Electrohydrodynamics of Atomic Force Microscopy Imaging of Biological Membranes

摘要CTS-0323564 A。Fedorov，格鲁吉亚TechOriginal研究提出了流体力学和质量/离子传输的几个领域，这些领域对原子力显微镜（AFM）的数据解释和仪器优化具有重要意义，可应用于生物细胞的原位，高空间和时间分辨率成像。提出了一系列日益复杂的原子力显微镜轻敲模式操作电流体动力学模型，这些模型基于连续输运理论，适用于原子力显微镜针尖半径大于10 nm和亚毫秒时间分辨率。具体地，基于第一性原理，（1）在AFM轻敲模式探测过程中，细胞内外流体的流体力学和细胞膜变形的影响将被量化，（2）在局部电化学平衡条件下，在生理系统中，细胞膜表面的电荷双电层对AFM针尖-生物膜相互作用的影响将被评估，（3）研究了离子在柔性生物膜中传输的基本原理，以建立电化学非平衡对AFM针尖-生物膜相互作用的电流体动力学的影响，以及（4）边界积分求解方法将扩展到模拟复杂的多物理场问题，如柔性生物样品的AFM成像。流体动力学，并预计在每一个领域，原子力显微镜被用来研究在液体环境中的软样品的性质。成功的AFM的电流体动力学的理论分析建议有一个最大的潜力，导致几乎立即改善细胞生物学，生物医学成像和扫描纳米探针的发展领域。具体而言，本研究将导致（1）定量解释AFM成像数据，以预测细胞形态，膜结构，表面电荷，机械性能和分子水平的相互作用，（2）优化AFM仪器的操作特性（例如，AFM针尖的形状和尺寸以及最佳轻敲模式频率和振幅），其导致最佳功能性（即，成像的最高空间和时间分辨率），以及（3）通过“虚拟”计算机实验为下一代集成AFM开发新的成像模式-的多功能扫描探针。此外，为了促进研究成果的传播和促进对最新科学进展的理解，还建议开展一项旨在展示和讨论原子力显微镜的物理原理的外联计划和技术的影响。由于原子力显微镜操作所依据的物理原理的简单性（即，一个原子尺度的手写笔工作的基础上质量和弹簧物理学），我们将开发一套基于互联网的讲座，描述流体力学方面的原子力显微镜成像模式成像的软膜结合的样品介绍给广大观众，包括学生在格鲁吉亚技术和高中在亚特兰大地区的格鲁吉亚技术学术指导下运作。讲座材料也将提供给公众被录像，并放在网站上的格鲁吉亚技术中心的教学和学习（CETL）的增强。此外，计算机可视化将伴随着当“大AFM”尖端探测填充有较重液体（例如，水）并放置在填充有透明、较轻流体（例如，硅油），并用示踪剂颗粒接种以用于流动可视化。这样的实验演示将提供一个机会，以简单的方式传达一些最基本的概念，流体力学，甚至超越AFM的应用，如，例如，缩放的流动现象和设计的工程实验。

AbstractCTS-0323564A. Fedorov, Georgia TechOriginal research is proposed in several areas of fluid mechanics and mass/ion transport which are significant to data interpretation and instrument optimization of the atomic force microscopy (AFM) with application to in-situ, high spatial and temporal resolution imaging of biological cells. The series of increasingly complex models of the electrohydrodynamics of AFM tapping mode operation are proposed, which are based on the continuous transport theory and applicable for the AFM tip radius greater than 10nm and the sub-millisecond temporal resolution. Specifically, based on the first-principles, (1) the effect of the fluid mechanics of the inner and outer cellular fluids and the cell membrane deformation during an AFM tapping mode probing process will be quantified, (2) the effect of the charge double layer at the cell membrane surface on the AFM tip-biomembrane interactions will be assessed in a physiological system under conditions of local electrochemical equilibrium, (3) fundamentals of the ion transport across the flexible biological membrane will be investigated to establish the effect of electrochemical non-equilibrium on electrohydrodynamics of AFM tip-biomembrane interactions, and (4) the boundary integral solution methodology will be extended to simulation of a complex multiphysics problem such as AFM imaging of flexible biological specimens.The scientific impact of the proposed research is beyond the realm of fluid dynamics and is expected in every field where atomic force microscopy is being used to investigate properties of soft samples in liquid environment. A success in the proposed theoretical analysis of electrohydrodynamics of AFM has a greatest potential to lead to almost immediate improvements in the fields of cellular biology, biomedical imaging, and scanning nanoprobe development. Specifically, this research will result in (1) quantitativeinterpretation of the AFM imaging data in order to predict the cell morphology, membrane structure, surface charge, mechanical properties and molecular level interactions, (2) optimization of the AFM instrument operational characteristics (e.g., shape and size of the AFM tip and optimal tapping mode frequency and amplitude) that result in optimal functionality (i.e., highest spatial and temporalresolution of imaging), and (3) development of new imaging modalities through "virtual" computer experiments for next generation of the integrated AFM-based multifunctional scanning probes.An outreach program focused on demonstration and discussion of physical principles underlying the atomic force microscopy is also proposed in order to facilitate dissemination of research results and to promote understanding of latest advances in science and technology by pre-college students and general public. Owing to simplicity of physical principles underlying operation of the atomic force microscopy (i.e., an atomic-scale stylus working based on mass-and-spring physics), we will develop a set of internet-basedlectures describing fluid mechanics aspects of AFM tapping-mode imaging of soft membrane-bound samples for presentation to a wide audience, including students at Georgia Tech and high schools in the Atlanta area which are operated under the Georgia Tech academic mentorship. The lecture material will also be made available to general public by being videotaped and placed on the website of the Georgia Tech's Center for Enhancement of Teaching and Learning (CETL). Further, the computer visualization will be accompanied by a simple, "macroscale" experimental demonstration of the fluid motion induced in the liquid by tapping mode action of the cantilever when "a large AFM" tip probes the flexible, membrane-like surface of the balloon filled with a heavier liquid (e.g., water) and placed inside of a container filled with a transparent, lighter fluid (e.g., silicon oil) and seeded with tracer particles for flow visualization. Such an experimental demonstration would provide an opportunity to convey in a simple manner some of the mostfundamental concepts of fluid mechanics even beyond AFM applications such as, for example, the scaling of the flow phenomena and design of engineering experiments.