Design of Low-Cost Ultrasensitive Polymer-Based ITO Piezoresistive BioMEMS Cantilever Sensor to Detect Heavy Metal Ions in Water

This study focuses on the design and simulation of a polymer-based piezoresistive microcantilever for the detection of Heavy Metal Ions (HMIs) in water. The proposed cantilever uses the SU-8 2005 polymer as a structural material to simplify fabrication while enhancing deflection and sensitivity. Indium Tin Oxide (ITO) is employed as the primary piezoresistive layer, replacing conventional polysilicon, which requires complex ion-implantation processes. The significant piezoresistive coefficient of ITO (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-6.72 \times 10^{-3} \, \rm {MPa}^{-1}$</tex-math></inline-formula>) ensures high sensitivity to pressure variations, while its compatibility with low-temperature deposition techniques further reduces the complexity of the fabrication. The cantilever, with dimensions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$300 \times 100 \, \mu m$</tex-math></inline-formula>, was modelled and simulated using COMSOL Multiphysics under an applied boundary load of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$32.68 \, \rm {Pa}$</tex-math></inline-formula> and a constant terminal voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3V$</tex-math></inline-formula> to achieve 1-100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{\mu }}$</tex-math></inline-formula>g/L Limit of Detection (LOD) specifications to detect HMIs. From the results of the designed cantilever, the sensitivity is calculated as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$51.965 \, \mu \Omega /\Omega /\rm {Pa}$</tex-math></inline-formula> for the Multi-Arm device. This work highlights the potential of polymer-based MEMS (Micro-Electromechanical Systems) for cost-effective and scalable environmental monitoring applications, offering a novel approach to toxic HMIs detection in water.