Quantitative Dielectric Measurements of Biomembranes and Oxides in Electrolyte Solutions at High Frequencies

Abstract

A unique hallmark of atomic force microscopy is the ability to investigate matter with nanoscale spatial resolution in liquid environment. This has enabled access to materials properties, such as surface stiffness, electrochemical activity, piezoelectric response and surface charge/potential, in liquid with a tremendous impact in biology and electrochemistry. Yet, to date dielectric polarization, the fundamental property of materials to orient permanent or induced electric dipoles in response to an external electric field, has remained precluded to AFM-based techniques in liquid environment.Here we show that by operating Electrostatic Force Microscopy in liquid at high frequency (>1 MHz) with a heterodyne detection scheme dielectric material contrast can be obtained [1, 3]. Furthermore we demonstrate for the first time that the dielectric response of thin insulating films such as oxides and biomembranes can be imaged and quantified in ionic solutions using an AFM-based technique [2]. These results open a range of exciting possibilities. On the one hand, they will allow exploiting the unique capabilities of electrical SPM techniques to probe the local dielectric properties of nanoscale objects and materials in liquid environment in a similar way as it can be done in air. On the other hand, and probably more importantly, they will allow accessing polarization properties of systems that are stable only in ion-containing aqueous solutions and that for this reason to date have remained precluded. In particular, this is of fundamental interest in biology and electrochemistry, in which polarization properties at the nanoscale are crucial.The work was supported by the EU-FP7 (PEOPLE-2012-ITN-317116 NANOMICROWAVE) and ELECTROBACTERIA project.