A triple-amplification SPR electrochemiluminescence assay for chloramphenicol based on polymer enzyme-linked nanotracers and exonuclease-assisted target recycling

The present study aimed to explore a novel triple-amplification electrochemiluminescence (ECL) assay for detecting of chloramphenicol (CAP). This strategy was based on single-stranded DNA-binding protein (SSB) and horseradish peroxidase (HRP) enzyme-linked polymer (EnVision reagent, EV) labeled on Au nanoparticles (EV-Au-SSB) as nanotracer and exonuclease-assisted target recycling. The composite probes were prepared via immunoreactions between the CdS nanocrystal (CdS NC)-functionalized partial complementary DNA and aptamer (CdSNCs/Apt-ssDNA1) as capture probes, and EV-Au-SSB as nanotracer. When the composite probe solution co-existed with CAP and Exo I, the aptamer on the capture probes preferentially combined with CAP, and then CAP-Apt and nanotracer complex were released into the solution. Subsequently, Exo I in the solution could further digest the CAP-Apt from the 3′-end of the aptamer and release CAP, which could participate in further reaction with the probes. It was worth mentioning that EV contained a large number of HRPs on its dendritic chain. In the EV-Au-SSB, Au could enhance ECL intensity of CdS NCs by surface plasmon resonance. What's more, HRPs on EV could catalyze the reaction of H2O2, which could obviously enhance ECL intensity of CdS NCs. This study demonstrated excellent performance of the triple-amplification ECL assay, which makes this aptasensor system suitable and promising for the practical application of CAP residues in fish samples. Moreover, the assay might provide a promising avenue to develop efficient aptasensors to determine small-molecule harmful substances in environmental monitoring and food safety.