Design and synthesis of a novel fluorescent-colorimetric chemosensor for selective detection of Zn(II) and Cu(II) ions with applications in live cell imaging and molecular logic gate

Abstract

We present here the synthesis of a simple and low-cost Schiff base chemosensor (HL) for selective detection of both Zn(II) and Cu(II) ions in HEPES buffer pH = 7.4. The chemosensor HL exhibits quick response through fluorescence and colorimetric changes for both Zn(II) and Cu (II) ions as examined by fluorescence and absorption titrations. Both the metal ions form 1:1L– Zn(II) (complex 1) and 1:1L– Cu(II) (complex 2) complexes, confirmed by Job's Plot. We are successful to elucidate the structure of complex 1 through X-ray diffraction analysis. Reversibility of the chemosensor in its binding with Zn(II) and Cu (II) ions separately is also examined in presence of Na2EDTA solution. The enhancement of fluorescence intensity of the chemosensor is based on the chelation-enhanced fluorescence (CHEF) effect of L–Zn(II) with the inhibition of both photoinduced electron transfer (PET) effect and C˭N isomerization in excited state and the quenching effect is due to the paramagnetic nature of Cu(II) to the L–Zn(II) system. Furthermore, the geometry and spectral property of HL and both the metal complexes have been studied by DFT, TD-DFT calculations. The limit of detection (LOD) values of both the ions are 2.29 × 10-9 M and 3.67 × 10-9 M, respectively. These values clearly suggests that HL is a promising chemosensor in monitoring Zn(II) and Cu(II) ions in the biological and environmental study with excellent accuracy and precision. The propensity of the chemosensor to detect intracellular Cu(II) and Zn(II) ions in Candida albicans cell lines by fluorescence imaging is also demonstrated in this study. Furthermore, molecular logic gates have been developed based on the idea where chemically encoded information as the input is converted into fluorescent signals as the output. In this work, the designed fluorescent chemosensor exhibits dual logic gates (XOR, AND) involving Zn(II), Cu(II) and Na2EDTA.