Improvements in the selectivity of electrochemical detectors for liquid chromatography and flow injection analysis using the self-assembled n-alkanethiol monolayer-modified au electrode

4-Aminophenol (4-AP), paracetamol (PRCT), norepinephrine (NE), and dopamine (DA) (all somewhat hydrophobic compounds) were HPLC electrochemically detected while the signals from uric acid (UA) and ascorbic acid (AA) (both hydrophilic compounds at the pH studied) were minimized, taking advantage of the permselectivity of the self-assembled n-alkanethiol monolayer (C-10-SAM)-modified Au electrodes based on solute polarity, The effects of various factors, such as the chain length of the n-alkanethiol modifier, modifying time, and pH value, on the permeability of C-10-SAM coatings were examined, The calibration curves, linear response ranges, detection limits, and reproducibilities of the EC detector for 4-AP, PRCT, NE, and DA were obtained, The result shows that the EC detector can be applied in the chromatographic detection of 4-AP, PRCT, NE, and DA in urine, effectively removing the influence of UA and AA in high concentrations existing in biological samples. As a result, a great improvement in the selectivity of EC detectors has been achieved by using Au electrodes coated with neutral n-alkanethiol monolayer.

Dendrimers as "controllers" for modulation of electrodeposited silver nanostructures

Electrodeposition of silver nanostructures on a polyamidoamine (PAMAM) dendrimers-modified surface has been reported. The assembled PAMAM monolayer film was used as a substrate for electrodeposition. We found that the PAMAM dendrimers obviously affected nucleation growth and silver nanostructures (spherical, dendritic and "fish bone" shapes) were obtained, which were different from those deposited on unmodified surfaces. It was attributed to the unique structures and properties of PAMAM dendrimers compared with linear polymers.

Heteroepitaxial gold (111) rings on mica substrates

Two-dimensionally arranged gold rings were prepared by depositing a polymeric membrane bearing a dense array of uniform pores onto a mica substrate, filling the pores with a solution of a gold precursor, evaporation of the solvent and calcinations. The epitaxy of gold rings is confirmed by x-ray diffraction measurements, and the epitaxial relationship between gold rings and the mica was found to be Au(111)[1-10]parallel to mica(001)[010]. The polar and azimuthal angular spreads are 0.3 degrees and 1 degrees, respectively, which is at least equal to or better than the quality of the corresponding epitaxial gold-film on mica. (c) 2005 American Institute of Physics.

以金属为缓冲层在Si（111）上分子束外延GaN及其表征

用电子束蒸发方法在Si（111）衬底上蒸发了Au/Cr和Au/Ti/Al/Ti两种金属缓冲层,然后在金属缓冲层上用气源分子束外延（GSMBE）生长GaN.两种缓冲层的表面都比较平整和均匀,都是具有Au（111）面择优取向的立方相Au层.在Au/Cr/Si（111）上MBE生长的GaN,生长结束后出现剥离.在Au/Ti/Al/Ti/Si（111）上无AlN缓冲层直接生长GaN,得到的是多晶GaN;先在800℃生长一层AlN缓冲层,然后在710℃生长GaN,得到的是沿GaN（0001）面择优取向的六方相GaN.将Au/Ti/Al/Ti/Si（111）在800℃下退火20min,金属层收缩为网状结构,并且成为多晶,不再具有Au（111）方向择优取向.

硅（111）和金（111）基底自组装膜表面纳米图案化与功能化

利用导电原子力显微镜在烷基化自组膜/Si(111)和巯基自组膜/Au(111)上加工纳米模板,结合组装的方法构建功能化纳米图案。在烷基化自组膜/Si(111)上施加偏压可以得到SiO2纳米图案,此图案可以做功能化模板,将图案化区域组装胺基作为端基的硅烷后,通过1-乙基-3-（3-二甲基氨基丙基）碳二亚胺盐酸盐(EDC)/N-羟基琥珀酰亚胺(NHS)试剂活化共价结合11-巯基十一酸(MUA)稳定的金纳米粒子,得到金纳米粒子功能化纳米图案。在烷基硫醇自组装膜/Au(111)施加偏压可以选择性移除自组装膜,移除自组装膜后新暴露的金可以用做纳米模板,在此模板上组装MUA后通过EDC/NHS活化共价键合溶菌酶,得到蛋白质功能化的纳米点阵图案。

