Multiple ion (Al3+, Cr3+, Fe3+, and Cu2+) sensing using a cell-compatible rhodamine-phenolphthalein-derived Schiff-base probe

In this study, a novel rhodamine-phenolphthalein derivative (RBPF) was designed, synthesized, and characterized. RBPF exhibited the selective and sensitive colorimetric detection of Cu2+ and Fe3+ and fluorometric detection of Al3+ and Cr3+, thus functioning as a multiple-channel probe in MeOH-H2O (v/v = 9/1, 5 µM HEPES, pH 7.2) in the presence of other cations. A strong enhancement of the absorbance at around 555 nm was observed for the four mentioned cations. In contrast, in the presence of Al3+ and Cr3+, emissions were intensified within the red region of the spectra (583 and 586 nm, respectively). The RBPF sensor was found to bind to the metal ions at a 1:2 stoichiometric ratio. The proposed mechanism for the observed sensing behavior is the opening of the spirolactam ring of the rhodamine core in the presence of the four mentioned metal ions. The detection limits for Cu2+, Fe3+, Al3+, and Cr3+ were calculated to be 1.21 µM, 1.75 µM, 2.27 µM, and 1.29 µM, respectively. To test the practical use of the probe, TLC-based paper strips were fabricated. In addition, cell-imaging analysis of Al3+ and Cr3+ ions in the A549 cancer cell line produced promising concentration and time-dependent detection results.