Gold Nanoparticles and Cancer Treatment
Nanoparticles are very small particles of a given substance; smoke is usually a cloud of nanoparticles. The laboratory tests used colloidal gold and single-walled carbon nanotubes (SWNT). While nanotubes are also nanoparticles, they are engineered as a hollow cylinder.
Localized and whole-body application of heat has been proposed as a technique for the treatment of malignant tumours. Intense heating will cause denaturation and coagulation of cellular proteins, rapidly killing cells within a tumour.
There are many techniques by which heat may be delivered. Some of the most common involve the use of focused ultrasound (FUS or HIFU), microwave heating, induction heating, magnetic hyperthermia, and direct application of heat through the use of heated saline pumped through catheters. Experiments with carbon nanotubes that selectively bind to cancer cells have been performed. Lasers are then used that pass harmlessly through the body, but heat the nanotubes, causing the death of the cancer cells. Similar results have also been achieved with other types of nanoparticles, including gold-coated nanoshells and nanorods that exhibit certain degrees of 'tunability' of the absorption properties of the nanoparticles to the wavelength of light for irradiation. The success of this approach to cancer treatment rests on the existence of an 'optical window' in which biological tissue (i.e., healthy cells) are completely transparent at the wavelength of the laser light, while nanoparticles are highly absorbing at the same wavelength. Such a 'window' exists in the so-called near-infrared region of the electromagnetic spectrum. In this way, the laser light can pass through the system without harming healthy tissue, and only diseased cells, where the nanoparticles reside, get hot and are killed.
Preclinical treatment involves using radio waves to heat up tiny metals that are implanted in cancerous tissue. Gold nanoparticles or carbon nanotubes are the most likely candidate. Promising preclinical trials have been conducted, although clinical trials may not be held for another few years.
Kanzius RF Therapy is a patented technology of ThermMed LLC, enterprise created by John Kanzius. The therapy aims to insert metallic nanoparticles in or around cancerous cells and then exciting these particles using radio waves; the energy from the radio waves creates heat which burns the cancerous cell cluster.
In a control experiment water and a solution of water and gold nanoparticles were exposed to a 50W, 13.56 MHz field for 5 minutes. The water's temperature did not increase in a significant manner (from 23°C to approximately 28°C) while the solution containing gold nanoparticles' temperature increased significantly (from 23°C to approximately 78°C, reaching 60°C near the one-minute mark). For five minutes of exposure at power outputs of 10W, 50W and 100W, temperature changes were 18°C, 47°C and 58°C respectively. Within the same study, HepG2 cells incubated in a solution containing gold nanoparticles and a control group were exposed to a 35W, 15.58 MHz field for seven minutes. The control cells suffered a small temperature increase (5°C) while the gold-incubated cells' temperature increased by 20°C, reaching approximately 52.5°C at the seven-minute mark. Reported cell death ranged approximately from 35% to 80% for three and seven minutes of exposure respectively.
A subsequent study challenged these results by reporting that the heating was primarily due to residual ions in solution rather than the gold nanoparticles themselves. When the nanoparticles were centrifuged and redispersed in water, negligible heating was observed. Further experimental and theortical studies support the idea that nanoparticles cannot absorb sufficient RF energy to cause heating.
A nanoshell, or rather a nanoshell plasmon, is a type of spherical nanoparticle consisting of a dielectric core which is covered by a thin metallic shell (usually gold). These nanoshells involve a quasiparticle called plasmon which is a collective excitation or quantum plasma oscillation where the electrons simultaneously oscillate with respect to all the ions.
Gold-shelled nanoparticles, which are spherical nanoparticles with silica cores and gold shells, are used in cancer therapy and bio-imaging enhancement. Theranostic probes – capable of detection and treatment of cancer in a single treatment - are nanoparticles that have binding sites on their shell that allow them to attach to a desired location (typically cancerous cells) then can be imaged through dual modality imagery (an imaging strategy that uses x-rays and radionuclide imaging) and through near-infrared fluorescence. The reason gold nanoparticles are used is due to their vivid optical properties which are controlled by their size, geometry, and their surface plasmons. Gold nanoparticles (such as AuNPs) have the benefit of being biocompatible and the flexibility to have multiple different molecules, and fundamental materials, attached to their shell (almost anything that can normally be attached to gold can be attached to the gold nano-shell, which can be used in helping identifying and treating cancer). The treatment of cancer is possible only because of the scattering and absorption that occurs for plasmonics. Under scattering, the gold-plated nano-particles become visible to imaging processes that are tuned to the correct wavelength which is dependent upon the size and geometry of the particles. Under absorption, photothermal ablation occurs, which heats the nanoparticles and their immediate surroundings to temperatures capable of killing the aids cells. This is accomplished with minimal damage to cells in the body due to the utilization of the "water window" (the spectral range between 800 and 1300 nm). As the human body is mostly water, this optimizes the light used versus the effects rendered.
These gold nanoshells are shuttled into tumors by the use of phagocytosis, where phagocytes engulf the nanoshells through the cell membrane to form an internal phagosome, or macrophage. After this it is shuttled into a cell and enzymes are usually used to metabolize it and shuttle it back out of the cell. These nanoshells are not metabolized so for them to be effective they just need to be within the tumor cells and photo-induced cell death (as described above) is used to terminate the tumor cells.
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