Regulated enzyme distribution for enhanced wearable sweat glucose monitoring

As an electrochemical cell and sweat reservoir, hydrogel plays a significant role in wearable sweat glucose sensing. However, the uncontrolled and randomly distributed network in the hydrogel, the aggregation of enzyme and leaching from the sensing surface often cause a concentration gradient of sweat glucose, which could lead to the distorted signal. In this study, a magnetic porous hydrogel is designed with uniformly embedded GOx. Such hydrogel is integrated with MWCNTs, CaCO₃, and glutaraldehyde-coated magnetic nanoparticles (G-Fe₃O₄ NPs). Acid etching of CaCO₃ forms the porous structure of hydrogel with high water absorbency. G-Fe₃O₄ NPs provide controllable cross-linkers between GOx and hydrogel. Guided by an external magnet, GOx distribution in the hydrogel is oriented in a constant and uniform order, thus can avoid non-quasi-equilibrium and distorted glucose sensing that caused by GOx aggregation and leakage. Importantly, MG-MFPH-GOx hydrogel show enhanced sensitivity when tested for both on-body and finger sweat glucose sensing and the detection limit reaches 0.25 μmol/L. Moreover, sweat glucose sensors based on MG-MFPH-GOx hydrogel show stable performance for 30 days. Therefore, the regulated enzymatic hydrogel prepared with the facility of an external magnetic field provides a new strategy for constructing wearable sensors.