Monofunctional and Bifunctional Boronic Acid Functionalized Squarylium Dyes as NonCovalent Protein Labels: A Fluorimetric Study - Abstract
A fluorimetry comparison study has been established for the labeling of human serum albumin (HSA) using two boronic acid functionalized squarylium dyes, one is monofunctional boronic acid dye (SQ-BA4) while the other one is bifunctional boronic
acid dye (SQ-DBA2). The spectral properties of these two squarylium dyes have been studied under a variety of solutions to explore the optimal conditions for non-covalent protein labeling. Both dyes exhibited very low fluorescence intensity in aqueous solutions presumably due to H-aggregate formation in absence of the protein but showed a significant enhancement in the fluorescence intensity with the addition of HSA in the optimal acidic citrate buffer. Stability constant studies were conducted and SQBA4 dye was shown to have much stronger binding affinity with HSA than SQ-DBA2. Also, the stoichiometries of non-covalent complexes were found to be (1:1) for SQ-BA4 and different (1:2) for SQ-DBA2 with HSA. These studies are claimed to be the optimal for CE-LIF work which will be progressed in our continuing project.