A multi-responsive squaraine-based turn on fluorescent chemosensor for highly sensitive detection of Al3+, Zn2+ and Cd2+ in aqueous media and its biological application

A novel multi-response squaraine-based fluorescent chemosensor SQ was designed and synthesized, which exhibited a high sensitivity for detecting Al3+, Zn2+ and Cd2+ in ethanol -water buffer solution and selectively responded to them in an order of Al3+ to Zn2+ to Cd2+ due to the differences of stability and binding mode when forming their respective metal-ligand complexes. Furthermore, in solution, SQ can restore A beta(1-42)-Al complex involving the potential relationships with the conformational aspects of Alzheimer's disease (AD) to A beta(1-42) efficiently by binding Al3+ in A beta(1-42)-Al complex, suggesting SQ may act as a protective agent by preventing or reverting A beta aggregation in the extracellular spaces, which can provide a better biological understanding for developing successful therapeutics for the treatment of AD. The binding properties of sensor SQ with metal ions were investigated by UV-vis, fluorescence, H-1 NMR and mass spectra. The results of various experiments and DFT/TDDFT calculations showed the chemosensor SQfollowed a turn on mechanism with the inhibition of C=N isomerization (cis -trans) and the activation of chelation enhanced fluorescence (CHEF). (C) 2017 Elsevier B.V. All rights reserved.