Selective fluorescence sensor based on ion-imprinted polymer-modified quantum dots for trace detection of Cr(VI) in...

A new fluorescence sensor (QDs-IIP), based on ion-imprinted polymers (IIP) as recognition element and Mn-doped ZnS quantum dots (QDs) as fluorophore, was synthesized for the selective and sensitive determination of hexavalent chromium (Cr(VI)) ions. The QD was first coated by SiO₂ layer, and then modified with Cr(VI)-imprinted polymer. Several parameters affecting fluorescence intensity such as tetraethylorthosilicate (TEOS) volume, ZnS:Mn@SiO₂ amount, and radiation time were investigated and optimized. The QDs-IIP was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscope (TEM), and scanning electron microscope (SEM). Furthermore, the fluorescence quenching mechanism was investigated by using UV-VIS and fluorescence spectrophotometer, and it was found that internal filtration effect was the main fluorescence quenching mechanism. The relative fluorescence intensity (F₀/F) increased linearly with the increase of Cr(VI) concentration in the range of 20 μg L^-1-1.0 mg L^-1. The QDs-IIP sensor showed high recognition selectivity for Cr(VI) in comparison with the QDs-NIP sensor with an imprinting factor (IF) of 2.53, and it could be reused 5 times. In addition, an analytical method of Cr(VI) based on the QDs-IIP sensor was established with a limit of detection of 5.48 μg L^-1, and was then applied to actual water samples with satisfactory results. Therefore, QDs-IIP can be deemed as a practicable fluorescent sensor for trace Cr(VI) detection. Graphical abstract.