Reversible and selective fluorescence detection of histidine using a naphthalimide-based chemosensing ensemble

We described a new ensemble-approach-based chemosensor, NCH-Cu²⁺, for highly selective and reversible detection of histidine (His) in aqueous solution and live cells. The ligand NCH exhibited specific binding with Cu²⁺ ions over other metal ions, accompanied with a 92.2% fluorescence quenching. The decomplexation of NCH-Cu²⁺ ensemble by His led to the liberation of the fluorophore, NCH, and thus the fluorescence was recovered. The specific fluorescence enhancement of NCH-Cu²⁺ towards His showed a good linearity with a detection of limit at 70 nm. Quantification of intracellular His at the single cell level was achieved by microscopy and flow cytometry. Besides the UV/Vis and emission titration, reversibility of the NCH-Cu²⁺ towards His was further confirmed by imaging and cytometry analysis. In addition, microscopy studies revealed that NCH-Cu²⁺ was distributed in the lysosome of live cells, where it could be employed as a fluorescent biosensor for imaging of His at subcellular level.