Achieving a Stable High Surface Excess of Glucose Oxidase on Pristine Multiwalled Carbon Nanotubes for Glucose Quantification.

In this study, glucose oxidase (GOx) immobilization onto ten different types of carbon modified GCEs and its direct electron transfer (DET) were investigated. A maximum amount of GOx immobilization (ΓGOx) of 2.9 nM/cm2 was achieved on the pristine multiwalled carbon nanotubes (PMWCNT) with high stability. Furthermore, the coefficient value for electron transfer (0.5) and the rate constant of 3.16 s-1 were measured from scan rate studies on PMWCNT/GOx. The derived electro-analytical parameters were superior in PMWCNT system than those of several CNT based nanocomposite materials published in the literature. The PMWCNT/GOx displayed a standard potential (E0') of -444 mV with perfect redox peaks, and appreciable peak separation (ΔEp) value of 22 mV in neutral electrolyte medium was noted. Glucose quantification was made using the mediator, ferrocene monocarboxylic acid (FMCA), and quantification was done with dissolved oxygen (O2) reduction caused by the glucose oxidase-mediated enzymatic catalysis of glucose. Sensor calibration results revealed a broad range from 0.2 to 5.8 mM with a lower limit of determination found to be 45 μM for glucose. A strong affinity between PMWCNT/GOx and glucose was assessed with Michaelis-Menten constant (2.24 mM). The proposed biosensor had excellent sensitivity and remained unaffected by the presence of other electroactive groups. This work demonstrates that pristine MWCNT can be used directly as an immobilization matrix for biosensing applications without cumbersome electrode preparation steps and the introduction of dopants.