Rational design and bioimaging application of water-soluble Fe 3+ fluorescent probes

Two water-soluble fluorescent probes, T1 , based on 5-carboxyl rhodamine and T2 , based on 6-carboxyl rhodamine, have been designed and synthesized. The introduction of a carboxyl group to the rhodamine scaffold improves the water-solubility of the probes. In water, T1 shows excellent selectivity for Fe 3+ over other common metal ions and good sensitivity with a linear range from 20 to 100 μM ( R 2 = 0.95725) and a detection limit of 5.2 μM. The cell imaging indicates that T1 is capable of detecting Fe 3+ in live cells. Notably, for good water-solubility of T1 only one washing step is needed to clear the extracellular T1 after incubation during cell imaging experiments. Meanwhile, we notice that T2 , an isomer of T1 , has an unacceptable performance in Fe 3+ detection, whether in vitro or in vivo . This kind of phenomenon is quite common and indicates that the 5-position and 6-position substituents at the bottom ring have different effects on the performance of xanthene-based probes.