A Dual-Ion Synergistic Catalysis Utilizing Zn²⁺-Regulated CdS_<i>y</i>Se_1–<i>y</i> ECL Immunosensor Employed for the Ultrasensitive CA19-9 Detection

Carbohydrate antigen 19-9 is a well-known malignancy biomarker, and its sensitive detection is particularly crucial in the diagnosis and assessment of pancreatic cancer. In this study, an ultrasensitive CA19-9 immunosensor was constructed using the Zn²⁺-regulated CdS_<i>y</i>Se_1-<i>y</i> (Zn-CdS_<i>y</i>Se_1-<i>y</i>) nanospheres (NSs) as the electrochemiluminescence (ECL) emitter and FeCoS₂ nano octahedrons (NOs) as a coreactant enhancer. The microstructure of ternary transition metal chalcogenide CdS_<i>y</i>Se_1-<i>y</i> was precisely tuned by Zn²⁺ doping to avoid aggregation and thus enable stable and efficient cathodic ECL responses. The bimetallic sulfide FeCoS₂ was synthesized using a metal organic framework (MOF) as the template by ion permeation. It was able to catalyze the coreactant efficiently due to the synergistic effect of the Fe²⁺ and Co²⁺. The immunosensor exhibited low detection limit (7.6 × 10^-5 U mL^-1) in the wide linear range of 0.0001-100 U mL^-1, offering a sensitive CA19-9 detection method.