Sweat Lactate Sensor Integrated with Microfluidicand Iontophoresis System for Analysing Sweat without Physical Activity

Abstract: Background: Understanding lactate levels can provide important information aboutour body’s condition. For athletes, this can improve their training and prevent earlyfatigue. In healthcare, monitoring lactate can provide valuable information and potentially prevent life-threatening episodes. Lactate can be measured non-invasively byanalyzing sweat. This is advantageous over the typical blood sampling since it is saferand pain-free. Sweat can be stimulated by using a method called iontophoresis. Itapplies a small current between two electrodes placed on the skin’s surface, deliveringsubstances to the inner layer of the skin. Objectives: The aim of this study was to design a device that implements iontophoresis to activate sweat production and uses a microfluidic system to collect thesweat and deliver it to a lactate sensor and provide a signal. Methodology: A device was designed in AutoCAD and 3D printed. It was improvedby trial and error. A sweat collecting test was performed to validate the iontophoresissystem. The efficiency of the microfluidic system was tested by recording the time ittakes to collect enough sweat to get a lactate signal. Finally, calibration tests wereperformed to validate the lactate signal in the form of batch-mode and flow-mode. Results: The sweat collection test produced 27 µL of sweat in 15 minutes and 49 µLin 30 minutes. The microfluidic system delivered sweat to the sensor and activated itin less than 3 minutes. The linearity of the batch-mode calibration, R2-value, was0.9994, and for the flow-mode it was 0.8908.Conclusions: The iontophoresis system stimulated sweat production, which themicrofluidic system delivered to the lactate sensor successfully. The lactate sensorwas implemented into the device, and a signal was detected. However, it could not becalibrated efficiently enough to display the electric signal as a lactate concentration.