Construction of a Self-Enhanced Electrochemiluminescent Sensor Based on Tandem Signal Amplification and a Self-Luminescent Lanthanide Covalent-Organic Polymer for Ochratoxin A Assay

Ochratoxin A (OTA) is a type of mycotoxin found in various contaminated foods, and it is highly toxic to the livers and kidneys of humans. Herein, we develop a self-enhanced electrochemiluminescent (ECL) sensor based on tandem signal amplification and a self-luminescent europium covalent-organic polymer (Eu-COPTMT-BPA) for OTA assay. Eu-COPTMT-BPA is a self-enhanced ECL emitter that is obtained by using 2,4,6-trimethyl-1,3,5-triazine (TMT) and 2,2′-bipyridine-5,5′-dicarbaldehyde (BPA) as the first and second ligands to form a highly conjugated structure for sensitizing the Eu3+ luminescence. In Eu-COPTMT-BPA, BPA can adjust the energy gap between the triplet ligand and Eu3+excited state to achieve rapid and effective energy transfer for the generation of an enhanced ECL signal. When target OTA is present, it binds with the aptamer segment of the hairpin aptamer probe (HAP) to form a tight structure. The exposed sequence of HAP subsequently binds with the hairpin probe 1/single-stranded DNA 1 (HP1/S1) hybrid to release OTA and trigger (S1). The released S1 can be recognized by a magnetic bead (MB)-capture probe conjugate to trigger a hybridization chain reaction (HCR) between Fc-labeled HP2 and Fc-labeled HP3, leading to the formation of long double-stranded DNA (dsDNA) nanowires on the MB surface and the accumulation of abundant Fc that can quench the ECL intensity of the Eu-COPTMT-BPA/TPrA system. This ECL sensor exhibits good stability, excellent specificity, and high sensitivity, with a detection limit (LOD) of 0.47 fg/mL and a linear range of 1 pg/mL–10 ng/mL, and it can quantitatively measure OTA in wine and coffee.