基于三维纳米银修饰电极的硝酸根微型传感芯片研究

研制一种基于金叉指微电极阵列(IDA)的电流型硝酸根离子(NO-3)微传感电极芯片.基于微机电系统(Micro-Electro-Mechanical Systems,MEMS)工艺制备金IDA微电极,通过电化学沉积技术在IDA微电极表面修饰三维枝状结构纳米银敏感膜,利用敏感膜对硝酸根离子良好的电催化还原性能,采用脉冲方波伏安(SWV)电化学测量方法,实现对硝酸根离子在25～1000μmol/L浓度范围内的快速检测,灵敏度达9.5 nA/(μmol/L),线性度为99.98%,检测下限为10μmol/L.考察水体中常见的NO-2,F-,3PO 4-,SO 42-,2CO3-,NH+4,Na+和K+等离子对该传感芯片的干扰性能,传感芯片表现出较好的抗干扰性能.制备的三维枝状结构纳米银修饰IDA微电极可实现水环境(pH 5.0～9.0)中NO-3的电化学检测,对应用于自然水环境中硝酸根离子的现场检测具有积极意义.     

An In Situ Copper Plated Boron‐Doped Diamond Microelectrode Array for the Sensitive Electrochemical Detection of Nitrate

The first example of using a copper microelectrode array for use in electroanalysis is explored and exemplified with the electroanalytical quantification of nitrate. The analytical approach is based upon the in situ deposition of copper at a boron‐doped diamond (BDD) microelectrode array. The immobilized copper layer is electrocatalytic for nitrate reduction and exhibits an analytically useful range from 1.2 to 124 μM with a marked selectivity for nitrate ion over nitrate, with a limit of detection of 0.76 μM. The analytical applicability was examined through standard addition determinations of nitrate in drinking and river water samples.     

Microdrop analysis of a bead-based immunoassay

The progress to electrochemical detection of a microbead-based immunoassay in small volumes has led to a reduced assay time and lower detection limits. Three electrochemical techniques are described for an immunoassay with detection in a microdrop. The techniques are amperometric detection with a rotating disk electrode (RDE), a microelectrode, and an interdigitated array (IDA) electrode. An enzyme-labeled sandwich immunoassay with mouse IgG as the model analyte is used to demonstrate the three techniques. The microbead assay is carried out in a test tube using a magnet to control bead collection. Once the immunocomplex is formed on the microbead, the beads are transferred to a microdrop where the enzyme, either alkaline phosphatase or β-galactosidase, generates 4-aminophenol (PAP). PAP is oxidized at the electrode with an applied potential of +290 mV vs. Ag/AgCl. For all three techniques, the upper limit of the dynamic range was 1000 ng/ml mouse IgG, and the detection limits were: 50 ng/ml for the RDE, 40 ng/ml for the microelectrode, and 26 ng/ml for the IDA electrode.     

Determination of the Apparent Michaelis Constant of Glucose Oxidase Immobilized on a Microelectrode with Respect to Oxygen

We report determination of the apparent Michaelis constant of glucose oxidase (GOx) immobilized on a microelectrode with respect to oxygen. We used a GOx‐modified microelectrode as a probe for scanning electrochemical microscopy. We detected hydrogen peroxide generated by the enzyme reaction at the microelectrode under controlling the oxygen concentration using water electrolysis at an interdigitated array (IDA) electrode. The response depends on the oxygen concentration, which is regulated by the microelectrode position and the potential applied to the IDA electrode. We estimated the apparent Michaelis constant with respect to oxygen in this experimental condition to be about 0.28 mM.     

