Reusable fluorescence nanoprobe based on DNA-functionalized metal-organic framework for ratiometric detection of mercury (II) ions.

A reusable fluorescent nanoprobe was developed using DNA-functionalized metal-organic framework (MOF) for ratiometric detection of Hg. We utilized a zirconium-based MOF (UiO-66) to encapsulate tris(bipyridine) ruthenium(II) chloride (Ru(bpy)), resulting in Ru(bpy)@UiO-66 (RU) with red fluorescence. The unsaturated metal sites in UiO-66 facilitate the attachment of thymine-rich single-strand DNA (T-ssDNA) through Zr-O-P bond, producing T-ssDNA-functionalized RU complex (RUT). The T-ssDNA selectively binds to Hg, forming stable T-Hg-T base pairs and folding into double-stranded DNA, which permits the intercalation of SYBR Green I (SGI) and activates its green fluorescence. In the presence of Hg, SGI fluorescence increases in a dose-dependent manner, while Ru(bpy) fluorescence remains constant. This fluorescence contrast enables RUT to serve as an effective ratiometric nanoprobe for Hg detection, with a detection limit of 3.37 nM. Additionally, RUT demonstrates exceptional reusability due to the ability of cysteine to remove Hg, given its stronger affinity for thiol groups. The RUT was successfully applied to detect Hg in real water samples. This work advances the development of ratiometric fluorescence nanoprobe based on DNA-functionalized MOFs.