A review of DNA functionalized/grafted carbon nanotubes and their characterization

The functionalized carbon nanotubes (CNTs) are believed to be very promising in the fields such as preparation of functional and composite materials and biological technologies. Immobilization of nanotubes with specific recognition biosystems indeed provides ideal miniaturized biosensor. A prerequisite for the search in this area is the development of chemical methods to immobilize biomolecules onto carbon nanotubes in a reliable manner. The DNA-based biomolecular recognition principle has been applied to CNTs to constant nanotube electronic devices as well as CNT-DNA electrochemical sensors. The sp(2) hybridization and the outstanding electronic properties of the nanotubes coupled with their specific recognition properties of the immobilized system indeed make CNTs, an ideal biosensor. DNA immobilization has been paid Great attention and considered as a fundamental methodology for the construction of DNA biosensors. Successful integration of CNTs in electronic devices and sensors requires controlled deposition at well-defined locations and appropriate electrical contacts to metal leads. Different methods for achieving this goal are directional growth of the tubes, alignment by mechanical forces, alignment by electric and magnetic fields, patterned- and self-assembly. Also the concept of using DNA to direct the assembly of nanotubes into nanoscale devices is attracting attention because of its potential to assemble a multicomponent system in one step by using different base sequence for each component. Thus, DNA functionalization of CNTs holds interesting prospects in various fields including solubilization in aqueous media, nucleic acid sensing, gene-therapy and controlled deposition on conducting or semiconducting substrates. This review highlights the functionalization/graffing of DNA onto single walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) with or without self-assembly which can be employed in fabricating biosensors for selective recognition of DNA. The review also addresses various characterization techniques that have been employed by various researchers to give the readers an insight into the planning of experiments and subsequent interpretation. (c) 2006 Elsevier B.V. All rights reserved.