The detection of Al3+ and Cu2+ ions using isonicotinohydrazide-based chemosensors and their application to live-cell imaging

Abstract

A new Schiff base receptor (3) was synthesized by an equimolar reaction between isonicotinic hydrazide and 2,4-dihydroxybenzaldehyde in ethanol. Receptor 3 demonstrated excellent selectivity and sensitivity towards Cu²⁺ ions and Al³⁺ ions by UV-vis absorption spectroscopy and fluorescence spectroscopy, respectively. Receptor 3 showed a detectable color change from colorless to yellow with a red-shift (Δλ ≈ 70 nm) in the absorption spectra in the presence of Cu²⁺. In the emission study of 3, Al³⁺ showed significant fluorescent enhancement (λ_em = 473 nm) over a wide range of tested metal ions. The quantum yield of receptor 3 (Φ = 0.0021) increases ∼230 folds in the presence of Al³⁺ ions to form receptor 3·Al³⁺ complex (Φ = 0.484). Receptor 3 showed high selectivity for Al³⁺ with a K_a of 4.8 × 10⁴ M⁻¹ and LOD of 3.0 nM. In comparison, K_a for Cu²⁺ was 1.3 × 10⁴ M⁻¹ and LOD of 1.9 μM. Receptor 3 is an excellent chemosensor for detecting Al³⁺ ions as indicated by its nanomolar range LOD. The quick response, easy-synthesis, and high sensitivity make receptor 3 an ideal sensor for detecting Al³⁺ ions in a semi-aqueous medium and living cells.