Ratiometric peptide-based fluorescent probe with large Stokes shift for detection of Hg and S 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 with high sensitivity (13.4 nM), specific selectivity (only Hg), 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 was determined to be 1:1 via Job's plot, ESI-HRMS and HNMR titration analysis. Subsequently, the in situ formation of DKA-Hg complex was used for highly selective detection of S as a novel fluorescence "on-off" probe, and the lowest detection limit for S was 12.9 nM. In addition, DKA possessed excellent cells permeation and low toxicity, and fluorescence imaging of Hg and S 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 and S without expensive equipment.