In this thesis, we have tried to highlight the electroanalytical capabilities of CNT electrode platforms for biosensing applications. Behind these promising electrochemical devices, there are still many fundamental issues that affect the electrochemical response and which are not so easy to be controlled. Such issues can be found right from the first steps of CNT growth, purification, separation, etc. Given the interfacial nature of electrochemistry we have made an effort to correlate CNT structure and surface with the electrochemical reactivity by establishing general trends. However, the scope of this thesis was not framed in merely fundamental electrochemical issues, and a more exhaustive study is needed to settle these points. Despite the fact that CNT edges and defects play a very important role in the electrochemical response, we are also aware that metal catalyst impurities (that cannot be completely removed mainly due to their sheathed nature) can also have some contribution. We have tried to minimize such effect, but it would be very interesting to go deeper in the fundamental studies and try to distinguish more precisely the electrochemical contributions of edges, defects, surface oxides, walls and sheathed catalyst particles. Special efforts should be taken to clarify the potential electrocatalytical mechanisms of carbon coated metal impurities to certain redox species. Such identification is very challenging and will require the use of experimental techniques that can visualize electrochemical activity at a local scale and relate this to the underlying structural and electrical properties of CNTs. Fundamental electrochemical studies on CNTs could be facilitated if CNT growth and processing could be better controlled. Advances in such issues could further improve nanotube uniformity, decrease the dispersion in the results of different research groups, improve the device efficiency and also provide further insights in electrochemical fundamental questions.