Key Findings
The implementation of differential sensing in organic electrochemical transistors significantly mitigates calibration drift in wearable cortisol sensors. In tests using artificial sweat over 14 days, the differential output shifted by 1% to 10% of its range, whereas the response of the MIP-coated transistor alone shifted by 15% to 22% on day 1. Furthermore, for individual pairs at concentrations of 1 to 10nM, the variation between days decreased by an average of 65% to 70%.
Technical Details
The sensor architecture utilizes PEDOT:PSS transistors. The system employs a differential pair consisting of:
- A transistor coated with a molecularly imprinted polymer (MIP) specifically for cortisol.
- A transistor coated with a non-imprinted polymer (NIP) of the same composition.
To obtain the final reading, the NIP response is subtracted from the MIP response. This configuration allows the system to cancel out signals unrelated to cortisol that typically cause output drift over several days.
Background & Context
Wearable cortisol sensors often suffer from output drift due to factors unrelated to the target analyte. This instability means that a calibration performed on the first day of use quickly becomes invalid, hindering the reliability of long-term monitoring. To validate the differential approach, the researchers tested the sensors with sweat from one participant. When measured against the day 1 calibration, both the MIP and differential outputs tracked the direction of changes in salivary cortisol; however, the MIP-only output diverged from the differential output, mirroring the drift observed in laboratory settings.
Significance & Outlook
By reducing the impact of non-specific drift, this differential OECT design enhances the accuracy of wearable cortisol sensing over extended periods. The reduction in daily variation at 1 to 10nM suggests a more robust calibration profile, potentially reducing the frequency of recalibration required for wearable health monitors.
Source: https://doi.org/10.64898/2026.10.31.763347
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