Waveguide surface plasmon resonance studies of surface reactions on gold electrodes

We describe the fabrication and characterisation of gold-coated graded index channel waveguide sensors designed for simultaneous electrochemical and surface plasmon resonance studies. The active sensing electrode area is a thin gold film between 0.5 and 5 mm in length and 200 microm wide deposited on top of a 3 microm wide waveguide which forms one arm of a Y-junction while the other arm of the Y-junction serves as a reference. Using these devices we have measured simultaneously the changes in transmittance through the device whilst carrying out cyclic voltammetry in either sulfuric or perchloric acid solution or during the deposition of an UPD layer of copper at the gold surface. In all cases we obtain stable and reproducible results which demonstrate the very high sensitivity of the devices to sub-monolayer changes occurring at the gold electrode surface. The response of these integrated optoelectrochemical devices is discussed in terms of a numerical model for the propagation of light within the waveguide structure.     

An electrochemical cell coupled with disposable screen-printed electrodes for use in flow injection analysis.

An electrochemical cell coupled with disposable screen-printed electrodes (SPEs) that is specifically designed for use in flow injection analysis (FIA) is described in this study. The cell is made of foldable polyoxymethylene (acetal) thick platelets with the bottom portion consisting of a cavity track to drag the SPEs in position and the top portion having predrilled T-like holes to arrange the Ag/AgCl reference electrode and stainless steel inlet & outlet. An "O ring" is suitably fixed on the top of the working electrode to form a thin-layer space where the electrochemical reaction can take place. Hydrodynamic characterization was validated by using a benchmark hexacyanoferrate redox couple. The results of practical analysis of glucose in human plasma clearly demonstrate the characteristics and applicability of the proposed wall-jet electrochemical cell in FIA.     

New spectrophotometer equipped with long light path length cells and two channel FIA for trace metals

New spectrophotometer was designed for the simultaneous assay of copper and iron using flow injection analysis and moreover, new 50 mm light path cells were equipped in the spectrophotometer to enhance the sensitivity. Both copper and iron at 2-10 ppb level were determined simultaneously and rapidly using water soluble reagent, 5-Br-PSAA. Determination limits were 1 ppb for copper and 1 ppb for iron. Relative standard deviations were about 1%.     

An improved cell for in-situ electrochemical ESR

An improved cell for simultaneous electrochemical ESR based on a coaxial cylindrical cavity is described and shown to have high sensitivity whilst behaving as a satisfactory hydrodynamic electrode as evidenced by Tafel analysis, by Levich analysis and comparison with theory for the dependence of the ESR signal on electrode currents and electrolyte flow rate.     

An electrochemical cell for simultaneous electrochemical and spectroelectrochemical measurements under semi-infinite diffusion conditions and thin-layer conditions

A combination cell to accomplish simultaneous electrochemical and spectroelectrochemical measurements under both thin-layer and semi-infinite diffusion conditions is described and characterized. Fibre optics and a reflective electrode are used to couple the cell to the spectrophotometer. This allows different electrode materials to be used. Moreover, the cell is thermostatically controlled and equipped with a magnetic stirrer, and can be used for temperatures down to −40°C.The application of electrochemical pulse and sweep techniques are demonstrated. Dynamic spectroelectrochemical techniques such as linear sweep and cyclic voltabsorptometry (LSVA and CVA) as well as the corresponding derivative voltabsorptometric techniques derivative linear voltabsorptometry (DLSVA) and derivative cyclic voltabsorptometry (DCVA) are also applicable under thin-layer conditions. DLSVA and DCVA are the optical analogues of linear sweep and cyclic voltammetry. No epoxy cement or other sealing compounds are required and the solution comes in contact with only quartz, Teflon and the electrodes. Under aprotic conditions the cell response is in accordance with theory down to a solution thickness of 15 μm, where rapid exhaustive electrolysis intrinsic to thin-layer electrochemistry can be achieved in less than 1 s.The electrochemical and spectroelectrochemical characterization of the cell demonstrated that this design is very well suited to different electrochemical pulse and sweep techniques with simultaneous spectroscopic characterization of reaction products under finite and semi-infinite diffusion conditions in organic solvents. This offers the opportunity for cross-correlations of the electrochemical and spectroscopic information, which should lead to more reliable results. The adjustment of different thin-layer thicknesses is highly reproducible and the exchange of the solution inside the thin-layer cavity with the bulk solution after each thin-layer experiment can be easily performed. The electrochemical behaviour of the cell is in accordance with theory for cyclovoltammetric measurements under both bulk and thin-layer conditions. Derivative voltabsorptometric techniques are applicable and the response of the cell is in accordance with theory, particularly under finite diffusion conditions. The use of a bifurcated optical fibre bundle allows a more flexible experimental arrangement, and the application of a triple split bundle for the investigation of light-sensitive electron-transfer compounds [34,35] is in progress. The third end of the optical fibre bundle will be used to apply additional selective irradiation to convert electron-transfer-active photochromic compounds inside the thin-layer cavity depending on the redox state.An additional aspect of the current investigations is the application of the present cell for electrogenerated chemiluminescence (ECL) [36,37]. The highly reflecting electrode and the integrated stirrer are advantageous for this type of measurement. Finally, further work is in progress to utilize the integrated temperature control of the cell for spectroelectrochemistry at low temperatures, particularly with more unusual solvents like liquid sulphur dioxide [38] and liquid dimethylamine [39].     

