基于挠曲电效应的DNA-微梁变形机理分析

Deformation mechanism analysis of DNA-microcantilevers based on flexoelectric effect. With the development of AFM and M/NEMS, the mechanism by biological/chemical reactions on microstructures has become an important frontier issue. DNA molecules adsorbed to microcantilever is taken as the research object in label-free biodetections. The macroscopic mechanical deformation of DNA-microcantilevers is theoretically studied according to flexoelectric effect. According to the flexoelectricity in biological membranes, the scaling theory of polymer brushes, the electric enthalpy, the ion Boltzmann distribution, and the two-variable method of multilayered beams, DNA molecular structure feature, response characteristics of the solution, electrical distribution, and mechanical properties of non-biological layers are presented. A theoretical model of DNA molecules modified to microcantilever is established according to flexoelectric effect. The relationships of geometrical-physical-chemical properties of DNA biological membranes, the strength-style-size properties of ionic solution, macroscopic mechanical properties of the substrates and deflections of microcantilever is obtained. Considering the substrate surface charge and external electric field, the above theoretical model is expanded. The mechanical response of DNA-microcantilevers is studied under the external electrical stimulation. The influence of external electrical stimulation on electric field of DNA biological membranes and static deflection of microcantilevers are investigated. The corresponding reliability and sensitivity analysis are also carried out. The purpose of this project is to provide a theoretical and technical basis for the transduction of biochemical reactions into nanomechanical response.

随着原子力显微镜和微纳机电系统的迅速发展，对于生化敏感作用在微结构上的信息转换机制研究成为了重要的前沿课题。本项目以无标记生物检测中DNA分子吸附在微梁上为研究对象，具有挠曲电效应的DNA膜与微梁宏观力学变形机理进行理论研究。利用生物膜挠曲电理论、聚合物刷标度理论、电学焓、离子Boltzmann分布以及层合梁两变量方法等，揭示DNA分子的几何结构、反应溶液特质、电荷分布以及层合梁的变形等特性，建立考虑挠曲电效应的DNA-微梁的理论模型，明确DNA膜的几何-物理-化学特性、溶液离子浓度-种类-尺寸特性、基底宏观力学性能与微梁挠度等之间的关系。考虑基底表面电荷、外加电场两方面，扩展以上理论模型，揭示外界环境电学刺激对DNA膜电势分布以及微梁静态挠度的影响机理，进而开展相应的可靠性和灵敏性分析。本项目旨在为基底表面的生化反应转换纳米力学响应提供理论基础和技术基础。

本项目以DNA-微梁复合系统为研究对象，基于挠曲电理论研究了无标记检测中生物传感器的力-电-化耦合特性。将DNA膜视为介电材料，采用自由能密度函数，并根据挠曲电材料理论与层合梁理论，利用变分法推导DNA-微梁的控制方程和边界条件，研究反应溶液离子特性、DNA膜的带电状态、非生物层基底力学特性、外界电学刺激等与微梁静态挠度的关系。（1）对于微纳米基底，研究了尺寸效应对层合结构基底的等效刚度、应力分布以及变形的影响；（2）对于DNA膜的力-电-化特性，利用实验数据，拟合了DNA膜的挠曲电系数。考察了溶液种类、基底非生物层的力学特性等对DNA-微梁静态响应的影响。挠曲电系数与微梁的弯曲方向密切相关；溶液种类、非生物层基底弹性模量以及厚度对DNA-微梁弯曲变形影响不可忽略；（3）对于基底表面带电特性，发展了上述DNA-微梁多场耦合模型，给出了基底表面电荷与DNA膜电势分布、离子浓度分布以及微梁静态挠度的解析关系，研究了表面电荷对DNA-悬臂梁、DNA-简支梁挠度大小以及方向的影响，并讨论了相应的检测失效特性；（4）对于外加电场刺激，构建了考虑电场作用的DNA-微梁理论模型，讨论了外加电场对DNA膜电势分布、离子浓度分布以及微梁静态挠度的影响，揭示了外加电场对微梁检测信号的调控。本项目有关研究结果可为基于微结构的DNA芯片的信号检测、优化设计、集成化制造等提供参考。