Indirect voltammetric detection of fluoride ions in toothpaste on a comb-shaped interdigitated microelectrode array

A novel technique based on dynamic electrochemistry for the detection of fluoride ions was developed. It is based on its strong complexation with ferric ion. Formed fluoroferric complex is cathodically inactive at the potential of the reduction of free ferric aquo ion. The voltammetric and amperometric response of platinum comb-shaped interdigitated microelectrode array is decreased after fluoride addition. This decrease serves for the quantification of fluoride ions added to the solution. The detection limit of 4.5 × 10⁻⁵ mol dm⁻³ was achieved when one of the segments of interdigitated microelectrode array (IDA) was used as an indicating electrode. The detection limit is about one order of magnitude lower than in the case of conventional platinum macroelectrode. In comparison with ISE electrodes this method is faster and also avoiding large error resulting from the antilogarithmization of ISE Nerstian response. The method was applied to the analysis of toothpaste.     

Self-assembled synthesis of SERS-active silver dendrites and photoluminescence properties of a thin porous silicon layer

Via electroless metal deposition, well-defined silver dendrites and thin porous silicon (por-Si) layers are simultaneously prepared in ammonia fluoride solution containing AgNO₃ at 50 °C. A self-assembled localized microscopic electrochemical cell model and a diffusion-limited aggregation mode are used to explain the growth of silver dendrites. The formation of silver dendritic nanostructures derives from the continuous aggregation growth of small particles on a layer of silver nanoparticles or nanoclusters (Volmer-Weber layer). Thin and homogeneous nanostructure por-Si layers display visible light-emission properties at room temperature. The investigation of the surface-enhanced Raman scattering (SERS) reveals that the film of silver dendrites on por-Si is an excellent substrate with significant enhancement effect.     

The detection of formaldehyde in textiles using interdigitated microelectrode array diffusion layer titration with electrogenerated hypobromite

An interdigitated microelectrode array (IDA) was applied to the determination of formaldehyde released from textiles produced in industry. The proposed method is based on formaldehyde reaction with hypobromite which is formed in weakly basic media by control current electrooxidation of bromide on the generator segment of the IDA array. The unreacted hypobromite diffuses through the gap between individually polarisable IDA segments and it is amperometrically detected on the collector segment of the IDA. The efficiency of this nonconvective transfer process in the absence of formaldehyde was substantially higher (78%) in comparison with that when using the rotating ring disc electrode. The influence of the added formaldehyde on the transfer process can be utilised to develop a simple and sensitive analytical procedure for formaldehyde detection with a detection limit of 4×10⁻⁶ mol dm⁻³.     

Electrochemical Detection of MS2 Phage Using a Bead‐based Immunoassay and a NanoIDA

A microbead based sandwich immunoassay for MS2 bacteriophage was developed using an interdigitated array (IDA) electrode with nanoscale dimensions (220 nm electrode width, 620 nm gap). The IDA was fabricated using an electron beam lithographic lift‐off technique. After an antibody‐assisted capture of MS2 using paramagnetic microbeads, a β‐galactosidase labeled secondary antibody was used to convert p‐aminophenyl‐β‐D ‐galactopyranoside (PAPG) into the redox active p‐aminophenol (PAP). Amperometric detection of PAP with IDA electrodes at +300 and ?200 mV vs. a Ag/AgCl reference electrode was used to measure the result, detecting MS2 concentrations as low as 10 ng/mL.     

3D aluminum/silver hierarchical nanostructure with large areas of dense hot spots for surface‐enhanced raman scattering

Plasmonic nanomaterials possessing large‐volume, high‐density hot spots with high field enhancement are highly desirable for ultrasensitive surface‐enhanced Raman scattering (SERS) sensing. However, many as‐prepared plasmonic nanomaterials are limited in available dense hot spots and in sample size, which greatly hinder their wide applications in SERS devices. Here, we develop a two‐step physical deposition protocol and successfully fabricate 3D hierarchical nanostructures with highly dense hot spots across a large scale (6 × 6 cm²). The nanopatterned aluminum film was first prepared by thermal evaporation process, which can provide 3D quasi‐periodic cloud‐like nanostructure arrays suitable for noble metal deposition; then a large number of silver nanoparticles with controllable shape and size were decorated onto the alumina layer surfaces by laser molecular beam epitaxy, which can realize large‐area accessible dense hot spots. The optimized 3D‐structured SERS substrate exhibits high‐quality detection performance with excellent reproducibility (13.1 and 17.1%), whose LOD of rhodamine 6G molecules was 10^?9 M. Furthermore, the as‐prepared 3D aluminum/silver SERS substrate was applied in detection of melamine with the concentration down to 10^?7 M and direct detection of melamine in infant formula solution with the concentration as low 10 mg/L. Such method to realize large‐area hierarchical nanostructures can greatly simplify the fabrication procedure for 3D SERS platforms, and should be of technological significance in mass production of SERS‐based sensors.     

