Hydrogel-Based
Glucose Sensors: Effects of Phenylboronic
Acid Chemical Structure on Response
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Abstract
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 p<i>K</i><sub>a</sub> 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