Widening effect of SICM topography measurement based on electrolyte concentration gradient with dual-barrel pipette

Scanning ion conductance microscopy (SICM) is a novel non-invasive, versatile and in-situ high-resolution scanning probe microscope technique, which can realize imaging of the topography, surface charge, mechanical and electrochemical properties of biological samples. It has become increasingly popular in recent years. By using dual-barrel pipette and applying a concentration gradient between two electrolytes filled its corresponding pipette barrels and sample solution, it can reduce the impact of the bath solution concentration even types on the sample, meeting the requirements of the sample for special liquid environments. However, the influence of the concentration difference between the pipette electrolyte and the sample solution, as well as the bias voltage applied between two electrodes on the topography measurement (widening effect) has not been studied in using this configuration. In this study, finite element modeling is utilized to study the effect of half-cone angle of the dual-barrel pipette tip, concentration difference of electrolyte between pipette barrel and sample solution, applied bias voltage on the measurement results of different slope topography. Then the approach curves and widening effect experiment are conducted using this pipette with different concentration gradient configuration and applied bias, respectively. Besides, the experimental results are compared with that of using conventional single-barrel pipette-based approach with a varied applied bias. It suggests that with the increase of the concentration difference or applied bias, the widening effect of the topography measurement increases under the same feedback threshold. While it is not affected by the increased bias in the topography measurement by using conventional single-barrel SICM pipette without concentration gradient.