Non‐invasive Analyte Access and Sensing through Eccrine Sweat: Challenges and Outlook circa 2016

TLDR

Eccrine sweat offers ergonomic advantages over traditional biofluids, yet its clinical use has been limited by low volumes, evaporation, dilution, contamination, and mixing, though these challenges are not considered insurmountable. The study aims to overcome barriers to sweat biosensing for sedentary users and low‑concentration analytes by advancing stimulation, collection, and sensor technologies. This requires significant progress in sweat stimulation, efficient sample collection, and compact sensor design. Recent wearable sweat devices have mitigated several historical challenges, yet their effectiveness remains confined to high‑concentration analytes at high sweat rates.

Abstract

Abstract Despite the many ergonomic advantages of eccrine perspiration (sweat) compared to other possible biofluids (particularly in “wearable” devices), sweat remains an underrepresented source of biomarker analytes compared to the established biofluids blood, urine, and saliva. Upon closer comparison to other non‐invasive biofluids, the advantages may even extend beyond ergonomics: sweat might provide superior analyte information. A number of challenges, however, have historically kept sweat from its place in the pantheon of clinical samples. These challenges include very low sample volumes (nL to µL), unknown concentration due to evaporation, filtration and dilution of large analytes, mixing of old and new sweat, and the potential for contamination from the skin surface. More recently, rapid progress in “wearable” sweat sampling and sensing devices has resolved several of the historical challenges. However, this recent progress has also been limited to high concentration analytes (µM to mM) sampled at high sweat rates (>1 nL/min/gland, e.g. athletics). Progress will be much more challenging as sweat biosensing moves towards use with sedentary users (low sweat rates or not sweating at all) and/or towards low concentration analytes (pM to nM). Addressing these unresolved challenges will require significant advances in sweat stimulation, sample collection efficiency, compact sensors, and likely more. Fortunately, none of the remaining challenges appear to be fundamentally blocking, and scientific and engineering innovations have the opportunity to enable broader application of sweat biosensing technology.