Sweat Sensor Measures Cholesterol Continuously Without Blood Draws

Researchers at Caltech have created a stick-on patch that can continuously measure cholesterol and triglyceride levels by analyzing sweat, potentially replacing periodic blood draws for lipid panels. The device was developed by a team led by Wei Gao, a professor in the Cherng Department of Medical Engineering, and is described in a paper published in Nature Sensors.

The sensor addresses a key chemical challenge: much of the cholesterol in sweat exists as esterified cholesterol, which cannot be detected directly. The researchers engineered a two-step enzymatic reaction that first converts esterified cholesterol into free cholesterol, then oxidizes it to produce hydrogen peroxide, which the sensor can measure.

A second hurdle involved sustaining the supply of adenosine triphosphate (ATP) needed for triglyceride sensing. The team embedded ATP in a special polymer within the patch that gradually releases the cofactor into sweat, enabling continuous operation for more than 20 hours.

Because the relationship between lipid levels in sweat and blood is not linear, the system uses a causal machine learning model that accounts for physiological variables such as body mass index, sex, and sweat rate. The model combines these factors with the sweat measurements to estimate blood lipid concentrations.

In preclinical testing with 24 participants, the wearable device predicted blood lipid levels with high accuracy, according to Gao. The lead authors of the study are José A. Lasalde-Ramírez, Chihyeong Won, and Sijie Ji from Gao's research group.

Gao noted that many people do not get regular blood draws, which limits early detection of cardiovascular and metabolic diseases. The noninvasive, continuous monitoring capability could provide earlier warning of such conditions.

The research was supported by the National Science Foundation, the National Institutes of Health, Samsung Research America, and the Heritage Medical Research Institute. Collaborators included researchers from UCLA and the David Geffen School of Medicine at UCLA.