Conducting Atomic Force Microscopy for Simultaneous Imaging of Structure and Ionic Current Through Nanopores

Abstract

Ionic currents through nanopores in both biological and synthetic materials play an important role in the function of the material. For biological systems, these pores are critical for normal physiological function and abnormalities lead to various disease states. The ability to measure the current through nanopores, while simultaneously relating their molecular and atomic structure, is currently limited in resolution. In order to perform structure-function measurements using an atomic force microscope (AFM), conducting cantilevered tips capable of measuring ionic currents in fluid were designed and fabricated using various techniques. Insulated tungsten wires with conducting tips were fixed to steel supports to create cantilevers for AFM imaging. Gold films in fluid were imaged with simultaneous electrical current measurements by the conducting cantilevers to reveal the topography of the film. These simultaneous recording of the current and the 3D structure demonstrate the conducting capabilities of the cantilever. Ionic currents through membrane filters were successfully measured through 20 nm pores in the membrane. The results from this technology show promise for future structure-function imaging of macromolecules, such as ion-channels in health and disease as well as for the synthetic nanopores for energy and environmental applications.