Determination of pharmaceutical dosage forms via diffusion layer titration at an interdigitated microelectrode array

This paper presents a method for the analysis of drugs in dosage form. It is based on galvanostatic generation of oxidation agent from a suitable precursor on one segment of interdigitated microelectrode array (IDA) and its consecutive amperometric detection on second segment. High collection efficiency of this process in comparison to rotational ring disc electrode (RRDE) is a unique feature of IDA system. The transfer of oxidation agent can be influenced by addition of species, which reacts with oxidant. This influence can be used for its determination. Evaluation of generator-collector current dependence (diffusion layer titration curve) reveals the value of generator current I(genE) of the end-point of titration. I(genE) is proportional to the bulk phase concentration of determined species. The method was applied to the analysis of pharmaceuticals Antabus (Disulfiram Alpharma NOR, tetraethylthiuram disulfide (TETD)), a popular drug for alcoholism treatment, and Celaskon (vitamin C, Léciva CZE, ascorbic acid (AA)). From model samples analysis rather low detection limits, 9x10(-7) mol dm(-3), respectively, 4x10(-6) mol dm(-3), were estimated which enables trace content analysis of the drugs. A small size of IDA sensor also makes it suitable for microanalytical improvement.     

Chemically Modified Electrodes for Recessed Microelectrode Array

Chemical modifications on recessed microelectrode array, achieved via electrodeposition techniques are reported here. Silicon-based gold microelectrode arrays of 10 μm microband and microdisc array were selected and functionalised using sol-gel and nanoporous gold (NPG) respectively. For electrochemically assisted self-assembly (EASA) formati6154on of sol-gel, electrode surface was first pre-treated with a self-assembled partial monolayer of mercaptopropyltrimethoxysilane (MPTMS) before transferring it into the sol containing cetyltrimethyl ammonium bromide (CTAB)/tetraethoxysilane (TEOS):MPTMS (90:10) precursors. A cathodic potential is then applied. It was found that larger current densities were required in ensuring successful film deposition when moving from macro- to micro- dimensions. For NPG modification, a chemical etching process called dealloying was employed. NPG of three different thicknesses have been successfully deposited. All the modified and functionalized microelectrode arrays were characterized by both optical (SEM) and electrochemical analysis (cyclic voltammetry and impedance spectroscopy). An increase in surface area and roughness has been observed and such will benefit for future sensing application.     

Silver spray deposition for AgLDI imaging MS of cholesterol and other olefins on thin tissue sections

Olefins such as cholesterol and unsaturated fatty acids play important biological roles. Silver‐assisted laser desorption ionization (AgLDI) takes advantage of the strong affinity of silver to conjugate with double bonds to selectively ionize these molecules for imaging mass spectrometry (IMS) experiments. For IMS studies, two main approaches for silver deposition have been described in the literature: fine coating by silver sputtering and spray deposition of silver nanoparticles. While these approaches allow for extremely high resolution IMS experiments to be conducted, they are not readily available to all laboratories. Herein, we present a silver nitrate spray deposition approach as an alternative to silver sputtering and nanoparticle deposition for routine IMS analysis. The silver nitrate spray has the same level of specificity and sensitivity for olefins, particularly cholesterol, and has shown to be capable of IMS experiments down to 10‐μm spatial resolution. Minimal sample preparation and the affordability of silver nitrate make this a convenient and accessible technique worth considering.     

