L-半胱氨酸自组装膜修饰金电极的电化学特性

采用电化学石英晶体微天平（EQCM）和循环伏安法（CV）研究了L-半胱氨酸在金电极表面形成自组装膜的机理及其电化学性质.结果表明, L-半胱氨酸分子在金电极表面有特性吸附，而且在等电点pH附近因静电引力和氢键作用形成分子对，从而自组装形成双层膜.该膜电极在0.2 mol•L－1的醋酸缓冲溶液中，于－0.2～0.5 V(vs SCE)间CV扫描出现了一对稳定的氧化还原峰，并对抗坏血酸的氧化有良好的催化作用.     

磷钼钨杂多酸-L-半胱氨酸自组装膜电极的电化学性质

磷钼钨杂多阴离子通过分子间静电作用吸附在L-半胱氨酸自组装单分子膜修饰金电极表面,制备了磷钼钨杂多酸-L-半胱氨酸自组装超分子膜电极,探讨了成膜条件.采用循环伏安(CV)、计时库仑(CC)、水平衰减全反射傅立叶变换红外光谱(ATR-FTIR)表征了膜的组成及电化学性质.实验发现,该膜电极在1.0 mol•L－1H2SO4溶液中,于0.8～－0.2 V(υs SCE)间CV扫描出现3对稳定、可逆的氧化还原峰,计时库仑法计算了薄膜内的电子传递系数D为 2.64×10－7 cm2•s－1,初步探讨了膜电极的氧化还原性能.     

二茂铁/L-半胱氨酸修饰电极的电化学行为及电催化性能

利用配对试剂将二茂铁酰胺键合在L-半胱氨酸自组装单层膜(SAM)表面, 制成稳定的二茂铁/L-半胱氨酸修饰电极, 该电极在pH 7.0的磷酸盐缓冲液中有一对很好的氧化还原峰. 运用循环伏安法和交流阻抗谱详细研究了修饰电极的电化学行为, 测得电子转移系数为0.66, 表观电极反应速率常数为6.86 s-1. 该修饰电极对肾上腺素有很好的催化作用, 峰电流与肾上腺素浓度在2.0×10-7～1.0×10-5 mol·dm-3范围内呈现良好的线性关系.     

亚硒酸钠在L-半胱氨酸自组装类生物膜修饰电极上的电化学行为

利用L-半胱氨酸自组装膜修饰金电极(L-Cys,Au/SAMs), 在0.05mol/L H_2SO_4 底液中研究了 Na_2SeO_3 的电化学特性.在0.00～1.30 V (vs. SCE) 电位范围内对微量Na_2SeO_3进行循环伏安扫描,发现L-Cys, Au/SAMs修饰电极在峰电位0.89 V处有灵敏的Se的氧化溶出峰.通过比较裸金电极和修饰电极在Na_2SeO_3 溶液中的电化学特性发现,修饰电极通过巯基中的S与Na_2SeO_3发生氧化还原作用生成Se,且修饰电极对沉积在电极表面的Se的氧化过程具有催化作用.根据Na_2SeO_3在单分子膜上的电化学行为,提出了单分子膜中硫(Au-S)与Se(Ⅳ)作用生成Se的反应机理、Se电化学催化氧化机理及巯基化合物通过生成纳米硒生物吸收Se的类生物膜模型.     

自组装分子印迹单层膜修饰电极对L-丝氨酸的检测

以电沉积多孔金膜为基底,L-丝氨酸为模板分子,L-半胱氨酸为功能单体构建了信号放大的自组装分子印迹单层膜修饰电极.电极对L-丝氨酸浓度响应的线性范围为5.0×10-6～2.0×10-4 mol/L,检出限为4.8×10-7 mol/L,灵敏度为215 mA·L·mol-1.由于多孔金膜有效增加了模板分子的固定量,印迹电极响应性能较无多孔金膜修饰的印迹电极有明显提高.     

席夫碱自组装单分子膜的电化学行为

利用自组装技术将席夫碱硫醇衍生物在金表面形成自组装单分子膜,并初步研究了此自组装单分子膜的电化学行为,发现该席夫碱分子在0.1 mol•L－1的KCl溶液中具有电化学不可逆氧化还原行为，且随着自组装时间的增加表观电极反应速率常数值显著减小,最后减小为0,并对此进行了解释.     

