Ultrastable Lactate Biosensor Linearly Responding in Whole Sweat for Noninvasive Monitoring of Hypoxia.

We report on the lactate biosensor with linear calibration range from 0.5 to 100 mM, which encircles possible levels of this metabolite concentration in both human sweat and blood. The linear calibration range at high analyte concentrations, which exceeds the Michaelis constant of lactate oxidase by several orders of magnitude, is provided by an additional perfluorosulfonated ionomer diffusion membrane. In contrast to the known lactate biosensors, which retain their response within less than a couple of hours, the reported system displays 100% response for dozens of hours even upon high analyte concentrations. The biosensors with an additional diffusion-limiting membrane have been validated for lactate detection both in human blood serum and in undiluted human sweat shortly after its secretion. Both linear response in the entire range of blood and sweat lactate concentrations and ultrahigh operational stability would provide the use of the elaborated biosensor in wearable devices for the monitoring of hypoxia.

Simultaneous monitoring of sweat lactate content and sweat secretion rate by wearable remote biosensors.

We report on the simultaneous monitoring of sweat lactate concentration and sweat secretion rate. For this aim lactate oxidase-Prussian Blue enzyme-nanozyme type lactate biosensors were elaborated. The use of siloxane-perfluorosulfonated ionomer composite membrane for enzyme-nanozyme immobilization results in the biosensor displaying flux independence in the whole range of physiological sweat secretion rates (0.025-2 µl cm-2 min-1). On the contrary, current response of the biosensor based on solely siloxane membranes becomes saturated at physiological sweat lactate concentration, depending mostly on the flow rate. Accordingly, for simultaneous monitoring of sweat lactate concentration and its secretion rate both flow-through biosensors were integrated with high-accuracy wearable electronic devices allowing real-time remote monitoring. As found, during exhaustive physical exercise sweat secretion rate and lactate content are independent of each other, thus, confirming that this excretory liquid is suitable for non-invasive diagnostics.