Optimisation of carbon nanotubes growth conditions by CVD and its application in amperometric glucose biosensor

Abstract

This thesis presents the fabrication of glucose biosensor by modifying the surface of the glassy carbon electrode (GCE) using optimized carbon nanotubes (CNTs). Chemical vapor deposition (CVD) method was utilized to grow vertically aligned carbon nanotubes (VACNTs) with various aspect ratios. Field emission scanning electron microscopy (FESEM) images coupled with Raman spectroscopy results highlighted the high aspect ratio as well as uniformity of the high crystalline carbon nanotubes. Transmission electron microscopy (TEM) images of the grown CNTs confirm the successful synthesis of multiwall carbon nanotube (MWCNTs) due to larger outer diameter of the CNTs. Furthermore, to increase the graphitic ratio of synthesized CNTs, sequential experimental strategies based on response surface methodology (RSM) was employed to investigate the crystallinity model of CNTs. In the next step, glucose oxidase (GOx) was immobilized on the optimized multiwall carbon nanotubes/gelatin (MWCNTs/Gl) composite using the entrapment technique to achieve enzyme-catalyzed oxidation of glucose at anodic potentials, which was drop-casted onto the GCE. Cyclic voltammetry (CV) results coupled with the chronoamperometric response obtained from modified GCE indicates that, GOx/MWCNTs/Gl/GC electrode can be utilized as a glucose biosensor with high direct electron transfer rate (8.42 s-1) between GOx and MWCNTs/Gl in a wide linearity range (8.9 mM) to glucose. The detection limit of the fabricated biosensor recorded was 0.59 mM by keeping its initial stability of 75.4% after 25 days. The performance of the fabricated biosensor as an electronic tongue was also investigated by designing a frequency based circuit attached to the electrochemical cell. The resistivity alteration of GOx/MWCNTs/Gl/GCE was recorded after each drop of glucose in the electrochemical cell. The oscilloscope results clearly showed that, by adding glucose to the circuit design, the output oscillation frequency changed and the square wave frequency reached a new stable value. These results indicated that, the modified GCE with the GOx/MWCNTs/Gl showed potential application in the determination of glucose in human serum samples as well as voltammetric based electronic tongue.