Co-CdO-Amplified Electrochemiluminescence of GSH-AuNCs Immobilized on Fe-MIL-88A for Ultrasensitive Immunosensing of Carbohydrate Antigen 15-3.

Gold nanoclusters (AuNCs) protected by sulfhydryl ligands exhibit excellent optical properties and good biocompatibility. However, the inefficient charge transfer during redox reactions, stemming from free vibration and rotation of the ligands, limits their application in electrochemiluminescence (ECL). To address this, glutathione-protected AuNCs (GSH-AuNCs) were immobilized onto Fe-MIL-88A nanoparticles, serving as the ECL emitter. The GSH-AuNCs@Fe-MIL-88A composite effectively suppressed energy dissipation caused by ligand motion, while simultaneously enhancing charge transfer and reducing nonradiative decay pathways through structural stabilization. Furthermore, Co-doped CdO was employed as a co-reaction accelerator to promote the generation of radical intermediates from N,N-diisopropylethylamine, thereby amplifying the ECL signal. Leveraging this enhanced system, a highly sensitive ECL immunosensor was constructed for the detection of the glycan antigen CA15-3. This immunosensor demonstrated excellent stability, reproducibility, and selectivity. Meanwhile, it exhibited a wide linear range from 0.1 pM to 100 nM for CA15-3 detection, with an impressively low limit of detection of 0.02 pM (S/N = 3). This work provides a novel strategy for utilizing gold nanoclusters in ECL applications and can be readily extended to detect other disease biomarkers.