Electrochemically Induced Iron Release of Adsorbed Horse Spleen Ferritin: Quantitation of Iron Using Long Optical Path Length Thin‐Layer Spectroelectrochemistry

In this work, long optical path length thin‐layer electrochemical cell was constructed using indium‐tin oxide on glass as the electrode material. Iron release from ferritin adsorbed on the electrode was induced by applying a negative potential sweep in the presence of 1,10‐phenanthroline. The usefulness of spectroelectrochemistry as a means of determining the quantity of iron released from an adsorbed layer of ferritin is demonstrated.     

Sandwich-type flow-through fiber-optic cells for optical absorbance measurements

The sandwich cell described by Pavon et al. and a similar sandwich cell, except with angled (45 degrees, confocal) single strand optical fibers and a conventional Z-type cell of 6-mm path length have been studied with respect to their performance for absorbance detection. Both sandwich cells show less susceptibility by one order of magnitude to artifact absorbance signals from RI changes than the Z-cell. The light throughput in the sandwich cells increase by an order of magnitude when an inert metallized reflector is used and this improves S/N. The overall light throughput is substantially greater for the angled entrance single strand fiber optic cell rather than the cell with the bifurcated fiber optic. Attainable limits of detection with these cells appear to be related to the pathlength for the cell dimensions studied.     

汞修饰掺锡三氧化二铟导电玻璃光透薄层电化学池的设计

报道了汞膜修饰掺锡三氧化二铟导电玻璃电极的制备及其薄层电化学池的设计，测试限电极和薄层的光、电化学性能，在水溶液中，与基底电极相比，该电极的负电位范围增加了７００ｍＶ，并表现出普通汞电极的电化学 性质，以此电极制得的电极制得的薄层层池可适用于氧化还原电位较负的电化学过程的光谱电化学研究及金属离子的电化学分析。     

肾上腺素电氧化生成肾上腺素醌的反应动力学

使用以铂片为工作电极的长光程薄层电化学池,采用单电位阶跃计时吸收法测定了1．0mol·L^-1H2SO4和冰醋酸中,肾上腺素电氧化生成肾上腺素醌的动力学参数．实验结果表明：肾上腺素在1．0mol·L^-1H2SO4介质中比在冰醋酸中容易被氧化．     

The In-cell iR Compensation Using a Four-electrode System

It is well known that the iR compensation is very important in electrochemistry, especially in fast, ultra-fast and transient voltammetry for kinetic and mechanistic studies. The modern design of potentiostat is usually of the three-electrode system, in w…     

New approaches on gas phase molecular absorption spectrometry detection in gas chromatography

A hyphenated technique for coupling a spectrophotometric detector to a gas chromatograph with a packed column is described. The packed column was connected directly to the flow cell (path length 1 cm) which was placed in a UV-visible molecular absorption spectrophotometer with diode array detector. This detection system was employed for separating and determining benzene, toluene, 1,4-xylene, 1,2-xylene and mesitylene. Molecular absorption spectra of all the separated compounds have also been obtained. A new possibility for coupling capillary gas chromatography and gas phase molecular absorption spectrometry is currently being tested. In this new case, two fibre optics are used and the measurement is performed in the capillary column.     

