Conducting Polymers for Electrochemical Sensing: From Materials and Metrology to Intelligent and Sustainable Biointerfaces

Highlights: What are the main findings? Reported performance metrics of conducting polymer–based electrochemical biosensors (LOD, sensitivity, linear range, stability) are strongly affected by metrological variability arising from polymer formulation, film morphology, electrode geometry, electrolyte composition, and measurement protocols. A critical analysis reveals that the apparent performance gains reported across PEDOT:PSS, polyaniline, polypyrrole, and polythiophenes are often not directly comparable due to non-standardized calibration procedures, reference electrode instability, and inconsistent data treatment. What are the implications of the main findings? The lack of standardized metrology represents a primary barrier to reproducibility, long-term reliability, and technology transfer of conducting polymer–based biosensors from laboratory demonstrations to real-world applications. The adoption of unified reporting frameworks—including explicit uncertainty analysis, statistically validated LOD definitions, and protocol-level transparency—is essential for meaningful benchmarking and rational device optimization. Conducting polymers (CPs) have become cornerstone materials in electrochemical sensors and biosensors due to their mixed ionic–electronic conduction, mechanical softness, and intrinsic biointerface compatibility. This review provides a comprehensive and critical overview of the field, tracing the evolution of CP-based devices from classical poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), polyaniline (PANI), and polypyrrole (PPy) electrodes to emerging nanostructured, hybrid, wearable, and transient systems. We discuss fundamental charge-transport mechanisms, doping strategies, structure–property relationships, and the role of morphology and biofunctionalization in dictating sensitivity, selectivity, and stability. Particular emphasis is placed on reliability challenges—including drift, dopant leaching, environmental degradation, and biofouling—and on the current lack of standardized metrology, which hampers cross-study comparability. We propose a framework for rigorous calibration, reference electrode design, and data reporting, enabling quantitative benchmarking across materials and architectures. To support meaningful cross-platform comparison, representative performance envelopes—including conductivity, limit of detection, sensitivity, selectivity strategies, and operational stability—are critically benchmarked across major CP families and sensing modalities. Finally, we explore future directions such as organic mixed ionic–electronic conductors, biohybrid and living polymer interfaces, Artificial Intelligence-driven modeling, and sustainable transient electronics.