Two-axis micro-tensile tester chip for measuring plant cell mechanics

The monolithically integrated two-axis microtensile/compression tester and its application to the stiffness measurement of individual plant cells are presented. It consists of a two-axis electrostatic actuator with capacitive position feedback and a two-axis capacitive micro-force sensor. The actuation range is +/-16 μm along both axes with a spatial resolution of 20 nm. The force sensing range is +/-60 μN with a resolution down to 60 nN. The position feedback as well as the force sensor are calibrated by direct comparison with reference standards. A complete uncertainty analysis through the entire calibration chain based on the Monte Carlo Method is presented. The functionality of the tensile tester is demonstrated by the automated stiffness measurement of the cells in plant hairs (trichomes) as a function of their size, motivated by the need to quantitatively measure material properties for modeling plant growth.