GOALI: Nonlinear, Multi-modal, and Stochastic Dynamics of Low-stiffness Microcantilevers in Liquid Environment Atomic Force Microscopy

Purdue University, West Lafayette IN

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This project seeks to study the nonlinear, multi-modal, and stochastic dynamics of microcantilevers tapping on samples in liquids to significantly improve next generation dynamic Atomic Force Microscopy (dAFM) for biology and medicine. The proposed work will develop new imaging modes and cantilever designs to greatly enhance nanoscale material property contrast, such as molecular elasticity and recognition, in liquids while applying gentle forces on fragile biological samples including cells, membranes, viruses, and proteins. Accurate mathematical models will be developed to simulate the dynamics of low-stiffness AFM microcantilevers in liquids by systematically including hydrodynamic coupling effects, stochastic Langevin forces, nonlinear tip-sample interactions such as chemical bond forces, and multiple cantilever eigenmodes. Investigations will focus on the dependence of momentary excitation, a non-resonant modal interaction, on: local elasticity and molecular recognition, and bifurcations from single to multiple tapping oscillations. New dAFM modes in buffer solutions will be developed based on these mode coupling phenomena to experimentally resolve variations in local elasticity and molecular recognition on biological molecules in buffer solutions. dAFM has become a major scientific technique for nanometer resolution imaging and materials property characterization. The development of new high-resolution, gentle force, material contrast modes for dAFM of biological samples in liquids would broadly benefit biology and medicine, for example, by providing sensitive maps of protein markers on a cancer cell or drug receptor sites on a cell, thus enabling discoveries in early disease detection and drug discovery. The results could also provide insight into the dynamics of a wider class of systems that are strongly affected by nonlinearities, hydrodynamics and Langevin forces, for example, particles in optical traps, nanomechanical cantilever sensors for biochemical detection in liquids, DNA, biopolymers, and cilia and flagella of eukaryotic cells.