A Compatible Sensitivity Enhancement Strategy for Electrochemiluminescence Immunosensors Based on the Biomimetic Melanin-Like Deposition

In this work, a compatible strategy was demonstrated for the enhancement of detection sensitivity of sandwich-type electrochemiluminescence (ECL) immunosensors. The enhanced signal response was based on the combination of biomimetic melanin-like deposition with the effective ECL quenching ability of quinone-rich biopolymers. Gold nanoparticle-loaded horseradish peroxidase (HRP) was used as a catalytic label for the secondary antibodies. The intrinsic catalytic property of HRP toward hydrogen peroxide (H2O2) generates reactive oxygen species, which highly promote the autopolymerization of catecholamines. The resulting fast deposition of quinone-rich biopolymers approaching the luminophor-incorporated sensing platform achieves an obvious ECL quenching. A broad-spectrum tumor marker alpha fetoprotein (AFP) was selected as a model analyte to demonstrate the feasibility of the proposed strategy. Under optimal conditions, a very low detection limit of 0.056 pg mL-1 was obtained. Two orders of magnitude enhancement was achieved in contrast to the signal response without the step of catalytic biopolymer deposition. The combination of compatible HRP labeling with unique melanin-like deposition has potential as a universal strategy in other ECL bioassays.