Analyses on intracellular Fe3+ with a rhodamine probe: “turn-on” response, specific recognition and bioimaging†
To overcome the existing difficulty in distinguishing ferric from ferrous ions, a rhodamine-containing probe was designed to combine with Fe3+ based on an opening–closing transformation of the spirolactam ring in the rhodamine moiety. Through a specific and stoichiometric fluorescence response towards Fe3+ by 1 : 1 binding accompanied by an obvious color change in the recognition process of Fe3+, a “naked-eye” detection method of Fe3+ in an aqueous environment is possible. Theoretical calculations gave a possible recognition mechanism of the probe–Fe3+ system. Further cytotoxicity and bioimaging in living L929 cells suggested the probe's future applications as a real-time analytical method for intracellular Fe3+ in clinical diagnosis. Besides, bioimaging applications enable the dynamic labelling and tracking of Fe3+ in biological systems.