Sandwich-type electrochemical immunosensor based on CuFe₂O₄-Pd for cardiac troponin I detection

A sandwich-type electrochemical immunosensor was designed by highly efficient catalytic cycle amplification strategy of CuFe₂O₄-Pd for sensitive detection of cardiac troponin I. CuFe₂O₄ with coupled variable valence metal elements exhibited favorable catalytic performance through bidirectional cycling of Fe²⁺/Fe³⁺ and Cu⁺/Cu²⁺ redox pairs. More importantly, Cu⁺ acted as the intermediate product of the catalytic reaction, promoted the regeneration of Fe²⁺ and ensured the continuous recycling occurrence of the double redox pairs, and significantly amplified the current signal response. Pd nanoparticles (Pd NPs) loaded on the surface of amino-functionalized CuFe₂O₄ (CuFe₂O₄-NH₂) served as electrochemical mediators to capture labeled antibodies (Ab₂), and also as co-catalysts of CuFe₂O₄ to further enhance the catalytic efficiency, thus improving the sensitivity of the electrochemical immunosensor. Under the optimal experimental conditions, the linear range was 0.001 ~ 100 ng/mL, and the detection limit was 1.91 fg/mL. The electrochemical immunosensor has excellent analytical performance, giving a new impetus for the sensitive detection of cTnI.