New approaches on gas phase molecular absorption spectrometry detection in gas chromatography

A hyphenated technique for coupling a spectrophotometric detector to a gas chromatograph with a packed column is described. The packed column was connected directly to the flow cell (path length 1 cm) which was placed in a UV-visible molecular absorption spectrophotometer with diode array detector. This detection system was employed for separating and determining benzene, toluene, 1,4-xylene, 1,2-xylene and mesitylene. Molecular absorption spectra of all the separated compounds have also been obtained. A new possibility for coupling capillary gas chromatography and gas phase molecular absorption spectrometry is currently being tested. In this new case, two fibre optics are used and the measurement is performed in the capillary column.     

Optical fiber coupled light emitting diode based absorbance detector with a reflective flow cell

We present a versatile, optical fiber coupled light emitting diode (LED) light source based flow-through optical absorbance detector. The LED source is readily changeable. Optical fibers are used to carry light from the electronics/display unit to a reflective flow-through cell and back. The cell can thus be located remotely from the electronics unit and the umbilical connection is not susceptible to electrical noise. The noise level of this detector with LEDs of different emission maxima were observed to be in the range of 3-20 muAU under actual use conditions, with a maximum short term drift of 4 muAU/min after the initial warm-up period. When the analyte absorbance is well matched with the source emission characteristics, the detector response is linear with concentration over at least two orders of magnitude. The liquid flow path through the cell is linear with a large exit aperture such that bubbles are not trapped in the optical path. The optical arrangement is such that the incident light crosses the liquid flow orthogonally and is reflected back by a rear mirror to the receiver fiber. This arrangement reduces the refractive index sensitivity by an order of magnitude relative to conventional Z-path flow cells.     

基于DFB型半导体激光器的腔增强吸收光谱研究

The Cavity enhanced absorption spectroscopy based on a tunable DFB diode laser (TDL-CEAS) was described. A brief introduction of cavity enhanced absorption spectroscopy development and experimental scheme was given, the effective absorption path of the medium in the optical cavity was interpreted from the way of Fabry Perot cavity. It is pointed out that the main reason why CEAS has high detection sensitivity is that the medium in the cavity can get a long absorption path. A tunable DFB diode laser which center wavelength is 1.573 μm was used as the light source, and an optical cavity which consists of two high reflectivity mirrors (near 1.573 μm, R about 0.994) separated at a distance of 34 cm was used as the absorption cell. Laser radiation was coupled into the optical cavity via accidental coincidences of laser frequency with the cavity mode when scanning the cavity and the laser. An absorption spectrum of carbon dioxide near 1.573 μm was obtained and a detection sensitivity of about 1.66×10-5 cm-1 was achieved. It is experimentally demonstrated that the CEAS is a highly sensitive and high resolution spectrum technology, and it has the advantage of simple experimental setup and easy operation.     

肾上腺素电化学氧化生成肾上腺素红反应机理的薄层光谱电化学研究

应用长光程薄层电解池(石墨电极和铂片电极),使用循环伏安法(CV)和单电位阶跃计时吸收法(SPS/CA),研究了肾上腺在pH=2.5～7.0的McIlvaine缓冲溶液中电氧化生成肾上腺素红的反应机理,测定了表观速率常数kobs.结果表明:溶液pH值对肾上腺素的电氧化反应有很大影响,肾上腺素生成肾上腺素红的kobs随溶液pH值的增加而增大.     

Comparison between electrochemical and optoelectrochemical impedance measurements for detection of DNA hybridization

The principles of the electrochemical and optoelectrochemical impedance measurements on bare electrolyte/dielectric/semiconductor structures are described. The analysis of the experimental curves allows access to several indications concerning the electrical behavior of such structures. The application of these techniques to follow the electrical behavior of structures modified with two biological systems was investigated. The antibody/antigen recognition did not change the surface charge and, therefore, did not affect the impedance curves with respect to the applied potential. By contrast, the hybridization of two complementary DNA strands on the surface of the structure induced a variation of flat band potential of the semiconductor leading to a shift of impedance curves along the potential axis. This means that it is possible to detect directly the DNA hybridization without the use of labeled probes. The use of light allows the surface to be probed locally. In the future, the application of this technique for direct detection of hybridization on DNA chips should be possible.     

