An ultra-sensitive fluorescence multi-channel and colorimetric probe based on salicylaldehyde hydrazone for Al3+ recognition with a 3 : 1 binding ratio†

An ultra-sensitive multi-channel fluorescence probe for the detection of Al³⁺ in aqueous solution, 4-(diethylamino)salicylaldehyde nicotinoyl hydrazone (SBN), was synthesized. Interestingly, when 365 nm and 425 nm are the excitation wavelengths, SBN exhibits high selectivity and ultra-sensitive fluorescence enhancement recognition for Al³⁺ with emission wavelengths of 459 nm and 512 nm, respectively. At the same time, when 459 nm and 512 nm are utilized as the emission wavelengths, SBN also exhibits high selectivity and ultra-sensitive fluorescence off–on recognition for Al³⁺. Moreover, the presence of Al³⁺ can change the color of SNB solution from colorless to yellow, which enables SBN to be used as a highly selective and sensitive colorimetric probe for Al³⁺. The results of HRMS confirm the formation of a complex between SBN and Al³⁺ with a 3 : 1 binding ratio. The density functional theory (DFT) calculation indicates that the hydroxyls and the nitrogen atoms on carbon nitrogen double bonds in the three SBN molecules can form three chelating rings with one Al³⁺ ion in the SBN–Al³⁺ complex. The binding mode induces the fluorescence groups of three SBN molecules to exhibit different π–π stacking at different spatial positions, which enables the probe to exhibit fluorescence response signals of different channels. Furthermore, SBN possesses a variety of superior properties, including a short response time, good photostability, a wide pH response range, good anti-interference and low cytotoxicity. Therefore, SBN was successfully applied to dual channel fluorescence detection of Al³⁺ in the living GS cells of Epinephelus coioides.