Naphthol-based fluorescent sensors for aluminium ion and application to bioimaging

• Three naphthol Schiff base-type fluorescent sensors have been compared.
• Coordination with Al3 + inhibited the CN isomerization of Schiff base
• L3 had higher sensitivity selectivity for Al3 + in HEPES buffer than L1 and L2
• L3 was applied as an excellent fluorescence probe for Al3 + in living cell.

Three naphthol Schiff base-type fluorescent sensors, 1,3-Bis(2-hydroxy-1-naphthylideneamino)propane (L1), 1,3-Bis(1-naphthylideneamino)-2-hydroxypropane (L2) and 1,3-Bis(2-hydroxy-1-naphthylideneamino)-2-hydroxypropane (L3), have been synthesized. Their recognition abilities for Al3 + are studied by fluorescence spectra. Coordination with Al3 + inhibited the CN isomerization of Schiff base which intensely increase the fluorescence of L1–L3. Possessing a suitable space coordination structure, L3 is a best selective probe for Al3 + over other metal ions in MeOH–HEPES buffer (3/7, V/V, pH = 6.6, 25 °C, λem = 435 nm). A turn-on ratio over 140-fold is triggered with the addition of 1.0 equiv. Al3 + to L3. The binding constant Ka of L3-Al3 + is found to be 1.01 × 106.5 M− 1 in a 1:1 complex mode. The detection limit for Al3 + is 0.05 μM. Theoretical calculations have also been included in support of the configuration of the L3-Al3 + complex. Importantly, the probe L3 has been successfully used for fluorescence imaging in colon cancer SW480 cells.

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