Wearable aptamer-field-effect transistor sensing system for noninvasive cortisol monitoring

TLDR

Wearable monitoring requires sensors for low‑concentration biomarkers, yet cortisol in sweat is only nanomolar and existing wearables detect only micromolar‑millimolar analytes. The study aims to develop a flexible field‑effect transistor biosensor array using a novel cortisol aptamer on nanometer‑thin In₂O₃ FETs to detect low‑concentration sweat cortisol. Detection relies on aptamer binding transduced to electrical signals on In₂O₃ FETs, with a custom multichannel, self‑referencing, autonomous unit enabling real‑time sweat cortisol measurement. The device successfully tracked salivary cortisol during stress tests, showed strong correlation with sweat cortisol, and was validated on‑body in a smartwatch for real‑time sweat monitoring.

Abstract

Wearable technologies for personalized monitoring require sensors that track biomarkers often present at low levels. Cortisol—a key stress biomarker—is present in sweat at low nanomolar concentrations. Previous wearable sensing systems are limited to analytes in the micromolar-millimolar ranges. To overcome this and other limitations, we developed a flexible field-effect transistor (FET) biosensor array that exploits a previously unreported cortisol aptamer coupled to nanometer-thin-film In2O3 FETs. Cortisol levels were determined via molecular recognition by aptamers where binding was transduced to electrical signals on FETs. The physiological relevance of cortisol as a stress biomarker was demonstrated by tracking salivary cortisol levels in participants in a Trier Social Stress Test and establishing correlations between cortisol in diurnal saliva and sweat samples. These correlations motivated the development and on-body validation of an aptamer-FET array–based smartwatch equipped with a custom, multichannel, self-referencing, and autonomous source measurement unit enabling seamless, real-time cortisol sweat sensing.