A new oil/membrane approach for integrated sweat sampling and sensing: sample volumes reduced from μL's to nL's and reduction of analyte contamination from skin

Abstract

Wearable sweat biosensensing technology has dominantly relied on techniques which place planar-sensors or fluid-capture materials directly onto the skin surface. This 'on-skin' approach can result in sample volumes in the μL regime, due to the roughness of skin and/or due to the presence of hair. Not only does this increase the required sampling time to 10's of minutes or more, but it also increases the time that sweat spends on skin and therefore increases the amount of analyte contamination coming from the skin surface. Reported here is a first demonstration of a new paradigm in sweat sampling and sensing, where sample volumes are reduced from the μL's to nL's regime, and where analyte contamination from skin is reduced or even eliminated. A micro-porous membrane is constructed such that it is porous to sweat only. To complete a working device, first placed onto skin is a cosmetic-grade oil, secondly this membrane, and thirdly the sensors. As a result, spreading of sweat is isolated to only regions above the sweat glands before it reaches the sensors. Best case sampling intervals are on the order of several minutes, and the majority of hydrophilic (low oil solubility) contaminants from the skin surface are blocked. In vitro validation of this new approach is performed with an improved artificial skin including human hair. In vivo tests show strikingly consistent results, and reveal that the oil/membrane is robust enough to even allow horizontal sliding of a sensor.

Thin, Soft, Skin‐Mounted Microfluidic Networks with Capillary Bursting Valves for Chrono‐Sampling of Sweat

“…The analytes explored here are not significantly affected by this form of contamination, but protein, glucose, calcium, and urea concentrations can be altered, especially in the sweat samples collected at or near the onset of sweating. For the wide application of this device, application of mineral oil on the skin could be an appropriate solution for obtaining sweat samples least contaminated at the sweat‐epidermal interface …”

Enhancing glucose flux into sweat by increasing paracellular permeability of the sweat gland

“…Skin surface contaminates become an even larger issue for small samples. These issues can be avoided by preventing sweat from contacting the epidermis by coating the skin with an occluding layer of petroleum jelly or oil [ 30 , 31 ] ( S4 Fig ).…”

CMOS Interfaces for Internet-of-Wearables Electrochemical Sensors: Trends and Challenges

“…This may be achieved through injury prevention and early detection [40], but also through the monitoring of effort and hydration in real time through sweat, which is the obvious sample medium to monitor, given its abundance during physical exertion [41]. In spite of this, sweat measurements also require choosing an adequate body area for sampling [17] and smart sweat management strategies [42], the most common of which are based on microfluidics [43][44][45] or on absorbents and lateral flow membranes [15,20,46].…”