High-κ GdTixOy sensing membrane-based electrolyte–insulator–semiconductor with magnetic nanoparticles as enzyme carriers for protein contamination-free glucose biosensing

•The EIS device featuring a novel high-κ GdTixOy sensing membrane exhibits high-performance pH sensing.•To overcome the protein adsorption and preservation of enzymatic activity, we used Fe3O4-based MNPs as enzyme carriers.•The application of enzyme-coupled MNPs as biological recognition elements holds great promise for biosensors.

This paper reports an electrolyte–insulator–semiconductor (EIS) device featuring a novel high-κ GdTixOy sensing membrane for high-performance pH sensing and glucose biosensing. The effect of the annealing temperature (700, 800, or 900 °C) on the sensing properties of the GdTixOy membranes was investigated. The GdTixOy EIS device annealed at 900 °C exhibited the greatest pH sensing performance, including the highest sensitivity (62.12 mV/pH), the smallest hysteresis voltage (5 mV), and the lowest drift rate (0.4 mV/h), presumably because of its well-crystallized GdTixOy structure. To overcome the problems typically encountered during the practical application of biosensors (e.g., protein adsorption; preservation of enzymatic activity), we employed Fe3O4-based magnetic nanoparticles (MNPs) as enzyme carriers. The adsorption of serum protein on the unmodified sensing membrane led to poor EIS-based pH sensing (r2=0.71); the performance was greatly improved, however, after attaching the MNPs to the sensing membrane, thereby blocking protein adsorption significantly (by 98%) and allowing excellent pH sensing (r2=0.99). Moreover, we prepared a hybrid configuration of the proposed GdTixOy membrane-EIS, with magnetically attached glucose oxidase-immobilized MNPs, for glucose biosensing. The use of MNPs as enzyme carriers effectively preserved the enzymatic activity of glucose oxidase, with 45.3% of the original enzymatic activity retained after 120 h of storage at 4 °C (compared with complete loss of the free enzyme's activity under the same storage conditions). In addition, the proposed biosensor exhibited superior detection sensitivity of 11.03 mV/mM relative to that (8.17 mV/mM) obtained using the conventional enzyme immobilization method. Finally, we established the accuracy of the proposed method for blood glucose measurement; gratifyingly, blood glucose detection was comparable with the high-sensitivity glucose quantification obtained using a commercial glucose assay kit.