Evaluation of Maleimide-Functionalized Poly(3,4-Ethylenedioxythiophene) (PEDOT-MA) as an Electrode Material for Impedimetric Biosensors

For developing functional biosensors, integrating specific recognition components is the most critical part of device fabrication. As opposed to physical immobilization, chemical immobilization, through the formation of covalent bonds between devices and biomolecules, is preferable in terms of binding stability, controllability, and reproducibility. In this study, we explored the potential of maleimide-functionalized poly(3,4-ethylenedioxythiophene) (PEDOT-MA) in the development of impedimetric biosensors. The additional chemical activity introduced by the maleimide functionality, which is absent in pristine PEDOT, was exploited for tethering recognition components through carefully designed post-treatment processes. Dopamine, an electrochemically active species, was initially used to test and validate this post-treatment process. After dopamine treatment, expected redox peaks with consistent peak intensities were noted in repetitive cyclic voltammetry (CV) scans of functionalized PEDOT-MA, indicating the successful immobilization of dopamine. The thickness of the PEDOT-MA coating was determined to be another critical factor dictating the optimal response of biosensors with immobilized Protein A (PrA) as the recognition component. To achieve the most sensitive biosensor, 4 × 10–3 C cm–2 charge density to electrodeposit PEDOT-MA, corresponding to a nominal film thickness of 100 nm, was required. Further improvements in sensitivity were obtained by utilizing a relatively low PrA concentration (0.001 mg mL–1) in the immobilization step. A calibration curve of the relative change of charge transfer resistance (ΔRct) vs. logarithm of Immunoglobulin G (IgG) concentration was constructed using the best-performing PrA-immobilized biosensors, and a positive slope (0.11 log–1(mg mL–1)) was obtained from the regression analysis of the response data, confirming that the impedimetric biosensors can distinguish between different IgG concentrations. X-ray photoelectron spectroscopy (XPS) analysis of PEDOT-MA at different stages of the post-treatment and sensing process revealed the expected changes in surface chemistry. Our findings demonstrate that PEDOT-MA, in combination with the proposed post-treatment process, is effective for fabricating impedimetric biosensors for biosensing applications.