Rational design and bioimaging application of water-soluble Fe3+ fluorescent probes

Abstract

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 Fe³⁺ over other common metal ions and good sensitivity with a linear range from 20 to 100 μM (R² = 0.95725) and a detection limit of 5.2 μM. The cell imaging indicates that T1 is capable of detecting Fe³⁺ 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 Fe³⁺ 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.