Ultrasensitive, robust, and selective detection of hepatitis B surface antigen enabled by vertical organic electrochemical transistor.

Early detection of hepatitis B virus (HBV) is essential for effective diagnosis and disease management. Hepatitis B surface antigen (HBsAg) is a key biomarker widely used for HBV screening. In this study, we report a vertical organic electrochemical transistor (vOECT)-based biosensor for label-free detection of HBsAg. The device employs a gold gate electrode functionalized with monoclonal HBV antibodies via carbodiimide coupling, providing covalent binding sites for the selective capture of HBsAg. Surface modification and immobilization processes are confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. The biosensor showed a wide linear detection range upon HBsAg binding from 100 pg/mL to 5000 ng/mL with a low detection limit of 42.7 fg/mL. Reproducibility tests showed relative standard deviation (RSD) values of 2.40% and 3.03% for 5.0 ng/mL and 5 μg/mL HBsAg, respectively, indicating high consistency across independently fabricated devices. The biosensor also exhibited strong selectivity against common biological interferents, including bilirubin, recombinant human serum albumin, carcinoembryonic antigen, creatinine, glucose and haemoglobin. Furthermore, stability studies show that more than 98% of the original response is retained after two weeks. These results highlight the potential of the vOECT platform as a sensitive, reliable and compact biosensing strategy for point-of-care HBV diagnostics.