Hybrid hydrogel films with graphene oxide for continuous saliva-level monitoring†
A glucose-sensitive hydrogel coated on a quartz crystal microbalance (QCM) sensor makes an important integrated system for achieving a continuous glucose monitoring system for diabetes, attributed to its high repeatability, rapid response time, and wide detection range. However, the poor viscoelasticity of the functional hydrogel film usually leads to the transport of water molecules out of the hydrogel matrix owing to the increased crosslinking density by molecular recognition, thus resulting in poor stability and limit of detection (LOD) of the hydrogel-coated QCM sensor, which limits its practical application in the detection of saliva glucose in low concentrations. Herein, this problem is solved by copolymerizing a rigid phenylboronic acid-containing graphene oxide (GO)-based monomer with a glucose-sensitive monomer (i.e., 3-acrylamidophenylboronic acid (3-APBA)) onto a double bond-modified QCM chip to fabricate a hybrid hydrogel-coated QCM sensor with improved viscoelasticity. Moreover, the 3-aminophenylboronic acid-grafted GO provides more reaction sites toward glucose, which is found to be beneficial for further improving the LOD of the hydrogel-coated QCM sensor. The experimental results show that the LOD of the hybrid hydrogel film (1 mg L−1) is about 10-fold and 900-fold lower than that of the hydrogel film (10 mg L−1) and polymer brushes (900 mg L−1) respectively. This study provides a new approach for continuous sensing of saliva glucose using a highly sensitive hybrid hydrogel-coated QCM sensor with improved properties, which contributes to the diagnosis, monitoring, and formulation of an appropriate treatment plan for patients suffering with diabetes.