Aptamer functionalized sheet-like α-Fe ₂ O ₃ /Fe ₃ O ₄ magnetic nanocomposite-based electrochemical nano-biosensor for the accurate detection of nucleolin

The detection of tumor biomarkers is critical in diagnostics, prevention, and therapeutics. As a significant biomarker of renal carcinoma, breast cancer, lymphocytic leukemia, and so on, the accurate detection of nucleolin (NCL) is of great significance in clinical examination. Due to the inherent limitations of complex operation, time consumption, and low sensitivity of traditional methods, there is an urgent need to develop rapid, sensitive, and simple detection strategies. In this project, α-Fe 2 O 3 /Fe 3 O 4 @Au magnetic nanocomposites (MNCs) were fabricated via a hydrothermal and calcination process with the reduction of chloroauric acid. Further, depending on the facile combination of Au and sulfur, α-Fe 2 O 3 /Fe 3 O 4 @Au-Apt/BSA probes were constructed. Subsequently, the aptamer on the probes could specifically recognize and bind to NCL through its high affinity for the target. The magnetic probes, after capturing the target, could self-assemble on the surface of a magnetic glassy carbon electrode (MGCE) under magnetic induction for electrochemical detection, which improved the operability and avoided possible bio-coating contamination. The nano-biosensors revealed favorable linear relationship (R 2 = 0.995) of the current signal and NCL concentration within 0.1 pg/mL-10 ng/mL, a low limit of detection (LOD) of 0.24 pg/mL, high stability with RSD of 1.04%, satisfactory guarantee period of 20 days, strong specificity, and favorable recoveries in human serum samples (98.09-105.65%), which outperformed conventional EC methods, suggesting the promising prospect of nano-biosensors for NCL detection in clinical examination.