Selective and Sensitive OECT Sensors with Doped MIP-Modified GCE/MWCNT Gate Electrodes for Real-Time Detection of...

Organic electrochemical transistors (OECTs) represent a promising platform for biosensing applications in aqueous environments, including the sensitive detection of neurotransmitter molecules, such as serotonin (SE). Conventional methods for SE detection, such as HPLC and ELISA, are time-consuming and expensive. Electrochemical sensors, while sensitive and cost-effective, often struggle with real-time detection and selectivity issues due to interference from similar biomolecules, such as dopamine (DA), ascorbic acid (AA), and uric acid (UA). These interferents are particularly challenging for the OECT detection because they are easier to oxidize than SE on the gate electrode. Molecularly imprinted polymer (MIP) has gained increasing interest in electrochemical analysis, providing a cost-effective method for the selective detection of various analytes by creating matching cavities in the polymer film. Herein, a glassy carbon/multiwall carbon nanotube (GCE/MWCNT) gate electrode was modified by a PSS^-doped overoxidized molecularly imprinted polymer (DOMIP) layer in an OECT sensor. Characterizations by cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), Raman spectroscopy, and wide-angle X-ray scattering (WAXS) demonstrate an improved conductivity of the gate electrode due to DOMIP modification. The resulting GCE/MWCNT/DOMIP sensor demonstrated a low detection limit of 0.31 μM for SE in real-time measurements, comparable to that of the GCE/MWCNT sensor. However, the GCE/MWCNT sensor showed little selectivity toward SE. In addition to the SE-templated cavities, the DOMIP gate electrode modification leveraged the electrostatic interactions between the negatively charged PSS^- dopant and the positively charged SE molecules to achieve a higher sensitivity toward SE compared to other negatively charged or neutral interferents in the concentration range of 0.31 μM - 3.1 μM. These findings suggest that combined with the GCE/MWCNT gate electrode, the doping strategy used in DOMIP-modified OECT sensors could provide a low-cost way for the selective and real-time monitoring of SE in complex biological samples without the usage of noble-metal electrode or expensive antibodies, which is potentially suitable for a large-scale medical diagnosis.