to obtain lower LODs.     

Fluorescence detection in short capillary and chip using a variable wavelength epi-fluorescence microscope

Fast, efficient separation of five free acid forms of porphyrins was achieved in a short capillary and a chip, respectively. The capillary was 6 cm long from injection end to detector with an electric field strength of 214 V cm(-1). Separations were performed within 5 min. A glass microchip device was fabricated using standard photolithographic procedures and chemical wet etching. The channels were sealed using a direct bonding technique. For a separation length of 2.8 cm with electric field strength of 500 V cm(-1), electrophoretic separations with baseline resolution were achieved in less than 2 min. A variable wavelength epi-fluorescence microscope was used as an on-column detector.     

Determination of oxalate in beer by zone electrophoresis on a chip with conductivity detection

The use of a poly(methylmethacrylate) capillary electrophoresis chip, provided with a high sample load capacity separation system (a 8500 nL separation channel combined with a 500 nL sample injection channel) and a pair of on‐chip conductivity detectors, for zone electrophoresis (ZE) determination of oxalate in beer was studied. Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed and electrophoresis was a dominant transport process in the separations performed on the chip. A low pH of the carrier electrolyte (3.8), implemented by aspartic acid and bis‐tris propane, provided an adequate selectivity in the separation of oxalate from anionic beer constituents and, at the same time, also a sufficient sensitivity in its conductivity detection. Under our working conditions, this anion could be detected at a 0.5 μmol/L concentration also in samples containing chloride (a major anionic constituent of beer) at a 1800 higher concentration. Such a favorable analyte/matrix concentration ratio made possible accurate and reproducible [typically, 2–5% relative standard deviation (RSD) values of the peak areas of the analyte in dependence on its concentration in the sample] determination of oxalate in 500 nL volumes of 20–50‐fold diluted beer samples. Short analysis times (about 200 s), minimum sample preparation, and reproducible migration times of this analyte (0.5–1.0% RSD values) were characteristic for ZE on the chip.     

Fabrication of a gold microelectrode for amperometric detection on a polycarbonate electrophoresis chip by photodirected electroless plating

A novel method of photoresist-free micropatterning coupled with electroless gold plating is described for the fabrication of an integrated gold electrode for electrochemical detection (ED) on a polycarbonate (PC) electrophoresis microchip. The microelectrode layout was photochemically patterned onto the surface of a PC plate by selective exposure of the surface coated without photoresist to 254 nm UV light through a chromium/quartz photomask. Thus, the PC plate was selectively sensitized by formation of reactive chemical moieties in the exposed areas. After a series of wet chemistry reactions, the UV-exposed area was activated with a layer of gold nanoparticles that served as a seed to catalyze the electroless plating. The gold microelectrode was then selectively plated onto the activated area by using an electroless gold plating bath. Nonselective gold deposition on the unwanted areas was eliminated by sonication of the activated PC plate in a KSCN solution before electroless plating, and the adhesion of the plated electrodes to the PC surface was strengthened with thermal annealing. Compared with the previously reported electroless plating technique for fabrication of microelectrodes on a microchip, the present method avoided the use of a membrane stencil with an electrode pattern to restrict the area to be wet-chemically sensitized. The CE with integrated ED (CE-ED) microchip was assembled by thermal bonding an electrode-plated PC cover plate to a microchannel-embossed PC substrate. The novel method allows one to fabricate low-cost, electrode-integrated, complete PC CE-ED chips with no need of a clean room. The fabricated CE-ED microchip was demonstrated for separation and detection of model analytes, including dopamine (DA) and catechol (CA). Detection limits of 0.65 and 1.03 microM were achieved for DA and CA, respectively, and theoretical plate number of 1.4 x 10(4) was obtained for DA. The plated gold electrode can be used for about 4 h, bearing usually more than 100 runs before complete failure.     

Determination of sugars, sugar degradation products and alcohols by high-performance liquid chromatography with electrochemical detection

Summary The use of an electrochemical, amperometric detector with nickel as a working electrode for the determination of carbohydrates and alcohols after separation by high-performance liquid chromatography (HPLC) is discussed. In order to get sensitive and stable signals pretreatment experiments were carried out and the combination of this detector with polymer-based cation-exchange columns as well as reversed phase columns is described.     

