STUDY OF GLUCOSE OXIDASE ACTIVITY IMMOBILIZED ON CARBON  NANOFIBRES

Gh. Mihailescu1, Liliana Olenic1, Stela Pruneanu1,2, D. Lupu1, Al. Biris1, Simina Dreve1

1 National Institute for R&D of Isotopic and Molecular Technologies,Cluj-Napoca 5, Donath Str, No.71-103,PO Box 700, Romania
2 University of Teesside, School of Science and Technology, Middlesbrough, UK

	Carbon nanofibres materials show very good electrodic properties and they can be used as supports for enzyme immobilization. Looking for new materials with high sensitivity and efficiency for the immobilization and detection of enzyme is of great importance in different biochemical applications.
In this paper we have used carbon nanofibres to coimmobilize enzyme (glucose oxidase GOX) and mediator, in order to create a glucose biosensor. The enzyme activity of immobilized GOX was determined by an original amperometric method. 
Electrochemical experiments were performed with CHI 900 electrochemical analyzer (CHI, USA), with conventional three-electrode system. The working electrode was made from carbon nanofibres paste.
Carbon nanofibers were synthesized by catalytic chemical vapor deposition (CCVD) method by decomposition of pure ethylene over Fe:Ni:Cu catalyst, into a quarz tube with the inner diameter of 27 mm,  placed in a 30 cm long horinzotal furnace.
An easy procedure was used for the fabrication of glucose biosensor.
Carbon nanofibres are typically hundreds of nanometers in diameter and many microns in lenght. They have some advantages like: small size with larger surface, easy electron transfer when used as electrode in electrochemical reactions and easy protein immobilization, with retention of activity as potential biosensors. Amperometric enzyme-based bioelectrodes are suitable for in vitro monitoring of glucose concentration. The second-generation of glucose biosensors have used redox mediators and have become insensitive to oxygen fluctuations. Also, the amperometric experiments can be performed at lower potentials, where the interfering reactions do not take place. In our case, although carbon nanofibres have also nanometric dimensions, no direct transfer of electrons between GOX  and electrode surface was evidenced. Therefore, potassium ferrocianide was used as mediator, during amperometric measurements. 
The sensor have linearly responded to glucose, in the concentration range from 1.7 mM to 7 mM. The time required to reach 95% of the maximum steady-state current was around 30 s. 
The amount of adsorbed enzyme was calculated from adsorption isotherms on carbon nanofibres.