Gold has been a popular material to make nanoparticles because of its biocompatibility, but to get it to do some neat tricks isn’t enough to simply produce spherical gold nanoparticles. One limitation in using gold for killing tumors has been that cheap spherical gold nanoparticles are not plasmonic to near-infrared light, meaning they don’t heat up when such light illuminates them. Making gold nanoparticles plasmonic requires forming shapes out of the element that have been expensive to produce. Researchers at ETH Zurich (Eidgenössische Technische Hochschule Zürich) have developed a new technique for cheap manufacturing of different shapes of plasmonic gold-based nanoparticles that may open new possibilities for cancer treatment.
Instead of creating new shapes purely out of gold, a difficult process, the team instead arranged readily available spherical gold nanoparticles coated with silicon dioxide into plasmonic shapes. The silicon dioxide works like a spacer, keeping the gold spheres at predefined distances from each other, guaranteeing a correct geometry that produces the plasmonic effect. The team tested the nanoparticles by embedding them inside human breast cancer tumors and killing them with a four minute pulse from a low energy near-infrared laser.
Some details from the study abstract in Advanced Functional Materials:
Hybrid plasmonic-superparamagnetic nanoaggregates (50–100 nm in diameter) consisting of SiO2-coated Fe2O3 and Au (≈30 nm) nanoparticles were fabricated using scalable flame aerosol technology. By finely tuning the Au interparticle distance using the SiO2 film thickness (or content), the plasmonic coupling of Au nanoparticles can be finely controlled bringing their optical absorption to the near-IR that is most important for human tissue transmittance. The SiO2 shell facilitates also dispersion and prevents the reshaping or coalescence of Au particles during laser irradiation, thereby allowing their use in multiple treatments. These nanoaggregates have magnetic resonance imaging (MRI) capability as shown by measuring their r2 relaxivity while their effectiveness as photothermal agents is demonstrated by killing human breast cancer cells with a short, four minute near-IR laser irradiation (785 nm) at low flux (4.9 W cm-2).
Study in Advanced Functional Materials: Photothermal Killing of Cancer Cells by the Controlled Plasmonic Coupling of Silica-Coated Au/Fe2O3 Nanoaggregates
Press release: Hot nanoparticles for cancer treatments