A novel hydrogen peroxide sensor based on horseradish peroxidase immobilized in DNA films on a gold electrode

A novel third-generation hydrogen peroxide (H2O2) biosensor was developed by immobilizing horseradish peroxidase (HRP) on a biocompatible gold electrode modified with a well-ordered, self-assembled DNA film. Cysteamine was first self-assembled on a gold electrode to provide an interface for the assembly of DNA molecules. Then DNA was chemisorbed onto the self-assembled monolayers (SAMs) of cysteamine to form a network by controlling DNA concentration. The DNA-network film obtained provided a biocompatible microenvironment for enzyme molecules, greatly amplified the coverage of HRP molecules on the electrode surface, and most importantly could act as a charge carrier which facilitated the electron transfer between HRP and the electrode. Finally, HRP was adsorbed on the DNA-network film. The process of the biosensor construction was followed by atomic force microscopy (AFM). Voltammetric and time-based amperometric techniques were employed to characterize the properties of the biosensor derived. The enzyme electrode achieved 95% of the steady-state current within 2 s and had a 0.5 mu mol l(-1) detection limit of H2O2. Furthermore, the biosensor showed high sensitivity, good reproducibility, and excellent long-term stability.

Self-assembling process of alkanethiol monolayers on gold surface via underpotential deposition

It was demonstrated feasible that underpotential deposition(UPD) of copper on a monolayer-modified gold substrate can be used to determine the gold electrode area. The deposition and stripping of a Cu adlayer can take Place reversibly and stably at a bared or a self-assembled monolayer modified gold electrode. The growth kinetics of decanethiol/Au was also investigated via Cu UPD. The difference between the assembling kinetics determined by UPD and that by quartz crystal microbalance measurements reveals the configuration transmutation of the assembled molecules from a disordered arrangement to an ordered arrangement during the self-assembling processes.

Electrochemical scanning tunneling microscopy and electrochemical quartz crystal microbalance study of the adsorption of phenanthraquinone accompanied by an electrochemical redox reaction on the Au electrode

In situ electrochemical scanning tunneling microscopy (ECSTM) and an electrochemical quartz crystal microbalance (EQCM) have been employed to follow the adsorption/desorption processes of phenanthraquinone (PQ sat. in 0.1 mol l(-1) HClO4, solution) accompanied with an electrochemical redox reaction on the Au electrode. The result shows that: (1) the reduced form PQH(2) adsorbed at the Au electrode and the desorption occurred when PQH(2) was oxidized to PQ; (2) the adsorption process initiates at steps or kinks which provide high active sites on the electrode surface for adsorption, and as the potential shifts to negative, a multilayer of PQH(2) may be formed at the Au electrode; (3) the reduced PQH(2) adsorbed preferentially in the area where the tip had been scanned continually; this result suggests that the tip induction may accelerate the adsorption of PQH(2) on the Au(111) electrode. Two kinds of possible reason have been discussed; (4) high resolution STM images show the strong substrate lattice information and the weak monolayer adsorbate lattice information simultaneously. The PQH(2) molecules pack into a not perfectly ordered condensed physisorbed layer at potentials of 0.1 and 0.2 V with an average lattice constant a = 11.5 +/- 0.4 Angstrom, b = 11.5 +/- 0.4 Angstrom, and gamma = 120 +/- 2 degrees; the molecular lattice is rotated with respect to the substrate lattice by about 23 +/- 2 degrees. (C) 1997 Elsevier Science S.A.

