Search for: All records

In recent years, the field of wearable sensors has undergone significant evolution, emerging as a pivotal topic of research due to the capacity of such sensors to gather physiological data during various human activities. Transitioning from basic fitness trackers, these sensors are continuously being improved, with the ultimate objective to make compact, sophisticated, highly integrated, and adaptable multi-functional devices that seamlessly connect to clothing or the body, and continuously monitor bodily signals without impeding the wearer’s comfort or well-being. Potentiometric sensors, leveraging a range of different solid contact materials, have emerged as a preferred choice for wearable chemical or biological sensors. Nanomaterials play a pivotal role, offering unique properties, such as high conductivity and surface-to-volume ratios. This article provides a review of recent advancements in wearable potentiometric sensors utilizing various solid contacts, with a particular emphasis on nanomaterials. These sensors are employed for precise ion concentration determinations, notably sodium, potassium, calcium, magnesium, ammonium, and chloride, in human biological fluids. This review highlights two primary applications, that is, (1) the enhancement of athletic performance by continuous monitoring of ion levels in sweat to gauge the athlete’s health status, and (2) the facilitation of clinical diagnosis and preventive healthcare by monitoring the health status of patients, in particular to detect early signs of dehydration, fatigue, and muscle spasms. 

Abstract The ability to miniaturize ion‐selective sensors that enable microsensor arrays and wearable sensor patches for ion detection in environmental or biological samples requires all‐solid‐state sensors with solid contacts for transduction of an ion activity into an electrical signal. Nanostructured carbon materials function as effective solid contacts for this purpose. They can also contribute to improved potential signal stability, reducing the need for frequent sensor calibration. In this Perspective, the structural features of various carbon‐based solid contacts described in the literature and their respective abilities to reduce potential drift during long‐term, continuous measurements are compared. These carbon materials include nanoporous carbons with various architectures, carbon nanotubes, carbon black, graphene, and graphite‐based solid contacts. The effects of accessibility of ionophores, ionic sites, and other components of an ion‐selective membrane to the internal or external carbon surfaces are discussed, because this impacts double‐layer capacitance and potential drift. The effects of carbon composition on water‐layer formation are also considered, which is another contributor to potential drift during long‐term measurements. Recommendations regarding the selection of solid contacts and considerations for their characterization and testing in solid‐contact ion‐selective electrodes are provided.