g-C₃N₅/AuNPs-based electrochemical aptasensor for ultrasensitive doxorubicin detection in human plasma and urine

Timely and precise assessment of anticancer agents, notably doxorubicin (DOX), is vital for dose optimization and for mitigating its cardiotoxic effects associated with dosage. While traditional analytical platforms such as HPLC and LC–MS/MS deliver high sensitivity, they involve sophisticated equipment, labor-intensive sample treatments, and are impractical for rapid, point-of-care diagnostics. In this study, we introduce a label-free aptasensor employing electrochemical impedance spectroscopy (EIS), constructed on a gold electrode integrated with nitrogen-enriched g-C₃N₅ nanosheets and electrochemically co-deposited gold nanoparticles (Au/g-C₃N₅–AuNPs/Apt) for the specific recognition of DOX. The g-C₃N₅ architecture offers abundant active sites and a large-surface scaffold, enabling uniform AuNPs distribution and efficient aptamer conjugation via Au-S bond. Interaction of DOX with the aptamer caused a discernible increase in charge-transfer resistance (R_ct), which was exploited as the detection signal. Critical preparation variables—such as aptamer coupling duration and analyte binding time—were systematically optimized. Under these optimized settings, the sensor achieved a linear detection span of 5–100 nM, with an LOD of 2 nM and an LOQ of 5 nM. The platform preserved strong selectivity over other structurally related anthracyclines and delivered recovery rates of 97.2–102.2 % in fortified human plasma and urine, consistent with ICH recommendations. These findings highlight a robust, sensitive, and portable detection system with significant promise for therapeutic drug monitoring of DOX at the clinical point-of-care.