Natural Enzyme Degrades Nanotubes

The potential environmental toxicity of single-walled carbon nanotubes could be abated by biodegrading the materials via enzymatic catalysis using horseradish peroxidase (HRP) and hydrogen peroxide, according to a study by Alexander Star and coworkers at the University of Pittsburgh (Nano Lett., DOI: 10.1021/nl802315h). Environmental toxicity is a potential problem that could come with the likely widespread use of carbon nanotubes and other nanomaterials. The researchers incubated carbon nanotubes with HRP and H₂O₂ at 4 °C under static conditions for 16 weeks. They suggest that a reactive intermediate produced by interaction of the enzyme and H₂O₂ oxidizes the nanotubes, leading to their breakdown. The researchers monitored the degradation with several analytical methods, including transmission electron microscopy, dynamic light scattering, gel electrophoresis, and optical spectroscopy. The nanotubes became progressively shorter over time, and globular material appeared within eight weeks. After 12 weeks, the nanotubes degraded enough that most of the material was globular, with very little apparent nanotube structure. "These results mark a promising possibility for carbon nanotubes to be degraded by HRP in environmentally relevant settings," the authors write. The toxicity of the resulting breakdown products remains unknown.