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 (approximate to 3.7 mu M). 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.