Voltammetric immunosensor based on a screen-printed electrode modified with polydopamine and bipyridinium derivative for determination of carcinoembryonic antigen and escherichia coli

This work presents a voltammetric immunosensor based on a screen‑printed carbon electrode modified with a composite layer of multi‑walled carbon nanotubes and polydopamine, which serves as a platform for covalent antibody immobilization. The sensor employs an immobilized redox label, an original bipyridinium derivative (MFB), which exhibits a pronounced electrochemical response in the cathodic potential region in aqueous media. Using a cathodic redox label in the negative potential region avoids interference from biological oxidants that usually complicate anodic detection. MFB immobilized in the polydopamine film provides stable signals without external redox mediators, enabling reagent-free analysis. The electrochemical behavior of MFB in aqueous buffer solution and within the modifier layer on the surface of a glassy carbon electrode was studied in detail. The kinetic parameters of electron transfer, calculated from the experimental data, together with the analytical and operational characteristics, enabled the use of MFB as a redox probe in the immunorecognition layer for the sensitive voltammetric determination of carcinoembryonic antigen (CEA) and Escherichia coli bacteria. Under the selected operating conditions, the linear range for CEA was 1–20 ng/mL with a detection limit of 0.086 ng/mL (R² = 0.995, n = 10, P = 0.95). For E. coli, the linear range was 10–10⁵ CFU/mL with a detection limit of 1 CFU/mL (R² = 0.997, n = 10, P = 0.95). The proposed approach is promising for the development of portable point‑of‑care diagnostic systems in clinical oncology, infectious disease diagnostics, and environmental monitoring.