The detection of carbohydrate antigen 19-9 (CA199), a critical biomarker for pancreatic, colorectal, and gastric cancers, is essential for early diagnosis and disease monitoring. Traditional antibody-based assays for CA199 detection are limited by high costs, time-consuming procedures, and susceptibility to nonspecific interference. This study presents an electrochemical biosensor based on a multifunctional poly(EDOT-PyBA-