Ru(bpy)32+-doped silica nanoparticles labeling for a sandwich-type electrochemiluminescence immunosensor

A new approach was established to construct a sandwich-type electrochemiluminescence (ECL) immunosensor by using Ru(bpy)32+-doped silica (abbreviated as Ru–SiO2) nanoparticles to label secondary antibody. Firstly, carboxylate-terminated multi-walled carbon nanotubes (MWCNTs) were modified on the electrode to bond with avidin. Subsequently, biotinylated antibodies were immobilized on the surface of the electrode by employing the specific interaction of biotin/avidin and the non-covalent and covalent conjugation function of MWCNTs. Later, the electrode was incubated with antigen of mouse IgG and then reacted with the secondary antibody which was labeled by Ru–SiO2. Accordingly, through the ECL response of Ru–SiO2 and tripropylamine (TPA), a strong ECL signal was obtained and an amplification analysis of protein interaction was achieved. The present immunosensor showed a wide linear range of 0.05–200.00 ng mL−1 for detecting mouse IgG, with a low detection limit of 17 pg mL−1. There was a 4–300-fold improvement in detection limit compared with other similar studies. The morphologies of Ru–SiO2 nanoparticles were characterized by using transmission electronic microscopy (TEM). The fabrication process of the immunosensor was studied by cyclic voltammetry (CV) and the performance of the immunosensor was monitored with an electrochemiluminescence analyzer. This new strategy for preparation of the ECL immunosensor could be easily realized and has potential application in ultrasensitive bioassays.