Ultrasensitive electrochemical sensor for HBV DNA detection based on exo III + HCR cascade amplification and...

Hepatitis B virus (HBV) infection is a leading cause of cirrhosis and hepatocellular carcinoma worldwide, and HBV DNA serves as a key molecular biomarker for diagnosis and therapeutic monitoring. Accurate and ultrasensitive quantification of HBV DNA is therefore crucial for early detection and clinical management. Herein, we developed an electrochemical DNA biosensor that integrates Exonuclease III (Exo III)-assisted target recycling with a hybridization chain reaction (HCR)-based cascade amplification. Platinum-decorated cobalt-copper carbon nanocubes (CoCu/CNC/Pt) nanozymes were employed as signal labels to synergistically amplify electrochemical responses, enabling highly sensitive detection of HBV DNA. Target DNA undergoes Exo III-catalyzed cyclic cleavage, releasing trigger strands (sDNA) that initiate the HCR process, driving the alternating hybridization of two hairpin probes (DNA1 and DNA2) into extended double-helical networks. These supramolecular structures present multiple terminal single-stranded regions that hybridize with complementary CoCu/CNC/Pt/aDNA probes, facilitating efficient anchoring of nanozyme labels on the electrode surface. The CoCu/CNC/Pt nanocomposites provide abundant redox-active sites and exhibit excellent catalytic activity toward H₂O₂ reduction, resulting in a markedly amplified electrochemical signal. The biosensor displayed a wide linear range from 100 aM to 10 nM (Y = 9.79X + 209.62, R² = 0.99) and an ultralow detection limit of 0.09 fM. Furthermore, the sensor exhibited excellent reproducibility, stability, and specificity, achieving recoveries of 93.3-107.0% in spiked serum samples. The developed platform offers strong potential for the detection of HBV DNA and can be extended to other pathogenic nucleic acids and clinically relevant biomarkers.