Sandwich-Type Electrochemiluminescence Sensor for Detection of NT-proBNP by Using High Efficiency Quench Strategy of Fe₃O₄@PDA toward Ru(bpy)₃²⁺ Coordinated with Silver Oxalate

Heart failure (HF) is a burgeoning public health problem trigged by a heart circulation disorder. N-terminal pro-B-type natriuretic peptide (NT-proBNP) has been acknowledged as a prognostic biomarker for cardiac disease. Herein, a sandwich-type electrochemiluminescence (ECL) immunosensor was introduced for sensitive detection of NT-proBNP. Gold nanoparticle modified graphene oxide-Ru­(bpy)₃²⁺/Ag₂C₂O₄ was used as a luminophore and a desirable platform for immobilization of the captured antibodies. The more stable immobilization of plentiful Ru­(bpy)₃²⁺ could be implemented by direct covalent bonding chelation with Ag₂C₂O₄. More importantly, significant quenching can be achieved by introducing polydopamine (PDA) coated Fe₃O₄ onto the electrode via sandwich immunoreactions. The quenching mechanism mainly showed that the excited states of Ru­(bpy)₃²⁺ could be annihilated by quinone units in PDA via energy transfer. The ECL quenching efficiency was logarithmically related to the concentration of the NT-proBNP in the range from 0.0005 ng/mL to 100.0 ng/mL with a detection limit of 0.28 pg/mL. Furthermore, this specific immunosensor presented good stability and repeatability as well as selectivity, which offers a guiding significance in both fundamental and clinical diagnosis of NT-proBNP