Ratiometric fluorescent immunoassay mediated by alkaline phosphatase-catalyzed Eu3+ coordination polymers for the detection of Ochratoxin A.

Ochratoxin A (OTA) contamination severely threatens global food safety. Herein, a ratiometric fluorescent immunoassay method was established for trace OTA detection based on an alkaline phosphatase (ALP)-catalyzed Eu3+ coordination polymer (Eu-CP). The Eu-CP probe is self-assembled from ciprofloxacin, adenosine monophosphate, and Eu3+. Upon activation by the Mg2+ cofactor, ALP drives the dephosphorylation and subsequent structural disassembly of the Eu-CP framework, which synchronously regulates dual-emission fluorescent signals. In indirect competitive reaction, OTA competes with bovine serum albumin-OTA for limited antibodies, and the bound ALP-labeled secondary antibody is inversely correlated with OTA concentration. Based on the ratiometric fluorescence signal (F618/F418), the proposed method exhibited a reliable linear range of 0.4883-62.5 ng/mL (R2 = 0.9909) and a limit of detection as low as 0.0273 ng/mL. Recoveries in corn, oat and rice were 97.07%-119.11% with inter-batch CV < 10%. This study provides a simple and sensitive method for trace OTA detection.