A sensitive electrochemical sensor for environmental toxicity monitoring based on tungsten disulfide nanosheets/hydroxylated carbon nanotubes nanocomposite

There has been growing concern about the toxic effects of pollutants in the aquatic environment. In this study, a novel cell-based electrochemical sensor was developed to detect the toxicity of contaminants in water samples. A screen-printed carbon electrode, which was low-cost, energy-efficient, and disposable, was modified with tungsten disulfide nanosheets/hydroxylated multi-walled carbon nanotubes (WS₂/MWCNTs-OH) to improve electrocatalytic performance and sensitivity. The surface morphology, structure, and electrochemical property of WS₂/MWCNTs-OH composite film were characterized by emission scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Raman spectroscopy, and electrochemical impedance spectroscopy. Grass carp kidney cell line was utilized as the sensor biorecognition element to determine the electrochemical signals and evaluate cell viability. The sensor was used to detect the toxicity of one typical contaminant (2,4,6-trichlorophenol) and two emerging contaminants (bisphenol AF and polystyrene nanoplastics). The 48 h half inhibitory concentration (IC₅₀) values were 169.96 μM, 21.88 μM, and 123.01 μg mL^-1, respectively, which were lower than those of conventional MTT assay, indicating the higher sensitivity of the proposed sensor. Furthermore, the practical application of the sensor was evaluated in chemical wastewater samples. This study provides an up-and-coming tool for environmental toxicity monitoring.

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. Graphical abstract Schematic presentation of an aptasensor for simultaneous detection of zearalenone, trichothecenes A and aflatoxin B₁ using aptamer modified time-resolved fluorescence nanoparticles as signalling probes and tungsten disulfide as the quencher. This assay shows lower detection limit and requires no washing steps.