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.