A team of researchers from ETH Zurich have found a way to use long-wavelength red light beams and a new type of nanoparticle in a way that has many applications such as a medium for contrast imaging, substance carrying vehicles, and heat-triggered drug release tools. The most important application for now is the targeting and killing cancer cells. The new type of nanoparticles are being called plasmonic particles that heat up when they absorb infrared light. When they heat up, they can be seen where they are in the human body and can be strategically placed in such a way that they kill cancer cells in tumor sites.
Lots of nanoparticles used in the treatment of diseases such as cancer are made from gold because it is hypoallergenic – most people tolerate the metal very well and it does not produce unwanted side effects and the body does not reject it. The problem with gold in this instance is that it has to be molded into a special shape, such as a rod or shell, in order to generate heat by absorbing the near-infrared light; gold is expensive and the molding process is complex.
The team, led by Sotiris Pratsinis, have found an easier way for the gold nanoparticles to generate heat through light absorption by aggregating gold spheres, coating each nanoparticle with a layer of silicon dioxide. The silicon dioxide creates designated places for each sphere, placing them strategically and at predetermined intervals of space. The precise configuration of the gold nanoparticles allows them to more easily absorb the infrared light, thus more easily generating heat.
Nanorods were also out of the question because they deform when heated up and when they lose their form they also lose their plasmonic functionality, rendering them unable to absorb light and create heat. The silicon dioxide surrounding the gold nanospheres not only spaces them out perfectly, it also helps the spheres retain their shapes when heated up so that their light absorption capabilities are not lost.
In an in-vitro test, the team tried out their gold nanospheres on breast cancer cells in a Petri dish. They found that, compared to the breast cancer cells in the control group, the cancer cells treated with their plasmonic particles were killed because, after being exposed to the near-infrared light, the nanoparticles were able to generate enough heat to exterminate them.
The way in which the gold spheres can be transported to cancer sites is by adding super-magnetic iron oxide nanoparticles into the gold nanospheres mix. This creates a nanoaggregate that can be controlled with magnetic fields that lead them and help them to accumulate in tumors.
The iron oxide offers a whole new possibility as well. The magnetic field associated with the iron oxide nanoparticles can create enough heat for the gold nanoparticles to get hot enough to kill cancer cells in places in the body where near-infrared beams would not be able to reach them. For instance, the magnetic field could heat the nanospheres at cancer sites that are hidden under layers of deep tissue.
This is an amazing breakthrough. However, the gold nanoparticle aggregates are not quite ready for human test subjects yet. Whereas we know how the body tolerates and excretes gold, silicon dioxide and iron oxide (the three major players in this new treatment), scientists are still unsure how the body will react to the aggregates that have been formed with them. More testing needs to be done to make sure the aggregates are excreted safely through pores or if they pose a danger by accumulating in the liver.
Sources: eurekalert.org, wikipedia.org, Photothermal Killing of Cancer Cells by the Controlled Plasmonic Coupling of Silica-Coated Au/Fe2O3 Nanoaggregates.