Electrohydrodynamics of Atomic Force Microscopy Imaging of Biological Membranes

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

Abstract CTS-0323564 A. Fedorov, Georgia Tech Original 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) quantitative interpretation 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 temporal resolution 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-based lectures 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 most fundamental concepts of fluid mechanics even beyond AFM applications such as, for example, the scaling of the flow phenomena and design of engineering experiments.