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

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 Al(3+) are studied by fluorescence spectra. Coordination with Al(3+) 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 Al(3+) over other metal ions in MeOH-HEPES buffer (3/7, V/V, pH=6.6, 25°C, λem=435nm). A turn-on ratio over 140-fold is triggered with the addition of 1.0 equiv. Al(3+) to L3. The binding constant Ka of L3-Al(3+) is found to be 1.01×10(6.5)M(-1) in a 1:1 complex mode. The detection limit for Al(3+) is 0.05μM. Theoretical calculations have also been included in support of the configuration of the L3-Al(3+) complex. Importantly, the probe L3 has been successfully used for fluorescence imaging in colon cancer SW480 cells.