CNTs are seamless, hollow tubes formed from graphene sheets. As with graphene the bonding is sp 2 , however σ-π rehybridization occurs due to the curvature of the tube. This effect is stronger as the diameter of the tube decreases which creates a rich π-electron conjugation outside the tube inducing greater electrochemical activity. Hence, the length of the CNT governs the rate of electron transport. As with nanoparticles they offer a high surface-to-volume ratio and promote electron transfer. Due to the π-π stacking and van der Waals interactions between CNTs in aqueous solution, aggregation occurs causing non-homogenous and unstable coatings for electrodes when absorbed directly onto the surface. For this reason, dispersal of CNTs through a suitable polymer has become a popular method of functionalising the electrode surface. Molecular linkers as proposed for NPs can also be used. Unlike typical NPs, CNTs have structural heterogeneity due to the discrepancy between the properties of the wall and the edges. The orientation of the CNTs on the electrode surface will affect the rate of electron transfer. Vertically aligned structures result in better electrochemical performance, as the edge of the tubes have faster electron transfer kinetics than the wall. Gooding et al. vertically aligned CNTs on gold electrodes using a mixed SAM layer of cysteamine and MPA, along with dicyclohexylcarbodiimide. The electron transfer of these CNTs in the presence of Fe(CN) 6 3-/4 was 40 times faster than CNTs randomly dispersed onto the electrode. Another way to beneficially influence the electrochemical behaviour CNTs is to produce oxygenated carbon species at the tips of the tubes. CNTs have also been used commonly in combination with other materials such as biocompatible polymer chitosan . For example, a recent study shows the development of an immobilisation matrix layer by layer based on chitosan and carboxylated MWCNTs in order to immobilise the anti-Staphylococcus aureus antibodies onto an interdigitated electrode . Developed impedimetric biosensor was capable of detecting S. aureus from milk samples with limit of detection between 0.26 -1.8 CFU/mL.