Originally Published EMDM January 2006
Technology News: Imaging
Researchers Set New Gold Standard for Medical Visualization
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| Gold nanorods, which fluoresce red, are photographed inside the blood vessels of a live mouse. The research conducted at Purdue University in the United States may lead to a new type of ultrasensitive medical imaging technique. |
Laser-illuminated gold nanorods may take ultrasensitive medical imaging technology to unprecedented levels. The technique involves injecting tiny gold rods into the bloodstream and shining a laser through the skin to illuminate them. In animal trials, this method yielded dramatically brighter images than those obtained using conventional fluorescent dyes. Researchers at Purdue University (West Lafayette, IN, USA) published their findings in the online Proceedings of the National Academy of Sciences (www.pnas.org) on 20 October.
Roughly 200X smaller than a red blood cell, a nanorod measures about 20 nm wide and 60 nm long. Researchers injected the nanorods into mice and took images of the structures as they flowed through blood vessels. The nanorods shone 58X brighter than the two-photon fluorescence from a single rhodamine molecule. (Rhodamine is commonly used to study the inner workings of cells and molecules.) The technique represents a possible way to overcome barriers in the use of light to analyze blood vessels and underlying tissue, according to reasearchers.
“Light in the visible spectrum does not pass through tissue very well,” explains Alexander Wei, an associate professor of chemistry who participated in the project. Imaging methods might be developed using laser pulses beyond the visible range in the near-infrared spectrum, he suggests. “There is a window of light in the near-infrared range—wavelengths from 800 to 1300 nm—that could be harnessed for new imaging technologies,” he adds. Tiny gold rods with a certain aspect ratio shine brightly when illuminated by light in this spectral region.
To detect cells at an early stage of disease, it is important to have a reliable technique that has sensitivity at the single-particle level, says Wei. “The gold nanorods demonstrate that [assistant professor of biomedical engineering and fellow researcher] Ji-Xin Cheng’s nonlinear imaging methods are capable of this level of detection.”
The research paper, “In Vitro and In Vivo Two-Photon Luminescence Imaging of Single Gold Nanorods,” can be purchased at www.pnas.org.
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