Orientation and electrocatalysis of riboflavin adsorbed on carbon substrate surfaces

Based on scanning tunnelling microscopy and electrochemical measurements, orientation and electrocatalytic function of riboflavin adsorbed on carbon substrates have been described for the first time. Scanning tunnelling micrographs show clearly that tip induction may result in an orientation change of the adsorbed riboflavin molecule on highly oriented pyrolytic graphite from the initially vertical orientation to the stable flat form. The adsorbed riboflavin as an effective mediator can accelerate the reduction of dioxygen which accepts two electrons from the reduced riboflavin to generate hydrogen peroxide. The rate constants of the electrocatalytic reaction in various pH solutions were determined using a rotating disc electrode modified with riboflavin. The pH effect and possible catalytic mechanism are discussed in detail.

DIRECT ELECTROCHEMICAL REACTIONS OF CYTOCHROME-C AT IODIDE-MODIFIED ELECTRODES

Quasi-reversible and direct electron transfer was observed between an iodide-modified Au electrode and cytochrome c, as well as between cytochrome c in an iodide-containing solution and a bare Au electrode. The results suggest that an electrostatic intera

分子组装体的扫描探针显微学研究

本文简要评述了扫描探针显微学研究的发展过程、目前状况及发展方向，着重介绍了扫描探针显微学(SPM)在分子组装体研究中的一些应用。采用扫描探针显微学结合电化学的方法对自组装膜(SAMs)、表面活性剂(surfactant)、纳米颗粒(nanoparticles)等分子组装体系进行了研究，并结合IR、QCM、XPS、XRD等多种手段对分子组装体在电极表面的形态和结构进行了探讨。主要结果如下：1．SPM研究以杂多酸为基础的分子组装体我们通过将AsMo_(11)V0_(40)~(4-)杂多酸阴离子从其酸性溶液中自吸附至金表面的方法，制备了一类新的无机自组装膜。我们利用QCM、STM和电化学方法分别研究了AsMo_(11)VO_(40)~(4-)自组装膜的吸附过程、在Au表面的结构和电化学性质。QCM数据表明这个自组装过程可以用Langmuir吸附等温式来描述，其吸附自由能为-20 KJ/mol。 通过QCM测得的AsMo_(11)VO_(40)~(4-)自组装膜的表面覆盖度的最大值为1.7 * 10~(-10)mol/cm~2，这相当于一个AsMo_(11)VO_(40)~(4-)阴离子的密堆积单层。AsMo_(11)VO_(40)~(4-)自组装膜的循环伏安图上出现三对可逆的氧化还原峰，每对峰所对应的自组装膜的表面覆盖度都亦为1.78 * 10~(-10) mol/cm2，和QCM结果一致。现场STM图像显示AsMo_(11)VO_(40)~(4-)自组装膜十分的均一没有如何多层或聚集体的结构。高分辨STM图进一步显示在Au(111)表面的sMo_(11)VO_(40)~(4-)自组装膜于+0.7 V(vs．