Continuous assessment of sweat lactic acid secretion using microfluidic sweat lactic acid monitoring system

Abstract

A microfluidic sweat lactic acid (LA) monitoring system for non-invasive and continuous assessment of sweat LA was constructed and tested. Our system transports whole secretions from the skin to an electrochemical LA biosensor using a continuous flow of phosphate buffered saline at the skin’s surface. The LA biosensor was fabricated by modifying screen printed carbon electrodes with osmium wired horseradish peroxidase and lactate oxidase. For continuous monitoring purposes, the microfluidic LA biosensor was connected with a flow cell made of polydimethylsiloxane (PDMS). The sampling device was fabricated by laminating a medical plaster on a PDMS flow-channel. Before the clinical tests, the characteristics of the LA biosensor were evaluated. Sufficient sensitivity (0.4232 nA/µM) and selectivity to LA (> 50fold against glucose, glutamic acid, phenylalanine, ammonia and ethanol) were confirmed. Besides, the medical plaster-based attachment contributed to the reduced leakage between the skin and the sampling device. Under the approval of the ethical committees, LA monitoring of patients with cardiovascular disease at the intensive care unit was carried out. As a result, temporal changes of sweat LA were successfully monitored.