This paper describes the development of glucose biosensors based on carbon nanotube (CNT) nanoelectrode ensembles (NEEs) for the selective detection of glucose. Glucose oxidase was covalently immobilized on CNT NEEs via carbodiimide chemistry by forming amide linkages between their amine residues and carboxylic acid groups on the CNT tips. The catalytic reduction of hydrogen peroxide liberated from the enzymatic reaction of glucose oxidase upon the glucose and oxygen on CNT NEEs leads to the selective detection of glucose. The biosensor effectively performs a selective electrochemical analysis of glucose in the presence of common interferents (e.g., acetaminophen, uric and ascorbic acids), avoiding the generation of an overlapping signal from such interferers. Such an operation eliminates the need for permselective membrane barriers or artificial electron mediators, thus greatly simplifying the sensor design and fabrication.Because of the high demand for blood glucose monitoring, significant research and development efforts have been devoted to producing reliable glucose sensors for in vitro or in vivo applications. 1-2 The measurement principle of oxidase-based amperometric biosensors previously relied upon the immobilization of oxidase enzymes on the surface of various electrodes and the detection of the current associated with the redox product in the biological reaction. To increase the selectivity and sensitivity of amperometric biosensors, artificial mediators and permselective coatings are often used in biosensor fabrication. Artificial mediators are used to shuttle electrons between the enzyme and the electrode to allow operation at low potentials. 3-5 This approach can minimize interference with coexisting electroactive species, but the stability and toxicity of some mediators limit their in vivo applications. Permselective membranes are also used to eliminate interference. 6-7 Effective, but incomplete, rejection has been reported in most cases. A mediator-free and membrane-free biosensor was described by Wang's method provides a means for measuring the cathodic current of enzymatically liberated hydrogen peroxide in metal-dispersed carbon paste biosensors. The idea of a mediator-free and membrane-free biosensor based on the reduction of hydrogen peroxide has provided a new approach for biosensor development.Recently, electrochemical properties of carbon nanotubes (CNTs) have been unveiled, and their application toward electrochemical sensors and biosensors has gained interest. [10][11][12][13][14][15][16][17][18][19][20][21][22]

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The length and the spacing of carbon nanotube (CNT) films are varied independently to investigate their effect on the field-emission characteristics of the vertically aligned CNT films grown by plasma-enhanced hot filament chemical vapor deposition using pulsed-current electrochemically deposited catalyst particles. It is shown that, in general, the macroscopic electric field Emac,1, defined as the electric field when the emission current density reaches 1 mA/cm2, can be reduced by increasing the length and the spacing of CNTs. However, for the very-high-density CNT films, the increase of length increases Emac,1 slightly, whereas for the very short CNT films, the increase of spacing does not effectively reduce Emac,1.