Generation of biotin/avidin/enzyme nanostructures with maskless photolithography

Micrometer-sized domains of a carbon surface are modified to allow derivatization to attach redox enzymes with biotin/avidin technology. These sites are spatially segregated from and directly adjacent to electron transfer sites on the same electrode surface. The distance between these electron transfer sites and enzyme-loaded domains must be kept to a minimum (e.g., less than 5 microns) to maintain the fast response time and high sensitivity required for the measurement of neurotransmitter dynamics. This is accomplished through the use of photolithographic attachment of photobiotin using an interference pattern from a UV laser generated at the electrode surface. This will allow the construction of microscopic arrays of active enzyme sites on a carbon fiber substrate while leaving other sites underivatized to facilitate electron transfer reactions of redox mediators, thus maximizing enzyme activity and detection of the enzyme mediator. The ultimate sensitivity of these sensors will be realized only through careful characterization of the carbon electrode surface with respect to its chemical structure and electron transfer properties following each step of the enzyme immobilization process. The characterization of specific modifications of micrometer regions of the carbon surface requires analytical methodology that has both high spatial resolution and sensitivity. We have used fluorescence microscopy with a cooled CCD imaging system to visualize the spatial distribution of enzyme immobilization sites (indicated by fluorescence from Texas Red-labeled avidin) across the carbon surface. The viability of the enzyme attached to the surface in this manner was demonstrated by imaging the distribution of an insoluble, fluorescent product. An atomic force microscope was used to obtain high-resolution images that probe the heterogeneity of the enzyme sites.     

Development of an amperometric flow injection immunoanalysis system for the determination of the herbicide 2,4-dichlorophenoxyacetic acid in water

An amperometric flow injection immunoanalysis (FIIA) system based on an immunoreactor with immobilized biocomponents on a silica surface has been developed for the determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). In the antigen coating mode the hapten was immobilized and monoclonal primary antibody against 2,4-D together with alkaline phosphatase (AP)-labelled secondary antibody were used as sensing elements in a titration assay. In the antibody coating mode a biotinylated monoclonal antibody was immobilized on the surface of the immunoreactor and a 2,4-D-AP-conjugate was used for detection. For electrochemical measurements p-aminophenol enzymatically generated from p-aminophenyl phosphate was oxidized at a carbon working electrode at +150 mV versus Ag/AgCl. The system enabled the determination of 2,4-D in drinking water samples in the range from 0.2 to 70 micrograms/l. The whole system was computer controlled with a measuring time of 12 min for one determination.     

An analysis of stress corrosion crack growth by anodic dissolution

An analysis of the distribution of electrode potential within a stress corrosion crack which is growing by an anodic dissolution process has been used to define the electrode potential at the tip of the crack. This potential is used to predict the kinetics of crack growth. The influence of the applied stress intensity and the electrochemical properties of the crack tip and surface on the growth rate have been considered for low alloy steels in concentrated hydroxide solution and aluminum alloys in acidic chloride solution. Crack growth rates obtained in high concentration solutions are extrapolated to lower concentration solutions which may be expected in service environments. Predicted crack growth rates are in good agreement with published data.     

采用SECM分析7075铝合金的局部腐蚀行为

使用0.6 mol/LNaCl溶液腐蚀7075铝合金, 采用扫描电化学显微镜进行逼近曲线、面扫描测试, 用X射线衍射仪对合金的形貌进行分析, 用能谱仪分析腐蚀产物成分, 研究7075铝合金局部腐蚀电化学机理.结果显示:逼近曲线呈现正反馈, 探针的电流随着与合金基底距离的减小变大; 合金表面的活性点因为氯离子活化作用不断增加, 形成大范围的点蚀; 氯离子通过吸附在合金表面钝化层并与之反应, 破坏钝化层使得内部裸露, 内部的第2相电极电位更负, 和铝基体构成腐蚀微电池, 第2相的阳极腐蚀溶解降低合金的强度和抗腐蚀能力.      

