An Ion-Sensitive Field Effect Transistor And Ion-Selective Polymer Membrane For Continuous Potassium Monitoring

Author

Huy Van Le, California Polytechnic State University, San Luis ObispoFollow

Available at: https://digitalcommons.calpoly.edu/theses/2776

Date of Award

3-2024

Degree Name

MS in Biomedical Engineering

Department/Program

Biomedical Engineering

College

College of Agriculture, Food, and Environmental Sciences

Advisor

Benjamin G Hawkins

Advisor Department

Biomedical Engineering

Advisor College

College of Engineering

Abstract

Ion sensitive field effect transistors (ISFETs) are semiconductor sensors that have the capability to determine the selected concentration of a specific ion in a solution. Most modern ISFETs utilize their ion selective properties for glucose monitors for diabetics. However, in this thesis, the ISFET fabricated is for the selective detection of K+. The goals of this thesis are to develop a functioning ion-selective polymer membrane, manufacture a working FET device, and implement the two aspects together into a working bench-top K⁺ selective ISFET device. Properties of a polymer composed of 33 wt.% polyvinyl chloride (PVC) 66 wt.% dioctyl sebacate (DOS) and 1 wt.% valinomycin applied to an ion-sensitive electrode (ISE) were investigated. The membrane generated a sensitivity value of -9.864E-08 Ω/log10(C_K). Though this data set was affected by both the maximum resolution of the I-V curve tracing device and the thin-membrane effect. Selectivity tests following the IUPAC two-solution method in the presence of Na⁺ as the interfering ion, provided selectivity values of 0.228 and 0.443 with higher ratios of primary ion to interfering ion resulting in higher selectivity coefficients. Additionally, utilizing an illumination test, dielectric constants of 17.71 and 10.88 were calculated dependent on the amount of solvent used during formulation. Fabrication of the FET device also resulted in developments in metal contact materials, nitride film processing, and physical vapor deposition (PVD) processes. With further improvements, it is possible to fabricate a biocompatible, wearable K⁺-selective monitor for continuously testing dialysis patients.