R&D DIGEST

The twinkling movement that makes stars stand out in the sky is a concept being applied to biomedical imaging. By developing gold nanostars that flicker, researchers can see the particles amidst the noisy backgrounds that are typically found during imaging. Due to their visibility at near infrared wavelengths, researchers have used gold nanoparticles as contrast agents in imaging.

The 100-nm gold nanostars, which contain an iron oxide core, spin when exposed to a rotating magnetic field. This process causes light to scatter and creates the twinkling effect. The method, called gyromagnetic imaging, was developed at Purdue University (West Lafayette, IN).

The researchers conduct the imaging by putting a sample of cells with nanostars under a standard microscope. A white light with a rotating magnet is sent into the cells via a polarizing beam splitter. The light reflects back into the splitter and to a camera that gathers images at 120 frames per second. It captures the nanostars' signal as they spin at about 5 rps. The twinkling is controlled by the speed of the magnetic field rotation.

“It was surprising how well this method enhanced the imaging,” says Kenneth Ritchie, associate professor of physics at Purdue. “It can improve the contrast of the particles to the background noise by more than 20 dB and can clearly reveal a gyrating nanostar, where[as] with existing direct imaging methods, in many cases you wouldn't be able to definitively find a particle.”

The imaging method allows researchers to focus on the nanostars by increasing signal strength. When a signal doesn't have a frequency that corresponds to the magnetic field, it is suppressed in the images.

“Gyromagnetic nanostars combine strong optical signaling with a unique mechanism for reducing noise, allowing one to pick out the proverbial needle from the haystack,” according to Alexander Wei, professor of chemistry at Purdue. “The key is to enable the nanostars to twinkle at a frequency of our choosing. Our analysis picks out signals at that frequency and translates that information into images of remarkable clarity.”

The imaging technique is also inexpensive compared with other specialized equipment. According to Ritchie, the Purdue method only requires a halogen lamp and a $10,000 camera.

During the course of the research, the nanostars were found to be biocompatible and mild cell growth stimulators. The researchers are examining whether the nanostars have biological effects inside cells. In a paper about their work, appearing in a July issue of the Journal of the American Chemical Society, they demonstrated using the gyromagnetic imaging of the nanostars inside tumor cells.

The National Institutes of Health provided research funding.

Copyright ©2009 Medical Device & Diagnostic Industry