卤离子对化学沉积镍的影响

用重量法测定了卤离子对化学沉积镍速度的影响．并借助电化学方法研究了卤离子对镍的化学沉积过程的极化曲线和稳定电位的影响．探讨了卤离子加速和稳定化学沉积镍的机理     

Temperature‐programmed capillary high‐performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry for analysis of fatty acid methyl esters

A new capillary high‐performance liquid chromatography method with atmospheric pressure chemical ionization mass spectrometry was developed for the analysis of fatty acid methyl esters and long‐chain alcohols. The chromatographic separation was achieved using a Zorbax SB‐C18 HPLC column (0.3 × 150 mm, 3.5 μm) with a mobile phase composed of acetonitrile and formic acid and delivered isocratically at a flow rate of 10 μL/min. The column temperature was programmed simply, using a common column oven. Good reproducibility of the temperature profile and retention times were achieved. The temperature programming during the isocratic high‐performance liquid chromatography run had a similar effect as a solvent gradient; it reduced retention times of later eluting analytes and improved their detection limits. Two atmospheric pressure chemical ionization sources of the mass spectrometry detector were compared: an enclosed conventional ion source and an in‐house made ion source with a glass microchip nebulizer. The enclosed source provided better detectability of saturated fatty acid methyl esters and made it possible to determine the double bond positions using acetonitrile‐related adducts, while the open chip‐based source provided better analytical figures of merit for unsaturated fatty acid methyl esters. Temperature‐programmed capillary high‐performance liquid chromatography is a promising method for analyzing neutral lipids in lipidomics and other applications.     

Recent developments in electrochemical detection for microchip capillary electrophoresis

Significant progress in the development of miniaturized microfluidic systems has occurred since their inception over a decade ago. This is primarily due to the numerous advantages of microchip analysis, including the ability to analyze minute samples, speed of analysis, reduced cost and waste, and portability. This review focuses on recent developments in integrating electrochemical (EC) detection with microchip capillary electrophoresis (CE). These detection modes include amperometry, conductimetry, and potentiometry. EC detection is ideal for use with microchip CE systems because it can be easily miniaturized with no diminution in analytical performance. Advances in microchip format, electrode material and design, decoupling of the detector from the separation field, and integration of sample preparation, separation, and detection on-chip are discussed. Microchip CEEC applications for enzyme/immunoassays, clinical and environmental assays, as well as the detection of neurotransmitters are also described.     

无铅镉化学镍沉积及其表征

优化无铅、无镉化学镍沉积工艺,应用扫描电子显微镜(SEM)、能量色散谱(EDS)、X射线衍射(XRD)和电化学方法表征化学镀镍层的形貌、组成、结构和电化学活性.结果表明,化学镍自催化沉积速率为22.4μm.h-1;沉积速率随溶液温度和pH值的提高而增大;比之硫酸镍,次磷酸钠对沉积速率的影响明显许多.化学镀镍层磷含量为7.8%(by mass),结构致密、晶粒细小,呈非晶态结构.在NaCl溶液中,镀层呈现良好的电化学耐蚀性.     

Microchip reversed-phase liquid chromatography with packed column and electrochemical flow cell using polystyrene/poly(dimethylsiloxane)

A microchip pressure-driven liquid chromatography (LC) with a packed column and an electrochemical flow cell has been developed by using polystyrene (PS) and poly(dimethylsiloxane) (PDMS). The cylindrical separation column with packed octadecyl silica particles was fabricated in the PS substrate. The three electrode system (working, reference, and counter electrode) for amperometric detection was fabricated onto the PS substrate, using the Au deposition, photolithography, and chemical etching. The detector flow cell was formed by sealing the electrode system with a PDMS chip containing a channel. In this flow cell, the effect of working electrode width (in the direction of flow) on chromatographic parameters, such as peak width and peak resolution were studied in electrode width ranging 50-5,000 microm. The effect of electrode width on sensitivity (current intensity, current density, and S/N ratio) was also examined. The sensitivity was discussed by simulating the concentration profile generated around the working electrode. The effects of the column packing size and the column size on the separation efficiency were examined. In this study, a good separation of three catechins was successfully achieved and the detection limits for (+)-catechin, epicatechin, and epigallocatechin gallate were 350, 450, and 160 nM, respectively.     

