A novel peptide-based relay fluorescent probe with a large Stokes shift for detection of Hg and S in 100 % aqueous medium and living cells: Visual detection via test strips and smartphone.

Herein, a novel relay peptide-based fluorescent probe DGRK was synthesized via solid phase peptide synthesis (SPPS) technology. DGRK exhibited excellent water-solubility, good stability, remarkably large Stokes shift (230 nm) and high selectivity response to Hg with a non-fluorescence complex DGRK-Hg formation via a 1:1 binding mode. Further studies indicated that the DGRK-Hg complex could act as a secondary probe for rapidly and sequentially detecting S based on fluorescent "off-on" response, and without interference from a range of anions. The limit of detection (LOD) for Hg and S were calculated to be 33.6 nM and 60.9 nM, respectively. In addition, The reversibility of interaction of confirmed that the continuous and reversible recognition behavior of Hg and S by the probe DGRK, and could be cycled more than 5 times. In addition, DGRK could be successfully applied to the fluorescence imaging of Hg and S in two living cells based on excellent cells permeability and low cytotoxicity. Meanwhile, DGRK was successfully used to create the low-cost and portable test strips for visual detection and rapid analysis under 365 nm UV lamp, and the test strips combined with a smartphone (RGB color) was successfully applied to the semi-quantitative analysis and monitoring of dynamic changes of Hg levels.