During the last decade, there have been many advances in the development of fluorescent chemosensors for sugar using arylboronic acid as a receptor. As the covalent interactions of arylboronic acid with sugar did not considerably change the fluorescence of the fluorophore, fluorescent chemosensors based on arylboronic acid have required certain processes for the change of fluorescence depending on the boronic acid-carbohydrate interactions such as an internal charge-transfer (ICT) process and a photoinduced electron transfer (PET) process.
In recent years, we have focused on the development of chemosensors based on peptides because of hydrophilicity, biological compatibility, and binding affinity for biomolecules. We synthesized a new ratiometric sensing system based on peptides for sugars capable of controlling the pyrene monomer and excimer emissions. Amphiphilic dipeptide containing phenylboronic acid aggregated in the absence of sugars in aqueous solutions resulting in a considerable excimer emission. The covalent bonding of the phenylboronic acid of the peptide with sugar converted the aggregates into a monomer form of the complex, resulting in a decrease of excimer emission and a concomitant increase of monomer emission intensity. Fluorescent chemosensors for heparin among polysaccharides were synthesized based on
heparin-binding peptides. The fluorescent peptidyl chemosensor showed a highly sensitive ratiometric response to nanomolar concentrations of heparin in aqueous solutions and in biological samples containing human serum. The detection limit was 34 pM for heparin in an aqueous buffer solution containing 5% human serum. The results indicated that peptide-base chemosensor provided a potential tool for monitoring sugar in aqueous buffered solutions.