Wireless electrochemical DNA microarray sensor

We report an electrochemical DNA microarray sensor whose function is controlled with just two wires regardless of the number of individual sensing electrodes. The bipolar sensing electrode is modified with probe DNA, and the anode end of each electrode is configured to emit light (electrogenerated chemiluminescence) upon hybridization of cDNA labeled with electrocatalytic (oxygen reduction) Pt nanoparticles at the cathode. The important finding is that DNA can be selectively detected at an array of three electrodes. In principle, however, this advance provides a means for controlling the potential of many electrodes using just two wires and then indirectly determining the current flowing through all of them simultaneously by correlating light emission to current.     

The electrochemical behavior of core-shell CdSe/CdS magic-sized quantum dots linked to cyclodextrin for studies of the encapsulation of bioactive compounds

Semiconductor nanocrystal quantum dots have been the subject of extensive investigations in different areas of science and technology in the past years. In particular, there are few studies of magic-sized quantum dots (MSQDs), even though they exhibit features such as extremely small size, fluorescence quantum efficiency, molar absorptivity greater than traditional QDs, and highly stable luminescence in HeLa cell cultures, thereby enabling monitoring of biological or chemical processes. The present study investigated the electrochemical behavior of free CdSe/CdS MSQDs using glassy carbon electrode and CdSe/CdS MSQDs immobilized on a gold electrode modified with a self-assembled cyclodextrin monolayer. The MSQDs showed two peaks in aprotic medium. The functionalized film modifier was prepared and characterized by means of cyclic voltammetry and electrochemical impedance spectroscopy using ferricyanide ions as a redox probe. The prepared modified electrode exhibited a stable behavior. The proposed method was successfully applied to encapsulation studies of mangiferin, a natural antioxidant compound, and cyclodextrin associated with the quantum dot, and the response was compared with that of the modified electrode without QD. The fluorescence study revealed that CdSe/CdS quantum dots emit blue light when excited by an optical source of wavelength of 350 nm and a significant increase in fluorescence and absorbance intensity is observed from the core-shell CdSe/CdS MSQDs when quantities of mangiferin are added to the solution containing thiolated cyclodextrin. CdSe/CdS MSQDs are optically and electrochemically sensitive and can be used for the detection and interaction of compounds encapsulated in cyclodextrin.     

全钒氧化还原液流电池用石墨毡电极的分步氧化活化

石墨毡电极是组成钒电池的关键材料,其较低的电化学活性是造成钒电池功率密度较低的关键因素之一. 本论文采用一种简便的石墨毡电极分步氧化活化法,先将石墨毡在高锰酸钾溶液中进行氧化,后置于活化溶液中激发其反应活性. 通过对处理后的石墨毡进行循环伏安、交流阻抗测试、XPS以及SEM表征,发现氧化时间和活化溶液组成是影响电极性能的因素,在本文中,先经过3天氧化时间,后在配比为3:1的活化溶液中处理的电极,较其他方法处理的电极,电荷传递电阻明显降低,其与溶液之间的接触电阻最低,为7.33 Ω·cm ²,氧化还原峰值比更接近于1,有效提高了反应的活性与可逆性,经X射线光电子能谱分析发现性能提高的原因与表面含氧官能团数目增加有关. 单电池性能测试结果进一步证实,利用该方法处理的石墨毡为电极的单电池,较未经处理的电池相比性能更优,有更高的放电容量和能量效率,在100 mA·cm ^-2电流密度下,能量效率较未处理电极高出7.47%. 与热处理法、酸处理法及电化学氧化法相比较,该方法不需要辅助设备,不消耗能源.     

Role of Hydrodynamic Conditions in the Distribution of Anodic Dissolution Rates in Cavity Etching Regions during Electrochemical Micromachining of Partially Insulated Surfaces

Experimental study of the distribution of local rates of electrochemical micromachining in the presence of photoresist masks in various hydrodynamic conditions (macroscopically nonuniform rotating disk electrode, sprayer flow, an electrode placed into a cell with chaotic bulk electrolyte mixing) shows that the maximum etching localization is achieved at the control of the dissolution rate by the mass transport rate (at achieving the anodic limiting current). The localization enhancement as compared to the primary current distribution takes place in the case of a turbulent flow at hydrodynamic conditions where the removal of dissolution products from the undercutting region is hindered. These conditions (electrochemical reaction limited by the ion mass transport rate, high resistance to the mass transport in the undercutting region) are necessary for the localization enhancement using a pulsed anodic–cathodic treatment.