Naked-eye colorimetric and turn-on fluorescent Schiff base sensor for cyanide and aluminum (III) detection in food samples and cell imaging applications

A new efficient Schiff base sensor SB3 for fluorescent and colorimetric “naked-eye” “turn-on” sensing of cyanide anion (CN–) with excellent sensitivity and selectivity was developed. The 4,4'-(perfluoropropane-2,2-diyl)bisphenol group and two phenyl groups were covalently linked by two C = N bonds to extend the conjugation length. The four hydroxyl groups can improve the water solubility of the SB3 sensor. The SB3 sensor exhibited high specificity towards CN− by interrupting its intramolecular charge transfer, resulting in a color change and remarkable “turn-on” green fluorescence emission. The sensing mechanism is caused by the nucleophilic addition of CN– toward imine groups of the SB3 sensor, leading to breaks of the conjugation, fluorescent spectral changes, and color change. It was confirmed by 1H NMR titration and Mass spectra. The detection limits for CN– and Al3+obtained by fluorescence spectrum are 0.80 µM and 0.25 µM, respectively. The SB3 sensor can act as an efficient chemical sensor for detecting the CN– and Al3+ ions under common environmental and physiological conditions (pH 5–12). Besides, the sensor can also detect CN− in food materials (such as sprouting potatoes and cassava flour) and imaging CN− in living cells with strong “turn-on” fluorescence at 490 nm. SB3 is an excellent CN– sensor that exhibits some advantages, including easy synthesis, distinct fluorescence and color change, high selectivity, low detection limit, and good anti-interference ability to analyze solution and food samples, together with fluorescence cell imaging.