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 Hg²⁺. We utilized a zirconium-based MOF (UiO-66) to encapsulate tris(bipyridine) ruthenium(II) chloride (Ru(bpy)₃²⁺), resulting in Ru(bpy)₃²⁺@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 Hg²⁺, forming stable T-Hg²⁺-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 Hg²⁺, SGI fluorescence increases in a dose-dependent manner, while Ru(bpy)₃²⁺ fluorescence remains constant. This fluorescence contrast enables RUT to serve as an effective ratiometric nanoprobe for Hg²⁺ detection, with a detection limit of 3.37 nM. Additionally, RUT demonstrates exceptional reusability due to the ability of cysteine to remove Hg²⁺, given its stronger affinity for thiol groups. The RUT was successfully applied to detect Hg²⁺ in real water samples. This work advances the development of ratiometric fluorescence nanoprobe based on DNA-functionalized MOFs.