Microchip capillary electrophoresis/electrochemical detection of hydrazine compounds at a cobalt phthalocyanine modified electrochemical detector

This article reports on the use of cobalt(II) phthalocyanine (CoPc)-modified carbon paste amperometric detector for monitoring hydrazine compounds following their microchip separation. The marked catalytic electrochemical properties of CoPc-modified electrode display enhanced sensitivity compared with unmodified carbon pastes at a relatively low detection potential (+0.5 V versus Ag/AgCl). Factors influencing the on-chip separation and detection processes have been optimized. Three hydrazines (hydrazine, 1,1 dimethylhydrazine, and phenylhydrazine) have been separated within 130 s at a separation voltage of 1 kV using a 10 mM phosphate run buffer (pH 6.5). The detection limits obtained from using the CoPc-modified carbon paste electrodes for hydrazine and phenylhydrazine are 0.5 and 0.7 μM, respectively, with linearity over the 20–200 μM range examined. Such miniaturization and speed advantages of microchip CE are coupled to the highly sensitivity and convenient preparation of CoPc-modified carbon paste electrode. The resulting microsystem should be attractive for field monitoring of toxic hydrazine compounds in environmental applications.     

A high-performance polycarbonate electrophoresis microchip with integrated three-electrode system for end-channel amperometric detection

A fully integrated polycarbonate (PC) microchip for CE with end-channel electrochemical detection operated in an amperometric mode (CE-ED) has been developed. The on-chip integrated three-electrode system consisted of a gold working electrode, an Ag/AgCl reference electrode and a platinum counter electrode, which was fabricated by photo-directed electroless plating combined with electroplating. The working electrode was positioned against the separation channel exit to reduce post-channel band broadening. The electrophoresis high-voltage (HV) interference with the amperometric detection was assessed with respect to detection noise and potential shifts at various working-to-reference electrode spacing. It was observed that the electrophoresis HV interference caused by positioning the working electrode against the channel exit could be diminished by using an on-chip integrated reference electrode that was positioned in close proximity (100 microm) to the working electrode. The CE-ED microchip was demonstrated for the separation of model analytes, including dopamine (DA) and catechol (CA). Detection limits of 132 and 164 nM were achieved for DA and CA, respectively, and a theoretical plate number of 2.5x10(4)/m was obtained for DA. Relative standard deviations in peak heights observed for five runs of a standard solution containing the two analytes (0.1 mM for each) were 1.2 and 3.1% for DA and CA, respectively. The chip could be continuously used for more than 8 h without significant deterioration in analytical performance.     

酸性化学镀镍磷合金的动力学机理

通过极化曲线研究了3种不同溶液（阴极液、阳极液和完整镀液）的电化学行为,测定了主盐、还原剂浓度以及镀液pH和体系温度对化学镀镍沉积速率的影响. 与直接在镁合金上化学镀镍并使用重量分析法得到的沉积速率相比较发现,完整镀液体系的极化曲线才能真实地反映化学镀镍的沉积过程,其过程不能简单视为由彼此完全独立毫无关联的阴阳极半反应构成. 根据Butler-Volmer公式,本化学镀液体系的化学镀镍过程属混合控制,其表观反应活化能为42.89 kJ·mol^-1.     

Copper nanoparticles seeded functionalized‐PVC plastic surface for electroless nickel deposition

A novel and facile activation process for electroless nickel deposition was developed. The semi‐interpenetrating polymer network hydrogel biofilm was used to functionalize the inert poly(vinyl chloride) (PVC) surface, and then Cu nanoparticles, which can initial the subsequent electroless nickel deposition successfully seeded on the functionalized‐PVC surface. The samples were characterized by scanning electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, and transmission electron microscopy. The results show that the hydrogel film provided the PVC surface with amino groups and Cu nanoparticles of 20–50 nm in size could be functioned as the catalytic nuclei for the subsequent electroless metal deposition on PVC plastic. It can be concluded that the novel Cu activation was effective for the nickel deposition on PVC surface, because of more chemisorption sites for Cu nanoparticles generated on PVC surface. Copyright © 2013 John Wiley & Sons, Ltd.