Poly(3,4-ethylenedioxythiophene) Nanotube-Decorated Screen-Printed Electrodes with a Ferrocene-Derived Built-in Probe Enables Alpha-Fetoprotein Detection

An easy-to-engineer nanobiosensor electrode platform was developed using commercial screen-printed electrode (SPE) as the sensor substrate, enabling cost-effective detection of alpha-fetoprotein (AFP), a clinically important biomarker of liver cancer. The electrode surface was modified with poly(EDOT-COOH-co-EDOT-EG3) and poly(EDOT-N3) nanotubes via a template-free electropolymerization approach. Incorporation of poly(EDOT-COOH) enables reactive carboxyl groups useful for covalent conjugation of the AFP antibody (AFP-Ab)─the biomarker detection probe through EDC/Sulfo-NHS coupling chemistry while poly(EDOT-EG3) imparted antifouling properties to minimize nonspecific biomolecular interactions. In addition, poly(EDOT-N3) introduced to facilitate the conjugation of ethynylferrocene through CuAAC click chemistry, thereby creating a built-in redox probe to bypass the need of a complex external probe, highlighting the key feature of this work. The nanostructure formation from the bilayer of poly(EDOT-COOH-co-EDOT-EG3) and poly(EDOT-N3) was optimized during electrochemical deposition and characterized through scanning electron microscopy (SEM) technique. The modified polymer surfaces were extensively characterized using quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS), Cyclic voltammetry (CV), and Differential Pulse Voltammetry (DPV) techniques. The SPE nanobiosensor platform successfully detected AFP in phosphate-buffered saline (PBS) using DPV across a wide range of concentrations (1 pg/mL to 1 μg/mL), with a good linearity (R2 = 0.9247) and a limit-of-detection (LOD) of 0.603 pg/mL. Furthermore, the SPE nanobiosensor demonstrated reliable stability, reproducibility, and excellent selectivity upon the addition of interfering compounds such as Bovine Serum Albumin (BSA), Tumor Necrosis Factor-α (TNF-α), Neuropeptide-Y (NPY), and Interleukin-6 (IL-6), highlighting its future practical utility to develop healthcare monitoring devices for point-of-care testing (POCT) applications.