BACKGROUND: Sweat chloride testing for diagnosis of cystic fibrosis (CF) 
involves sweat induction, collection and handling, and measurement in an 
analytical lab. We have developed a wearable sensor with an integrated salt 
bridge for real-time measurement of sweat chloride concentration. Here, in a 
proof-of-concept study, we compare the performance of the sensor to current 
clinical practice in CF patients and healthy subjects.
METHOD: Sweat was induced on both forearms of 10 individuals with CF and 10 
healthy subjects using pilocarpine iontophoresis. A Macroduct sweat collection 
device was attached to one arm and sweat was collected for 30 min and then sent 
for laboratory analysis. A sensor was attached to the other arm and the chloride 
ion concentration monitored in real time for 30 min using a Bluetooth 
transceiver and smart phone app.
RESULTS: Stable sweat chloride measurements were obtained within 15 min 
following sweat induction using the wearable sensor. We define the detection 
time as the time at which the standard deviation of the real-time chloride ion 
concentration remained below 2 mEq/L for 5 min. The sweat volume for sensor 
measurements at the detection time was 13.1 ± 11.4 μL (SD), in many cases lower 
than the minimum sweat volume of 15 μL for conventional testing. The mean 
difference between sweat chloride concentrations measured by the sensor and the 
conventional laboratory practice was 6.2 ± 9.5 mEq/L (SD), close to the 
arm-to-arm variation of about 3 mEq/L. The Pearson correlation coefficient 
between the two measurements was 0.97 highlighting the excellent agreement 
between the two methods.
CONCLUSION: A wearable sensor can be used to make real-time measurements of 
sweat chloride within 15 min following sweat induction, requiring a small sweat 
volume, and with excellent agreement to standard methods.