It showed a low potential detection of glucose with high sensitivity, low detection limit, good reproducibility, long term stability, fast response, and high specificity. This biosensor was applied in the determination of glucose in real blood and urine samples with satisfactory results. Yang et al. prepared MWCNTs composite using Pt NP doped sol/gel solution as a binder and incorporated ZSTK474 GOx for glucose biosensor. The sensitivity enhanced 4 times when Pt nanoparticles were loaded. A glucose biosensor, developed by Rivas and co workers was based on the electrocatalytic activity of copper and iridium microparticles incorporated within the CNTs paste electrode containing GOx. This biosensor detected glucose at very low potentials with high sensitivity and selectivity. Yao and Shiu examined the electrochemical and electrocatalytic properties of different types of CNTs material and used them for fabricating glucose biosensors.
They found Brivanib that the electrodes modified with SWCNTs usually had better electron transfer and electrocatalytic properties than the corresponding MWCNTs modified electrodes. Recently, Jia et al. reported the fabrication of needle type glucose biosensor by packing a mixture of MWCNTs, graphite powder, and freeze dried GOx powder into a glass capillary of 0.5 mm inner diameter. It showed an improved sensitivity and stability when the experimental condition was optimized. Zhu and co workers proposed a bienzymatic mediatorless glucose biosensor based on co immobilization of GOx and horseradish peroxidase in an electropolymerized PPy film on a SWCNTs modified electrode. They took advantage of direct electron transfer characteristics of HRP with CNTs electrode and realized a lower operational potential for selective determination with a minimized interference.
The detection of hydrogen peroxide is very important because many enzymatic biosensors rely on the detection of H2O2 generated by an enzymatic reaction. Since the amount of generated H2O2 from an enzymatic reaction is very low, the fabrication of a highly sensitive H2O2 biosensor is needed. CNTs can be used in the fabrication of highly sensitive H2O2 biosensors. There have been many reports on CNTs based H2O2 biosensors. Chen and Lu reported the encapsulation of hemoglobin in the composite film of carboxylic acid functionalized MWCNTs and polyelectrolyte surfactant polymer to develop a H2O2 biosensor. Faradic response of the Hb was observed and it exhibited excellent electrocatalytic activity to reduce H2O2. Chen et al.
proposed an amperometric thirdgeneration H2O2 biosensor based on the immobilization of Hb on the nanohybrid film of MWCNTs and gold colloidal nanoparticles. A wide range of linear response from 0.21 M to 3.0 mM with a detection limit of 80 nM was obtained. Tripathi et al. entrapped HRP in an ormosil composite doped with ferrocene monocarboxylic acid bovine serum albumin conjugate and MWCNTs for a H2O2 biosensor. MWCNTs improved the conductivity of the composite film and HRP provided a fast amperometric response to H2O2. A wide linear range between 20 M and 4.0 mM with a detection limit of 5.0 M was achieved. Luo et al. developed a H2O2 biosensor with an improved performance based on the immobilization of HRP onto electropolymerized PANI films doped with CNTs. It was found that the existence of CNTs in the biosensor system could effectively increase the amount and stability of the immobilized HRP as well as the performance of the biosensor.