We have previously developed a simple pyrolytic method for large-scale production of aligned multi-wall carbon nanotube arrays perpendicular to the substrate. These aligned carbon nanotube arrays can be transferred onto various substrates of particular interest (e.g. polymer films for organic optoelectronic devices) in either a patterned or non-patterned fashion. The well-aligned structure provides additional advantages for not only an efficient device construction but also for surface functionalization. The surface functionalization of aligned carbon nanotubes is particularly attractive, as it allows surface characteristics of the aligned carbon nanotubes to be tuned to meet specific requirements for particular applications while their alignment structure can be largely retained. These aligned carbon nanotubes with tunable surface characteristics are of great significance to various practical applications ranging from sensors to electronics. Single-strand DNA chains could be covalently immobilized onto plasma-activated aligned carbon nanotubes for sensing complementary DNA and/or target DNA chains of specific sequences with a high sensitivity and selectivity. Furthermore, glucose oxidase (GOX) could also be immobilized onto the aligned carbon nanoutbe arrays by electropolymerization of pyrrole in the presence of GOX. The resultant GOX-containing polypyrrole-carbon nanotube coaxial nanowires were shown to be promising new sensing active materials for making advanced glucose sensors with a high sensitivity.