A smartphone sensing system for solid-contact ion-selective electrodes

Developing a portable ion-sensing platform with solid-contact ionselective electrodes (SCISEs) and a smartphone has great potential in on-site ion measurement and electronic tongue applications. Therefore, this study attempted to develop a smartphone-based SCISE sensing system, which integrates SCISEs with a smartphone-based sensing device. SCISEs were fabricated with screen-printed carbon electrodes (SPCE). After electrodeposition of a solid-contact (SC) layer, the ion-selective membranes were drop-casted on the SC-SPCE to make the SCISEs. We chose potassium (K
⁺
), ammonium (NH
₄
⁺
) and calcium (Ca
²⁺
) as target ions. The smartphone-based sensing device measures concentration with potentiometric method. The measured signals were controlled and computed by a microcontroller, then were sent to a smartphone by Bluetooth. Next, the results were computed, calibrated and displayed by the smartphone. The developed system could simultaneously measure different ions and display the result by the smartphone. Each SCISE in this study has Nernstian response and the linear range for detection was from 10
^-1
to 10
^-5
M. Finally, the smartphone-based SCISE sensing system was used to measure hydroponic samples during the cultivation of lettuce. The result show that the smartphone-based SCISE sensing system has the potential for on-site measurement. Further, the system could be used in electronic tongue applications.