Carbon nanotubes (CNTs) have been broadly studied due to their exceptional structural, electronic and mechanical properties, and their use have been proposed for many applications. The number of biosensing applications of CNTs has increased in the past few years. Nevertheless, in order to use CNTs as standard materials in the biosensing field and to take full advantage of their unique properties, several problems must be solved. For example, the solubility of CNTs, especially in aqueous solvents, needs to be improved. Furthermore, reliable methodologies for the easy, reproducible and efficient incorporation of CNTs into solid substrates must be developed. Chemical functionalization of CNTs with biomolecules, and specifically with DNA, provides an alternative to the previous challenges. This review will present a brief overview of the methods available for the chemical functionalization of CNTs with DNA by either covalent or non-covalent means. Moreover, the main scope will be on describing the use of DNA-CNT complexes in biosensing applications. Detection of ions, glucose, peroxide and DNA hybridization using the DNA-CNT hybrids will be discussed.