Nanoparticles Switch On Light Inside Thick Layer of Human Tissue

There is new way to look at tissues under the skin. An international team of researchers from the   University at Buffalo and other institutions in the U.S., China, South Korea and Sweden have designed a unique photoluminescent nanoparticle for deep tissue imaging.

The unique photoluminiscent nanoparticles glow clearly through more than 3 centimeters of biological tissue. This unique factor increases its demand for new approaches in providing high-resolution and high-contrast optical bioimaging. These images could be used by the doctors and scientists to identify tumors and other abnormalities deep inside the skin.

Consisting of a nanocrystalline core containing thulium, sodium, ytterbium and fluorine, all encased inside a square, calcium fluoride shell, the newly created nanoparticles are special for several reasons.

Initially, they not only absorb and emit near-infrared light, with the emitted light having a much shorter wavelength than the absorbed light. But are very different from how molecules in biological tissues absorb and emit light. The scientists can use the particles to gain deeper and high contrast imaging than traditional fluorescence based technique.

The calcium fluoride shell is found in the bone and tooth mineral, making it well-matched with human biology. This compatibility drops the risk of adverse affects. This kind of shell increases the photoluminescence efficiency.

How do the particles work? The particles engage in a process known as near-infrared-to-near-infrared up-conversion, or 'NIR-to-NIR' in order to emit light. During this process they gulp in pairs of photons and unite them into single higher-energy photons to glow.

The scientists tested the particles in experiments by injecting into mice and imaging a capsule full of the particles through a slice of pork more than 3 centimeters thick. In each case, the researchers were able to obtain vibrant, high-contrast images of the particles shining through tissue.

The study was led by Paras N. Prasad, a SUNY distinguished professor and executive director of UB's Institute for Lasers, Photonics and Biophotonics (ILPB), and Gang Han, an assistant professor at University of Massachusetts Medical School. It was published online on Aug. 28 in the ACS Nano Journal.

"We expect that the unprecedented properties in the core/shell nanocrystals we designed will bridge numerous disconnections between in vitro and in vivo studies, and eventually lead to new discoveries in the fields of biology and medicine," said Han, expressing his excitement about the research findings.

According to co-author Tymish Y. Ohulchanskyy, a deputy director of ILPB, the 3-centimeter optical imaging depth is unprecedented for nanoparticles that provide such high-contrast visualization.

"Medical imaging is an emerging area, and optical imaging is an important technique in this area," said Ohulchanskyy. "Developing this new nanoplatform is a real step forward for deeper tissue optical bioimaging."

The next step in the research is to explore ways of targeting the nanoparticles to cancer cells and other biological targets that could be imaged.