Colorimetric ELISA for ochratoxin A detection based on the urease-induced metallization of gold nanoflowers

This study reports a novel enzyme-induced metallization plasmonic enzyme-linked immunosorbent assay (pELISA) for ultrasensitive detection of ochratoxin A (OTA) in rice, corn, wheat, and white wine samples. OTA-labeled urease was used as competing antigen to hydrolyze urea into ammonia. Silver ions were reduced by the formyl group from glucose to generate a silver shell on the surface of gold nanoflowers (33 nm, AuNFs) in the presence of ammonia molecules. The color of the solution changed from blue to brownish red. Various parameters that influenced the sensitivity of colorimetric pELISA were investigated and optimized. Under the optimized conditions, the colorimetric pELISA exhibited a high sensitivity for qualitative detection of OTA by the naked eye with a cutoff limit of 40 pg/mL, and a favorable linear range of 5.0-640 pg/mL for quantitative detection of OTA with a limit of detection at 8.205 pg/mL. These values are 15.6- and 14.3-folds lower than those of horseradish peroxidase (HRP)-based ELISA. The method also showed excellent specificity against four other mycotoxins including deoxynivalenol, zearalenone, fumonisin B-1, and aflatoxin B-1. Moreover, the recoveries for OTA-spiked rice, corn, wheat, and white wine samples ranged from 81.5% to 106%, with coefficient of variation ranging from 6.13% to 18.7%. These results showed a good agreement with those obtained by an ultra-performance liquid chromatography fluorescence detector (UPLC-FLD) method. Hence, the proposed method exhibited excellent robustness and reliability for quantitative detection of OTA in different food samples. This work provides a simple, sensitive, robust, and high-throughput screening method for qualitative or quantitative detection of mycotoxins or other pollutants in food safety monitoring. (C) 2018 Elsevier B.V. All rights reserved.