Function-oriented synthesis of fluorescent chemosensor for selective detection of Al3+ in neat aqueous solution: Paperstrip detection & DNA bioimaging

A bisalicylhydrazone based fluorescent probe for detecting Al3+ with high sensitivity and selectivity and imaging in living cells

A bisalicylhydrazone based fluorescence probe, bisalicyladehyde benzoylhydrazone (BS-BH), has been designed to detect Al3+. It exhibited high sensitivity and selectivity towards Al3+ in methanol-water media in physiological condition. Large stokes shifts (∼122 nm) and over ∼1000-fold enhanced fluorescence intensity were observed, which was ascribed to the formation of the two relatively independent rigid extended π conjugated systems bridged by biphenyl group when binding with Al3+. A 1:2 binding ratio between BS-BH and Al3+ was shown by Job's plot. Based on the fluorescence titration data, the detection limit was down to 3.50 nM and the association constant was evaluated to be 1.12 × 109 M-2. The plausible fluorescence sensing mechanism of suppressed ESIPT, inhibited PET, activated CHEF and restricted C = N isomerization was confirmed by a variety of spectral experiments and DFT / TD-DFT calculations. The reversibility of recognition of Al3+ for probe BS-BH was validated by adding Na2-EDTA. In addition, the MTT assay showed the good biocompatibility of BS-BH and BS-BH could be used for imaging Al3+ in living cells.

Modulation of aluminum sensing properties of a sulphone group containing chemosensor and its biological applications

A chemosensor with two binding pockets facilitates binding of one metal ion in either of the pockets providing a better chance for the interaction and hence recognition of the cation. We report here a chemosensor, namely 2,2'-(1E)-(5,5'-sulfonylbis(2-hydroxy-5,1-phenylene))bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dinaphthalen-1-ol (H₄L-naph), for selective sensing of Al³⁺ in DMF- HEPES buffer (1:4, v/v, pH 7.4). It shows almost 100-fold fluorescence enhancement at 532 nm (λ_ex = 482 nm) in the presence of Al³⁺. Its quantum yield and excited state lifetime enhances significantly with the cations. H₄L-naph forms a 1:2 complex with Al³⁺ with an association constant value of 2.18 × 10⁴ M^-2. Fluorescence enhancement may be attributed to CHEFF mechanism and restriction of >CN isomerization. Effect of the presence of naphthyl rings instead phenyl ring of a previously reported probe has resulted shifting of excitation/emission peak towards longer wavelength. The probe has been applied to image Al³⁺ in L6 cells with no significant cytotoxicity.