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

In this work, a 'signal on' electrochemiluminescence (ECL) strategy was proposed to detect Apolipoprotein-A1 (Apo-A1), a common tumor biomarker for bladder cancer. The luminophor of tris(2,2’-bipyridyl)-ruthenium(II) [Ru(bpy)32+] was used as luminophore captured by three-dimensional (3D) zinc oxalate metal−organic frameworks (MOFs), which constructed as the ECL nanoprobe (denoted as Ru-MOF) for detecting Apo-A1. Meanwhile, L-cysteine (L-Cys) as the co-reactant was linked to the Pd@Au core-shell nanostructure through Au-S bond, which was directly modified on the glassy carbon electrode (GCE) to significantly reduce the electron transfer distance between the luminophor and co-reactant. The ECL intensity was obviously enhanced when the ECL probe of Ru-MOF was linked to the electrode by the immunoreaction of antigen-antibody. Based on these principles, the quantitative relationship between the concentration of Apo-A1 and the change of ECL intensity was obtained in the range of 1.00 fg∙mL-1 to 1.00 ng∙mL-1 with a linear coefficient of 0.9968. The proposed ECL immunosensor exhibited some great advantages, such as simplification, rapidity, stability and selectivity. It was also successfully applied for the determination of Apo-A1 in patient’s serum and urine samples with the recovery of 98.0% ~ 115.0% (RSD < 5.2%). To sum up, a 'signal on' ECL immunosensor was successfully constructed for Apo-A1 detection, and it may facilitate the diagnosis of bladder cancer in clinic.