硒杂环化合物(4,5-苯并苤硒脑)在金表面上的自组装

为了寻求新的自组装单分子膜体系,构建新的功能膜,研究了具备平面型的大环共轭硒杂环化合物-- 4,5-苯并苤硒脑(苯并[c]硒二唑,简称苤硒脑)在金表面的自组装单分子膜.通过X射线光电子能谱(XPS)和电化学手段对其进行表征.XPS研究结果表明,自组装形成单分子膜后,苤硒脑分子中Se3d结合能从57.4 eV下降到57.1 eV;表明硒杂环化合物是通过金硒键固定在金表面上的;电化学循环伏安法实验表明,金电极表面上自组装该有机硒后, Fe(CN)63-/4-的氧化还原峰几乎完全消失;以四硼酸钠为底液,测得该化合物自组装在金表面上时,其还原电位在-0.66 V,与在溶液中用裸金电极测得的还原峰电位基本一致.     

金电极上L-半胱氨酸短链分子自组装单层的电化学性能和拉曼光谱研究

用循环伏安法分别测定了金电极表面L-半胱氨酸(L-Cys)和十二硫醇自组装单分子层的电化学行为, 实验发现虽然单层结构排列致密, 但并不能有效地阻碍铁氰化钾与电极间异相电子转移过程, 同时观察到十二烷基硫醇自组装层能较好地阻碍电子转移作用. 运用表面增强拉曼散射光谱技术, 以十二烷基硫醇作为缺陷探针, 从分子水平上证实了L-半胱氨酸自组装单层的稳定性和致密性.     

巯基钴卟啉自组装膜的表征及催化性能

用自制的新型尾式巯基钴（Ⅱ）卟啉在金电极上制成自组装单分子膜,并用ＸＰＳ,ＳＥＭ和电化学的方法进行了表征。该膜对抗坏血酸具有良好的催化作用,其氧化过电位较裸金电极上降低了１４０ ｍＶ,响应电流与抗坏血酸（ＡＡ）的浓度在 ７．８ × １０－５ｍｏｌ／Ｌ～１．０×１０－２ｍｏｌ／Ｌ的范围内具有良好的线性关系,相关系数为 ０．９９８１;检测下限为 １．３ × １０－８ｍｏｌ／Ｌ（富集 １０ｍｉｎ）。     

偶氮苯衍生物自组装膜的表征及组装动力学

报导了4-正辛基-4′-（3－巯基丙氧基）偶氮苯（简称C8AzoC3）自组装膜（Self-AssembledMonolnyersSAMs）的表征及其自组装成膜动力学，接触角滴定、原子力显微镜（AFM）及电化学的实验结果表明，C8AzoC3分子在金表面自组装形成致密有序的流水性单分子膜，并且在电极上没有明显的电化学响应．通过控制组装时间，考察了偶氮苯自组装形成单分子膜的动力学过程，从接触角和电化学数据得到组装过程的速率常数kad为（1.2±0.2）×103mol-1·dm3·s－1；依据不同组装时间形成的自组装膜的特征循环伏安行为，提出了C8AzoC3分子在金表面自组装过程的动态模型．     

Electroanalytical applications of cationic self-assembled monolayers: square-wave voltammetric determination of dopamine and ascorbate

Gold electrodes modified with cationic self-assembled monolayers (SAMs) of 2,2'-dithiobisethaneamine (CYST) and 6,6'-dithiobishexaneamine (DTH) were used for the simultaneous determination of dopamine (DA) and ascorbate (AA). The cationic SAM modified electrodes have several advantages over the bare electrode for the oxidation of AA. A very large (approximately 450 mV) decrease in the overpotential for the oxidation of AA when compared with the bare electrode has been observed at the cationic monolayer-modified electrode. The electrostatic interaction of negatively charged AA with the monolayer shift the oxidation peak potential of AA to less positive potential and enhances the peak current. On the other hand, the positively charged DA is repelled from the monolayer and the oxidation potential shifts to more positive potential when compared to the bare electrode. The electrochemical oxidation of AA at the mixed monolayer of CYST and diethyl disulfide (DEDS) supports the influence of cationic terminal group of the monolayer on the oxidation of AA. Since the oxidation of AA occurs well before the oxidation potential of DA is reached, the homogeneous catalytic oxidation of AA by the oxidized DA has been advantageously eliminated at the monolayer-modified electrode. The cationic self-assembled monolayers successfully detect DA in the presence of high concentration of AA. The sensitivity of the electrode modified with CYST monolayer was found to be 0.036 and 0.021 microA/microM towards AA and DA, respectively.     

