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.