The immobilisation of proteins in carbon nanotubes

Carbon nanotubes, fullerene-related structures, have been used for the immobilisation of proteins and enzymes. We have been able to demonstrate, for the first time, direct imaging by high resolution transmission electron microscopy of Zn2Cd5-metallothionein, cytochromes c, c3, and β-lactamase I. This was achieved, without modification, because the biomolecules encapsulated within nanotubes appear to be shielded from the consequences of exposure to the intense electron beam. The results indicate that the internal surface of the nanotubes interacts strongly with the enzymes resulting in their immobilisation. In some cases, the proteins are seen to be distorted giving a concave meniscus inside the tubes. Single protein molecules, their dimers, tetramers and higher oligomers are observed inside the central cavity. Comparison of the catalytic activities of immobilised β-lactamase I on or in nanotubes with the free enzyme in the hydrolysis of penicillin, however, showed a significant amount of the immobilised enzyme remained catalytically active, implying that no drastic conformational change had taken place. The carbon nanotube appears to act as a benign host in its ability to encapsulate protein molecules within an environment which offers some protection.