The Integration of Reference Electrode for ISFET Ion Sensors Using Fluorothiophenol-Treated rGO

Abstract

Ion-sensitive field-effect transistors (ISFETs) detect specific ions in solutions that enable straightforward, fast, and inexpensive sensors compared to other benchtop equipment. However, a conventional reference electrode (RE) such as Ag/AgCl is limited on the miniaturization of the sensor. We introduce reduced graphene oxide (rGO), which serves as a new RE, when fluorinated (F-rGO) using fluorothiophenol through the π–π interaction. The circular RE is integrated between a fabricated microscale two-channel ISFET, which is capable of detecting two kinds of ions on an indium tin oxide (ITO) thin-film substrate, using the photolithography process. F-rGO bound to this circular region to function as an RE in the ISFETs sensor, which operated stably in solution and showed a relatively high transconductance (gm) value (1.27 mS), low drift characteristic (3.2 mV), and low hysteresis voltage (±0.05 mV). It detected proton (H+) ions in a buffer solution with high sensitivity (67.1 mV/pH). We successfully detected Na+ (62.1 mV/dec) and K+ (57.6 mV/dec) ions in human patient urine using a two-channel ISFET with the F-rGO RE. The F-rGO RE will be a suitable component in the fabrication of low-cost, mass-produced, and disposable ISFETs sensors.

High-Performance Potassium-Selective Biosensor Platform Based on Resistive Coupling of a-IGZO Coplanar-Gate Thin-Film Transistor

“…Since Bergveld et al first introduced the concept of a field-effect transistor (FET) that is sensitive to ions in the 1970s, there has been growing interest in applying the ion-sensitive field-effect transistor (ISFET) concept for converting chemical signals into electrical signals in various sensing applications [ 6 ]. In particular, ISFETs based on CMOS technology are very promising devices for sensing ionic activity in the human body because of their many beneficial features, such as their low cost, fast response time, small size, solid-state structure, easy signal processing, and label-free detection [ 7 , 8 , 9 , 10 ]. However, in conventional ISFETs, the polysilicon gate of a metal–oxide–semiconductor field-effect transistor (MOSFET) is removed, replaced by ion-sensitive membrane materials, and then immersed in target solutions to measure the electrochemical potential between the electrolytes and the sensing membrane due to the ion activity of the target solution.…”