Rhodamine probes for Fe: theoretical calculation for specific recognition and instant fluorescent bioimaging.

To overcome the existing difficulty in distinguishing Fe(III) from Fe(II), rhodamine-containing Fe probes, giving off different fluorescence responses to ferric and ferrous ions, were synthesized. Color change in Fe recognition, accompanying spirolactam opening-closing, could be used for 'naked-eye' detection. Theoretical calculations revealed the possible Fe-probe combination mechanism. Apart from the probes' specific response toward Fe, the Fe-probe demonstrated highly quantitative relationships in fluorescence titration, instant labeling and dynamic tracking of intracellular Fe in bioimaging. Cytotoxity and bioimaging in living L929 suggested the probes' future applications as real-time detection methods for Fe in clinical diagnosis. Instant and time-lapse imagings, based on fluorescence-time stability of Fe-probe, enables the dynamic labeling and tracking of Fe in living systems.