On-demand lactate monitoring towards assessing physiological responses in sedentary populations

Identification of diseases in sedentary populations on a timely basis before reaching a critical stage is a continuing challenge faced by emergency care centers. Lactate is a key biomarker for monitoring restricted oxygen supply essential for assessing the physiological responses of the user for clinical diagnostics. The novelty of this work is the development of a non-invasive, mediator-free, stick and remove biosensor for the on-demand measurement of lactate in passive sweat targeted towards sedentary populations. The conformable interface of the biosensors with skin can be engineered to extract relevant biochemical signals and quantify the in situ sweat biomarker levels. In this work, we demonstrate a highly sensitive and specific on-demand biosensor with a fabricated hybrid nanotextured Au/ZnO electrode stack embedded within a flexible nanoporous material to capture the temporal dynamics of passive sweat lactate. The biosensor exhibits a lactate specific response in human sweat with a 1 mM lower limit of detection and a wide dynamic detection range of 1-100 mM (R² = 0.98). The proposed biosensor has a sensitivity of 8.3% mM^-1 while selectivity studies reveal negative interactions with non-specific molecules. The sensor stability studies showed an ∼30% degradation in the lactate biosensing response over a 4-day duration when stored at 4 °C. Non-faradaic electrochemical spectroscopy is employed as the detection modality to quantify the enzymatic catalysis of sweat lactate at the electrode-sweat interface. Spectroscopic characterization techniques such as XPS, ATR-FTIR, and zeta potential measurements confirm the enzymatic assay binding efficacy on a qualitative scale.