Wireless, Flexible, Ion-Selective Electrode System for Selective and Repeatable Detection of Sodium

Abstract

Wireless, flexible, ion-selective electrodes (ISEs) are of great interest in the development of wearable health monitors and clinical systems. Existing film-based electrochemical sensors, however, still have practical limitations due to poor electrical contact and material–interfacial leakage. Here, we introduce a wireless, flexible film-based system with a highly selective, stable, and reliable sodium sensor. A flexible and hydrophobic composite with carbon black and soft elastomer serves as an ion-to-electron transducer offering cost efficiency, design simplicity, and long-term stability. The sensor package demonstrates repeatable analysis of selective sodium detection in saliva with good sensitivity (56.1 mV/decade), stability (0.53 mV/h), and selectivity coefficient of sodium against potassium (−3.0). The film ISEs have an additional membrane coating that provides reinforced stability for the sensor upon mechanical bending. Collectively, the comprehensive study of materials, surface chemistry, and sensor design in this work shows the potential of the wireless flexible sensor system for low-profile wearable applications.

Development of Flexible Ion-Selective Electrodes for Saliva Sodium Detection

“…Selectivity analysis, carried out with the most abundant interference ions in body fluids, resulted in good coefficient (log K) values of −2.68, −7.52, and −6.57 for K + , Mg 2+ , and Ca 2+ , respectively ( Figure 2 h). The selectivity coefficient is calculated by a separate solution method by using the potential at 0.1 M [ 31 , 32 ], while detailed calculation methods are provided in our previous works [ 18 , 33 ]. Collectively, the sensing capability and signal stability are achieved by constructing multiple layers of the electrode structure, improving interlayers’ adhesion and encapsulating all contact areas that can cause signal noises.…”

“…The advancement in SS-ISEs has successfully removed the use of the fragile parts and minimized the sensor’s size by direct contact between all-solid-state layers of an electron collector, ion-to-electron transducer, and ion-selective membrane [ 7 ]. By developing a materials’ structure and detection system, the SS-ISE functioned well through a few steps of pre-stabilization for the surface hydration, calibration in the range of ion levels of interest, and detection of the analytes via a small voltage-reading circuit [ 18 ]. Indeed, the urgent need is to compare the ion levels in blood with the non-invasive salivary ions measured from a small SS-ISE system in clinical settings [ 19 ].…”

Biomedical and Tissue Engineering Strategies to Control Foreign Body Reaction to Invasive Neural Electrodes

“…Such brilliant strategy could be further implemented for peripheral nerve electrodes, envisioning exciting opportunities for their chronic implants. Wireless and flexible film-based ion-selective electrodes (ISEs) have also been recently developed as miniaturized systems for performing highly sensitive and non-invasive measurements ( Lim et al, 2020 ). These sensor systems, made of carbon–polymer composite transducers integrated onto a flexible circuit, enable ions detection in body fluids with high accuracy and selectivity and for prolonged lifetime, showing great potential for their application also in health studies and clinical systems.…”

Molecular and physical technologies for monitoring fluid and electrolyte imbalance: A focus on cancer population

“…Lim et al also developed a wireless flexible film-based system with a Na + sensor using hydrophobic composite, carbon black, and soft elastomer. 118 The sensor system demonstrates a repeatable analysis of selective Na + detection in saliva, and shows good sensitivity, stability, and selectivity coefficient of Na + against K + . Most recently, Sempionatto et al developed a flexible skin-mounted microfluidic potentiometric device for simultaneous electrochemical monitoring of Na + and K + in sweat.…”