4.1. Reagents and instrumentation

Phosphate buffered saline (PBS) at pH 7.3 and the cross‐linker DTSSP (3,3′‐dithiobis [sulfo‐succinimidyl propionate]) were purchased from Thermo Fisher Scientific (Waltham, MA). The high‐performance liquid chromatography (HPLC) purified 85‐mer cortisol binding ssDNA aptamer (100 ng), Hydrocortisone (corticosteroid) stress hormone, and IDTE resuspension buffer (10 mM Tris and 0.1 mM EDTA at pH 8.0) were purchased from Integrated DNA Technologies (Coralville, IA). The glucose oxidase enzyme (synthesized from Aspergillus niger) and D‐(+)‐glucose analyte was purchased from Sigma‐Aldrich Chemicals (St. Louis, MO). In‐house‐made synthetic sweat at pH 7.2 was used for sensor characterization.³⁹ The Roche Accu‐check Gluco‐meter was purchased from Amazon.com, Inc. (Seattle, WA) for BG testing.^{40, 41} Standard chemical analyses like the Enzyme‐linked immunosorbent assay method (ELISA) and LUMINEX were applied as reference methods. The ELISA kit was a customized kit purchased⁴² from Fab‐Gennix International Inc. (Frisco, TX) and LUMINEX‐xmap technology‐based Cortisol Human Procarta Plex ⁽™⁾ Simplex Kit was purchased⁴³ from Thermo‐Fisher Scientific, (Waltham, MA). These reference tests were chosen to compare the WATCH sweat sensing device performance to commercially available technology.