Fluorescence and absorbance dual-mode immunoassay for detecting Ochratoxin A

In this work, a simple dual-mode immunoassay for detecting Ochratoxin A (OTA) was developed by mixing G-quadruplex/N-methylmesoporphyrin IX (G4/NMM) and 3,3',5,5'-tetramethylbenzidine (TMB). The fluorescence of G4/NMM can be quenched by oxidized TMB (oxTMB) because the absorbance of oxTMB overlapped with the fluorescence emission of G4/NMM. In the absence of OTA, large amounts of oxTMB were formed with blue color and the fluorescence of G4/NMM was quenched. In the presence of OTA, the concentration of oxTMB was decreased, therefore the fluorescence of G4/NMM increased. The linear range of fluorescence immunoassay was 0.195-25 ng/mL, and the linear range of the absorbance immunoassay was 0.049-1.563 ng/mL. Thus, the linear range of this dual-mode immunoassay can be expanded to 0.049-25 ng/mL. Meanwhile, the new method showed good selectivity for OTA. Besides, the satisfactory recovery rates implied the new method had a potential value for practical sample detection.