Solvent-assisted selective detection of sub-micromolar levels of Cu2+ ions in aqueous samples and live-cells

Two new rhodamine–indole conjugates 1 and 2 were synthesized for studying their ability to probe specific metal ions at physiological pH in the presence of other competing metal ions. In non-aqueous medium, probe 1 predominantly binds Cu(2+) ions with considerable interference from Fe(3+) and Ni(2+) ions. However, in aqueous medium, 1 exhibits a higher degree of selectivity for Cu(2+) ions with little interference from Fe(3+) ions, and no interference from Ni(2+) ions. The probe 2, obtained by tethering a triazole moiety with probe 1, selectively binds Cu(2+) ions in aqueous medium even in the presence of other metal ions including Fe(3+) ions. The sensitivity of probe 2 to pH variation and interaction with various amino acids were also investigated. The excellent stability of 2 in physiological pH conditions, non-toxicity, non-interference of amino acids in the detection process, and the remarkable selectivity for Cu(2+) ions in aqueous medium allowed the use of 2 in the imaging of live fibroblast cells treated with Cu(2+).