Finite Element Analysis of Interface Dependence on Nanomechanical Sensing

Kosuke Minami,Genki Yoshikawa

doi:10.3390/s20051518

Abstract

Nanomechanical sensors and their arrays have been attracting significant attention for detecting, discriminating and identifying target analytes. The sensing responses can be partially explained by the physical properties of the receptor layers coated on the sensing elements. Analytical solutions of nanomechanical sensing are available for a simple cantilever model including the physical parameters of both a cantilever and a receptor layer. These analytical solutions generally rely on the simple structures, such that the sensing element and the receptor layer are fully attached at their boundary. However, an actual interface in a real system is not always fully attached because of inhomogeneous coatings with low affinity to the sensor surface or partial detachments caused by the exposure to some analytes, especially with high concentration. Here, we study the effects of such macroscopic interfacial structures, including partial attachments/detachments, for static nanomechanical sensing, focusing on a Membrane-type Surface stress Sensor (MSS), through finite element analysis (FEA). We simulate various macroscopic interfacial structures by changing the sizes, numbers and positions of the attachments as well as the elastic properties of receptor layers (e.g., Young’s modulus and Poisson’s ratio) and evaluate the effects on the sensitivity. It is found that specific interfacial structures lead to efficient sensing responses, providing a guideline for designing the coating films as well as optimizing the interfacial structures for higher sensitivity including surface modification of the substrate.

Highlights

Nanomechanical sensors and their arrays have gained significant attention as a powerful tool for detecting, discriminating and identifying target analytes [1,2,3,4], especially various odors composed of a complex mixture of gaseous molecules [5,6,7]
We focus on a nanomechanical sensor, especially a Membrane-type Surface stress Sensors (MSS), which is one of the optimized nanomechanical sensors for static operation based on the integrated piezoresistive read-out with high sensitivity [3,4,5,6,7,11,12,17,18,19,20]
To investigate the effects of the domain sizes of the interfacial attached points, we first simulated the interfacial structures with uniformly distributed pillars as a function of area

Summary

Introduction

Nanomechanical sensors and their arrays have gained significant attention as a powerful tool for detecting, discriminating and identifying target analytes [1,2,3,4], especially various odors composed of a complex mixture of gaseous molecules [5,6,7] The versatility of these sensors and their arrays are based on physical and chemical properties of a receptor layer coated on a sensing element. The microscopic interface phenomena, such as the lap shear or the interfacial slip, reported as the molecular level effects or the finite size effects for surface stress-based signal responses [21,22,23] are not taken into account The reason for this assumption is based on the experimental observation; we sometimes encounter a sudden decrease in sensing signals when a receptor layer-coated MSS is exposed to some target analytes, indicating a partial detachment of the receptor layer. To understand the effects of these partial interfacial attachments on the nanomechanical sensing including the domain sizes of the partial attachments as well as the distributions of the partial attachment points, we modeled various macroscopic structures at the interface between the membrane surface of MSS and the receptor layers

Simulation

The concentrations of was coated water

Results and Discussion

As observed in the result ofwith

As observed

Conclusions