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

Abstract

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.

Monolayer nanosheets formed by liquid exfoliation of charge-assisted hydrogen-bonded frameworks

“…This quenching mechanism is widely employed by other nanosheet systems in a variety of biological and environmental sensing applications, particularly by quenching of dye-labelled single-stranded DNA for biomolecular detection. 60–63 …”

Organic ultrathin nanostructure arrays: materials, methods and applications

“… 69 For instance, Wong et al obtained easily Hofmann-type MOF (hMOF) monolayer nanosheets via a top–down method ( Fig. 3d–f ), 70 and hMOF nanosheets as an axial coordination platform for DNA detection exhibited excellent quenching ability to fluorophores via a ligand-to-metal charge-transfer mechanism.…”

Modulation of the spin transition in 2D Hofmann frameworks via π⋯π stacking between the axial 2,5-dipyridyl-1,3,4-oxadiazoles

“…5–11 Among them, Fe 2+ Hofmann-type SCO frameworks are one of the most notable systems. 6,10–35 These frameworks generally contain neutral bimetallic layers consisting of Fe 2+ ions and [M(CN) 4 ] 2− anions (M = Pt 2+ , Pd 2+ , Ni 2+ ) in the equatorial plane, which allow a large number of linear N-donor ligands to coordinate axially to the Fe 2+ centers in order to produce 2D/3D Hofmann SCO materials. 10 If the linear exo -bidentate ligands are used as pillars, 3D porous Hofmann SCO frameworks can be constructed, 11 while 2D Hofmann SCO networks will be built if the axial ligands are merely monodentate.…”