General Strategy to Fabricate Electrochemiluminescence Sandwich Type Nanoimmunosensors Using CdTe@ZnS Quantum Dots as Luminescent Labels and Fe3O4@SiO2' Nanoparticles as Magnetic Separable Scaffolds

This work aims to develop universal sandwich type electrochemiluminescence (ECL) nanoimmunosensors for quantitative detection of biomarkers. A series of low-toxic CdTe@ZnS QDs with different core sizes have been synthesized via hydrothermal method and characterized by UV-vis spectra, photoluminescence spectra, TEM, EDS, and XRD. Especially, the ECL behaviors of CdTe@ZnS QDs have been investigated carefully. The CdTe@ZnS QDs with the highest ECL quantum yields have been chosen as ECL labels for conjugation with secondary antibodies. The QDs-labeled antibodies have been characterized by agarose gel electrophoresis. Meanwhile, Fe3O4@SiO2 magnetic nanoparticles were utilized as nanocarriers for the immobilization of primary antibodies due to magnetic separation ability, large specific surface area, and ease of amination for biofunctionalization. Successful fabrication of the nanoimmunosensor was confirmed by SEM and electrochemical impedance spectroscopy. Carcinoembryonic antigen was detected as a model to prove the feasibility of the above strategy. Under the optimal conditions, the proposed nanoimmunosensor exhibited a wide linear range of 0.01 to 125 ng mL(-1) for carcinoembryonic antigen determination with a low detection limit of 3.0 pg mL(-1) (S/N = 3). Moreover, the nanoimmunosensor also displayed excellent selectivity, good stability, and acceptable reproducibility, indicating its potential applications in clinical diagnostics and immune research.