Epifluidic Colorimetric Patch For On-Skin Analysis Of Regional Sweat Chloride Concentration During Laboratory-Based Exercise

Assessing regional sweat electrolyte concentrations using standard patch techniques requires post-collection benchtop harvesting and analysis of sweat, which precludes real-time feedback to athletes. A technique enabling on-skin analysis is needed to advance the practicality of sweat testing. PURPOSE: To determine the accuracy and reliability of a novel epidermal microfluidic patch with built-in colorimetric assay (Epifluidic patch) to measure regional sweat [Cl-]. METHODS: Twenty-three subjects (15 male, 8 female; 18-42 y; 72.3±11.2 kg) cycled at 85% HRmax in a warm laboratory (30°C, 50% rh) while sweat was collected from the right and left ventral forearms with an Absorbent patch (3M Tegaderm+Pad) and Epifluidic patch (Epicore Biosystems, Inc.), respectively. A subset of subjects (n=9) completed two identical trials 2-4 days apart to determine test-retest reliability. Immediately after removal of the Absorbent patch, an image was taken of the Epifluidic patch on-skin with a digital single-lens reflex camera for analysis of [Cl-] via colorimetry. Sweat from the Absorbent patch was extracted via centrifuge and subsequently analyzed for [Cl-] by ion chromatography. Data are shown as mean±SD. RESULTS: There was no difference in sweat [Cl-] between Absorbent and Epifluidic patches (32.9±16.8 vs. 34.5±19.6 mmol/L, p=0.21). Bland-Altman Limits of Agreement between methods was -10.1 to 13.3 mmol/L. There was a significant correlation between patches (r=0.96, p<0.0001) and the coefficient of determination (r2) for predicting Absorbent from Epifluidic patch [Cl-] was 0.92. Based on Deming regression analysis, the slope and intercept of the regression line describing Absorbent vs. Epifluidic patch sweat [Cl-] were not different than 1 and 0, respectively. Sweat [Cl-] was not different between repeat trials for the Absorbent (1.4±4.4 mmol/L, p=0.36) or Epifluidic patch (-0.4±1.6 mmol/L, p=0.51) and test-retest CVs were 12% and 4%, respectively. CONCLUSIONS: The Epifluidic patch provides accurate and reliable data for forearm sweat [Cl-] estimation during exercise in controlled laboratory conditions. Future research is needed to evaluate the Epifluidic Colorimetric Patch for on-skin analysis of sweat [Cl-] at other regional sites as well as during live practices and games.