微生物燃料电池碳基阳极材料的研究进展

微生物燃料电池（Microbial fuel cells, MFCs）是一种绿色能源技术,通过微生物的催化氧化代谢污水中的有机物同时产生电能,具有清洁环境和产电的双重优势,为可生物降解及可循环利用的废弃物转变成清洁能源提供了潜在的机会,在环境治理和能源利用方面表现出较好的应用前景。然而,目前相对较低的产电效率限制了MFCs的实际应用,其中阳极电极是产电微生物富集和传递电子的重要场所,与电池极化、电子导电性、生物相容性密切相关,是影响电池性能和运行成本的关键因素。碳纳米材料具有导电性好、比表面积大、孔隙率高、成本低等特点,被认为是微生物燃料电池重要的阳极材料,得到了广泛的研究和关注。本文主要从阳极电极种类、电极结构设计和电极材料改性等方面总结改善电极生物相容性、增加产电微生物附着量、提高反应活性位点的方法,并对提高产电性能的机理进行论述。最后对碳基电极材料进行展望,以期为制备高电化学活性的阳极材料提供理论指导。      

层层自组装纳米金/硫堇修饰玻碳电极测定亚硝酸根

研究了纳米金/硫堇多层膜修饰玻碳电极的制备以及亚硝酸根在该电极上的电化学行为。在稀硝酸溶液中,通过恒电位法将玻碳电极活化,使其表面产生-COH等含氧基,然后将其浸泡在硫堇溶液中,硫堇中的-NH2与玻碳电极表面的-COH基团发生席夫碱反应,将硫堇固定在电极上。最后将电极浸泡在纳米金溶液中,通过纳米金与硫堇的相互作用将纳米金修饰到电极表面,从而制得纳米金/硫堇多层膜修饰玻碳电极。实验结果表明,该修饰电极能显著促进亚硝酸根在电极表面的电化学过程,电化学响应信号与亚硝酸根的浓度在20×10-6~50×10-5 mol/L和50×10-5~20×10-3 mol/L范围内呈良好的线性关系,检出限为5×10-8 mol/L (S/N=3)。方法用于水样中亚硝酸根的测定,相对标准偏差为22%~32%,回收率在98%~104%范围。     

Electrocatalytic surface for the oxidation of NADH and other anionic molecules of biological significance

A simple electrochemical treatment of a carbon fiber electrode surface has been found to dramatically improve the voltammetry of NADH and several other anionic molecules under steady-state and fast scan (100 V/s) conditions. The electrocatalytic surface is generated through the electrochemical oxidation of NADH on a carbon fiber electrode that exhibits product adsorption. The oxidative product is reacted with ascorbic acid at elevated temperatures to create a surface which has very little overpotential for the oxidation of dopamine and many metabolites such as NADH, DOPAC, uric acid, and ascorbate. The electrochemical properties of the modified surface were examined voltammetrically at both slow and fast scan rates. The surface shown in this paper shifts the oxidation overpotentials different magnitudes for each analyte tested, thus allowing discrimination between analytes of interest and their major interferences. Another benefit of this new electrocatalytic wave is that it decreases the limit of detection for NADH by approximately 1 order of magnitude. Therefore, this new carbon surface not only gives better discrimination between two analytes but also gives better detection limits for certain analytes of interest.     

Voltammetric behaviour of mitoxantrone at a DNA-biosensor

The surface of an electrochemical glassy carbon electrode was modified with a layer of double-stranded DNA (dsDNA) or with double-stranded DNA conditioned in single-stranded DNA (ssDNA) and was used to investigate mitoxantrone-DNA interactions. Differential pulse and square wave voltammetry were applied to develop an electroanalytical procedure for the determination of mitoxantrone and evaluate its interaction with dsDNA or ssDNA immobilized on the electrode surface. The results demonstrate that MTX interaction with DNA is not specific to either guanine or adenine bases. The kinetics of the mitoxantrone-DNA interaction is slow and damage to DNA was followed with time.     

