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

Abstract

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.