Session: 14-04-01: Micro/Nano Devices and Medical Systems

Paper Number: 164011

Study of the Equivalent Model of Silk Fibroin Based Relative Humidity Sensor 

A humidity sensor is a device that measures the amount of water vapor in the air. They can be used to monitor air quality and make adjustments to prevent the air from becoming too dry or humid. This humidity sensor is researched and developed to monitor the humidity levels required for an actuating device fabricated from water responsive paper. In this paper the humidity sensor sensitive layer is fabricated from biomaterials. Humidity sensors utilizing biomaterials as the sensitive layer often rely on naturally hygroscopic properties of organic materials like silk cellulose, gelatin, or proteins, which change their electrical conductivity or physical properties when exposed to varying levels of humidity, allowing for detection of moisture content in the surrounding environment; examples include using silk fibroin (SF), cellulose-based paper, gelatin films, or modified plant extracts as the sensing element in a humidity sensor. In this research the sensitve layer for humidity detection is SF.  Silk fibroin is a protein derived from silkworm cocoons. It's a biomaterial that's used in a variety of applications, including tissue engineering, drug delivery, and corneal bioengineering. 

This study explores the relationship between electrical resistance and relative humidity (RH) in a SF-based humidity sensor. In order to produce dynamic response of the water responsive paper, the relative humidity should alternate between high level and low level of humidity. A humidity sensor with short response time that is sensitive and linear is required for this application. 

The sensor is fabricated by drop-casting SF solution onto an interdigital electrode (IDE) and allowing it to dry, forming a humidity-sensitive layer. IDEs are designed with two separately addressable electrode arrays, such that the resulting electrode structure is in a zipper-like or comb-shaped arrangement. The fabrication of the IDEs chip primarily involves using photolithography to create a "comb-like" pattern of electrodes on a substrate, where alternating fingers of conductive material interdigitate with gaps between them, allowing for high sensitivity in applications like electrochemical sensors, biosensors, and pressure transducers due to the large surface area and efficient analyte diffusion within the gaps. The lift-off technique is used for the metal deposition for IDEs.

An electrical model consisting of resistors and capacitors is developed to analyze the sensor's impedance. The resistance in this model is computed across varying RH levels, and a mathematical expression is derived based on IDE geometry and the humidity-dependent conductivity of SF. The findings enhance the understanding of SF’s resistive response to moisture, highlighting its potential for flexible humidity sensing applications.

Presenting Author: Ioana Voiculescu The City College of New York

Presenting Author Biography: Ioana Voiculescu is an Associate Professor in the Mechanical Engineering Department, the City College of New York, New York. She received her PhD in Mechanical Engineering from the Technical University Politehnica Timisoara, Romania, and her ScD in Mechanical Engineering from the George Washington University, Washington, DC, in 2005. Since 2002, Dr. Voiculescu is a member of the ASME and IEEE. She published several journal articles in the area of microelectromechanical systems (MEMS) chemical and biological sensors. She also has two U.S. patents in her name.

Authors:

Shuo Fang The City College of New York
Yuchen Zhang The City College of New York
Maheen K. Khan The City College of New York
Xi Chen The City College of New York
Ioana Voiculescu The City College of New York