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纳米笼－－通过光热转换，能有效杀死癌细胞
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Nanocages feel the heat Researchers in the US and China have made a new class of gold nanostructures that could be used to photothermally destroy cancer cells. Xingde Li and Younan Xia of the University of Washington and colleagues at the Chinese Academy of Sciences and Johns Hopkins University made gold "nanocages" that were tailored to strongly absorb light in the near-infrared region. This light was then converted into heat, which was used to kill breast cancer cells in vitro.
SK-BR-3 breast cancer cells that were treated with immuno gold nanocages and then irradiated by an 810 nm laser at a power density of 1.5 W/cm2 for 5 min showed a well-defined circular zone of dead cells as revealed by: (A) calcein AM assay (where green fluorescence indicates the cells were live), and (B) ethidium homodimer-1 (EthD-1) assay (where red fluorescence indicates the cells were dead). In the control experiment, cells irradiated under the same conditions but without immuno gold nanocage treatment maintained viability, as indicated by (C) calcein fluorescence assay and (D) the lack of intracellular EthD-1 uptake. Cells treated with immuno gold nanocages but irradiated at a lower power density (0.5 W/cm2) for 5 min remained alive, as shown by (E) calcein fluorescence assay and (F) the lack of intracellular EthD-1 uptake. Copyright 2007 American Chemical Society Gold nanostructures are promising candidates for biomedical research because of their unique optical and chemical properties, combined with their excellent biocompatibility. They strongly absorb light, which means they can be used in photothermal therapy – a technique that is less invasive than chemotherapy or surgery. Here, optical radiation is absorbed and transformed into heat that is then used to thermally denature proteins and DNA in a cell, and coagulate tissue. This irreversibly damages the targeted diseased cells, while minimising damage to surrounding healthy tissue. Previous work has shown that combining the gold nanostructures with specific antibodies or viral vectors means they can be used to damage targeted cancerous tissue, when illuminated with light at wavelengths around the absorption peak of the gold nanoparticles. Until now, however, most gold nanostructures absorbed light in the visible range, which does not penetrate very deeply into tissue compared to near-infrared light. Moreover, most of the structures that did absorb light in the near-infrared range were bigger than 50 nm in diameter, which made it difficult to target specific areas of tissue while retaining strong light absorption. Now, Li and colleagues have overcome these challenges by making gold nanocages that are less than 50 nm across and have a strong resonance absorption peak in the near-infrared region. Compared to other photothermal therapeutic agents, such as organic dyes, gold nanorods and nanoshells, gold nanocages are easy to make. They are made using a galvanic replacement reaction between silver nanocubes and chloroauric acid. This one-step process leads to the silver nanocubes dissolving and a gold shell being deposited around each silver nanocube. The final structures are single-crystal gold nanocages, or hollow nanoboxes. The researchers calculated that their nanocages have large light absorption cross-sections of 3.48 × 10–14 m2, which means the structures can easily convert near-infrared radiation into heat. The team then conjugated the nanocages with monoclonal antibodies to target "epidermal growth factors" that are over-expressed on the surface of breast cancer cells. Preliminary results showed that the nanocages strongly absorbed near-infrared light with an intensity threshold of 1.5&thinspW/cm2 and thermally destroyed the cancer cells in vitro. Li and Xia's team will now investigate the efficiency of their immuno-nanocages as thermal agents for treating tumours in vivo. "The hollow interior of the nanocages is an extra bonus and we are currently exploring the possibility of loading the structures with certain drugs for targeted and controlled release with light modulation based on the photothermal effect," Li told nanotechweb.org. The researchers reported their work in Nano Lett.. [ Last edited by 604gq on 2007-5-15 at 23:15 ] |
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