Asymmetric Schiff base-based colorimetric and fluorescent sensor for Al ³⁺ detection in real samples and live-cell bioimaging

A novel asymmetric heterocyclic Schiff base chemosensor, (<i>E</i>)-1-(((2-amino-5-methylpyridin-3-yl)imino)methyl)naphthalen-2-ol (AMMN), was synthesized and thoroughly characterized using microanalysis, FTIR, ESI-MS, ¹H NMR, and ¹³C NMR. The interaction of AMMN with various metal ions was investigated <i>via</i> UV-visible and fluorescence spectroscopy. The sensor displayed high selectivity and a sensitive fluorescence response toward Al³⁺ in a DMSO/HEPES buffer solution (1 : 9, v/v) at pH 7.4. The binding constant of AMMN with Al³⁺ was determined using the Benesi-Hildebrand plot, yielding values of 2.90 × 10³ M^-1 and 9.69 × 10³ M^-1 based on UV-visible and fluorescence spectroscopic analyses, respectively. The detection mechanism was identified as a 1 : 1 binding interaction between AMMN and Al³⁺, as confirmed by ESI-MS, Job plot analysis, and ¹H NMR titration. The sensor exhibited excellent linearity, with low detection limits of 1.7 × 10^-6 M and 5.3 × 10^-7 M, as determined by UV-visible and fluorescence titration studies, respectively. Furthermore, theoretical analysis using density functional theory (DFT) was conducted to support the experimental results for both AMMN and its AMMN-Al³⁺ complex.