Chemiluminescent Fe₃O₄@Nickel–Cobalt Double Hydroxide Magnetic Core–Shell Nanomaterial as an Analytical Interface for Label-Free CYFRA21-1 Immunosensing

Cytokeratin 19 fragment (CYFRA21-1) is considered to be a potential marker for the diagnosis and of classification of lung cancer. It is highly desired to develop rapid and highly sensitive label-free chemiluminescence (CL) immunosensors for the detection of CYFRA21-1. In this work, magnetic core-shell nanocomposite Fe₃O₄@nickel-cobalt double hydroxide (Fe₃O₄@DH) was used for the first time as a carrier to synthesize N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and gold and silver nanocluster (AuAgNC) bifunctionalized magnetic nanomaterials Fe₃O₄@DH/AuAgNCs-ABEI. The resulting Fe₃O₄@DH/AuAgNCs-ABEI demonstrated excellent CL performance, attributed to the exceptional catalytic capability of nickel-cobalt double hydroxide (NiCo-DH) and AuAgNCs, as well as the large specific surface area of NiCo-DH for AuAgNCs and ABEI enrichment. Moreover, Fe₃O₄@DH/AuAgNCs-ABEI exhibited superior stability compared to Fe₃O₄-based CL-functionalized magnetic nanomaterials, owing to the presence of NiCo-DH shells. On this basis, a label-free CL immunosensor using CYFRA21-1 antibody-modified Fe₃O₄@DH/AuAgNCs-ABEI as an analytical interface was constructed for the detection of CYFRA21-1 in the range from 1.0 × 10^-13 to 1.0 × 10^-8 g/mL. The detection limit of this CL immunosensor was 47.7 fg/mL, 4 orders of magnitude lower than existing CL methods. The CL immunosensor was able to accurately detect the concentration of CYFRA21-1 in serum samples, as evidenced by ELISA results. More importantly, it not only distinguished well between healthy persons and lung cancer patients (90.0% sensitivity and 90.0% specificity), but also effectively distinguished between patients with non-small cell lung cancer and small cell lung cancer (80.0% sensitivity and 86.7% specificity).