Hydrogel-Based Glucose Sensors: Effects of Phenylboronic Acid Chemical Structure on Response

Phenylboronic acids (PBAs) are being considered for glucose sensing and controlled insulin release, because of their affinity for diol-containing molecules. The interaction of immobilized PBAs in a hydrogel matrix with glucose can lead to volumetric changes that have been used to monitor glucose concentration and release insulin. Although the interaction of PBAs with diol-containing molecules has been intensively studied, the response of PBA-modified hydrogels as a function of the specific PBA chemistry is not well understood. To understand the interaction of immobilized PBAs with glucose in hydrogel systems under physiological conditions, the glucose-dependent volumetric changes of a series of hydrogel sensors functionalized with different classes of PBAs were investigated. The volume change induced by PBA-glucose interactions is converted to the diffracted wavelength shift by a crystalline colloidal array embedded in the hydrogel matrix. The PBAs studied contain varying structural parameters such as the position of the boronic acid on the phenyl ring, different substituents on PBAs and different linkers to the hydrogel backbone. The volumetric change of the PBA modified hydrogels is found to be highly dependent on the chemical structure of the immobilized PBAs. The PBAs that appear to provide linear volumetric responses to glucose are found to also have slow response kinetics and significant hysteresis, while PBAs that show nonlinear responses have fast response kinetics and small hysteresis. Electron-withdrawing substituents, which reduce the pKa of PBAs, either increase or decrease the magnitude of response, depending on the exact chemical structure. The response rate is increased by PBAs with electron-withdrawing substituents. Addition of a methylene bridge between the PBA and hydrogel backbone leads to a significant decrease in the response magnitude. PBAs with specific desirable features can be selected from the pool of available PBAs and other PBA derivatives with desired properties can be designed according to the findings reported here.