High resolution BioMEMS force sensors

Accurate measurement of forces and displacements exerted by cells both in vivo and in vitro is an essential step in elucidating the link between cellular force transduction and function. Micromechanical sensors are especially suited for these studies because of their small size, which allows for easy interfacing with individual cells, and fine force/displacement resolution that makes them capable of measuring very small forces/displacements.

Typically, force sensors that have high resolution have a limited force measurement range and vice versa. We have developed a set of displacement-based micromechanical force sensors that combine high resolution (50 pN)  with a large force measurement range (1 μN).  In addition, these sensors have a highly linear force–displacement response over the entire measurement range.

One of the key requirements for force sensors in biological studies is that they must be capable of operating in a liquid environment. This is often a major constraint for MEMS devices because the capillary forces that develop during the immersion and removal of these devices can cause extensive structural damage and compromise their functionality. To circumvent this problem, we have developed a novel technique to insulate our force sensors from capillary forces during their operation in aqueous environments.

Scanning electron micrograph of the MEMS force sensor. An aluminum film holds the beams together and prevents damage when the force sensor is first immersed into liquid. A magnified view of the probe and the reference beam is shown on the right. In this particular case, a trench was made near the probe tip using focused ion beam milling to enable easier gripping of the axons.

Related Publications

1. J. Rajagopalan and M. T. A. Saif, “MEMS sensors and microsystems for cell mechano-biology,” Journal of Micromechanics and Microengineering 21, 054002, 2011 (pdf)

2.  J. Rajagopalan, A. Tofangchi and M. T. A. Saif, “Linear, high-resolution bioMEMS force sensors with large measurement range,” Journal of Microelectromechanical Systems 19, 1380-1389, 2010 (pdf)

3. J. Rajagopalan, A. Tofangchi and M. T. A. Saif, “Highly linear, ultra sensitive bio-MEMS force sensors with large force measurement range,” IEEE 23rd International Conference on Micro Electro Mechanical Systems (MEMS), 88-91,  2010 (pdf)

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