Laser-triggered carbon nanomaterials have selectively eliminated yeast, bacteria and even cancer cells, but the challenge up until now has been to tackle much smaller organisms, such as viruses.

CNH's are useful when it comes to medical applications. The high surface area material is produced without using metallic catalysts and is considered to be non-toxic in the short term. Supplied by NEC, the raw CNHs are prepared at room temperature by irradiating a graphite rod with a high-power CO2 laser in an argon atmosphere.

Modification and testing
To make its antiviral CNH complex, the group adds a T7 tag antibody and a phospholipid moiety to a functionalized version of the material. The T7 tag provides a recognition site for the target virus (T7 bacteriophage) and the lipid helps to disperse the modified CNH in water.

A solution of the CNH complex was added to phosphate buffered saline (PBS) and exposed to an infrared laser (Nd:Yag, 5W). A sample of PBS without CNHs was also irradiated as a control. When CNHs were present, the local solution temperature (measured away from the beam) was around 50 °C higher following 5 minutes of continuous irradiation.

Real-time result
Pleased with the outcome, the group added its CNH complex to a suspension of T7 bacteriophage and monitored the result under a fluorescent microscope. By using a dye to reveal the dead microorganisms, the researchers were able to observe the antiviral activity in real-time (see video).

A CNH concentration of just 30 µg/ml was sufficient to exhibit photoexothermic elimination of the target virus. Untagged versions of the complex were also able to deactivate the virus, but only at much higher concentrations.

The hope is that CNH's can be used to treat major infections, such as human immunodeficiency virus (HIV), severe acute respiratory syndrome (SARS) and avian influenza, but much work remains to be done.

"Currently, we do not have a blueprint for treating a human patient," Eijiro Miyako of AIST's Health Technology Research Center told "Biocompatibility of functionalized CNHs is one of the most important factors and the toxicity bioassay of nanomaterials must be further explored."

The researchers presented their work in Nanotechnology.