Long-Term Stable Wearable Electrochemical Aptamer Sensor for Cortisol in Artificial Sweat Based on a Gold Nanoparticle–Carboxymethyl Cellulose–Methylene Blue Interface

A wearable electrochemical aptamer sensor for cortisol was developed on a screen-printed electrode bearing a gold nanoparticle–carboxymethyl cellulose–methylene blue interface. The redox layer was formed by on-electrode electropolymerization of methylene blue in the presence of gold nanoparticles and carboxymethyl cellulose, which helps stabilize the film and supports Au–S anchoring of the thiolated aptamer. Analytical cortisol measurements were performed in artificial sweat with controlled ionic strength and pH. The sensor provided a limit of detection of 0.09 pg mL–1 and a linear range of 0.0001–1000 ng mL–1 (mean ± SD, n ≥ 3). Interference from common sweat constituents was minimal, and batch-to-batch reproducibility was good. The device retained 93.4% of its initial response after 56 days of storage at 4 °C (RSD = 2.4%). These results demonstrate a stable wearable transducer platform for cortisol sensing in artificial sweat, and validation in real human sweat will be pursued in future work.