Multi-Variate Bio Wearable Sensor Patch for Glucose, Lactate, pH and Temperature Sensing Using Human Sweat

Wearable biosensors are gaining importance as they can now be more reliably used for detection of several biomarkers. Human sweat, which can be used non-invasively, has been shown to be rich in biomarkers with values in sweat showing a good correlation to the blood [1,2]. Glucose, lactate, pH and temperature are some of the important biomarkers which can indicate a lot about the individual’s health. This type of multi-variate bio wearable has applications in athletes, diabetic patients and for monitoring other health conditions.<br/><br/>Here, we present an integrated design for a bio wearable patch with glucose, lactate, pH and temperature detection. All the sensors are integrated in an area of 3cm*4cm on a 1mil Kapton patch which is integrated with a ZIF connector to the readout circuit. For the glucose and lactate sensors, we have utilized organic electrochemical transistors (OECTs) due their high transconductance and being able to work in aqueous environment. pH and temperature sensor were developed as resistive sensors using carbon nanotubes as the sensing element. The temperature sensor was developed using CNT with thermoplastic to develop a nanocomposite. The pH sensor was developed utilizing functionalized CNTs. All the sensors were printed using Optomec Aerosol Jet 5X printer with gold, Au, as the electrode material and platinum as the gate for the OECT devices. PEDOT:PSS was used as the channel material for the OECT and polyimide layer was used as the insulator layer to prevent the shorting in presence of aqueous media. Glucose oxidase (GOx) and lactate oxidase (LOx) were used for functionalizing the OECT gate for detection of glucose and lactate, respectively. Gelatin was dropped casted on glucose, lactate and pH sensors for increasing stability and repeatability of the device while temperature sensor was encapsulated with another piece of Kapton to prevent direct contamination with the skin. The optimized glucose sensor has a linear detection range between 1.3mM-50mM with a sensitivity of 0.317 NR/dec and the limit of detection (LoD) is 1uM. The lactate sensor demonstrated three linear ranges 0.1-1mM, 1-10mM and 10-50mM with a sensitivity of 87.5uA/mM, 8uA/mM and 0.72uA/mM. A sensitivity of 114 ohm/°C was extracted from the temperature sensor between 20°C and 60°C, while the pH sensor can detect a pH variation from 4 to 7 with a sensitivity of 439 ohm/pH and 7 to 10 with a sensitivity of 155 ohm/pH. All the detection ranges are sufficient for detection of these variables in human sweat (0.06-0.2mM, 16-30mM, 35.5-37.7°C, 4.5-7 for sweat glucose concentration, lactate concentration, temperature and pH, respectively [2-5]. The patch can be worn continuously for a several hours for continuous data which is transmitted via BLE or WIFI to a computer. Testing results from this integrated bio wearable patch will be presented.<br/><br/>[1] Karpova EV, Andreev EA, Karyakina EE, Karyakin AA, Laptev AI. Relationship Between Sweat and Blood Lactate Levels During Exhaustive Physical Exercise.<br/>[2] Moyer, James and Wilson, Donald and Finkelshtein, Irina and Wong, Bruce and Potts, Russell. Correlation Between Sweat Glucose and Blood Glucose in Subjects with Diabetes.<br/>[3] Derbyshire PJ, Barr H, Davis F, Higson SPJ. Lactate in human sweat: a critical review of research to the present day.<br/>[4] B. F. Jones and P. Plassmann, Digital infrared thermal imaging of human skin.<br/>[5] Pablo Escobedo, Celia E. Ramos-Lorente, Antonio Martínez-Olmos, Miguel A. Carvajal, Mariano Ortega-Muñoz, Ignacio de Orbe-Payá, Fernando Hernández-Mateo, Francisco Santoyo-González, Luis F. Capitán-Vallvey, Alberto J. Palma, Miguel M. Erenas,<br/>Wireless wearable wristband for continuous sweat pH monitoring.