A Dual-Ion\nSynergistic Catalysis Utilizing Zn<sup>2+</sup>-Regulated CdS<sub><i>y</i></sub>Se<sub>1–<i>y</i></sub> ECL\nImmunosensor Employed for the Ultrasensitive\nCA19‑9 Detection

Carbohydrate\nantigen 19-9 is a well-known malignancy biomarker,\nand its sensitive detection is particularly crucial in the diagnosis\nand assessment of pancreatic cancer. In this study, an ultrasensitive\nCA19-9 immunosensor was constructed using the Zn<sup>2+</sup>-regulated\nCdS<sub><i>y</i></sub>Se<sub>1–<i>y</i></sub> (Zn-CdS<sub><i>y</i></sub>Se<sub>1–<i>y</i></sub>) nanospheres (NSs) as the electrochemiluminescence\n(ECL) emitter and FeCoS<sub>2</sub> nano octahedrons (NOs) as a coreactant\nenhancer. The microstructure of ternary transition metal chalcogenide\nCdS<sub><i>y</i></sub>Se<sub>1–<i>y</i></sub> was precisely tuned by Zn<sup>2+</sup> doping to avoid aggregation\nand thus enable stable and efficient cathodic ECL responses. The bimetallic\nsulfide FeCoS<sub>2</sub> was synthesized using a metal organic framework\n(MOF) as the template by ion permeation. It was able to catalyze the\ncoreactant efficiently due to the synergistic effect of the Fe<sup>2+</sup> and Co<sup>2+</sup>. The immunosensor exhibited low detection\nlimit (7.6 × 10<sup>–5</sup> U mL<sup>–1</sup>)\nin the wide linear range of 0.0001–100 U mL<sup>–1</sup>, offering a sensitive CA19-9 detection method.