No abstract

No abstract

A new homogeneous electrochemical immunosensing platform was designed for sensitive detection of aflatoxin B (AFB) in foodstuff. The system consisted of anti-AFB antibody labeled DNA (Ab-DNA), AFB-bovine serum albumin (BSA)-conjugated DNA (AFB-DNA), and methylene blue functionalized hairpin DNA. Owing to a specific antigen-antibody reaction between anti-AFB and AFB-BSA, the immunocomplex formed assisted the proximity hybridization of DNA with DNA, thus resulting in the formation of an omega-like DNA junction. Thereafter, the junction opened the hairpin DNA to construct a new double-stranded DNA, which could be readily cleaved by exonuclease III to release the omega-like DNA junction and methylene blue. The dissociated DNA junction could repeatedly hybridize with residual hairpin DNA molecules with exonuclease III-based isothermal cycling amplification, thereby releasing numerous free methylene blue molecules into the detection solution. The as-produced free methylene blue molecules could be captured by a negatively charged indium tin oxide electrode, each of which could produce an electronic signal within the applied potentials. On introduction of target AFB, the analyte competed with AFB-DNA for the conjugated anti-AFB on the Ab-DNA, subsequently decreasing the amount of omega-like DNA junctions formed, hence causing methylene blue labeled hairpin DNA to move far away from the electrode surface. Under optimal conditions the detectable electrochemical signal decreased with increasing amount of target AFB in a dynamic working range of 0.01-30 ng mL with a detection limit of 4.8 pg mL. In addition, the precision and reproducibility of this system were acceptable. Finally, the method was further evaluated for analysis of naturally contaminated or AFB-spiked peanut samples, giving results that matched well with those obtained with a commercial AFB ELISA kit.

No abstract

Two-dimensional (2D) MoS 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 MoS for ssDNA is considerably larger than that for dsDNA, it will be adsorbed on the electrode by binding to the auxiliary DNA. Notably, 2D MoS 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 to 1.0 ng·mL, with a lower detection limit of 0.23 pg·mL. 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 MoS as a nano-binder to catalyze the amplification of electrochemical signal from hydroquinone/benzoquinone system.