Dispersion of multi-wall carbon nanotubes in glucose oxidase: Characterization and analytical applications for glucose biosensing

In this work we report for the first time the use of the enzyme glucose oxidase (GOx) to efficiently disperse multiwall carbon nanotubes (CNT) and to confer biorecognition properties to the dispersed nanotubes. The optimum dispersion was obtained by sonicating for 15 min 1.0 mg/mL CNT in 1.0 mg/mL GOx solution prepared in 50:50 ethanol/water. The dispersion was evaluated by Scanning Electron Microscopy (SEM), Infrared (FT-IR) and Ultraviolet–visible (UV–vis) Spectroscopy. The electrochemical characterization of glassy carbon electrodes (GCE) modified with the dispersion (by dropping) was performed by Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV), and Amperometry. The amount of electroactive GOx deposited on GCE (GCE/CNT–GOx) was 1.02 × 10−10 mol cm−2 and the rate constant for the electron transfer between FAD center and the electrode was (2.9 ± 0.1) s−1 according to Laviron and (9.2 ± 1.3) s−1 considering the model proposed by Albery. The enzyme demonstrated to keep its biocatalytic activity even after dissolution in 50/50 v/v, ethanol–water solution and sonication for 15 min using either ferrocene methanol or oxygen as redox mediators. The sensitivity to glucose at 0.700 V obtained for seventeen electrodes prepared with 6 different dispersions was (3.2 ± 0.2) × 102 μA M−1, (r = 0.997), with an R.S.D. of 6.0%. The sensitivity remained highly constant after 30 days at room temperature (25 °C) and 4 °C, with average values of (3.21 ± 0.07) × 102 μA M−1, r = 0.9992 and (3.59 ± 0.08) × 102 μA M−1, r = 0.9990, respectively. The GCE/CNT–GOx can be used as platform to build supramolecular architectures for biosensing through the self-assembling of polyelectrolytes, opening the doors to new and exciting possibilities for the development of biosensors.