Ratiometric Peptide-Based Fluorescent Probe with Large Stokes Shift for Sequential Detection of Hg2+ and S2− and its Applications in Cells Imaging and Smartphone-Assisted Recognition

Abstract

In this work, a simple ratiometric fluorescent probe DKA was synthesized based on the double sides of lysine backbone conjugated with alanine and dansyl groups. DKA exhibited fluorescence ratiometric and “off-on” response for Hg2+ with high sensitivity (19.6 nM), specific selectivity (only Hg2+), strong anti-interference ability (no interference), quick response time (within 60 s) and wide pH range (5-10). The stoichiometry of binding of DKA and Hg2+ was determined to be 1:1 via Job’s plot, ESI-HRMS and 1HNMR titration analysis. Subsequently, the in situ synthesis of DKA-Hg2+ complex was used for highly selective detection of S2− through reversible formation-separation as a novel fluorescence “on-off” probe, and the lowest detection limit for S2− could reach 12.4 nM. In addition, DKA possessed excellent cells permeation and low toxicity, and was used for fluorescence imaging of Hg2+ and S2− in living Hacat cells. Most importantly, the digital imaging using a smartphone color recognition APP indicated that DKA can detect Hg2+ and S2− semi-quantitatively and visually in the field without valuable equipment.

Keywords: Ratiometric probe, Cu2+, S2−, Cells imaging, Smartphone-assisted recognition