A bifunctional AuNP probe-based enzyme-linked immunosorbent assay for facile and ultrasensitive detection of trace zearalenone in coix seed

Herein, we present a bifunctional gold nanoparticles (AuNP) probe-based enzyme-linked immunosorbent assay (nano-ELISA) for detecting zearalenone (ZEN) in the popular edible and medicinal food coix seed. This nano-ELISA takes advantage of the convenient labeling property of AuNPs, which allows the horseradish peroxidase and antibody were successively immobilized onto AuNPs by electrostatic adsorption to construct a bifunctional probe for identification and signal amplification. In our model system, a time-saving direct competitive ELISA scheme was selected, in which mutual optimization of biomolecules, a two-stage process for incubation, and comparison of different particle sizes were performed to reach higher sensitivity. The proposed method achieves a limit of detection of 8 μg/kg and a limit of quantitation of 22 μg/kg, which is an approximately 7-fold and 5-fold improvement over the traditional ELISA, respectively. The calibration curve for the analyte was linear over the concentration range of 22–508 μg/kg. The recoveries for ZEN spiked coix seed samples ranged from 98.67 to 113.5 % with a relative standard deviation of less than 8 %. Moreover, the developed nano-ELISA could overcome the interference from the sample matrix. A good correlation was observed between the results from nano-ELISA and liquid chromatography-tandem mass spectrometry (r2 = 0.9757, n = 69), which paves the useful and practicable way for accurate bioanalysis for trace hazardous substances in food.