Turn-on detection of Al3+ ion by quinoline based tripodal probe: Mechanistic investigation and live cells imaging applications

An easily synthesizable Schiff base probe TQSB having quinoline fluorophore has been demonstrated as a fluorescent and colorimetric turn-on sensor for Al3+ ion in semi-aqueous medium (CH3CN/water, 4:1, v/v). Absorption, emission as well as colorimetric studies clearly exhibited that TQSB displayed a high selectivity toward Al3+ stemming from its excellent binding constant (Kb = 3.8 x 106 M−1) and detection limit (7.0 nM) values. TQSB alone was almost non-fluorescent in nature; however, addition of Al3+ induced an intense fluorescence at 414 nm most likely due to a combined CHEF (chelation-enhanced fluorescence) and restricted PET effects. The sensing mechanism has been established via Job’s plot, NMR, ESI-mass, and density functional theory (DFT) analyses. Furthermore, for its applied potential, the sensing ability of probe TQSB has been exploited in real sources such as soil sample and Al3+-containing gastric Digene tablet as well as onto low-cost filter paper strips. Fluorescence microscopic imaging experiments further displayed that TQSB could be utilized as an effective probe to recognize intracellular Al3+ in live cells with no cytotoxicity.