A new pyrido[1,2-a]benzimidazole-rhodamine FRET system as an efficient ratiometric fluorescent probe for Cu in living cells.

A novel fluorophore pyrido[1,2-a]benzimidazole was synthesized and used as a donor to construct FRET system. The probe shows a large Stokes shifts (190 nm), high selectivity, fast response (within 2 min), and high sensitivity toward Cu (detection limit 42 nM). A significant colour change from colourless to pink could be observed, enabling naked-eye detection of Cu. Furthermore, it could be used for imaging Cu in living cells which demonstrated its value of practical applications in biological systems.