An enzyme-free wearable sweat sensor based on a Cu metal-organic frame composite material for monitoring lactate metabolism

Wearable sweat sensors have made significant progress in the field of human health monitoring, with the ability to achieve continuous collection, monitoring, and transmission of sweat. Current wearable sweat sensors are predominantly enzyme-based, which presents limitations such as high cost, inadequate long-term stability, and vulnerability to environmental conditions. In this study, we present a printed enzyme-free wearable potentiometric sensor for monitoring sweat lactate. Specific and highly sensitive electrocatalysis of sweat lactate was achieved by constructing composite nanomimetic enzyme materials, which involved modifying a screen-printed working electrode with multi-walled carbon nanotubes (MWCNTs) and copper metal-organic framework materials (Cu-HHTP). The conversion of divalent copper ions (Cu²⁺) in Cu-HHTP to monovalent copper ions (Cu⁺) in the presence of sodium chloride (NaCl) led to the rapid electrocatalytic oxidation of lactate into pyruvate. The incorporation of MWCNTs enhanced the conductivity and electron transport efficiency of Cu-HHTP, thereby improving the sensitivity. The sensor exhibited an exceptionally low detection limit (1.09 μM), remarkably high sensitivity in the ranges of 1–10 mM (118.55 mV/decade) and 10–50 mM (47.98 mV/decade), as well as outstanding selectivity, reproducibility, and stability. Finally, the developed wearable potentiometric sensor continuously and dynamically monitored changes in sweat lactate levels during physical exercise. This study presents a novel enzyme-free method for the detection of sweat lactate, which holds promise as a valuable support for personalized health diagnosis.