Development of a fused imidazo[1,2- a ]pyridine based fluorescent probe for Fe 3+ and Hg 2+ in aqueous media and HeLa cells.

A new fluorescent sensor 5 based on a fused imidazopyridine scaffold has been designed and synthesized via cascade cyclization. The reaction features the formation of three different C-N bonds in sequence. Imidazopyridine based fluorescent probe 5 exhibits highly sensitive and selective fluorescent sensing for Fe 3+ (' turn-on ') and Hg 2+ (' turn-off '). The excellent selectivity of imidazopyridine for Fe 3+ /Hg 2+ was not hampered in the presence of any of the competing cations. The limit of detection (LOD) of 5 toward Fe 3+ and Hg 2+ has been estimated to be 4.0 ppb and 1.0 ppb, respectively, with a good linear relationship ( R 2 = 0.99). Notably, 5 selectively detects Fe 3+ /Hg 2+ through fluorescence enhancement signalling both in vitro and in HeLa cells.