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

This paper reports an electrolyte-insulator-semiconductor (EIS) device featuring a novel high-κ GdTi_xO_y 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 GdTi_xO_y membranes was investigated. The GdTi_xO_y EIS device annealed at 900°C exhibited the greatest pH sensing performance, including the highest sensitivity (62.12mV/pH), the smallest hysteresis voltage (5mV), and the lowest drift rate (0.4mV/h), presumably because of its well-crystallized GdTi_xO_y 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 GdTi_xO_y 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 120h 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 11.03mV/mM relative to that (8.17mV/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.