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

Although wearable technologies have recently seen a water-shed moment in their commercialization, the introduction of new capabilities has not kept pace with rapidly rising expectations in the medical, industrial, and consumer markets. This is partly because today s wearable technologies remain heavily reliant on decades-old techniques for accessing information from the body. Many wearable technologies, for example, simply electrically or optically interrogate the body from outside skin, which severely limits the specificity of their detection. The identification and quantification of most biomarkers (ions, molecules, proteins, etc.), is instead only possible through a probe that relies on direct chemical interaction with the analyte. Creating such chemical sensors in a wearable format remains a significant challenge, but, as revealed in this special issue of Electroanalysis, appears promising. However, even if you can make such sensors [1], there remains a second, perhaps even greater challenge: how does one reliably and non-invasively extract biomarker analytes from the body? It has been recently postulated by several groups that this second challenge can be resolved by sampling and sensing of analytes in eccrine sweat (Fig. 1), as supported by emergent theory [2] and recent technological demonstrations [1–6]. This article reviews the status of wearable biosensing of analytes in eccrine sweat, including both challenges and outlook circa 2016. Eccrine sweat has many inherent advantages over other non-invasive biofluids (tears, saliva, urine), but also has numerous and unique challenges. This article may serve useful for those considering exploration of sweat biosensing, but also raises many issues that are relevant to biosensing with other non-invasive or minimally invasive techniques.