Modulation of the binding sites for an adaptable DNA interactive probe: efficient chromo-fluorogenic recognition of Al3+ and live cell bioimaging†

Herein, a chromone-based simple reversible fluorescent “turn-on” probe, HMCP [6-(hydroxymethyl)-N′-((6-methyl-4-oxo-4H-chromen-3-yl)methylene)picolinohydrazide], was successfully utilized to detect Al³⁺ over a group of other coexisting metal cations in MeOH/H₂O (9 : 1, v/v) (HEPES buffer, pH = 7.2). The “turn on” emission response along with the effective enhancement of the fluorescence intensity upon addition of Al³⁺ can be attributed to the inhibition of photo-induced electron transfer (PET) and CN isomerization, as well as the initiation of chelation-enhanced-fluorescence (CHEF). The HMCP sensor binds Al³⁺ in a 1 : 1 stoichiometry with an excellent binding constant and good detection limit on the orders of 10³ M⁻¹ and 10⁻⁷ M, respectively. The mode of binding interaction between HMCP with Al³⁺ was evidenced by ¹H NMR titration, HRMS, and Job's plot analyses. Theoretical calculations and molecular logic gate applications were also used to demonstrate the binding mode. A DNA binding study was also executed to elucidate the possible bioactivity of the probe and found that HMCP interacts with DNA more effectively than the other analogues studied. Furthermore, the applicability of the probe in a live cell imaging study indicated that HMCP is highly efficient for the detection of exogenous Al³⁺ in living cells. In addition, real water sample analysis and a dip-stick experiment demonstrate that the probe can be used in a wide range of practical and convenient applications.