Carbon Nanotubes in Electrochemical Sensors

Nanoscale materials, defined as having at least one dimension less than 100 nm, have received steadily growing interest due to their unique properties and application potential. Typical examples include zero-dimensional nanoparticles, one-dimensional nanowires, and two-dimensional graphenes. Because of the quantum confinement of electrons in one or more dimensions, novel electrical, optical, and magnetic properties can be achieved in nanostructures. Nowadays carbon nanotubes (CNTs) are among the most promising nanomaterials. Depending on the chirality along the graphene sheet, either semiconducting or metallic electronic states are created. There are numerous studies on carbon nanotubes applications. For example, CNTs has been widely used in structure of different sensors. Various advantages of CNTs as sensor materials have been shown for analysis of diversified chemicals of food quality, clinical and environmental interest. High thermal conductivity, remarkable mechanical properties, chemically stability and high surface to volume ratio of CNTs is very appealing for sensing applications. Electrochemical sensors (ECS) have been proven as an inexpensive and simple analytical method with remarkable detection sensitivity, reproducibility, and ease of miniaturization rather than other instrumental analysis methods. Since CNTs possess interesting electrochemical properties, contributed by the activity of edge-plane-like graphite sites at the CNT ends, it can be used for construction of electrochemical sensors (CNT-ECS). CNTECS exhibit low detection limit, high sensitivity and fast response due to the signal enhancement provided by high surface area, low overvoltage, and rapid electrode kinetics. Because of importance of electrochemical sensors and CNTs, this chapter is focused on advantages and applications of CNTs in electrochemical sensors. At first, CNTs are introduced and different electrochemical sensors are defined based on the type of output signal. Afterwards, different methods are investigated and classified for preparation of electrochemical sensors based on CNTs. These strategies have been applied for the immobilization of CNTs on electrochemical transducers. The one common way is coating the electrode surface with a CNT suspension and in another approach the CNT is mixed with mineral oil to fabricate paste electrode. Some other methods, such as selfassembly and polymerization, are used less frequently. Finally, the advantages and applications of CNTs are investigated in different ECSs (potentiometry and voltammetry). In potentiometric sensors, CNTs similar to other nanostructure materials have been proposed as alternative solid-state transducers that can