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. Graphical abstract Herein we construct a convenient electrochemical aptasensor for sensitive monitor of ochratoxin A by using 2D MoS₂ as a nano-binder to catalyze the amplification of electrochemical signal from hydroquinone/benzoquinone system.