Gold atoms will absorb infra-red light and generate heat when gold is moulded into shapes rods or shells, according to research undertaken by scientist at ETH Zurich, and while these desirable shapes are difficult and expensive to produce, the Swiss solution is to make sphere-shaped gold nanoparticles that aggregate into formations that absorb infra-red light and heat up.
The scientists tested the new particle constellations on cancer cells in a Petri dish. Targeting a near infra-red laser on the cell culture for 4 minutes heated it up enough to kill off the cancer cells. Without the nanoparticles present, cells survived the laser. Iron oxide particles were also mixed with the gold. This allowed aggregates to be controlled via magnetic fields and could boost accumulation in a tumour.
“We managed to synthesize in a scalable, reproducible and cost-effective way multifunctional gold-iron oxide nanoparticles that efficiently transform light into heat, so they can heat up when infrared light illuminates them. Then we showed that if such particles are close to – or inside – breast cancer cells and infrared light shines on them, the temperature increase they achieve is high enough to kill the cancer cells,” explained Georgios Sotiriou, lead author of the research paper in Advanced Functional Materials at ETH Zurich and now at Harvard University.
These particles could assist drug delivery in a number of ways. “Capitalising on their small size, if specific drug molecules are attached on their surface, they can be selectively delivered at the cancer site,” Sotiriou told in-Pharmatechnologist.com. “Furthermore, such particles may also be incorporated in heat-responsive drug carriers that release the drug only when a specific temperature is exceeded.”
Once the carrier arrived at the target location, near-IR irradiation would trigger the release of the drug. Such targeted delivery could mimimise drug side effects in the rest of the body.
One vital ingredient to the gold nanoparticles was a silicon dioxide coating. This coating tuned particle distance, prevented reshaping and melting of the gold nanostructures, and helped improve dispersibility in solutions, including biological fluids. It also facilitated surface functionalization of the nanoparticles to allow biomolecules to be attached.
The hybrid iron oxide-gold nanoparticles may allow the particles to be heated even when they are deep within the body, beyond where IR radiation can penetrate, by applying a magnetic field. The hybrid particles could also be used as a contrast medium for imaging processes in diagnostics by magnetic resonance imaging; this has been investigated in collaboration with University Hospital Zurich.
Although gold, silicon dioxide and iron oxide are all well tolerated, what happens to the aggregates in the body needs to be investigated. “A lot of questions still need to be answered before the particles can be used in humans,” Jean-Christophe Leroux, professor of drug formulation and delivery at ETH Zurich, said in a press statement.