Ratiometric absorbance and fluorescence dual model immunoassay to detect ochratoxin a based on ZIF-8@uranine and p-nitrophenol

Ochratoxin A (OTA) as a mycotoxin has strong carcinogenicity and can affect human health. Thus, it is necessary to establish an accurate method to detect OTA. Herein, a ratiometric absorbance and fluorescence dual model immunoassay based on ZIF-8@uranine (ZIF-8@UR) and p -nitrophenol (PNP) was developed. In this new immunoassay, alkaline phosphatase-labeled secondary antibodies (IgG-ALP) were used to associate OTA with signal output. The IgG-ALP can hydrolyze 4-nitrophenyl phosphate salt (PNPP) to generate yellow PNP and phosphate (Pi). Then, the Pi triggered the decomposition of ZIF-8@UR to release UR with a fluorescence signal. The absorbance ratio of PNP and UR was taken as a ratiometric absorbance signal. The ratiometric absorbance and fluorescence modes exhibited linear ranges of 0.781–50.0 ng/mL and 1.563–100.0 ng/mL, with limits of detection (LODs) of 0.112 ng/mL and 0.147 ng/mL, respectively. Meanwhile, the new immunoassay showed high specificity for OTA and satisfactory recovery rate in actual samples.