Piezoresistive Micropillar Sensors for Nano-Newton Cell Traction Force Sensing

Several studies demonstrate that large variations in biologically cell-generated forces are strong indicators of diseases in the body. To realize the full potential of single-cell biomechanical properties as label-free, non-invasive biomarkers in cell-based disease diagnoses, we need high-throughput test platforms that interrogate single cells individually while allowing measurement of thousands of cells at a time. This work presents a piezoresistive sub-N-u lateral force sensing approach using vertical pillars as structural elements and silicon-based, N-type piezoresistors embedded underneath the pillars for stress-sensing. Experimental testing of the first generation of sensors developed shows excellent F(x )sensing resolution down to similar to 70 nN. Measured sensitivities of devices with different pillar geometries range from Delta R/R = 0.05% to 0.14% uN(-1) and are varied by simply scaling pillar geometry. While having a comparable resolution to existing MEMS in-plane sensors, the sensor design sets itself apart from existing approaches with its 3D printed pillar-based approach, which is combined with traditional nanofabrication to achieve 500 nm to 3 um width, in-substrate piezoresistors. Effective device footprint is a compact few um(2) on substrate which makes the sensor design ideal for implementation in large, dense sensing arrays with $\mu$ m-scale sensor-to-sensor pitches in both in-plane axes. 2023-0190