| In this paper, a series of cerium double-ligand coordination compounds (Ce-dCOPs) electrochemical signal probes have been synthesized by hydrothermal method using 2,2':6',2"–terpyridine-4-carboxylic acid (Hmctpy) and thionine (Thi) as organic ligands and lanthanide Ce3+ as metal coordination center. The electrochemically active Thi molecules are directly bound to the Ce-dCOPs in the form of ligands, which avoids the shedding of signal molecules during the detection process and significantly improves the stability of the sensor. In addition, Ce3+ will be converted into Ce4+ during a certain voltage scanning process, and Ce3+/Ce4+ has efficient catalytic activity on Thi, so the addition of substrates in the detection substrate is avoided, the external interference is reduced, and the detection accuracy is increased. Subsequently, gold nanoparticles were coated on the surface of Ce-dCOP (AuNPs@Ce-dCOP) in situ to overcome the poor electrical conductivity of the complex. Finally, using AuNPs@Ce-dCOP as the signal probe and catalytic hairpin assembly (CHA) signal amplification strategy, a biosensor for highly sensitive detection of breast cancer marker microRNA-21 (miRNA-21) was successfully constructed. In the concentration range of 100.0 amol·L-1 to 1.0 nmol·L-1, the detection limit of miRNA-21 was as low as 86.1 amol·L-1 (S/N = 3). The recovery rates of miRNA-21 in actual serum samples were 99.96%-106.00%, indicating that this study not only provides a simple, effective and accurate detection method for the detection of tumor markers, but also provides ideas for the synthesis of electrochemical signal probes. |