Flex-GO (Flexible graphene oxide) sensor for electrochemical monitoring lactate in low-volume passive perspired human sweat.

In this work, a low volume, sweat lactate sensor functioning on passively expressed eccrine sweat was designed, fabricated and tested in human sweat and its performance was benchmarked against a standard reference; Lactate Plus meter. This novel sensor comprises of graphene oxide (GO) nanosheets integrated into a nanoporous flexible electrode system for low-volume (1-5 µL) ultrasensitive impedance based detection of lactate using non-faradaic electron-ionic charge transfer. Lactate oxidase (LOD) enzyme was immobilized on the surface of GO nanosheets towards developing an affinity biosensor specific to the physiological relevant range (4-80 mM) of lactate in perspired human sweat. Sensing was achieved by measuring impedance changes specific to lactate binding along the GO nanosheet interface using electrochemical impedance spectroscopy. The sensor demonstrated a dynamic range from 1 to 100 mM spiked in synthetic and human sweat with a limit of detection of 1 mM. A specificity study conducted using cortisol expressed in sweat revealed a negative response to the lactate oxidase. Continuous lactate sensing studies were performed during which the sensor was responsive to concentrations of lactate up to 138.6 mM. Correlation of the sensor response with actual lactate concentration (1.3-113.4 mM) was found to be 0.955.