Polydopamine-mediated quantity-based magnetic relaxation sensing for the rapid and sensitive detection of chloramphenicol in fish samples

Chloramphenicol is an antibiotic that cause adverse effects in humans. In this work, a novel quantity-based magnetic relaxation switching (sMRS) sensor using polydopamine (PDA) for signal amplification was successfully developed for the rapid and sensitive detection of chloramphenicol in fish samples. We first prepared the conjugation of large magnetic nanoparticles (MNPs) and CAP antigen (MNP-antigen), which performed a competitive immune reaction with chloramphenicol and chloramphenicol antibody. Horseradish peroxidase, that can bind to antibody at the surface of large MNPs, was employed to catalyze the rapid polymerization of dopamine to PDA, which was easily deposited onto the surface of large MNPs. The concentration of chloramphenicol is inversely proportional to the content of HRP after reaction, in other words, it is inversely proportional to the content of PDA. PDA then reacted with 30 nm-diameter amine-functionalized MNPs (NH2-MNP30), the consumption of which resulted in a decrease in the concentration of free NH2-MNP30 particles in solution. After magnetic separation, the remaining free NH2-MNP30 served as the magnetic probe for signal readout. The limit of detection of the sMRS assay for detecting chloramphenicol was 16.6 pg/mL, which was 49-fold lower than MRS sensor without signal amplification. This quantity-based MRS sensor can provide a powerful platform for enabling the rapid and sensitive detection of chloramphenicol in food samples.