Mo₅N₆ nanosheets for fluorescent quenching and target recognition: Highly selectively sensing of sodium...

Typical fluorescent biosensors use fluorescently labeled ssDNA for target recognition and nanomaterials for signal transduction. Herein, we propose a reverse sensing strategy that Mo₅N₆ nanosheets are used for target recognition while fluorescein (FAM)-labeled ssDNA only serves for signal generation. We discover that Mo₅N₆ nanosheets show high fluorescence quenching ability (>95%) and selective recognition for sodium hexametaphosphate (SHMP). After FAM-labeled ssDNA is adsorbed on Mo₅N₆ nanosheets, the fluorescence is quenched due to the photoinduced electron transfer (PET) effect between FAM and Mo₅N₆ nanosheets. SHMP can specifically displace the adsorbed FAM-labeled ssDNA from Mo₅N₆ nanosheets, resulting in more than 80% fluorescence recovery on addition of 5 μmol L^-1 SHMP. This biosensor can sensitively detect SHMP down to 150 nmol L^-1 and selectively recognize SHMP over glucose, lactose, common amino acids, Zn²⁺, Mg²⁺, Ca²⁺ and other phosphates (such as Na₂HPO₄, sodium pyrophosphate, sodium tripolyphosphate). This biosensor also shows great potential for the detection of SHMP in bacon sample. This work not only provides a facile sensitive and selective biosensor for SHMP but also exploits the application of transition metal nitrides in the field of sensing and biosensing.