Development of a scanning ion conductance microscope (sicm) prototype with afm and optical modules
The SICM microscope works with ionic solution, and can perform imaging of biological samples without mechanical interaction. By suitably varying the hydrostatic pressure present at the mouth of the capillary tube with which it performs the scan, the SICM can exert small forces (down to a few pN) on the sample.
Recently, this technique has been used not only to perform 3D-imaging, but also to measure the mechanical properties of the cell.
In our lab a prototype is specifically developed for this purpose, combining together SICM, atomic force microscopy (AFM) and inverted optical microscopy. In this setup, SICM and AFM can be alternatively used, while the optical microscope helps to guide the micro/macroscopic positioning of the probe. The SICM probe, a micropipette filled with saline solution, can be operated at atmospheric pressure or at a slightly higher pressure (DP =10<sup>2</sup>-10<sup>3</sup> Pa). The overpressure produces an electrolyte flow at the pipette aperture. The AFM module can then be used to directly measure the mechanical forces exerted on the underlying surface, down to about 10 pN.
With a variation of 1 mm of the filling level of a pipette of 1 micron aperture, the force applied on the sample varies only by 8 pN. So this setup is also a powerful tool for measuring the elasticity of cell membranes.
Starting from the results achieved in recent years a configuration of a coupled AFM / SICM will be considered and a new version of the instrument will be designed and built, optimized for reliable use in the biomedical field.
Several structural aspects of the prototype are currently under refinement. For example, a new design of the piezo translator block is under study, to improve the control of the planarity of the scanning area. In addition, the feasibility of using ac instead of dc current to pilot the feedback keeping the working distance is also under study. If successfull, the use of ac current would allow faster scanning operation.
Will be devised a method for measuring the mechanical properties of cells with stimuli from a few piconewton by means of the small pressures applied with the SICM micro-pipette with an aperture below the micron.