Atomic Layer Deposition of Cobalt Phosphide for Efficient Water Splitting

Transition‐metal phosphides (TMP) prepared by atomic layer deposition (ALD) are reported for the first time. Ultrathin Co‐P films were deposited by using PH₃ plasma as the phosphorus source and an extra H₂ plasma step to remove excess P in the growing films. The optimized ALD process proceeded by self‐limited layer‐by‐layer growth, and the deposited Co‐P films were highly pure and smooth. The Co‐P films deposited via ALD exhibited better electrochemical and photoelectrochemical hydrogen evolution reaction (HER) activities than similar Co‐P films prepared by the traditional post‐phosphorization method. Moreover, the deposition of ultrathin Co‐P films on periodic trenches was demonstrated, which highlights the broad and promising potential application of this ALD process for a conformal coating of TMP films on complex three‐dimensional (3D) architectures.     

Boron-doped diamond microdisc arrays: electrochemical characterisation and their use as a substrate for the production of microelectrode arrays of diverse metals (Ag, Au, Cu)via electrodeposition

A novel boron-doped diamond (BDD) microelectrode array is characterised with electrochemical and atomic force microscopic techniques. The array consists of 40 micron-diameter sized BDD discs which are separated by 250 microns from their nearest neighbour in a hexagonal arrangement. The conducting discs can be electroplated to produce arrays of copper, silver or gold for analytical purposes in addition to operating as an array of BDD-microelectrodes. Proof-of-concept is shown for four separate examples; a gold plated array for arsenic detection, a copper plated array for nitrate analysis, a silver plated array for hydrogen peroxide monitoring and last, cathodic stripping voltammetry for lead at the bare BDD-array.     

Voltammetric determination of iodide by use of an interdigitated microelectrode array

An interdigitated microelectrode array (IDA) sensor has been applied to the determination of iodide in mineral water. It is based on reversible charge transfer in the redox system I2/2I- at a platinum microelectrode. The analytical signal from the IDA system was obtained by use of a bipotentiostat in dual mode. One segment of the IDA (generator) was polarized to the limiting current for oxidation of iodide to iodine in 0.1 mol L(-1) HClO4. The second segment (collector) was fixed at a potential value corresponding to the limiting current of iodine reduction. The geometrical arrangement of the IDA enables this transfer with high efficiency. Because the diffusion layer of both segments overlaps the iodide produced on the collector, the iodide diffuses back to the generator where it is reoxidized. Therefore, redox cycling will enhance the voltammetric signal of the IDA. The signal obtained with a vertically separated IDA was 20 times higher than that in the single mode. Because multiplication of the signal reduces the detection and determination limits, direct voltammetric determination of iodide in mineral water is possible.     

Catalytic Adsorptive Stripping Chronopotentiometric Determination of Hexavalent Chromium at a Silver Amalgam Film Electrode of Prolonged Application

The paper reports on the application of stripping chronopotentiometry for the determination of chromium(VI) at a silver‐based amalgam film electrode. It is the first attempt to apply such a detection system for the speciation of chromium. The procedure utilized catalytic reduction of nitrate ions induced by the instantaneous chromium(III)‐DTPA complex, accumulated at the electrode surface. The chronopotentiometric step is realized in the constant current mode. Several key parameters, such as the deposition potential, deposition time, nitrate concentration and stripping current were optimized. The detection limit obtained for 15 s of accumulation time was estimated at 0.025 µg/L. The repeatability of the signal was 6.1 %.     

