Engineering electropolymerized molecularly imprinted polymer films for redox-integrated, reagent-free cortisol detection: The critical role of scan rate

Abstract

Electropolymerized molecularly imprinted polymers (eMIPs) represent a versatile platform for electrochemical biosensing, offering tailored specificity, high stability, and cost-effectiveness through direct synthesis on electrodes. This study investigates the fabrication-property-performance relationship of eMIPs for enhanced cortisol biosensing, with a focus on the interplay between scan rate and the number of polymerization cycles during cyclic voltammetry-based electropolymerization. The thickness, density, and morphology of the eMIP films were systematically characterized using electrochemical quartz crystal microbalance (EC-QCM), field-emission scanning electron microscopy (FE-SEM), and profilometry. Lower scan rates (25 mV s^-1) produced denser and smoother polymer film compared to higher scan rates (50 mV s^-1), highlighting the critical influence of scan rate on polymer properties. The eMIP films fabricated with different parameters were integrated with a Prussian Blue nanoparticles layer on screen-printed carbon electrodes for reagent-free cortisol detection. Square wave voltammetry (SWV) was used to evaluate sensor performance, which demonstrates that lower scan rates (25 mV s^-1) combined with increased polymerization cycle counts yielded a denser and thicker film, resulting in enhanced sensitivity and selectivity. The sensor achieved a limit of detection (LOD) of 26 pM for cortisol. These findings provide valuable insights into the critical role of electropolymerization parameters in tailoring film properties (i.e., thickness and density), enhancing eMIP sensor design, and advancing biosensor technology through precise control of electropolymerization parameters.

Keywords: Cortisol detection; Electrochemical sensors; Electropolymerization; Film properties; Molecularly imprinted polymers; Scan rate.