Flexible HSA-interactive phenolphthalein based probe proficient at selective turn-on sensing for Zn2+ & Al3+

Abstract

A phenolphthalein based fluorescent probe, 3, 3-Bis-[4-hydroxy-3-(pyridine-2-yliminomethyl)-phenyl]-3H-isobenzofu ran-1-one (PHPA), has been synthesized. It exhibits high sensitivity and selectivity towards Zn2+ and Al3+over other relevant water soluble metal ions and also display novel aggregation-induced emission enhancement (AIEE) characteristics. Both complexes followed 2:1 metal to ligand stoichiometry calculated from Job's plot. A significant fluorescence enhancement with a turn-on ratio of ∼94-fold was triggered via chelation-enhanced fluorescence through sensor complex (Zn2+-PHPA) and∼245-fold increase for sensor complex Al3+-PHPA. In addition, the binding sites of both sensor complexes (PHPA-Zn2+ & PHPA-Al3+) have been confirmed through 1H NMR, 13C NMR, FT-IR and ESI-MS spectroscopy. The detection limits is found to be 8.5 × 10−8 M for complex PHPA-Zn2+ and 1.88 × 10−7 M for complex PHPA-Al3+, respectively. The reversible detection of Zn2+ and Al3+ complexes in methanol are also ascertained in the presence of Na2EDTA, enabling the construction of a molecular Logic gate. An advanced-level NOT-AND-OR logic gate has been constructed from a different chemical combinational input and emission output. Human serum albumin (HSA) binding studies were performed by various spectroscopic methods to expound possible bioactivity of PHPA. Interestingly; the AIEE properties of PHPA may advance its impact as studied in methanol-water mixtures with high water contents. To gain the knowledge into the AIEE mechanism of the PHPA, the size and growth process of particles in different volume percentage of water and methanol mixture were studied using time-resolved photoluminescence, dynamic light scattering, and optical microscopic image. The probe PHPA has also been used to detect intracellular Zn2+ ion in A549 cells.