A novel reversible fluorescent probe for sequential detection of Al³⁺ and HPO₄^2- based on caffeic acid and its applicability in cell imaging

In this work, we focused on synthesizing a new fluorescent probe HBA based on caffeic acid for detecting Al³⁺/HPO₄^2- by the mode of "off-on-off". HBA alone exhibited a weak fluorescence emission in aqueous solution. When Al³⁺ was added into the HBA solution, a significant green fluorescence was found at 498 nm. However, the introduction of HPO₄^2- to the solution of [HBA-Al³⁺] complex induced the disappearance of green fluorescence. The detection limit of HBA was calculated as low as 41.7 nM for Al³⁺ and 62.1 nM for HPO₄^2-, respectively. Probe HBA exhibited good cell-membrane penetrability and had the potential to trace Al³⁺/HPO₄^2- in biological systems.