A Novel Ochratoxin A Aptasensor Based on Three-Dimensionally Ordered Macroporous RGO-AuNPs-MoS₂ Enhanced Electrocatalysis of Methylene Blue and AuNPs-Fe₃O₄@C Composite as Signal Probe Carrier

In this work, a novel electrochemical aptasensor for the detection of ochratoxin A (OTA) was developed using a three-dimensionally ordered macroporous (3DOM) reduced graphene oxide–Au nanoparticles–molybdenum disulfide (RGO-AuNPs-MoS₂) composite material as the sensing interface and Au nanoparticles–carbon-coated ferroferric oxide (AuNPs-Fe₃O₄@C) composite as the signal amplifier. The 3DOM RGO-AuNPs-MoS₂ composite exhibited excellent conductivity and catalytic activity. The 3DOM RGO-AuNPs-MoS₂ film was electrodeposited onto the Au electrode surface to immobilize DNA capture probe (CP), which was then hybridized with DNA helper strands (HS) and OTA aptamer (OPT) to form a Y-shaped structure. In the presence of OTA, the OPT was released from the electrode and then combined with AuNPs-Fe₃O₄@C containing the signal DNA1-metheylene blue (S1-MB) and DNA2-metheylene blue (S2-MB). The current response coming from MB was proportional with the OTA concentration. Under optimal conditions, the linear range of the aptasensor was 1 fg/mL to 0.1 μg/mL, with a detection limit as low as 0.56 fg/mL. The aptasensor was also used to detect OTA in rice and wheat samples, and the results were in agreement with those obtained by liquid chromatography-mass spectrometry (HPLC-MS).