Sensor-tissue interactions in neurochemical analysis with carbon paste electrodes in vivo

Characterization of voltammetric signals recorded with microelectrodes in the living brain is fraught with difficulties. In addition to being anatomically complicated, brain tissue presents the analytical electrochemist with a complex chemical environment that includes surfactants (lipids), electrode poisons (proteins), electrocatalysts such as glutathione and ascorbic acid, and a tissue matrix that both restricts mass transport to the electrode surface and reacts physiologically to the presence of the probe. Identification of electrochemical signals recorded in vivo with carbon paste electrodes is discussed in the context of these problems. This examination shows that modification of both the electrode surface by tissue, and of the tissue environment by the electrode have important implications for voltammetric signal analysis in vivo. Despite these problems, valuable data on the relationship between behaviour and chemical changes in the brain can be obtained using in vivo electrochemical techniques.     

Electrochemistry in microscopic domains. 1. The electrochemical cell and its voltammetric and amperometric response

Microscopic aqueous sample droplets of nano- and picoliter volumes were formed on the bottom of a polystyrene dish under water-saturated heptane. The electrochemical cell consisted of a beveled carbon fiber microdisk working electrode and a reference electrode with a miniature junction, both inserted into the studied droplet. Both electrodes had a nominal tip diameter of 7.5 microns. Cyclic voltammetry and chronoamperometry in droplets of 3.3 mM ruthenium hexaammine trichloride in 0.1 M KCl solution were performed with this system. The experiments revealed for the first time major deviations in both voltammetric and amperometric microelectrode behavior in picoliter domains as compared to nanoliter volume and bulk solution. The concept and criteria of electrochemical microscopicity of volume is discussed. This work also provides a simple and robust experimental model system to verify electrochemical experiments in restricted domains such as in or near single biological cells or in microscopic tissue cavities. The methodology developed has, however, more general analytical and physicochemical applications as well.     

电极端面尺寸对IF钢镀锌板点焊性能的影响

对DX54D冷轧IF钢镀锌板进行点焊试验,研究了焊接工艺参数及电极端面尺寸对镀锌板点焊性能、焊点拉剪性能及熔核尺寸的影响。结果表明:随着焊接电流的增加,焊点的拉剪强度和熔核尺寸均增大,当电流过大而发生飞溅时,焊点的拉剪强度和熔核尺寸开始降低。随着电极端面半径的减小,电极与工件的实际接触面积减小,引起电流密度升高,导致在相同焊接时间条件下得到相同熔核尺寸和焊点拉剪强度所需焊接电流降低。     

活性炭纤维负载CuO改性及其性能表征

以Cu(NO_3)_2溶液作为前躯体,采用浸渍–煅烧法对盐酸预处理后的活性炭纤维(activated carbon fiber,ACF)毡进行负载氧化铜化学改性,制备CuO/ACF电极材料。通过扫描电镜(SEM)、X射线光电子能谱仪(XPS)、比表面积及孔径分析仪以及傅立叶变换红外光谱仪(FTIR)对ACF及其负载CuO后的形貌与结构、元素组成、比表面积、孔径等进行观察与分析,并利用电化学工作站测试其电化学性能。结果表明:经过负载CuO化学改性的CuO/ACF电极材料,比表面积及孔容较改性前分别下降31.94%和33.95%,表面含氧基团增多,出现明显的Cu—O键,CuO/ACF电极材料中Cu元素的质量分数为13.7%;负载CuO后比电容升高17.95%,电吸附性能提高。CuO/ACF材料可作为电极材料用于去除废水中的无机盐离子。     

