Analysis and improvement of positioning reliability and accuracy of theta pipette configuration for scanning ion conductance microscopy

Scanning ion conductance microscopy (SICM) as an emerging non-contact scanning probe microscopy technique and featuring its strong in-situ detectability for soft and viscous samples, is increasingly used in biomedical and materials related studies. In SICM measurements, employing theta pipette as SICM probe to scan sample is an effective method to extend the applications of SICM for multi-parameter measurement. There are two crucial but still unclear issues that influence the reliability and accuracy of the usage of theta pipette in the SICM measurements, which are the safe feedback threshold and the horizontal measurement offset. In this work, aiming at the theta pipette configuration of SICM, we systematically investigated the two issues of the theta pipette by both finite element method (FEM) simulation and SICM experiments. The FEM analysis results show that the safe feedback threshold of the one side barrel of the theta pipette is above 99.5%, and the horizontal measurement offset is similar to 0.53 times of the inner radius of the probe tip. Based on this, we proposed an improved scanning method used by the theta pipette to solve the reliability and accuracy problems caused by the feedback threshold too close to the reference current (100%) and the measurement offset error at the tip radius level. Then through testing the polydimethylsiloxane (PDMS) samples with different embossed patterns with the improved method of SICM, we can conclude that the improved method can enhance the scanning reliability by adding the double barrels approaching process and increase the positioning accuracy by compensating an offset distance. The theoretical analysis and the improved scanning method in this work demonstrate more property and usage details of the theta pipette, and further improve the reliability and accuracy of the diversified multifunctional applications of the theta pipette for SICM to meet the increasingly complex and precise research needs.