Contraction-type glucose-sensitive microgel functionalized with a 2-substituted phenylboronic acid ligand

Abstract

A new glucose-sensitive microgel, the poly(N-isopropylacrylamide-co-2-acrylamidophenylboronic acid) (P(NIPAM-2-AAPBA)) microgel, which contracts instead of expanding in the presence of glucose, was synthesized. The configuration of 2-AAPBA allows for the occurrence of an intramolecular B–O coordinated interaction, which stabilizes the tetrahedral form of the phenylboronic acid (PBA) group and makes it the dominant form in the microgel. Upon addition of glucose, with the formation of a 1 : 2 glucose–phenylboronate complex, the microgel size shrinks monotonously with increasing glucose concentrations. Addition of glucose also shifts the volume phase transition temperature of the microgel to lower temperatures. The glucose sensitivity of the microgel can be influenced by temperature, ionic strength and PBA content, but pH variation within the physiological range shows no influence. The P(NIPAM-2-AAPBA) microgel displays good glucose sensitivity at physiological pH and ionic strength. In addition, interference from fructose, galactose, and lactate is negligible. The new contraction-type glucose-sensitive microgel is expected to find applications in self-regulated insulin release and glucose sensing.