Electrohydrodynamics of Atomic Force Microscopy Imaging of Biological Membranes

摘要CTS-0323564A。费多罗夫，佐治亚州理工学院提出了在流体力学和质量/离子传输的几个领域的原创性研究，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，原子力显微镜应用于生物细胞的原位、高空间和时间分辨率成像。基于连续输运理论，建立了适用于原子力显微镜针尖半径大于10 nm、时间分辨率为亚毫秒级的一系列日益复杂的原子力显微镜攻丝电动力学模型。具体地说，基于第一原理，(1)将量化AFM攻丝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，(2)将在局部电化学平衡条件下在生理系统中评估细胞膜表面的电荷双层对AFM针尖-生物膜相互作用的影响，(3)将研究离子通过柔性生物膜的基本原理，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)将边界积分方法扩展到模拟复杂的多物理问题，如柔性生物样品的AFM成像。所提出的研究的科学影响超越了流体动力学领域，并有望应用于所有使用原子力显微镜来研究液体环境中软样品的性质的领域。所提出的原子力显微镜电流体动力学理论分析的成功极有可能在细胞生物学、生物医学成像和扫描纳米探针开发领域带来几乎立即的改进。具体地说，这项研究将导致(1)对AFM成像数据进行定量解释，以预测细胞形态、膜结构、表面电荷、机械性能和分子水平相互作用，(2)优化AFM仪器的操作特性(例如，AFM尖端的形状和大小以及最佳敲击模式频率和幅度)，从而产生最佳功能(即，成像的最高空间和时间分辨率)，(3)通过“虚拟”计算机实验开发新的成像模式，用于下一代基于AFM的集成多功能扫描探头。还提出了一个外展计划，重点演示和讨论原子力显微镜背后的物理原理，以促进研究成果的传播，并促进大学预科学生和普通公众对科学技术最新进展的了解。由于原子力显微镜操作的物理原理很简单(即，一种基于质量和弹簧物理的原子尺度触针)，我们将开发一套基于互联网的讲座，描述AFM轻拍模式下软膜结合样本成像的流体力学方面，并向广大听众介绍，包括佐治亚理工学院的学生和亚特兰大地区的高中学生，这些学生在佐治亚理工学院的学术指导下操作。授课材料还将通过录像并放在佐治亚理工学院加强教学中心(CETL)的网站上向公众提供。此外，伴随着计算机可视化的将是简单的、通过轻敲悬臂的模式作用在液体中诱导的流体运动的实验演示，该悬臂的模式作用是当“大的AFM”尖端探测充满较重的液体(例如水)的气球的柔性膜状表面并且放置在充满透明、较轻的流体(例如硅油)并播撒示踪剂颗粒用于流动显示的容器内时在液体中诱导的流体运动。这样的实验演示将提供一个机会，以一种简单的方式传达一些最基本的流体力学概念，甚至超越原子力显微镜的应用，例如，流动现象的缩放和工程实验的设计。

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.