(Nanowerk Spotlight) Among the many potential biology-related applications proposed for carbon nanotubes (CNTs) are high-sensitivity biosensors and bio-fuel cells. In order to create the synergy between the biomolecules and CNTs required to realize these applications, biomolecules, such as proteins and DNAs, must be connected to the CNTs. A useful, simple and universal method to attach biomolecules onto carbon nanotubes with covalent bonding was developed by researchers at Rensselaer Polytechnic Institute.
Before their paper, titled "Protein immobilization on carbon nanotubes via a two-step process of diimide-activated amidation", published in issue 1, 2004 of Journal of Materials Chemistry not a lot of work was done on attaching proteins to CNTs. In the research that was done, proteins were either noncovalently bonded on CNTs or were attached through a harsh process, so the final connection is either very loose or the survival chance of attached protein is very small.
The work done by the Rensselaer scientists provides a universal approach of forming bio-nano materials which have numerous applications. Kuiyang Jiang, first author of the paper, explained to Nanowerk the three core findings of their research:
"We developed an attachment process operated at room temperature and in buffer solution, which could greatly increases the survival possibility of attached proteins;
We developed a covalent process, which provides a robust connection between protein and carbon nanotubes; and
we developed a two-step attachment process, in which the interconnection of COOH and NH2 groups in/between different proteins are greatly inhibited. No protein aggregation means high protein efficiency in any applications."
Schematic view of diimide-activated attachement process (Source: Rensselaer Polytechnic Institute)
The covalently bonding of molecules to the CNTs was done in a two-step process, carried out at room temperature in buffer solutions and was accomplished in a short time, which maximizes the survival rate of biomolecules.
Jiang explains the two-step process: "carboxylic acid groups are first converted to active esters via diimide-activation, and then the active esters are reacted with the amine groups on proteins without the presence of diimide. This two-step process avoids intermolecular conjugation and guarantees the uniform attachment on carbon nanotubes."
Follow-up work to this initial research was done by attaching PAMAM dendrimer onto CNTs through a similar approach as the one described above. This approach provides a universal and efficient method to attach nano-entities with NH2 groups to carbon nanotubes at ambient conditions.
TEM Image of PAMAM-MWNT Heterostructure (Source: Rensselaer Polytechnic Institute)
This work, titled "Covalent Bonding of Nano-entities with NH2 Groups onto Multi-walled Carbon Nanotubes" was presented at the 2004 MRS Fall meeting in Boston.
By Michael Berger, Copyright 2006 Nanowerk LLC. All rights reserved.
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