An “On–Off” Electrochemiluminescence Aptasensor for Ochratoxin A Detection Based on CdS-Apt and Ru(bpy)32+

An “on–off” electrochemiluminescence (ECL) aptasensor was proposed for the highly sensitive and selective detection of ochratoxin A (OTA) in cereals. The substrate nanomaterial employed in the ECL experiments was titanium carbide (Ti3C2Tx) MXene, while cadmium sulfide quantum dots (CdS QDs) were used as coreactants of the ECL reagent tris (2,2′-bipyridyl) ruthenium(II) (Ru(bpy)32+). Compared to tripropylamine, a more toxic conventional coreactant, CdS QDs can react efficiently with Ru(bpy)32+ in the ECL reaction, and the reaction principles of both were also investigated. The effective connection between CdS QDs and Ru(bpy)32+ via the aptamer resulted in a shortened electron transfer distance, which in turn led to an improvement in ECL intensity and the achievement of the first “on” state. The introduction of OTA resulted in the loss of the effective connection between the CdS QDs and Ru(bpy)32+, which caused the sensor to enter an “off” state. The high ECL intensity of the sensor in the “on” state, in contrast with the low ECL intensity of the “off” state, resulted in an increase in the sensitivity and stability of the sensor. The established aptasensor exhibited a low limit of detection (LOD) of 0.03 ng/mL within a linear range of 0.1 ∼ 100 ng/mL, with spiked recoveries ranging from 93.7% to 105.1%, showing good selectivity, stability, and reproducibility for the detection of OTA in cereals.