Boronic acid functionalized boron dipyrromethene fluorescent probes: preparation, characterization, and saccharides...

Fluorescent probes based on boron dipyrromethene functionalized with a phenylboronic acid group (BODIPY-PBAs) were synthesized in high yield for the first time by Suzuki coupling of bis(pinacolato)diboron and 8-(4-bromophenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY). Wavelength tuning of the fluorophores was achieved by attaching an auxochromic substituent to the 5-position of the BODIPY core structure through Knoevenagel condensation. The emission intensity of fluorophores increases when binding to the analytes with diol groups and forming boronic esters at fixed pH. These compounds can detect monosaccharides in the concentration range of 0.1-100 mM. Whereas glycogen was found to quench the fluorescence of BODIPY-PBAs in an aqueous solution due to the self-quenching of the fluorophores after attaching in the extensively branched and compact glucose polymer, further addition of d-fructose to the solution can release the fluorophores from the polymer and the fluorescence regains. The BODIPY-PBA fluorophore has been applied in polymeric optodes containing anion exchangers to perform repetitive measurement. Such sensors respond to different monosaccharides in the range of 0.1-100 mM and demonstrate an improved selectivity toward d-fructose over other saccharides, compared to the results obtained from homogeneous assay.