Sensitive Detection of Sweat Cortisol Using an Organic Electrochemical Transistor Featuring Nanostructured Poly(3,4-Ethylenedioxythiophene) Derivatives in the Channel Layer

In this study, we examined the influence of functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) nano-structures decorated on the channel layer of an organic electrochemical transistor (OECT) for the detection of sweat cortisol, an adrenocorticosteroid stress hormone. The OECT device featured a bilayer channel confined by a PEDOT:polystyrenesulfonate (PSS) underlayer and a nanostructure-decorated upper layer engineered from the monomers EDOT-COOH and EDOT-EG3 through template-free electrochemical polymerization. This molecular design allowed antibody conjugation using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysulfosuccinimide coupling through the carboxylic acid side chain, with EDOT-EG3 known to minimize nonspecific binding of biomolecules. We also engineered an OECT device having a channel area without any nanostructures to gain insight into the effect of the nanostructures on cortisol sensing. Our new nanostructure-embedded OECT device facilitated real-time detection of cortisol at concentrations ranging from 1 fg/mL to 1 mu g/mL with a detection limit of 0.0088 fg/mL with good linearity (R-2 = 0.9566), in addition to excellent selectivity toward cortisol among other structurally similar interfering compounds and high stability and reproducibility. With its rapid response for the detection of 100 ng/mL cortisol-spiked artificial sweat, this nanostructure-decorated OECT device has potential clinical practicality and utility in wearable sensors for future healthcare applications.