(324a) Osmotic-Capillary Principle Inspired Biofluid Sampling and Sensing

The current market for biosensor-based health monitoring is continuously rising. The demand for biosensors is proportionally rising majorly due to the following two reasons: (a) Biosensors as either wearables, or in-situ point-of-care (POC) testing platforms allow rapid, on-site monitoring of several disease biomarkers under decentralized settings, (b) Such platforms can allow continuous tracking of one’s health status non-invasively and without the intervention of trained medical professionals. Despite the research progress with alternative (to blood) biofluids as essential candidates for disease biomarker detection, a majority of these remain difficult to be released continuously.^[1] As an alternative, sweat can be generated continuously on-skin via physical exertion and is an useful repository for disease biomarkers. However, conventional sweat-based devices function with active perspiration (sweat on skin prior testing), which makes them inoperative under exertion-free low sweat rate conditions. We demonstrate a new principle for the design of wearable patches which are capable of extracting sweat under both resting and actively perspiring conditions using osmotic pressure difference for pumping, and evaporation for liquid disposal.^[2] Our patch is composed of silicone, hydrogel, and a paper microfluidic conduit with a site of evaporation at the end (evaporation pad). The hydrogel (pump) is equilibrated with a high concentrated solution to build up the desired osmotic strength to extract sweat from the skin under rest.² The sampled sweat analytes can be analyzed directly on the paper channel with both colorimetric^[3] and electrochemical sensing^[4] methods. The analyte amount also depends on the dimensions of the paper channel, hydrogel area and paper pore size. Human trials have shown the potential to extract sweat and analyze it for lactate under both resting and non-resting conditions. We chose lactate as a concept biomarker since its concentration in sweat ranges ~ mM. Our group is currently investigating how this sweat sampling concept can be further integrated with microneedle patches for long-term interstitial fluid (ISF) sampling and on the fingertip for biofuel cell applications.

[1] T. Saha, R. Del Caño, E. la De Paz, S. S. Sandhu, J. Wang, Small 2022, 2206064, 2206064.

[2] T. Shay, T. Saha, M. D. Dickey, O. D. Velev, Biomicrofluidics 2020, 14, 034112.

[3] T. Saha, J. Fang, S. Mukherjee, M. D. Dickey, O. D. Velev, ACS Appl. Mater. Interfaces 2021, 13, 8071.

[4] T. Saha, T. Songkakul, C. T. Knisely, M. A. Yokus, M. A. Daniele, M. D. Dickey, A. Bozkurt, O. D. Velev, ACS Sensors 2022, 7, 2037.

[5] J. Moon, R. Del Caño, C. Moonla, K. Sakdaphetsiri, T. Saha, L. Francine Mendes, L. Yin, A. Chang, S. Seker, J. Wang, ACS Sensors 2022, 7, 3973.