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- <tex-math notation="LaTeX">μ</tex-math> N 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 <tex-math notation="LaTeX">ₓ</tex-math> sensing resolution down to <tex-math notation="LaTeX">~</tex-math> 70 nN. Measured sensitivities of devices with different pillar geometries range from <tex-math notation="LaTeX">Δ</tex-math> R/R <tex-math notation="LaTeX">$=$</tex-math> 0.05% to 0.14% <tex-math notation="LaTeX">μ</tex-math> N <tex-math notation="LaTeX">⁻¹</tex-math> 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 <tex-math notation="LaTeX">μ</tex-math> m width, in-substrate piezoresistors. Effective device footprint is a compact few <tex-math notation="LaTeX">μ</tex-math> m <tex-math notation="LaTeX">²</tex-math> on substrate which makes the sensor design ideal for implementation in large, dense sensing arrays with <tex-math notation="LaTeX">μ</tex-math> m-scale sensor-to-sensor pitches in both in-plane axes. 2023-0190