Selective detection of Al(3+) and citric acid with a fluorescent amphiphile

An amphiphilic fluorescent dye with a disulfonated BODIPY head group and a heptadecyl side chain is described. In buffered aqueous solution, the amphiphile can form aggregates with a critical micelle concentration of ∼20 μM. The aggregation of the dye is associated with a strong quenching of its fluorescence. Al(3+) promotes aggregation, whereas other metal ions have a much smaller effect, in particular when histidine is added as masking agent. The Al(3+)-induced aggregation can be used to sense Al(3+) in the low micromolar concentration range with high selectivity. Furthermore, we demonstrate that a dye-Al(3+) mixture can be used as a sensing ensemble for the detection of citric acid. The assay allows quantifying the citric acid content of commercial beverages such as energy drinks.