谷氨酸-纳米金-石墨烯修饰的离子液体碳糊电极测定水样中铅的研究

制备了谷氨酸-纳米金-石墨烯新型修饰电极, 并用该电极实现了水样中铅的灵敏测定。用电化学方法依次将石墨烯和纳米金电沉积在以N-丁基吡啶六氟磷酸盐为粘合剂和修饰剂的碳糊电极表面, 戊二醛通过共价键合连接谷氨酸, 制备了谷氨酸-纳米金-石墨烯修饰的离子液体碳糊电极。结果表明, 该电极表面存在的石墨烯和纳米金, 极大地提高了电极的电化学性能, 谷氨酸和石墨烯分别具有良好选择性和导电性, 使传感器对Pb²⁺的信号响应和选择性均得到提高。在最佳实验条件下, pH 5.3的醋酸盐缓冲溶液中, 铅离子的浓度在1.0 × 10^-9~ 4.0 × 10^-6 mol/L范围内与峰电流呈良好的线性关系, 检出限为3.0 × 10^-10 mol/L(3σ)。建立的方法应用于工业和生活废水、井水、雨水样品的测定, 测定结果与原子吸收光谱法的测定结果一致, 相对标准偏差在3.0%～3.8%之间。     

A new technique for measuring the temporal characteristics of the carbon fibre microelectrodes in in vivo voltammetry at millisecond time intervals

A common approach to test the time-response of carbon fibre microelectrodes entails the use of a flow injection system which allows delivery of a bolus of test compound in the flow stream to a detector electrode. The introduced bolus is distorted from its original form by convective and dispersive forces during the period of transport from the injector to the detector electrode in the connection tubing and couplings. Thus, the flow injection system allows one to change the medium in the vicinity of the electrode in about 100-200 ms. We describe here a simple falling drop system, which is an easy to use for calibration of the carbon fibre microelectrodes with respect to their sensitivity and time-response. This system does not have a loop injector and minimizes problems associated with convective and dispersive bolus distortion. It allows one to change the medium in the vicinity of the electrode in less than 10 ms. With this system, the sensitivity and the temporal resolution of the electrodes may be easily and rapidly estimated in a single experiment. The temporal resolution of the untreated, uncoated carbon fibre cylinder electrode of 300 microns tip length in response to dopamine was estimated as 1.49 +/- 0.1 microM/ms (M +/- SEM, n = 36, rise) and 0.051 +/- 0.003 microM/ms (n = 36, wash-out) on the half of amplitude of electrochemical response which was monitored by constant potential amperometry.     

Memory complaints in epilepsy: correlations with cognitive performance and neuroticism

Experimental results are presented to show that the adhesion force is the single most important limiting factor in high-resolution atomic force microscopy of DNA in air, prepared by the cytochrome-C-assisted spreading method. It is also shown that humidity plays a minor role in the control of probe force. Using a pure carbon film as the substrate to clean the AFM tip prior to imaging, it is demonstrated that 4-6 nm resolution on DNA can be routinely obtained by the atomic force microscope with commercial Si3N4 pyramid cantilevers. We also show that in organic solvents a resolution of up to 3 nm can be obtained under optimal conditions.     

以阵列二氧化钛纳米棒为载体制备一体化析氧电极

以碳纸为支撑体,氯铱酸为前体,利用二氧化钛纳米棒阵列作为载体,采用浸渍-热分解法成功制备IrO₂-TiO₂/C一体化析氧电极.通过扫描电镜 (SEM)、XRD、XPS和电化学方法——循环伏安 (CV)、交流阻抗 (EIS) 等手段,研究载体形貌对析氧电极性能的影响.结果表明:二氧化钛载体能有效抑制支撑体碳纸在高电位下的腐蚀,当电压为2.4 V时,极化电流才仅为13.2 mA/cm2,一体化析氧电极积分电荷由87.2 mC/cm2增至178.5 mC/cm2,电极电化学反应阻抗由3.13 Ω·cm2降低到1.62 Ω·cm2,极大地提高了析氧电极的接触面积和催化剂的电催化活性.      

