The adsorption of dopamine on gold and its interactions with iron(III) ions studied by microcantilevers

The adsorption of dopamine (DA) molecules on gold and their interactions with Fe3+ were studied by a microcantilever in a flow cell. The microcantilever bent toward the Au side with the adsorption of DA due to the change Of Surface stress induced by the intermolecular hydrogen bonds of DA or the charge transfer effect between adsorbates and the Substrate. The interaction process between DA adsorbates and Fe3+ was revealed by the deflection curves of microcantilever. As indicated by the appearance of a variation during the decline of curves, two steps were observed in the curve at relative high concentrations of Fe3+. In this case, Fe3+ reacted with DA molecules only in the outer layers and the complexes removed with solution. Then Fe3+ reacted further with DA molecules forming the surface complex in the first layer next to the gold. At this stage, the stability Of Surface complexes was time dependent, i.e., unstable initially and stable finally. This may be due to the surface complexes change from mono-dentate to bi-dentate complexes. In another case, i.e., at relative low concentration of Fe3+, only the first step was observed as indicated by the absence of a variation.

Interaction Between Tripeptide Gly-Gly-His and Cu2+ Probed by Microcantilevers

Gly-Gly-His tripeptide modified microcantilever was developed by carbodiimide attachment of the Gly-Gly-His tripeptide onto a 3-mercaptopropionic acid(MPA) modified gold surface. The interaction of peptide with Cu2+ ion was studied. At a relative high concentration of Cu2+, the cantilever bent toward the gold side initially as the N atom of imidazole ring and carboxyl group in different peptide coordinate with Cu2+, which results in a tensile surface stress. And then the reversed deflection of microcantilever was observed, which implies that the peptide-Cu2+ complex are formed with conformation transition. In another case, i.e., at a relative low concentration Of Cu2+, only the process of conformation transition was observed due to the coordination mode can not be formed initially. The influences of pH and salt concentration of the test solution on the performance of the sensor were studied. The results show that the maximum deflection was obtained at pH 7 and the bonding Of Cu2+ to the Gly-Gly-His tripeptide was inhibited due to the formation Of CuClx2-x.

Deformation Of Pdms Membrane And Microcantilever By A Water Droplet: Comparison Between Mooney-Rivlin And Linear Elastic Constitutive Models

In this paper, we studied the role of vertical component Of Surface tension of a water droplet on the deformation of membranes and microcantilevers (MCLs) widely used in lab-on-a-chip and micro-and nano-electromechanical system (MEMS/NEMS). Firstly, a membrane made of a rubber-like material, poly(dimethylsiloxane) (PDMS), was considered. The deformation was investigated using the Mooney-Rivlin (MR) model and the linear elastic constitutive relation, respectively. By comparison between the numerical solutions with two different models, we found that the simple linear elastic model is accurate enough to describe such kind of problem, which would be quite convenient for engineering applications. Furthermore, based on small-deflection beam theory, the effect of a liquid droplet on the deflection of a MCL was also studied. The free-end deflection of the MCL was investigated by considering different cases like a cylindrical droplet, a spherical droplet centered on the MCL and a spherical droplet arbitrarily positioned on the MCL. Numerical simulations demonstrated that the deflection might not be neglected, and showed good agreement with our theoretical analyses. (C) 2008 Elsevier Inc. All rights reserved.

微悬臂传感器研究生物相关分子与金属离子相互作用

利用微悬臂传感器研究了生物相关分子与金属离子的相互作用过程及检测。本论文取得的主要成果如下： （1）利用微悬臂传感器在流动体系中研究了多巴胺在金表面的吸附过程及其与铁离子的相互作用与检测。结果表明，多巴胺在金表面多层吸附，通过分子间氢键和表面电荷转移效应诱导悬臂向镀金面偏转。多巴胺与铁离子的作用过程可以分为两个阶段：第一阶段，铁离子与外层多巴胺络合，并脱离悬臂表面；第二阶段，铁离子与靠近金表面层多巴胺形成化合物，并且可能先以不稳定的单齿络合，而后生成稳定的双齿螯合。利用电化学和XPS手段对上述过程进行了表征，并设计实验对推理进行了验证。多巴胺修饰的悬臂还是一个很好的铁离子传感器，具有较高的灵敏度和选择性，检测限能达到510-10 mol/L。 （2）利用微悬臂传感器在流动体系中研究了组氨酸在金表面的吸附过程及其与铁离子的相互作用与检测。考察了不同pH值和Cl-浓度对组氨酸吸附及其与铁离子作用的影响。结果表明，随着pH值的增加，组氨酸的吸附构象会发生变化，并且导致组氨酸的吸附稳定性、吸附量和分子间静电斥力增大。在碱性溶液中咪唑环较羧基基团优先在金表面发生吸附。组氨酸修饰悬臂与铁离子作用的结果表明，在中性和碱性溶液中组氨酸能与铁离子在悬臂表面形成稳定的化合物。两者的作用过程分为两个阶段：第一阶段组氨酸中咪唑环上远离金表面的N3原子与铁离子形成单齿配合物，此时化合物之间通过静电斥力使得悬臂向下偏转；第二阶段，组氨酸上靠近金表面的N1原子开始与铁离子作用，通过分子构象的改变最终与邻近的单齿配合物形成双齿配合物，并开始逐渐覆盖悬臂表面，形成网络结构使得悬臂表面形成一种收缩的应力，而使悬臂向镀金面偏转。第二阶段不但与作用时间有关，而且同氯离子的浓度紧密关联。只有当氯离子浓度大于或等于50mmol/L时，才会出现悬臂向镀金面偏转的现象。组氨酸修饰的悬臂还是一个很好的铁离子传感器，检测限能达到510-9 mol/L级。 （3）将肽（Gly-Gly-His）共价键合到MPA修饰的悬臂表面，首先研究肽与Cu2+ 的相互作用过程。研究发现作用过程与Cu2+ 的浓度有关，高浓度时Cu2+ 与肽快速吸附，并通过与不同肽链上的羧基和咪唑环配位诱导悬臂向镀金面偏转；而后肽链上的氮原子与Cu2+配位，同时构象发生变化，由直链转变成折叠状，进而增加链间的作用力使悬臂向反向偏转；而铜离子浓度低时不能实现悬臂表面快速的形成向内的拉力，所以不会产生向镀金面偏转，而直接在构象变化推动悬臂反向偏转。考察了检测过程中溶液pH、离子强度和干扰离子对检测的影响。结果表明该传感器对铜离子有较宽响应范围，最低响应浓度为210-10 mol/L。