Ratiometric peptide-based fluorescent probe with large Stokes shift for detection of Hg 2+and S 2-and its applications in cells imaging and smartphone-assisted recognition

In this work, a new ratiometric fluorescent probe DKA was synthesized based on the double sides of lysine backbone conjugated with alanine and dansyl groups. DKA exhibited fluorescence ratiometric response for Hg 2+ with high sensitivity (13.4 nM), specific selectivity (only Hg 2+ ), strong anti -interference ability (no interference), fast recognition (within 60 s) and wide pH range (5 -10). The stoichiometry of binding of DKA and Hg 2+ was determined to be 1:1 via Job 's plot, ESI-HRMS and 1 HNMR titration analysis. Subsequently, the in situ formation of DKA -Hg 2+ complex was used for highly selective detection of S 2- as a novel fluorescence "on -off " probe, and the lowest detection limit for S 2- was 12.9 nM. In addition, DKA possessed excellent cells permeation and low toxicity, and fluorescence imaging of Hg 2+ and S 2- was performed in living Hacat cells. Most importantly, the digital imaging using a smartphone color recognition APP indicated that DKA could semi -quantitatively and visually detected Hg 2+ and S 2- without expensive equipment.