Low-Cost, Point-of-Care Potassium Ion Sensing Electrode in EGFET Configuration for Ultra-High Sensitivity

This paper presents the development of a non-toxic and low-cost potassium ion sensor utilizing an Extended Gate Field-Effect Transistor (EGFET) configuration with all-solid-state electrodes fabricated on a printed circuit board (PCB) substrate. An Ag/AgCl-based pseudo-reference electrode (PRE) has been fabricated planar to a ion-selective membrane (ISM) coated on the gold solid-contact electrode (SCE). The PRE has shown <inline-formula> <tex-math notation="LaTeX">$\lt 1~mV/day$ </tex-math></inline-formula> drift potential, exhibiting exceptional stability and reproducibility. While the SCE has demonstrated a high sensitivity of <inline-formula> <tex-math notation="LaTeX">$49~mV/log[K^{+}]$ </tex-math></inline-formula>, covering a wide linear detection range from <inline-formula> <tex-math notation="LaTeX">$10^{-4}~M$ </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">$1~M$ </tex-math></inline-formula> with a rapid response time of less than 10 seconds. The sensor has displayed minimal hysteresis (<inline-formula> <tex-math notation="LaTeX">$\lt 15~mV$ </tex-math></inline-formula>) and remained stable over a broad pH range (<inline-formula> <tex-math notation="LaTeX">$pH~4$ </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">$pH~10$ </tex-math></inline-formula>). These uni-planar, all-solid-state electrodes along with off-the-shelf FET mitigate the requirement of additional wire bonding by utilizing a common PCB platform for sensing as well as circuitry area. Additionally, the PRE, SCE and the FET in the EGFET-configuration-based sensing system have exhibited a high current sensitivity of <inline-formula> <tex-math notation="LaTeX">$1.43~(\mu A)^{1/2}/log[K^{+}]$ </tex-math></inline-formula>. Our sensor presents a practical and reliable solution for soil nutrient measurement in precision agriculture, offering significant advantages over existing potassium sensors in terms of cost-effectiveness, sensitivity, stability, and environmental safety. The presented approach holds promise for optimizing agricultural productivity and minimizing environmental impact through efficient nutrient monitoring and smart irrigation and fertilization management systems.