Indole-based colori/fluorimetric probe for selective detection of Cu²⁺ and application in living cell imaging

A highly sensitive and selective indole-based probe IHT exhibited obvious color change from colorless to violet easily detected by naked eye as well as 'turn on' fluorescence response to Cu²⁺ ion at physiological pH condition. The detection limit was determined to be as low as 8.93 × 10^-8 M, which was much lower than drinking water permission concentrations by the United States Environmental Protection Agency. The 1:2 binding mechanism was well confirmed by fluorescence titration, Job's plot, HRMS, IR analysis and DFT calculations. Furthermore, the probe IHT was successfully used for fluorescence imaging of Cu²⁺ ion in living cells.