Cross-Linking-Enabled Core–shell Nanostructure Based on Conductive Polymer Hydrogels/Carbon Nanotubes for Salivary Glucose Biosensor

Due to the 3-fold increase in the number of people with diabetes, there is an urgent need for noninvasive, user-friendly glucose monitoring technologies. However, current noninvasive methods are limited by low accuracy and susceptibility to interference. In this work, we develop a noninvasive salivary glucose biosensor using a core-shell nanostructure of conductive polymer hydrogels/carbon nanotubes (CNTs) on carbon paper. With the electrostatic interaction between the functional groups on CNTs and pyrrole monomer, the cross-linked polypyrrole (PPy) hydrogel can form in situ on the CNTs surface. The 3D interconnected networks of core-shell PPy/CNTs feature high surface area, porosity, and flexibility, facilitating efficient electron and ion transport, thereby leading to a superior glucose sensing sensitivity of 119.74 μA mM^-1 cm^-2 in the region of 50-700 μM. Additionally, this biosensor exhibited an ultralow Michaelis-Menten constant of 0.33 mM and high specificity toward glucose, even in the presence of various interferences, demonstrating a high affinity for the enzyme toward PPy/CNTs. This facile, controlled synthesis of core-shell PPy/CNTs offers a promising avenue for constructing enzymatic biosensors for accurate and regular monitoring of blood glucose via saliva tests.