Wavelength-ratiometric probes for the selective detection of fluoride based on the 6-aminoquinolinium nucleus and boronic acid moiety.

Herein we report a set of new water-soluble fluorescent probes (N-boronobenzyl-6-aminoquinolinium bromides, BAQBAs) sensitive to aqueous fluoride. These probes shows spectral shifts and intensity changes in the presence of fluoride, in a wavelength ratiometric and colorimetric manner, enabling the detection of fluoride concentrations at visible wavelengths, in the concentration range approximately 1-300 mM. Although the sensing mechanism is different for fluoride as compared to the other halides, we have tested the utility of these probes towards the other halides, and the results reveal that the BAQBAs are in fact potential candidates towards the sensing of the all the halides, but in different concentration ranges. As the probes are based on the boronic acid moiety, which is a well-known fluoride and sugar chelator group, we have investigated the response of sugars (such as glucose and fructose, which are present in biological fluids and foodstuffs) as interferences in fluoride detection using these probes. Interestingly, the BAQBAs show a suppressed sugar response potentially allowing for the predominant fluoride sensitivity. In addition to physiological sugars, we also have assessed the response of aqueous halides as potential interferents, or indeed analytes to be sensed, and show that the new boronic acid containing probes respond well to aqueous fluoride in the presence of a high background of other species, such as in a biological cocktail of 50 mM Glucose, 50 mM aqueous Chloride and 5 mM Fructose.