A Wearable Electrochemical Platform for Noninvasive Simultaneous Monitoring of Ca²⁺ and pH

TLDR

Ionized calcium homeostasis is essential for human physiology, yet its measurement is difficult because it requires strict procedures and is sensitive to pH, which itself influences metabolic reactions. The study presents a wearable electrochemical platform that continuously monitors ionized calcium and pH in body fluids via a disposable, flexible sensor array linked to a flexible PCB. The platform performs real‑time quantitative analysis of sweat, urine, and tears, with sensor accuracy confirmed against ICP‑MS for calcium and a commercial pH meter. The sensors exhibit high repeatability and selectivity, and real‑time on‑body measurements reveal that calcium concentration rises as pH falls, indicating the platform’s potential for diagnosing conditions like primary hyperparathyroidism and kidney stones.

Abstract

Homeostasis of ionized calcium in biofluids is critical for human biological functions and organ systems. Measurement of ionized calcium for clinical applications is not easily accessible due to its strict procedures and dependence on pH. pH balance in body fluids greatly affects metabolic reactions and biological transport systems. Here, we demonstrate a wearable electrochemical device for continuous monitoring of ionized calcium and pH of body fluids using a disposable and flexible array of Ca(2+) and pH sensors that interfaces with a flexible printed circuit board. This platform enables real-time quantitative analysis of these sensing elements in body fluids such as sweat, urine, and tears. Accuracy of Ca(2+) concentration and pH measured by the wearable sensors is validated through inductively coupled plasma-mass spectrometry technique and a commercial pH meter, respectively. Our results show that the wearable sensors have high repeatability and selectivity to the target ions. Real-time on-body assessment of sweat is also performed, and our results indicate that calcium concentration increases with decreasing pH. This platform can be used in noninvasive continuous analysis of ionized calcium and pH in body fluids for disease diagnosis such as primary hyperparathyroidism and kidney stones.