Development of Flexible Ion-Selective Electrodes for Saliva Sodium Detection

• Authors: Hyo-Ryoung Lim, Georgia Institute of Technology; Soon M Lee, Yonsei University; Musa Mahmood, Georgia Institute of Technology; Shinjae Kwon, Georgia Institute of Technology; Yun-Soung Kim, Georgia Institute of Technology; Yongkuk Lee, Wichita State University; Woon-Hong Yeo, Emory University
• Journal Title: SENSORS
• Volume: Volume 21, Number 5
• Publisher: MDPI | 2021-03-01, Pages 1-11
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.3390/s21051642
• Subjects: Engineering, Mechanical; Engineering, Biomedical
• Keywords: Science & Technology; Physical Sciences; Technology; Chemistry, Analytical; Engineering, Electrical & Electronic; Instruments & Instrumentation; Chemistry; Engineering; saliva-to-blood sodium levels; electrochemical sensor; ion-selective electrode; non-invasive diagnosis

Abstract

Saliva can be used for health monitoring with non-invasive wearable systems. Such devices, including electrochemical sensors, may provide a safe, fast, and cost-efficient way of detecting target ions. Although salivary ions are known to reflect those in blood, no available clinical device can detect essential ions directly from saliva. Here, we introduce an all-solid-state, flexible film sensor that allows highly accurate detection of sodium levels in saliva, comparable to those in blood. The wireless film sensor system can successfully measure sodium ions from a small volume of infants’ saliva (<400 µL), demonstrating its potential as a continuous health monitor. This study includes the structural characterization and error analysis of a carbon/elastomer-based ion-selective electrode and a reference electrode to confirm the signal reliability. The sensor, composed of a pair of the electrodes, shows good sensitivity (58.9 mV/decade) and selectivity (log K = −2.68 for potassium), along with a broad detection range of 5 × 10−5 ≈ 1 M with a low detection limit of 4.27 × 10−5 M. The simultaneous comparison between the film sensor and a commercial electrochemical sensor demonstrates the accuracy of the flexible sensor and a positive correlation in saliva-to-blood sodium levels. Collectively, the presented study shows the potential of the wireless ion-selective sensor system for a non-invasive, early disease diagnosis with saliva.