Nano-yarn carbon nanotube fiber based enzymatic glucose biosensor

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A novel brush-like electrode based on carbon nanotube (CNT) nano-yarn fiber has beendesigned for electrochemical biosensor applications and its efficacy as an enzymaticglucose biosensor demonstrated. The CNT nano-yarn fiber was spun directlyfrom a chemical-vapor-deposition (CVD) gas flow reaction using a mixture ofethanol and acetone as the carbon source and an iron nano-catalyst. The fiber, 28 µm in diameter, was made of bundles of double walled CNTs (DWNTs) concentricallycompacted into multiple layers forming a nano-porous network structure. Cyclicvoltammetry study revealed a superior electrocatalytic activity for CNT fiber compared tothe traditional Pt–Ir coil electrode. The electrode end tip of the CNT fiber wasfreeze-fractured to obtain a unique brush-like nano-structure resembling a scale-downelectrical ‘flex’, where glucose oxidase (GOx) enzyme was immobilized using glutaraldehydecrosslinking in the presence of bovine serum albumin (BSA). An outer epoxy-polyurethane(EPU) layer was used as semi-permeable membrane. The sensor function was tested againsta standard reference electrode. The sensitivities, linear detection range and linearityfor detecting glucose for the miniature CNT fiber electrode were better thanthat reported for a Pt–Ir coil electrode. Thermal annealing of the CNT fiber at250 °C for 30 min prior to fabrication of the sensor resulted in a 7.5 fold increase in glucosesensitivity. The as-spun CNT fiber based glucose biosensor was shown to bestable for up to 70 days. In addition, gold coating of the electrode connectingend of the CNT fiber resulted in extending the glucose detection limit to 25 µM. To conclude, superior efficiency of CNT fiber for glucose biosensing was demonstratedcompared to a traditional Pt–Ir sensor.