A water soluble AIE-gen for organic-solvent-free detection and wash-free imaging of Al3+ ions and subsequent sensing of F- ions and DNA tracking

A water-soluble aggregation-induced emission (AIE)-active probe (TPE-diBuS) showed selective turn-on fluorescence response and wash-free non-invasive cellular imaging towards Al3+ ions, based on ionic interactions of Al3+ ions with diagonally located sulfonate groups of the tetraphenylethylene derivative (TPE-diBuS) under organic-solvent-free conditions. The high selectivity of the probe towards Al3+ resulted from the strong affinity of sulfonate groups with Al3+, which was confirmed by discerning Al3+ over a range of metal ions in a complex mixture. Density functional theory (DFT) studies also confirmed the highest stability for the TPE-diBuS-Al ensemble over other probe–metal complexes in a model study. The limit of detection (LOD) of the probe was determined as 5.0 × 10−8 M for Al3+. Moreover, taking advantage of its high water solubility and good biocompatibility, wash-free imaging of Al3+ ions was successfully conducted in live human kidney (HK) cells and bright blue fluorescence from intercellular regions of Al3+-contaminated cells was observed. The stronger affinity of fluoride ions towards Al3+ was utilized for subsequent detection of F− ions via a turn-off fluorescence response as the TPE-diBuS-Al ensemble disintegrates into water-soluble non-emissive probe molecules, and the detection limit of F− ions was found to be 6.0 × 10−7 M. Furthermore, in a demonstration study, it was shown that the TPE-diBuS-Al ensemble could subsequently facilitate tracking of DNA in solution by interaction with calf thymus DNA (ctDNA). Simple synthesis, water solubility, high selectivity and low LOD are some of the key merits of the current probe over existing probes for the detection and quantitation of Al3+ ions in water, as well as in biological systems.