One of the most promising nanomedicine applications currently being researched involves the use of gold nanoparticles to locate and treat cancerous cells. Most of the current research involving cancer treatments with gold nanoparticles involves some form of drug delivery, but this new research supports another method of treating and killing carcinoma cells using nanoshell-mediated photothermal destruction. The nanospheres are specifically engineered to be attracted to diseased cells, allowing direct treatment of those cells. Once attached to the tumor, the nanoparticles are exposed to near infrared light. When the light wave passes through sphere, the atom absorbs the energy contained in the wave. After a certain threshold, the atoms cannot continue to absorb the energy from the waves so they vibrate to release it. These vibrations cause friction between the atoms, and the expelled energy is then transferred to the carcinoma cell that the nanosphere is attached to. After just minutes of exposure, enough heat from the friction is generated to causes irreparable damage to the carcinoma cells. This method transfers heat directly to the cancerous cells allowing the healthy cells to be unaffected during treatment, unlike chemotherapy.
The gold nanoparticle’s chemical properties are what give it an affinity for carcinoma cells. These metal nanoshells consist of a very thin gold outer layer with a dielectric core, is often made of silica. The silica cores are grown and the thin metal layer is added to the surface by placing the silica spheres in a gold colloid then removing them after some period of time. Because of the properties of gold, the nanoshells possess strong optical absorption and reflection abilities when exposed to light. By adjusting the thickness of the gold layer and the diameter of the sphere, one change how the particle interacts with light waves. Gold nanoshells can be designed to either absorb or scatter light by adjusting their size relative to the wavelength of light being emitted. The thickness of the gold outer layer is directly related to the amount of time the silica is immersed in the gold colloid. The longer it is exposed, the thicker the outer gold layer. One can then synthesize particles to either locate the cancer cells by reflecting light, or destroy the cells by absorbing it. This property of nanoshells is its defining characteristic and what sets it apart from other optical absorption nanostructures.
Destruction of Tumor:Calcein AM staining of cells (green fluorescence indicates cellular viability). Left: cells after exposure to laser only (no nanoshells). Middle: cells incubated with nanoshells but not exposed to laser light. Right: cell incubated with nanoshells after laser exposure. The dark circle seen in the image on the right corresponds to the region of cell death caused by exposure to laser light after incubation with nanoshells.
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Unlike the chemical properties of drugs, exploitation of the properties of the materials being used are what allow this technology to outperform any other. A drug cannot always be controlled once in the body and has the potential to kill healthy cells if exposed. This is why chemotherapy takes such a toll on the patients because it attacks cells throughout the entire body in hopes of killing the cancerous ones. Now the process is simplified and the body is exposed only to non-harmful compounds that congregate in the cancerous areas instead of all throughout the patient. This new method allows for targeted cancer treatment with no known side-effects to other parts of the body.
As of now there are no known side effects that result from photothermal cancer treatment. This technology deals with the treatment of cancer in individuals so it has little to no impact on the environment, but there could be some possible risks associated with personal health. The excess nanoparticles injected into the patient are nonreactive and remain in the body as inerts. They stay in the blood stream or gather in specific areas of the body that have increased blood flow like the spleen and liver. Tumors require excess blood flow that is why it is exposed to the nanospheres allowing the technology to work. If the patient were exposed to an x-ray or MRI, these particles could react in some way causing undesired destruction of healthy cells, but the possible side effects would be very case specific. More research through animal testing is being done to identify possible risks that might arise.
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