Enzyme immobilization and characterizations of glucose oxidase (GOx) on MOF-199 and SiO2 for glucose biosensing applications by electrostatic adsorption

Abstract

The glucose oxidase (GOx) was immobilized on metal orgnaic framework 199 (MOF-199) and silica spheres (SiO2/GOx) by electrostatic adsorption. The characterizations analyses were conducted to analyze the morphological analysis, the optimization studies and chemical properties of GOx between before and after immobilization of GOx on MOF-199 and SiO2. The activities of GOx were measured using optical and amperometric measurements for both MOF-199/GOx and SiO2/GOx. In addition, The imit of detection (LOD) and stability studies forimmobilized GOx were also studied. Based on the morphological results, both of MOF-199/GOx and SiO2/GOx nanostructured composites observed with the presence of GOx particles attached to both of MOF-199 and SiO2 respectively. Both of MOF-199/GOx and SiO2/GOx reacted optimally at pH and temperature of 7.0 and 50°C (313 K) accordingly. UV-Vis analysis results exhibited the presence of a new broad peak for SiO2/GOx sample at 250 nm to 280 nm and one narrow peak around MOF-199/GOx suggesting the presence of amino group from GOx. The FT-IR analysis showed that both MOF-199/GOx and SiO2 exhibited one new absorbance peak at ca. 1720 cm-1 and 1722 cm-1 attributed to the bending vibration (bend) of C=O aldehyde obtained from GOx particles. The increase of glucose concentration from 1.0 mM to 5.0 mM resulted to the increment of absorbance value (UV-Vis) and current (mA) for both MOF-199/GOx and SiO2/GOx suggesting successful immobilization of GOx on MOF-199 and SiO2. From the limit of detection (LOD) analysis, both MOF-199/GOx and SiO2/GOx exhibited LOD of 0.2 mM and 0.3 mM respectively. The half lives of MOF-199/GOx and SiO2/GOx were 23 and 21 days. Meanwhile, GOx’s half life was 11 days before losing enzymatic activities.The stabilization study also demonstrated higher stability (days) for MOF-199/GOx and SiO2/GOx reacted with glucose as compared to actual GOx. These results suggested successful immobilization method using new method (electrostatic adsorption) which was more facile than current immobilization method which was also providing high LOD for glucose sensing and could sustain the activities of GOx for the application of glucose biosensors. Therefore, these results may provide towards the initial step to non-invasive glucose measurement practices particularly in salivary glucose detection.