Water-soluble aluminium fluorescent sensor based on aggregation-induced emission enhancement

In the present work, we propose a new salicylaldehyde azine based water-soluble fluorescent sensor (PSSA – 4-propoxysulfonate salicylaldehyde azine) dedicated to aluminium(III) detection in aqueous solutions. The introduction of sulfonate functional groups provides the probe with enhanced water-solubility, which is crucial for the direct analysis of polluted samples. We proved that aluminium(III) complexation with PSSA in water induces an aggregation-induced emission enhancement (AIEE) process leading to the formation of well-defined dendritic structures which have been characterized by different analysis techniques (DLS, SEM, and FLIM). A limit of detection towards aluminium(III) of 153 nM has been determined, which is more than one order of magnitude below the World Health Organization (WHO) guideline (≈3.7 μM). Moreover, satisfactory selectivity for this compound has been demonstrated over a large variety of metal cations. Finally, PSSA has been introduced into a digital microfluidic sensor chip, thus providing a sub-micromolar portable detection device devoted to aluminium(III) polluted water samples.