A simple naphthalene-based fluorescent probe for high selective detection of formaldehyde in toffees and HeLa cells via aza-Cope reaction

•A simple naphthalene-based “turn-on” fluorescent probe (AENO) for formaldehyde (FA).•The probe AENO used to detect FA with high sensitivity and excellent selectivity.•The probe AENO can quantitatively detect FA with a detection limit of 0.57 μM.•The proposed mechanism as 2-aza-Cope rearrangement for AENO after reaction with FA.•The probe AENO can detect the level of FA in toffee samples and HeLa cells.

A simple naphthalene-based fluorescent probe (AENO) for formaldehyde (FA) was successfully synthesized, which exhibited a significant fluorescence turn-on response towards FA in aqueous solution. The probe could quantitatively determine the concentration of FA (0–1.0 mM) with excellent selectivity, high sensitivity and low limit of detection (0.57 µM). The sensing mechanism was proposed as 2-aza-Cope rearrangement for AENO after reaction with FA, which was confirmed by 1H NMR, HR-MS, FT-IR, UV–vis and fluorescence spectra. The probe has been employed to determine the FA contents in several commercially available toffee samples with satisfactory performance. Thus, AENO might be used as a promising tool for quantitative detection of FA in food. Furthermore, fluorescence imaging of HeLa cells indicated that the probe was cell membrane permeable and could be used for visualizing/imaging the FA trace/transportation in cancer cells.

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