Vertically aligned CNTs can be coupled with enzymes to provide a favorable surface orientation and act as an electrical connector between their redox center and the electrode surface. Figure 3 showed the assembly of the CNT electrically contacted WYE-354 GOx electrode. Plugging enzymes into the CNTs by this way. Different types of glucose biosensors have been developed in recent years. Tsai and co workers developed a nanobiocomposite film by incorporating functionalized MWCNTs and GOx into polypyrrole film for a highly sensitive glucose biosensor. The amperometric response of the optimized biosensor displayed a sensitivity of 95 nA/mM, a linear range up to 4 mM, and a response time of about 8 sec. Huang et al. loaded MWCNTs and GOx on a graphite disk using a LBL assembly technique to construct a glucose biosensor.
The current response to glucose was highly dependent on the number of layers and the maximum response was obtained at 6 layers of MWCNTs/GOx with the detection limit of 90 M. Liu and Lin also applied LBL assembly technique to construct a sandwich like structure, PDDA/GOx/PDDA/CNTs, for a reproducible and stable glucose biosensor GDC-0449 while Zhao and Ju added poly with PDDA to construct multilayer membranes. They modified gold electrode with 3 mercapto 1 propanesulfonic acid and then bilayers of the PDDA and PSS were formed on the modified Au surface. PDDA wrapped MWCNTs and GOx was then assembled through LBL technique. Wang et al. functionalized gold electrodes with the negatively charged 11 mercaptoundecanoic acid and then apply the LBL assembly of a positively charged redox polymer, poly, and the negatively charged GOx/SWCNTs for glucose sensor.
Liu et al. developed an amperometric glucose biosensor based on electrostatic assembly of GNPs/MWCNTs/GOx. Positively charged poly was used to connect them in a LBL pattern. The electrode showed an excellent electrocatalytic activity for glucose sensing at a relatively low potential. Xu et al. described an amperometric glucose biosensor based on an alternating electrostatic selfassembling GOx and dendrimer encapsulated Pt nanoparticles on MWCNTs. The excellent electrocatalytic activity of CNTs and Pt DENs toward H2O2 and special three dimensional structure of the enzyme electrode resulted in a low detection limit with a wide linear response range, a high sensitivity with a good precision, and an enhanced operational stability.
Shirsat et al. fabricated an amperometric glucose biosensor by applying a LBL assembly of SWCNTs and PPy multilayer film on a platinum coated with polyvinylidene fluoride membrane. GOx was immobilized on the film by cross linking through glutaraldehyde and a linear response range from 1 mM to 50 mM of glucose concentration with the sensitivity of 7.06 uA/mM was achieved. A glucose sensor based on the LBL assembly of functionalized MWCNTs and poly multilayer film was also suggested. This electrode showed a significant improvement of redox activity showing a synergic effect of excellent electron transfer capability of CNTs and PNR. Another type of glucose biosensor was constructed by immobilizing GOx onto the electrode surface using GA.