Square wave voltammetric sensing of uric acid using the self-assembly of mercaptobenzimidazole

The self-assembled monolayer of a heterocyclic thiol, mercaptobenzimidazole (MBI) on gold (Au) electrode is successfully utilized for the voltammetric sensing of uric acid (UA). The self-assembly of MBI separates the voltammetric signal of UA from the interfering ascorbate (AA). Selective detection of UA in the presence of a large excess of AA or the simultaneous detection of UA and AA is achieved at the MBI monolayer-modified electrode. This electrode can detect as low as 1 microM of UA in the presence of 100-fold excess of AA with excellent reproducibility. The practical utility of the electrode is demonstrated by measuring the concentration of UA in human serum.     

The Influence of Gold Nanoparticles on Simultaneous Determination of Uric Acid and Ascorbic Acid

A three-dimensional L-cysteine (L-cys) monolayer assembled on gold nanoparticles (GNP) providing simultaneous detection of uric acid (UA) and ascorbic acid (AA) was studied in this work. The cyclic voltammetry demonstrated that, at a bare glassy carbon electrode (GCE) or planar gold electrode, the mixture of UA and AA showed one overlapped oxidation peak; whereas when the electrode was modified with GNP, the oxidation peaks for UA and AA were separated. While a GNP modified electrode was further modified with L-cys monolayer (L-cys/GNP/GCE), namely, three-dimensional L-cys monolayer, a better separation for UA and AA response was obtained. Interestingly, the L-cys monolayer-modified planar gold electrode presented a block effect on the oxidation of AA, which was facilitated by the three-dimensional L-cys monolayer attributed to its distinct structure. The pH of solution presented a noticeable effect on the separation of UA and AA at GNP modified electrodes with or without L-cys monolayer. Wide concentration ranges from 2 × 10^?6?1 × 10^?3 M to UA and 2 × 10^?6?8 × 10^?4 M to AA could be obtained at L-cys/GNP/GCE.     

Sodium dodecyl sulfate-modified carbon paste electrodes for selective determination of dopamine in the presence of ascorbic acid

A carbon paste electrode (CPE) modified by a monolayer film of sodium dodecyl sulfate (SDS) was used for detection of dopamine (DA). Cyclic voltammetry demonstrated improved response of the DA sensor. This suggests the effectivity of surface modification of CPE by SDS. Impedance spectroscopy was used for the characterization of CPE surface properties. The effect of SDS concentration on the electrode quality also reveals that SDS formed a monolayer on CPE surface with a high density of negative-charged end directed outside the electrode. As a result, the carbon paste electrode modified with SDS (SDS/CPE) exerted discrimination against ascorbic acid in physiological circumstance. Thus, it can selectively determine dopamine even in the presence of 220-fold AA combined with differential pulse stripping voltammetry. In pH 7.40 phosphate buffer solution, the oxidation peak current on differential pulse voltammograms increases linearly with the concentration of DA in the range of 5.0 x 10(-7) to 8.0 x 10(-4) mol . L(-1) with a detection limit of 5.0 x 10(-8) mol . L(-1). Satisfying results are achieved when detecting the DA in injection and simulated biology sample.     

Electrochemical determination of dopamine in the presence of ascorbic acid and uric acid using the synergistic effect of gold nanoflowers and L-cysteamine monolayer at the surface of a gold electrode

This paper describes a facile and effective method to synthesize gold nanoflowers (AuNFs) by a controllable electrodeposition method induced by a L-cysteamine (L-Cys) monolayer self-assembled on the surface of a gold electrode. The AuNFs/L-Cys/Au electrodes were characterized by field emission scanning electron microscopy (FE-SEM), cyclic voltammetry, and AC impedance spectroscopy methods. This obtained AuNFs/L-Cys/Au electrode exhibits excellent electrocatalytic activity towards the oxidation of dopamine (DA) due to the synergistic effect of AuNFs and a L-Cys monolayer. Differential pulse voltammetry (DPV) experiment results show that the oxidation peak of DA is separated from the oxidation peaks of ascorbic acid (AA) and uric acid (UA), which can be used to detect DA in the presence of AA and UA, and the results are satisfactory.     

