Micelle-Type Sensor for Saccharide Recognition by Using Boronic Acid Fluorescence Amphiphilic Probe and Surfactants

Controlling molecular assembly by analytes is attractive for analytical techniques. Herein, we designed and synthesized amphiphilic boronic acid fluorescent probes (B-Nap-C8) possessing naphthaleneboronic acid as a saccharide recognition site and alkyl chain as a hydrophobic moiety. We evaluated their saccharide recognition function in relation to the fluorescent or absorption intensity changes of the assembled B-Nap-C8. Also, we evaluated the saccharide recognition function of B-Nap-C8 by the effect of co-surfactants. B-Nap-C8 forms micelles and recognizes fructose at pH 10. In the presence of surfactants, B-Nap-C8 with the cetyltrimethylammonium bromide (CTAB) micelle can recognize fructose at neutral pH. On the other hand, B-Nap-C8 with the sodium dodecyl sulfate (SDS) micelle recognizes fructose at pH > 10. This is caused by the decrease of the apparent pK _a of B-Nap-C8 on the surface of the cationic CTAB micelle. The micelle formation of B-Nap-C8 with CTAB was confirmed by TEM observation, and the critical micelle concentration of B-Nap-C8 with CTAB was determined to be 1.79 mM from the CTAB titration measurements. From the saccharide titration experiments, B-Nap-C8 with CTAB micelles selectively recognizes fructose at neutral pH. The selectivity for saccharides was not observed in the saccharide titration of B-Nap-C8 with SDS. Thus, the co-surfactant systems with B-Nap-C8 were found to control the selectivity for saccharide recognition in water.