Lab Intern Applied Cognition Los Altos Hills, California, United States
Introduction: The measurement of blood lactate presents provides a unique biomarker for endurance athletes that can help them build stamina and ability in their sport. Current measurement devices are limited to rely on a blood draw method that is costly, time-taking, and not continuous. We present a non-invasive, continuous lactate monitor that will enable athletes to make full use of lactic acid concentrations in their competitive sport.
Materials and
Methods: The monitor was designed using sweat as a substrate for a reaction with Lactate Oxidase, an enzyme that breaks down lactate into pyruvate and hydrogen peroxide. The hydrogen peroxide is then oxidized in a redox reaction with Prussian Blue, generating an electrical current that is measured by the sensor and reported as a concentration of lactate. This multi-step reaction occurs at the surface of a working electrode, used along a counter and reference electrode to perform amperometric measurements. This occurs inside of a microfluidics channel that is worn on the skin and carries sweat past the electrodes for measurement. The first iterations of the working electrode were tested in artificial sweat solutions in bulk solutions, where lactate concentrations were varied between 0-900 nM to identify the dynamic range of the sensor. To allow for a greater range of millimolar concentrations to be measured, comparable to human sweat lactate concentrations, the biosensor was coated with a cap layer consisting of Polyvinyl chloride and ETH-500, a lipophilic electrolyte, acting as a lactate diffusion membrane and tested in lactate concentrations reaching 20µM.
Results, Conclusions, and Discussions: We found that the non-invasive approach allows for a continuous measurement of lactate that is not represented in commercial lactate sensors. The sensor without the PVC diffusion layer reported sensitivity within the 0-900 nM range, while the added PVC diffusion layer improved the dynamic range up to 5 micromolar lactate concentrations. Ongoing optimization shows range up to 15 micromolar. The increased dynamic range is suitable for on-body applications where the lactate concentration in sweat can range from 1 to 50 mM.
We developed a prototype device capable of measuring sweat lactate continuously with a large dynamic range suitable for on-body applications for athletes in training and competition. Continuous lactate monitoring holds promise for endurance athletes and sports, with the potential to reshape the use of biomarkers in sports similar to the introduction of continuous heart rate monitors.
