Colorimetric and ratiometric fluorescent dual-mode sensitive detection of Hg²⁺ based on UiO-66-NH₂@Au composite

A colorimetric and ratiometric fluorescent dual-mode assay is constructed for sensitive and specific Hg²⁺ sensing based on UiO-66-NH₂ and Au composite (UiO-66-NH₂@Au). The addition of Hg²⁺ stimulates the peroxidase-like activity of UiO-66-NH₂@Au by the formation of Au-Hg amalgam, promoting the oxidizing of chromogenic substrate OPD to DAP with the aid of H₂O₂, which lead to the change of colorimetric and fluorescent signals. The absorbance of the sensing system at 450 nm is linear positive correlation with Hg²⁺ concentration of 30-1400 nM and the color of the solution under visible light shaded from light yellow to dark yellow. With the increase of Hg²⁺ concentration, the fluorescence signal at 570 nm (DAP) increased whereas that at 455 nm (intrinsic fluorescence of UiO-66-NH₂) decreased due to inner filter effect (IFE), the fluorescence intensity ratio (F₄₅₅/F₅₇₀) decreasing linearly with Log [Hg²⁺] over the range 60-1700 nM; the fluorescence emission of sensing system under UV excitation changed from blue to yellow, which can easily be discerned visually. This assay was successfully applied to the determination of Hg²⁺ in tap water and river water. The results indicate that the colorimetric and ratiometric fluorescent dual-mode assay based on UiO-66-NH₂@Au realized visual determination of Hg²⁺ rapidly and reliably, revealed application prospect in Hg²⁺ monitoring.