Sweat, Interstitial Fluid, and Saliva-Based Wearable Devices for Continuous Monitoring of Metabolites and Biomarkers

Biomedical diagnosis, a key component of healthcare, has witnessed considerable efforts toward moving from invasive blood-centered diagnostics, mainly implemented in hospital settings, to personalized, decentralized, and remote diagnostics. In this regard, wearable sensing platforms have become the center of attention not only for remote patient monitoring but also for other potential applications, from wellness and nutrition monitoring to tracking safety and security. While initial efforts in the wearable sensing field focused on monitoring vital signs and physical metrics, recent attempts have mainly been directed at realizing wearable chemical sensors capable of tracking the body’s physiological state at the molecular level. Wearable devices are rapidly developing enabling users to monitor their health parameters with wireless-enabled devices. Such next-generation minimally invasive or noninvasive devices can continuously measure the dynamically changing levels of clinically informative biomarkers/therapeutic drugs in peripheral biofluids, such as sweat, saliva, tears, and interstitial fluid. This chapter focuses on the recent developments of such wearable technologies and devices employing microneedles, tattoos, mouthguards, textiles, and glove-based sensing strategies.