Hydration force in the atomic force microscope: A computational study

Using a hard sphere model and numerical calculations, the effect of the hydration force between a conical tip and a flat surface in the atomic force microscope (AFM) is examined. The numerical results show that the hydration force remains oscillatory, even down to a tip apex of a single water molecule, but its lateral extent is limited to a size of a few water molecules. In general, the contribution of the hydration force is relatively small, but, given the small imaging force ( approximately 0.1 nN) typically used for biological specimens, a layer of water molecules is likely to remain "bound" to the specimen surface. This water layer, between the tip and specimen, could act as a "lubricant" to reduce lateral force, and thus could be one of the reasons for the remarkably high resolution achieved with contact-mode AFM. To disrupt this layer, and to have a true tip-sample contact, a probe force of several nanonewtons would be required. The numerical results also show that the ultimate apex of the tip will determine the magnitude of the hydration force, but that the averaged hydration pressure is independent of the radius of curvature. This latter conclusion suggests that there should be no penalty for the use of sharper tips if hydration force is the dominant interaction between the tip and the specimen, which might be realizable under certain conditions. Furthermore, the calculated hydration energy near the specimen surface compares well with experimentally determined values with an atomic force microscope, providing further support to the validity of these calculations.     

Optimizing recording capabilities of the Utah Intracortical Electrode Array

The Utah Intracortical Electrode Array is a unique silicon-based monolithic structure designed for use as a multichannel interface to the central nervous system. In this paper, we describe a series of acute experiments designed to determine the neural recording capabilities of this electrode array and the dependence of the signal-to-noise ratio (SNR) of the recordings on the electrode surface area (length of metallized tip). We found that both separable unit and multiunit cluster responses could be recorded. Additionally, high SNR recordings could be achieved for some electrodes (with electrode tip lengths of 30-220 microns), while recordings with signals substantially greater than the noise could be made from most of the electrodes provided that the proper electrode surface area was used. The demonstrated recording capabilities of the Utah Intracortical Electrode Array and its unique three-dimensional structure should form the basis for innovative physiological investigations into the functional organization of the cortex as well as for long term neuroprosthesis development.     

聚L-天冬氨酸/多壁碳纳米管复合膜修饰玻碳电极测定亚硝酸根

采用滴涂法和电聚合法制备了聚L-天冬氨酸/多壁碳纳米管复合膜修饰玻碳电极,利用循环伏安(CV)法研究了亚硝酸根 ( NO^-₂) 在该修饰电极上的电化学行为,建立了一种电化学测定NO^-₂的新方法。实验结果表明,该修饰电极对于 NO^-₂的氧化具有良好的电催化性能,并且显著促进 NO^-₂在电极表面的电化学过程。利用差分脉冲伏安法测定,在2.0 × 10^-6~2.0 × 10^-4 mol/L浓度范围内,NO^-₂的氧化峰电流与浓度呈现良好的线性关系,相关系数为 0.998 9。信噪比为 3 时,NO^-₂的检出限为 2.0 × 10^-7 mol/L。方法成功地用于环境水样中NO^-₂测定。     

碳/氧化锌纳米线阵列/泡沫石墨烯电化学检测叶酸

通过化学气相沉积法制备三维(3D)泡沫石墨烯(GF),然后利用水热合成法在泡沫石墨烯表面生长氧化锌纳米线阵列(ZnO NWAs),再利用化学气相沉积法在其表面沉积碳(C),得到碳/氧化锌纳米线阵列/泡沫石墨烯(C/ZnO NWAs/GF)复合材料.用该复合材料做电极,采用电化学方法检测叶酸(FA).结果表明,三维泡沫石墨烯具有和模板泡沫镍一样的三维孔状结构,ZnO NWAs均匀且垂直地生长在泡沫石墨烯表面,碳沉积在ZnO NWAs表面.在线性范围为0~60 μmol·L-1内,C/ZnO NWAs/GF电极检测FA时,灵敏度为0.13 μA·μmol-1·L,且在尿酸(UA)干扰下检测FA具有良好的选择性.C/ZnONWAs/GF电极有良好的稳定性和重复性.