Scanning Ion Conductance Microscopy

Abstract

In the present work, the development of a combined specialized scanning ion-conductance microscope (SICM) and fluorescence microscope for non-invasive topographical and optical studies on soft samples immersed in electrolyte solution is reported. In SICM, the scanning probe is an electrolyte-filled glass-nanopipette with a tip aperture diameter of about 50 nanometers. Conductivity of an ionic current through the tip, driven by electrodes inside and outside of the pipette, depends on the distance between tip and sample surface (topographical mapping) and on the sample's chemical properties (chemical mapping). For enhancing the sensitivity of the microscope, it is operated in alternating current mode by applying an oscillation to the probe and using a lock-in detection of the modulated current as feedback signal. The presented combination of scanning ion-conductance and fluorescence microscopy demonstrates parallel acquisition of correlated topographical and chemical or optical information. Characterization of the microscope's properties is presented with a detailed analysis of the interaction of all essential elements participating in its operation. Conceptual design and implementation of the control-software that operates on the instrument's specialized real-time hardware is described. Successful employment of the SICM at a resolution beyond the Rayleigh criterion combined with fluorescence-optical studies is presented, demonstrating the manifold capabilities of this instrument for applications in the interacting fields of physics, biology, and chemistry.