Lanthanide-based metal-organic framework nanosheets with unique fluorescence quenching properties for two-color intracellular adenosine imaging in living cells

Two-dimensional (2D) materials have attracted tremendous interest as fluorescence quenchers of dye-labeled biomolecules for application in biosensing. Metal- organic framework (MOF) nanosheets, as a new type of 2D material, have rarely been studied as bioanalytical platforms. Herein, we synthesize a series of ultrathin lanthanide-based MOF (MOF-Ln) nanosheets as a dye- labeled aptamer platform. The fluorescence quenching or recovery on the MOF-Ln nanosheets is determined by the charge properties (positive or negative) of the labeled fluorophores. The negatively charged fluorophores experience a fluorescence 'turn-down followed by turn-down' process, whereas the positively charged fluorophores experience a fluorescence 'turn-down followed by turn-up' process. The interesting fluorescence quenching properties of the MOF-Ln nanosheets make them an excellent two-color sensing platform for the intracellular detection of biomolecules.