A new pyrido[1,2-a]benzimidazole-rhodamine FRET system as an efficient ratiometric fluorescent probe for Cu2+ in living cells

•A Cu2+ ratiometric fluorescent probe based on new pyrido[1,2-a]benzimidazole fluorescent dye has been synthesized.•The probe exhibits highly sensitivity and selectivity toward Cu2+ (detection limit: 42 nM).•The ratiometric fluorescent probe displays a remarkable emission shift (up to 190 nm).•The probe show low cytotoxicity and can be applied in 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 Cu2+ (detection limit 42 nM). A significant colour change from colourless to pink could be observed, enabling naked-eye detection of Cu2+. Furthermore, it could be used for imaging Cu2+ in living cells which demonstrated its value of practical applications in biological systems.

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