Linear high-resolution BioMEMS force sensors with large measurement range

We present a set of displacement-based high-resolution (50 pN) micromechanical force sensors with a large force measurement range (1 μN). Typically, force sensors that have high resolution have a limited force measurement range and vice versa. The force sensors presented here overcome this limitation and, in addition, have a highly linear forcedisplacement response. The sensors (≈ 3 mm× 4 mm× 150μm) are composed of a series of flexible beams attached to a rigid probe that deform when subjected to an external force. The force is obtained by optically measuring the displacement of the probe with respect to a fixed reference beam. The force sensors are fabricated using a simple two-mask process that allows for their stiffness to be varied over a wide range. Furthermore, we have developed a novel scheme to avoid capillary forces during the immersion and removal of these sensors from aqueous environments, which makes them highly suited for biological studies. We illustrate the capability and versatility of these sensors by measuring the in vivo force-deformation response of axons in Drosophila melanogaster (fruit fly).