Improved enzyme immobilization for enhanced bioelectrocatalytic activity of glucose sensor

In this work, we report the development of a highly sensitive and stable glucose sensor based on the synergetic effect of multi-walled carbon nanotubes (MWNTs) and ZnO nanoparticles. Since the isoelectric point (IEP) of glucose oxidase (GOx) is significantly different from that of ZnO nanoparticles, GOx was electrostatically bound to ZnO nanoparticles decorated onto a negatively charged MWNTs layer at the electrode surface via VLS growth. A cationic polydiallyldimethylammonium chloride (PDDA) layer was further coated onto the GOx-contained ZnO nanoparticle layer to prevent the leakage of GOx. This unique multi-layer structure (PDDA/GOx/ZnO/MWNTs) provided a favorable microenvironment to maintain the bioactivity of GOx, which led to rapid amperometric response toward glucose. By loading 0.5-U GOx at the sensor surface, we obtained a wide linear response range of 0.1–16 mM for this sensor. High sensitivity of 50.2 mA cm−2 M−1 was obtained with increased loading of GOx (2.0 U), leading to an even lower detection limit of 250 nM. This nanomaterials-based glucose sensor was highly sensitive and showed favorable stability over a relatively long-term storage (160 days). Importantly, we challenged our sensor with 100 human blood serum samples, and obtained consistent results with the classic spectrometric assay (correlation coefficient, 0.997).