DNA-modified ultra-sensitive electrochemical aptasensor for detection of 3,3′,4,4′-tetrachlorobiphenyl and its ecological risk assessment

Despite the global ban on 3,3 ',4,4 '-tetrachlorobiphenyl (PCB77) for decades, this persistent pollutant remains prevalent in the environment, posing significant risks to ecosystems and human health. Accurate detection of its environmental concentration is critical, yet conventional methods (e.g., GC-MS, LC-MS, non-biological sensors, and biosensors) are hindered by strict sample preprocessing, high equipment costs, lengthy analysis times, complex operations, and elaborate modification procedures. To address these limitations, developing a sensor for PCB77 that balances operational simplicity and minimizes practical errors is essential for real-world applicability. A novel electrochemical aptasensor (Apt@Au@Fe3O4@MGCE) was developed, leveraging Fe3O4 magnetism for facile assembly and Au-S bond chemistry to stabilize aptamer immobilization. Key optimized parameters included 100 nm Fe3O4 particles, a 1:100 Apt-to-TCEP molar ratio, a Tris-HCl pH of 7.4, and 5 h aptamer adsorption time. The sensor exhibited a wide linear response to PCB77 (1 x 10-3 to 1 x 102 ppb), with an ultralow detection limit of 1.8 x 10-4 ppb (S/N = 3), alongside excellent selectivity (resisting structural analog interference), stability, and reproducibility. Field validation in the Dasha River revealed low ecological risk for PCB77, with results consistent with GC-MS analysis, confirming its practical utility. This work introduces an electrochemical aptasensor that integrates Fe3O4 magnetism and Au-S bonding to enable simple assembly, stable aptamer immobilization, and reduced non-specific adsorption. A direct methylene blue (MB) modification strategy eliminates false positives, ensuring high selectivity. The sensor offers a cost-effective solution with a broad linear range, ultra-low detection limit, and robust stability/reproducibility, addressing the limitations of traditional methods. Its successful application in the Dasha River demonstrates a viable, practical strategy for efficient monitoring of persistent environmental pollutants, advancing real-world contamination assessment and risk management.