A continuous control mode with improved imaging rate for scanning ion conductance microscope (SICM)

Scanning ion conductance microscopy (SICM), one kind of scanning probe microscopy technique, featuring the advantage of non-contact imaging of sample surfaces in three dimensions with high resolution, has been widely applied in characterizations of sample topography, especially for soft materials. However, the time consuming imaging process of SICM restricts its further applications, such as in characterization of dynamic change of sample surface. In this work, a fast control mode of SICM, named as a continuous control mode, has been developed. In this mode, the SICM probe (i.e., pipette) is controlled by speed instructions in the axial direction of pipette (Z axis), and the pipette position is determined by the position sensor. Compared to the conventional piezo control mode of SICM (i.e., the stepwise control mode), in which the pipette is controlled by the position instructions and moves step by step, the continuous control mode can perform the continuous movement of the pipette in Z axis and overcome the time consuming problem caused by the repeated acceleration and deceleration of the pipette during the stepwise mode. Moreover, the imaging resolution in Z axis is not restricted by the pipette movement step and the imaging rate in the continuous control mode can be significantly enhanced without losing imaging quality. The approach speed of pipette in the continuous control mode can reach at 300 nm/ms, which is much faster than that in the stepwise mode. The surfaces of the soft polydimethylsiloxane (PDMS) samples with three different patterns, the hard metal grating sample and the cardiac fibroblasts as the biological sample demo were comparably scanned by SICM using the continuous control mode and the stepwise approach mode, respectively. The obtained SICM images of the sample topography prove that the continuous control mode can not only reduce the imaging deviation, but also efficiently improve the scanning rate of SICM. Furthermore, the continuous control mode can reconstruct the sample topography more stably compared to the stepwise control mode. The continuous control mode developed in this work can provide an efficient and reliable control strategy for improving the imaging performance of SICM system, and therefore can be potentially applied in dynamic characterizations of various samples in material science, biology and chemistry fields.