Single-walled carbon nanotubes (SWCNTs) have a wide range of unique electrical, mechanical and chemical properties and are thus promising for organic electronic applications, such as thin-film transistors, conducting electrodes and biosensors. Researchers have also recently been looking at using the nanostructures in biotechnology thanks to their exceptional electronic properties and the fact that the surfaces of SWCNTs can be functionalized. Indeed, the materials have already begun to find their way into bioelectronic devices, like drug delivery carriers and even scaffolds for tissue engineering.

Although some previous studies showed that SWCNTs were non-toxic to biological cells, scientists are still unsure and would ideally like to make the nanomaterials more biocompatible. Other research has revealed that shorter tubes are more dangerous while short and long nanotubes with modified surfaces are less so.

Hybrid conducting surface
Zhenan Bao's team began by soaking substrates, such as glass slides or silicon oxide wafers, in a solution of poly-L-lysine (PLL). The researchers then deposited spin-coated carbon nanotubes onto the surface of the substrates to create a hybrid material that had a conducting surface. The process can also be tuned to deposit specific amounts of SWCNTs on the slides and wafers.

Bao and colleagues say that the technique is an effective way of depositing a carbon nanotube network onto the substrates. Using optical and scanning electron microscopy, they investigated how biocompatible the SWCNT-PLL hybrid materials were by looking at the shape changes in biological cells placed on the surfaces. Cellular morphology is a good parameter to measure in this respect because it is an accurate way to monitor cell metabolism and health.

Safer SWCNTs
The cells did not show any irregular features or protrusions and retained a healthy, elongated shape, which – according to the researchers – indicates that the SWCNTs have little toxicity. Other preliminary experiments, which involved monitoring mitochondrial activity in the cells, also suggest that the SWCNTs are safe over the timescales used in the study.

"We hope that our work will help in the development of more biocompatible SWCNT surfaces for the field of bioelectronics," team member Debora Lin told nanotechweb.org. "Many researchers are investigating the cytotoxicity of carbon nanotubes and some functionalize the tubes to make them more biocompatible. Such functionalization is sometimes tedious and not always very efficient. In contrast, our technique is simple and quick and may be used to develop conductive surfaces for biomedical applications."

The work was presented in ACS Nano.