Function-oriented synthesis of fluorescent chemosensor for selective detection of Al3+ in neat aqueous solution: Paperstrip detection & DNA bioimaging

Abstract

Fluorescence based sensors have gained popularity in quick response devices for detection of different analytes selectively. Most of them being organic conjugated scaffolds, often lack solubility in water that limits their application. Herein we report a completely water-soluble sulfonated derivative of salicylaldehyde, designed for selective detection of Aluminium ions in neat aqueous solution. The photophysical properties of S1 & a π-conjugated sulfanilinic acid analogue SA1 was studied and they were screened for their selectivity, sensitivity, binding modes & applications in spot paper tests as well as bioimaging. Both the sensor molecules exhibited high degree of selectivity towards Al3+ in preference to other metal ions. They displayed large Kb values of nearly 104 with a stoichiometry of 3:1 as evidenced by B-H & quantitation plots which was subsequently validated by ESI-MS. Exceptional fluorescent responses were observed with increasing Al3+ concentration exhibiting detection limits of 0.827 μM & 1.67 μM for S1 &SA1 respectively. These values are far lower than the permissible limits of Al(III) in potable water according to WHO guidelines. The binding modes and stoichiometry were confirmed by DFT studies on optimised geometries of the sensors and their complexes using B3LYP hybrid functional which correlates well with experimental findings. Excellent water solubility and a resultant biomembrane permeability facilitated its application in bioimaging of DNA. We have demonstrated fluorescence microscopic imaging of onion root tip cells for different mitotic phases. Furthermore, the sensor has also been applied in qualitative visual detection of Al(III) ions in aqueous solution by using paper strip test.