All living cells, including cancer cells, can be destroyed by heating them up. While some cancer cells may be resistant to chemotherapy, all cells can be denatured by heat – providing the temperature is high enough. Radiofrequency ablation and high-intensity focused ultrasound is routinely employed to thermally ablate tumours but a team of researchers, led by Steve Evans of the School of Physics and Astronomy at Leeds has now found that gold nanotubes irradiated with near-infrared (NIR) light can also be used to photothermally destroy cancer cells.

Evans and colleagues say that they have succeeded in controlling the lengths of the nanotubes and were thus able to produce nanostructures with just the right dimensions to optimally absorb light in the NIR part of the electromagnetic spectrum. The light absorbed by the tubes heats them up, and by using a single-wavelength pulsed laser beam, the Leeds researchers were able to rapidly increase the temperature in the vicinity of the tubes so that it was high enough to destroy cancer cells.

Image or destroy

And that is not all: by adjusting the brightness of the laser pulse, Evans and colleagues say that they could use the nanotubes to either destroy cancer cells or to image tumours.

For the imaging part, they made use of a new type of technique called multispectral optoacoustic tomography (MSOT) in which they detected the ultrasound waves produced by the gold nanotubes in colorectal cancer cells in mice. In their experiments, the researchers intravenously injected the nanotubes into the animals and observed that the nanomaterials accumulated at the tumour sites. This is the first time that NIR-light absorbing gold nanotubes have ever been used in a biomedical application, says the team.

Minimal toxicity

Since the nanotubes have a hollow central core, they can be loaded with anticancer drugs too, says team member James McLaughlan from the School of Electronic and Electrical Engineering. “Combining targeting and localised release of therapeutic agents in this way could be used to identify and treat cancer with minimal toxicity to the patient.” Indeed, the researchers say that the mice excreted the gold nanotubes in around 72 hours, so they are therefore unlikely to be toxic to living organisms – an important point to consider when developing nanoparticles for biomedical applications. The fact that the tubes are coated with poly(sodium 4-styrenesulfonate) (PSS) also makes them less toxic to healthy cells while they are in the bloodstream.

Younan Xia of Georgia Tech in the US, who was not involved in this work, told “although other types of gold structures, including nanocages, nanorods, and nanoshells have been used to destroy tumours before now, the new aspect in this work is the potential improvement in terms of tumour targeting efficacy by altering the shape or morphology of the nanostructures.”

Full details of the research are reported in Advanced Functional Materials DOI: 10.1002/adfm.201404358.