# Effect of Microresistor Topology on the Sensing Characteristics of MoS2-Based Chemoresistive Cortisol Sensors

## TL;DR

This paper studies how the design of microresistors affects the performance of flexible cortisol sensors made of MoS2, aiming to improve their reliability and sensitivity for wearable devices.

## Contribution

The study introduces a new microresistor topology with mechanical ribs that significantly improves mechanical stability and sensitivity of MoS2-based cortisol sensors under strain.

## Key findings

- Adding mechanical ribs to the long-shoulder topology improves sensitivity from 0.9 kΩ/ng/mL to 130.6 kΩ/ng/mL after bending.
- The long-shoulder design with ribs outperforms the short-shoulder design in mechanical stability and sensing reliability.
- The proposed design offers a simpler and more cost-effective solution for wearable cortisol monitoring compared to microfluidic or optical systems.

## Abstract

This study investigates the impact of microresistor topology on the sensing characteristics of MoS2-based chemoresistive cortisol sensors. It is done to address the critical need for robust, non-invasive cortisol monitoring in wearable applications, where mechanical stability under strain is paramount, and to explore underexplored topological effects on sensor performance. The research is conducted by fabricating MoS2-based meander structures on flexible PDMS substrates, featuring various microresistor designs, including long-shoulder and short-shoulder topologies, both with and without integrated mechanical ribs. Sensor performance is evaluated in resistance change mode across a range of cortisol concentrations (2.5 to 500 ng/mL) and subjected to significant mechanical bending stress. Electrical parameters such as contact resistance and parasitic capacitance, as well as temperature dependence, are also analyzed. The results demonstrate that the incorporation of ribs significantly enhances the mechanical stability and preserves the reliable sensing function of the long-shoulder topology under bending stress, improving sensitivity from 0.9 kΩ/ng/mL (without ribs) to 130.6 kΩ/ng/mL (with ribs) after bending. While temperature influences baseline resistance and response magnitude consistent with MoS2 semiconductor properties and aptamer binding kinetics, the short-shoulder design, even with ribs, showed less optimal performance. The primary advantage of the proposed device lies in its enhanced mechanical reliability under continuous strain, crucial for wearable electronics, alongside a simpler design compared to complex microfluidic or optical systems, thus enabling lower manufacturing costs and easier mass production.