Fig. 5: Light-adaptive, power-efficient sensor for sweat rate, sweat loss and sweat biomarker concentrations.
a Top view schematic illustration of the microfluidic system and diagram of the mechanism of colorimetric sensing by use of ambient light and block diagram of the electronics and microfluidics. b Exploded view schematic illustration that highlights the PV cell, the microfluidic structure, BLE SoC, and the pair of LiPo batteries, all attached via an fPCB platform and housed in a silicone encapsulation structure. c Pictures of the sweat sensing part of the system for measuring sweat rate and sweat loss with an arrow that highlights propagation of ionic liquid during operation in daylight (left images) and in the dark (right images). (The red scale bar is 3 mm, and the white scale bar is 3 mm). Pictures that highlight changes in color of the (d) chloride (e) glucose (f) pH assays at different concentrations. The bottom graph shows results of colorimetric sensing based on ambient light (E355998 LED Lamp, Great Eagle), with a log scale representation of the ratio of the photovoltage measured by the sample and reference PDs, a different concentrations (n = 5). The minimum and maximum values (top and bottom lines), the IQR, which spans from the 25th to the 75th percentiles (boundaries of the box), and the median of the dataset (represented by a circle) are shown in the box plots. Whiskers extend to 1.5 times the IQR. g The voltage profile of the reference and sensing PDs (black) and log scale representation of the ratio of these two voltages (red) for cases of injection of a 50 mM NaCl solution after a 25 mM NaCl solution under microscopes light (SCW-PGC, Carton Optical Industries). h Results of colorimetric sensing of chloride concentration using PL and ratio of photovoltages between the sample and reference PDs at different chloride concentrations in a dark environment(n = 7). The top and bottom lines, the boundary of the box, and the circle shape indicate the minimum and maximum results, the IQR within the 25th to the 75th percentiles, and the median. Whiskers extend to 1.5 times the IQR. The inset image shows a cross-sectional illustration of the reservoir with a PL channel structure for operation at night. i Dependence of VPV on time for sensors with and without the aPM module, operated in Evanston, IL.
