Evaluation of on-Body Performance of a Sweat-Based Lactate Sensor from Low Volumes of Passive Eccrine Sweat

Abstract

Lactate is a critical biomarker that can be used to monitor physical performance in sports medicine and restricted oxygen supply to tissues during anaerobic respiration for diagnosing clinical conditions such as hypoxia, cystic fibrosis, and ischemia. Recent advances have been made towards understanding accessible human biofluids to non-invasively monitor biomarkers that reflect the state of the body. Passive eccrine sweat is a potential candidate containing valuable information due to its ease of access, collection, and analysis. Literature studies have shown clinical correlations between sweat lactate and blood lactate levels which confirm that there is value in investigating sweat lactate for investigating clinical conditions. Existing wearables devices monitor only digital biomarkers to track heart rate and physical activity, however, there is no information obtained on human health status which can be understood by probing biochemical markers. The motivation of this study is to demonstrate on-body, low-volume detection of lactate in passive eccrine sweat. An electrochemical biosensor fabricated on a flexible, nanoporous substrate that can wick sweat is placed on the subject’s lower back and is utilized to detect and quantify sweat lactate levels. Label- free AC- based electrochemical impedance spectroscopy (EIS) is the signal transduction technique used to report the impedance in response to the lactate present in the passive body sweat. Prior to on-body testing, the functionality and the metrics of the lactate sensor in detecting sweat lactate within the physiological relevant ranges (5- 60mM) will be tested in controlled lab- environment to build a calibration response of curve of mapping impedance ranges to the lactate level for dynamic reporting of lactate concentrations when placed on-body. Sensor metrics obtained in human sweat from current bench top testing have yielded a 1mM as the lower limit of detection and a dynamic range of 1- 100mM. The on-body impedance response profiles produced corresponding to the lactate levels in continuous, real- time detection mode on integration with portable electronics will allow for translation into wearable biosensing applications.