A simple, highly selective and ultra-sensitive "off-on-off" fluorescent chemosensor for successive detection of aluminum ion and phosphate in water samples

A simple, highly selective and ultra-sensitive "off-on-off" fluorescent chemosensor L for successive detection of Al3+ and PO43+ was synthesized and characterized. Sensor L showed a remarkable and highly selective fluorescence enhancement towards Al3+ against other interfering cations, owing to the suppression of intramolecular charge transfer (ICT) mechanism and CH=N isomerization. A good linear relationship (R-2 = 0.9974) was obtained between the fluorescence emission intensity of L and the concentration of Al3+ (0.025-2.0 mu M) with the detection limit of 3.8 nM, which is much lower than the most literature reported. And the binding stoichiometry between L and Al3+ is 1:1 according to Job's Plot and ESI-MS. The resultant complex can be further utilized as a secondary probe for determination of PO43- with the detection limit as low as 0.56 mu M. Meanwhile, the sensor L was successfully applied to detect Al3+ in real water, illustrating that sensor L was a promising alternative route for Al3+ detection. Additionally, the sensing mechanism of L to Al-3(+) was further demonstrated in detail by IR and H-1 NMR titration experiment. The successive recognition feature of sensor L has the potential to quantitative analysis of Al3+ and PO43- in environment samples.