Skin-interfaced wearable systems with integrated colorimetric assays, microfluidic channels, and electrochemical sensors offer powerful capabilities for noninvasive, real-time sweat analysis. This Perspective details recent progress in the development and translation of novel wearable sensors for personalized assessment of sweat dynamics and biomarkers, with precise sampling and real-time analysis. Sensor accuracy, system ruggedness, and large-scale deployment in remote environments represent key opportunity areas, enabling broad deployment in the context of field studies, clinical trials, and recent commercialization. On-body measurements in these contexts show good agreement compared to conventional laboratory-based sweat analysis approaches. These device demonstrations highlight the utility of biochemical sensing platforms for personalized assessment of performance, wellness, and health across a broad range of applications.

State of Sweat: Emerging Wearable Systems for Real-Time, Noninvasive Sweat Sensing and Analytics.

The rise of wearable sensors to measure lactate content in human sweat during sports activities has attracted the attention of physiologists given the potential of these "analytical tools" to provide real-time information. Beyond the assessment of the sensing technology per se, which, in fact, has not rigorously been validated yet in controlled conditions, there are many open questions about the true usefulness of such wearable sensors in real scenarios. On the one hand, the evidence for the origin of sweat lactate (e.g., via the sweat gland, derivation from blood, or other alternative mechanisms), its high concentration (1-25 mM or even higher) compared to levels in the blood, and the possible correlation between different biofluids (particularly blood) is rather contradictory and generates vivid debate in the field. On the other hand, it is important to point out that accurate detection of sweat lactate is highly dependent on the procedure used to collect and/or reach the fluid, and this can likely explain the large discrepancies reported in the literature. In brief, this paper provides our vision of the current state of the field and a thoughtful evaluation of the possible reasons for present controversies, together with an analysis of the impact of wearable sweat lactate sensors in the physiological context. Finally, although there is not yet overwhelming scientific evidence to provide an unequivocal answer to whether wearable sweat lactate sensors can contribute to sports physiology, we still understand the importance to bring this challenging question up-front to create awareness and guidance in the development, validation, and implementation of wearable sensors.

https://biblio.ugent.be/publication/8726796/file/8726797.pdf

Can Wearable Sweat Lactate Sensors Contribute to Sports Physiology

Conventional electronic (e‐) skins are a class of thin‐film electronics mainly fabricated in laboratories or factories, which is incapable of rapid and simple customization for personalized healthcare. Here a new class of e‐tattoos is introduced that can be directly implemented on the skin by facile one‐step coating with various designs at multi‐scale depending on the purpose of the user without a substrate. An e‐tattoo is realized by attaching Pt‐decorated carbon nanotubes on gallium‐based liquid‐metal particles (CMP) to impose intrinsic electrical conductivity and mechanical durability. Tuning the CMP suspension to have low‐zeta potential, excellent wettability, and high‐vapor pressure enables conformal and intimate assembly of particles directly on the skin in 10 s. Low‐cost, ease of preparation, on‐skin compatibility, and multifunctionality of CMP make it highly suitable for e‐tattoos. Demonstrations of electrical muscle stimulators, photothermal patches, motion artifact‐free electrophysiological sensors, and electrochemical biosensors validate the simplicity, versatility, and reliability of the e‐tattoo‐based approach in biomedical engineering.

A Personalized Electronic Tattoo for Healthcare Realized by On‐the‐Spot Assembly of an Intrinsically Conductive and Durable Liquid‐Metal Composite

A self-driven sensor that can detect urine and urine sugar and can be mounted on diapers is desirable to reduce the burden of long-term care. In this study, we created a paper-based glucose biofuel cell that can be mounted on diapers to detect urine sugar. Electrodes for biofuel cells were produced by printing MgO-templated porous carbon on which poly(glycidyl methacrylate) was modified using graft polymerization. A new bioanode was prepared through covalently modifying flavin-adenine-dinucleotide-dependent glucose dehydrogenase and azure A with pendant glycidyl groups of poly(glycidyl methacrylate). We prepared a cathode with covalently bonded bilirubin oxidase. Covalent bonding of enzymes and mediators to both the bioanode and biocathode suppressed elution and improved stability. The biofuel cell could achieve a maximum output density of 0.12 mW cm-2, and by combining it with a wireless transmission device, the concentration of glucose sensed from the transmission frequency was in the range of 0-10 mM. The sensitivity of the sensor was estimated at 0.0030 ± 0.0002 Hz mmol-1 dm3. This device is expected to be a new urine-sugar detection device, composed only of organic materials with a low environmental load and it can be useful for detecting postprandial hyperglycemia.

Self-Powered Diaper Sensor with Wireless Transmitter Powered by Paper-Based Biofuel Cell with Urine Glucose as Fuel.

Self-powered and wearable biosensors for healthcare

Continuous Sweat Lactate Monitoring System with Integrated Screen-Printed MgO-templated Carbon-Lactate Oxidase Biosensor and Microfluidic Sweat Collector

Masaya Mitsumoto

Papers

Continuous Sweat Lactate Monitoring System with Integrated Screen-Printed MgO-templated Carbon-Lactate Oxidase Biosensor and Microfluidic Sweat Collector