Scientists from University of Washington and University of Michigan, Ann Arbor have devised a novel nanoparticle powered imaging technique that may soon be able to pinpoint individual cells among a larger mass of tissue. The method uses well-defined iron oxide and gold-coupled core-shell nanoparticles that, when attached to given tissue, can be made to vibrate and to show up on a photoacoustic imager.
University of Washington press office explains:
Nanoparticles are promising contrast agents for ultrasensitive medical imaging. But in all techniques that do not use radioactive tracers, the surrounding tissues tend to overwhelm weak signals, preventing researchers from detecting just one or a few cells.
"Although the tissues are not nearly as effective at generating a signal as the contrast agent, the quantity of the tissue is much greater than the quantity of the contrast agent and so the background signal is very high," said lead author Xiaohu Gao, a UW assistant professor of bioengineering.
The newly presented nanoparticle solves this problem by for the first time combining two properties to create an image that is different from what any existing technique could have produced.
The new particle combines magnetic properties and photoacoustic imaging to erase the background noise. Researchers used a pulsing magnetic field to shake the nanoparticles by their magnetic cores. Then they took a photoacoustic image and used image processing techniques to remove everything except the vibrating pixels.
Gao compares the new technique to "Tourist Remover" photo editing software that allows a photographer to delete other people by combining several photos of the same scene and keeping only the parts of the image that aren’t moving.
The 30-nanometer particle consists of an iron-oxide magnetic core with a thin gold shell that surrounds but does not touch the center. The gold shell is used to absorb infrared light, and could also be used for optical imaging, delivering heat therapy, or attaching a biomolecule that would grab on to specific cells.
Researchers tested the method for photoacoustic imaging, a low-cost method now being developed that is sensitive to slight variations in tissues’ properties and can penetrate several centimeters in soft tissue. It works by using a pulse of laser light to heat a cell very slightly. This heat causes the cell to vibrate and produce ultrasound waves that travel through the tissue to the body’s surface. The new technique should also apply to other types of imaging, the authors said.
Top image: On top are photoacoustic images taken for gold nanorods (left), the new UW particle that has a magnetic core and surrounding gold shell (center), and a simple magnetic nanoparticle (right). Below is the same image after processing to remove pixels not vibrating with the magnetic field. The center blob is retained because of the particles’ magnetic core and is bright because of the particles’ gold shell.
Abstract in Nature Communications: Multifunctional nanoparticles as coupled contrast agents
Press release: Multifunctional nanoparticle enables new type of biological imaging…
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