Hofmann Metal–Organic Framework Monolayer Nanosheets as an Axial Coordination Platform for Biosensing

Two-dimensional (2D) nanomaterials are remarkably attractive platform candidates for signal transduction through fluorescence resonance energy transfer or photo-induced electron-transfer pathway. In this work, a 2D Hofmann metal organic framework (hMOF) monolayer nanosheet was developed as an axial coordination platform for DNA detection via a ligand-to-metal charge-transfer quenching mechanism. Through modulating the position of phosphonate groups of rigid ligands, a layer-structured hMOF was synthesized. The single crystals showed that the adjacent layers were linked via hydrogen bonds between diethyl 4-pyridylphosphonate and the solvent. Furthermore, the 2D hMOF monolayer nanosheets were obtained easily via a top-down method. More significantly, the quenching mechanism was identified as an axial coordination between the open Fe²⁺ sites of hMOF nanosheets and fluorophores with 91% quenching efficiency, constituting an excellent signal transduction strategy. The smart use of hMOF monolayer nanosheets as an axial coordination platform could lead to promising applications in signal switching or/and sensing devices.