Ultrasensitive “signal-on” sandwich electrochemiluminescence immunosensor based on Pd@Au-L-cysteine enabled multiple-amplification strategy for Apolipoprotein-A1 detection

•A “signal on” electrochemiluminescence (ECL) immunosensor was proposed to detect Apolipoprotein-A1 (Apo-A1), a common tumor biomarker for bladder cancer.•The Pd@Au-L-Cys nanocomposites were used to immobilize the human Apo-A1 biotinylated antibody (Ab1) and the Ru-MOF was used as the probe for human Apo-A1 antibody (Ab2).•The ECL immunosensor exhibited a good rapidity, stability and selectivity.•The developed immunosensor was successfully applied for the determination of Apo-A1 in real samples.