l-Cysteine-Tuned the Hierarchical Structure Based on Benzimidazole: Synthesis, Characterization, and Application in Ratiometric Electrochemiluminescence Immunoassay

Efficient and robust electrochemiluminescence (ECL) emitters are crucial for enhancing the ECL immunosensor sensitivity. This study introduces a novel ECL emitter, CoBIM/Cys, featuring a hierarchical core-shell structure. The core of the structure is created through the swift coordination between the sulfhydryl and carboxyl groups of l-cysteine (l-Cys) and cobalt ions (Co²⁺), while the shell is constructed by sequentially coordinating benzimidazole (BIM) with Co²⁺. This design yields a greater specific surface area and a more intricate porous structure compared to CoBIM, markedly enhancing mass transfer and luminophore accessibility. Moreover, the l-Cys and Co²⁺ core introduces Co-S and Co-O catalytic sites, which improve the catalytic decomposition of H₂O₂, leading to an increased production of hydroperoxyl radicals (OOH^•). This mechanism substantially amplifies the ECL performance. Leveraging the competitive interaction between isoluminol and BIM for OOH^• during ECL emission, we developed a ratiometric immunosensor for cardiac troponin I (cTnI) detection. This immunosensor demonstrates a remarkably broad detection range (1 pg mL^-1 to 10 ng mL^-1), a low detection limit (0.4 pg mL^-1), and exceptional reproducibility and specificity.