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[Display omitted] • The CPNs(Ⅳ) was stable and the preparation of the CPNs(Ⅳ) was simple. • The newly proposed method exhibited high sensitivity and wide detection range. • The analysis results had good reliability for detecting OTA in actual samples. • The mutual verification between fluorescence and color mode guaranteed the accuracy of this new method. Ochratoxin A (OTA) is a widely distributed mycotoxin that seriously endangers food safety and human health. Therefore, establishing a sensitive and simple method for detecting OTA is crucial to ensure food safety. A fluorescence and colorimetric dual-mode immunoassay was established using cerium-based nanoparticles CPNs(Ⅳ) for detection of OTA. CPNs(IV) with good oxidase activity can catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to produce visible blue color signal. Under the catalysis of ALP, the ascorbic acid 2-phosphate (AA2P) was hydrolyzed to form ascorbic acid (AA), which reduced CPNs(Ⅳ) to CPNs(III). The produced CPNs(III) can emit significant fluorescence signal. Because the concentration of OTA was inversely proportional to the concentration of IgG-ALP in the microplate, the fluorescence signal was gradually decreased and the blue color signal gradually increased with the addition of OTA. The limits of detection (LODs) of this dual-mode immunoassay were 0.404 ng/mL (for fluorescent mode) and 0.962 ng/mL (for colorimetric mode). The recoveries of OTA were 97.60 %–103.55 % for the fluorescence mode and 99.12 %–102.60 % for the colorimetric mode in corn samples. These results indicated the dual-mode immunoassay was sensitive and reliable for detection of OTA in actual samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A turn-on fluorescence immunoassay triggered by alkaline phosphatase was established. • The AuNCs was simple to prepare and had good stability. • The turn-on fluorescence can reduce false positive and improve sensitivity. • The proposed immunoassay had higher sensitivity for detection of OTA. Ochratoxin A (OTA) is a highly toxic mycotoxin which can cause a variety of diseases. Sensitive detection of OTA is significant for food safety. Herein, a feasible and sensitive immunoassay was established for OTA detection by alkaline phosphatase (ALP) triggered gold nanoclusters (AuNCs) turn-on fluorescence. The fluorescence of the AuNCs can be quenched by Cr6+ induced aggregation of AuNCs and the fluorescence resonance energy transfer (FRET) between AuNCs and Cr6+. Under the catalytic action of ALP-labelled IgG (IgG-ALP), the ascorbic acid 2-phosphate (AA2P) was hydrolyzed to ascorbic acid (AA) for the reducing of Cr6+ to Cr3+. As a result, the degrees of AuNCs aggregation and FRET were weakened and the fluorescence of AuNCs was turned on. The amount of OTA in the sample was negatively correlated with the amount of IgG-ALP captured by anti-OTA monoclonal antibody (McAb) in the microplate. In optimal conditions, the turn-on fluorescence immunoassay had a good linear range of 6.25–100 ng/mL, and the detection limit was 0.693 ng/mL. The recoveries of OTA from corn were 95.89%-101.08% for the fluorescence immunoassay. This work provided a feasible, sensitive and good selectivity fluorescence method for OTA detection. [ABSTRACT FROM AUTHOR]

In this work, a dual-mode immunoassay to detect Ochratoxin A (OTA) was developed relied on p -nitrophenyl phosphate (PNPP) and 2-aminoterephthalic acid (PTA-NH 2). This proposed immunoassay based on microplate immunoenzyme technique used alkaline phosphatase (ALP) as a label for forming immune complexes. The ALP was used to catalyze the dephosphorization of PNPP to generate yellow p -nitrophenol (PNP). Since the absorption wavelength of PNP overlapped with the fluorescence emission of PTA-NH 2 , the fluorescence of PTA-NH 2 can be quenched by PNP. The color of PNP and the fluorescence of PTA-NH 2 were used as double signals to detect OTA. In this dual-mode immunoassay, the limit of detection (LOD) and the linear detection range of fluorescence mode were 0.57 ng/mL (about 0.57 μg/kg) and 1.56–50.00 ng/mL (about 1.56–50.00 μg/kg), respectively. For absorbance mode, the LOD and linear range were 0.07 ng/mL (about 0.07 μg/kg) and 0.39–25.00 ng/mL (about 0.39–25.00 μg/kg), respectively. Both detection modes showed good selectivity for OTA. The recoveries rates of fluorescence mode and absorption mode in maize flours were 91.80–128.85% and 100.10–114.00%, respectively. • The dual-mode immunoassay was developed based on PNPP and PTA-NH 2. • This assay based on microplate immunoenzyme technique used ALP as a label for forming immune complexes. • The mutual verification of the two modes improved the accuracy of analysis method. • The dual-mode immunoassay had a wide linear range and low LOD. [ABSTRACT FROM AUTHOR]