A lysosome-targetable fluorescent probe for imaging trivalent cations Fe3+, Al3+ and Cr3+ in living cells.

An effective morpholine-type naphthalimide chemsensor, N-p-chlorophenyl-4-(2-aminoethyl)morpholine-1,8-naphthalimide (CMN) has been developed as a lysosome-targeted fluorometric sensor for trivalent metal ions (Fe3+, Al3+ and Cr3+). Upon the addition of Fe3+, Al3+ or Cr3+ ions, the probe CMN showed an evident naked-eye color changes which pale yellow solution of CMN turned deepened and it displayed turn-on fluorescence response in methanol. CMN showed a significant selective and sensitive toward Fe3+, Al3+ or Cr3+ ions, while there was no obvious behavior to other monovalent or divalent metal ions from the UV-vis and fluorescence spectrum. Based on the Job's plot analyses the 1:1 coordination mode of CMN with Fe3+, Al3+ or Cr3+ was proposed. The limit of detection (LOD) observed were 0.65, 0.69 and 0.68 μM for Fe3+, Al3+ and Cr3+ ions, respectively. The N-atom of morpholine directly involved in complex formation, CMN emitted fluorescence through inhibition of photoinduced electron transfer (PET). This probe exhibited excellent imaging ability for Fe3+, Al3+and Cr3+ ions in living cells with low cytotoxicity. Significantly, the cellular confocal microscopic research indicated that the lysosome-targeted group of morpholine moiety was introduced which realized the capability of imaging lysosomal trivalent metal ions in living cells for the first time.