Two-dimensional MoS2 as a nano-binder for ssDNA: Ultrasensitive aptamer based amperometric detection of Ochratoxin A

Two-dimensional (2D) MoS2 is found to possess different affinities for ssDNA and dsDNA. This finding is exploited in an amperometric aptamer-based method for the determination of the mycotoxin ochratoxin A (OTA). Initially, a dsDNA probe (formatted through the hybridization of OTA-aptamer with an auxiliary DNA) is self-assembled on a gold electrode. Upon introduction of OTA, it will bind to the aptamer and cause the unwinding of dsDNA, while the auxiliary DNA (with single-stranded structure) remains on the electrode. Since the affinity of 2D MoS2 for ssDNA is considerably larger than that for dsDNA, it will be adsorbed on the electrode by binding to the auxiliary DNA. Notably, 2D MoS2 possesses peroxidase-like activity. Hence, it can catalyze the amplification of electrochemical signal of the hydroquinone/benzoquinone redox system. Under optimal conditions, the amperometric signal (best measured at -0.2 V vs. SCE) increases with increasing OTA concentration in the range from 0.5 pg.mL(-1) to 1.0 ng.mL(-1), with a lower detection limit of 0.23 pg.mL(-1). The method was applied to the determination of OTA in spiked red wine.