A novel dual-emission ratiometric fluorescent nanoprobe for sensing and intracellular imaging of Zn2+

The integration of unique characteristics of nanomaterials with highly specific recognition elements, such as biomolecules and organic molecules, are the foundation of many novel nanoprobes for bio/chemical sensing and imaging. In the present report, branched polyethylenimine (PEI) was grafted with 8-chloroacetyl-aminoquinoline to synthesize a water-soluble and biocompatible quinoline-based Zn2+ probe PEIQ. Then the PEIQ was covalently conjugated to [Ru(bpy)3]2+-encapsulated SiNPs to obtain the ratiometric fluorescence nanoprobe which exhibits a strong fluorescence emission at 600 nm and a negligible fluorescence emission at 500 nm in the absence of Zn2+ upon a single wavelength excitation. After the addition of different amounts of Zn2+, the fluorescence intensity at 500 nm increased continuously while the fluorescence intensity at 600 nm remained stable, thus changing the dual emission intensity ratios and displaying continuous color changes from red to green which can be clearly observed by the naked eye. The nanoprobe exhibits good water dispersivity, biocompatibility and cell permeability, high selectivity over competing metal ions, and high sensitivity with a detection limit as low as 0.5 μM. Real-time imaging of Zn2+ in A549 cells has also been realized using this novel nanoprobe.