A reusable electrochemical biosensor for monitoring of small molecules (cortisol) using molecularly imprinted polymers

This paper establishes the feasibility of a reusable biosensor that can be operated and stored at room temperature, for detection of small molecules in low resource settings. The sensor was fabricated using molecularly imprinted polymers (MIP) and cortisol was chosen as a model analyte. Cortisol imprinted polymer films were prepared by electropolymerizing pyrrole on an electrode surface in the presence of cortisol. Electrochemical over-oxidation of polypyrrole (PPy) was performed for the controlled release of cortisol templates and to create cortisol specific imprinting sites. Stepwise fabrication of imprinted sensors was characterized through cyclic voltammetry (CV) and scanning electron microscopy (SEM). The sensor exhibited a detection limit of 1 pM L−¹ for cortisol. A unique feature of the sensor was that cross-reactivity with prednisolone (which has 100% interference in ELISA), was minimized to 18.3% compared to ELISA. The sensitivity of the sensor remained over 90% after 7 cycles of elution/rebinding, while the sensitivity decreased by 10% after 4 weeks of storage at room temperature, suggesting the sensor can be used multiple times and used with low overhead costs in low resource settings such as agricultural fields. The sensor was used for detection of cortisol in saliva samples of farm workers; benchmarking with ELISA showed excellent correlation. These findings indicate that such a sensor can be used for in-field measurements of small molecules (e.g. cortisol).