Chromogenic ‘Naked Eye’ and ‘Turn-On’ Fluorescent Sensor for Detection of Al3+ Ion Based on Naphthalene Carbohydrazide: Mimicking Logic Gate Applications

Abstract

The naphthalene carbohydrazide colorimetric and fluorimetric chemosensor (E)-N′-(4-(diethylamino)-2-hydroxybenzylidene)-1-naphthohydrazide (MKG-12) was designed, synthesized and evaluated for cation sensing via excited state intermolecular proton transfer (ESIPT) mechanism. The chemosensor MKG-12 shows a high sensitivity and selectivity to Al³⁺ ion detection in 10% aq.-DMSO solution (HEPES buffer, pH 7.4) with a 1:1 binding stoichiometry. The emission intensity of chemosensor MKG-12 was selectively enhanced by Al³⁺ ion, and an observable change in colour from colourless to fluorescent green was observed. Chemosensor MKG-12 shows limit of detection 8.79 × 10⁻⁸ μM and K_abs = 1.32  $\times$ 10⁴ M⁻¹ and K_em = 3.08  $\times$ 10⁴ M⁻¹ binding constant with Al³⁺ ion. Further, the interaction between the chemosensor MKG-12 and the Al³⁺ ion was supported by mass spectroscopy and DFT. Additionally, the chemosensor MKG-12 has been utilized as a small colorimetric kit for Al³⁺ ion on paper test strips and is also accomplished for detection of Al³⁺ ion in real water samples from different sources. Chemosensor MKG-12 was constructed as INHIBIT logic gate based on reversibility behaviour with EDTA.