September 29, 2008---A team of scientists at the Penn State Milton S. Hershey Medical Center, Penn State College of Medicine, and the departments of Materials Science and Engineering and Physics at Penn State have developed a new imaging method for breast cancer. The Sept. 19 online issue of ACS Nano features their research using encapsulated fluorescent molecules in calcium-phosphate nanoparticles and non-toxic near infrared imaging (NIR).
More effective early detection of diseases is one of the promises of nanotechnology. Current imaging methods, such as x-rays and magnetic resonance imaging, are limited in the size of tumors they can detect, the depth they can penetrate the body, and by their potential side effects. Another promising imaging technique, NIR bioimaging, is a noninvasive, painless, and non-ionizing form of radiation that operates at wavelengths just above that of visible light. By combining NIR imaging with nanoparticles containing a NIR fluorescing dye, indocyanine green, the researchers were able to detect 5 mm diameter breast cancer tumors in a live mouse model over a period of four or more days.
Indocyanine green is the only NIR organic dye approved by the Food and Drug Administration (FDA) for use in the human body. The nanoparticles, which are around 20 nm in diameter--one five thousandth the diameter of a human hair--are made of calcium phosphate, a biocompatible material that has long been used as a bone replacement. Unlike other nanoparticles considered for imaging and drug delivery, for example, semiconductor quantum dots, the biodegradable components of calcium-phosphate nanoparticles are already widely present in the bloodstream.
The Hershey group, led by pharmacologist Mark Kester, showed that their nanoparticles provide the fluorescent dye with 200% greater photoefficiency compared to indocynine green injected into the bloodstream, with a 500% greater photostability. In a separate experiment discussed in the paper, the researchers were able to image through 3 cm of dense pig muscle tissue, which should correlate to at least 10 cm, and likely much deeper, in patients, according to Adair.