Integrated Microanalytical System for Simultaneous Voltammetric Measurements of Free Metal Ion Concentrations in Natural Waters

A complexing gel integrated microelectrode (CGIME) for direct measurements of free metal ion concentrations in natural waters has been developed. It is prepared by the successive deposition of microlayers of a chelating resin, an antifouling agarose gel and Hg on a 100‐interconnected Ir‐based microelectrode array. The trace metals of interest are in a first step accumulated on the chelating resin in proportion to their free ion concentration in solution, then released in acidic solution and detected simultaneously by using square wave anodic stripping voltammetry (SWASV). The reliability of this sensor for the simultaneous measurement of copper, lead and cadmium has been studied by a series of replicate laboratory tests. The proportionality between the voltammetric peak current intensity and the free metal ion concentrations in solution has been demonstrated by using malonate as a model ligand. Finally, the CGIME sensor was applied to the Cu and Pb free concentration measurement in sea water samples and the results compared to the free metal ion concentrations measured using hollow fiber based permeation liquid membrane (HF‐PLM) coupled to inductively coupled plasma mass spectrophotometer (ICP‐MS). Comparable concentration values were found for both metals with both techniques allowing to validate the CGIME measurements in complex media.     

Microanalytical Determination of Formaldehyde by Direct Titration with Hydroxylamine Using Interdigitated Microelectrode Array Biamperometric End-Point Indicator

 An interdigitated microelectrode array (IDA) biamperometric titration is presented for the microdetermination of formaldehyde. It is based on a direct titration of formaldehyde with hydroxylamine under the formation of formaldoxime. The released hydrogen cations react with hydroxyl anions in 0.1 M NaOH. The interdigitated pair of two individually polarizable microelectrodes serves as a biamperometric end-point indicator. Hydroxylamine together with dissolved free oxygen behave as a quasi reversible mixed redox system, therefore a significant increase of current flowing between the IDA segments polarized by 100 mV is observed when the first excess of titrant appears in the titrated solution. Because of the small dimension of the IDA sensor this principle can be extended for a microanalytical variant of this method. Formaldehyde contents down to 10⁻³ M in small volume waste water samples could be determined by this technique. These samples usually contain carboxylic acids which interfere in iodimetric determinations, but do not influence the titration of formaldehyde with hydroxylamine. Received January 21, 2002; accepted August 7, 2002     

Calibrationless determination of electroactive species using chronoamperograms at collector segment of interdigitated microelectrode array

The possibility of calibrationless chronoamperometric determination is described using a pair of individually addressable and diffusion layers interacting segments of interdigitated microelectrode array (IDA). It utilizes dual voltammetric mode where the first segment is polarized with potential corresponding to the limiting current of determined species electrode reaction and the second segment is polarized with potential corresponding to the opposite electrode reaction limiting current. Time at which the current of the collector segment reaches one half of the steady state is hyperbolically dependent on the diffusion coefficient of analyte. The determination of diffusion coefficient allows direct calculation of bulk concentration avoiding calibration with a standard solution. The equipment for measuring of fast response of IDA arrays in dual mode has been developed using a bipotentiostat connected with A/D transducer. It allows less than 1 ms sampling period for ultrafast registration of chronoamperogram. The method was tested and validated with [Fe(CN)₆]⁴⁻, [Ru(NH₃)₆]Cl₃, and ferrocene model samples using various types of IDA arrays.     

基底对电沉积制备ZnO纳米棒阵列的影响

采用恒电位电沉积方法, 在未经修饰的ITO导电玻璃基底上通过控制实验条件制备出不同形貌的纳米ZnO结构, 而在经过ZnO纳米粒子膜修饰后的ITO导电玻璃基底上, 制备出透明、高取向、粒径小于30 nm的ZnO纳米棒阵列. 用扫描电子显微镜(SEM)、X射线衍射(XRD)以及透射光谱对制备出的ZnO纳米棒阵列的结构、形貌和透明性进行了表征. 测试结果表明, ZnO纳米棒阵列的平均直径为21 nm, 粒径分布窄, 约18～25 nm, 择优生长取向为[001]方向, 垂直于基底生长. 当入射光波长大于400 nm时, ZnO纳米棒阵列的透光率大于95%.