Ag | AgCl)表现出二维有序的四方晶体结构，晶格间距为10-11 A。这个值与sMo_(11)VO_(40)~(4-)阴离子的直径十分接近。从STM图我们也估算出AsMo_(11)VO_(40)~(4-)自组装膜的表面覆盖度为1.8 * 10~(-10) mol/cm~2，这和QCM以及电化学的实验结果都很接近。我们进一步研究了一种新的以杂多酸为基础的有机无机复合膜--砷钼钒杂多酸的十一烷基吡啶盐(CPMVA)--的制备、结构和电催化性质。通过在这种盐的丙酮溶液中循环电位扫描，我们可以在HOPG电极表面制备稳定的CPMVA膜。我们利用XPS、STM和电化学多种手段来表征CPMVA膜的结构和性质。这些研究表明：在新剥离HOPG表面CPMVA膜的结构为自聚集的分子团，而在预阴极化HOPG表面CPMVA膜的结构为自有序单层。CPMVA膜在酸性和丙酮溶剂中部表现出可逆的氧化还原动力学行为，这说明这种新类型的膜甚至能在有机溶剂中用作催化剂。当溶液的pH值大于7.O时，CPMVA膜也能维持其稳定性，它对pH值的依赖程度明显小于其无机物形式的膜(H_4AsMo_(11)VO_(40))对pH值的依赖程度。CPMVA膜对Br0_3-的还原表现出很好的电催化活性，催化电流与BrO_3~-的浓度的平方成正比。这种有很高稳定性的新类型杂多酸膜在催化剂领域中将有很广阔的应用前景。2．电化学STM研究吸附在金属表面的表面活性剂聚集体由于电位诱导引起的结构变化表面活性剂在表面的吸附已广泛地被用于限制电极表面的活性和稳定溶液中的胶体和纳米粒子，但是人们对表面活性剂在电极表面的结构和由于电位变化所引起的结构改变并不清楚。在这个工作中我们利用现场STM观察了电位控制下表面活性剂十二烷基磺酸钠(SDS)在Au(111)表面的吸附。STM图像显示通过控制电位SDS在Au(111)表面有一从半圆柱胶束单层向致密双层膜过渡的构象变化。我们也建立了SDS聚集体在Au(111)表面电位诱导结构变化的模型。就我们所知，这是第一次系统地研究表面活性剂聚集体在金属表面的电位诱导结构变化。3．在固体表面构筑有序的聚苯胺分子导线我们提出了一种新的通过分子设计构筑有序聚苯胺分子导线的新方法。首先，根据Saveant的方法我们在HOPG表面修饰上有序的4-氨基苯单层，然后溶液中的苯胺分子通过阶跃的方法被层层电聚合在4-氨基苯单层修饰的HOPG表面，形成有序的聚苯胺分子导线。FTIR-ERS和XPS结果证实HOPG表面上形成了聚苯胺。SPM图显示在HOPG表面的聚苯胺平面结构为有序的3~(1/2) * 3~(1/2) R 30°。小角X-射线反射结果表明聚苯胺分子导线是垂直站立在HOPG表面。电化学测量进一步表明聚苯胺分子导线的形成有利于加速电子传递速率。这种先分子设计后电聚合的方法可能会成为一类在固体表面制备有序导电聚合物分子导线的新方法。依据上一个实验，我们在金表面通过自组装的方法构筑了绝缘分子导线。我们选择β-环糊精(β-CD)作为包络4-氨基硫酚的理想主体分子。β-CD和4-氨基硫酚形成的包络物首先被自组装到Au表面，然后也通过阶跃的方法被层层电聚合在自组装膜修饰的Au表面，形成有序的聚苯胺分子导线。FTIR-ERS和XPS结果证实Au表面上形成了聚苯胺。低电流STM(LC-STM)图像表明在Au(111)表面的聚苯胺分子线为六角的二维有序，分子与分子之间的最相邻距离为15.5±0.5 A。这种先进行CD超分子自组装后电聚合的方法可能会成为一类制备导电聚合物绝缘分子导线的新方法。4．SPM研究在HOPG表面电化学合成的纳米材料我们通过脉冲恒电位方法从稀的苯胺酸性溶液(1mM苯胺 + 1 M HClO_4)在HOPG表面制备聚苯胺纳米颗粒。我们利用FTIR-ERS、XPS、TM-AFM手段来表征聚苯胺纳米颗粒的组成和结构。FTIR-ERS和XPS结果表明制得的聚苯胺纳米颗粒主要以亚胺形式存在。TM-AFM图像显示分散于HOPG表面的聚苯胺纳米颗粒的表面覆盖度约为10~(10)cm~(-2)。这些纳米颗粒都为圆盘型，直径为200到600埃，高度为10到30埃。这些纳米颗粒的大小随聚合电量由5.7 μC/cm~2增加到19.3 μC/cm~2而增大。我们提出了一种通过分子设计在HOPG表面制备金属纳米粒子的新方法。第一步，根据Saveant的方法我们在HOPG表面修饰上一个4-氨基苯单层。第二步，通过配位相互作用Ag~+能在4-氨基功能化的HOPG表面形成单层。第三步，通过脉冲恒电位方法我们就能在4-氨基苯功能化的HOPG制备Ag纳米颗粒。电化学测量证明了在HOPG表面上Ag纳米颗粒的形成。STM图像显示通过这种方法制得的Ag纳米颗粒的大小十分均一且在HOPG表面上的分散度很高。这种新方法可被广泛地用来在碳表面制备各种金属纳米粒子。

