rhodamine spirolactam

Mito-RhFe is a Fluorescent probe for mitochondrial labile Fe³⁺ monitoring via imaging and flow cytometry. This probe is a rhodamine-based construct with a spirolactam fluorescence signaling group and an N2-hydroxyethyldiethylenetriamine chelator; its delocalized positive charge enables mitochondria-targeting ability in live cells, and it exhibits fine cell membrane permeability. In its native state, it exists in the non-fluorescent spirolactam form, but upon binding to Fe³⁺, it undergoes a ring-opening conversion to the fluorescent rhodamine form, triggering a turn-on fluorescent response; this process is reversible, as the addition of the metal chelator TPEN removes Fe³⁺ and converts the probe back to its non-fluorescent spirolactam form, and re-addition of Fe³⁺ restores fluorescence. The probe shows high selectivity for Fe³⁺ over most other metal cations present in living systems, with a ~90-fold fluorescence enhancement upon binding to 20 equiv of Fe³⁺. Mito-RhFe has excitation/emission wavelengths of Ex/Em = 540/578 nm, with an ~8 nm bathochromic shift in emission upon Fe³⁺ binding, and it can also be excited at 543 nm for confocal imaging with emission detected at 570-620 nm[1].