Abstract
Wearable sensors based on solid-contact ion-selective electrodes (SC-ISEs) are currently attracting intensive attention in monitoring human health conditions through real-time and non-invasive analysis of ions in biological fluids. SC-ISEs have gone through a revolution with improvements in potential stability and reproducibility. The introduction of new transducing materials, the understanding of theoretical potentiometric responses, and wearable applications greatly facilitate SC-ISEs. We review recent advances in SC-ISEs including the response mechanism (redox capacitance and electric-double-layer capacitance mechanisms) and crucial solid transducer materials (conducting polymers, carbon and other nanomaterials) and applications in wearable sensors. At the end of the review we illustrate the existing challenges and prospects for future SC-ISEs. We expect this review to provide readers with a general picture of SC-ISEs and appeal to further establishing protocols for evaluating SC-ISEs and accelerating commercial wearable sensors for clinical diagnosis and family practice.
Highlights
With the rapid growth of personal healthcare and fitness systems, wearable devices that can provide real-time and continuous monitoring of an individual’s physiological state have attracted great attention in recent years
The results showed a standard potential (259.3 ± 1.3 mV) and small drift (0.23 mV/day), which were comparable with conventional Ca-Ion-selective electrodes (ISEs)
Compared with traditional liquid-contact ion-selective electrodes (LC-ISEs), solid-contact ion-selective electrodes (SC-ISEs) reveals the advantages for wearable sensors that can be miniaturized and integrated for continuously detecting the ions in body fluids like sweat, interfacial fluid or saliva in a non-invasive way
Summary
With the rapid growth of personal healthcare and fitness systems, wearable devices that can provide real-time and continuous monitoring of an individual’s physiological state have attracted great attention in recent years. An example of the SC-ISEs for wearable sensor solid ion-to-electron transducer layer and ISM. For the solid-contact transducer materials, classic conductive mechanisms including redox capacitance and electric-double-layer (EDL) capacitance-based potential polymers and carbon materials and other nanomaterials (e.g., Au nanomaterials) will be illustrated stabilization will be discussed. For SC-ISEs with an EDL capacitance mechanism (Figure 2B), the ion-to-electron transduction is formed from the EDL between the ISM and the SC interface. It can be described as an asymmetric capacitor where one side is formed by electrons (or holes) and the other side is balanced by ions (cations or anions) from the ISM.
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