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Nanotech News
Rapid One-Pot Syntheses Developed For Quantum Dots Efficient and highly scalable new chemical synthesis methods developed at the University at Buffalo have the potential to revolutionize the production of quantum dots for bioimaging and other applications. The fabrication method developed by the researchers involve using a single container, or "pot," and take just a few hours to prepare. Quantum dots are tiny semiconductor particles generally no larger than 10 nanometers that can be made to fluoresce in different colors depending on their size. Scientists are interested in quantum dots because they last much longer than conventional dyes used to tag molecules, which usually stop emitting light in seconds.
The researchers report that one of their rapid-solution synthesis methods enabled them to prepare robust, water-dispersible quantum dots for bioimaging, while the other one allowed them to prepare organically soluble quantum dots ready to be sequestered into a polymer shell. The new synthesis methods are truly scalable and can be used to produce large quantities of quantum dots, according to Paras Prasad, Ph.D., who led the research team. "This fast-reaction chemistry will allow us to exploit the true potential of quantum dots, whether it be for delivery into human cells for imaging biological processes in unprecedented detail or for the development of far more efficient devices for solar conversion," he said. In a paper published in the Journal of the American Chemical Society, the investigators reported what they believe to be the first successful demonstration of so-called III-V semiconductor quantum dots as luminescence probes for bioimaging that appear to be non-toxic. "Three-five," and other such classifications refer to the position on the periodic table of the elements that make up semiconductors. Until now, only II-VI quantum dots have been produced for these applications. However, they are highly toxic to humans. The new quantum dots are made of indium phosphide (InP). The InP nanocrystals are as efficient at emitting light as other quantum dots, but they also emit light in longer wavelengths in the red region of the spectrum. "This is a key advantage because red-light emission means these quantum dots will be capable of imaging processes deeper in the body than commercially available quantum dots, comprised of cadmium selenide, which emit mostly in the lower wavelength range," said Prasad. Like those cadmium selenide quantum dots, the nanocrystals also exhibit two-photon excitation, absorbing two photons of light simultaneously, which is necessary for high-contrast imaging. The new quantum dots are composed of an InP core surrounded by a zinc selenide shell to protect the surface. An organic group is then attached to this shell, as well as a targeting group, in this case, folic acid. Folate receptors are targeted commonly by drugs in diseases such as cancers of the breast, ovary, prostate and colon. In their experiments, the investigators showed that the quantum dot system recognized the folate receptor and then penetrated the cell membrane, Prasad explained. The entire system is water dispersible, which is critical, Prasad said, if quantum dots are to be widely used for bioimaging. The other scalable chemical fabrication procedure developed by the Prasad’s group allowed them to prepare quantum dot-polymer nanocomposites that absorb photons in the infrared region. This work was detailed a paper titled, "Efficient photoconductive devices at infrared wavelengths using quantum dot-polymer nanocomposites.” This paper was published online in advance of print publication in the journal Applied Physics Letters. An abstract is available at the journal’s website. The work with indium phosphide nanocrystals is detailed in a paper titled, “Folate-receptor-mediated delivery of InP quantum dots for bioimaging using confocal and two-photon microscopy.” An abstract is available through PubMed. |
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