纳米功能界面的电化学和扫描探针显微镜（SPM）研究

本文简要评述了扫描探针显微学研究的发展过程、目前状况及发展方向，着重介绍了扫描探针显微学(SPM)在分子组装体研究中的一些应用。采用扫描探针显微学结合电化学的方法对自组装膜(SAMs)、纳米颗粒(nanoparticles)、有机无机纳米复合材料(composite material)体系进行了研究，并结合XPS、SEC等多种手段对分子组装体在电极表面的形态和结构进行了探讨。主要结果如下：1．STM研究金属纳米颗粒的隧道成像机理利用柠檬酸三钠还原高氯酸金的反应制备了金的溶胶纳米粒子。将对氨基硫酚自组于金单晶面(Au(111))上形成致密有序的单层；并以此为基底进一步将金溶胶纳米粒子组装于自组膜表面，得到固定化纳米粒子的次单层。用扫描隧道显微镜进行了表征，对金溶胶纳米粒子隧道成像的微观机理作了探讨，提出双势垒隧穿的电子传输界面模型。对扫描隧道显微镜下金溶胶纳米粒子的图像失真作解释。2．共轭有机小分子的导电性的研究利用保护和去保护的方法对带巯基的共轭有机小分子进行了合理地操纵，使其稳定性在我们构筑电化学界面的过程中得到了保证。我们用自组装(SAM)技术将这种共轭有机小分子首先吸附于金电表面，然后用稀氨水将其水解得到致密的共轭有机小分子的单层。在金/SAM二次基底的基础上利用巯基于金的强烈的化学键合力用电化学沉积的方法和湿化学还原的方法得到的金纳米粒子组装于电极表面，得到了金/有机分子层/金的夹心结构，并对构筑这种夹心结构的每一步骤用扫描探针显微镜(SPM)和电化学循环伏安法(CV)进行了表征，实验结果表明，此种共轭有机小分子利用巯基化学键合金属金时，电子能够快速通过这种夹心结构，为分子电子学中之基本问题“分子导线”连接纳米级的分子器件时电子能否在其间传导给出了直接的电化学证明。3．纳米复合材料的合成与表征我们用相转移方法合成了表面功能化的纳米粒子。首先，根据将HAuCl_4溶解于水相中，将Bu_4NClO_4作为相转移试剂、带巯基的有机小分子作为表面修饰剂，NaBH_4和柠檬蒜三钠作为还原剂溶解于硝基苯有机相中。将两相剧烈混合，在混合过程中HAuCl_4在水/硝基苯界面处被有机相中的还原剂还原成金属纳米粒子，刚生成的纳米粒子由于强烈的金硫键合作用而被带巯基的有机小分子表面功能化，而且能在有机溶剂中稳定存在。于是得到的表面功能化的纳米粒子在有机溶剂中的稳定胶体溶液。我们合成了表面被12烷基硫醇和巯基噻酚修饰的金纳米粒子。基于这些表面功能化且带有电化学反应性功能基团的纳米粒子，我们在电化学合成聚噻酚的系统中加入这种具有表面反应性的纳米粒子得到了有机/无机纳米复合材料。对这种复合材料我们用扫描探针显微镜(SPM)、电化学交流阻抗谱(ElS)、X-射线光电子能谱(XPS)进行了表征，结果表面纳米粒子能稳定存在于聚合物基体中，而且这种复合材料的电子传输性能远远大于同等条件下的聚合物膜。