在抗坏血酸存在下用L-赖氨酸修饰玻碳电极测定多巴胺

采用电化学氧化法制备了L-广赖氮酸单分子层修饰玻碳电极，研究了多巴胺（DA）和抗坏血酸（AA）在该电极上的电化学行为。结果表明，L-广赖氨酸单分子层修饰玻碳电极不仅能改善多巴胺和抗坏血酸的电化学行为，而且能将多巴胺和抗坏血酸二者在裸电极上的完全重叠的单氧化峰分开成为两个完全独立的氧化峰，循环伏安（CV）图上峰间距为507mV，差分脉冲伏安（DPV）图上峰间距为460mV，由此可实现在AA的共存下对样品中的DA进行选择性测定。     

Simultaneous determination of dopamine and ascorbic acid at a poly(toluidine blue) modified electrode.

A novel polymer modified electrode is discussed in this paper. This resulting electrode can catalyze remarkably toward the electrochemical oxidations of dopamine (DA) and ascorbic acid (AA). Moreover, it can clearly discriminate the electrochemical oxidations of DA from that of AA based on their semi-derivative voltammograms. Hence, a simultaneous determination of DA and AA based on semi-derivative voltammetry at a poly(toluidine blue) modified electrode is suggested. The detection linear range for DA is 0.4 micromol L(-1)-1.5 mmol L(-1), and AA 0.2 micromol L(-1)-2.4 mmol L(-1), respectively. The resulting modified electrode was tentatively used to determine DA and AA in brain tissue.     

Nanostructured gold colloid electrode based on in situ functionalized self-assembled monolayers on gold electrode

A novel method for fabricating nanostructured gold colloid electrode based on in situ functionalization of self-assembled monolayers (SAMs) of 4-aminothiophenol (4-ATP) on gold electrode is proposed. The in situ functionalization of 4-ATP SAMs yields a redox active monolayer of 4′-mercapto-N-phenylquinone diimine (NPQD). When the amino-rich surface is exposed to gold colloid, the citrate-stabilized gold nanoparticles (GNPs) can be anchored onto the surface of the in situ functionalized electrode by the electrostatic interactions and a new nanostructured gold colloid surface was obtained. The mixed monolayers of in situ functionalized product, NPQD, and 1,4-benzenedimethanethiol (BDMT) can provide a more compact and order platform to fabricate GNPs on the electrode surface. The film formed by this technique has the advantages of high organization and uniformity, which could provide a desirable microenvironment to assemble GNPs and facilitate the concentration of the analyte from the bulk solution to the electrode surface. The nanostructured gold colloid electrode has favorable effect on the electrochemical oxidation of naphthol isomers.     

Rapid assembly of photosystem I monolayers on gold electrodes

Photosystem I (PSI) has drawn widespread interest for use in biomimetically inspired energy conversion devices upon extracting it from plants or cyanobacteria and assembling it at surfaces. Here, we demonstrate that a critically dense monolayer of spinach-derived PSI must be formed on an electrode surface to achieve optimal photocurrents, and we introduce a new method for preparing these dense PSI monolayers that reduces the time required for assembly by approximately 80-fold in comparison to that for adsorption from solution. This method consists of applying a vacuum above the aqueous PSI solution during assembly to concentrate PSI and precipitate it into a thick layer onto the surface of various self-assembled monolayers or directly onto the electrode surface. Rinsing with water yields a dense monolayer of PSI that draws approximately 100 nA/cm2 of light-induced current from the gold electrode in the presence of appropriate mediators.     

Electron Transfer through Monolayers of Mixed Long-chain Aliphatic Acids and Alcohols

Properties of monolayers of cetyl, stearyl, and eicosyl alcohols and stearic and behenic acids and their mixtures are studied, along with the kinetics of a redox reaction of hemin adsorbed on these monolayers. Three-dimensional computer models of corresponding monolayers are constructed and compared with their electrochemical behavior. Properties of monolayers of cetyl alcohol in acid and alkaline solutions and stearyl alcohol in acid solutions correspond to package of molecules in a stretched conformation oriented normally to the electrode surface; for the other one-component systems, the monolayer structure is less regular. The hemin redox reaction rate has no correlation whatsoever with the monolayer thickness and is defined by the length of the electron transfer path (over a chain of covalent bonds and through van der Waals contacts between molecules). The stronger the deviation of the conformation of molecules from the stretched one, the shorter the effective path of the electron transfer. In mixed films of stearic acid and cetyl alcohol (1 : 6), it is sometimes possible to keep molecules of stearic acid in a stretched conformation, thus inhibiting the electron transfer along the hydrocarbon chain of this molecule to a maximum extent. The other mixed systems, while making the conformation more stretched, fail to provide for a completely regular structure.