A novel near-infrared fluorescent and colorimetric probe for selective detection of Ag⁺ and Hg²⁺

It is particularly important to develop effective and specific detection methods for harmful metal ions such as the silver ion (Ag+) and mercury ion (Hg2+). In this article, a new near-infrared (NIR) fluorescent probe (N-FP) based on intramolecular charge transfer (ICT) effect was designed and synthesised, which exhibited the characteristics of large Stokes shift (163 nm) and excellent stability. Addition of Ag+ or Hg2+ to the N-FP solution in ethanol/water (9:1, v/v) caused remarkable enhancement of fluorescence emission at 661 nm, bathochromic shift of ultraviolet-visible absorption wavelength, and colour change from orange to red or purple. While adding other metal ions including Li+, Na+, K+, Ag+, Cu2+, Fe2+, Zn2+, Co2+, Ni2+, Mn2+, Sr2+, Ca2+, Mg2+, Al3+, Cr3+ and Fe3+ did not bring about substantial spectral and colour change. The detection limit of the N-FP for Ag+ and Hg2+ was calculated to be 1.1 and 0.72 mu M, respectively. The N-FP could be used to recognise Ag+ and Hg2+ in a wide pH range of 1-10. The sensing mechanism was proposed and demonstrated by proton nuclear magnetic resonance (H-1-NMR), high-performance liquid chromatography (HPLC) and mass spectrometry (MS) measurements