This work demonstrates a continuous, noninvasive wearable sensor for the measurement of inflammation in sweat via disease-specific and general markers Calprotectin and Interleukin-6 (IL-6), respectively. 12 subjects wore the sensor over a two-day period, during which their Calprotectin and IL-6 levels were measured continuously from sweat expired passively at the skin surface, according to Figure 1, a schematic of the sensor’s mechanism of detection which utilizes electrochemical impedance spectroscopy (EIS). Target markers Calprotectin and IL-6 bind to antibody-functionalized electrodes at the sensor surface, thereby creating a measurable impedance change. Sensor impedance was recorded continuously with a sampling rate of 1-1.5 minutes for a period of 40 hours. Sensor stability was demonstrated through continuous relative humidity and temperature measurements of the sensor-skin interface over the study period. Measurements were validated by comparison to synchronously collected salivary measurements.
Calprotectin and IL-6 were measured in sweat and saliva of 2 chronically inflamed subjects and 10 healthy subjects over a two-day period. Temporal 40-hour continuous tracking of sweat Calprotectin demonstrated higher basal Calprotectin in chronically inflamed subjects over a healthy subject. Between sweat and saliva, Calprotectin and IL-6 demonstrated a strong linear relationship (R²>0.7) and strong to moderate linear relationships between Calprotectin and IL-6 in sweat and saliva, respectively. Bland-Altman analysis and Deming regression analysis determined low incidence of outliers and similar ranges of Calprotectin and IL-6 expression between sweat and saliva. Diurnal observations of Calprotectin expression demonstrated significantly higher sweat Calprotectin and higher median Calprotectin measured in the morning-afternoon than measured in the evening among inflamed and healthy subjects, respectively.

Figure 1. Overview of the wearable inflammation sensor and device design.

Kai-Chun Lin

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