WEARABLE DEVICE FOR REAL TIME pH MEASUREMENT IN SWEAT

Abstract

Nowadays, it is more and more common to find devices that permits to everybody carry out analysis of different analytes of interest as glucose in blood or creatinine in urine by themselves, thanks to the development of the Point-of-Care (POC) devices. POC’s permit the in situ analysis of the samples, in an easy way, quickly and by the use of a small amount of sample in the sampling area of the device, obtaining result with no need of instrumentation or by the use of a very simple one. In order to match these objectives and make the device useful for everybody in any condition, the WHO has described the ASSURED guidelines for the POC devices[1]. In the recent years, and thanks to the capillary properties of different materials as paper, thread or cloth, the development of the POC devices are turning to a new strategy that implies the inclusion of the POC devices in t-shirts, bracelets or patches obtaining in this way wearables sensors. In this kind of sensor, instead of the addition of the sample in the sampling area, it moves through the device arriving to recognition/transduction area were the property of the sensor changes and can be measured and related to the concentration of the analyte. In this work, we present a wearable POC that permits the real-time determination of the pH in sweat. For this purpose, we have developed a μCAD (Figure) that contains a pH indicator (4-[4-(2-hydroxyethanesulfonyl)-phenylazo]-2,6-dimethoxyphenol (GJM-534) [2]) covalently immobilized on cotton cloth, which color is going to change from yellow (pH around 6) to pink (pH around 9) depending on the pH. The size and shape of the μCAD (see Figure) was designed taking into account the low flow rate of sweat generated in the wrist when sweating (0.01 μL/min) including a superabsorbent material working as passive pump to avoid the saturation of sample of the μCAD. The colorimetric device was calibrated using the H parameter from the HSV color space as analytical parameter, obtaining the calibration function and analytical parameters of the device, the reversibility of the μCAD, response time and stability. Finally, the μCAD was integrated into a bracelet that includes a color detector and a microprocessor that registered the color of the μCAD in real-time and send the information via Bluetooth to a smartphone, obtaining and registering the pH of the sweat while doing exercise.