A “turnon” aptasensor for simultaneous and time-resolved fluorometric determination of zearalenone, trichothecenes A and aflatoxin B₁ using WS₂ as a quencher

A “turn on” time-resolved fluorometric aptasensor is described for the simultaneous detection of zearalenone (ZEN), trichothecenes A (T-2), and aflatoxin B₁ (AFB₁). Multicolor-emissive nanoparticles doped with lanthanide ions (Dy³⁺, Tb³⁺, Eu³⁺) were functionalized with respective aptamers and applied as a bioprobe, and tungsten disulfide (WS₂) nanosheets are used as a quencher of time-resolved fluorescence. The assay exploits the quenching efficiency of WS₂ and the interactions between WS₂ and the respective DNA aptamers. The simultaneous recognition of the three mycotoxins can be performed in a single solution. In the absence of targets, WS₂ is easily adsorbed by the mixed bioprobes via van der Waals forces between nucleobases and the WS₂ basal plane. This brings the bioprobe and WS₂ into close proximity and results in quenched fluorescence. In the presence of targets, the fluorescence of the bioprobes is restored because the analytes react with DNA probe and modify their molecular conformation to weaken the interaction between the DNAs and WS₂. Under the optimum conditions and at an excitation wavelength of 273 nm, the time-resolved fluorescence intensities (peaking at 488, 544 and 618 nm and corresponding to emissions of Dy³⁺, Tb³⁺ and Eu³⁺) were used to quantify ZEN, T-2 and AFB₁, respectively, with detection limits of 0.51, 0.33 and 0.40 pg mL⁻¹ and a linear range from 0.001 to 100 ng mL⁻¹. The three mycotoxins can be detected simultaneously without mutual interference. The assay was applied to the quantification of ZEN, T-2 and AFB₁ in (spiked) maize samples. This homogeneous aptamer based assay can be performed within 1 h. Conceivably, it can become an alternative to other heterogeneous methods such as the respective enzyme-linked immunosorbent assays. [Figure not available: see fulltext.].