The last decade saw the development of electrochemical paper-based analytical devices (ePADs).

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This current Review focuses on recent contributions of wearable and biodegradable sensors dedicated to health and environmental applications. Recent examples reported in the literature are presented and critically discussed in order to diagnose diseases and their response to treatment with a focus on cancer and Parkinson’s disease. Advances in devices for body temperature, humidity (skin hydration), human physiological signals, and metal detection in body fluids are demonstrated concerning simple and portable platforms. Studies performed outside the controlled laboratory environment can rapidly help in point-of-care analyses or self-examination by the patients. Environmental approaches are also outlined, aiming at gas detection, metal sensing, and environment humidity, including different substrates showing not only flexible and biodegradable sensors but also wireless detection and data communication. The discussed examples for health and environmental analyses have successfully demonstrated the considerable potential of wearable devices for real-time and on-site applications, highlighting the self-monitoring capacity. Future investigations should consider the device’s operational simplicity with a more straightforward interpretation of results to make them affordable for the market. The huge potential of wearable and biodegradable devices enables them as emerging and powerful platforms for replacing current gold standard methods for rapid health screening and environmental monitoring in the near future. The next trend in the technological field of the development and application of new biodegradable materials to wearable devices should focus on studies involving the stability, toxicity, and biocompatibility of the final devices.

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β-Hydroxybutyrate (HB) is one of the main physiological ketone bodies that play key roles in human health and wellness. Besides their important role in diabetes ketoacidosis, ketone bodies are currently receiving tremendous attention for personal nutrition in connection to the growing popularity of oral ketone supplements. Accordingly, there are urgent needs for developing a rapid, simple, and low-cost device for frequent onsite measurements of β-hydroxybutyrate (HB), one of the main physiological ketone bodies. However, real-time profiling of dynamically changing HB concentrations is challenging and still limited to laboratory settings or to painful and invasive measurements (e.g., a commercial blood ketone meter). Herein, we address the critical need for pain-free frequent HB measurements in decentralized settings and report on a reliable noninvasive, simple, and rapid touch-based sweat HB testing and on its ability to track dynamic HB changes in secreted fingertip sweat, following the intake of commercial ketone supplements. The new touch-based HB detection method relies on an instantaneous collection of the fingertip sweat at rest on a porous poly(vinyl alcohol) (PVA) hydrogel that transports the sweat to a biocatalytic layer, composed of the β-hydroxybutyrate dehydrogenase (HBD) enzyme and its nicotinamide adenine dinucleotide (NAD+) cofactor, covering the modified screen-printed carbon working electrode. As a result, the sweat HB can be measured rapidly by the mediated oxidation reaction of the nicotinamide adenine dinucleotide (NADH) product. A personalized HB dose–response relationship is demonstrated within a group of healthy human subjects taking commercial ketone supplements, along with a correlation between the sweat and capillary blood HB levels. Furthermore, a dual disposable biosensing device, consisting of neighboring ketone and glucose enzyme electrodes on a single-strip substrate, has been developed toward the simultaneous touch-based detection of dynamically changing sweat HB and glucose levels, following the intake of ketone and glucose drinks.

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Much effort was made in the literature to put pencil-drawing as an attractive way to fabricate electrochemical sensors. The pencil drawing is one of the easiest, cost-effective, unique single-step methods for fabricating paper-based devices without necessitating any expensive instrumentation by merely transferring the carbon by exfoliation abrasion on paper. Additionally, much has to be done to improve the quality of this transfer carbon to achieve a suitable sensing platform for electrochemical measurements. Hence, this review article aims to bring the new approaches developed in the last five years to circumvent some fabrication problems and enhance this “carbonization” step for electrochemistry detection using paper-based sensors. We will start the discussion on the carbon materials moving to the substrate and finally discuss the strategies to produce the conductive tracks and enhance their properties for sensing applications.