New NIR spectroscopic probe with a large Stokes shift for Hg and Ag detection and living cells imaging.

A new near-infrared (NIR) probe based on a coumarinyl ligand (CL) was designed and synthesized. The probe CL can be used for simultaneous fluorescent turn-on and colorimetric detection of Hg and Ag in ethanol/water medium. Colorless solution of probe CL changed to light yellow or dark yellow after addition of Hg or Ag ions. Meanwhile the maximum absorption band shifted from 379 nm to 404 nm and the intensity increased enormously (for Hg) or moderately (for Ag). Probe CL displayed an extraordinarily large Stokes shift of 316 nm and addition of Hg or Ag to probe CL induced enhancement in the intensity of fluorescence emission at 695 nm by 15 or 8 fold. The detection limit of CL for Hg and Ag ions is 0.83 and 8.8 μM, respectively. The applicable pH for sensing Hg by probe CL is in a broad range of 2-12. Application of probe CL for in vitro U87MG cell imaging to detect Hg ions was confirmed.